NO328145B1 - Well tractor with equipment for detecting tractor housing displacement and method for the same. - Google Patents

Abstract

A hydraulically driven tractor (100) adapted to move forward through a borehole, the tractor including an elongate body, rear and front gripper assemblies (104, 106) and a valve control assembly (102) disposed in the elongate body. Rear and front gripper assemblies (104, 106) are adapted for selective engagement with the inside of a borehole. The valve control assembly (102) includes a gripper control valve (312) that directs pressure fluid to the rear and front gripper assemblies (104, 106). The valve control assembly (102) also includes a propulsion control valve (310) that directs fluid to a rear or front working chamber to propel the body forward relative to the activated gripper assembly. Rear and front mechanically actuated valves (322, 324) may be provided to regulate the position of the gripper control valve (312) by detecting and signaling when the body has completed a forward projection relative to an activated gripper assembly. Rear and front sequence valves (314, 316) can be provided to control the propulsion control valve (310) by detecting when the gripper assembly is fully activated. Furthermore, a pressure relief valve (306) is preferably provided along a supply line (302, 352) to limit the pressure in the fluid flowing into the valve control assembly (102).

Description

WELL TRACTOR WITH EQUIPMENT TO DETECT TRACTOR BODY DISPLACEMENT AND PROCEDURE FOR THE SAME

The present patent application claims priority from US provisional patent application serial number 60/446,644, filed February 10, 2003, and US provisional patent application serial number 60/448,163, filed February 14, 2003.

This invention generally relates to tractors for moving equipment through passages, and more specifically to a hydraulically driven tractor with an improved valve system.

Being able to move equipment through vertical, inclined and horizontal passages plays an important role within many industries, such as the petroleum, mining and communications industries. In the petroleum industry, for example, it is often necessary to move drilling, intervention, well completion and other types of equipment through boreholes drilled into the ground.

One way to move equipment through a well is to use rotary drilling equipment. In traditional rotary drilling, vertical and deviated wells are usually drilled by attaching a rotating drill bit and/or other equipment (together known as bottom hole assembly = BHA (bottom hole assembly)) to the end of a rigid drill string. The drill string is typically made up of a series of interconnected drill pipe joints that extend between the bottom hole string and equipment on the surface of the earth. As time goes by

the drill string and drill bit are guided into the ground, a passage is drilled. A drilling fluid, such as drilling mud, is pumped from surface equipment through an internal flow channel in the drill string and to the drill bit. The drilling fluid is used to cool and lubricate the bit, as well as to remove drilling residues and pieces of rock from the borehole. The drilling fluid flows back to the surface and carries the cuttings and residues through the annulus between the outside of the drill pipe and the inside of the borehole/well. As the drill string is raised or lowered in the borehole, you must constantly add or remove drill pipe joints on the surface, which entails significant costs and time consumption.

Another way of moving equipment in a borehole involves the use of well tools commonly called "tractors". A tractor can grip the borehole and push itself and other equipment through it. A self-propelled tractor of this type can be used to push and pull adjacent equipment through awiks wells or horizontal wells. Tractors can be fixed to rigid drill strings or can be used in conjunction with coiled tubing equipment.

Coiled pipe equipment usually includes a non-rigid, yielding pipe which in this document will simply be referred to as "coiled pipe", and through which the tractor is supplied with operating fluid. The operating fluid can supply hydraulic power to propel the tractor and the equipment, and in drilling applications can be used to lubricate the drill bit. In such systems, the operating fluid can also deliver the force necessary for the tractor to grip the inside of the well. Compared to rotary equipment, the use of coiled tubing combined with a tractor is usually less expensive, simpler, less time-consuming and provides better control over speed and well loads. In addition, coiled tubing, as a result of greater compliance and flexibility, will enable the tractor to pass sharper curves in the borehole than rotary equipment.

As a result of their versatility, self-propelled tractors can be used in many areas. A tractor can, for example, be used in connection with well completion and production work when producing oil from an oil well, installation and maintenance of pipelines, laying and moving communication lines, borehole logging, washing and acid treatment of sand and solids, collecting tools and drilling residues, etc. One type of tractor has a long body that can be attached to the lower end of a drill string. The body may include one or more jointed shafts associated with a housing for a control assembly or valve system.

Tractors typically include at least one anchor or gripper assembly adapted to grip the inside of the borehole. Upon activation of the gripper assembly, hydraulic power from the operating fluid can be used to propel the body axially through the borehole. The gripper assembly is in longitudinally movable engagement with the tractor body, so that the body and the drill string can move axially through the borehole while the gripper assembly is anchored inside the passage. US Patent No. 6,464,003, to Bloom et al., describes several embodiments of a fluid powered gripper assembly. In one highly effective embodiment, the gripper assembly includes a plurality of flexible arms that expand radially through interaction between ramps and rollers to engage and thereby grip the inside of the passage.

Tractors are typically configured with two or more sets of grapple assemblies, providing an opportunity for at least one grapple to be anchored in the borehole at any given time. Through this configuration, the tractor can move largely uninterrupted through the passage. Forward movement in the longitudinal direction (unless otherwise indicated, the terms "longitudinal direction" and "axial direction" will be used interchangeably in this document and refer to the longitudinal axis of the tractor body) is achieved by driving the tractor body forward relative to an activated first gripper assembly ( a "working stroke" relative to the first gripper assembly) while simultaneously moving a retracted second gripper assembly forward relative to the tractor body (a "reset stroke" for the second gripper assembly). At or near the completion of the working stroke of the first gripper assembly, the second gripper assembly is activated and the first gripper assembly is retracted. The tractor is then driven forward while the second gripper assembly is activated (a working stroke relative to the second gripper assembly), and the retracted first gripper assembly performs a reset stroke. At or near the completion of these respective strokes, the first gripper assembly is activated and the second gripper assembly is retracted. The work cycle is then repeated. In this way, each of the gripper assemblies operates in a cycle of actuation, working stroke, retraction and reset stroke, resulting in longitudinal movement of the tractor.

Several very effective tractor designs that make use of this configuration are described in US Patent No. 6,003,606, to Moore et al., where several embodiments of a tractor known as the "Puller-Thruster Downhole Tool" are described; US Patent No. 6,241,031, to Beaufort et al.; and US Patent No. 6,347,674, to Bloom et al., which describes an "Electrically Sequenced Tractor" (EST = Electrically Sequenced Tractor).

US patent 6241031, which is mentioned above, describes an electro-hydraulic steered tractor which uses an open system and which is driven by fluid which is pumped to the tractor through a barrel which extends to the tractor. The tractor has an elongated housing and pistons attached in relation to this. Two f-rein-drive spool internals engage the housing and enclose the pistons in the housing. A fluid-activated gripper is attached to each of the free-drive spindles. A gripper control valve spindle has a first position where it directs fluid to a first gripper and a second position where it directs fluid to a second gripper. One end of the valve spindle is exposed to the fluid pressure from one of the propulsion cylinders, and the other end of the spindle is exposed to the fluid pressure from the other propulsion cylinder. The valve spindle alternates between two positions as the pressure in the two propulsion cylinders changes.

WO document 98/01651 describes a well tractor system where fluid from a closed hydraulic system is used to drive the tractor system. A number of valves are used to alternatively control the fluid to a pair of tractor units which grip the borehole and which displace the tractor body in the borehole. The valves are reversed mechanically when the tractor body reaches a certain position relative to the tractor unit.

As mentioned above, the force required to activate the gripper assemblies, to push the tractor body forward during the work strokes and to reset the gripper assembly longitudinally during the reset strokes can be provided through pressurized operating fluid supplied to the tractor via the drill string. One or more flow-regulating devices, such as valves for example, are typically arranged in the tractor body to distribute the operating fluid to the tractor's gripper assemblies, push chambers and reset chambers.

Certain tractor types, including several versions of the "Puller-Thruster Downhole Tool", are operated entirely hydraulically. Pressure-sensitive/pressure-influenced valves will typically move back and forth between different positions based on the pressure in the operating fluid at the various locations in the tractor. In one configuration, a pressure-sensitive valve can be in the form of a slide valve which is open at both ends to different fluid chambers or passages. Accordingly, the valve position depends on the pressure difference between the fluid chambers. Fluid at a higher pressure in a first chamber exerts a greater force against the valve than fluid at a lower pressure in a second chamber, which drives the valve to one extreme position. The valve moves to another extreme position when the pressure in the second chamber exceeds the pressure in the first chamber. Another type of pressure-sensitive valve is in the form of a spring-loaded slide valve with at least one end open to fluid. The fluid pressure force is oppositely directed to the spring's biasing force, so that the valve is only opened or closed when the fluid pressure exceeds a threshold value.

In other configurations, tractors can be provided with one or more valves that are controlled by means of electrical signals sent from a control system on the surface, possibly on the tractor itself. For example, the above EST includes both electrically controlled valves and pressure sensitive valves. The electrically controlled valves are controlled using electrical control signals sent from a control device placed in the tractor body. For drilling workers, it may be that EST is preferred over fully hydraulic tractors because electric control of the valves enables a very precise regulation of important drilling parameters, such as speed, position and driving force.

Fully hydraulic tractors, including several versions of the Puller-Thruster Downhole Tool, are, on the other hand, preferred for so-called intervention work. As used in this document, the term "intervention" refers to the return to a previously drilled well with the aim of increasing well production, thereby increasing production. As the wells get older, the production from them decreases, for several reasons. This makes it necessary to "intervene" with many different tools. Hydraulic tractors are generally preferred over electrically controlled tractors in intervention work, because hydraulic tractors cost less to operate, and intervention work does not require precise control of speed or position.

Tractors used in conjunction with coiled tubing equipment are particularly useful in intervention work, as in many cases the wells were originally drilled using rotary drilling equipment with the capacity to drill very deep wells. It is more expensive to bring the rotary equipment back in than to bring in a coiled tubing assembly. In many situations, however, the coiled tubing assembly will not be able to reach long distances in the borehole without the aid of a tractor. The tractor is particularly useful when it comes to reaching locations in deviated or horizontal wells.

Professionals in the field will realize that tractors of the type generally described above can be exposed to many different conditions. For example, depending on the application, there can be large variations in the operating fluid's pressure, weight and density. Furthermore, the shape and angle of the borehole can vary. In addition, the weight of the equipment the tractor must pull and/or push will vary for the various applications.

Although tractors will be subject to many different conditions, the present inventors have found that existing tractors, and in particular all-hydraulic tractors, are only configured to operate effectively within a relatively small range of conditions. This can constitute a significant weakness that increases costs and limits the tractors' activities in the field.

A desire therefore exists for an improved valve system that enables a tractor to operate efficiently under a large number of conditions. In one embodiment, such a valve system can control tractor operation independently of the tractor's load. ning and speed. It may also be desirable that such a valve system should not be subjected to hasty changes in valve position when there are pressure fluctuations in the operating fluid. There may also be a desire for such a valve system to protect the internal components from damage. In addition, it may be desirable that such a valve system should make it possible to drive the tractor relatively inexpensively and simplify the operation of the tractor in the field by reducing or eliminating the steps involved in calibration, operation and troubleshooting in the well. It may also be desirable for such a valve system to be adapted for use at a large number of different flow rates and to be compatible with a large number of wellbore string components. In addition, it is desirable that such a valve system should allow highly efficient movement by reducing unnecessary holding time between the steps in the functional sequence.

The pressure in the operating fluid in a tractor can fluctuate greatly as the valve system controls fluid that will activate grippers and/or drive the pistons (or other similar mechanisms) during the tractor's forward movement through the passage. In some applications, it is not unusual for the pressure to vary by as much as 1000 psi. When used in the field, the present inventors have found that the pressure fluctuations can make other equipment unusable or incompatible, especially if the other equipment is adapted for use within a limited pressure range. As a result, the user may have limited use of the tractor together with other equipment.

Furthermore, the present inventors have found that the large pressure fluctuations impose unwanted fatigue cycles on the internal tractor components and/or the associated tools. This can limit the expected lifespan of the tractor and/or other associated tools, and can thus have a major impact on the operating costs resulting from tractor use.

Furthermore, the present inventors have found that pressure operated valves may have a tendency to switch prematurely as a result of pressure spikes or other large fluctuations in fluid pressure. Testing has similarly shown that the valves can be particularly susceptible to premature switching if the tractor system is exposed to large loads and/or large dynamic pressure waves ("water hammer" effect) caused by the opening and closing of other valves in the control assembly. In some applications, premature valve replacement can significantly limit the tractor's functional range and efficiency.

In various embodiments of the present invention, an improved valve system adapted for use with a tractor has been provided, which system overcomes the above-mentioned problems with prior art. These designs represent a major advance in the tractor area, and especially in the area that includes well intervention tools. Compared to prior art, some versions of the improved valve system can provide better control over the tractor movements and function very efficiently within a much larger parameter range. By providing better control over the fluid pressure, some versions of the improved valve system can also extend the life of internal components and thus reduce operating costs.

In one aspect, a tractor for moving a component through a borehole comprises an elongate body to which are coupled rear and front gripper assemblies movable in the longitudinal seal. Rear and front gripper assembly is preferably hydraulically operated for selective engagement with an inside borehole. The rear and front propulsion assembly are arranged to drive the body through the borehole in relation to the rear and front gripper assembly, respectively. A gripper control valve is provided to send pressurized fluid to the rear and front gripper assemblies. The gripper control valve preferably has a first position for directing pressure fluid to the rear gripper assembly and a second position for directing pressure fluid to the front gripper assembly. An important feature is that a rear and a front mechanically operated valve are located along the body to demonstrate the progress of the body in relation to the mentioned rear or front gripper assembly respectively, which is a mechanism that improves the time management and efficiency of the tractor works. In particular, rear and front mechanically operated valves are in fluid communication with the gripper control valve to cause the gripper control valve to change position after the body has completed a forward stroke through the borehole relative to said rear or front gripper assembly.

In another aspect, a tractor for moving a component through a borehole comprises an elongate body through which extends an internal channel which supplies pressurized fluid to a downhole string. The rear and front gripper assemblies are longitudinally displaceably connected to the elongate body. Rear and front gripper assembly is preferably hydraulically operated for selective engagement with an inside borehole. A rear and a front propulsion assembly are arranged to drive the body through the borehole in relation to the rear and front gripper assembly respectively. A gripper control valve is provided to send pressurized fluid to the rear and front gripper assembly. The gripper control valve preferably has a first position for directing pressure fluid to the rear gripper assembly and a second position for directing pressure fluid to the front gripper assembly. A propulsion control valve is also arranged in the body, and this has a first position for directing pressure fluid to the rear propulsion assembly and a second position for directing pressure fluid to the forward propulsion assembly. A supply line supplies pressurized fluid from a surface supply source to the gripper control valve and the propulsion control valve. A pressure relief valve is placed in said tractor body to regulate the fluid pressure in the internal channel. The pressure relief valve also regulates the pressure in the fluid that flows in through the tractor's valve system. In one variant, the valve system may include a start/stop valve that prevents fluid from flowing into the gripper control valve and the propulsion control valve. The outlet from the start/stop valve can be used to control the pressure relief valve and thus provide a mechanism for turning off the pressure relief valve as desired.

In a further aspect, a tractor for moving a component through a borehole comprises an elongate body through which an internal channel extends longitudinally. Rear and front gripper assemblies are slidably connected to the elongate body. Rear and front gripper assembly is preferably hydraulically operated for selective engagement with an inside borehole. The rear and front propulsion assembly is adapted to drive said body through the borehole in relation to the rear and front gripper assembly, respectively. The elongate body houses a hydraulic valve system configured to receive a portion of the pressure fluid from the internal channel and direct the fluid to the rear or front gripper assembly in the desired sequence to effect movement of the tractor through the borehole. A pressure relief valve is arranged to limit the fluid pressure in the internal channel and the hydraulic valve system, and where the pressure relief valve is adapted to vent fluid from the internal channel to an annulus when the fluid pressure in the internal channel exceeds a preselected threshold value. A first fluid path runs from said internal channel to the hydraulic valve system. A second fluid path runs from the internal channel to the pressure relief valve.

In yet another aspect, a device for movement through a borehole comprises an elongate body formed with an internal channel extending therethrough longitudinally. Rear and front gripper assemblies are slidably connected to the elongate body. Rear and front gripper assembly is preferably driven hydraulically for selective engagement with the inside of the borehole. Rear and front drive assemblies are adapted to drive said body through the borehole in relation to the rear and front gripper assembly, respectively. The elongate body houses a hydraulic valve system configured to receive a portion of the pressure fluid from the internal channel and to direct the fluid to the rear or front gripper assembly in the desired sequence to effect movement of the tractor through the borehole. A pressure relief valve is arranged to limit the fluid pressure in the internal channel and the hydraulic valve system, and where the pressure relief valve is adapted to vent fluid from the internal channel and into an annulus when the fluid pressure in the internal channel exceeds a preselected threshold value. A first fluid path runs from said internal channel to the hydraulic valve system. A second fluid path runs from the internal channel to the pressure relief valve.

These and other embodiments are intended to be within the scope of the invention described in this document. These and other embodiments of the present invention will be clearly apparent to those skilled in the art from the subsequent, detailed description of the preferred embodiments, which are connected with the attached drawings, the invention not being limited to any particular of the described embodiments. Figure 1 is a schematic diagram of the main components in one embodiment of a tractor according to the present invention, where this is used together with a coiled pipe system; Figure 2 is a front perspective drawing of a preferred embodiment of the tractor; Figure 3 is a schematic diagram showing a preferred embodiment of a valve control assembly for use with the tractor; Figure 4 is a longitudinal section showing a preferred embodiment of a pressure relief valve; Figure 5 is an exploded view showing the components of a preferred embodiment of a start/stop valve; Figure 6 is a longitudinal section showing a preferred embodiment of an air valve assembly; Figures 7A and 7B are exploded views of an axle assembly for use with the tractor; Figure 8 is a longitudinal section showing a preferred embodiment of a piston/plate valve which is integrated in a piston; Figure 9 is an exploded view of the middle housing of the valve control assembly; Figure 10 is an exploded view of the transition areas located at the rear and front ends of the valve control assembly; Figure 11 is a schematic diagram showing another preferred embodiment of a valve control assembly for use with the reversible tractor; Figure 12 is a perspective drawing of a gripper assembly with rollers attached to the arms, shown in a retracted or non-grip position; Figure 13 is a longitudinal cross-section of a gripper assembly with rollers attached to the arms, shown in the activated or gripper position; Figure 14 is a partially cut-away perspective drawing of the gripper assembly in Figure 12; Figure 15 is an exploded view of one set of rollers for an arm in the gripper assembly of Figure 14; Figure 16 is a perspective drawing of a gripper assembly with rollers attached to the push member; Figure 17 is a longitudinal cross-section of a gripper assembly with rollers attached to the pusher; Figure 18 is a perspective drawing of a retracted gripper assembly with knee joints which effect radial displacement of the arms; and Figure 19 is a longitudinal cross-section of the gripper assembly of Figure 18, shown in the activated or gripper position. Figure 1 is a schematic diagram showing a hydraulic tractor 100 in use for moving equipment in a passage. The tractor is shown used together with a coiled pipe system 20 for drilling and associated well equipment 32. The coiled pipe drilling system 20 may include a power supply 22, pipe drum 24, pipe guide 26, pipe injector 28 and coiled pipe 30, all of which are well known in the art. The tractor 100 is configured to move in a borehole with an inside 42. An annular space 40 is provided between the outside of the tractor 100 and the inside 42 of the borehole.

The well equipment 32 can include various types of equipment that the tractor 100 is designed to move in the passage. The equipment 32 may include, for example, a perforating gun assembly, an acid treatment assembly, a sand washing assembly, a drill plug setting assembly, an E-wire, a borehole measurement assembly, a borehole lining assembly, a MUB assembly (measuring while drilling) or a fishing gear. As an alternative, the equipment 32 may comprise a combination of these. If the tractor 100 is used for drilling, the equipment 32 will preferably include a MUB system 34, a drill motor 36 and a drill bit 38, all of which are known in the field. The well equipment 32 can of course include many other types of equipment for applications other than drilling, for example intervention and completion applications. Although the equipment 32 is shown at the front end of the tractor, the well equipment in alternative configurations can be connected to the rear or front of the tractor.

Those skilled in the art will appreciate that a hydraulic tractor of the type shown can be used to move a large variety of tools and equipment in a borehole or other passage. The tractor can, for example, be used for well completion and production activities, laying and maintaining pipelines, laying and moving communication lines, well drilling, washing and acid treatment of sand and solids, collecting tools and drilling residues, etc. In addition, the tractor, although it is preferably used in intervention work, can also be used in drilling applications, including drilling for petroleum and ore deposits. The tractor can be used in combination with various types of drilling equipment, including equipment for rotary drilling and coiled pipe equipment.

A professional will understand that the completion of oil and gas wells normally requires the reservoir to be logged (measured) using many different sensors/measuring devices. These sensors can work through the use of specific resistance, radioactivity, acoustics and the like. Other borehole measurements include measurement of formation inclination and borehole geometry, formation sampling and production measurements. With the help of a tractor, these completion activities can be carried out in a variety of deviated and horizontal boreholes. The tractor can, for example, deliver these sensors or measurement transmitters to the relevant location or it can wait in a stationary position while measurements are taken at the desired points. The tractor can also be used to pick up sensors from the well.

Examples of production activities that can be performed with a hydraulic tractor include washing and acid treatment of sand and solids. It is known that wells are sometimes clogged by sand, hydrocarbon residues and other solid components that prevent the free flow of oil through the borehole. To remove these drilling residues, specially constructed washing equipment is brought to the area, and fluid is injected to wash out the area. The fluid and drilling residues then flow back to the surface. Such equipment includes, among other things

acid washing equipment. This washing equipment can be taken to the relevant area to carry out the washing work and then taken

back to the surface by means of a preferred embodiment of the invention.

In another example, a hydraulic tractor can be used to pick up objects such as damaged equipment and drilling debris from the borehole. Equipment can become detached from the drill string, or objects can fall into the borehole. These objects must be picked up, otherwise the borehole must be plugged and abandoned. As plugging and abandoning a borehole is very expensive, it is preferred that the object be picked up if this is possible. There are many different tools in the industry that can be used to pick up these objects. In this application, the tractor is used for transporting retrieval tools to the relevant location, retrieving the object, and then returning the retrieved object to the surface.

In a further example, the hydraulic tractor can be used for coiled pipe completions. As is well known, the deployment of a continuous completion drill string for driving in production pipes in areas where it is not desirable to damage delicate formations is becoming increasingly important. This work requires the installation and retrieval of fully assembled completion drill strings in boreholes with surface pressure. The tractor can be used in connection with deployment of traditional speed string and installations of simple primary production pipes. The tractor can also be used when deploying artificial lifting devices such as gas lift and flow regulating devices in the well.

In a further example, a tractor can be used to service blocked pipelines or similar passages. It is often difficult to inspect pipelines due to physical limitations such as their location in deep water or proximity to urban areas. Today, there are various types of cleaning devices for cleaning pipelines. These different types of cleaning equipment can be attached to the tractor, so that the cleaning equipment can be moved in the pipeline.

In a further example, a tractor can be used to move communication lines or equipment in a passage. It is often desirable to be able to run or move different types of cables or communication lines through different types of pipes. The tractor can move these cables to the desired location in a passage.

Figure 2 shows one preferred embodiment of the tractor 100, shown with the rear end on the left and the front end on the right. The tractor 100 generally includes a center steering assembly 102, a rear gripper assembly 104, a front gripper assembly 106, a rear propulsion cylinder 108, a front propulsion cylinder 114, a rear axle assembly 118, a front axle assembly 124, pipe coupling assemblies 116 and 129 and elbows or adapters 120 and 128 .The tubing coupling assembly 116 is located along the rear end of the rear axle assembly 118 to connect the drill string (eg, coiled tubing) to the rear axle assembly 118. The rear gripper assembly 104, rear propulsion cylinder 108, and flex link 108 are assembled end to end, and are all in axially slidably engage with the rear axle assembly 118. Similarly, the forward gripper assembly 106, forward propulsion assembly 114 and flexure joint 128 are assembled end to end and are axially slidably engaged with the forward axle assembly 124. The pipe coupling assembly 129 is preferably con figured to connect the tractor 100 to the well equipment 32, as shown in figure 1. The rear axle assembly 118, the steering assembly 102 and the front axle assembly 124 are axially stationary in relation to each other, and are referred to in this document largely as the body of the tractor. The tractor body is usually axially stationary in relation to the drill string and well equipment.

The gripper assemblies 104, 106 and the propulsion cylinders 108, 114 are axially displaceable along the body in order for the tractor 100 to be able to pull and/or push well equipment 32 of different weight through the borehole (or passage). In one embodiment, the tractor 100 can pull and/or push a total weight of 100 pounds (about 45 kg) in addition to the weight of the tractor itself. In various other designs, the tractor can pull and/or push a total weight of 500, 3,000 and 15,000 pounds (about 225, 1,350 and 6,800 kg).

In order to prevent damage to the surrounding formation or casing wall, the gripper assemblies 104, 106 are preferably designed to limit the radial gripping load (ie, force) exerted against a face. In one embodiment, the gripper assemblies exert no more than 25 psi (about 172 kPa) against a surface surrounding the tractor. This design is particularly useful in softer formations such as gumbo. In various other embodiments, gripper assemblies 104, 106 exert no more than 100, 3000, and 50,000 psi (approximately 690, 20,700, and 345,000 kPa) against a surface surrounding the tractor. At radial grip loads of 50,000 psi (approx. 345,000 kPa) or less

the tractor can usually be used safely in steel pipe liners.

The tractor 100 preferably receives pressurized operating fluid from a surface supply. A supply line extends down from the surface and passes through an internal channel in the tractor to deliver operating fluid to the well equipment. As the operating fluid flows through the internal channel, a portion of the fluid is directed to the control assembly 102 to deliver hydraulic power to the tractor. More specifically, the control assembly 102 houses a valve system that distributes operating fluid to and from the gripper assemblies 104, 106 and the propulsion cylinders 108, 114 to control tractor movement. Preferred embodiments of the control assembly and the valve system are described in more detail below. By using the patent description and drawings in the present patent application together with construction principles and principles for planning space distribution known to professionals through the present applicant's jointly owned US patent no. 6,347,674 and US patent no. 6,679,341, a person with general knowledge within the field could understand how to build a tractor with an improved valve system as described in this document.

The tractor 100 can have any desired length, but for use in an oil field the length is typically approx. 25 to 35 feet (7.6 to 10.7 m). The tractor's maximum diameter will vary with the hole size, the need for thrust and the constrictions that the tractor must pass. The gripper assemblies 104, 106 can be designed to work in boreholes of various sizes, but are typically configured to expand to a diameter of 3.75 to 7.0 inches (about 95 to about 178 mm).

The bending transitions 120 and 128 are preferably hollow structural elements which form an area with less bending stiffness (ie greater flexibility). This area with less bending stiffness facilitates the tractor's ability to pass sharp curves. In one preferred embodiment, the transition pieces are made of a material with low bending strength, for example copper beryllium (CuBe) and/or titanium. At times there will be applications that make it necessary to use non-magnetic materials in the tractor. Otherwise, depending on the demands placed on the tractor's ability to turn, and the resulting loads, different types of stainless steel can be used in many parts of the tractor. The pipe coupling assembly 116 preferably connects the rear end of the rear axle assembly 118 to a coiled pipe drill string, preferably via a threaded connection. As mentioned above, well equipment can also be placed at the rear end of the tractor, connected to pipe connection assembly 116. In a typical operation, however, pipe connection assembly 129 will be connected to well equipment. The connection threads on the pipe-coupling assemblies are preferably API threads or trademarked threads (eg Hydril liner threads). The pipe coupling assemblies can be finished to a specific torque, for example 1000-3000 Ibs ft, (approx. 1350-4060 Nm) using traditional equipment (pliers). The pipe-coupling assemblies can be made from many different materials, including CuBe, steel and other metals.

As mentioned above, the rear and front axle assembly 118 and 124 together with the steering assembly 102 constitute the body of the tractor 100. The rear and front axle assembly 118 and 124 are preferably both formed with a part having an enlarged diameter, this part forming a piston. The rear and front pistons preferably have outside diameters that are essentially equal to the inside diameter of the rear and front propulsion cylinders 104, 108. The rear and front pistons are displaceably located in the rear and front propulsion cylinders 104, 108 and divide the inside of each cylinder into a working chamber and a reset chamber. Accordingly, rear and front propulsion cylinders 104, 108 constitute, at least in part, rear and front propulsion assemblies configured to move the tractor body forward through the borehole relative to the rear and front gripper assemblies. Although preferred embodiments of the tractor make use of rear and front propulsion cylinders, it will be understood that many different rear and front propulsion assemblies can be used to effect propulsion of the tractor body.

As will appear in more detail from the following description, pressure fluid is alternately supplied to the working chamber in the rear or front propulsion cylinder to propel the body forward through the borehole when the rear or front gripper assembly is anchored inside. Pressurized fluid is alternately supplied to the reset chamber in the rear or front propulsion cylinder to return the rear or front gripper assembly to position relative to the body (ie, in preparation for a new stroke) while the rear or front gripper assembly is disengaged. Thus, the tractor moves incrementally through the borehole by pushing forward relative to the rear or front gripper assembly.

Rear and front axle assemblies 118 and 124 may be made of any suitable material. In one preferred version, the axles are made of a flexible material such as CuBe, to enable the tractor 100 to pass sharper curves. In other designs, CuBe is not used, as this is relatively expensive. Other acceptable materials include titanium and steel (where little ductility is sufficient). In a preferred configuration, each shaft includes a central, internal bore which together partially forms the internal channel for the flow of pressurized operating fluid to the well equipment and to the control assembly 102. The bore in each of the shaft assemblies preferably extends over the entire length of the shaft. Each shaft may also include several other passages for the flow of fluid to the gripper assemblies and the propulsion cylinders. These fluid passages vary in length and are equal to or less than the total length of the tractor. Several fluid channels can be drilled in the shaft for the same function, for example for supply to a single propulsion chamber. The bore and the other internal fluid channels are preferably arranged so that they provide the least possible load and provide enough space and strength for other construction features, such as for example the pistons which are displaceably placed in the cylinders. Preferably, each of the shafts is threaded at one end for connection to the drill pipe coupling assemblies 116 and 129, and with a flange at the other end to enable it to be bolted to the steering assembly 102.

Those skilled in the art will understand that the tractor 100 described in this document is particularly suitable for intervention applications. Although intervention tractors can be made in any size, they are typically used in 5 inch (127 mm) or 7 inch (178 mm) casing. The inside diameter of a 5 inch casing can vary from 4.5 inches (114 mm) to 4.8 inches (122 mm). The inside diameter of a 7 inch casing can vary from 5.8 inches (147 mm) to 6.4 inches (163 mm). The main structural parts of the tractor 100 are the axles 118 and 124. In a preferred embodiment, the axles have an outside diameter of 1.75 inches (44.5 mm) and an inside bore diameter of 0.8 inches (20.3 mm). The other fluid channels in the axles are preferably smaller. The pistons can have varying outside diameters.

The tractor 100 described in this document is very reliable and efficient in intervention applications. Prior art intervention tools utilizing rotary drill strings are as much as 150% more expensive than the shown tractor 100 used with coiled tubing equipment. In addition, the tractor 100 is more time-saving, as the long set-up time associated with rotary equipment is avoided. Furthermore, it is particularly advantageous to use coiled tubes when operating perforating guns.

The tractor 100 is driven at least partially hydraulically by means of the operating fluid that is pumped down through the drill string, for example brine, seawater, drilling mud or another hydraulic fluid. As mentioned above, the same fluid supply line that drives the well equipment 32 (see Figure 1) will preferably also drive the tractor. This makes it unnecessary to arrange several fluid channels in the tool. Liquid brine or seawater is preferably used in an open system. Alternatively, if desired, fluid can be used in a closed system. Referring again to figure 1, operating fluid in use will flow from the drill string 30 through the tractor 100 and down to the well equipment 32.

The control assembly 102 preferably contains a plurality of hydraulically and/or electrically operated valves configured to selectively regulate the flow of operating fluid to and from the gripper assemblies 104 and 106 and to and from the propulsion cylinders 108 and 114 to effect movement of the tractor. It is understood that the term "valve", as used in this document, is a general term which in its generality refers to any device that can regulate or control the distribution of fluid. The valves located inside the control assembly 102 are preferably controlled entirely hydraulically. Hydraulically controlled valves are generally more applicable than electrically controlled valves, especially for intervention applications, because they are less expensive and usually safer to use in combination with certain types of well equipment, such as perforating guns. In addition, hydraulically controlled valves mean that you do not need electronic components, which thus saves space and enables larger internal flow channels. As a result, tractors that use hydraulically controlled valves are usually faster and more powerful than tractors that use electrically controlled valves. Preferred embodiments of the present invention describe an improved valve system which provides a significant improvement compared to previously known valve systems. For example, embodiments of the improved valve system described herein will provide much greater control over tractor movement compared to existing hydraulically controlled tractors. The improved valve system also provides a better regulation of fluid pressure and enables the tractor to operate efficiently within a larger parameter range. Furthermore, the improved valve system is configured to increase operational reliability and extend the lifetime of the internal components, which will thus save time and reduce costs.

Referring to Figure 3, for illustrative purposes, one preferred embodiment of an improved valve system 300 is schematically shown. The part of the valve system 300 that is contained within the control assembly 102 generally includes a start/stop valve 308, a progress control valve 310 (or main sequence valve), a gripper control valve 312 (or pilot valve), a rear sequence valve 314, a front sequence valve 316, a rear vent valve 318, a front vent valve 320 and a pressure reduction valve 326. In addition, a pressure relief valve 306 is arranged which regulates the inlet pressure in the internal channel. The pressure relief valve 306 is preferably included in the control assembly. However, it can be placed elsewhere, for example on the surface.

In order to be able to effectively control the sequence of valve functions, it is desirable to be able to detect when the tractor body has completed a forward stroke in relation to the anchored rear or front gripper assembly. Due to pressure fluctuations in the valve system, the use of pressure sensitive valves is not always effective in detecting and signaling the end of a forward stroke. Accordingly, one embodiment of an improved valve system for an intervention tractor includes at least one mechanically actuated valve mechanism in the propulsion control assembly to quickly and accurately detect and signal the completion of a piston stroke.

In one preferred embodiment, the mechanically activated valve is a poppet valve which is integrated into the piston. As the piston completes its stroke, the poppet valve (or other mechanically actuated valve) is mechanically actuated to open a closure thereby allowing fluid flow through a passage. As a result, the outlet flow from the poppet valve can be used to activate or control another valve. The use of a poppet valve to detect the end of the piston stroke, instead of a pressure-actuated valve, provides increased performance and operational reliability for the hydraulic control assembly.

Figure 3 is a schematic diagram of a rear piston/poppet valve 322 and a front piston/poppet valve 324 which both cooperate with the valves in the control assembly 102 to control tractor movement. As will be described in more detail below, the rear and front piston/poppet valves 322, 324 are preferably integrated into the rear and front pistons of the rear and front axle assembly. In preferred embodiments, the rear and front piston/plate valve 322, 324 are preferably substantially identical in terms of construction and operation.

With continued reference to Figure 3, one embodiment of an improved valve system is shown where the tractor receives pressurized fluid from the surface through a supply line 302. As the fluid flows into the internal channel in the tractor body, part of the fluid is led from the supply line 302 and to a pressure relief valve 306 along the flow path 352. In addition, part of the fluid is led from the supply line 302 and to the start-stop valve 308 along the flow path 350. The remaining pressure fluid flows through the internal channel to the well equipment along the flow path 303.

In the embodiment shown, the pressure relief valve 306 regulates the fluid pressure in the supply line 302. As a result, the pressure relief valve 306 will also regulate the pressure in the "working fluid" that flows into the start-stop valve 308 along the flow path 350. The working fluid provides hydraulic power that causes tractor movement. Accordingly, it will be understood that the pressure relief valve regulates the pressure in the fluid that flows into the gripper assemblies 104, 106 and the propulsion cylinders 108, 114 (see Figure 2). Furthermore, the pressure relief valve 306 regulates the pressure in the fluid delivered to the well equipment along the flow path 303. Although the pressure relief valve is preferably placed inside the control assembly (as shown in Figure 3), it can also be arranged elsewhere, such as along other parts of the tractor or on the surface.

In a preferred embodiment, the pressure relief valve 306 has an adjustable opening which opens as a function of the fluid pressure. If the pressure in the supply line 3 02 rises quickly, the adjustable opening will open more to release more fluid. As a result, the pressure relief valve 306 reacts quickly, and fluid in the supply line 302 can advantageously be kept at a regulated pressure.

When the pressure difference between the supply line 302 and the annulus 40 during operation rises above a preselected threshold value, the pressure relief valve 306 opens to release fluid to the annulus 40, thereby reducing the pressure in the supply line. In various embodiments, the preselected differential pressure threshold value is preferably at least 600 psi, 800 psi, 900 psi, 1100 psi, 1200 psi, 1400 psi, and 1600 psi (approximately 4140, 5520, 6210, 7590, 8270, 9650, and 11030 kPa ).'In a preferred embodiment, the preselected threshold value is 1400 psi (about 9650 kPa). Under certain conditions, it may also be desirable to have other preselected threshold values for pressure. The pressure relief valve is preferably sized to direct fluid to the annulus 40 at a maximum flow rate of up to 20 to 25 gallons per minute (76 to 95 liters per minute). In preferred embodiments, one can choose to make the pressure relief valve 306 non-operational (i.e. it is switched off) when it is desirable to supply high-pressure fluid to the well equipment for certain works.

The pressure relief valve 306 is particularly useful when used with valve systems that use a relatively large percentage of the current through the supply line 302 to power the tractor. Valve systems that use a large percentage of the system flow typically generate large pressure fluctuations in the system during operation. For example, the change in valve position when the tractor completes a working stroke could lead to a temporary stop in the flow of fluid through the system. Without the pressure relief valve, the flow reduction would cause a large fluctuation in system pressure, which could lead to jerky movement, unstable valves or stalling in the tractor. Accordingly, those skilled in the art will appreciate that the embodiments of the pressure relief valve 306 described herein represent a major advance in the tractor field.

Referring to Figure 4, a cross-section of the internal components 400 in one preferred embodiment of a pressure relief valve is shown. The pressure relief valve is preferably a pilot-operated, spring-loaded two-position valve which is controlled by means of the pressure in the fluid path 354 from the start/stop valve 308 (as shown in figure 3). The internal components 400 of the pressure relief valve generally comprise a body 402 formed with a hollow interior, and a slide 404 slidably located in the interior cavity. A first and second inlet opening 430, 432 and first and second outlet opening 434, 436 are made through the body 402 to provide fluid communication with the internal cavity.

In the embodiment shown, a spring insert 414 is connected to the left end of the slide 404 via a ball 412. The spring insert 414 and the slide 404 are axially stationary in relation to each other. The right end of the insert 414 is slidably held within the body 404 by means of a holder 410. A coil spring 422 extends around a central portion of the spring insert 414. As shown, the left end of the spring 422 is in contact with a fixed stop 426, which prevents that the spring 422 moves away from the body 402 (on the left in Figure 4). The spring 422 is preferably pressed together between the fixed stopper 426 and a flange 428 on the insert 414. The spring 422 causes a biasing force which drives the insert 414 and the slide 404 away from the body 402 (right in figure 4). The pressure relief valve is preferably configured so that the biasing force varies according to the pressure in the annulus, so that the pressure relief valve acts on the basis of a pressure difference between the supply line and the annulus. A stopper 406 is placed in the housing 402 to limit the displacement of the slide 404 to the right. A control spindle 418 is displaceably placed in the control assembly 416 in such a way that the left end of the spindle 418 is in contact with the right end of the slide 404.

Figure 4 shows the internal components 400 of the pressure relief valve in an open position where pressure fluid can flow through. In operation, pressurized fluid flows into the steering assembly 416 through a steering opening 420. The fluid flows into a chamber 424 where the fluid pressure acts against one end of the steering spindle 418. When the slide is in contact with the stopper 406, the inlet openings are blocked, so that no fluid can flow through the pressure relief valve. When the fluid pressure is sufficient to overcome the biasing force of the spring, the spindle 418 moves to the left and thereby causes the slide 404 to move to the left through the body 402. As the slide 404 moves to the left, the spring 422 is compressed. As the slide 404 moves to the left relative to the body 402, the inlet openings 430, 432 open to allow fluid into the hollow interior of the body. The fluid flows around the slide and out through the outlet openings 434, 436, preferably to the annulus. Due to the configuration of the slide and the inlet openings, the first and second inlet openings 430, 432 open further as the slide moves further to the left to let more fluid through. In a preferred configuration, the first and second inlet openings 430, 432 are offset relative to each other, so that the first inlet opening 430 opens before the second inlet opening 432. Accordingly, the pressure relief valve will only release a small amount of fluid when the fluid pressure is only slightly above the threshold value. When the fluid pressure is significantly higher than the threshold value, however, both the first and the second inlet opening 430, 432 will be open to let a larger amount of fluid through.

Referring again to Figure 3, the pressure relief valve 306 will advantageously provide an opportunity to regulate the pressure in the fluid which is delivered both to the valve system (via the flow path 350) and to the well equipment (via the flow path 303). One advantage of this arrangement is that the fluid that flows in via the valve system is regulated independently of the tractor's load and speed. Another advantage is that the valve system is protected against large pressure fluctuations that can damage the internal equipment. Another advantage is that the tractor is prevented from suddenly accelerating or stopping as a result of large pressure fluctuations in the supply line. Furthermore, the tractor is more compatible with well equipment because the pressure in the flow path 303 is controlled. Moreover, the controlled pressure will make it possible to use preferred versions of the tractor over a much larger range of flow rates. The extended range gives even greater opportunities to use the tractor with a large selection of well equipment within different areas of application.

Referring again to Figure 3, a portion of the pressure fluid is preferably led from the supply line 302 (ie internal channel) to the flow path 350 to supply hydraulic power for movement of the tractor through the borehole. A filter 304 is preferably arranged along the flow path 350 for removing particles from the fluid. Removing large particles from the fluid protects internal valve components (eg the slide in the valve) used to control tractor operation.

As shown in Figure 3, the pressurized fluid in the flow path 350 flows into the start/stop valve 308. The start/stop valve 308 is preferably an actuated, spring-loaded, indexed, two-position two-way valve which is controlled by means of the pressure in the fluid in the flow path 350. In the closed position, the start /stop valve 3 08 prevent fluid from flowing through the valve system, thereby rendering the tractor inoperable. In the open position, the start/stop valve 308 allows fluid to flow through to the flow path 354. The pressurized fluid in the flow path 354 flows to the propulsion control valve 310 and the pressure reduction valve 326 and thereby enables operation of the tractor. The start/stop valve 308 is configured to move to the open position when the fluid pressure in the flow path 350 (ie, the supply line) exceeds a preselected pressure threshold value. However, the start/stop valve 308 has an indexing which is such that one can choose to prevent the valve from opening when the fluid pressure exceeds the preselected threshold value.

Referring to Figure 5, an exploded view of one preferred embodiment of a start/stop valve 308 is shown. The main components of the start/stop valve 308 generally comprise a body 502 which is designed with a hollow interior and a displaceable in the interior cavity placed slide 506. The displaceable slide 506 is preferably connected at a first end to a spring insert 524 via a ball 522. In one embodiment, the ball 522 is made of stainless steel. The slide 506 is preferably connected at a second end to an indexing sleeve 510 with a spacer 512 placed between them. An indexing guide ring 508 extends through a middle part of the indexing sleeve 510, and a gasket 514 is placed between these. The slide 506, the indexing guide 508 and the indexing sleeve 510 are all slidably located in the body 502. The spring insert 524 is preferably connected to a first end of the body 502 by means of a retainer 504 having a slot therein. The spring insert is configured to drive the slide 506 to the closed position . A control assembly 520 is preferably connected to a second end of the body 502 via a holder 518. When the fluid pressure is high enough, the control assembly 520 compresses the spring on the spring insert 524 to cause the indexing sleeve 510 to change position and move the slide to the open position.

When the pressure in the flow path 350 during operation rises above a pre-selected threshold value (e.g. 900 psi), the fluid pressure will act on the control assembly 520, which in turn causes the indexing sleeve 510 to rotate about the indexing control 508. The indexing sleeve 510 rotational position determines whether the start- the stop valve 308 opens or remains closed after the fluid pressure rises above the preselected threshold value. Thus, the start-stop valve 308 constitutes a mechanism for switching the tractor on and off by varying the input pressure. If the indexing sleeve 510 is in the off position, a pressure cycle (for example lowering the pressure to 0 psi and then increasing it to 900 psi again) will move the indexing sleeve 510 into the on position. When the indexing sleeve 510 is in the on position, the slide can be displaced within the internal cavity of the body 502 to open a passage between the inlet and outlet openings (not shown) and thereby enable fluid to flow through the start/stop valve 308. More details whether valves with indexed cylinders can be found in the present applicant's US Patent No. 6,679,341.

Referring again to Figure 3, the fluid pressure in the flow path 354 from the start-stop valve 308 is used in preferred embodiments to control the pressure relief valve 306. As a result, the pressure relief valve is only operative when the start/stop valve 308 is in the open position. Accordingly, the pressure relief valve 306 is effectively "turned off" when the indexing sleeve is in the off position, so that the start/stop valve will not open regardless of the fluid pressure in the flow path 350. This is an important feature, because it enables the fluid pressure in the internal channels 302, 303 above the pressure relief valve's pressure threshold value. This has the advantage that the operator will have the option of delivering fluid at any pressure to the downhole string or other well equipment when this is desired.

As mentioned above, pressurized operating fluid will flow through passage 354 to propulsion control valve 310 when start/stop valve 308 is open. In a preferred embodiment, the propulsion control valve 310 is a two-position directional flow valve with a slide. In a first position, shown in Figure 3, the slide in the valve 310 provides a flow path 360 for fluid flow to the working chamber in the rear cylinder, and also to the reset chamber in the front cylinder. In the first position, the valve 310 also provides a flow path 362 for fluid flow from the working chamber in the front cylinder and to the annulus 40, and from the reset chamber in the rear cylinder and to the annulus 40.

The slide in the propulsion control valve 310 also has a second position (eg moved to the left in Figure 3). When the slide in the valve 310 is in its second position, the valve 310 provides a flow path 362 for fluid flow to the working chamber in the front cylinder, and also to the reset chamber in the rear cylinder. In the second position, the valve 310 also provides a flow path 360 for fluid flow from the working chamber in the rear cylinder to the annulus 40 and from the reset chamber in the front cylinder to the annulus.

With continued reference to Figure 3, the slide in the propulsion control valve 310 has a first end surface 330 and a second end surface 332. The first end surface 330 is in fluid communication with the rear gripper assembly along the fluid path 364. The second end surface 332 is in fluid communication with the front gripper assembly along the fluid path 366. The first and second end surfaces 330 and 332 of the propulsion control valve 310 are configured to receive respective fluid pressure forces acting against the valve slide. The first end surface 330 is exposed to a pressure force from the fluid in the rear gripper assembly which tends to move the slide in the valve 310 towards its first position (for example to the right in figure 3). The other end surface 332 is exposed to a pressure force from the fluid in the front gripper assembly which tends to move the slide towards its second position (for example moved to the left in figure 3).

With continued reference to Figure 3, a rear sequence valve 314 is preferably located along the fluid path 364, which extends from the rear gripper assembly to the first end surface 330. In addition, a front sequence valve 316 is provided along the fluid path 366, from the front gripper assembly and to the other end face 332.

Since, for purposes of illustration, reference is only made to the rear sequence valve 314, this will open when the fluid pressure in the flow path 364 exceeds a preselected threshold value (for example, 900 psi differential pressure). When the rear sequence valve 314 is open, the fluid pressure in the flow path 364 acts against the first end surface 330 to drive the propulsion control valve to the right in Figure 3. When the fluid pressure in the flow path 364 is lower than the preselected threshold value, the rear sequence valve 314 is closed , so that the fluid pressure in the flow path 364 cannot act against the first end surface 330. In addition, fluid in the part of the flow path that lies between the rear sequence valve 314 and the propulsion control valve 310 is released to the annulus 40 when the rear sequence valve 314 is closed, and removes thus any remaining force acting against the first end surface 330. It is understood that the front sequence valve 316 preferably acts in the same way as the rear sequence valve 314.

Rear and front sequence valves 314, 316 used in conjunction with the forward control valve 310 make tractor operation significantly more efficient. In particular, the rear and front sequence valve 314, 316 will ensure a reliable and constant pressure threshold in the flow paths 364, 366, where this must be exceeded in order to be able to control the propulsion control valve 310. As the rear and front sequence valve 314, 316 provide a reliable pressure threshold, can the flow rates through the valve system are greatly increased without having any negative effect on tractor operation. As a result, the gripper assemblies can be activated more quickly, which in turn reduces the holding time (ie the delay time between working strokes) and gives a significant increase in the total speed of the tractor through the borehole. Furthermore, the operational reliability of the tractor will reduce the need for training and skills of service personnel, which thus reduces operating costs.

Referring to Figure 6, a longitudinal section through the main components 600 of one preferred embodiment of a rear sequence valve is shown (see element 314 of Figure 3). The components 600 in the rear sequence valve are preferably identical to the components in the front sequence valve, and therefore only the components in the rear sequence valve will be described. The shown components 600 of the rear sequence valve generally comprise a body 602 which is formed with a hollow interior and a slide 610 slidably located in the interior cavity. An inlet opening 620, a working opening 622 and an outlet opening 624 are made through the body 602 for communication with the hollow interior. A bore 632 is formed through the slide 610. The displaceable slide 610 is preferably connected to a spring guide 614 via a ball 612. In one embodiment, the ball 612 is made of silicon nitride. A spring 616 extends around the conductor 614 and is in contact with a stopper 618 at one end. A plug 604 at the other end of the body 602 provides a fluid-tight seal. The plug 604 and the stopper 618 are preferably connected to the body 602 via a pin or dowel 608.

In use, pressurized fluid (for example from fluid path 364, as shown in Figure 3) flows into inlet opening 620 in the rear sequence valve. The fluid flows into the annular area 630 which is located between the slide 610, the body 602 and the plug 604. The fluid pressure drives the slide 610 to the left. At the same time, the spring 616 provides a biasing force that drives the slide to the right. When the fluid pressure in the annulus 630 exceeds a preselected threshold value (for example 900 psi), the slide 610 will move enough to the left that the bore 632 is in communication with the working opening 622. As a result, fluid can flow from the inlet opening through the bore 632 and out through the working opening 622 (for example for controlling the propulsion control valve 310 in figure 3). When the pressure is below the threshold value, the slide 610 is all the way over to the right, as shown in Figure 6. In this position, the fluid can move back through the working opening 622, into the annular gap 634 and out through the outlet opening 624 to the annulus. This property makes it possible to "vent" fluid to the annulus when the fluid in the flow path 364 or 366 (see Figure 3) is not pressurized.

Referring again to figure 3, the outlet flow from the start/stop valve 308 along the fluid path 354 in a preferred embodiment will flow through the pressure reduction valve 326 before it flows into the gripper control valve 312. The pressure reduction valve 326 is preferably a directly activated valve that limits the pressure in the operating fluid in the rear and front gripper assembly, and this is thus a means of preventing damage to the gripper assembly components.

When the pressure downstream of the pressure relief valve 326 rises above a preselected threshold value (eg, 1400 psi differential pressure), the pressure relief valve closes to protect the gripper assemblies from overpressure. Thus, the pressure reduction valve 326 places an upper limit on the pressure in the passage 356 and thereby prevents overpressure in the gripper assemblies by venting the excess pressure to the annulus 40. With continued reference to Figure 3, the gripper control valve 312 directs fluid to either the rear gripper assembly or the front gripper assembly. In the embodiment shown, the gripper control valve 312 is preferably a two-position directional valve with a slide, which essentially functions in the same way as the propulsion control valve 310 described above. For more details on preferred embodiments of the valves 310 and 312, reference is made to the present applicant's US Patent 6,679,341.

The slide in the gripper control valve 312 has a first position (as shown in Figure 3) where the gripper control valve 312 provides a flow path 370 to the rear gripper assembly. When the slide in the valve 312 is in its first position, the valve 312 also provides a flow path 372 for fluid flow from the forward gripper assembly to the annulus 40. The slide in the gripper control valve 312 also has a second position, not shown in Figure 3. In the second position gripper control valve 312 provides a flow path 372 to the forward gripper assembly. When the slide in the valve 312 is in its second position, the valve also provides a flow path 370 for fluid flow from the rear gripper assembly to the annulus 40.

The slide in the gripper control valve 312 has a first end surface 334 and a second end surface 336. The first end surface 334 is in fluid communication with the forward piston/poppet valve 324 along the flow path 380. The second end surface 336 is in fluid communication with the rear piston/poppet valve 322 along the flow path 382 The first and second end surfaces 334 and 336 are configured to receive respective fluid pressures from flow paths 380 and 382, where these pressures act against the slide in the valve. The first end surface 334 receives a pressure force from the outlet of the front piston/plate valve 324, which force tends to move the slide in the gripper control valve 312 towards its first position, as shown in Figure 3. The second end surface 336 receives a pressure force from the outlet pet from the rear piston/poppet valve 322, which force tends to move the slide towards its second position, which will be a displacement to the left in Figure 3. The construction and operation of preferred embodiments of the rear and front poppet valve 322, 324 is described in more detail below.

With continued reference to Figure 3, a rear vent valve 318 is preferably arranged along the fluid path 382, which extends from the rear piston/plate valve 322 and to the first end surface 336 of the gripper control valve 312. In addition, a front vent valve 320 is preferably arranged along the fluid path 380, which extends from the front piston/poppet valve 324 and to the other end surface 334 of the gripper control valve 312. In the same manner as the rear and front sequence valves 314, 316 described above, both the rear and front vent valves 318, 320 will prevent fluid from to flow through their respective fluid paths unless the pressure in the fluid along the path exceeds a preselected threshold value. Accordingly, the rear and front vent valve ensures safe position change of the slide in the gripper control valve 312 and provides a further improvement in the timing and efficiency of the valve system. When the pressure falls below the pre-selected threshold value, the rear and front vent valves 318, 320 enable the fluid in the fluid paths between the vent valves and the end faces to be released into the annulus 40. In preferred embodiments, the rear and front vent valves 318, 320 are constructed in total substantially identical to the rear and front sequence valve 314, 316 described above with reference to Figure 6.

Referring again to Figure 2, to the rear and front ends of the steering assembly 102 are connected the rear and

front axle assemblies 118, 124. Rear and front axle assemblies 118, 124 together with the steering assembly 102 constitute the tractor body 100. The rear gripper assembly 104 and rear propulsion cylinder 108 are displaceable

coupled to the rear axle assembly 118. The front gripper assembly 106 and front propulsion cylinder 114 are slidably coupled to the front axle assembly 124.

Referring to Figure 7A, an exploded view of the rear axle assembly 118 combined with the rear cylinder 108 and rear pipe coupling assembly 116 is shown for illustrative purposes. The rear axle assembly 118 generally includes an elongated axle 150 having a substantially cylindrical shape. In a preferred embodiment, the rear cylinder 108 is essentially tubular and is displaceably placed over the shaft 150, so that an annular space is formed between them. The rear cylinder 108 is sealed at the rear end by means of the bending joint 120. The rear cylinder is sealed at the front end by means of a stuffing box 704. The rear cylinder 108 is thus sealed at both ends and displaceably accommodates the rear piston, and thus constitute the rear propulsion assembly. When fully assembled, a gripper assembly (not shown) is also slidably positioned over the axle and is preferably coupled to the flexure joint 120 along the rear end.

Referring to Figure 7B, an enlargement of the rear piston 700 is shown for illustration purposes. The rear piston 700 is fixedly connected to the rear shaft 150 and includes the rear piston/poppet valve (see element 322 in Figure 3). The rear piston 700 slides inside the rear cylinder 108 and separates the working chamber from the retraction chamber. Figure 8 is a longitudinal section showing the rear piston 700, which includes the rear piston/poppet valve (see element 322 in Figure 3). Referring to both Figures 7B and 8, the rear piston 700 generally includes a flange 708 and a hub 710. The flange 708 and the hub 710 separate the working and retraction chambers of the rear cylinder 108. The flange 708 is surrounded by a wear guide 746 and comprises a seat 730. The seat 730 is held in place by means of an internal retaining ring 74 8 at the rear end. A spring 712 is located adjacent to the seat 730 and extends from the flange 708 into the hub 710. A spindle 714 is connected to the spring 712 and is slidably located in the hub 710. A part of the spindle 714 protrudes from an end face of the name for contact with the stuffing box seal 704. The protruding end of the spindle 714 is guided in a spindle guide 742 which is carried by an O-ring 740 and a retaining ring 744.

The protruding end of poppet valve stem 714 is positioned to contact stuffing box 704, or another internal wall, when the piston reaches the end of its stroke. As the valve stem 714 contacts the stuffing box 704, the valve stem slides axially relative to the hub 710. As the stem slides, a packing disc 728 and a valve cover 732 are displaced from a valve seat 750 in the piston hub 710. As a result, pressurized fluid flows from the working chamber in the cylinder through a gap 716 between the piston flange 708 outer diameter and the cylinder 108 inner diameter. The fluid continues to flow through a space 718 between the flange 708 and the hub 710, around the valve stem 714 and through the piston hub 710. The fluid then flows radially through an opening 722 and then into the control channel 706. The fluid in the control channel 706 can then be sent to the control assembly to control the position of the gripper control valve, as shown schematically and described above with reference to Figure 3.

With continued reference to Figures 7B and 8, as the piston 700 moves away from the stuffing box 704, the valve spring 712 will exert a biasing force which puts the packing disc 728 back on the valve seat 750 in the piston hub 710. As a result of this, the control channel is blocked 706 against the fluid pressure on both sides of the piston. In an important aspect of the above-described embodiment, the presence of pressurized fluid in the control channel 706 is a means of accurately detecting and indicating the completion of a work stroke. This provides a significant advantage over pressure-sensitive valves, which can change position prematurely as a result of pressure fluctuations.

The mechanically activated valve is, as shown, preferably arranged in the form of a piston/plate valve. Used with preferred versions of the tractor, piston/plate valves have certain advantages over other mechanically activated valves, such as operational reliability and small size. In alternative embodiments, however, other types of mechanically activated valves can also be used to demonstrate the completion of a work stroke. For example, a diaphragm valve can be used to signal the completion of a work stroke. The diaphragm valve is activated mechanically in a similar way to the poppet valve described above to indicate the completion of a working stroke. In another preferred embodiment, a cutting edge can be used to signal completion of the piston stroke. The shear valve includes a floating seal that is displaced to

open or close an opening. The shear valve can be activated mechanically in a similar manner to the poppet valve described above to indicate the completion of a working stroke. In addition, one will realize that a piston/poppet valve (or other mechanically actuated valve) can be placed in many different places

and still have the ability to demonstrate completion of a piston stroke. Furthermore, in versions of a reversible tractor, piston/disc valves or other mechanical devices can be arranged

actuated valves on both sides of a piston to detect completion of a piston stroke in either direction.

Referring to Figures 9 and 10, a preferred embodiment of the control assembly (see element 102 in Figure 2) is shown partially taken apart. Figure 9 shows a control housing 202 which forms the main part of the control assembly. Figure 10 shows the rear transition housing 204, the filter housing 206 and the front transition housing 208. Coupling elements 220 are arranged to connect the rear transition housing 204 together with the rear axle, and coupling elements 222 are arranged to connect the front transition housing 208 together with the front axle . Coupling elements 226 connect the rear transition housing 204 and filter housing 206 to the control assembly 202. Coupling elements 224 connect the front transition housing 208 to the control assembly 202.

Referring again to Figure 9, one preferred embodiment of the control housing 202 houses the propulsion control valve 310, the gripper control valve 312, the pressure relief valve 306, the pressure reduction valve 326, the start-stop valve 308, the rear sequence valve 314, the front sequence valve 316, the rear vent valve 318 and the front air valve 320. Each of the valves preferably comprises a slide within an elongated valve housing which delimits a slide channel. In one configuration, the valves are located in recesses along the outside of the control housing 202.

The forward control valve 310, gripper control valve 312, pressure reduction valve 326, vent valves 318, 320 and rack and pinion valves 314, 316 are preferably all configured in the same manner for ease of manufacture. In particular, each valve is housed in an elongated housing that fits into a recess along the outside of the control assembly 202. The valve housings are all attached to the body of the control assembly via two bolts or other suitable fasteners. The pressure relief valve 306 and the start/stop valve 308 are preferably both attached to the body of the control assembly via four bolts or other suitable fastening devices.

The main housing 202 includes several internal fluid channels for controlled flow of operating fluid to the well equipment (see element 32 in Figure 1), between the valves, to the gripper assemblies and to the propulsion cylinders. In one preferred embodiment, the fluid channels are configured to form the valve system shown schematically in Figure 3. Some of the fluid channels extend to corresponding fluid channels in the end surfaces of the transition housings 204, 206 and 208. In a preferred embodiment, the internal main channel is moved away from the middle to get maximum space for the various valves and internal fluid channels.

An internal duct 250 extends through the rear transition housing 204, the filter housing 206 and the front transition housing 208. The internal duct also extends through the rear and front axle and the control housing 202, so that pressurized fluid from the supply line can flow through the tractor body and to the wellbore assembly. As shown in Figure 10, the filter housing 206 houses the filter/diffuser 304. The filter/diffuser 304 is generally cylindrical and has a plurality of side holes 210 that allow filtered fluid to flow from the internal channel to the start-stop valve 308 (as shown schematically in Figure 3 ). In one preferred embodiment, the side holes 210 are angled in such a way that the fluid that flows forward through the filter/diffuser 304 must subsequently turn slightly to pass through. This prevents larger particles in the operating fluid from entering the start-stop valve 308, as it is more difficult for the larger particles to overcome the forward momentum and flow through side openings. Professionals with general knowledge in the field will understand that instead of the diffuser 304 shown, any one of many types of filters can be used.

Referring again to Figure 3, pressure fluid is supplied to the control assembly from a source (for example, on the surface) via a supply line 302. The supply line 302 preferably extends through an internal channel in the elongated tractor body to supply pressure fluid to the well equipment. When the pressure in the supply line 302 exceeds a pre-selected threshold value (for example 900 psi), the start-stop valve 308 opens if the index is in the on position. If the index is in the off position, a pressure cycle (for example lowering the pressure to 0 psi and then raising it to 900 psi again) will cause the indexing cylinder to move to the on position. When the start-stop valve 308 is open, the supply flow will follow parallel paths to the pressure relief valve 306, the propulsion control valve 310 and the pressure reduction valve 326.

As mentioned above, it has been found that the pressure from the operating fluid in the supply line 302 can fluctuate strongly during movement of the tractor and/or operation of the well equipment. Under certain circumstances, the pressure fluctuations can be significant and can damage internal components and render other hydraulically coupled tools inoperable or incompatible. Consequently, the pressure relief valve 306 is arranged to regulate the fluid pressure in the supply line 302 (ie in the internal channel) and thus in the valve system located inside the control assembly. In an important aspect, the pressure in the fluid that flows both to the control assembly and the well equipment is preferably regulated. This property increases the efficiency of the downhole strings and extends the life of the machine components. Also, the pressure relief valve 306 is off when the start/stop valve 308 is closed. This feature advantageously makes it possible to selectively lead high-pressure fluid (ie not regulated) to the well equipment when desired.

After it has passed through the start/stop valve 308, the pressure fluid flows along the path 354 and to the pressure reduction valve 326 and then on to the gripper control valve 312. In the configuration shown, the gripper control valve 312 is shifted to the right, so that the fluid in the flow path 370 is pressurized and the fluid in the flow path 372 is depressurized. As a result, the rear gripper assembly begins to expand in the radial direction for engagement with the inside of the borehole, and the front gripper assembly contracts in the radial direction for disengagement with the inside of the borehole. When the rear gripper assembly is fully activated, fluid flow through flow path 370 will stop and, as a result, the fluid pressure increases sharply (ie, to system pressure) in flow paths 370 and 364. During this, pressure relief valve 326 protects the rear gripper assembly from damage caused by overpressure.

When the rear gripper assembly is sufficiently engaged, the pressure in the flow path 364 will exceed the preselected threshold value (eg, 900 psi differential pressure) for the rear sequence valve 314. As a result, fluid will flow through the rear sequence valve 314 and act against the first end surface 330 of the propulsion control valve 310 and thereby causing the slide to move to the right (see Figure 3). Accordingly, the valve system is configured so that the gripper assembly is fully activated before the propulsion control valve initiates a working stroke.

In this position, pressure fluid flows through the propulsion control valve 310 and to the working chamber in the rear cylinder and to the reset chamber in the front cylinder. As fluid flows into the working chamber of the rear cylinder, the pressurized fluid pushes against the rear piston and thereby causes the tractor body to move forward through the bore relative to the rear gripper assembly (which is anchored internally). This type of movement is generally referred to in this document as a work stroke. At the same time, as fluid flows into the reset chamber in the front cylinder, the pressure fluid will push the front cylinder and front gripper assembly forward relative to the tractor body. This movement resets the front gripper assembly and prepares the front cylinder for a subsequent working stroke. This type of movement is generally referred to in this document as a reset stroke. Because the resistance to a reset stroke is relatively small, the reset stroke is usually completed before the working stroke is completed.

As the tractor body reaches the end of the working stroke in relation to the rear cylinder, the rear piston/plate valve 322 is activated. This happens when a spindle in the rear piston/plate valve comes into contact with part of the rear cylinder, so that the spindle is pressed down mechanically. When the spindle is pushed down, pressurized fluid flows into a flow channel 328. When the pressure in the flow path 382 becomes high enough, the rear vent valve 318 opens to allow pressurized fluid to flow through to the other end face 336 of the gripper control valve 312. The fluid pressure causes the slide in gripper control valve 312 to shift to the left (ie to the position not shown in Figure 3).

After the gripper control valve 312 changes position, the fluid in flow path 370 is depressurized, and the fluid in flow paths 366 and 372 is pressurized. When the pressure in the flow path 366 becomes high enough, the forward sequence valve 316 opens, so that pressurized fluid acts against the other end surface 332 of the propulsion control valve 310 and causes the slide to shift to the left (ie to the position not shown in figure 3). The pressure in the flow path 366 becomes high enough to open the forward sequence valve after the forward gripper assembly contacts the inside of the borehole and is thus prevented from expanding further. When the forward gripper assembly stops expanding, flow to the forward gripper assembly through flow path 372 stops, causing an increase in fluid pressure.

As the slide in the propulsion control valve 310 changes position, pressurized fluid flows in the flow path 354 through the propulsion control valve 310 and into the front chamber of the front cylinder and the rear chamber of the rear cylinder. At the same time, fluid in the rear chamber of the front cylinder and fluid in the front chamber of the rear cylinder flows back through the propulsion control valve 310 and into the annulus 40. This causes the front piston, and thus the entire tractor body, to be pushed forward through the bore in relation to it activated front gripper assembly in a new working stroke. At the same time, the rear cylinder is pushed forward in relation to the piston and the tractor body in a reset stroke.

As the tractor body reaches the end of the working stroke in relation to the front cylinder, the front piston/poppet valve 324 is activated. This happens when a spindle on the front piston/poppet valve comes into contact with part of the front cylinder, so that the spindle on the front piston /disc valve is pressed down mechanically. When the spindle is depressed, pressurized fluid flows in the flow channel 380. When the pressure in the flow path 380 is high enough to exceed the preselected pressure threshold, the front vent valve 320 opens to allow pressurized fluid to pass through to the first end face 334 of the gripper control valve 312. The fluid pressure causes the slide in the gripper control valve 312 to move back to the right (ie to the position shown in Figure 3). At this point, all the valves have returned to their initial positions (ie to the positions generally shown in Figure 3). What is described above is thus a complete work cycle for the valve system during forward movement.

It should be noted that during forward or backward movement the gripper assemblies preferably alternate between two extreme positions. First, the grapple assemblies move as far apart as possible toward opposite ends of the tractor. Next, the gripper assemblies move as close together as possible (with the propulsion cylinders and steering assembly between them). During most of the tractor's operation, one gripper assembly is in a working stroke, while the other is in a reset stroke. When they change direction, they also change gripper function. Consequently, the tractor always moves in one longitudinal direction.

A major advantage of the preferred configuration of the valve system is that it is certain that the tractor body completes the forward movement (ie, the working stroke) before the gripper assemblies alternate between the activated and retracted positions. As mentioned above, one can achieve greater reliability and efficiency in the tractor movement by including the mechanically activated valves (for example piston/plate valve) in the valve system. The piston/poppet valves are a mechanism that detects and signals the completion of a working stroke. In addition, the outlet from the gripper control valve 312 is used to control the forward control valve 310. As a result, the system ensures that the gripper is fully activated before a work stroke is initiated.

In one preferred embodiment, the amount of operating fluid flowing into the valve system of the control assembly may be up to 23 gallons per minute (about 87 liters per minute). Large displacement pumps are usually used on the surface to pump fluid down through the coil pipe and through the internal channel in the tractor body. Such pumps typically deliver a system flow rate of up to 120 gallons per minute (about 460 liters per minute). In connection with one typical mode of operation, the valve system typically receives 20% of the fluid that flows through the internal channel in the tractor body. In connection with other operating modes, the valve system receives approx. 5%, 10%, 15% or 25% of the fluid flowing through the internal channel.

In a preferred version of the tractor where the valve system is fully hydraulic, the tractor's maximum speed can be greater than for an electrically controlled tractor. The valve system does not include electrical conductors and other electrical elements, which makes it possible to use larger internal fluid channels, larger flow rates and greater power density. A higher maximum speed of the tractor leads to lower operating costs, especially for intervention applications. In one preferred embodiment of the invention, the tractor can travel at speeds greater than or equal to 1350 feet per hour (410 meters per hour).

In another preferred embodiment, the tractor may be able to move both forwards and backwards through a channel. Referring to Figure 11, one embodiment of an improved valve system 800 for use with a reversible tractor is shown. Similar to the valve system described above with reference to Figure 3, the improved valve system 800 shown in Figure 11 receives pressurized fluid from a supply line 302. The pressurized fluid passes through a start-stop valve 308 to deliver hydraulic power to the tractor steering assembly 102 In order for the operator of the tractor to be able to perform a selective reversal of the tractor's direction, the valve system 800 in the control assembly further comprises a main reversing valve 390, a rear reversing valve 392, a front reversing valve 394 and a grab reversing valve 396. The main reversing valve 390 is controlled by means of the fluid pressure in the supply line 302. The main reversing valve in turn controls the rear reversing valve 392, the front reversing valve 394 and the gripper reversing valve 396.

In the same manner as for the embodiment described above with reference to Figure 3, the improved valve system 800 for use with a reversible tractor preferably comprises a rear piston/poppet valve 322 and a front piston/poppet valve 324. Rear and front piston/poppet valve 322, 324 is adapted to detect the completion of the piston stroke during forward movement through the channel. Also, the improved valve system shown in Figure 11 includes a forward reversing piston/poppet valve 323 and a rear reversing piston/poppet valve 325 to demonstrate completion of the piston stroke during rearward movement through the passage. Thus, the improved valve system 800, as shown in figure 11, is equipped with two piston/plate valves on both the front and rear piston. As a result, the tractor can provide accurate and efficient valve sequencing during movement either forward or backward. Due to the fact that each piston contains two piston/disc valves, two independent control channels are ideally arranged in the shaft wall for each piston.

When the main reversing valve 390 is in the closed position during use (as shown in Figure 11), no fluid flows through the main reversing valve, and the valve system 800 functions in a similar manner to that described above with reference to Figure 3. But when the pressure in the supply line 302 is increased above a pre-selected threshold value (for example 2000 psi), the main reversing valve 3 90 is switched to the open position. As a result, the pressure fluid in the supply line 302 flows through the main reversing valve 390 and to the rear reversing valve 392, the front reversing valve 394 and the gripper reversing valve 396. The fluid pressure causes the rear reversing valve 392, the front reversing valve 394 and the gripper reversing valve 396 to change position and change thus the sequencing of the valve functions. In particular, the rear and front reversing valves 392, 394 enable the front reversing piston/poppet valve 323 and the rear reversing piston/poppet valve 325 to control the rear and front vent valves during rearward movement through the passage. Furthermore, the gripper reversing valve 396 will change the flow path from the gripper control valve 312 in such a way that the desired gripper assembly is activated before a working stroke is initiated.

In preferred, alternative configurations, the improved valve system shown in Figure 11 may also include a pressure relief valve 306 and rear and forward sequence valves 314, 316, as generally described above in connection with Figure 3. More details of a tractor capable of change direction can be found in the present applicant's US Patent No. 6,679,341.

Preferred embodiments of the tractor described herein may be used with a number of different grapple assemblies. In preferred embodiments, however, the gripper assemblies 104 and 106 are implemented as a plurality of arms that can be extended radially to engage the inside of a borehole. Figures 12-19 show various preferred configurations of preferred grapple assemblies adapted for use with a tractor. More details can be found in the present applicant's corresponding US patent application no.

10/004,963, entitled "Improved Gripper Assembly for Downhole Tractors", filed December 3, 2001. In a preferred embodiment, gripper assemblies 104 and 106 are substantially similar. Thus, the gripper assembly configurations such as

shown in Figures 12-19, is considered to describe both rear and front gripper assemblies 104 and 106.

Figure 12 shows one preferred embodiment of a gripper assembly 1000. The gripper assembly shown includes an elongate, generally tubular stem 1002 that is configured to be slid longitudinally along a length of the tractor 50. The interior of the stem 1002 preferably has a grooved or wedged boundary surface (for example tongue/spring configuration) towards the outside of the shaft, so that the stem 1002 can slide freely in the longitudinal direction, but is still prevented from rotating relative to the shaft. Another embodiment does not include grooves. Fixed trunk lids 1004 and 1010 are connected respectively to the front and rear ends of the trunk 1002. At the front end of the trunk 1002, near the trunk lid 1004, there is a sliding arm holder 1006 in longitudinal, displaceable engagement with the trunk 1002. The sliding arm holder 1006 is preferably prevented from rotating relative to the stem 1002, for example through wedge action between them. At the rear end of the trunk, a cylinder 1008 is placed next to the trunk lid 1010, which cylinder encloses the trunk concentrically, so that an annular space is formed between them. As shown in Figure 12, this annulus houses a piston 1038, a rear portion of a piston rod 1024, a spring 1044 and fluid seals, for reasons that will become apparent later.

The cylinder 1008 is stationary in relation to the stem 1002. An arm holder 1018 is fixedly mounted on the front end of the cylinder 1008. A plurality of gripper parts 1012 are attached to the gripper assembly 1000. In the embodiment shown, the gripper parts comprise flexible arms or rods 1012. The arms 1012 has ends 1014 that are pivotally attached or hinged to the fixed arm holder 1008, and ends 1016 that are pivotally attached or hinged to the sliding arm holder 1006. As used herein, the terms "swingably attached" or "hinged" describe a connection that enables rotation, for example by means of a shaft, pin or a hinge. The ends of the arms 1012 are preferably engaged with shafts, rods or pins which are attached to the arm holders.

Those skilled in the art will appreciate that any number of arms 1012 may be provided. As more arms are added, the maximum radial shear load that can be transmitted to the borehole surface increases. This gives the gripper assembly 1000 increased clamping force and therefore gives the tractor higher radial pressure and greater drilling capacity. However, three arms 1012 are preferred so that the gripper assembly 1000 will have a more secure grip on the inside of the drill hole. A four-arm design could, for example, lead to only two arms making contact with the borehole surface in oval boreholes. Moreover, an increase in the number of arms will also lead to an increased possibility of problems with synchronization and alignment of the arms. Moreover, at least three arms 1012 are preferred in order to essentially prevent the possibility of tractor rotation about a transverse axis, i.e. one which is generally normal to the longitudinal axis of the tractor body. For example, the articulated gripper described above with three swing arms has only two articulated connections. Even when both joints are activated, the tractor body can rotate about the axis indicated by the joints' two points of contact with the borehole surface. A three-arm design of the present invention will essentially prevent such turning. Furthermore, gripper assemblies with at least three arms 1012 are better able to cross over pores or pockets in a borehole.

A drive mechanism or push element 1022 is in displaceable engagement with the stem 1002 and is longitudinally generally positioned about a longitudinally central area of the arms 1012. The push element 1022 is positioned radially within the arms 1012, for reasons that will become apparent. A tubular piston rod 1024 is slidably engaged with the stem and connected to the rear end of the push member 1022. The piston rod 1024 is partially enclosed by the cylinder 1008. The push member 1022 and the piston rod 1024 are preferably prevented from rotating relative to the stem 1002, for example by means of a wedge or groove interface between such elements and the stem.

Figure 13 shows a longitudinal section through a gripper assembly 1000. Figures 14 and 15 show a gripper assembly 1000 partially in sectional perspective. As seen in the figures, the sliding element 1022 includes a plurality of wedges or ramps 1026. Each ramp 1026 slopes between an inner radial level 1028 and an outer radial level 1030, the inner radial level 1028 being radially closer to the surface of the stem 1002 than the outer level 1030. The sliding element 1022 preferably includes at least one ramp 1026 for each. arm 1012. The push member can obviously include any number of ramps 1026 for each arm 1012. In the shown embodiments, the push member 1022 includes two ramps 1026 for each arm 1012. As more ramps 1026 are installed for each arm, the amount of force is reduced which each ramp must transmit, which gives the ramps a longer life. In addition, the arrangement of several ramps will lead to a more balanced radial displacement of the arms 1012, and also radial displacement of relatively more of the length of the arms 1012, where both parts lead to a generally better roof in the borehole surface.

In a preferred embodiment, two ramps 1026 are placed with a

spacing that is generally equal to the length of the center region 1048 of each arm 1012. In this embodiment, when the gripper assembly is actuated to grip a borehole surface, the center regions 1048 of the arms 1012 will generally have a greater tendency to remain linear. This gives a larger

contact surface between the arms and the borehole surface, for a better grip overall. The load is also distributed more evenly across the arms to enable a better grip. With more than two ramps, there is a greater propensity for uneven loading as a result of manufacturing deviations in the ramps' 1026 radial dimensions, nos which can cause early fatigue failure.

Each arm 1012 is provided in the middle area with an element for interaction with the drive mechanism. The interaction elements interact with the drive mechanism or push element 1022 to vary the radial position of the arms 1012 center regions 1048. The drive mechanism and the interaction elements are preferably configured to interact substantially without generating sliding friction between them. In the shown embodiments, the interaction element comprises one or more rollers 1032 which are rotatably attached to the arms 1012 and configured to roll on the inclined rafts of the ramps 1026. There is preferably one roller 1032 for each ramp 1026 on the sliding element 1022. In the shown embodiments, the rollers 1032 on each arm 1026 located in a recess 1034 on the radially inner side of the arm, the recess 1034 extending in the longitudinal direction and being of such a size that it accommodates the ramps 1026. The rollers 1032 revolve around shafts 1036 which extend across in the recess 1034. The ends of the shafts 1036 are fixed in holes in the side walls 1035 which delimit the recess 1034.

The piston rod 1024 connects the push element 1002 to a piston 1038 which is enclosed by the cylinder 1008. The piston 1038 is essentially tubular. The piston 1038 has a rear or activation side 1039 and a front or retraction side 1041. The piston rod 1024 and the piston 1038 are in longitudinal, displaceable engagement with the stem 1002. The front end of the piston rod 1024 is attached to the push member 1022. The rear end of the piston rod 1024 is attached to the retraction side 1042 of the piston 1038. The piston 1038 fluidly divides the annulus between the stem 1002 and the cylinder 1008 into a rear or activation chamber 1040 and a front or retraction chamber 1042. A seal 1043, such as an 0-ring in rubber, is preferably placed between the outside of the piston 1038 and the inside of the cylinder 1008. A return spring 1044 is engaged with the piston rod 1024 and enclosed within the cylinder 1008. The spring 1044 has a rear end which is attached to and/or biased against the retraction side 1041 of the piston 1038. A front end of the spring 1044 is attached to and/or biased towards the inside of the front end of the cylinder 1008. The spring 1044 biases the piston 1038, the piston rod 1024 and the push element 1022 towards the rear end of the stem 1002. In the embodiment shown, the spring 1044 comprises a coil spring. The number of rings and the diameter of the spring are preferably selected based on the requirements for return load and available space. Professionals with general knowledge in the area will understand that other types of springs or biasing devices can be used.

Figures 16 and 17 show a gripper assembly 1055 according to an alternative embodiment of the invention. In this embodiment

the rollers 1032 are located on a drive mechanism or a push element 1062. The arms 1012 include an element for interaction with the drive mechanism, which element interacts with the drive mechanism to vary the radial position of the arms

middle parts 1048. In the embodiment shown, the interaction element comprises one or more ramps 1060 on the inside of the middle parts 1048. Each ramp 1060 slopes from a bottom 1064 and

to a top 1063. The sliding member 1062 includes external recesses sized to accommodate the top

1063 of the ramps 1060. The roller shafts 1036 extend across these recesses, into holes in the side walls of the recesses. The end of the roller shafts 1036 is preferably located in one or more lubrication reservoirs in the push element 1062. Most preferably, such lubrication reservoirs are pressure equalized by means of pressure equalization pistons, as described above in connection with the designs shown in figures 12-15.

Although the gripper assembly 1055 shown in Figures 16 and 17 has four arms 1012, those of ordinary skill in the art will appreciate that any number of arms 1012 may be used. However, it is preferred to use three arms 1012 to obtain a safer and more efficient contact with the inside of a passage or borehole. As in the previous embodiments, each arm 1012 may include any number of ramps 1060, although two is preferred. It is desirable that there is at least one ramp 1060 per roller 1032.

The gripper assembly 1055 shown in Figures 16 and 17 operates in a similar manner to the gripper assembly 1000 shown in Figures 12-14. Activation and retraction of the gripper assembly is controlled through the position of the piston 1038 in the cylinder 1008. The fluid pressure in the activation chamber 1040 regulates the position of the piston 1038. Forward movement of the piston 1038 also causes a forward movement of the push element 1062 and the rollers 1032. The rollers roll against the inclined surfaces of the ramps 1060 and press the middle portions 1048 of the arms 1012 outwards in the radial direction.

Figures 18 and 19 show a gripper assembly 1070 with knee joints 1076 for radial displacement of the arms 1012. A push member 1072 has knee joint notches 1074 configured to receive the end of the knee joints 1076. Similarly, the arms include

1012 knee joint notch 1075 which is also configured to receive the ends of the knee joints. Each knee joint 1076 has a first end 1078 which is received in a notch 1074 and rotatably held on the push member. Each knee joint 1076 also has a second end 1080 which is accommodated in a notch 1075 and is rotatably held on one of the arms 1012. The ends 1078 and 1080 of the knee joints 1076 can be pivotally attached to the sliding element 1072 and the arms 1012, for example by means of guide pins or hinges which are connected to the push member 1062 and the arms 1012. Those skilled in the art will appreciate that the notches 1074 and 1075 are not required. The purpose of the knee joint 1076 is to rotate and thereby radially displace the arms 1012. This can be achieved without a notch for the knee joint ends, for example through rotatable connection of the ends.

In the embodiment shown, there are two knee joints 1076 for each arm 1012. Those skilled in the art will understand that any number of knee joints can be arranged for each arm 1012. However, it is preferred to use two knee joints with other ends 1080 generally located at or near the end of the center portions 1048 of each arm 1012. This configuration gives the center portion 1048 a more linear shape when the gripper assembly 1070 is activated to grip a borehole surface. This results in a larger contact surface between the arm 1012 and the borehole, which provides a better grip and more efficient transfer of loads to the borehole surface.

Gripper assembly 1070 functions similarly to gripper assemblies 1000 and 1055 described above. The gripper assembly 1070 has an activated position where the arms 1012 are bent radially outward, and a retracted position where the arms 1012 are relaxed. In the retracted position, the knee joints 1076 are generally oriented parallel to the stem 1002, so that the other ends 1080 are relatively close to the surface of the stem. As the piston 1038, piston rod 1024 and push member 1072 move forward, the first ends 1078 of the knee joints 1076 also move forward. However, the other ends 1080 of the knee joints are prevented from moving forward by the notches 1075 on the arms 1012. Consequently, the knee joints 1076 will pivot outward as the push member 1072 moves forward, so that the knee joints 1076 orient themselves diagonally or even nearly normal to the stem 1002 .As the knee joints 1076 rotate, the other ends 1080 move radially outward, causing a radial displacement of the center portions 1048 of the arms 1012. This corresponds to the activated position of the gripper assembly 1070. If the piston 1038 moves back toward the rear end of the stem 1002 , the knee joints 1076 turn back to the starting position, essentially parallel to the stem 1002.

Compared to the grabber assemblies 1000 and 1055 described above, the grabber assembly 1070 does not transmit radial loads of any significance to the borehole surface when the arms 1012 are only slightly offset in the radial direction. However, the gripper assembly 1070 represents a significant improvement over the previously known three bar articulated gripper. The arms 1012 of the gripper assembly 1055 comprise contiguous bars, as opposed to multi-bar joints. Interconnected rods have a significantly greater torsional stiffness than multi-rod connections, due to the absence of hinges, bolted connections or shafts connecting the various parts of the arm to each other. Thus, the gripper assembly 1070 is much more resistant to unwanted rotation or twisting when activated and in contact with the borehole surface. In addition, continuous bars involve few or no stress concentrations, and therefore tend to last longer than jointed connections. Another advantage of the gripper assembly 1070 in relation to the multi-joint rod construction is that the knee joints 1076 provide a radial force at the middle portions 1048 of the arms 1012. The multi-joint rod construction, on the other hand, means that the opposite ends of the joint connection are moved towards each other to push a middle joint outwards towards the borehole surface. Accordingly, the gripper assembly 1070 involves a more direct application of force at the center portion 1048 of the arm 1012, which is in contact with the borehole surface. Another advantage of the gripper assembly 1070 is that it can be activated and retracted without sliding friction.

Claims (14)

1. A tractor (100) for moving a component (32) through a borehole, comprising: an elongated body (118, 102, 124); rear and front gripper assemblies (104, 106) which are in longitudinal movable engagement with said body (118, 102, 124), said rear and front gripper assembly (104, 106) being hydraulically actuated for selective engagement with an inside (42) of the borehole; rear and front propulsion assemblies adapted to drive said body (118, 102, 124) forward through the borehole relative to said rear and front gripper assemblies (104, 106), respectively; and a gripper control valve (312) has a first position where said gripper control valve (312) directs pressure fluid to said rear gripper assembly (104), and a second position where said gripper control valve (312) directs pressure fluid to said front gripper assembly (106), characterized in that the tractor (100) further comprises a device for detecting forward movement of said body (118, 102, 124) in relation to said rear or front gripper assembly (104, 106); and where said device which detects forward movement of said body causes said gripper control valve (312) to change position after said body (118, 102, 124) has completed a forward stroke through the borehole in relation to said rear or front gripper assembly (104, 106 ). 2. Tractor (100) according to claim 1, characterized in that: said rear and front gripper assemblies (104, 106) both exhibit engagement surfaces which are configured for selective engagement with the inside (42) of a borehole; wherein said device for detecting movement comprises a rear and a front mechanically activated valves (322, 324) which are located along said body (118, 102, 124) and configured to detect forward movement of said body (118, 102, 124) in relation to said respectively rear or front gripper assembly (104, 106); and and where said rear and front mechanically activated valves (322, 324) are in fluid communication with said gripper control valve (312), so that fluid pressure causes said gripper control valve (312) to change position after said body (118, 102, 124) has completed a forward stroke through the borehole in relation to said rear or front gripper assembly (104, 106). 3. Tractor (100) as stated in claim 1, characterized in that said rear and front mechanically activated valve (322, 324) are poppet valves (322, 324). 4. Tractor (100) as stated in claim 1, characterized in that it further comprises a rear vent valve (318) which allows fluid to flow from said rear mechanically activated valve (322) to said gripper control valve (312) only when a pressure in the fluid exceeds a preselected pressure threshold value. 5. Tractor (100) as stated in claim 2, characterized in that it further comprises a front vent valve (320) which allows fluid to flow from said front mechanically activated valve (324) to said gripper control valve (312) only when a pressure in the fluid exceeds a preselected pressure threshold value. 6. Tractor (100) as stated in claim 2, characterized in that it further comprises rear and front air valves (318,320), said rear and front mechanically activated valves (322, 324) being configured to conduct fluid to control said respective rear and front vent valves (318, 320), said rear and front vent valves (318, 320) being configured to direct fluid to control said gripper control valve (312). 7. Tractor (100) as stated in claim 6, characterized in that it further comprises a propulsion control valve (310), said propulsion control valve (310) having a first position where said propulsion control valve (310) directs pressure fluid to said rear propulsion assembly, and a second position where said propulsion control valve (310) directs pressurized fluid to said forward propulsion assembly. 8. Tractor (100) as stated in claim 7, characterized in that said propulsion control valve (310) is controlled by means of fluid pressure in said rear and front gripper assemblies (104, 106), and where pressure is exerted by said surfaces on said rear or front gripper assembly (104, 106), exceeds a preselected threshold value before said propulsion control valve (310) changes position. 9. Tractor (100) as set forth in claim 1, characterized in that said rear and front propulsion assembly comprises respectively a rear and front cylinder (108, 114), and where said body (118, 102, 104) further comprises rear (700) and front pistons displaceably located in said rear and front cylinders (108, 114), respectively, said rear (700) and front pistons being configured to be displaced by the pressure fluid in said rear and front cylinders (108, 114) to drive the body (118, 102, 104) forward through the borehole. 10. Tractor (100) as stated in claim 9, characterized in that said rear and front mechanically activated valves (322, 324) are placed on said rear (700) and front pistons, said rear and front mechanically activated valves (322, 324) is activated mechanically through contact with said rear and front cylinders (108, 114). 11. Tractor (100) as stated in claim 10, characterized in that both said rear and front mechanically activated valve (322, 324) is a poppet valve (322, 324). 12. Tractor (100) as stated in claim 2, characterized in that it further comprises a propulsion control valve (310), said propulsion control valve (310) having a first position where said propulsion control valve (310) directs pressurized fluid to said rear propulsion assembly, and a second position where said propulsion control valve (310) directs pressurized fluid to said forward propulsion assembly. 13. Tractor (100) as stated in claim 12, characterized in that said propulsion control valve (310) is controlled by means of fluid pressure in said rear and front gripper assemblies (104, 106), and where pressure is exerted by said surfaces on said rear or front gripper assembly (104, 106), exceeds a preselected threshold value before said propulsion control valve (310) changes position. 14. A method of moving a component (32) through a borehole, comprising: providing a tractor (100) with an elongate body (118, 102, 124), rear and front gripper assemblies (104, 106) that are longitudinal, movable engagement with said body (118, 102, 124), wherein said rear and front gripper assembly (104, 106) is hydraulically actuated for selective engagement with an inside (42) of the borehole, and rear and front propulsion assemblies (108, 114) which are adapted to drive said body (118, 102, 124) forward through the borehole relative to said rear and front gripper assembly (104, 106), respectively; attaching the component (32) to the elongate body (118, 102, 124) for; feeding a pressurized fluid through a supply line (302) to said elongate body (118, 102, 124) to drive the tractor movement; - passing pressurized fluid through said elongate body (118, 102, 124) to the component (32); directing a portion of the pressure fluid through a valve system (300) in the elongate body (118, 102, 124) for selective delivery of fluid to said rear and front gripper assemblies (104, 106) and said rear and front propulsion assemblies (108, 114 ) to produce tractor movement, characterized in that the method further comprises mechanically demonstrating the completion of a forward movement of said elongated body (118, 102, 124) in relation to said rear and front propulsion cylinders (108, 114) in order to obtain said rear and front gripper assemblies (104, 106) to alternately engage the inside (42) in a desired working order.