NO319610B1 - Electrical Sequence Tractor - Google Patents

Description

ELECTRO SEQUENCE TRACTOR

The invention area

The present invention relates to downhole drilling and in particular an electrosequence tractor (EST) for controlling the movement of a downhole drilling tool in a borehole.

Known technique

The art of drilling vertical, inclined and horizontal boreholes plays an important role within many industries such as the petroleum, mining and communications industries. In the petroleum industry, for example, a typical oil well comprises a vertical borehole drilled by a rotating drill bit attached to the end of a drill string. The drill string is typically made up of a series of interconnected links of drill pipe that extend between equipment on the ground surface and the drill bit. A drilling fluid, such as drilling mud, is pumped from the ground surface equipment through an internal flow channel in the drill string to the drill bit. The drilling fluid is used to cool and lubricate the drill bit and to remove waste and stone chips from the borehole, which are formed during the drilling process. The drilling fluid returns to the surface carrying the cuttings and waste through the annulus between the outer surface of the drill pipe and the inner surface of the borehole.

The procedure described above is often called "rotary drilling" or "traditional drilling". Rotary drilling often requires drilling numerous boreholes to extract oil, gas and mineral deposits. For example, drilling for oil usually involves drilling a vertical borehole until the petroleum reservoir is reached, often at great depth. Oil is then pumped from the reservoir to the surface of the earth. Once the oil is fully recovered from a first reservoir, it is typically necessary to drill a new vertical well from the surface of the earth to recover oil from a second reservoir close to the first. Often, a large number of vertical wells must be drilled within a small area to extract oil from several nearby reservoirs. This requires a large investment of time and resources.

In order to extract oil from several nearby reservoirs without incurring the costs of drilling a large number of vertical boreholes from the surface, it is desirable to drill inclined and horizontal boreholes. In particular, it is desirable initially to drill vertically downwards to a predetermined depth and then drill at an oblique angle from there to reach a desired target. This allows oil to be extracted from several underground locations nearby while minimizing drilling. In addition to the extraction of oil, boreholes with a horizontal component can also be used for a number of other purposes, such as the extraction of coal and the construction of pipelines and communication lines.

Two methods for drilling vertical, inclined and horizontal boreholes are the previously mentioned rotary drilling and coiled pipe drilling. In rotary drilling, a rigid drill string consisting of a number of interconnected segments of drill pipe is guided down from the earth's surface using surface equipment such as a tower or winch. Attached to the lower end of the drill string is a bottom casing which may comprise a drill bit, weight pipe, stabilizers, sensors and a recovery bit, weight pipe, stabilizers, sensors and a control device. In one application, the upper end of the drill string is connected to a rotary table or upper drive system located on the ground surface. The upper drive system rotates the drill string, downhole assembly and drill bit, allowing the rotating drill bit to penetrate the formation. In a vertically drilled hole, the drill bit is forced into the formation by the weight of the drill string and downhole assembly. The weight of the drill bit can be varied by controlling the amount of support that the derrick provides to the drill string. This allows, for example, drilling into different types of formations and controlling the speed at which the borehole is drilled.

The inclination of the borehole drilled by rotary drilling can be gradually changed using known equipment such as a downhole motor with an adjustable bent housing to create inclined and horizontal boreholes. Downhole motors with bent housings allow the surface operator to change the orientation of the drill bit, for example with pressure pulses from the surface pump. Typical rates of change in the drill string inclination are relatively low, approximately 3 degrees per 30 m borehole depth. Furthermore, the inclination of the drill string can be changed from vertical to horizontal over a vertical distance of approximately 900 m. The essentially rigid drill string's ability to bend is often too limited to reach desired locations in the earth. In addition, the drilling unit's friction on the casing or the lined hole often limits the distance that can be achieved with this method of drilling.

As mentioned above, another type of drilling is coiled pipe drilling. In coiled pipe drilling, the drill string is a non-rigid, generally pliable pipe. The pipe is fed into the borehole by an injector unit on the ground surface. The coiled tubing drill string may have specially designed weight tubes located near the drill bit, which apply weight to the drill bit to penetrate the formation. The drill string is not rotated. Instead, the drill bit is fed rotation by a downhole motor. Since the coiled pipe is not rotated or is not usually used to force the drill bit into the formation, the strength and stiffness of the coiled pipe is typically much less than that of the drill pipe used in comparable rotary drilling. The thickness of the coiled pipe is thus usually smaller than the thickness of the drill pipe used in rotary drilling, and the coiled pipe cannot usually withstand the same rotational, compression and tensile forces compared to the drill pipe used in rotary drilling.

One advantage of coiled pipe drilling over rotary drilling is the potential for greater flexibility in the drilling unit to allow sharper deflections to more easily reach desired locations in the earth. A drilling tool's ability to bend from vertical to horizontal depends on the tool's flexibility, strength and the load that the tool carries. With greater loads, the tool has less ability to bend due to friction between the drill hole and the drill string and the drill unit. As the deflection angle increases, it also becomes more difficult to transfer weight to the drill bit. At loads of only 8,888 newtons or less, existing coiled tubing tools pushed through the hole due to the gravity of the weight load can bend as much as 90° per 30 m of travel, but are typically capable of a horizontal travel of only 762 m or less. At loads of up to 13,332 newtons, by comparison, existing rotary drilling tools, whose drill strings are thicker and stiffer than coiled tubing, can only bend as much as 30°-40° per 30 m movement and is typically limited to horizontal distances of approx. 1,500-1,800 m. Again, such rotary tools are pushed through the hole by gravity in the weight loads.

In both rotary and coiled tubing drilling, downhole tractors have been used to apply axial loads to the drill bit, downhole assembly and drill string, and usually to move the entire drilling rig into and out of the borehole. The tractor may be designed to be secured between the lower end of the drill string and the upper end of the downhole assembly. The tractor may have anchors or grippers adapted to grip the borehole wall close to the drill bit. When the anchors engage the borehole, hydraulic power from the drilling fluid can be used to axially force the bit into the formation. The anchors can advantageously be slidably engaged with the tractor body, so that the drill bit, the body and the drill string (together the "drilling tool") can move axially into the formation while the anchors grip the borehole wall. The anchors serve to transfer axial loads and torsional loads from the tractor body to the borehole wall. One example of a downhole tractor is described in assigned US Patent Application No. 08/694,910 to Moore ("Moore '910"). The Moore '910 prescribes a very efficient tractor design compared to existing alternatives.

It is known to have two or more sets of anchors (in this paper also called "grippers") on the tractor, so that the tractor can move continuously inside the borehole. For example, Moore "910 describes a tractor having two grippers. Longitudinal (unless otherwise indicated, the terms "longitudinal" and "axial" are used interchangeably hereinafter and refer to the longitudinal axis of the tractor body) movement is achieved by driving the drill tool forward relative to a first gripper that is activated (a "work stroke"), and simultaneously move a retracted second gripper forward relative to the drilling tool ("reset") for a subsequent work stroke. Upon completion of the work stroke, the second gripper is activated, and the first gripper is retracted. The drill tool is then driven forward while the second gripper is activated, and the retracted first gripper is simultaneously reset for a subsequent work stroke. Thus, each gripper is operated in a cycle of activation, work stroke, retraction, and reset, resulting in longitudinal movement of the drilling tool.

It has been suggested that the force required to activate the anchors, axially advance the drilling tool and axially reset the anchors, can be provided by the drilling fluid. In the tractor described by Moore '910 for example, includes inflatable engagement bladders. The Moore tractor uses hydraulic power from the drilling fluid to inflate and expand the bladders radially, so that they grip the borehole walls. Hydraulic power is also used to propel cylindrical pistons located in propulsion cylinders which are slidably engaged with the tractor body. Each such cylinder is rigidly attached to a bladder, and each piston is axially fixed relative to the tractor body. When a bladder is inflated to engage the borehole, drilling fluid is directed to the proximal side of the piston in the cylinder attached to the inflated bladder to propel the piston forward relative to the borehole. The forward hydraulic shock on the piston results in a forward shock on the entire drilling tool. Furthermore, hydraulic power is also used to reset each cylinder when its associated bladder is emptied by directing drilling fluid to the distal side of the piston inside the cylinder.

Tractors may employ a system of pressure-responsive valves to sequence the distribution of hydraulic power to the tractor's anchor, shock, and reset sections. For example, the tractor according to Moore '910 includes a number of pressure-sensitive valves which move back and forth between their various positions based on the pressure in the drilling fluid at the various locations in the tractor. In one design, a valve can be exposed to different fluid flows on both sides. The position of the valve depends on the relative pressure of the fluid flows. A higher pressure in a first stream exerts a greater force on the valve than a lower pressure in a second stream, whereby the valve is forced into one extreme position. The valve moves to the second extreme position when the pressure in the second stream is greater than the pressure in the first stream. Another type of valve is spring biased on one side and exposed to fluid on the other, so that the valve will be activated against the spring only when the fluid pressure exceeds a threshold value. The Moore tractor uses both of these types of pressure-actuated valves.

It has also been proposed to use electromagnetically controlled valves in tractors. In one design, solenoids electrically trigger the reciprocating movement of the valve from one extreme position to another. Electromagnetically controlled valves are not pressure activated. Instead, these valves are controlled by electrical signals that are sent from an electrical control system on the ground surface.

Various types of radially expanding anchors have been used in downhole tractors, such as rigid friction blocks, flexible rods and engagement bladders. Some advantages of the bladders are that they can be expanded more radially and thus can operate within certain cavities in the earth. The bladders can also conform to different geometries of the borehole wall. A known bladder design comprises a combination of fiber and rubber. Previous designs used nylon fibers and nitrile butadiene rubber (NBR). The lifetime to material fatigue of current bladder designs is such that the bladders can achieve as much as 7,400 inflation cycles.

One problem with blisters is that they do not resist torque in the tractor body. As the drill bit rotates into the formation, the earth transfers a reactive torque to the bit, which is transmitted proximally through the tractor body. When an engagement bladder is inflated to engage the borehole wall, the compliant bladder tends to allow the tractor body to twist to some extent due to the torque therein. Such rotation can confuse the tool direction sensors, which requires an approximate calculation of such opposite twist in the algorithm for controlling the drilling direction.

Tractors according to the prior art have used anchors that allow at least some degree of rotation of the tractor body when the anchor is engaged with an underground borehole wall. A disadvantage of this design is that it causes the drill string to absorb reaction torque from the formation. During drilling, the drill bit exerts a drilling torque on the formation. At the same time, the formation exerts an equal and opposite torque on the tractor body. This torque is partly taken up by the drill string since the design allows rotation of the tractor body when the anchor is activated. This causes the drill string to twist. If all the anchors are pulled back, which can happen when the tool is to be retrieved, the drill string is prone to twisting back again, which can cause uneven progress as it moves.

There is thus a need for a tractor for downhole drilling, which overcomes the above-mentioned limitations of prior art.

Purpose of the invention

A principal purpose of the present invention is to overcome some or all of these limitations of the known technique and thereby provide an improved tractor for downhole drilling.

How the purpose is achieved

The object of the invention is achieved by its features indicated in the following description and in subsequent claims.

The structural construction of the tractor, which allows it to operate under the difficult conditions and the limited space inside the borehole in an oil well, is an important aspect of the invention. An important aspect of the invention is the structural construction which allows the tractor to fit into a casing no more than 21.6 cm in diameter and preferably no more than 7.3 cm. This relatively small diameter allows the tractor to work with standard oil well equipment designed for boreholes of 7.3-21.6 cm in diameter. Another important aspect of the present invention is the structural construction which allows the tractor to make relatively sharp deflections. More specifically, the tractor desirably has a length of no more than 46 m, more desirably no more than 30 m, more desirably no more than 23 m, more desirably no more than 15 m and even more desirably no more than 12 m. Preferably, the tractor's length approximately 9.7 m. The tractor can advantageously bend at least 60° per 30 m movement. Yet another important aspect of the invention is a structure that allows the tractor to operate at downhole pressures of up to 1,103 bar and preferably 345-689 bar and downhole temperatures of up to 149 °C and preferably 93-121 °C. Preferably, the tractor can operate at a pressure difference in the range of 14-172 bar, and more specifically in the range of 34-110 bar (the pressure difference between the EST's inside and outside, thus across the internal flow channel and the annulus that surrounds the tractor).

One limitation of prior art tractors which have valves, the positions of which control fluid flow which provides impact in the tractor body, is that such valves tend to operate only in extreme positions. These valves can be characterized as having distinct positions where the valve is either on or off, open or closed, etc. As a result, these valves fail to provide fine-tuned control over tractor position, speed, impact and direction.

Common to all of the present well tractor designs is that the well tractor comprises: (1) a tractor body; (2) a shock receiving portion associated with a propulsion system; and (3) a valve system to control the movement of the well tractor.

In another instance, the present invention provides a tractor to move within a borehole, and which is capable of reacting exceptionally quickly to variations in load exerted on the tractor by the borehole or by external equipment, such as a downhole unit or drill string. The tractor comprises: a tractor body which is sized and shaped to move within a borehole; a valve on the tractor body; an engine on the tractor body; and a coupling. The valve is located along a flow path between a fluid source and a shock-receiving portion of the body. The valve comprises a fluid port and a flow restrictor. The flow restrictor has: a first position in which the restrictor completely blocks fluid flow through the fluid port; a range of other positions in which the restrictor allows a first fluid flow level through the fluid port; and a third position in which the restrictor allows a second fluid flow level through the fluid port. The second fluid flow level is higher than the first fluid flow level. The coupling connects the motor and the flow restrictor so that movement of the motor causes the restrictor to move between the first position, the range of second positions and the third position. The motor is designed to be able to move the limiter so that the net two-shock absorbed by the shock-receiving part can be changed by 444 newtons within 0.5 seconds.

One object of the present invention is to provide a downhole tractor that provides an exceptional level of control over the tractor's position, speed, shock and direction change inside a borehole, compared to prior art tractors. Accordingly, the present invention provides in one case a tractor to move inside a borehole. The tractor comprises: a tractor body which has several impact-receiving parts; at least one valve on the tractor body positioned along at least one of a plurality of fluid flow paths between a fluid source and "the impact receiving portions; an electronically controllable motor coupled to the valve for directing fluid to at least one of the impact receiving portions; and a plurality of grippers. In the longitudinal direction, each of the plurality of grippers in movable engagement with the body Each of the plurality of grippers has an activated position in which the gripper restricts its movement relative to an inner surface of the borehole, and a retracted position in which the gripper permits substantially free relative movement of the gripper relative to to the inner surface The plurality of grippers, the plurality of shock receiving portions and the at least one valve are designed so that the tractor is self-propelled at a sustained speed of less than 15 m per hour and at a sustained speed of greater than 30 m per hour.

In other embodiments, the tractor is self-propelled in that its plurality of shock-receiving portions and the at least one valve are designed to allow the tractor to move at a sustained speed of less than 9 m/s. hour, and at a sustained speed greater than 30 m per hour. hour; respectively less than 3 m per hour and greater than 30 m per hour; respectively less than 1.5 m per hour and greater than 30 m per hour; respectively less than 15 m per hour and greater than 76 m per hour; and respectively less than 15 m per hour and greater than 152 m per hour. In another embodiment, the tractor is designed to operate at a pressure difference in the range of 14-172 bar between the fluid source and the shock-receiving parts. In another embodiment, the tractor is designed to operate at a pressure difference in the range of 34-110 bar between the fluid source and the shock-receiving parts. In another embodiment, the tractor can be arranged to be able to change the speed with which it propels itself forward, without a change in the pressure difference between the fluid source and the shock-receiving parts. In various embodiments, the tractor has a length that is preferably less than 46 m, more preferably less than 30 m, even more preferably less than 23 m, even more preferably less than 15 m and most preferably less than 12 m. In various embodiments, the tractor has a maximum diameter that is preferably less than 20.3 cm, more preferably less than 15.2 m, and even more preferably less than 10.2 cm.

In another instance, the present invention provides a tractor comprising: a tractor body sized and shaped to move within a borehole; and a valve on the tractor body. The valve is located along a fluid flow path between a fluid source and a shock receiving portion of the tractor body, such as a tubular piston. The shock-receiving part is sized and designed to receive hydraulic shocks from the fluid source.

The construction of the valve makes it easier to have improved control over the previously mentioned properties. In particular, the valve allows precise control over the flow rate of the fluid along the flow path of the shock-receiving part.

In one embodiment, the valve may comprise a fluid port and a flow-limiting body. Said fluid flow path passes through the fluid port. The flow-limiting body has one or more recesses on the edges of the flow-limiting body.

The flow restricting body has first, second and third position areas. Within the first position range, the flow restricting body completely blocks fluid flow through the fluid port. Within the second position range, the flow restricting body allows fluid flow through the fluid port only through the recesses. Within the third position range, the flow-limiting body allows fluid flow through the fluid port at least partially outside the recesses. Advantageously, the flow rate of fluid flowing along the fluid flow path can be controlled by controlling the position of the flow limiting body within the first, second and third position areas.

This tractor design can also include an engine on the tractor body, and a coupling that connects the engine and the flow-limiting body. Operation of the motor thereby causes the flow limiting body to move within the first, second and third position areas. The motor may also be arranged to move the flow restricting body sufficiently fast to change the net shock absorbed by the shock receiving portion by 444 newtons within 0.1-2 seconds.

In another embodiment, said valve can comprise a valve body and an elongated valve slide. The valve body has an elongated slide passage which defines a slide axis, and at least one first fluid port which is in communication with the slide passage. The fluid flow path passes through the slide passage and through at least the first fluid port. The valve slide is engaged inside the slide passage and is movable along the slide axis. The slide has a flow-limiting segment which defines a first chamber inside the slide passage at a first end of the flow-limiting segment, and which defines a second chamber inside the slide passage at a second end of the flow-limiting segment. The flow-limiting segment has an outer radial surface which is designed to slide along inner walls in the slide passage in order to thereby fluid-seal the first chamber against the second chamber. The flow restricting segment also has one or more recesses on one of its first and second ends and on its outer radial surface.

The slide has first, second and third position areas. Within the first position range, the slide's flow-limiting segment completely blocks fluid flow through the first fluid port. Within the second position range, the flow limiting segment allows fluid flow through the first fluid port only through the recesses. Within the third position area, the flow limiting segment allows fluid flow through the first fluid port at least partially outside the recesses. Advantageously, the flow rate of fluid flowing along the fluid flow path can be controlled by controlling the position of the valve slide within the first, second and third position ranges.

Said recesses may be generally pyramidal. A total cross-sectional area of the recesses can be delimited through the intersection of a transverse plane with the recesses, the transverse plane being generally perpendicular to the slide axis. The cross-sectional area of the recesses can have a maximum value at one end of the flow-limiting segment. The cross-sectional area of the recesses can decrease to zero as the recesses extend towards a midpoint in the longitudinal direction of the flow-limiting segment.

The tractor body can also be fitted with logic components that can control the position of the valve slide. The logic components may be arranged to transmit command signals to a motor which controls the position of the valve slide. The logical components can also be arranged to receive and process pressure signals from pressure sensors on the tractor body. One of these pressure signals can be made up of the pressure in fluid that flows along the fluid flow path from the valve to the impact-receiving part.

Furthermore, the tractor may comprise a traversing mechanism which is adapted to convert rotation of an output shaft from said engine, to movement of the valve slide generally along the slide axis, where the logic components are adapted to receive and process signals from an engine output sensor which measures the rotation of the output shaft . Such a motor output sensor may comprise a rotational accelerometer and/or a potentiometer.

Said traversing mechanism may comprise: a threaded lead screw coupled to the output shaft; a lead screw housing enclosing the lead screw, the lead screw housing having an elongate slot generally parallel to the lead screw; a lead screw nut that is in threaded engagement with the lead screw, the lead screw nut having a key that engages with the slot in the lead screw housing; and a stem having a first end connected to the lead screw nut and a second end connected to the valve slide. Rotation of the lead screw causes the lead screw nut to rotate relative to the lead screw and move along it due to the engagement of the wedge in the slot.

In another embodiment, the valve controls the flow rates of fluid to several different surfaces on the impact-receiving part, and the valve thereby controls the net impact on the tractor body. In yet another embodiment, the tractor body has a second impact-receiving part. A second valve controls the flow rate of fluid flowing to the second impact receiving portion.

In another embodiment, the tractor comprises: a tractor body, a slide valve; an engine; a coupling; and a gripper. The tractor body has a shock-receiving portion which has a first surface and a second, opposite surface. The first surface may be a rear surface, and the second surface may be a front surface. The slide valve comprises a valve body and an elongated slide. The valve body has a slide passage that delimits a slide axis, as well as fluid ports that are connected to the slide passage.

When the slide is received in the slide passage, the slide is movable along the slide axis to control flow rates along fluid flow paths through the fluid ports and slide passage. The slide has a first position range within which the valve allows fluid flow from a fluid source to the first surface of the impact receiving portion and blocks fluid flow to the second surface. The flow rate of the fluid flow to the first surface varies depending on the position of the slide within the first position range. The fluid flow to the first surface imparts a shock to the body to propel the body in a first direction in the borehole. How strong the impact in the first direction is depends on the flow rate of the fluid flow (with associated pressure) to the first surface. The slide also has a second position range within which the valve allows fluid flow from the fluid source to the second surface of the impact receiving portion and blocks fluid flow to the first surface. The flow rate of the fluid flow to the second surface varies depending on the position of the slide within the second position range. The fluid flow to the second surface shocks the body to propel the body in a second direction in the borehole. The first direction can be down the hole, and the second direction can be up the hole. How strong the shock in the other direction is depends on the flow rate of the fluid stream to the other surface.

The engine is inside the tractor body. The coupling connects the motor and the slide, so that operation of the motor causes the slide to move along the slide axis. is In the longitudinal direction, the gripper is in movable engagement with the tractor body. The gripper has an activated position in which the gripper limits its movement in relation to an inner surface in the borehole, and a retracted position in which the gripper allows substantially free relative movement of the gripper in relation to the inner surface. The motor can advantageously be arranged to be able to move the slide along the slide axis sufficiently quickly to change the net shock absorbed by the shock-receiving part, by 444 newtons within 2 seconds, and preferably within 0.1-0.2 seconds.

In one embodiment, the tractor further comprises one or more sensors and an electronic logic component on the tractor body. The sensors are designed to generate electrical feedback signals indicating one or more of: fluid pressure in the tractor; the position of the tractor body in relation to the gripper; longitudinal load exerted on the tractor body by equipment outside the tractor or by the inner walls of the borehole; and rotational position of an output shaft from the motor. The output shaft controls the slide's position along the slide axis. The logic component is designed to receive and process the electrical feedback signals and to transmit electrical command signals to the motor. The motor is designed to be controlled by the electrical command signals. The command signals control the slide's position.

Said sensors may include a first pressure sensor which is designed to measure fluid pressure on the rear surface of the shock-receiving part of the tractor body, and a second pressure sensor which is designed to measure fluid pressure on the front surface of the shock-receiving part. The sensors may also include a rotational accelerometer designed to measure the angular velocity of the output shaft, and/or the sensors may include a potentiometer designed to measure the rotational position of the output shaft.

In another case, the present invention provides a tractor which has a valve whose position controls the position, speed and thrust of the tractor body, and where fluid pressure resistance to valve movement is minimized. Accordingly, the tractor comprises: a body; a valve; an engine; a coupling; and a pressure compensation piston, all inside the body. The valve is located along a fluid flow path from a source of a first fluid to a shock receiving portion of the body. The valve can generally be moved along the valve axis. The valve has a first position in which the valve completely blocks fluid flow along the fluid flow path, and a second position in which the valve allows fluid flow along the fluid flow path. The coupling connects the motor and the valve, so that operation of the motor causes the valve to move along the valve axis. The pressure compensating piston is exposed on a first side to the first fluid and on a second side to a second fluid. The first and the second fluid are separated from each other. The first fluid may comprise drilling mud, and the second fluid may comprise oil. The compensating piston is designed to move in response to pressure forces from the first and second fluids to thereby effectively equalize the pressure in the first and second fluids. The valve is exposed to the first fluid, and the engine is exposed to the second fluid. The compensating piston acts advantageously to minimize the net fluid pressure force acting on the valve along the valve axis, thereby minimizing resistance to valve movement and allowing improved control over the tractor's position, speed, impact and change of direction.

Since the tractor is electric and the movement is controlled electrically, the present invention allows the use of several tractors connected in series and simultaneous sequencing or non-simultaneous sequencing of the tractors' grippers, for example packing feet, for different functions. In other words, any number of tractors can operate simultaneously as a group. Some tractors may also be disabled while others are in operation. In one example, one tractor can be used for normal drilling at low speeds (0.08-229 m per hour) and a second tractor in the drill string can be designed for high speeds (229-1,524 m per hour) for faster progress in the borehole . In another example, two or more tractors can be used with similar performance characteristics. This type of device would be useful for applications where long and heavy devices need to be pulled into long or deep boreholes. Another example is the use of two or more tractors that perform different functions. This type of unit can have one tractor set up for milling and a second tractor for drilling after the milling job is completed, thereby requiring fewer trips to the ground surface. Any combination of different or similar types of tractors is possible.

In another design variant, the tractor can be made of cheaper materials such as steel, which leads to reduced performance for the tractor. Such an affordable tractor can be used for special applications such as pulling special equipment for oil production into the borehole and then leaving it in the hole. Inner groove pipe with sand filter sliding sleeve can be installed in this way.

Another object of the present invention is to provide a downhole tractor for drilling or moving within a borehole, which is capable of deflecting at remarkably large angles while pulling or pushing a large load and/or while minimizing twisting of the tractor body. Accordingly, in another instance, the present invention provides a tractor for movement within a borehole. The tractor comprises: an elongated body; a gripper; and a propulsion system on the body. The body is designed to push or pull equipment inside the borehole, as the equipment exerts a longitudinal load on the body. In the longitudinal direction, the gripper is in movable engagement with the body. The gripper has an activated position in which the gripper restricts movement between the gripper and an inner surface in the borehole, and a retracted position in which the gripper allows substantially free relative movement between the gripper and the inner surface. The propulsion system is designed to propel the body forward through the borehole while the gripper is in its activated position, the gripper being able to have a length of at least 25.4 cm. This propulsion system may include at least one propulsion control valve coupled to an electronically controllable motor to direct fluid to a shock receiving tractor portion designed to propel the body forward through the borehole. The body can have longitudinal boreholes for transporting fluid through the body, where the boreholes are deeply drilled.

The body is advantageously arranged sufficiently flexibly, so that the tractor can preferably bend up to 30°, more preferably 45°, and even more preferably 60°, per 30 m displacement, while pushing or pulling a longitudinal load. The exact load that the body can push or pull while exhibiting this deflection capability depends on the diameter of the body. Various embodiments of the invention include tractors having diameters of 5.5 cm, 8.6 cm, 12.1 cm and 15.2 cm. Please note that other designs are also conceivable, for example designs where the diameter of the body is at least 2.5 cm and its length is at least 3 m. A tractor that has a diameter of 5.5 cm preferably has the above-mentioned deflection ability while it is pushing or pulling loads of up to 4,444 newtons and more desirable up to 8,888 newtons. The same information for other versions is set out in the table below:

It should be noted that as the maximum diameter of the tractor's pistons, axles and steering unit increases, the maximum shock pull and maximum speed must also increase. These and other design considerations can be adjusted for optimal performance in relation to maximum and minimum speed, maximum and minimum draft shock, steering reaction times, deflection radius and other desirable performance features.

The elongated body of the tractor may also comprise an outer cylinder and an inner cylinder (480) bound to each other by diffusion. One of the cylinders has longitudinal interruptions which form longitudinal passages between the cylinders, where the longitudinal passages are designed to transport fluid through the body.

In one embodiment, the tractor has large diameter segments and small diameter segments. The large diameter segments include one or more of: (1) a valve housing having valves designed to control fluid flow to components of the propulsion system; (2) a motor housing with motors designed to control the valves; (3) an electronics housing with logic components designed to control the motors; (4) one or more propulsion chambers designed to receive fluid for propulsion of the body; (5) pistons that are axially movable within the propulsion chambers; and (6) the gripper. For the tractor that has a diameter of 8.6 cm, the large diameter segments have a diameter of at least 7.9 cm. The small diameter segments have a diameter of 5.2 cm or less and a modulus of elasticity of 131,000 N/mm<2> or more. Essentially all bending in the tractor takes place in the small diameter segments. Said pistons can be fixed on the body and be movable along a stroke length inside the propulsion chambers, the stroke length being at least 25 cm. The total length of said large-diameter segments can amount to at least 50-80% of the tractor's length. The large diameter segments may also include the propulsion chambers and the pistons within the propulsion chambers, where the pistons are fixed to the body. Each of the pistons may surround a segment of the body and have an annular surface generally perpendicular to the body, the annular surface being designed to receive impact from a fluid flowing to the piston. The stamps can have a diameter of at least 3.8 cm.

In another case, the present invention provides a tractor to move inside a borehole, and which comprises an elongated body; at least one first gripper; and a propulsion system on the body. The elongated body defines a longitudinal axis and is designed to transmit torque through the body. In particular, the body is designed so that when the body is subjected to a torque about the longitudinal axis of up to a certain value, for example 678 newton metres, the twist in the body is limited to 5° per step of the tractor, for example to 5° per movement of a gripper, i.e. per stroke of a propulsion cylinder. These values vary depending on the diameter of the tractor and are set out in the table below: EST diameter Twisting torque - at lower torque twists

the body see less than 5° per beats

5.5 cm 339 newton meters

8.6 cm 678 newton meters

12.1 cm 1.356 newton meters

15.2 cm 4.068 newton meters

The first gripper is in axially movable engagement with the body. The first gripper has an activated position in which the first gripper limits its movement relative to an inner surface in the borehole, and a retracted position in which the first gripper allows substantially free relative movement between the first gripper and the inner surface. The first gripper is fixed against rotation in relation to the body, so that the first gripper counteracts rotation of the body in relation to the borehole when the first gripper is in the activated position. A second gripper may also be provided and be designed identically to the first gripper. Thereby, the second gripper is also in axially movable engagement with the body and has an activated position and a retracted position, as for the first gripper. The propulsion system is designed to propel the body forward when at least one of the grippers is in its activated position. The body is advantageously arranged sufficiently flexibly so that the tractor can bend up to 60° per 30 m travel, i.e. longitudinal movement, of the tractor. The propulsion system may include at least one propulsion control valve which is connected to an electronically controllable motor to direct fluid to a shock-receiving portion which is designed to propel said body.

The latter tractor can also have segments with a large diameter and segments with a small diameter. The large diameter segments may include: one or more valve bodies with valves designed to control fluid flow to components of the propulsion system; a motor housing with motors designed to control the valves; an electronics housing with logic components designed to control the motors; one or more propulsion chambers designed to receive fluid for propulsion of the body; pistons which are axially movable within the propulsion chambers; and said first and second grippers. The large diameter segments may have a diameter of at least 7.9 cm, while the small diameter segments may have a diameter of 5.2 cm or less. Essentially all bending in the tractor takes place in the small diameter segments.

The elongated body may have a diameter of at least 2.5 cm. The grippers can also be designed to transmit a torque of up to 678 newton meters to the borehole. Another aim of the present invention is to provide an improved gripper, for example in the form of a packing foot, for a downhole tractor used for movement inside a borehole. In yet another case, the invention accordingly provides a tractor which is to move inside a borehole, and which comprises an elongated body and a gripper, for example said packing foot, designed to provide improved radial expansion compared to prior art. Each of the first and second grippers in the preceding tractor design can thereby comprise such an improved gripper.

The improved gripper includes a generally tubular spindle which is in concentric sliding engagement with the elongate body. The spindle has one or more longitudinal grooves which engage with lugs on the outer surface of the body, so that the spindle is prevented from rotating relative to the body. The improved gripper also includes an inflatable bladder fixed to the spindle.

Each such improved gripper may further comprise one or more flexible rods extending longitudinally across the bladder. The rods are designed to bend and grip the inner surface of the bore when the bladder is inflated. The rods are designed to transfer torque from the body to the inner surface of the borehole.

The tractor can optionally be equipped with grippers, for example packing feet, of different sizes, which allows the tractor to enter and work in a number of hole sizes. The tractor can also have a "flex toe packing foot", where separate components provide outward radial force for gripping in the borehole and transmission of torque from the tractor body to the borehole. Said bladder has an inflated position and a deflated position. In the inflated position, the bladder or rods restrict movement of the gripper relative to an inner surface of the borehole. In the deflated position, the bladder or rods allow substantially free relative movement between the gripper and the inner surface.

The bladder may be formed of an elastomeric material reinforced with fibers oriented in two directions which cross each other at an angle of between 0° and 90° and which are woven together, more preferably between 14° and 60° and even more preferably between approximately 30° and 40°.

The above-described embodiments of the invention, which use the drilling fluid to provide power to the tool, have specific considerations in the design to optimize the tool's operating life. Experiments have shown that drilling fluids can quickly erode many metals, including Stabaloy and copper beryllium, if the drilling fluid velocities inside the tool are exceeded. On straight sections inside the tool, fluid velocities should be limited to less than 10.7 m per second unless very wear-resistant materials are used, or other geometric considerations have been taken into account in the flow path. It is known that at higher speeds erosion occurs inside the tool, which limits the service life of tractor components. Operating life is important as failure down the hole and tool retrievals are extremely expensive.

With the aim of summarizing the invention and the achieved advantages over prior art, certain objectives and advantages of the invention have been described above in this document. Of course, it should be understood that not necessarily all such goals or advantages can be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will understand that the invention can be implemented or carried out in a way that achieves or optimizes one advantage or group of advantages as described herein, without necessarily achieving other objectives or advantages that may be described or implied herein writing.

All these embodiments are intended to be within the scope of the invention described in this document. These and other embodiments of the present invention will readily become apparent to those skilled in the field from the following detailed description of preferred embodiments with reference to the attached figures, the invention not being limited to any particular preferred (preferred) embodiment(s). which is described.

Brief description of drawings for the designs

Fig. 1 is a schematic representation of the main components in one embodiment of a coiled pipe drilling system; Fig. 2 is a perspective view of the electrosequence tractor (EST) according to the present invention, seen from the front; Fig. 3 is a perspective view of the EST's control unit seen from behind; Figures 4A-4F are schematic representations illustrating an operating cycle of the EST; Fig. 5 is a perspective elevation of the rear transition housing in the EST, seen from behind; Fig. 6 is a perspective view of the rear transition housing in fig. 5, front view; Fig. 7 is a sectional view of the rear transition housing, taken along line 7-7 in fig. 5; Fig. 8 is a perspective view of the electronics housing in the EST, seen from behind; Fig. 9 is a perspective view of the front end of the electronics housing in fig. 8, front view; Fig. 10 is a front view of the electronics housing in fig. 8; Fig. 11 is a longitudinal sectional view of the electronics housing, taken along line 11-11 in fig. 8; Fig. 12 is a cross-sectional elevation of the electronics housing, taken along line 12-12 in fig. 8; Fig. 13 is a perspective elevation of the pressure converter manifold in the EST, seen from the rear; Fig. 14 is a perspective view of the pressure converter manifold in fig. 13, front view; Fig. 15 is a cross-sectional elevation of the pressure converter manifold, taken along line 15-15 of Fig. 13; Fig. 16 is a cross-sectional elevation of the pressure converter manifold, taken along line 16-16 of Fig. 13; Fig. 17 is a perspective elevation of the EST's engine housing, seen from the rear; Fig. 18 is a perspective elevation of the engine housing in fig. 17, front view; Fig. 19 is a perspective view of the engine mounting plate in the EST, seen from the rear; Fig. 20 is a perspective view of the motor mounting plate in fig. 19, front view; Fig. 21 is a perspective elevation of the EST's valve housing, seen from the rear; Fig. 22 is a perspective view of the valve housing in fig. 21, front view; Fig. 23 is a front view of the valve housing in fig. 21; Fig. 24 is a side view of the valve housing and shows the viewing angle 24 in fig. 23; Fig. 25 is a side view of the valve housing and shows the viewing angle 25 in fig. 23; Fig. 2 6 is a side view of the valve housing and shows the viewing angle 2 6 in fig. 23; Fig. 27 is a side view of the valve housing and shows the viewing angle 27 in fig. 23; Fig. 28 is a perspective elevation of the EST's forward transition housing seen from the rear; Fig. 29 is a perspective elevation of the front transition housing in fig. 28, front view; Fig. 30 is a cross-sectional elevation of the front transition housing, taken along line 30-30 in fig. 28; Fig. 31 is a perspective elevation of the EST's spreader, seen from the rear; Fig. 32 is a sectional view of the spreader, taken along line 32-32 in fig. 31; Fig. 33 is a perspective elevation of the fail-safe valve slide and the fail-safe valve body of the EST, seen from the rear; Fig. 34 is a side view of the fail-safe valve slide in fig. 33; Fig. 35 is a plan view, seen from below, of the fail-safe valve body; Fig. 36 is a longitudinal sectional view of the fail-safe valve in the closed position; Fig. 37 is a longitudinal sectional view of the fail-safe valve in the open position; Fig. 38 is a rear perspective view of the EST's rear propulsion valve slide and rear propulsion valve body; Fig. 39 is a cross-sectional elevation of the rear propulsion valve slide, taken along line 39-39 of Fig. 38; Fig. 40 is a longitudinal sectional view of the rear propulsion valve in the closed position; Fig. 41 is a longitudinal sectional view of the rear propulsion valve in a first open position; Fig. 42 is a longitudinal sectional view of the rear propulsion valve in a second open position; Figures 43A-43C are exploded longitudinal sectional views of the rear propulsion valve illustrating various flow-restricting positions of the valve slide; Fig. 44A is a longitudinal view partially in section of the EST showing the rear propulsion valve lead screw assembly,-Fig. 44B is a sectional elevation of the lead screw assembly of FIG. 44A; Fig. 45 is a longitudinal view partially in section of the EST showing the fail-safe valve spring and pressure compensating piston; Fig. 46 is a longitudinal sectional view of the EST's relief valve element and relief valve body; Fig. 47 is a perspective elevation of the relief valve element in fig. 46, rear view; Fig. 48 is a longitudinal sectional view of the EST and shows relief turned in the unit; Fig. 49A is a perspective elevation of the rear section of the EST, seen from the front and shown disassembled; Fig. 49B is a sectional elevation of a front end of the rear axle shown in Fig. 49A; Fig. 50 is a side view of the rear axle of the EST; Fig. 51 is a front view of the rear axle of fig. 50; Fig. 52 is an elevation of the rear axle of fig. 50, rear view; Fig. 53 is a side view of the rear axle of fig. 50, shown rotated 180° about its longitudinal axis; Fig. 54 is a front view of the rear axle of fig. 53; Fig. 55 is a cross-sectional elevation of the rear axle, taken along line 55-55 shown in fig. 49 and 50; Fig. 56 is a cross-sectional elevation of the rear axle, taken along line 56-56 shown in Fig. 49 and 50; Fig. 57 is a cross-sectional elevation of the rear axle, taken along line 57-57 shown in Fig. 49 and 50; Fig. 58 is a cross-sectional view of the rear axle, taken along line 58-58 shown in Fig. 49 and 50; Fig. 59 is a cross-sectional elevation of the rear axle, taken along line 59-59 shown in Fig. 49 and 50; Fig. 60 is a perspective elevation of the rear packing foot of the EST, seen from the rear and shown disassembled; Fig. 61 is a side view of the EST's rear packing foot; Fig. 62 is a longitudinal sectional view of the rear packing foot in fig. 61; Fig. 63 is a sectional elevation of the rear end of the rear packing foot of fig. 62; Fig. 64 is a sectional elevation of the front end of the rear gasket foot of fig. 62; Fig. 65 is a perspective elevation of a rear packing foot with flexi toe, seen from behind and shown disassembled; Fig. 66 is a perspective view of the spindle in the gasket foot with flexible toe in fig. 65, rear view; Fig. 67 is a cross-sectional elevation of the bladder in the gasket foot with flexi toe in fig. 65; Fig. 68 is a cross-sectional elevational view of a shaft in the EST, formed by diffusion bonding; Fig. 69 schematically illustrates the relationship between fig. 69A-D; Figures 69A-69D are a schematic representation of one embodiment EST's electronics design; Fig. 70 is a graph illustrating the EST's speed range and load carrying capability range; Fig. 71 is a sectional longitudinal elevation of a stepped valve slide; Fig. 72 is a sectional longitudinal elevation of a stepped conical valve slide; Fig. 73A is a tape illustrating the deflection capability of the EST; Fig. 73B is a schematic representation illustrating the bending characteristic of the EST's rear axle assembly; Fig. 74 is a perspective elevation of an inflated packing foot, seen from the rear; Fig. 75 is a cross-sectional elevation of a packing foot; Fig. 76 is a side view of an inflated gasket foot with a flexi toe; Fig. 77A is a perspective elevation of a Wiegand wheel assembly, seen from the front and shown disassembled; Fig. 77B is a perspective elevation of the Wiegand wheel assembly of Fig. 77A, front view and shown disassembled; Fig. 77C is a front elevational perspective view of a piston having a Wiegand displacement sensor; Fig. 78 is a graph illustrating the relationship between longitudinal displacement of a propulsion valve slide in the EST and flow rate of fluid admitted into the propulsion cylinder; and Fig. 79 is a perspective elevation of a notch in a propulsion valve slide in the EST.

Detailed description of preferred designs

It must be emphasized that the following describes one design of the EST. However, numerous variations are possible. These variations in structure result in different ranges of performance characteristics. Several physical constraints require the EST to be innovative with regard to the utilization of available space inside the borehole. The physical limitations are the result of the drilling environment. First, the tool's maximum diameter is limited by the diameter of the drilled hole and the amount and pressure of the drilling fluid that is pumped through the tool's internal bore and returns to the earth's surface with cuttings. Then, the physical length of the tractor is limited by the size of the handling equipment on the surface and the space on the rig. The temperature and pressure downhole are the result of conditions in the underlying formation. The desired impact capacity for the EST is determined through the size of the drill bit, the downhole motor's impact capability and basic characteristics. The desired pulling capacity of the tool is determined by the weight of the drill string and the downhole assembly in the drilling fluid, taking into account the friction of the components against the borehole wall or the casing wall or by the requirements for the desired function, such as the amount of force required to move a sliding sleeve in a casing. The desired maximum speed is influenced by the rig economy, which includes the related costs for labour, material, facilities at the drilling, costs of capital, risk and other economic factors. The lowest desirable speed is determined by the type of operation, such as penetration rate in a particular formation or speed when milling casing. In addition, drilling tradition has led to numerous standard sizes that are used when drilling. These size limitations are generally a function of the bit size available, the size of casing available, the size of surface equipment and other parameters.

For example, the EST design described in this document has a maximum diameter of 8.6 cm for use in a 9.5 cm hole. However, several other designs are conceivable, including a 5.4 cm diameter tool for use in a 7.3 cm hole, a 12.1 cm diameter tool for use in a 15.2 cm hole, and a 15.2 cm diameter tool for use in a 21.6 cm hole.

However, it is believed that for a given set of operational criteria, such as a requirement that the tool should operate in a borehole with a diameter of 9.5 cm and have a given maximum length, the present invention has numerous advantages over tractors according to the prior art. For example, having a single tractor that can fit into a given borehole, and which can maintain both low speeds for activities such as milling, and high speeds for activities such as extracting from a borehole, is very valuable in that it saves both the expense of having another tractor and the time that would otherwise be necessary to change tractors.

Fig. 1 shows an electrosequence tractor (EST) 100 for moving equipment inside a passage, which electrosequence tractor 100 is designed in accordance with a preferred embodiment thereof. In the embodiments shown in the accompanying figures, the electrosequencing tractor (EST) can be used together with a coiled tubing drilling system 20 and a downhole unit 32. The system 20 may include power supply 22, tubing spool 24, tubing 26, tubing injector 28 and coiled tubing 30, all of which are well known in the art . The unit 32 may include measurement-while-drilling (MUB) system 34, downhole motor 36 and drill bit 38, all of which are also known in the art. The EST is designed to move within a borehole having an inner surface 42. An annulus 40 is defined in the space between the EST and the inner surface 42.

It should be understood that the EST can be used to move a wide range of tools and equipment inside a borehole. The EST can also be used in conjunction with numerous types of drilling, including rotary drilling and the like. In addition, it should be understood that the EST can be used in many areas including petroleum drilling, drilling for mineral deposits, installation and maintenance of pipelines, transport and the like. It should also be understood that the device and the method for moving equipment inside a passage can be used in many areas of use in addition to drilling. For example, these other application areas include well completion and production work for the production of oil from an oil well, pipeline work and communication activities. It should be understood that these areas of application may require the use of other equipment together with an EST according to the present invention. Such equipment, generally called a work unit, depends on the particular use to be carried out.

For example, an ordinary professional in the field will understand that the completion of oil and gas wells requires that the reservoir be logged using a number of different sensors. These sensors can operate by using resistivity, radioactivity, acoustics and the like. Other logging activities include measurement of formation slope and borehole geometry, formation sampling and production logging. These completion activities can be carried out in inclined and horizontal boreholes using a preferred embodiment of the EST. For example, the EST can deliver these different types of logs to relevant areas. The EST can either place the sensors at the desired location, or the EST can rest in a stationary position to allow the measurements to be taken at the desired locations. The EST can also be used to retrieve the sensors from the well.

Examples of production work that can be performed with a preferred embodiment of the EST include washing and acid treatment of sand and solid particles. It is known that wells occasionally become plugged with sand, hydrocarbon waste and other solid particles that prevent the free flow of oil through the wellbore 42. To remove this waste, specially designed washing tools, known in the industry, are delivered to the area and fluid is injected to to wash the area. The fluid and waste then return to the surface. Such tools include acid washing tools. These washing tools can be delivered to the relevant area for carrying out washing activity and then returned to the earth's surface by a preferred embodiment of the EST.

In another example, a preferred embodiment of the EST can be used to retrieve objects, such as damaged equipment and waste, from the borehole. For example, equipment can become separated from the drill string, or objects can fall into the borehole. These objects must be taken out again, or the borehole must be provided and plugged. Since abandoning and plugging a borehole is very expensive, retrieval of the object is usually attempted. A number of different tools known within the industry can be used to capture these lost items. The EST can be used to transport retrieval tools to the correct location, to retrieve the object, and to return the retrieved object to the surface.

In yet another example, a preferred embodiment of the EST can also be used for coiled pipe completions. As is known in the field, the use of drill string for continuous completion is becoming increasingly important in areas where it is not desirable to damage sensitive formations in order to install production pipes. These operations require the installation and retrieval of fully assembled completion drill string in boreholes with surface pressure. The EST can be used in conjunction with the use of traditional speed string and simple pipe installations for primary production. The EST can also be used with the use of artificial lift devices such as gas lift and downhole flow control devices.

In a further example, a preferred embodiment of the EST can be used to service plugged pipelines or other similar passages. It is often difficult to service pipelines due to physical limitations such as location in deep water or located near metropolitan areas. Different types of cleaning devices are available today for cleaning pipelines. These different types of cleaning tools can be attached to the EST, so that the cleaning tools can be moved inside the pipeline.

In yet another example, a preferred embodiment of the EST can be used to move communication lines or equipment within a passage. It is often desirable to pull or move different types of cables or communication lines through different types of channels. The EST can move these cables to the desired location within a passage.

Overview of EST components

Fig. 2 shows a preferred embodiment of an electrosequence tractor (EST). The EST 100 comprises a central control unit 102, an uphole or rear packing foot 104, a downhole or front packing foot 106, rear propulsion cylinders 108 and 110, forward propulsion cylinders 112 and 114, a drill string coupling 116, shafts 118 and 124, flexible couplings 120, 122 , 126 and 128 and a bottom hole unit coupling 129. Drilling pressure coupling 116 connects a drill string, such as coiled tubing, to shaft 118. Rear packing foot 104, rear drive cylinders 108 and 110 and couplings 120 and 122 are assembled end to end and are all axially slidably engaged with shaft 118. Similarly, forward packing foot 106, forward propulsion cylinders 112 and 114, and couplings 126 and 128 are assembled end to end and are slidably engaged with shaft 124. Coupling 129 provides a connection between the EST 100 and downhole equipment such as a bottomhole unit. The shafts 118 and 124 and the control unit 102 are axially fixed in relation to each other and are occasionally referred to in this document as the body of the EST. The EST's body is thus fixed in relation to the drill string and the downhole unit.

Schematic design and other ways of working for the EST

Fig. 4A-4F schematically illustrates a preferred design and mode of operation for the EST. The rear propulsion cylinders 108 and 110 are axially slidably engaged with the shaft 118 and form annular chambers surrounding the shaft. Annular pistons 140 and 142 are located inside the annular chambers formed by the cylinders 108 and 110 respectively, and are axially fixed on the shaft 118. The piston 140 fluidly divides the annular chamber formed by the cylinder 108 into a rear chamber 166 and a front chamber 168. Such rear and front chambers are fluidically sealed to essentially prevent fluid flow between the chambers or leakage to the annulus 40. In a similar way, the piston 142 fluidly divides the annular chamber formed by the cylinder 110 into a rear chamber 170 and a front chamber 172.

The front propulsion cylinders 112 and 114 are designed in a similar manner to the rear propulsion cylinders. Cylinders 112 and 114 are axially slidably engaged with shaft 124. Annular pistons 144 and 146 are axially fixed to shaft 124 and are enclosed in cylinders 112 and 114, respectively. Piston 144 fluidly divides the chamber formed by cylinder 112 into a rear chamber 174 and a front chamber 176. The piston 146 fluidly divides the chamber formed by cylinder 114 into a rear chamber 178 and a front chamber 180. The chambers 166, 168, 170, 172, 174, 176, 178 and 180 have varying volumes, depending on the pistons 140, 142 , 144 and 146 positions in them.

Although two rear propulsion cylinders and two front propulsion cylinders (along with two associated rear pistons and front pistons) are shown in the illustrated embodiment, any number of rear cylinders and front cylinders may be provided, including only a single rear cylinder and a single front cylinder. As described below, the hydraulic shock exerted by the EST increases as the number of propulsion cylinders increases. In other words, the hydraulic power provided by the cylinders is additive. Four propulsion cylinders are used to provide the desired thrust of approximately 46,661 newtons for a tractor with a maximum outside diameter of 8.6 cm. It is believed that a design having four propulsion cylinders is preferable because it allows the generation of relatively powerful shock while limiting the length of the tractor. Alternatively, fewer cylinders can be used, which will reduce the resulting maximum-pull shock for the tractor. Alternatively, more cylinders can be used, which will increase the maximum output power from the tractor. The number of cylinders is chosen to provide sufficient power for the expected loads for a given hole size.

The EST is driven hydraulically by a fluid such as drilling mud or hydraulic fluid. Unless otherwise stated, the terms "fluid" and "drilling fluid" are used interchangeably in what follows. In a preferred embodiment, the EST is powered by the same fluid that lubricates and cools the drill bit. Drilling mud is preferably used in an open system. Thereby, the need to provide additional fluid channels in the tool for the fluid that drives the EST is avoided. Alternatively, hydraulic fluid can be used in a closed system, if desired. Reference is made to fig. 1, where drilling fluid in operation flows from the drill string 30 through the EST 100 and down to the drill bit 38. Reference is again made to fig. 4A-4F, where the spreader 148 in the control unit 102 diverts a portion of the drilling fluid to operate the EST. Preferably, the spreader 148 filters out larger fluid particles that can damage internal components of the control unit, such as the valves.

Fluid exiting the spreader 148 flows into a spring-actuated fail-safe valve 150. The fail-safe valve 150 serves as an entry point to a central channel 155 (illustrated as a flow path in Figs. 4A-4F) in the control unit, which communicates with a relief valve 152, a packing foot valve 154 and advancement valves 156 and 158. When the pressure difference in the drilling fluid approaching the fail-safe valve 150 is below a threshold value, the fail-safe valve 150 remains in an off position, where fluid inside the central channel escapes to outlet line E, i.e. to the annulus 40. Unless otherwise stated, hereinafter "pressure difference" or "pressure" at a particular location refers to the difference between the pressure at that location and the pressure in the annulus 40. When the pressure difference rises above the threshold value, the spring force is overcome and the fail-safe valve 150 opens to allow drilling fluid to flow into the central channel 155. The fail-safe valve 150 prevents premature starting of the EST and provides a fail-safe means of stopping the EST by pressure reduction in the drilling fluid in the coiled tubing drill string. The valve 150 thus acts as an on/off valve for the system. The threshold value for opening the fail-safe valve 150, i.e. for turning the system on, is controlled by the stiffness of a spring 151 and can be any value within the expected operating drilling pressure range for the tool. A preferred threshold pressure is approximately 34 bar overpressure.

Drilling fluid inside the central channel 155 is in contact with all the valves in the EST 100. A spring-actuated relief valve 152 protects against too high pressurization of the fluid inside the tool. The relief valve 152 works in a similar way to the fail-safe valve 150. When the fluid pressure in the central channel 155 is below a threshold value, the valve remains closed. When the fluid pressure exceeds the threshold, the spring force of a spring 153 is overcome, and the relief valve 152 opens to allow fluid in the channel 155 to escape to the annulus 40. The relief valve 152 protects pressure-sensitive components of the EST, such as the bladders in the packing feet 104 and 106, which may burst at high pressures. In the illustrated embodiment, the relief valve 152 has a threshold pressure of approximately 110 bar overpressure.

The gasket foot valve 154 controls the inflation and deflation of the gasket foot 104 and 106. The gasket foot valve 154 has three positions. In a first extreme position (shown in Fig. 4A), fluid from the central channel 155 is allowed to flow through a passage 210 into the rear packing foot 104, and fluid from the front packing foot 106 is discharged through a passage 260 to the annulus 40. When the valve 154 is in this position, the rear packing foot 104 is prone to inflation, and the front packing foot 106 is prone to deflation. In a second extreme position (Fig. 4D), fluid from the central channel is allowed to flow through the passage 260 and into the front packing foot 106, and fluid from the rear packing foot 104 is released through the passage 210 to the annulus 40. When the valve 154 is in this position, the rear gasket foot 104 is prone to deflation, and the front gasket foot 106 is prone to inflation. A middle third position for the valve 154 allows limited flow from the channel 155 to both gasket feet. In this position, both gasket feet can be inflated for a double shock stroke, as described below.

In normal operation, the rear and front packing feet are activated alternately. When rear packing foot 104 is inflated, front packing foot 106 is deflated and vice versa. The position of the packing foot valve 154 is controlled by a packing foot motor 160. In a preferred embodiment, the motor 160 can be controlled electrically and can be operated via a programmable logic component on the EST 100, such as in the electronics housing 130 {fig. 8-12) to sequence the inflation and deflation of the packing feet. Although the illustrated embodiment uses a single gasket foot valve that controls both gasket feet, two valves could be provided, so that each valve controls one of the gasket feet. An advantage of a single gasket foot valve is that it requires less space than two valves. An advantage of the design with two valves is that each gasket foot can be controlled independently. The packing feet can also be inflated more quickly at the same time for a double impact stroke.

The propulsion valve 156 controls the flow of fluid to and from the rear propulsion cylinders 108 and 110. In one extreme position {shown in fig. 4B) the valve 156 allows fluid from the central channel 155 to flow through the passage 206 to the rear chambers 166 and 170. When the valve 156 is in this position, the rear chambers 166 and 170 are connected to the drilling fluid, which has a higher pressure than the posterior chambers. This causes the pistons 140 and 142 to move toward the bottom of the cylinders due to the volume of incoming fluid. At the same time, the front chambers 168 and 172 decrease in volume, and fluid is forced out of the front chambers through the passage 208 and the valve 156 out to the annulus 40. If the packing foot 104 is inflated to grip the borehole wall 42, the pistons move down the hole relative to the wall 42. If the packing foot 104 is emptied, the cylinders 108 and 110 move upwards in the hole in relation to the wall 42.

In its second extreme position (Fig. 4E), the valve 156 allows fluid from the central channel 155 to flow through the passage 208 to the front chambers 168 and 172. When the valve 156 is in this position, the chambers 168 and 172 are in communication with the drilling fluid, which have a higher pressure than the anterior chambers. This causes the pistons 140 and 142 to move toward the cylinder noses in a hollow manner due to the volume of incoming fluid. At the same time, the rear chambers 166 and 170 decrease in volume, and fluid is forced out of the rear chambers through the passage 206 and the valve 156 and out to the annulus 40. In a central position, the propulsion valve 156 blocks any fluid communication between the cylinders 108 and 110, the channel 155 and the annulus 40. If the packing foot 104 is inflated to grip the borehole wall 42, the pistons move up the hole relative to the wall 42. If the packing foot 104 is deflated, the cylinders 108 and 110 then move down the hole relative to the wall 42.

The propulsion valve 158 is designed in a similar manner to the valve 156. The propulsion valve 158 controls the flow of fluid to and from the forward propulsion cylinders 112 and 114. In one extreme position (FIG. 4E), the valve 158 allows fluid from the central channel 155 to flow through a passage 234 to the rear chambers 174 and 178. When the valve 156 is in this position, the rear chambers 174 and 178 are in contact with the drilling fluid, which has a higher pressure than the rear chambers. This causes the pistons 144 and 146 to move toward the downhole ends of the cylinders due to the volume of incoming fluid. At the same time, the front chambers 176 and 180 decrease in volume, and fluid is forced out of the front chambers through a passage 236 and the valve 158 and out to the annulus 40. If the packing foot 106 is inflated to grip the borehole wall 42, the pistons move down the hole in relative to the wall 42. If the packing foot 106 is emptied, the cylinders 108 and 110 then move upwards in the hole relative to the wall 42.

In its second extreme position (Fig. 4B), the valve 158 allows fluid from the central channel 155 to flow through the passage 236 to the front chambers 176 and 180. When the valve 158 is in this position, the chambers 176 and 180 are in communication with the drilling fluid, which is at a higher pressure than the rear chambers 174 and 178. This causes the pistons 144 and 146 to move toward the cylinder bore ends due to the volume of incoming fluid. At the same time, the rear chambers 174 and 178 decrease in volume, and fluid is forced out of the rear chambers through the passage 234 and the valve 158 and out to the annulus 40. If the packing foot 106 is inflated to grip the borehole wall 42, the pistons move up the hole in relation to the wall 42. If the packing foot 106 is emptied, the cylinders 108 and 110 then move down the hole relative to the wall 42. In a central position, the advance valve 158 blocks any fluid communication between the cylinders 112 and 114, the channel 155 and the annulus 40.

In a preferred embodiment, the propulsion valves 156 and 158 are designed to form a controllable variable flow restriction between the central channel 155 and the chambers of the propulsion cylinders. The physical design of the valves 156 and 158 is described below. To illustrate the benefits of this feature, look at valve 156. When valve 156 deviates slightly from its center position, it allows a limited volume flow rate from the central channel 155 into the rear propulsion cylinders. This flow rate in volume can be increased or decreased precisely by varying the flow restriction, i.e. by opening the valve further or blocking it further. By precisely positioning the valve, the volumetric flow rate of fluid into the rear propulsion cylinders can be controlled. The valve's flow-limiting positions are indicated in fig. 4A-4F by flow lines crossing as X's. The flow limiting positions allow precise control of: (1) the longitudinal hydraulic force absorbed by the pistons; (2) the longitudinal position of the pistons inside the rear propulsion cylinders; and {3) the rate of longitudinal movement of the pistons between positions. The propulsion valve 158 may be similarly designed to allow the same degree of control over the forward propulsion cylinders and pistons. As will be shown below, the control of these attributes makes it easier to gain better control over the EST's thrust and speed, and further over the drill bit.

In a preferred embodiment, the position of the propulsion valve 156 is controlled by a rear propulsion motor 162, and the position of the propulsion valve 158 is controlled by a front propulsion motor 164. These motors can preferably be controlled electrically and can be operated via a programmable logic component on the EST 100, such as in the electronics unit 92 (Fig. 3) to precisely control the expansion and contraction of the rear and front chambers of the rear and front propulsion cylinders.

The above-described design of the EST allows greatly improved control over the tractor's impact, speed and direction of movement. The EST 100 may be moved down the hole in accordance with the cycle illustrated in FIG. 4A-4F. As shown in fig. 4A, the packing foot valve 154 is moved as a shuttle to a first outer position, allowing fluid to flow from the central channel 155 to the rear packing foot 104, and also allowing fluid to be discharged from the front packing foot 106 to the annulus 40. The rear packing foot 104 is blown up and grabs the borehole wall 42, whereby the rear propulsion cylinders 108 and 110 are anchored. The front packing foot 106 is emptied, so that the front propulsion cylinders 112 and 114 are free to move axially in relation to the borehole wall 42. Then, as shown in fig. 4B, the propulsion valve 156 is moved toward its first outer position, allowing fluid to flow from the central channel 155 into the rear chambers 166 and 170, and also allowing fluid to be discharged from the front chambers 168 and 172 to the annulus 40. The incoming fluid causes the rear chambers 166 and 170 to expand due to hydraulic force. Since the cylinders 108 and 110 are fixed relative to the borehole wall 42, the pistons 140 and 142 are forced down the hole to the front end of the pistons, as shown in fig. 4C. Since the pistons are fixed to the shaft 118 of the EST body, the forward movement of the pistons drives the EST body down the hole. This is known as a working stroke.

Simultaneously with or independently of the working stroke of the rear pistons 140 and 142, the propulsion valve 158 is moved to its second extreme position shown in fig. 4B. This allows fluid to flow from the central channel 155 to the front chambers 176 and 180 and from the rear chambers 174 and 178 to the annulus 40. The incoming fluid causes the front chambers 176 and 180 to expand due to hydraulic force. Accordingly, the advancing cylinders 112 and 114 move down the bore relative to the pistons 144 and 146, as shown in FIG. 4C. This is known as a reset stroke.

After the rear propulsion cylinders have completed a working stroke, and the forward propulsion cylinders have completed a reset stroke, the packing foot valve 154 is moved as a shuttle to its second extreme position, shown in FIG. 4D. This causes the front packing foot 106 to inflate and grip the borehole wall 42 and also causes the rear packing foot 104 to deflate. The propulsion valves 156 and 158 are then reversed, as shown in fig. 4E. This causes cylinders 112 and 114 to perform a work stroke and also causes cylinders 108 and 110 to perform a reset stroke, shown in FIG. 4F. The packing foot valve 154 is then shuttled back to its first extreme position and the cycle is repeated.

Those skilled in the art will appreciate that the EST 100 can move in reverse, i.e., uphole, simply by reversing the sequencing of the packing foot valve 154 or the advance valves 156 and 158. When the packing foot 104 is inflated to grip the wellbore wall 42, the advance valve is brought 156 in position to deliver fluid to the forward chambers 168 and 172. The incoming fluid imparts an uphole hydraulic force to the pistons 140 and 142, causing the cylinders 108 and 110 to perform an upward stroke. At the same time, the propulsion valve 158 is brought into position to supply fluid to the rear chambers 174 and 178, so that the cylinders 112 and 114 perform a reset stroke. The packing foot valve 154 is then moved to inflate the packing foot 106 and empty the packing foot 104. The advance valves are then reversed, so that cylinders 112 and 114 perform an upward working stroke in the borehole, while cylinders 108 and 110 perform a reset stroke. The cycle is then repeated.

The EST can advantageously shift into reverse before reaching the end of a particular power or reset stroke. The tool can be reversed simply by reversing the positions of the propulsion valves, so that the hydraulic power is provided on opposite sides of the annular pistons in the propulsion cylinders. This feature prevents damage to the drill bit, which can be caused by hitting an obstacle in the formation.

The provision of separate valves controlling: (1) the inflation of the packing feet, (2) the release of hydraulic power to the rear propulsion cylinders, and (3) the release of hydraulic power to the forward propulsion cylinders, permits a double-stroke operation and, in effect, a doubling of axial impact on the EST body. For example, the packing foot valve 154 can be moved to its center position to inflate both packing feet 104 and 106. The propulsion valves 156 and 158 can then be brought into position to supply fluid to the rear chambers of their respective propulsion cylinders. This would lead to a doubling of impact on the EST body down the borehole. In a similar manner, the propulsion valves can also be brought into position to deliver fluid to the front chambers of the propulsion cylinders, resulting in a double thrust up the hole. Double thrust can be useful when penetrating harder formations.

As mentioned above, the packing foot valve motor 160 and the advance valve motors 162 and 164 can be controlled by an electronic control system. In one embodiment, the EST's control system includes a surface computer, electrical cables (fiber optic or wires) and a programmable logic component 224 (Fig. 69) located in the electronics housing 130. The logic component 224 may include electronic circuits, a microprocessor, EPROM and/or tool control software. The tool control software is preferably provided on a programmable integrated chip (PIC) on an electronic circuit board. The control system works as follows: An operator enters commands on the surface, such as the desired EST speed, direction, thrust, etc. The software on the surface converts the operator's commands into electrical signals that are transmitted downhole through the electrical cables to the logic component 224. The electrical cables are preferably located inside the combined coil tube and connected by electrical wires inside the EST, which extend to the logic component 224. The PIC converts the operator's electrical commands into signals that control the motors.

As part of its control algorithm, the logic component 224 may also process various feedback signals containing information regarding states of the tool. For example, the logic component 224 may be designed to process pressure and position signals from pressure transducers and position sensors throughout the EST, a weight-on-the-bit (WOB) signal from a sensor that measures the load on the bit, and/or a pressure signal from a sensor that measures the pressure difference across the drill bit. In a preferred embodiment, the logic component 224 is programmed to intelligently operate the valve motors 160, 162 and 164 to control the valve positions based at least in part on one or both of two different characteristics, which are pressure and displacement. Based on pressure information, the control system can determine and regulate the impact acting on the EST body. Based on displacement information, the control system can determine and regulate the EST's speed. In particular, the logic component 224 may control the valve motors in response to: (1) the pressure differential for fluid in the rear and front chambers of the propulsion cylinders and at the inlet of the failsafe valve; (2) the positions of the annular pistons relative to the propulsion cylinders; or (3) both.

The actual command logic and software for controlling the tractor will depend on the desired performance characteristics of the tractor and the environment in which the tractor will be used. It is believed that once the performance characteristics have been determined, a person skilled in the art will readily determine the desired logic sequences and software for the control. It is believed that the structure and methods described in this document offer numerous advantages over the prior art, regardless of the performance characteristics and software chosen. It is therefore believed that even if a prototype of the tractor uses a special software (developed by the Halliburton Company in Dallas, Texas) a wide variety of software could be used to operate the system.

Pressure transducers 182, 184, 186, 188 and 190 may be provided on the tool to measure the pressure differential for fluid in respectively; (1) the posterior chambers 166 and 170; (2) the anterior chambers 168 and 172; (3) the posterior chambers 174 and 178; (4) the anterior chambers 176 and 180; and (5) in the inlet to the failsafe valve 150. These pressure transducers send electrical signals to the logic component 224 which are proportional to the sensed differential fluid pressure. In addition, as shown in fig. 4A-4F, displacement sensors 192 and 194 are provided on the tool to measure the position of the annular pistons relative to the advance cylinders. In the illustrated embodiment, sensor 192 measures the axial position of piston 140 relative to cylinder 110 and sensor 194 measures the axial position of piston 144 relative to cylinder 112. Sensors 192 and 194 may also be located on pistons 140 and 146, or additional displacement sensors may be provided if desirable.

Rotational accelerometers or potentiometers are preferably provided to measure the rotation of the motors. By monitoring the rotation of the motors, the position of the motorized valves 154, 156 and 158 can be determined. Like the signals from the pressure transducers and displacement sensors, the signals from the rotational accelerometers or potentiometers are fed back to the logic component 224 for controlling the valve positions.

Detailed structure of the EST

The largest units in the EST are the rear section, the control unit and the front section. Reference is made to fig. 2, where the largest components in the rear section include the shaft 118, the rear packing foot 104, the rear propulsion cylinders 108 and 110, the couplings 120 and 122 and a rear transition housing 131. The rear section includes a central channel for transporting drilling fluid supply from the drill string to the control unit 102 and to the drill bit. The rear section also includes passages for fluid flow between the control unit 102 and the rear packing foot 104 and the rear propulsion cylinders 108 and 110. The rear section further includes at least one passage for wiring for transmission of electrical signals between the ground surface, the control unit 102 and the downhole unit. A drill string coupling 116 is attached to the rear end of the rear section for fluidly coupling a coiled tubing drill string to the shaft 118, as is known in the art.

The front section is structurally almost identical to the rear section, with the exceptions that the components are in reverse order, and the front section does not include a rear transition housing. The front section includes the shaft 124, the front drive cylinders 112 and 114, the couplings 126 and 128 and the front packing foot 106. The front section includes a central conduit for transporting drilling fluid supply to the drill bit. The forward section also includes passages for fluid flow between the control unit 102 and the forward packing foot 106 and the forward propulsion cylinders 112 and 114. The forward section further includes at least one passage for wiring for transmission of electrical signals between the ground surface, the control unit 102 and the downhole unit. A coupling 129 is attached to the forward end of the forward section for connecting the shaft 124 to downhole components such as the downhole assembly, as known in the art.

St vr in norwegian units

Reference is made to fig. 2 and 3, where the control unit 102 comprises a rear transition housing 131 (Fig. 2), the electronics unit 92, a motor unit 94, valve unit 96 and front transition unit 98. The electronics unit 92 includes an electronics housing 130 which contains electronic components such as the logic component 224 for control of the EST. The motor assembly 94 includes a motor housing 132 containing the motors 160, 162 and 164. These motors respectively control the packing foot valve 154 and the propulsion valves 156 and 158. The valve assembly 96 includes a valve housing 134 containing these valves as well as the failsafe valve 150. Front transition assembly 98 includes a forward transition housing 136 containing the spreader 148 (not shown) and relief valve 152.

The first component of the control unit 102 is a rear transition unit 90. The rear transition housing 131 is shown in fig. 5-7. The housing 131 is connected to and is supplied with drilling fluid from the shaft 118. The housing 131 moves the drilling fluid supply from the middle of the tool to one side to make room for an electronics package 224 in the electronics unit 92. Fig. 5 shows the rear end of the housing 131, and fig. 6 shows its front end. The rear end of the housing 131 is attached to a flange 366 (Fig. 49A-49B) on the shaft 118. In particular, the housing 131 has threaded coupling bores 200 arranged in a pentagon, which align with similar bores 365 in the flange 366. Coupling pins or bolts of high strength is accommodated in bores 365 and bores 200 to fasten the flange and housing 131 together. The flange 366 has recesses 367, via which nuts can be attached to the rear ends of the coupling pins, against the surfaces in the recesses 367. Suitable coupling bolts are non-magnetic bolts MP33 which have high strength, elongation and toughness. At its front end, the housing 131 is attached to the electronics housing 130 in a similar manner, which therefore does not need to be described in more detail. Moreover, all the adjacent housings can be attached to each other and to the axles in the same or similar way and therefore do not need to be described in more detail either.

It should be understood that the components of the EST include numerous passages for transporting drilling fluid and electrical wiring through the tool. The rear transition housing 131 includes several longitudinal bores which form part of these passages. Longitudinal passage 202 transports the drilling fluid supply (from the drill string) down the hole. As shown in fig. 7, the passage 202 is moved from the center axis of the tool at the rear end of the housing 131 to an off-center position at the front end. A longitudinal wire passage 204 is provided for electrical wires. A longitudinal conduit passage 205 is provided at the front end of housing 131 and extends over approximately half the length of the housing. The passages 204 and 205 are connected to each other through an elongated opening 212 in the housing 131. In a preferred embodiment, wires from the surface are separated at the opening 212 and connected to a 7-pin connector element 209 (fig. 69) and a 10- pin connecting element 211. The connecting elements 209 and 211 fit respectively into the passages 204 and 205 in the front end of the housing 131 and are connected to corresponding openings in the electronics housing 132. The passage 206 allows fluid connection between the rear propulsion valve 156 and the rear chambers 166 and 170 in the rear propulsion cylinders 108 and 110. Passage 208 allows fluid connection between valve 156 and front chambers 168 and 172 in cylinders 108 and 110. Passage 210 allows fluid connection between packing foot valve 154 and rear packing foot 104.

Figs. 8-12 show the electronics housing 130 in the electronics unit 92, which contains an electronic logic component or package 224. The housing 130 includes longitudinal bores for the passages 202, 204, 205, 206, 208 and 210. The electronics package 224 is located in a lot with large diameter of the passage

205 inside the housing 130. The above-mentioned 10-pin connector 211 at the front end of the rear transition housing 131 is connected to the electronics package 224. The passage 205 is preferably sealed at the rear and front ends of the electronics housing 130 to prevent damage to the electronics package 224 caused by the housing is exposed to high pressure from the annulus 40, which can be as high as 1103 bar. A suitable seal, with specification 1379 bar is sold by Green Tweed, Inc., which has offices in Houston Texas. Preferably, the housing 130 is made up of a material that is sufficiently heat-resistant to protect the electronics package 224 from damage that can be caused by it being exposed to high temperatures down in the hole. A suitable material is Stabaloy AG 17.

As shown in fig. 9 and 11, a recess 214 is provided in the front end of the electronics housing 130 to receive a pressure converter manifold 222 (fig. 13-16) which includes the pressure converters 182, 184, 186, 188 and 190 (fig. 3). The passages 206, 208 and 210 are shifted transversely towards the central axis of the electronics housing 130 to make room for the pressure converters. Reference is made to fig. 12, where transverse offset bores 216, 218 and 220 are provided to offset passages 206, 208 and 210, respectively, to their forward end positions shown in FIG. 9 and 10. The displacement bores 216, 218 and 220 are plugged at the radially outer side of the housing 130 to prevent leakage of fluid to the annulus 40. Figs. 13-16 show the pressure transducer manifold 222 which is designed to accommodate the pressure transducers for measuring the pressure difference in drilling fluid that passes through the various manifold passages. The pressure transducers 182, 184, 186, 188 and 190 are accommodated in transducer bores 225, 226, 228, 230 and 232, respectively, which extend radially inwards from the outer surface of the manifold 222 to the longitudinal bores therein. The longitudinal bores for the passages 205, 206, 208 and 210 extend through the length of the manifold 222 and align with corresponding bores in the electronics housing 130. In addition, the longitudinal bores extend rearward from the front end of the manifold 222 without reaching the rear end, forming passages 234, 236 and 238. The passage 234 is in fluid communication with the rear chambers 174 and 178 in the forward propulsion cylinders 112 and 114. The passage 236 is in fluid communication with the forward chambers 176 and 180 in the cylinders 112 and 114. The passage 238 is in fluid communication with the front packing foot 106. As shown in fig. 15 and 16, the transducer bores 225, 226, 228, 230 and 232 are in connection with passages 206, 208, 234, 236 and 238, respectively. As will be described below, the pressure transducers are exposed to drilling fluid internally and to oil externally. The oil is maintained at the pressure in the annulus 40 via a pressure compensation piston 248 (Fig. 45) to produce the desired pressure difference measurements.

Figs. 17 and 18 show the motor housing 132 in the motor assembly 94. Attached to the front end of the electronics housing 130, the housing 132 includes longitudinal bores for the passages 202, 204, 206, 208, 210, 234, 236 and 238 which are aligned with the corresponding bores in the electronics housing 130 and the pressure converter manifold 222. The housing 132 also includes longitudinal bores for passages 240, 242 and 244 which respectively house the packing foot motor 160, the rear propulsion motor 162 and the forward propulsion motor 164. In addition, a longitudinal bore for a passage 246 houses a pressure compensating piston 248 in its rear end and a fail-safe valve spring 151 (fig. 45) at its front end. The composition and operation of the motors, valves, pressure compensation piston and fail-safe valve spring are described below.

A motor mounting plate 250 shown in fig. 19 and 20 are attached between the front end of the engine housing 132 and the rear end of the valve housing 134. The motors are enclosed in lead screw housing 318 (described below) which is secured to mounting plate 250. Plate 250 includes bores for passages 202, 204, 206, 208, 210, 234, 236, 238, 240, 242, 244 and 246 which are aligned with corresponding bores in the motor housing 132 and the valve housing 134. As shown in fig. 20, the bores for passages 240 (gasket foot motor), 242 (rear propulsion motor) and 244 (forward propulsion motor) on the face of plate 250 are countersunk to receive mounting bolts 334 (Fig. 44). The bolts 334 attach the lead screw housings 318 to the rear of the plate 250.

Figs. 21-27 show the valve housing 134 in the valve assembly 96. Attached to the front end of the engine mounting plate 250, the housing 134 has longitudinal recesses 252, 254, 256 and 258 in its outer radial surface, which respectively accommodate the fail-safe valve 150, the gasket foot valve 154, the rear propulsion valve 156 and the front propulsion valve 158. The housing 134 has bores for the passages 202, 204, 206, 208, 210, 234, 236, 238, 240, 242, 244 and 246 which are aligned with corresponding bores in the engine mounting plate 250. In the front end of the housing 134, a central longitudinal bore is provided which forms a rear part of the channel 155. The channel 155 does not extend to the rear end of the housing 134 since its purpose is to convey fluid from the outlet of the fail-safe valve 150 to the other valves . In addition, a longitudinal bore is provided in the front end of the housing 134 for a passage 260. The passage 260 allows fluid connection between the packing foot valve 154 and the front packing foot 106.

As shown in fig. 24-27, the valve body 134 includes various cross bores extending from the valve recesses to the longitudinal fluid passages for fluid communication with the valves. As described below, the valves 150, 154, 156 and 158 are slide valves each comprising a slide designed to move within a valve body. In operation, the slides move longitudinally within the bores in the valve bodies and communicate with the fluid passages to provide the behavior shown schematically in fig. 4A-4F. Fig. 24 shows the openings of the transverse bores inside the fail-safe valve's recess 252 which accommodates the fail-safe valve 150. The bores form passages 2 62, 264, 2 66 and 268 which extend inwards between the fail-safe valve 150 and various internal passages. In particular, passages 262 and 266 extend inwardly to passage 238 (the outlet of spreader 148), and passages 264 and 268 extend to channel 155. As will be described below, failsafe valve 150 distributes fluid from passage 238 to channel 155 when the fluid pressure in passage 238 exceeds the desired "on/off" threshold. Fig. 25 shows the openings of the transverse bores in the forward propulsion valve recess 258. The bores form passages 270, 272 and 274 which extend from the forward propulsion valve 158 to the passage 236, the channel 155 and the passage 234 respectively. Fig. 26 shows the openings of the transverse bores inside rear propulsion valve recess 256. The bores form passages 276, 278 and 280 which extend from rear propulsion valve 156 to passage 208, channel 155 and passage 206 respectively. Fig. 27 shows the openings of the cross bores in the packing foot valve recess 254. The bores form passage 282, 284, and 286 extending from packing foot valve 154 to passage 260, passage 155, and passage 210, respectively. As mentioned above, propulsion valves 156 and 158 distribute fluid from passage 155 to the rear and front chambers of rear and front propulsion cylinders 108, 110, 112 and 114. The gasket foot valve 154 distributes fluid from the channel 155 to the rear and front gasket feet 104 and 106. Fig. 28-30 show r front adapter housing 136 in the front adapter assembly 98 which connects the valve housing 134 to the front shaft 124 and houses the relief valve 152 and the spreader 148. To simplify the manufacture of the tool, the rear and front shafts 118 and 124 are preferably identical. Thus, the housing 136 repositions the various passages extending through the tool, via transverse offset bores (Fig. 30) as described above, to align the passages with corresponding passages in the forward shaft 124. Note that the offset bores are plugged on the outer radial surface of the housing 136 to prevent leakage of fluid to the annulus 40. As seen in the figures, the rear end of the housing 136 has longitudinal bores for the passages 155, 202, 204, 234, 236, 238 and 260 which are aligned with corresponding bores in the valve housing 134. The supply passage 202 passes from the lower part of the housing at the rear end to the central axis of the housing at the front end to align with a central bore in the front shaft 124. The conduit passage 204 is enlarged in the front end of the housing 136 to facilitate connection to the wiring passages in the front axle 124. Also note that the passage 238 does not extend to the front end of the housing 136. Purpose with the passage 238 is to advance fluid from the spreader to the fail-safe valve 150.

Reference is still made to fig. 28-30 where the spreader 148 (Figs. 31 and 32) is received in the passage 202 at the front end of the housing 136. Fluid that passes through the spreader wall flows into the passage 238 and flows back towards the valve housing 134 and to the fail-safe valve 150. A further passage 238A is in fluid communication with passage 238 via a transverse displacement bore. Fluid in the passage 238A exerts an axial force directed upwards in the borehole on the fail-safe slide and further on the spring 151 (Fig. 45) to open the valve. The channel 155 extends forward to the upper outlet opening 288 in the housing 136, in which the relief valve 152 (Figs. 46-48) is accommodated. The design and operation of the spreader 148 and the valves in the tool are described below.

One embodiment of the spreader 148 is shown in fig. 31 and 32. As shown, the spreader 148 is a cylindrical tube having a flange at its forward end and holes 290 which slope backward in the tube. Most of the drilling fluid that flows through the passage 202 in the front transition housing 136 flows through the spreader 148 tube and down to the bottom hole assembly. However, some of the fluid flows back up the wellbore through the holes 290 and into the passage 238 which supplies the failsafe valve 150. It is believed that the larger fluid particles will not normally change direction to the opposite direction, but will be forced downward

in the borehole of the flow. The holes 290 form an angle of about 135° with the flow of fluid, but an angle of at least 110° with the flow of fluid is believed to be sufficient to reduce blockage. Further, the rear slanted holes 290 are sized to restrict the flow of larger fluid particles to the valve housing 134. Preferably, the holes 290 have a diameter of 3.2 mm or less. Those skilled in the art will understand that a number of different types of spreaders or filters can be used, taking into account the purpose of preventing larger fluid particles from entering and possibly clogging the valves. If the valves are designed so that clogging is not a significant problem, or if the fluid is sufficiently free of harmful larger fluid particles, the spreader 148 can of course be omitted from the EST.

Reference is made to fig. 33-37, where the fail-safe valve 150 comprises a valve slide 292 which is engaged in a valve body 294. The slide 292 has segments 293 of larger diameter. The body 294 has a central bore 298 which receives the slide 292, and fluid ports in its lower wall for the fluid passages 262, 264, 266 and 268 described above. The diameter of the bore 298 is such that the slide 292 can be slidably accommodated in it, and so that the segments 293 of the slide 292 can slide against the inner wall of the bore 298 in an effective fluid-sealing relationship. The central bore 298 has a slightly enlarged diameter at the axial portions for the passages 264 and 268. These portions are shown in the figures as areas 279. The areas 279 allow inflowing fluid to move into or out of the valve with less erosion of the valve body or the valve slide. The body 294 is dimensioned to fit fluid-tightly and axially slidably in the fail-safe valve's recess 252 in the valve housing 134. The body 294 has inclined end surfaces 296 which lie pressed between similarly inclined portions of the valve housing 134 and the forward transition housing 136 which delimits the ends of the recess 252 Such pressing keeps the body 294 tightly attached to the outer surface of the valve housing 134. Furthermore, a spacer, such as a flat plate, can be provided in the recess 252 between the front end of the valve body 294 and the front above the passage housing 136. The spacer can be sanded to accommodate tolerances in the construction of such mutually fitting parts. In an EST having a diameter of 8.6 cm, the ports 262, 264, 266 and 268 in the valve body 294 have a diameter of preferably 2.5 mm to 12.7 mm and more preferably 5.1 mm to 6.4 mm . In the same embodiment, the passage 298 preferably has a diameter of 10.2 mm to 12.7 mm.

A tap opening 300 in the valve body 294 allows fluid to be released from the passage 298 to the annulus 40. The ports in the valve body 294 are in fluid communication with each other depending on the position of the slide 292. Figs. 36 and 37 are longitudinal sectional elevations of the fail-safe valve 150. Note that ports 264 and 268 are shown in phantom because these ports are not on the center axis of body 294. Nevertheless, the positions of ports 264 and 268 are indicated in the figures. In the closed position, shown in fig. 36, slide 292 allows fluid from passage 268 (which communicates with channel 155) to flow to tap opening 300 (which communicates with annulus 40). In the open position, shown in fig. 37, slide 292 allows fluid flow from passages 264 and 268 (which communicate with channel 155) to passages 262 and 266 (which communicate with spreader outlet 238).

As mentioned above, the fail-safe valve 150 allows fluid to flow into the channel 155 in the valve assembly 96. The desired volumetric flow rate into the channel 155 depends on the tractor size and the activity to be performed, and is set out in the table below. The value ranges set out below are the flow rates (in liters per minute) through the valve 150 and into the channel 155 when milling, drilling, driving into an unlined or lined borehole, for different EST diameters. The flow rate into the channel 155 depends on the dimensions of the failsafe valve body and ports.

If desired, the failsafe valve 150 stroke can be limited to a stroke of 0.32 cm (from closed to open position) to minimize the load on the relief valve 152. The failsafe valve slide stroke is limited by the compression of the spring 151. For an EST having a diameter of 8.6 cm, this stroke results in a maximum flow rate in volume of 45.4 liters per minute from the spreader outlet 238 to the channel 155, with an average flow rate of approximately 30.3 liters per minute. The fail-safe valve 150's flow rate capacity by volume is preferably substantially more than, and preferably double, the capacity of the propulsion valves 154 and 156 to ensure sufficient flow to drive the tool.

In the illustrated embodiment, the advance valves 156 and 158 are identical and the packing foot valve 154 is structurally similar. As shown in fig. 23-28, in particular, the locations of the fluid ports for the gasket foot valve 154 are slightly different than those for the forward valves 156 and 158 due to space limitations that limit the location of the internal fluid passages in the valve body 134. However, it should be understood that the gasket foot valve 154 acts on a substantially similar to the propulsion valves 156 and 158. Thus, only the rear propulsion valve 156 needs to be described in more detail in this document. Figs. 38-42 show the rear propulsion valve 156, which is designed essentially like the fail-safe valve 150. The valve 156 is a four-way valve comprising a slide 304 and valve body 306. The slide 304 has segments 309 with a larger diameter and segments 311 with a smaller diameter. As shown in fig. 39, the segments 309 include one or more notches 312 that allow variable flow restriction between the various flow ports in the valve body 306. The valve body 306 has a design similar to the design of the failsafe valve body 294 except that the body 306 has three ports in its lower wall for the fluid passages 276, 278 and 280, described above, and two tap openings 308 and 310 which are in fluid communication with the annulus 40. A central bore 307 has a diameter designed to receive the slide 304, so that the segments 309 slide along the inner wall of the bore 307 in a effective fluid sealing conditions. Since the positions of the notches 312 along the circumference of the segments 309 may, but need not, be adjacent to the fluid ports in the valve body, the bore 307 preferably has a slightly enlarged diameter at the axial portions of the passages 276 and 280, so that the ports can communicate with all the chops. That is, the inner radial surface of the valve body 306 which delimits the bore 307 has a larger diameter than the other inner radial surfaces which limit the path of movement of the slide 304 segments 309. These parts with an enlarged diameter are shown in the figures as areas 279. The valve body 306 is dimensioned to fit tightly into the rear propulsion valve recess 256 in the valve body 134. A spacer may also be provided as described above in connection with the failsafe valve body 294. Figs. 40-42 are longitudinal sectional elevations of the rear propulsion valve 156. Note that ports 276 and 280 are shown in phantom drawing because these ports are not located on the central axis of the valve body 306. Nevertheless, the positions of the ports 276 and 280 are indicated in the figures. The body's 306 ports are in fluid communication with each other depending on the slide's 304 axial location. When the rear propulsion valve 156 is in the closed position, shown in fig. 40, the slide 304 completely restricts fluid flow to and from the rear propulsion cylinders. In another position, shown in fig. 41, slide 304 allows fluid flow from passage 278 (which communicates with channel 155) to passage 280 (which communicates with rear chambers 166 and 170 of rear propulsion cylinders 108 and 110), and from passage 276 (which is connected to the front chambers 168 and 172 in the cylinders 108 and 110) to the tap opening 310 (which is connected to the annulus 40). In this position, the valve 156 supplies hydraulic power for a forward stroke in the rear propulsion cylinders, during which fluid is supplied to the rear chambers 166 and 170 and discharged from the front chambers 168 and 172. In another position, shown in fig. 42, slide 304 allows fluid flow from passage 278 (which communicates with channel 155) to passage 276 (which communicates with anterior chambers 168 and 172) and from passage 280 (which communicates with posterior chambers 166 and 170 ) to the tapping opening 308 (which is connected to the annulus 40). In this position, the valve 156 supplies hydraulic power for a reset stroke in the rear propulsion cylinders, during which fluid is supplied to the front chambers 168 and 172 and discharged from the rear chambers 166 and 170.

It should be understood that the volumetric flow rate of drilling fluid into the rear propulsion cylinders 108 and 110 can be precisely controlled by controlling the axial position of the valve slide 304 within the valve body 306. The volumetric flow rate of fluid through any given fluid port in the body 306 depends on which extent a large diameter segment 309 of the slide 304 blocks the port.

Figures 43A-43C illustrate this principle. Fig. 43A shows the slide 304 which has a position such that a segment 309 completely blocks a fluid port in the body 306. In this position there is no flow through the port. When the slide 3 04 slides a certain distance in one direction, as shown in fig. 43B, some fluid flow is allowed through the port via the notches 312. In other words, segment 309 allows fluid flow through the port only through the notches. This means that all fluid that passes through the port passes through the areas defined by the notches 312. The volumetric flow rate through the port is relatively small in this position due to the small opening through the notches. Generally, the flow rate depends on the shape, dimensions and number of the notches 312. The notches 312 preferably have decreasing depth and width as they extend towards the middle of the length of the segment 309. This allows the flow restriction, and further the volumetric flow rate, to be very finely regulated as a function of the slide's axial position.

In fig. 43C, the slide 304 is moved further, so that the fluid can freely flow past the segment 309 without necessarily

flow through the notches 312. In other words, the segment 309 allows fluid flow through the port at least partially outside the notches. This means that some of the fluid that passes through the port does not flow through the areas defined by the notches

312. In this position, the flow restriction is significantly reduced, resulting in a higher flow rate through the port. The EST's valve structure thus allows more precise control over the flow rate of fluid to the annular pistons in the propulsion cylinders and further over the speed and impact of the tractor.

Fig. 78 graphically illustrates how the fluid flow rate to either the rear or the front chambers of the propulsion cylinders varies as a function of the axial displacement of the propulsion valve slide. Section A of the curve corresponds to the waiting position shown in fig. 43B, i.e. when the fluid flows only through the notches 312. Section B corresponds to the valve position shown in fig. 43C, i.e. when the fluid can freely flow past the edge of the large diameter segment 309 of the slide. As shown, the flow rate gradually increases in section A and then increases much more significantly in section B. Section A is thus an area corresponding to fine-tuned control over the EST's speed, thrust and position.

The valve slide 304 preferably includes at least two, advantageously between two and eight, and more preferably three notches

312 on the edges of the large diameter segments 3 09. As shown in fig. 79, each notch 312 has an axial length L extending inwardly from the edge of the segment 309, a width W at the edge of the segment 309, and a depth D. For an EST having a diameter of 8.6 cm, L is preferably about 1 .4-1.8 mm, W is preferably about 2.9-3.8 mm, and D is preferably about 1.5-1.8 mm. For ESTs of larger dimensions, the notch dimensions are preferably larger, and/or more notches are provided to thereby produce higher flow rates through the notches. The notch size significantly affects the possibility of continuous flow of fluid into the pistons and further continuous movement of the tractor at low speeds. The notches actually allow a significantly improved control over the tractor at low speeds compared to prior art. However, some drilling fluids (especially barite muds) tend to stop flowing at low flow rates and form a blocking bridge in small channels such as those in these valves. Greater volume in the notches allows more mud to flow before bridging occurs, but also results in less steering at low speeds. As an alternative means of controlling the tractor at very low speeds, the slide can be open for a specific period of time and then closed and opened again in a "trembling" motion, providing an almost continuous low speed of the tractor.

The valve slides can also have alternative designs. For example, the segments 309 may have a single region of smaller diameter at their axial ends to provide an annular flow channel for the drilling fluid. In other embodiments, the slides may be provided with multiple steps and shapes that would allow different sludge flow rates through the EST. For example, several tapers 550 can be provided as shown in fig. 71. Alternatively, several conical tapers 552 may be provided as shown in fig. 72. The slide designs shown in fig. 71 and 72 allow the slide to "tremble" more quickly into and out of the various positions. "Jittering" would add pressure peaks to the advance valves, which could provide a more responsive tool feed but less fine-tuned control. A stepped design of the conings on the slide also tends to prevent drilling mud from stopping into openings between the slide and the valve body.

Although the slide designs described above can be used to provide different possibilities for flow rate regulation, the notched design in fig. 38. The notches 312 have a larger minimum dimension than tapers or conical tapers as shown in FIG. 71 and 72. The notches 312 will thus be less likely to be clogged by larger fluid particles, which could make the slide ineffective. The notches are also less affected by fluid boundary layers on the slides because fluid boundary layers represent a smaller percentage of the total cross-sectional area bounded by the notches.

When designing the slide valves, the radial clearance between the valve body and the slide is important. This clearance is preferably made sufficiently large to resist potential clogging from large particles in the drilling fluid, but sufficiently small to prevent leakage which could prevent control of the EST. This behavior can be attributed to the tendency of some muds (especially those containing barite) to bridge, or clog, small openings. The clearance is dimensioned within the typical operating characteristics for most residential waste liquids. Preferably, the clearance is about 0.015 mm-0.058 mm.

As mentioned above, the design of the valves 154, 156 and 158 allows precise control of the volumetric flow rate of fluid to the propulsion cylinders 108, 110, 112 and 114 and the packing feet 104 and 106. In the illustrated embodiment of the EST, the volumetric flow rate of fluid to the propulsion cylinders more specifically are controlled and maintained at any flow rate to a minimum of preferably 2.3 liters per minute, more preferably 0.2 liters per minute and even more preferably 0.02 liters per minute, which corresponds to fluid flow only through the notches 312. The ability to control and maintain a substantially constant volumetric flow rate at such low flow rates allows the EST to operate at low speeds. For an EST having a diameter of 8.6 cm, the stroke of the propulsion valve slides is preferably limited, so that the maximum volumetric flow rate into the propulsion cylinders is approximately 0-34.1 liters per minute. Preferably, the maximum stroke length from the closed position is 6.4 mm, as shown in fig. 40.

As mentioned above, the packing foot valve 154 and the rear and front propulsion valves 156 and 158 are controlled by motors. In a preferred embodiment, the structural design that allows the motors to communicate with the valves is similar for each motorized valve. Thus, only the rear propulsion valve 156 motor is described in this document. Figures 44A and 44B illustrate the structural design of the EST, which allows the rear propulsion motor 162 to control the valve 156. This design converts output torque from the motor into axial movement of the valve slide 304. The motor 162 is cylindrical and is mounted within a tubular lead screw housing 318. The motor 162 and the lead screw housing 318 are located in the bore 242 in the motor housing 132. The front end of the lead screw housing 318 is held in contact with the motor mounting plate 2 50 via a mounting bolt 334 which extends through the mounting plate 250 and is in threaded engagement with the inner surface of the housing 318.

Inside the lead screw housing 318, the motor 162 is connected to a lead screw 322 via the motor coupling 320, so that output torque from the motor causes the lead screw 322 to rotate. A bearing 324 is provided to hold the lead screw 322 along the center axis of the housing 318, which is aligned with the rear propulsion valve slide 304 in the valve housing 134. The lead screw 322 is in threaded engagement with a lead screw nut 326. A longitudinal key 325 on the lead screw nut 326 engages with a longitudinal slot 328 in the lead screw housing 318. This prevents the nut 326 from rotating relative to the lead screw housing 318, whereby the nut 326 is influenced to rotate only along the threads of the lead screw 322. Thus, rotation of the lead screw 322 causes axial movement of the nut 326 along the lead screw 322 A stem 330 is attached to the front end of the nut 326. The stem 330 extends forward through an annular narrowing ring 333 which separates oil in the engine housing 132 from drilling fluid in the valve housing 134. The drilling fluid is separated from oil by a T-seal 332 in the narrowing 333. The front end of the stem 330 is attached to the valve slide 304 via a slide bolt 336 and the split holder 338. The stem 330 is preferably relatively thin and flexible, so that it can compensate for any error in the alignment between the stem and the valve slide.

It can thus be seen that output torque from the engines is transformed into axial movement of the valve slides via the lead screw units as described above. The displacement of the valve slides is monitored by constant measurement of the engine revolutions. Preferably, rotational accelerometers or potentiometers are built into the engine chambers to measure the revolutions of the engines, as is known in the art. The electrical signals from the accelerometers or potentiometers can be transmitted back to the logic component 224 via electrical lines 536 and 538 (Fig. 69).

The motors 160, 162 and 164 are preferably stepper motors, which require fewer wires. Stepper motors are advantageous without brushes. If, on the other hand, motors with brushes are used, threads from the brushes, when these break down, can make the oil electrically conductive. Importantly, stepper motors can be instructed to rotate a given number of steps, facilitating precise control of the valves. Each motor insert may include a gearbox to generate sufficient torque and angular velocity to rotate the lead screw at the desired speed. The engine gearbox unit should desirably be able to generate an output force of at least 22.2 newtons, more desirably at least 44.5 newtons and even more desirably at least 222.3 newtons of force and angular velocity of at least 75-180 revolutions per minute. minute. The motors are preferably designed to rotate 12 steps for each full revolution of the motors' output shafts. For an EST with a diameter of 8.6 cm, the unit with the motor, gearbox and accelerometer should preferably have a diameter of no more than 2.22 cm (and preferably 1.9 cm) and a length of no longer than 7, 8 cm. A suitable motor is article no. DF7-A sold by CD Astro Intercorp, Inc. of Deerfield, Florida.

For optimal control of the EST's speed and impact, it is desirable to know the relationships between the angular positions of the motor shafts and the flow rates through the valves of the propulsion cylinders. Such conditions depend on the cross-sectional areas of the flow restrictors which act on the fluid flows through the valves and thus on the dimensions of the slides, the valve bodies and the fluid ports in the valve bodies. Such conditions also depend on the thread pitch of the lead screws. In a preferred embodiment, the lead screws are approximately 0.794-3.175 mm

(8-32 threads per inch).

Inside the motor housing 132, bores 240, 242 and 244 contain the motors as well as the electrical wiring that extends rearward to the electronics assembly 92. For optimum performance, these bores are preferably filled with a non-electrically conductive fluid to reduce the risk of inefficient electrical transmission through the wires. Since the pressure in the engine chambers is also preferably equalized to the pressure in the annulus 40 via a pressure compensating piston (as described below), such fluid preferably has a low compressibility to minimize the longitudinal travel of the compensating piston. A preferred fluid is oil since the compressibility of oil is much less than that of air. At the rear end of the engine housing 132, these bores are open for fluid to the space surrounding the pressure converter manifold 222. Thus, the outer ends of the pressure converters 182, 184, 186, 188 and 190 are also exposed to oil.

Fig. 45 illustrates the composition and operation of the fail-safe valve 150. The rear end of the fail-safe valve slide 292 rests against a spring guide 340 which slides inside the passage 246 in the motor housing 132, the motor mounting plate 250 and the valve housing 134. Inside the motor housing 132, the passage 246 has an annular spring stopper 342 which is fixed in relation to the housing 132. The guide ring 340 has an annular flange 344. The fail-safe valve spring 151, preferably a coil spring, is located in the passage 246 so that its ends abut against the stopper 342 and the flange 344. Fluid in the passage 238A (from the outlet of the spreader 148) exerts a axial force on the front end of the slide 292, which is counteracted by the spring 151. As shown, a spacer can be provided having a passage 238B to accommodate tolerances between the mating surfaces of the valve housing 134 and forward transition housing 136. The passage 238B stands in fluid communication with the passage 238A and with the slide passage 298 in the failsafe valve body 294. When the fluid pressure in the passage 238A exceeds a particular threshold, overcome es the spring force to open the fail-safe valve 150 as shown in fig. 37. The spring 151 can be carefully selected to be compressed at a desired fluid pressure threshold in the passage 238A.

When the EST is removed from a borehole, drilling fluid residue is likely to remain in the passage 246 of the motor housing 132. As shown in FIG. 17-18, a pair of cleaning holes 554 may be provided which extend into the passage 246. Such holes allow the passage 246 to be cleaned by spraying water through the passage so that the spring 153 functions properly in use. In use, the holes 554 can be plugged, so that the drilling fluid does not escape to the annulus 40.

Reference is made to fig. 44A-44B, where the lead screw assemblies for the motorized valves contain drilling fluid from the annulus 40. Such fluid flows into the lead screw assemblies via the outflow openings in the valve bodies and surrounds portions of the valve slides and stems 330 in front of the annular restrictors 333. As mentioned above, the chambers are behind the restrictors 333 filled with oil. To move the valve slides, the motors must produce sufficient torque to overcome: (1) the pressure differential between the drilling fluid and the oil; and (2) the sealing friction caused by the T-seals 332. Since the fluid pressure in the annulus 40 can be as high as 1,103 bar, the oil pressure is preferably equalized to the fluid pressure in the annulus 40, so that the pressure difference across the seals 332 is zero. In the absence of such oil pressure compensation, the engine would have to work extremely hard to advance the slides towards the drilling fluid which is under high pressure. A significant pressure difference can cause the engines to stop. If the pressure difference across the seals 332 is sufficiently high, the seals will also have to be very tight to prevent fluid flow past the seals. If the seals were very tight, however, they would inhibit, and probably prevent, movement of the stems 330 and further the valve slides.

Reference is made to fig. 45, where a pressure compensating piston 248 is preferably provided to avoid the above problems. Preferably, the piston 248 is located in the passage 246 of the motor housing 132. The piston 248 seals against drilling fluid at its front end and against oil at its rear end and is designed to slide axially in the passage 246. When the pressure in the annulus 40 increases, the piston 248 slides backwards for to equalize the oil pressure to the drilling fluid pressure. And conversely, when the pressure in the annulus 40 decreases, the piston 248 slides forward. Advantageously, the piston 248 effectively neutralizes the longitudinal net fluid pressure force acting on each of the valve slides, through the drilling fluid and the oil. The piston 248 also creates a pressure differential of zero across the seals 332 in the valve lead screw assemblies.

Fig. 46-48 illustrate the design and operation of the relief valve 152. The relief valve 152 comprises a valve body 348, valve element 350 and coil spring 153. The body 348 is generally tubular and has a nose 351 and an internal valve seat 352. The valve element 350 has a rounded end 354 designed to abut against the valve seat 352 to block the valve. The valve element 350 also has several longitudinal ribs 356 between which fluid can flow to and out to the annulus 40. Inside the front transition housing 136, the relief valve accessory 348 is located, placed in a diagonal part 349 of the channel 155, which extends to the opening 288 and out to the annulus 40. The body 348 is tightly and securely taken up in the rear end of the diagonal bore 349. A tube 351 is located in front of the body 348. The tube 351 houses the relief valve spring 153. The valve element 350 is slidably received in the body 348. The valve element's 350 front end rests against spring 153 rear end. The front end of the spring 153 is held by an internal annular flange in the pipe 351. In operation, the drilling fluid inside the channel 155 exerts a force on the rounded end 354 of the valve element 350, which force is counteracted by the spring 153. When the fluid pressure rises, the force on the end also rises 354. If the fluid pressure in the channel 155 exceeds a threshold pressure, the spring force is overcome, forcing the end 354 to lift off the valve seat 3 52. This allows fluid from the channel 155 to be discharged to the annulus 40 through the bore 349 and between the ribs 356 of the valve element 350.

In a preferred embodiment, the control unit 102 is substantially cylindrical with a diameter of approximately 8.6 cm and a length of approximately 118.6 cm. The housings 130, 131, 132, 134 and 136 are preferably constructed of very strong material to prevent erosion caused by being exposed to coarse drilling fluids such as calcium bromide or cesium formate mud. How severe and extensive the erosion is usually depends on the velocity of the drilling fluid to which the material is exposed, the solid material in the fluid and the angle at which the fluid hits the surface. During operation, the control unit housings are exposed to drilling mud velocities of 0 to 16.8 meters per second. second, with typical average operating speeds of less than 9 m per second. second (except inside the valves). Under these conditions, a suitable material for the control unit housings is Stabaloy, especially Stabaloy AG 17. In the valves, the mud flow velocities can be as high as 46 meters per hour. second. Thus, the valves and valve bodies are preferably formed from an even more erosion resistant material, such as tungsten carbide, Ferro-Tec (a brand name steel formed from titanium carbide supplied by Alloy Technologies International, Inc. of West Nyack, New York) or similar materials . The housings and valves can be made of other materials with due regard to the aim of resisting erosion.

Axle units

In a preferred embodiment, the front and rear axle units are substantially the same. Thus, only the rear axle unit is described in more detail in this document. Fig. 49 shows the design of the rear axle unit. The rear packing foot 104, the flexible coupling 120, the cylinder 108, the flexible coupling 122 and the cylinder 110 are connected end to end and are slidably assembled in engagement on the rear shaft 118. The annular pistons 140 and 142 are attached to the shaft 118 via bolts fixed in bolt holes 360 and 362 respectively. O-rings or specially designed elastomeric seals may be provided between the pistons and the shaft to prevent fluid flow under the pistons. Cylinders 108 and 110 enclose pistons 140 and 142, respectively. The front and rear ends of each propulsion cylinder are sealed via T-seals, O-rings or other means to prevent fluid from escaping from within the cylinders to annulus 40. It is also provided seals between the outer surface of the pistons 140 and 142 and the inner surface of the cylinders 108 and 110 to prevent fluid from flowing between the front and rear chambers of the cylinders. Couplings 120 and 122 may be attached to packing foot 104 and cylinders 108 and 110 via threaded engagement to ensure complete high pressure tightness and avoid the use of multiple bolts and screws. Beveled surfaces may be provided on the leading edges of the couplings 120 and 122 and the sealing cap 123 attached to the front end of the cylinder 110. Such beveled surfaces help to prevent the assembly from hooking on sharp surfaces such as milled casing passages.

Several elongated rotation limiters 364 are preferably attached to the shaft 118, which prevent the packing foot 104 from rotating relative to the shaft. The limiters 364 are preferably spaced equidistant along the circumference of the shaft 118 and may be attached via bolts as shown. Four limiters 3 64 are preferably provided. The packing foot 104 is designed to engage with the limiters 364 to thereby prevent rotation of the packing foot in relation to the shaft, as described in more detail below.

Figs. 50-59 illustrate in more detail the design of the shaft 118. At its front end, the shaft 118 has a flange 366 which is curved for more even distribution of load. The flange 366 includes bores for the fluid passages 202, 206, 208 and 210 which line up with corresponding bores in the rear transition housing 131. Note that the dimensions of these passages can be varied to provide different flow rate and velocity capabilities of the EST . In addition, a pair of wire passages 204A are provided, one or both passages being aligned with the wire bore 204 in the housing 131. Electrical wires 502, 504, 506 and 508 (Fig. 69) which extend up to the surface and in one embodiment to a position sensor on piston 142, is located in passage 204A. As shown in fig. 52, only the conduit passages 204A and the supply passage 202 extend to the rear end of the shaft 118.

As shown in fig. 55, the fluid passages 206, 208 and 210 inside the shaft 118 comprise a pair of passages each, 206A, 208A and 210A respectively. The passages preferably divide into pairs within the flange 366. In the illustrated embodiment, pairs of pipe-bored passages are provided instead of a single larger passage, because larger diameter passages would pose a risk to the structural integrity of the shaft. Reference is made to fig. 53, where the passages 206A lead fluid to the rear chambers 166 and 170 in the propulsion cylinders 108 and 110 via fluid ports 368 and 370, respectively. Fig. 58 shows the ports 370 which are connected to the rear chamber 170 in the cylinder 110. These ports are transverse in relative to the shaft's 118 longitudinal axis. The ports 368 are designed in a similar manner to the ports 370. Reference is made to fig. 50, where the passages 208A deliver fluid to the front chambers 168 and 172 in the cylinders 108 and 110 via the fluid port 372 and 374 respectively. The ports 374 are shown in fig. 56. Ports 372 are designed in a similar manner to ports 374. Passages 206A and 208A are provided for the purpose of supplying fluid to the propulsion cylinders. Furthermore, passages 206A and 208A do not extend rearward past position 380 in the longitudinal direction.

Reference is made to fig. 53, where the passages 210A deliver fluid to the rear packing foot 104 via multiple fluid ports 378. The ports 378 are preferably arranged linearly along the shaft 118 to provide fluid throughout the interior of the packing foot 104. In the preferred embodiment, nine ports 378 are provided. Fig. 59 shows one of the ports 378 in fluid communication with each of the passages 210A. Since the passages 210A are provided for the purpose of supplying fluid to the rear packing foot 104, such passages do not extend rearward past position 382 in the longitudinal direction.

Reference is made to fig. 50, where a wiring port 376 is provided in the shaft 118. The port 376 allows electrical connection between the control unit 102 and the position sensor 192 (FIGS. 4A-4F) on the piston 142. For example, a Wiegand sensor or a magnetometer device (described below) may be located on the piston 142. The gate 376 is also shown in fig. 57.

In a preferred embodiment, some of the components of the EST are made of a flexible material, so that the tool's bilingual flexibility is increased. The components of the tool are preferably also non-magnetic, since magnetic materials can interfere with the function of the magnetic displacement sensors. If magnetic displacement sensors are not used, then magnetic materials are of course not problematic. A preferred material is copper beryllium (CuBe) or CuBe alloy, which material has trace amounts of nickel and iron. This material is non-magnetic and has high strength and low tensile modulus. Reference is made to fig. 2, where the shafts 118 and 124, the propulsion cylinders 108, 110, 112 and 114 and the couplings 120, 122, 126 and 128 may be formed of CuBe. The pistons 140 and 142 may also be formed of CuBe or CuBe alloy. The cylinders are preferably chrome-plated so that the seals in them will have maximum service life.

In a preferred embodiment, each axle is approximately 3.7 m long, and the overall length of the EST is approximately 9.8 m. Preferably, the propulsion cylinders are approximately 65.3 cm long and 8 cm in diameter. In the middle, the couplings 120, 122, 126 and 128 are preferably smaller in diameter than the propulsion cylinders and packing feet. The couplings preferably have a diameter of no more than 7 cm and preferably no more than 5.2 cm. This leads to areas on the EST that are more flexible than the propulsion cylinders and control unit 102. Accordingly, most of the bending in the EST takes place within the couplings and shafts. In one version, the EST can bend up to 60° per 30 m drilled arch. Fig. 73A shows an arc which is curved to schematically illustrate the deflection capability of the tool. Fig. 73B schematically shows the bending of the EST's rear axle assembly. The degree of bending is somewhat exaggerated for the sake of clarity. As shown, the bending is concentrated to the rear axle 118 and the couplings 120 and 122. The axles 118 and 124 can be constructed according to several different methods. One method is diffusion bonding where each axle comprises an inner axle and an outer axle, as shown in fig. 68. An inner shaft 480 includes a central bore for the fluid supply passage 202 and ribs 484 along its length. The inner shaft 480 outside diameter at the ribs 484 is equal to an outer shaft 482 inside diameter, so that the inner shaft 480 fits snugly into the outer shaft 482. Substantially the entire outer surface of the ribs 484 engages the inner surface of the shaft 482. Longitudinal passages are formed between the shafts. In the rear axle 118, these passages are 204 (lines), 206 (fluid to the rear power cylinders rear chambers), 208 (fluid to the rear power cylinders front chambers) and 210 (fluid to the rear packing foot).

Inner and outer shafts 480 and 482 may be formed by a co-extrusion process. The shafts 480 and 482 are preferably made of CuBe alloy and tempered with an 11 bore treng" hardening process (tempering hardening and heat aging) which provides excellent mechanical properties (tensile strength of 758-896 N/mm<2>, and elongation of 8 -10% at room temperature). The inner and outer shafts are then diffusion bonded to each other. Accordingly, the shafts are coated with silver, and the inner shaft is placed inside the outer shaft. The unit is pressurized internally, compressed externally and heated to approximately 816 °C. The CuBe shafts expand under heat to form a tight fit. Heat also causes the silver to diffuse into the CuBe material, thereby forming the diffusion bond. Tests on short pieces of diffusion bonded shafts have shown compressive density in the many passages .Tests with short pieces have also shown diffusion bond shear strengths of 2,896-3,378N/mm<*>.

After the shafts are bonded to each other, the unit is chrome-plated by electrolysis to increase the life of the seals on the shaft. Care is taken to minimize the thickness of the chrome to allow both longevity and flexibility in the shaft. The use of diffusion bonding allows the unique geometry shown in fig. 68 which maximizes fluid flow channel area and at the same time maximizes the shaft's torsional stiffness. In a similar diffusion bonding process, the flange portion 366 (Figs. 49A-49B) can be bonded to the end of the shaft.

Alternatively, other materials and constructions can be used. For example, Monel or titanium alloys can be used with suitable welding methods. Monel is an acceptable material due to its non-magnetic nature. However, Monel's high modulus of elasticity or Young's modulus tends to limit the deflection radius of the tractor to less than 40° per 30 meter drilled arch. Titanium is an acceptable material due to its non-magnetic nature such as high tensile strength and low Young's modulus (compared to steel). However, titanium welds are known to have a relatively short life before fatigue when exposed to drilling environments.

In another method for constructing the shafts 118 and 124, the longitudinal conduit and fluid passages are formed by so-called "gun-drilling", a well-known process for drilling long holes. Advantages of deep drilling include moderately lower torsional and bending stiffness than the diffusion bond design and lower costs since deep drilling is a more developed technique. When deep drilling a hole, the maximum length and accuracy of the hole depends on the hole diameter. - The larger the hole diameter, the longer and more accurately the hole can be deep drilled. Since the shafts have a relatively small diameter and have numerous internal passages, however, too large a hole diameter may result in the shafts being unable to withstand bending and torsional loads during operation. When choosing a suitable hole diameter, the shaft's strength must therefore be balanced against the ability to deep drill accurate holes.

The shaft desirably has a diameter of 2.5-8.9 cm and a fluid supply passage of preferably 1.5 to 4.5 cm in diameter and more preferably at least 2.5 cm in diameter. In a preferred embodiment of the EST, the shaft diameter is 4.43-4.44 era, and the diameter of the fluid supply passage 202 is 2.54 cm. For an EST that has a diameter of 8.6 cm, the axles are designed to survive the stresses that come from the combined load of 1,356 newton meters of torque, pulling/bouncing loads of up to 28,886 newtons and bending of 60° per 30 m walk. Under these limitations, a sustainable design is shown in fig. 55 showing the shaft 118. The passages 204A, 206A, 208A and 210A comprise pairs of holes located between and substantially equidistant from the inner surface of the passage 202 and the outer surface of the shaft 118. A couple of holes have been provided for each passage, so that the passages have sufficient capacity to accommodate the desired residential waste flow rates during operation. This design is chosen instead of a single larger hole because a larger hole can understandably weaken the axle. Each hole has a diameter of 4.8 mm. The holes in each individual pair are spaced at a distance of approximately one hole diameter. For a hole diameter of 4.8 mm, it may not be possible to deep drill through the entire length of each shaft 118 and 124. In that case, each shaft can be made by deep drilling the holes in two or more shorter shafts and then welding them together end to end end by electron beam welding (EB/electron beam).

The welded shaft is then preferably heat annealed to obtain the desired physical properties, which include a modulus of elasticity of about 131,000 N/mm2, tensile strength of about 758-896 N/mm2 and an elongation of about 8-12%. The shaft can be baked at 777 °C for 1-8 hours depending on the desired characteristics. Details regarding procedures for tempering after welding can be found in the literature on CuBe. After the heat-tanning step, the welded shaft is then finished, machined, ground and chrome-plated.

Paknin<g>feet

Fig. 60-64 and fig. 74-75 show one embodiment of rear packing foot 104. The major components of packing foot 104 include a spindle 400, bladder assembly 404, end clamp 414 and coupling 420. Spindle 400 is generally tubular and has internal grooves 402 sized and designed for sliding engagement with the rotation limiters 364 on the rear axle 118 (Fig. 49A). The spindle 400 can thus slide longitudinally, but cannot rotate, relative to the shaft 118. The bladder unit 404 generally comprises rigid tube portions 416 and 417 attached to each end of a substantially tubular inflatable engagement bladder 406. The unit 404 generally encloses the spindle 400. At the rear end of the packing foot 104, the unit 404 is attached to the spindle 400 via eight bolts 408 which are received in the bolt holes 410 and 412 in the unit 404 and the spindle 400 respectively. An end clamp 414 is used as a guard to protect the leading edge of the bladder 406 and is fixed via bolts on the end 417 of the unit 404. If desired, an end clamp can also be fixed on the end 416 of the unit 404. The coupling 420 is attached to the spindle 400 via eight bolts 422 which are occupied in the bolt holes 424 and 426. The coupling 420 provides a connection between the gasket foot 104 and the flexible coupling 120 (Fig. 49A).

The ends of the bladder assembly 404 are preferably designed to move longitudinally toward each other to promote the radial expansion of the bladder 406 when inflated. In the illustrated embodiment, the rear end 416 of the assembly 404 is attached to the spindle 400, and the front end 417 is slidably engaged with segment 418 of the spindle 400. This allows the front end 417 to slide against the rear end 416 when packing the inflation foot is inflated, whereby the radial expansion of the bladder 406 is increased. The EST's packing feet are designed to traverse holes up to 10% larger than the drill bit without losing grip. For example, a typical drill bit size and the associated drilled hole is 9.5 cm in diameter. A similarly sized packing foot can traverse a hole of 10.4 cm. Likewise, a hole with a diameter of 11.4 cm can be traversed with a gasket foot that has the ability to expand to a minimum of 12.7 cm. Furthermore, the sliding connection of the bladder unit 404 with the segment 418 tends to prevent the fibers in the bladder 406 from overstretching since the bladder tends not to stretch as much. Alternatively, the bladder unit can be designed so that its front end is fixed on the spindle, and its rear end can slide towards the front end. However, this can cause the bladder to undesirably expand when the tractor is pulled up and out of a borehole, which can cause the tractor to "stick" on the borehole walls. Cams 419 on the front end of the unit 404 engage with grooves inside the coupling 420, so that the end 417 cannot rotate in relation to the spindle 400.

One or more fluid ports 428 are provided along a length of the spindle 400, which communicate with the bladder 406 interior space. The ports 428 are preferably arranged around the circumference of the spindle 400, so that fluid is introduced evenly throughout the entire inner space of the bladder. Fluid from the rear packing foot passage 210 reaches the bladder 406 by flowing through the ports 378 in the shaft 118 (Figs. 53 and 59) to the inner space of the spindle 400 and then through the ports 428 to the inner space of the bladder 406. Suitable fluid seals, such as O-rings, are provided at the ends of the packing foot 104 between the spindle 400 and the bladder assembly 404 to prevent fluid inside the bladder from leaking out to the annulus 40.

In a preferred embodiment, the bladder 406 is constructed of high strength fibers and rubber in a particular orientation that maximizes strength, radial expansion and life before material fatigue. The rubber component can be nitrile butadiene rubber (NBR) or a tetrafluoroethylene (TFE) rubber, such as the rubber sold under the trade name AFLAS. NBR is preferred for use with invert sludge (sludge which per volume has a greater content of diesel oil than water). AFLAS material is preferred for use with some specialty drilling fluids, such as calcium formate mud. Other additives can be added to the rubber to improve wear resistance or reduce hysteresis, such as carbon, oil, plasticizers and various coatings including bonded Teflon type materials.

Fibers of high strength are included in the bladder, such as S-glass, E-glass, Kevlar (polyamides) and various graphites. The preferred material is S-glass, due to its high strength (3,654 N/mm<2>) and high elongation (5-6%), resulting in greatly improved fatigue life compared to previous designs. For example, if the fatigue life criterion for the bladder is that the working load will remain below about 25-35% of the absolute maximum load on the fibers, previous designs were capable of achieving 7,400 inflation cycles. In contrast, the life expectancy of the bladders of the present invention under combined loading is estimated to be over 25,000 cycles. More inflation cycles advantageously result in increased operating time downhole and lower rig costs.

The fibers are advantageously arranged in several layers, a cross-layer pattern. The fibers are preferably oriented at angles +oc relative to the longitudinal axis of the tractor, where a is preferably between 0° and 45°, more preferably between 7° and 30°, even more preferably between 15° and 20°, and most preferably about 15° . This allows maximum radial expansion without excessive bulging of the bladder into the areas between the gasket foot toes, described below. It also allows optimal lifetime before fatigue at the criterion described above.

When the bladder 406 is inflated to engage with a borehole wall 42, it is desirable that the bladder does not block the upward return flow of drilling fluid and cuttings in the annulus 40. To prevent this, elongated toes 430 are tied or attached to other view the outer surface of the rubber bladder 406, as shown in fig. 60 and 75. The toes 430 can have a triangular or trapezoidal cross-section and are preferably arranged in a rib-like manner. When the bladder engages the borehole wall, gaps are formed between the toes 430 and the wall, allowing flow of drilling fluid and cuttings past the packing foot. The toes 430 are preferably designed to be: (1) sufficiently large to provide grip against the borehole wall; (2) sufficiently small in cross-section to maximize upward return flow of drilling fluid past the packing foot in annulus 40; (3) sufficiently flexible to deform during inflation of the bladder; and (4) elastic to assist in the expulsion of drilling fluid from the packing foot during emptying. Preferably, each toe has an outer radial width of 0.25-1.52 cm and a modulus of elasticity in excess of 131,000 N/mm<3>. Toes 430 may be formed of CuBe alloy. The ends of the toes 430 are attached to the ends 416 and 417 of the bladder assembly 404 via material band 432, preferably a high strength non-metallic material such as Stabaloy. The straps 432 prevent the toes 430 from detaching from the bladder during forced expansion, thereby preventing the formation of "fish hooks" which could undesirably prevent the extraction of the EST from the borehole. Fig. 74 shows the gasket foot 104 inflated.

A protective shield of plastic or metal can be placed in front of the leading end of the packing foot to channel the fluid flow of the annulus up onto the inflated packing foot and thereby protect the leading end of the bladder from erosion from the fluid and its particulate content.

Fig. 65-67 and fig. 76 illustrates an alternative embodiment of a rear packing foot, herein called a "flex toe packing foot". The rear and front flex-toe packing feet may be provided in place of the previously described packing feet 104 and 106. Unlike bladder-type anchors of the prior art, the flex-toe packing foot utilizes separate components for force for radial expansion and torque transmission in the anchors. In particular, the provider blisters force for radial expansion to grip a borehole wall, while the "flexitarian" transmits torque from the EST body to the borehole. The flexiters comprise rods which bend elastically within a plane parallel to the tractor body. Advantageously, the flexitarians essentially resist rotation of the body while the packing foot is in engagement with the borehole wall. Other benefits of the flexible toe packing foot include longer life before material fatigue, greater expandability, shorter length and lower operating costs.

The figures show one embodiment of a rear flexi toe seal foot 440. Since the front flexi toe seal foot is structurally similar to the rear flexi toe seal foot 440, it is not described in this document. The major components of the rear flex toe packing foot 440 include a spindle 434, attached end piece 436, two guide pin assemblies 438, two wedge nuts 442, shuttle 444, slide track end piece 446, spacer tube 448, coupling 450,

four bladders 452, four bladder covers 454 and four flexitarians 456.

Reference is made to fig. 66, where the spindle 434 is substantially tubular, but has a generally rectangular bladder mounting segment 460 that includes several elongated openings 462 arranged around the sides of the segment 460. In the EST, the bladders 452 are clamped onto the segment 460 of bladder covers 454 to thereby cover and seal the openings 462. In operation, fluid is fed to the inner chamber of the spindle 434 via the ports 378 in the shaft 118 (Figs. 53 and 59) to inflate the bladders. Although four bladders are shown in the drawings, any number of bladders may be provided. In an alternative embodiment shown in fig. 76, one continuous bladder 452 is used. This design prevents concentrations of load at the edges of the several bladders and gives the bladder a longer lifetime before the material fatigues.

Reference is made to fig. 65, where the bladder covers 454 are mounted on the spindle 434 via bolts 468 which pass through holes on the side edges of the covers 454 and extend into threaded holes 464 in the spindle 434. The bolts 468 seal the bladders 452 against fluid against the spindle 434 and prevent the bladders from loosening from the spindle 434 due to the fluid pressure inside the bladder. Since the pressure inside the bladders can be as high as 165 bar, a large number of bolts 468 are preferably provided to increase the strength of the seal. In the illustrated embodiment, 17 bolts 468 are arranged linearly on each side of the covers 454. Wedge nuts 442 tighten the rear and front ends of the bladder covers 454 onto the spindle 434 to seal the rear and front ends of the bladders against fluid. The individual bladders can be easily replaced by removing the associated bladder cover 454, which significantly reduces replacement costs and time compared to designs according to prior art. The bladder covers 454 are preferably made of CuBe or CuBe alloy.

Reference is made to fig. 65, where the fixed end piece 436 is attached to the rear end of the spindle 434 via bolts extending into holes 437. In front of the bladders, the shuttle 444 is slidably engaged on the spindle 434. A guide pin assembly 438 is mounted on the end piece 436, and another assembly 438 is mounted on the shuttle 444. In the illustrated embodiment, each of the units 438 comprises four guide pin supports 439 which support the ends of the guide pins 458. The guide pins hold the ends of the flexitarians 456 like a hinge. The end piece 436 and the shuttle 444 have four hinge parts 466 which have holes which receives the guide pins 458. During operation, inflation of the bladders 452 causes the bladder covers 454 to expand radially. This causes the flexitarian teeth 456 to move like a hinge at the pins 458 and bend outward to engage the borehole wall. Fig. 76 shows an inflated flexi-toe packing foot (which has a single, continuous bladder), where the flexi-tears 456 grip the borehole wall 42. The shuttle 444 can freely slide axially against the attached end piece 436, thereby promoting the radial expansion of the flexi-tears. Those skilled in the art will appreciate that each end of the flexitarians 456 can be allowed to slide along the spindle 434. However, it is preferred that the front end of the flexitarians is allowed to slide, while the rear end is fixed to the spindle. This prevents the sliding end of the flexitarians from shifting axially at the borehole wall during removal of the tool, which could cause the flexitarians to bend outwards and prevent the removal of the tractor.

The sliding track end piece 446 is attached to the spindle 434 via bolts that extend into threaded holes 472. At the point of attachment, the end piece 446's inside diameter is approximately equal to the spindle 434's outside diameter. Behind the attachment point, the inner diameter of the end piece 446 is slightly larger, so that the shuttle 444 can slide inside the end piece 446. The end piece 446 also has longitudinal grooves in its inner diameter, which occupy the lugs 470 on the outer surface of the shuttle 444. This prevents the shuttle 470 and further the front ends of the flexitarians 456 from rotating relative to the spindle 434. Since both the front and rear ends of the flexitarians 456 are prevented from rotating relative to the spindle 434, the flexitarians thus essentially prevent the tool from rotating or twisting itself when the packing foot engages with the borehole wall.

In the same manner as described above with respect to the spindle 400 in the packing foot 104, the spindle 434 in the packing foot 440 has flexi-toe grooves on its inner surface to slidably engage the rotation limiters 364 on the shaft 118. The spindle 434 can thus slide longitudinally, but can not rotate relative to the shaft 118. The limiters 364 transmit torque from the shaft 118 to a borehole wall 42. The packing foot 440 components are preferably made of a flexible, non-magnetic material, such as CuBe. The flexi toes 456 may include outer surfaces that are made uneven for improved grip against the borehole wall.

The spacer tube 448 is used as a transition piece to allow interchangeability between the flexi toe gasket foot 440 and the previously described gasket foot 104 (Fig. 60). The coupling 450 is connected to the spindle via the set screws. The connector 450 connects the gasket foot 440 to the flexible connector 120 (Fig. 49A) in the EST.

Fig. 67 shows the cross-sectional design of one of the bladders 452 used in the flexi toe seal foot 440. In its non-inflated state, the bladder 452 has a design with multiple folds as shown. This allows for greater radial expansion when the bladder is inflated, caused by the unfolding of the bladder. The bladders also do not stretch that much in use, compared to bladders according to known technology. This leads to a longer life for the bladders. The bladders are made of rubber reinforced with cloth, and can be constructed in several designs. From the inside to the outside of the bladder, a typical structure is rubber/fibre/rubber/fibre/rubber. Rubber is needed on the inside to maintain pressure. Rubber is needed on the outside to prevent damage to the cloth from drill cuttings passing the bladder. The rubber can be NBR or AFLAS (TFE rubber). Suitable cloths include S-glass, E-glass, Kevlar 29, Kevlar 49, steel cloth {for ESTs that do not have magnetic sensors), various types of graphite, polyester poly-acrylate fiber or metallic fibers. Different designs of fiber reinforcement and different fabric weights can be accepted. In the illustrated embodiment, the bladder can withstand inflation pressures of up to 103 bar. This inflation strength is achieved with a Kevlar-29 fabric 400 denier in a 4 thread x 4 thread basket weave. The design takes into account material fatigue at a maximum load criterion of 25% of the fibers' maximum elongation. During tests, it has been determined that rubber with a minimum thickness of 0.23 cm is required on the inner surface to ensure pressure tightness.

For the designs both with and without flexi toe, the packing feet are preferably placed near the outer ends of the EST to promote the tool's ability to cross cavities down in the earth. The packing feet are preferably approximately 100 cm long. The metallic parts in the gasket feet are preferably made of CuBe alloy, but other non-magnetic materials can be used.

In use, the packing feet (all the above-described designs, i.e. Figs. 60 and 65) can attach grips to an undrilled or drilled hole in the desired manner in order to avoid slipping under high longitudinal loads as well as torsional loads. In other words, the borehole's normal force against each gasket foot must be high enough to prevent slippage, due consideration being given to the coefficient of friction (typically about 0.3). The normal force depends on the area of the contact surface between the packing foot and the drill hole and the pressure inside the packing foot's bladder, which will normally be between 35-110 bar and can be as high as 166 bar. In the inflated state, the area of the contact surface between each packing foot and the borehole is preferably at least 38.7 cm<2>, more preferably at least 58.1 cm<2>, even more preferably at least 83.9 cm<s>, and most preferably at least 116, 1 cm<2>.

Those skilled in the art will appreciate that fluid seals are preferably provided throughout the EST to prevent leakage of drilling fluid, which could put the tool out of service. For example, the propulsion cylinders and packing feet are preferably sealed to prevent leakage to the annulus 40. The annular pistons 140, 142, 144 and 146 are preferably sealed to prevent fluid flow between the rear and front chambers of the propulsion cylinders. The boundary layers between the various housings in the control unit 102 and the flanges on the shafts 118 and 124 are preferably sealed to prevent leakage. The compensating piston 248 is sealed to provide a fluid seal for the oil in the electronics housing 130 and motor housing 132 against drilling fluid in the annulus 40. Various other seals are also provided throughout the tractor. Suitable seals include rubber 0-rings, T-seals or special elastomeric seals. Suitable sealing materials include AFLAS or NBR rubber.

Sensors

As noted above, the control algorithm for controlling the motorized valves 154, 156 and 158 is preferably based at least in part on: (1) pressure signals from the pressure transducers 182, 184, 186, 188 and 190 (FIGS. 3 and 4A-4F); (2) position signals from displacement sensors 192 and 194 (Figs. 4A-4F) on the annular pistons inside the rear and front drive cylinders; or (3) both.

The pressure transducers measure pressure differences between the various fluid passages and the annulus 40. When pressure information from the above-mentioned pressure transducers is combined with the pressure difference across the pressure difference transition piece for the downhole motor, the speed can be controlled to between 0.08-610 meters per hour. This means that the tractor can maintain speeds of 0.08 m per hour, 610 meters per hour and also intermediate speeds. In a preferred embodiment, such speeds can be maintained as long as necessary and essentially indefinitely, as long as the tractor does not encounter an obstacle that will not allow the tractor to move at such speeds. Pressure difference information is particularly useful for regulating relatively higher speeds such as those used when driving in and out of a borehole (76-305 m per hour), fast controlled drilling (1.5-45.7 m per hour) and short trips (9-305 m per hour). The EST can maintain speeds within all these ranges. Suitable pressure transducers for the EST are article no. 095A201A, which is manufactured and sold by Industrial Sensors and Instruments Incorporated, located in Roundrock, Texas. These pressure converters are designed for an operating pressure of 1,034 bar and pressure differences of 172 bar (overpressure).

The position of the annular pistons in the propulsion cylinders can be measured using any of a variety of suitable sensors, including Hall-Effect transducers, MIDIM devices (Mirror Image Differential Induction Amplitude Magnetometer, sold by Dinsmore Instrument Co., Flint, MI), traditional magnetometers, Wiegand sensors, and other magnetic and distance sensing devices. If magnetic displacement sensors are used, then the components of the EST are preferably made of non-magnetic materials that will not interfere with the sensors' performance. Suitable materials are CuBe and Stabaloy. Magnetic materials can be used if non-magnetic sensors are used.

For example, displacement of the rear piston 142 can be measured by placing a MIDIM in the coupling 122 and a small magnetic source in the piston 142. The MIDIM transmits an electrical signal to the logic component 224, which is inversely proportional to the distance between the MIDIMs -et and the magnetic source. As the piston 142 moves toward the MIDIM, the signal increases, thereby providing an indication of the relative longitudinal positions of the piston 142 and the MIDIM. Of course, this gives an indication of the relative positions in the longitudinal direction of the rear packing foot 104 and the tractor body, i.e. the axles and the steering unit 102. In addition, displacement information can easily be transformed into speed information by measuring displacement at different times.

Another type of speed sensor that can be used is a Wiegand sensor. In one embodiment, a wheel is provided on one of the annular pistons in such a way that the wheel rotates as the piston moves axially within one of the propulsion cylinders. The wheel includes two small oppositely charged magnets located on opposite sides of the wheel's outer circumference. In other words, the magnets are separated by 180°. The Wiegand sensor registers reversals in the polarity of the two magnets, which occurs every time the wheel rotates 180°. For each polarity reversal, the sensor sends a signal in the form of an electrical pulse to the logic component 224. As the piston 142 moves axially within the cylinder 110, causing the wheel ril to rotate, the Wiegand sensor transmits a stream of electrical pulses for every 180° wheel rotation. The position of the piston 142 relative to the propulsion cylinder can be determined by monitoring the number of pulses and the direction of piston travel. The position can be calculated from the wheel diameter, since each pulse corresponds to half the wheel circumference.

Figures 77A-77C illustrate one embodiment of a Wiegand sensor device. As shown, the annular piston 142 includes recesses 574 and 576 in its outer surface. The recess 574 is sized and designed to receive a wheel unit 560, shown in fig. 77A and 77B. The wheel unit 560 comprises a piston fastening element 562, arms 564, a wheel holder element 572, axle 570 and wheel 566. The wheel 566 rotates on an axle 570 which is received in holes 569 in the wheel holder element 572. The elements 562 and 572 have holes for receiving arms 564. The wheel unit 560 can be fixed in the recess 574 via a screw which is received in a hole in the piston fastening element 562. The arms 564 are preferably somewhat flexible to bias the wheel 566 against the inner surface of the propulsion cylinder 110, so that the wheel rotates when the piston 142 moves inside the cylinder 110. The wheel 566 has oppositely charged magnets 568 separated by 180° about the center of the wheel. The recess 576 is sized and designed to receive a Wiegand sensor 578 which registers reversals in the polarity of the magnets 568, as described above. The figures do not show the electrical wires through which the electrical signals pass. Preferably, the wires are twisted to prevent electrical interference from the motors or other components of the EST.

Those skilled in the art will appreciate that the relevant displacement information can be obtained by measuring the displacement of any point on the EST's body (shafts 118, 124, control unit 102) relative to each of the packing feet 104 and 106. A suitable method is to measure the displacement of the annular pistons (which are fixed to the shafts 118 and 124) relative to the propulsion cylinders or couplings (which are fixed to the packing feet). In one embodiment, the displacement of the piston 142 is measured relative to the coupling 122. Alternatively, the displacement of the piston 142 may be measured relative to an inner wall of the propulsion cylinder 110 or to the control unit 102. The same information is obtained by measuring the displacement of the piston 140. Those skilled in the art in the field will understand that it is sufficient to measure the position of only one of the pistons 140 and 142 and only one of the pistons 144 and 146 in relation to the gasket foot 104, respectively 106.

Electronic design

Fig. 69 illustrates one embodiment of the electronic design of the EST. All the wires shown are inside the wiring passages described above. As shown, five wires extend up the borehole to the surface, including two 30 volt power lines 502, one RS-232 bus line 504, and two 1.553 bus lines 506 (MIL-STD-1553). The wires 502

supplies power to the EST for controlling the motors and is electrically connected to a 10-pin connector that is plugged into the electronics package 224 in the electronics housing 130. Wire 504 is also connected to the electronics package 224. Desired

EST parameters, such as velocity, impact, position, etc. can be sent from the surface to the EST via wire 504. Wires 506 transmit signals downhole to the downhole assembly. Commands can be sent from the surface to the downhole assembly via the wires 506, such as commands to the motor that controls the drill bit.

A pair of wires 508 allows electrical connection between the electronics package 224 and the rear displacement sensor, such as a Wiegand sensor as shown. Likewise, a pair of wires 510 also allow connection between the package 224 and the front displacement sensor. Wires 508 and 510 transmit position signals from the sensors to package 224. Another RS-232 bus 512 extends from package 224 downhole to communicate with the downhole assembly. Line 512 transmits signals from downhole sensors, such as bit weight and pressure differential across the bit, to package 224. Another pair of 30 volt lines 514 extend from package 224 downhole to interface with and supply power to the bottom hole unit.

A 29 pin connector 213 is provided for connection

between the electronics package 224 and the motors and pressure converters in the control unit 102. The signals from the five pressure converters can be calibrated by calibration resistors 515. Alternatively, the calibration resistors can be omitted. Leads 516 and 518 and lead pairs 520, 522, 524, 526 and 528 are provided for reading

of electronic pressure signals from the pressure transducers in a manner known within the art. The lines 516 and 518 extend to each of the resistors 515 which are connected via four lines each to one pressure converter. The wire pairs 520, 522, 524, 526 and 528 extend to the resistors 515 and the pressure transducers.

Wire groups 530, 532 and 534 with 4 wires each extend to the motor 164, 162 and 160 respectively which are controlled in a manner known to those skilled in the art. Three wires 536 and one wire 538 extend to the motors' rotational accelerometers 531 for transmitting motor feedback to the electronics package 224 in a manner known to those skilled in the art. In particular, each wire 536 extends to one accelerometer for a positive signal. Wire 538 is a common ground and is connected to all the accelerometers. In an alternative embodiment, potentiometers may be provided instead of the rotational accelerometers. Note that potentiometers measure the rotational displacement at the outlet in the motor.

EST performance

A particular advantage of the EST is that it can maintain both high and low speeds. The EST can thus be used for a number of different activities such as drilling, milling casing, driving into a borehole and bottom marking (all described below). The EST can maintain any speed, preferably in a range of 0.08-610 m/s. hour, more preferably in an area of 3-229 m per hour, and even more preferably in a range of 10.7-213 m per hour. More importantly, the EST can maintain both high and low speeds, preferably less than 0.08 m per hour and more than 610 m per hour. The table below lists speed pairs (in meters per hour) where a single EST or a "string" of interconnected ESTs (any number of which may be operational) can desirably maintain speeds lower than the lowest speed in the pair , and can preferably maintain speeds greater than the largest speed in the pair. Movement of the tractor into and out of an unlined hole (section without casing) at high speeds is known in the art as "tripping" into the borehole. "Tripping" rates tend to have a significant influence on the overall cost of the drilling process. Higher speeds result in shorter operating times and lower costs. "Tripping" speeds usually depend on the size of the load the tractor is carrying. The higher the load, the lower the tractor's maximum speed. For example, one embodiment of an EST has a diameter of 8.6 cm and, while carrying a load of 39,995 newtons, can travel at speeds up to preferably within a range of 0-54.9 m per second. hour and more preferably in an area of 36.6-45.7 m per hour. While carrying a load of 16,443 newtons, the same EST can travel at speeds preferably in the range of 137-175 meters per second. hour, and more preferably within an area of 152-160 meters per hour. These speeds constitute a significant improvement over tractors according to prior art.

As mentioned above, a string of several tractors can be connected end to end to provide greater overall capacity. For example, one tractor may be better suited for tripping, another for drilling and another for milling. Any number and any combination of tractors can be provided. Any number of the tractors may be operational, while others are disabled. In one embodiment, a set of tractors includes a first tractor designed to travel at speeds within 183-610 meters per hour. hour, a second tractor built to move at speeds within 3-76 meters per hour. hour and a third tractor designed to move at speeds within 0.3-3 meters per hour. hour. On the other hand, a single tractor in the illustrated EST, by providing multiple processors or a processor capable of processing the motors in parallel, can move at approximate speeds between 3 and 230 meters per second. hour.

Fig. 70 shows the velocity modulation curve, as a function of load, for one embodiment of the EST, which has a diameter of 8.6 cm. Curve B indicates the performance limits imposed through the fail-safe valve 150, and curve A indicates the performance limits imposed through the relief valve 152. The fail-safe valve 150 sets a minimum pressure for supply and thereby speed for the tractor's operation. The relief valve 152 sets a maximum pressure for supply and thereby speed.

The EST is capable of continuous motion due to its independently controllable propulsion cylinders and independently inflatable packing feet.

When drilling a hole, it is desirable to drill continuously as opposed to periodically. Continuous drilling increases the life of the drill bit and maximizes the penetration rate when drilling, thereby reducing costs. It is also desirable to maintain a constant load on the drill bit. However, the physical mechanics of the drilling process make it difficult to maintain a constant load on the drill bit. The drill string (coil pipe) behind the tractor is prone to hooking up in the borehole wall in some parts of the well and then suddenly letting go, which causes large fluctuations in the load. The bit can also encounter variations in the hardness of the formation it is drilling into. These and other factors can contribute to creating a load on the tractor, which varies over time. Tractors according to the prior art are not equipped to respond effectively to such load variations, which often leads to damage to the drill bit. This is partly due to the fact that, according to known technology, tractors have their control systems located on the surface. Sensor signals must therefore travel from the tool up to the surface to be processed, and control signals must travel from the surface back to the tool.

Suppose, for example, that a drilling tool according to known technology is placed 4,570 m down into the earth. During drilling, the tool may encounter a load variation caused by an obstacle down in the borehole, such as hard rock. To prevent damage to the drill bit, the tool must reduce the drill advance to an acceptable level or perhaps stop altogether. With the tool control system on the surface, the time required for the tool to communicate the load variation to the control system and for the control system to process the load variation and transmit tool command signals back to the tool would likely be too long to prevent damage to the drill bit.

In contrast, the EST's unique design allows the tractor to react very quickly to load variations. This is partly because the EST incorporates electronic logic components on the tool rather than on the surface, which reduces the communication time between the logic unit, the sensors and the valves. The feedback control loop is thus significantly faster than with tools according to known technology. The EST can respond to changes in crown weight of 444 newtons preferably within 2 seconds, more preferably within 1 second, even more preferably within 0.5 seconds, even more preferably within 0.2 seconds and most preferably within 0.1 seconds . That is, the weight of the drill bit can preferably be changed at a rate of 444 newtons within 0.1 seconds. If that change is insufficient, the EST can continue to change the weight of the crown at a rate of 444 newtons per second. 0.1 seconds until a desired control setting is achieved (the pressure differential from the drill motor is reduced, preventing the motor from stopping). For example, if the weight of the drill bit suddenly goes from 8,888 newtons to 13,332 newtons due to external conditions, the EST can compensate, i.e. reduce the load on

the drill bit from 13,332 newtons to 8,888 newtons on

1 second.

Typically, the drilling process involves the setting of casing in boreholes. It is often desirable to mill a hole in the casing to initiate a borehole that has a horizontal component. It is also desirable to mill at extremely low speeds, such as 0.08-1.22 m per hour to prevent sharp ends from forming in the milled casing, which can damage drill string components or cause the string to become stuck in the milled hole. The unique design of the advance valves 156 and 158 coupled with the use of displacement sensors allows a single EST to mill at speeds lower than 0.3 meters per second. hour, and more preferably as low as or lower than 0.08 meters per hour. Suitable milling areas for an EST are thus 0.08-7.62 meters per hour, 0.08-3.04 meters per hour and 0.08-1.82 meters per hour with suitable non-barite-containing drilling fluids.

After milling a hole in the casing, it is often desirable to mill out of the hole at a deflection with a large angle. The EST is equipped with flexible couplings 120, 122, 126 and 128 between the packing feet and the propulsion cylinders, as well as flexible shafts 118 and 124. These components have a smaller diameter than the packing feet, propulsion cylinders and the control unit and are formed from a flexible material such as CuBe. The couplings and shafts are desirably formed from a material which has a modulus of elasticity of preferably at least 199,948 N/mm<2> and more preferably at least 131,000 N/mm<2>. This results in areas of the EST with higher flexibility, which act as hinges to allow the tractor to make large angle deflections. In one embodiment, the EST can bend off with an angle of up to 60° per 30 meter drilled arc, and can then add horizontal distances of up to 7,620-15,240 metres. The tractor design balances such flexibility against the desirability of having relatively long propulsion cylinders and packing feet. It is desirable to have longer propulsion cylinders, so that the stroke length of the pistons is greater. The stroke length of pistons in an EST having a diameter of 8.6 cm is preferably at least 25.4-50.8 cm, and more preferably at least 30.5 cm. In other designs, the stroke length can be as large as 152.4 cm. It is also desirable to have gasket feet of a suitable length, so that the tool can more efficiently engage with the borehole's inner surface. The length of each packing foot is preferably at least 38 cm, and more preferably at least 102 cm, depending on the type of design. As the length of the drive cylinders and packing feet increases, the tool's ability to deflect at large angles decreases. The EST achieves the above deflection capability in a design where the combined length of the propulsion chambers, control unit and packing feet preferably constitutes at least 50% of the EST's overall length and in other design variations, 50-80%, and more preferably at least 80% of the overall length length of the EST. Despite such flexibility, an EST with a diameter of 8.6 cm is strong enough to push or pull longitudinal loads preferably as large as 46,661 newtons.

Advantageously, one aspect of the invention is that a single EST can generate a shock to push and/or pull various loads. The desired impact capacities of ESTs of different sizes are set out in the following table:

In addition, the EST resists buckling under torsional forces, e.g. twisting, about its longitudinal axis. During drilling, the formation exerts a reaction torque through the bit and into the body of the EST. When the rear packing foot is engaged with the bore, and the front packing foot is retracted, the portion of the body in front of the packing foot twists slightly. Consequently, when the front packing foot engages the bore, and the rear packing foot is emptied, the part of the body behind the front packing foot tends to move out of torsion. This causes the drill string to twist gradually. This also causes the body to gradually rotate about its longitudinal axis. The tool direction sensors must continuously take such rotation into account. Compared to prior art tractors, the EST body is advantageously designed to substantially limit such twisting. Preferably, the shaft diameter is at least 4.4 cm, and the control unit diameter is at least 8.6 cm for this design. When such an EST is subjected to a twisting load as high as 678 newton meters about its longitudinal axis, the axles and the steering unit preferably twist less than 5° per second. steps of the tractor. The above problems are advantageously substantially prevented or minimized. Furthermore, the EST design includes a non-rotatable engagement between the packing feet and the shafts, via the rotation limiters 364 (Fig. 49A). This prevents torque from being transferred to the drill string, which would cause the drill string to rotate. The EST's flexi-toe packing feet provide improved torque transfer to the borehole wall via the flexi-toes.

When further drilling begins at the bottom of a borehole, it is desirable to "mark the bottom" before drilling. Marking the bottom involves moving at an extremely low speed when approaching the end of the borehole, and reducing the speed to zero the moment the bit reaches the end of the formation. This makes it easier for the bit to start smoothly, resulting in longer bit life, fewer trips to change the bit and further lower drilling costs. The EST has excellent speed control and can reverse direction to allow efficient marking of the bottom and starting of the crown. Typically, the EST will move at near maximum speed until the last 15 meters before the bottom of the hole. Once within 15 meters, the EST's speed is desirably reduced to approximately 3.7 m per second. hour until the EST is within about 3 meters of the bottom. The speed is then reduced to a minimum. The tractor is then reversed and moved backwards 0.3-0.6 meters and then slowly moved forwards.

When drilling horizontal boreholes, the drill cuttings from the bit can come to rest on the bottom of the hole. Such cuttings must be periodically swept out by circulating drilling fluid near the cuttings beds. The EST has the ability to reverse direction and go backwards as it pulls the bit, the nozzles of which sweep the cuttings backwards and out.

When fluid moves through a hole, the hole wall tends to deteriorate and become larger. The EST's packing feet are designed to traverse holes up to 10% larger than the drill bit without losing grip.

Although this invention has been described in connection with certain preferred embodiments and examples, it should be understood by those skilled in the field that the present invention extends beyond the specifically described embodiments to other alternative embodiments and/or other uses of the invention as well as obvious modifications thereof. It is thus intended that the scope of the present invention described in this document shall not be limited by the specially described embodiments described above, but shall only be determined through a proper reading of the claims that follow.

Claims (60)

1. Tractor (100) which is to move inside a borehole (42), characterized in that it comprises: - a tractor body (102, 118, 124) which is dimensioned and shaped to move inside the borehole (42); - a valve (150, 152, 154, 156, 158) on the tractor body, where the valve is placed along a flow path between a fluid source and a shock-receiving part of the body, and where the valve (150, 152, 154, 156, 158) comprises: - a fluid port (262, 264, 266, 268, 276, 280, 368, 370, 372, 374, 378, 428); and - a flow restrictor having a first position in which the restrictor completely blocks fluid flow through the fluid port (262, 264, 266, 268, 276, 280, 368, 370, 372, 374, 378, 428); a range of other positions in which the restrictor allows a first fluid flow level through the fluid port; and a third position in which the restrictor allows a second fluid flow level through the fluid port, the second fluid flow level being higher than the first fluid flow level; - a motor (160, 162, 164) on the tractor body (102, 118, 124); and - a coupling connecting the motor (160, 162, 164) and the flow restrictor such that movement of the motor causes the restrictor to move between the first position, the range of second positions and the third position; and that the motor (160, 162, 164) is arranged to be able to move the limiter so that the net shock absorbed by the shock-receiving part can be changed by 444 newtons within 0.5 seconds. 2. Tractor (100) which is to move inside a borehole (42), characterized in that it comprises: - a tractor body (102, 118, 124) which has several shock-receiving parts; - at least one valve (150, 152, 154, 156, 158) on the tractor body located along at least one of several fluid flow paths between a fluid source and the shock-receiving parts; - an electronically controllable motor (160, 162, 164) which is connected to the valve (150, 152, 154, 156, 158) to direct fluid to at least one of the impact receiving parts; - several grippers (104, 106, 440), where each of the several grippers (104, 106, 440) in the longitudinal direction is in movable engagement with the body (102, 118, 124), where each of the several grippers (104, 106 , 440) has an activated position in which the gripper (104, 106, 440) restricts its movement relative to an inner surface of the borehole {42), and a retracted position in which the gripper (104, 106, 440) allows substantially free relative movement of the gripper in relation to the inner surface, and where the several grippers (104, 106, 440), the several shock-receiving parts and the at least one valve (150, 152, 154, 156, 158) are designed so that the tractor (100 ) is self-propelled at a sustained speed of less than 15 meters per hour. hour, and at a sustained speed greater than 30 meters per hour. hour. 3. Tractor (100) according to claim 2, characterized in that the tractor (100) is designed to operate at a pressure difference in the range of 14-172 bar between the fluid source and the shock-receiving parts. 4. Tractor (100) according to claim 2, characterized in that the tractor (100) is designed to operate at a pressure difference in the range 34-110 bar between the fluid source and the shock-receiving parts. 5. Tractor (100) according to claim 2, characterized in that the tractor (100) is designed to be able to change the speed at which it propels itself forward, without a change in the pressure difference between the fluid source and the shock-receiving parts. 6. Tractor (100) according to claim 2, characterized in that the tractor (100) has a length of less than 46 metres. 7. Tractor (100) according to claim 2, characterized in that the tractor (100) has a length of less than 30 metres. 8. Tractor (100) according to claim 2, characterized in that the tractor (100) has a length of less than 23 metres. 9. Tractor (100) according to claim 2, characterized in that the tractor (100) has a length of less than 15 metres. 10. Tractor (100) according to claim 2, characterized in that the tractor (100) has a length of less than 12 metres. 11. Tractor (100) according to claim 2, characterized in that the tractor (100) has a maximum diameter that is less than 20.3 centimeters. 12. Tractor (100) according to claim 2, characterized in that the tractor (100) has a maximum diameter that is less than 15.2 centimeters. 13. Tractor (100) according to claim 2, characterized in that the tractor (100) has a maximum diameter that is less than 10.2 centimeters. 14. Tractor (100) according to claim 2, characterized in that the several shock-receiving parts and the at least one valve (150, 152, 154, 156, 158) are designed to allow the tractor (100) to move at a sustained speed which is less than 9 meters per hour, and at a sustained speed greater than 30 meters per hour. hour. 15. Tractor (100) according to claim 2, characterized in that the several shock-receiving parts and the at least one valve (150, 152, 154, 156, 158) are designed to allow the tractor (100) to move at a sustained speed which is less than 3 meters per hour, and at a sustained speed greater than 30 meters per hour. hour. 16. Tractor (100) according to claim 2, characterized in that the several shock-receiving parts and the at least one valve (150, 152, 154, 156, 158) are designed to allow the tractor (100) to move at a sustained speed which is less than 1.5 meters per hour, and at a sustained speed greater than 30 meters per hour. hour. 17. Tractor (100) according to claim 2, characterized in that the several shock-receiving parts and the at least one valve (150, 152, 154, 156, 158) are designed to allow the tractor (100) to move at a sustained speed which is less than 15 meters per hour, and at a sustained speed greater than 76 meters per hour. hour. 18. Tractor (100) according to claim 2, characterized in that the several shock-receiving parts and the at least one valve (150, 152, 154, 156, 158) are designed to allow the tractor (100) to move at a sustained speed which is less than 15 meters per hour, and at a sustained speed greater than 152 meters per hour. hour. 19. Tractor (100) which is to move inside a borehole (42), characterized in that it comprises: - a tractor body (102, 118 124) with a shock-receiving part which has a rear surface and a front surface; - a slide valve (150, 154, 156, 158) comprising: - a valve body (294, 306) with a slide passage (298, 307) delimiting a slide axis, where the valve body (294, 306) has fluid ports (262, 264, 266, 268, 276, 280, 368, 370, 372, 374, 378, 428) which is in connection with the sled passage (298, 307); and - an elongated slide (292, 304) which is engaged within the slide passage (298, 307) and is movable along the slide axis to control flow rates along fluid flow paths through the fluid ports (262, 264, 266, 268, 276, 280, 368, 370, 372, 374, 378, 428) and the slide passage (298, 307), wherein the slide (292, 304) has a first position range within which the valve allows fluid flow from a fluid source to the rear surface of the impact receiving portion and blocks fluid flow to the front surface, the rate of fluid flow to the rear surface varying depending on the position of the slide (292, 304) within the first position area, and the fluid flow to the rear surface emitting a downward impact on the body (102) in the borehole (42) , 118, 124), whose downward thrusts have a magnitude dependent on the flow rate of the fluid stream to the rear surface, and wherein the slide (292, 304) has a second position range within which the valve allows fluid flow from the source of the front surface of the impact receiving portion and blocks fluid flow to the rear surface, the flow rate of the fluid flow to the front surface varying depending on the position of the slide (292, 304) within the second position range, and the fluid flow to the front surface emitting an in-bore (42) upward thrust on the body (102, 118, 124), the upward thrust having a magnitude dependent on the flow rate of the fluid flow to the front surface; - a motor (160, 162, 164) on the tractor body (102, 118, 124); - a coupling connecting the motor (160, 162, 164) and the slide (292, 304), so that operation of the motor causes the slide to move along the slide axis; and - a gripper (104, 106) which in the longitudinal direction is in movable engagement with the tractor body (102, 118, 124), where the gripper (104, 106) has an activated position in which it limits its movement in relation to an inner surface in the borehole (42), and a retracted position in which the gripper (104, 106) allows substantially free relative movement of the gripper relative to the inner surface; and that the motor (160, 162, 164) is arranged to be able to move the slide (292, 304) along the slide axis sufficiently quickly to change the net shock absorbed by the shock-receiving part by 444 newtons within 2 seconds. 20. Tractor (100) according to claim 19, characterized in that the motor (160, 162, 164) is arranged to be able to move the slide (292, 304) along the slide axis sufficiently quickly to change the net shock absorbed by the shock-receiving part, with 444 newton within 0.2 seconds. 21. Tractor (100) according to claim 19, characterized in that the motor (160, 162, 164) is arranged to be able to move the slide (292, 304) along the slide axis sufficiently quickly to change the net shock absorbed by the shock-receiving part, with 444 newtons within 0.1 seconds. 22. Tractor (100) according to claim 19, characterized in that it further comprises: - one or more sensors (182, 184, 186, 188, 190, 192, 194, 578) on the tractor body (102, 118, 124), where the sensors is designed to generate electrical feedback signals indicative of one or more fluid pressures within the tractor (100), indicative of longitudinal stress exerted on the tractor body (102, 118, 124) by equipment external to the tractor (100) or by interior walls of the borehole (42), and which indicates the rotational position of an output shaft from the motor (160, 162, 164), the output shaft controlling the position of the slide (292, 304) along the slide axis; and - an electronic logic component (224) on the tractor body (102, 118, 124), where the component is designed to receive and process the electrical feedback signals, the logic component (224) being designed to transmit electrical command signals to the engine (160 , 162, 164); and that the motor (160, 162, 164) is arranged to be able to be controlled by the electrical command signals that control the position of the slide (292, 304). 23. Tractor (100) according to claim 22, characterized in that the sensors (182, 184, 186, 188, 190, 192, 194, 578) include a first pressure sensor (182, 184, 186, 188, 190) which is designed to measuring fluid pressure on the rear surface of the impact receiving portion of the tractor body (102, 118, 124), and a second pressure sensor (182, 184, 186, 188, 190) designed to measure fluid pressure on the front surface of the impact receiving portion . 24. Tractor (100) according to claim 22, characterized in that the sensors (182, 184, 186, 188, 190, 192, 194, 578) include a rotational accelerometer which is designed to measure the output shaft's angular velocity. 25. Tractor (100) according to claim 22, characterized in that the sensors (182, 184, 186, 188, 190, 192, 194, 578) include a potentiometer designed to measure the rotational position of the output shaft. 26. Tractor (100) which is to move inside a borehole (42), characterized in that it comprises: - a tractor body (102, 118, 124) which is dimensioned and shaped to move inside the borehole (42); and - a valve (150, 154, 156, 158) on the tractor body (102, 118, 124), where the valve is located along a fluid flow path between a fluid source and a shock-receiving part of the tractor body (102, 118, 124), which shock-receiving part is dimensioned and designed to receive shock from the fluid source, and where the valve comprises: - a fluid port (262, 264, 266, 268, 276, 280, 368, 370, 372, 374, 378, 428), where the fluid flow path passes through the fluid port; and - a flow-limiting body (292, 304) which has one or more recesses (312) on edges of the flow-limiting body (292, 304), where the flow-limiting body (292, 304) has a first position area within which the flow restricting body completely blocks fluid flow through the fluid port (262, 264, 266, 268, 276, 280, 368, 370, 372, 374, 378, 428), a second position range within which the flow restricting body (292, 304) allows fluid flow through the fluid port only through the recesses (312), and a third position range within which the flow restricting body (292, 304) allows fluid flow through the fluid port (262, 264, 266, 268, 276, 280, 368, 370, 372, 374, 378, 428) at least partially outside the recesses (312); in that the flow rate of fluid flowing along the fluid flow path can be controlled by controlling the position of the flow-limiting body (292, 304) within the first, second and third position areas. 27. Tractor (100) according to claim 26, characterized in that it further comprises: - a motor (160, 162, 164) on the tractor body (102, 118, 124); and - a coupling connecting the motor (160, 162, 164) and the flow restricting body (292, 304), such that operation of the motor (160, 162, 164) causes the flow restricting body (292, 304) to move within the first, second and third position areas; and that the motor (160, 162, 164) is arranged to be able to move the flow limiting body (292, 304) sufficiently fast to change the net shock absorbed by the shock-receiving part by 444 newtons within 2 seconds. 28. Tractor (100) according to claim 27, characterized in that the motor (160, 162, 164) is arranged to be able to move the flow-limiting body (292, 304) sufficiently quickly to change the net shock received by the shock-receiving part, with 444 newton within 0.1 seconds. 29. Tractor (100) which is to move inside a borehole (42), characterized in that it comprises: - a tractor body (102, 118, 124) which is dimensioned and shaped to move inside the borehole (42); and - a valve (150, 144, 156, 158) on the tractor body (102, 118, 124), where the valve is located along a fluid flow path between a fluid source and an impact-receiving part of the tractor body (102, 118, 124), which shock-receiving part is dimensioned and designed to receive shock from the fluid source, and where the valve comprises: - a valve body (294, 306) with an elongated slide passage (298, 307) which delimits a slide axis, where the valve body (294, 306) has a first and a second fluid port (262, 264, 266, 268, 276, 280, 368, 370, 372, 374, 378, 428) which are in communication with the slide passage (298, 307), and where the fluid flow path passes through the slide passage ( 298, 307) and through the first and second fluid ports; and - an elongated valve slide (292, 304) which is engaged within the slide passage (298, 307) and which is movable along the slide axis, where the slide (292, 304) has a flow-restricting segment (293, 309) which defines a first chamber within the slide passage (298, 307) at a first end of the flow-limiting segment (293, 309), and defining a second chamber within the slide passage (298, 307) at a second end of the flow-limiting segment (293, 309 ), and where the flow-limiting segment (293, 309) has an outer radial surface which is designed to slide along inner walls of the slide passage (298, 307) to thereby fluid-seal the first chamber against the second chamber, and where flow-limiting segment (293, 309) has one or more recesses (312) on one of said first and second ends and on the outer radial surface, and where the slide (292, 304) has a first position area within which the current ning limiting segment (293, 309) completely block r for fluid flow through the first fluid port; a second position range within which the flow-limiting segment (293, 309) allows fluid flow through the first fluid port only through the recesses (312); and a third position area within which the fluid limiting segment (293, 309) allows fluid flow through the first fluid port at least partially outside the recesses (312); wherein the flow rate of fluid flowing along the fluid flow path can be controlled by controlling the position of the valve slide (292, 304) within the first, second and third position areas. 30. Tractor (100) according to claim 29, characterized in that a total cross-sectional area of the recesses (312) is delimited through the intersection of a transverse plane with the recesses (312), said transverse plane being generally perpendicular to the slide axis, and the cross-sectional area of the recesses (312) having a maximum value at one end of the flow-limiting segment (293, 309). 31. Tractor (100) according to claim 30, characterized in that the cross-sectional area of said recesses (312) decreases to zero as the recesses (312) extend towards a midpoint in the longitudinal direction of the flow-limiting segment (293, 309). 32. Tractor (100) according to claim 29, characterized in that the recesses (312) are generally pyramidal. 33. Tractor (100) according to claim 29, characterized in that the tractor body (102, 118, 124) is provided with logical components (224) which can control the position of the valve slide (292, 304). 34. Tractor (100) according to claim 33, characterized in that the logical components (224) are arranged to transmit command signals to a motor (160, 162, 164) which controls the position of the valve slide (292, 304). 35. Tractor (100) according to claim 34, characterized in that the logical components (224) are arranged to receive and process pressure signals from pressure sensors (182, 184, 186, 188) on the tractor body (102, 118, 124). 36. Tractor (100) according to claim 35, characterized in that one of the pressure signals is the pressure in fluid that flows along the fluid flow path from the valve (156) to the shock-receiving part. 37. Tractor (100) according to claim 34, characterized in that it further comprises a traversing mechanism which is arranged to convert rotation of an output shaft from the engine (160, 162, 164) into movement of the valve slide (292, 304) generally along the slide axis , where the logic components (224) are adapted to receive and process signals from a motor output sensor which measures the rotation of the output shaft. 38. Tractor (100) according to claim 37, characterized in that the engine output sensor comprises one of a rotational accelerometer and a potentiometer. 39. Tractor (100) according to claim 37, characterized in that the traversing mechanism comprises: - a threaded lead screw (322) which is connected to the output shaft; - a lead screw housing (318) which encloses the lead screw (322), where the lead screw housing (318) has an elongated slot (328) which is generally parallel to the lead screw (322); - a lead screw nut (326) which is in threaded engagement with the lead screw (322), where the lead screw nut (326) has a wedge (325) which engages with the slot (328) in the lead screw housing (318); and - a stem (330) having a first end connected to the lead screw nut (326) and a second end connected to the valve slide (292, 304); as rotation of the lead screw (322) causes the lead screw nut (326) to rotate in relation to the lead screw (322) and move along it due to the engagement of the wedge (325) in the slot (328). 40. Tractor (100) which is to move inside a borehole (42), characterized in that it comprises: - a body (102, 118, 124); - a valve (150, 154, 156, 158) on the body (102, 118, 124), where the valve is located along a fluid flow path from a source of a first fluid to an impact-receiving part of the body (102, 118 , 124), and wherein the valve (150, 154, 156, 158) is generally movable along a valve axis, and wherein the valve (150, 154, 156, 158) has a first position in which the valve completely blocks fluid flow along the flow path, and a second position in which the valve (150, 154, 156, 158) allows fluid flow along the flow path; - a motor (160, 162, 164) on the body (102, 118, 124); - a coupling connecting the motor (160, 162, 164) and the valve (150, 154, 156, 158), so that operation of the motor causes the valve to move along the valve axis; and - a pressure compensation piston (248) which is exposed on a first side to the first fluid, and which is exposed on a second side to a second fluid, the first and second fluids being separated from each other, where the piston (248) is designed to move in response to pressure forces from the first and second fluids, thereby effectively equalizing the pressure in the first and second fluids; in that the valve (150, 154, 156, 158) is exposed to the first fluid, while said motor (160, 162, 164) is exposed to the second fluid. 41. Tractor (100) according to claim 40, characterized in that the first fluid comprises drilling mud, and the second fluid comprises oil. 42. Tractor (100) which is to move inside a borehole (42), characterized in that it comprises: - an elongated body (102, 118, 124) which is designed to pull equipment inside the borehole (42), the said equipment exerts a longitudinal load on the body (102, 118, 124); - a gripper (104, 106, 440) which in the longitudinal direction is in movable engagement with the body (102, 118, 124), where the gripper (104, 106, 440) has an activated position in which the gripper (104, 106, 440) limits movement between the gripper and an inner surface of the borehole (42), and a retracted position in which the gripper (104, 106, 440) allows substantially free relative movement between the gripper and the inner surface; and - a propulsion system on the body (102, 118, 124), wherein the propulsion system includes at least one propulsion control valve which is coupled to an electronically controllable motor to direct fluid to an impact receiving portion, and wherein the impact receiving portion is designed to propel the body ( 102, 118, 124) through the drill hole (42) while the gripper (104, 106, 440) is in the activated position; and that the body (102, 118, 124) is arranged sufficiently flexibly so that the tractor (100) can bend up to 60° for every 30 meters of travel while the longitudinal load is at least 23,330 newtons. 43. Tractor (100) according to claim 42, characterized in that the body (102, 118, 124) is arranged sufficiently flexibly so that the tractor (100) can bend up to 45° per 30 meters of travel while the longitudinal load is at least 23,330 newtons. 44. Tractor (100) according to claim 42, characterized in that the body (102, 118, 124) is arranged sufficiently flexibly so that the tractor (100) can bend up to 30° per 30 meters of travel while the longitudinal load is at least 23,330 newtons. 45. Tractor (100) according to claim 42, characterized in that the tractor (100) has segments (102, 104, 106, 108, 110, 112, 114, 116, 129, 131) with a large diameter and segments (118, 120, 122 , 124, 126, 128) of small diameter, where the large diameter segments include: one or more valve bodies (134) with valves (150, 154, 156, 158) designed to control fluid flow to components of the propulsion system; a motor housing (132) with motors (160, 162, 164) designed to control the valves (150, 154, 156, 158); an electronics housing (130) with logic components (224) designed to control the motors (160, 162, 164); one or more propulsion chambers (166, 168, 170, 172; 174, 176, 178, 180) configured to receive fluid for propulsion of the body (102, 118, 124); pistons (140, 142, 144, 146) which are axially movable within the propulsion chambers (166, 168, 170, 172; 174, 176, 178, 180); as well as the gripper (104, 106, 440), and where the large-diameter segments (102, 104, 106, 108, 110, 112, 114, 116, 129, 131) have a diameter of at least 7.9 centimeters, as all bending of the tractor (100) essentially occurs in the small diameter segments (118, 120, 122, 124, 126, 128). 46. Tractor (100) according to claim 42, characterized in that the body (102, 118, 124) has a diameter of at least 2.5 centimeters. 47. Tractor (100) according to claim 42, characterized in that the tractor (100) has a length of at least 3 metres. 48. Tractor (100) according to claim 45, characterized in that the pistons (140, 142, 144, 146) are fixed on the body (102, 118, 124) and are movable along a stroke inside the propulsion chambers (166, 168, 170, 172 ; 174, 176, 178, 180), where the stroke length is at least 25 centimeters. 49. Tractor (100) according to claim 45, characterized in that the total length of the segments (102, 104, 106, 108, 110, 112, 114, 116, 129, 131) with a large diameter constitutes at least 50-80% of the tractor ( 100) its length. 50. Tractor (100) according to claim 42, characterized in that the tractor (100) is designed to be sufficiently flexible so that the tractor (100) can bend up to 60° per 30 meters of travel while the longitudinal load is up to 46,661 newtons. 51. Tractor (100) according to claim 42, characterized in that the body (102, 118, 124) has longitudinal boreholes (202, 204, 206, 208, 210, 234, 236, 260) for transporting fluid through the body (102, 118 , 124), where the boreholes are deep drilled. 52. Tractor (100) according to claim 42, characterized in that the body (102, 118, 124) comprises an outer cylinder (482) and an inner cylinder (480) bound to each other by diffusion, where one of the cylinders (482, 480) has longitudinal interruptions forming longitudinal passages (202, 204, 206, 208, 210, 234, 236, 260) between the cylinders (482, 480), and where the longitudinal passages (202, 204, 206, 208, 210, 234, 236 , 260) is designed to transport fluid through the body (102, 118, 124). 53. Tractor (100) according to claim 45, characterized in that the segments (102, 104, 106, 108, 110, 112, 114, 116, 129, 131) with a large diameter include the propulsion chambers (166, 168, 170, 172 ; 174, 176, 178, 180) and the pistons (140, 142, 144, 146) inside the propulsion chambers, where the pistons (140, 142, 144, 146) are fixed on the body (102, 118, 124), and where each of the pistons (140, 142, 144, 146) surrounds a segment of the body (102, 118, 124) and has an annular surface generally perpendicular to the body (102, 118, 124), and wherein the annular surface is designed to receive impact from a fluid flowing to the piston (140, 142, 144, 146), and where the pistons (140, 142, 144, 146) have a diameter of at least 3.8 centimeters. 54. Tractor (100) according to claim 42, characterized in that the gripper (104, 106, 440) has a length of at least 25.4 centimeters. 55. Tractor (100) which is to move inside a borehole (42), characterized in that it comprises: - an elongated body (102, 118, 124) which defines a longitudinal axis, and which is designed to transmit torque through the body, where the body (102, 118, 124) is designed so that when the body is subjected to a torque about the longitudinal axis of up to 678 newton metres, the twist in the body (102, 118, 124) is limited to 5° per steps of the tractor (100); - a first gripper (104, 106, 440) which is in axially movable engagement with the body (102, 118, 124), where the first gripper (104, 106, 440) has an activated position in which the first gripper limits its movement in relative to an inner surface in the borehole (42), and a retracted position in which the first gripper (104, 106, 440) allows substantially free relative movement between the first gripper and the inner surface, and where the first gripper (104 , 106, 440) is fixed against rotation in relation to the body (102, 118, 124), so that the first gripper (104, 106, 440) counteracts rotation of the body (102, 118, 124) in relation to the borehole (42 ) when the first gripper (104, 106, 440) is in the activated position; - a second gripper (104, 106, 440) which is in axially movable engagement with the body (102, 118, 124), where the second gripper (104, 106, 440) has an activated position in which the second gripper limits its movement in relative to an inner surface in the borehole (42), and a retracted position in which the second gripper (104, 106, 440) allows substantially free relative movement between the second gripper and the inner surface, and where the second gripper (104, 106, 440) is fixed against rotation in relation to the body (102, 118, 124), so that the second gripper counteracts rotation of the body (102, 118, 124) in relation to the borehole (42) when the other gripper (104, 106, 440) is in the activated position; and - a propulsion system on the body (102, 118, 124), wherein the propulsion system includes at least one propulsion control valve which is coupled to an electronically controllable motor to direct fluid to an impact receiving portion, and wherein the impact receiving portion is designed to propel the body ( 102, 118, 124) when at least one of the grippers (104, 106, 440) is in the activated position; and that the body (102, 118, 124) is arranged sufficiently flexibly so that the tractor (100) can bend up to 60° per 30 meter walk. 56. Tractor (100) according to claim 55, characterized in that the tractor (100) has segments (102, 104, 106, 108, 110, 112, 114, 116, 129, 131) with a large diameter and segments (118, 120, 122 , 124, 126, 128) of small diameter, where the large diameter segments include: one or more valve bodies (134) with valves (150, 154, 156, 158) designed to control fluid flow to components of the propulsion system; a motor housing (132) with motors (160, 162, 164) designed to control the valves (150, 154, 156, 158); an electronics housing (130) with logic components (224) designed to control the motors (160, 162, 164); one or more propulsion chambers (166, 168, 170, 172; 174, 176, 178, 180) configured to receive fluid for propulsion of the body (102, 118, 124); pistons (140, 142, 144, 146) which are axially movable within the propulsion chambers (166, 168, 170, 172; 174, 176, 178, 180); and the grippers (104, 106, 440), and where the large diameter segments (102, 104, 106, 108, 110, 112, 114, 116, 129, 131) have a diameter of at least 7.9 centimeters, and the segments ( 118, 120, 122, 124, 126, 128) of small diameter have a diameter of 5.2 centimeters or less, with all bending in the tractor (100) essentially occurring in the segments (118, 12 0, 122, 124, 12 6, 128) with a small diameter. 57. Tractor (100) according to claim 55, characterized in that the body (102, 118, 124) has a diameter of at least 2.5 centimeters. 58. Tractor (100) according to claim 55, characterized in that the grippers (104, 106, 440) are designed to transmit a torque of up to 678 newton meters to the borehole (42). 59. Tractor (100) according to claim 55, characterized in that each of the grippers (104, 106, 440) comprises: - a generally tubular spindle (400, 434) which is in concentric sliding engagement with the body (102, 118, 124), where the spindle (400, 434) has one or more longitudinal grooves which engage with lugs (419) on the outer surface of the body (102, 118, 124), so that the spindle (400, 434) is prevented from rotating relative to the body (102, 118, 124); and - an inflatable bladder (406, 452) which is fixed on the spindle (400, 434). 60. Tractor (100) according to claim 59, characterized in that each of the grippers (104, 106, 440) further comprises one or more flexible rods (430, 456) which extend lengthwise over the bladder (406, 452), where the rods ( 430, 456) are designed to bend and engage the inner surface of the borehole (42) when the bladder (406, 452) is inflated, and where the rods (430, 456) are designed to transmit torque from the body (102, 118 , 124) to the inner surface of the borehole (42).