US20160090832A1

US20160090832A1 - Electrical controller for anti-stall tools for downhole drilling assemblies and method of drilling optimization by downhole devices

Info

Publication number: US20160090832A1
Application number: US14/964,371
Authority: US
Inventors: Philip Wayne Mock
Original assignee: WWT North America Holdings Inc
Current assignee: WWT North America Holdings Inc
Priority date: 2010-10-20
Filing date: 2015-12-09
Publication date: 2016-03-31

Abstract

A method of operating a bottom hole assembly having a drill pipe, an anti-stall tool, a motor and a drill bit in real-time including entering an upper torque threshold and a lower torque threshold as operating parameters for the bottom hole assembly into the anti-stall tool, continuously sensing torque of the bottom hole assembly by a torque sensor in the bottom hole assembly, electronically determining if the sensed torque has exceeded the upper torque threshold or the lower torque threshold for a specified duration of time requiring an intervention by the anti-stall tool, and communicating instructions to the anti-stall tool for proper hydro-mechanical adjustment of the anti-stall tool.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation-in-part of U.S. patent application Ser. No. 13/267,654, filed Oct. 6, 2011, which claims priority to and the benefit of U.S. Provisional Application No. 61/405,066, filed Oct. 20, 2010, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present invention provides an improvement in anti-stall tool controllers, and more specifically is an electrical controller to operate an anti-stall tool (AST) and mechanical specific energy drilling systems for controlling weight-on-bit during drilling operations and a method of drilling optimization by use of downhole devices.
Coiled tubing drilling requires the use of a downhole positive displacement motor (PDM) to rotate the drill bit. During drilling operations, the unloaded PDM rotates at a constant RPM and achieves a “freespin” motor pressure, with respect to the fluid flow rate. As the drill bit encounters the bottom of the hole and force is transferred to the bit, referred to as weight-on-bit (WOB), the motor will sense an increase in torque. This increase in torque is a result of increased resistance to rotating at the constant RPM (assuming a constant flow rate). In turn, the PDM requires additional pressure to turn the motor at the constant RPM while under increased resistance. If the resistance increases to a condition which prohibits the PDM from rotating (i.e. excessive WOB), a motor stall is encountered. During a motor stall, the motor stops turning, the downhole fluid path is severely restricted, and the surface pump pressure dramatically increases. This event can eventually cause a motor failure, which requires the drilling process to be stopped, and the coiled tubing to be fatigue-cycled as the bit is pulled off bottom and run back into the hole to start drilling again. An anti-stall tool (AST) is described in U.S. Patent Publication No. 2009/0173540 to Mock, et al.
A downhole tool that monitors motor pressure and sharply reduces the occurrence of motor stalls will increase overall drilling efficiency by:
(1) Increasing the average rate of penetration. This is achieved by reducing the occurrences of pulling off-bottom every time the motor stalls.
(2) Decreasing the damage to PDMs through repeated motor stalls, thereby decreasing occurrence of downhole failure.
(3) Decreasing the fatigue cycles on the coiled tubing. This increases the number of wells a coiled tubing string can service.
By achieving a more efficient drilling operation, the operators can substantially increase the cost savings of drilling a well.
There are several inherent limitations of current drilling systems. First, they rely on surface measurements and surface equipment manipulation to control the downhole interaction of the bit and the formation. Second, the use of downhole equipment for measurements contain a time delay from instrumentation measurement to operator response which also assumes the operator knows the correct response. Lastly, current drilling systems require significant expense and training, equipment and system monitoring of the process to maximize its efficiency.
Consequently, the current limitations allow for downhole parameters to exceed the operational limitations and result in tool failures. One significant source of the problems associated with non-productive time (NPT) is the failure of positive displacement motors (PDM) also referred to as mud motors. The failures are a result of the PDM exceeding the operational envelope and stalling. These issues eventually cause the rubber stator of the PDM to wear, resulting in poor performance or failure.
Another significant problem with drilling, especially in deep water offshore wells is stick-slip. Stick-slip is erratic changes in the downhole RPM of the drilling assembly. Stick-slip is measured by different metrics but most are based on changes in RPM, and changes in RPM near the drill bit are reflected as changes in torque at the bottom hole assembly. Frequently when drilling deep water offshore wells and/or highly deviated directional wells, a rotary steerable tool is used in the bottom hole assembly. Rotary steerable tools are subject to premature failure when exposed to significant stick-slip. Therefore, a device that helps ameliorate stick-slip could reduce the estimated sixty percent of premature failures of rotary steerable tools with significant savings and preventing loss of rig time and tool repair.
Previous embodiments of an anti-stall stool, hereinafter also referred to as an anti-stall device (ASD), responding to changes in downhole pressure relative to internal settings required extensive modeling and planning to set the operational pressure set points to function correctly with the pre-selected motor and bit. The fundamental problem with this concept is the lack of operational functionality and variability. Reacting to the change in motor back pressure is an indirect measurement of motor torque. The back pressure of the motor is a derivative of the resistance the motor encounters while rotating. However, other factors such a fluid properties, plugged nozzles, and worn motor components can also effect the back pressure. Once downhole, any change in the fluid system or any change in the tools causing back pressure, will alter the system environment and render the tool inoperable.
Consequently a need exists for a self-contained, automatic feedback, real-time, downhole assembly and method of operation that provides optimization of the rate of penetration via the manipulation of weight-on-bit or to prevent the downhole parameters from exceeding the operational limitations. Similarly, a method that ameliorates stick-slip is of significant importance to drilling cost production. The present invention circumvents the limitations recited above and offers the opportunity for all of the benefits of increased rate of penetration resulting in lower drilling costs per well.
The present invention provides an electrical controller for an anti-stall tool that controls WOB during drilling operations, resulting in improved overall drilling efficiency. The present invention also provides methods of drilling optimization through the use of downhole devices.

SUMMARY OF THE INVENTION

Briefly, the invention comprises an electrical controller for an anti-stall tool for use in a downhole assembly near the bottom of the tubing adjacent a positive displacement motor (PDM) and the drill bit. In one embodiment, the tubing comprises a coiled tubing, although the invention also can be used in rotary drilling applications. The electrical controller controls the force applied to the drill bit during drilling to prevent the drill bit from stalling under load. A working pressure range of the PDM is sensed during use by a hydraulic valve control system and is used as an input to the controller. The controller alters weight-on-bit (WOB) if the downhole pressure goes beyond either end of a preset working pressure range of the system. The controller keeps the drill bit rotating by (1) maintaining WOB during normal drilling operations, (2) increasing WOB if sensed PDM working pressure indicates that drill bit loading is low, and (3) reducing WOB which reduces PDM back-pressure to retract the drill bit from the bottom if excessive working pressure is sensed due to increased torque at the PDM.
The anti-stall tool generally comprises one or more hydraulic cylinders for applying an axial force either in a forward direction or a reverse direction. The electrical controller comprises electronics and a system of hydraulic valves adapted to control piston force in either the forward or reverse directions. An active stage of the anti-stall tool reacts to the PDM producing low downhole pressures (e.g. below a preset low pressure) by actuating one or more of the pistons in the downhole direction to increase WOB which increases PDM back-pressure. When the PDM is operating within its normal operating pressure range, the controller locks the pistons in a passive mode, in which the pistons are sealed and the anti-stall tool transfers force from the tubing to the drill bit. If the controller senses a preset high pressure or greater due to high torque at the PDM, the valve system reverses hydraulic flow to the pistons, which reduces WOB to force the drill bit away from the bottom to reduce PDM back-pressure.
One embodiment of the invention comprises an anti-stall method for controlling drilling operations in a downhole assembly which includes a tubing that extends downhole, a drill bit carried on the tubing, a positive displacement motor (PDM) for rotating the drill bit, and an anti-stall tool adjacent the PDM. The method comprises sensing pressure in the PDM, providing a range of operating pressures for the PDM defined by high and low limits of operating pressures, and operating the anti-stall tool in: (1) an active stage for increasing WOB forces in the downhole direction when the low limit of operating pressure is sensed, (2) a reverse stage for providing a WOB force in the reverse direction when the high limit of operating pressure is sensed, and (3) an optional passive stage in which the anti-stall tool is locked to transfer WOB directly from the tubing to the drill bit when the PDM is operating within the limits of its normal operating pressure range.
Another embodiment of the invention comprises a spring-operated anti-stall tool adapted for use in a downhole assembly which comprises a tubing for extending downhole, a drill bit carried on the tubing, and a positive displacement motor (PDM) adjacent the drill bit for rotating the drill bit during drilling operations. A spring-operated anti-stall tool is carried on the tubing and positioned adjacent the PDM for preventing stalling of the PDM due to excessive loads on the drill bit. The spring-operated anti-stall tool comprises at least one piston in a cylinder having a forward piston area and a reverse piston area, and an electrical controller comprising electronics and a hydraulic valve system for controlling operation of the piston. The forward piston area receives hydraulic fluid to produce a force in the downhole direction. The reverse piston area contains a load spring adapted to apply an upward spring force on the piston. The electrical controller adjusts WOB in response to sensed PDM sets operating pressure. The controller inputs a desired range of operating pressures for the PDM, including an upper limit and a lower limit. The controller operates a valve system to: (1) supply hydraulic fluid to the forward piston area to increase WOB force in the downhole direction when operating pressure in the PDM surpasses the lower limit; this compresses the load spring as the cylinder moves in the downhole direction; (2) vent the piston volume in the forward piston area so the compressed spring will push the tool uphole, to reduce WOB when operating pressure in the PDM exceeds the upper limit; and (3) optionally lock the piston in a passive state when the PDM is operating within its normal operating pressure range.
Another embodiment comprises an improved anti-stall tool which produces a controlled translational motion of the drill bit that increases drilling efficiency. The anti-stall tool controls the force applied to the drill bit during drilling to prevent the drill bit from stalling under load. The anti-stall tool comprises one or more hydraulic cylinders for applying an axial force in either a forward or reverse direction, and an electrical controller adapted to control the force applied by the one or more hydraulic cylinders to the drill bit in response to sensed working pressure of the drive motor during drilling operations. The controller comprises a system for adjusting WOB when working pressure exceeds either end of a working pressure range of the drive motor. The system includes (1) a passive stage for maintaining WOB when working pressure is within a preset normal operating range, (2) an active stage for applying pressure to the one or more cylinders to increase WOB when sensed working pressure is below a preset limit, and (3) a reverse stage for reversing pressure to the one or more cylinders to reduce WOB and thereby retract the drill bit from the bottom when sensed working pressure is above a preset limit. The tool is normally controlled to apply WOB at pressures within a desired wide range of pressures. When reaching a preset anti-stall pressure, the tool is reversed to reduce WOB and does not resume applying WOB over a preset wide range of PDM back-pressure drop.
In another embodiment, the tool can apply WOB during the wide range of operating pressures via at least two stages, one where pressure is increasing up to a set desired operating pressure, and then switches the tool to a locked position at that pressure and higher up to a preset anti-stall limit at which flow to the pistons is reversed to lift the drill bit. The two stages can be operated as active/reverse stages as well.
In another embodiment, a mechanical specific energy downhole drilling assembly as disclosed in U.S. Pat. No. 8,833,347, the contents of which are incorporated herein by reference include a bottom hole assembly including drill pipe and a drill bit, a weight-on-bit and torque sub for sensing torque, weight-on-bit and revolutions per minute of the drill bit, a command and control sub for receiving input from the weight-on-bit and torque sub for determining instantaneous mechanical specific energy of the downhole drilling assembly and an anti-stall tool responsive to real-time mechanical specific energy information from the command and control sub to adjust the weight on the drill bit to maximize rate of penetration of the drill bit.
The present invention is also directed to methods of operating a drilling assembly using a rotary anti-stall tool or device. A typical drilling assembly includes a drill pipe, a drill bit and a rotary anti-stall device wherein the method provides a response to real-time input information from onboard sensors to adjust the weight on the drill bit to maximize rate of penetration of the drill bit and/or reduce stick-slip. The present invention provides a downhole drilling assembly and drilling method to increase and maximize rate of penetration and reduce stick-slip impacting the bottom hole assembly. The rotary anti-stall device consists of at least one sensing section, computerized downhole computation capability and a controlled downhole weight modification section. The drilling method used with the rotary anti-stall device consists of three reactive modes, tool extension, tool lock, tool retraction and one passive mode including torque monitoring and a method for set-up. Each mode of the set-up have different steps to achieve the directed action.
The rotary anti-stall device and its method were designed to be set-up at the well site based on the actual equipment at the site. This concept eliminates the logistical planning necessary to pair the anti-stall device with other pre-selected tools. This allows infinite variability with bottom hole assembly set-ups and unlimited set-up options. The rotary anti-stall device will be programmed at site based on the expected operational characteristics of the particular motor or drilling system. All changes to the fluid system or other changes in the pressure environment will not alter the operation of the tool. In one embodiment, the rotary anti-stall device includes sensors that directly measure downhole torque and therefore is not affected by any changes in the downhole environment. Once downhole, the anti-stall device will operate directionally off of torque and not a derivative of torque. Using a downhole microprocessor, the anti-stall device can be set-up using multiple threshold limits and durations to control the tool response which contributes to the ability to refine the tool actions downhole.
The anti-stall device set-up includes programming an upper threshold limit and a lower threshold limit to enhance the operating envelope of the mud motor or drilling system. The anti-stall device will alter weight-on-bit and attempt to bring the downhole torque back into the defined operating envelope. An electrical connection is inserted into the tool which is then programmed to input the upper torque threshold, lower torque threshold and pause duration from event to tool reaction. Determination of set points is established by other bottom hole assembly and operating parameters such as downhole motor performance and bottom hole assembly elements.
The drill string torque below the anti-stall device to the bit is continuously monitored by the anti-stall device torque sensor. This sensor has been designed to eliminate the effects of bending, differential pressure and weight-on-bit. In this method the sensor continuously monitors and processes the torque and then determines if the threshold limits have been exceeded for a specified duration which requires intervention.
The processor uses a sophisticated algorithm to determine the tool actions based on the pre-programmed threshold limits, values and set points. Enhanced firmware developed for the anti-stall device of the present invention includes advanced analog and digital filtering to negate the effect of high frequency sensor spikes derived from the drilling environment. A third step in the method includes after the sensor algorithm determines the appropriate action, the processor communicates to the electric motor(s) to position a valve(s) in the precise location for the required hydro-mechanical tool response. In a fourth step, a communication loop to the electric motors then feeds back to resolve the motor actuation and verify position. In a fifth step, all sensor information and motor actuations are recorded, including accurate downhole torque measurements to optimize the rotary anti-stall device tools set-up and enhance future drilling operations.
The method for the anti-stall device downhole extension includes an initial step of monitoring downhole torque which decreases below the lower threshold limit beyond the specified time duration. In a second step, the anti-stall device signals a motor sequence to place the tool in extend mode, a communication loop to the electric motors is fed back to resolve the motor actuation, verify position and record movement. In a third step, a two position, four-way valve directs pressurized fluid flow into the hydraulic cylinder volumes resulting in the regulated telescopic extension of the anti-stall device. In fourth step, the valve position vents the volume of fluid retained in the retraction side of the pistons. In a fifth step, the extension results in a weight-on-bit increase of the drill string by generating a force vector in the downhole direction. The rotary anti-stall device tool will extend until it reaches the end of a stroke or a threshold limit is exceeded. The magnitude of this vector is a function of the anti-stall tool piston area which can be verified during assembly and centerline pressure of the drilling system as realized at the anti-stall device tool location. As seen on the surface, the result is an increase in weight-on-bit and centerline pressure.
The method for the anti-stall device downhole hydraulic lock includes an initial step wherein downhole torque within the range of the lower threshold limit and upper threshold limit is experienced for a specified time duration. In a second step, the anti-stall device signals a motor sequence to place the tool in lock mode, a communication loop to the electric motors is fed back to resolve the motor actuation, verify position and record movement. In a third step, the two position, four-way valve is positioned to prevent pressurized fluid flow into or out of the hydraulic cylinder volumes, resulting in the hydraulic lock of the anti-stall tool. This condition results in a complete weight-on-bit transfer from the drill string to the bit. As seen on the surface, the result shows normal drilling parameters and that current surface operating settings have not exceeded downhole operating limits.
A method for the anti-stall tool downhole retraction includes in a first step, the downhole torque increases above the upper threshold limit beyond the specified time duration. In a second step, the anti-stall device signals the motor sequence to place the tool in retract mode, a communication loop to the electric motors is fed back to resolve the motor actuation, verify position and record movement. In a third step, the two position, four-way valve directs pressurized fluid flow into the hydraulic cylinder volumes resulting in the telescopic collapse of the anti-stall device. In a fourth step, the valve vents the volume of fluid retained in the extension side of the pistons. In a fifth step, this collapse results in a weight-on-bit reduction of the drill string by generating a force vector in the uphole direction. The anti-stall device will retract until it reaches the end of stroke or a threshold limit is exceeded. The magnitude of this vector is a function of the rotary anti-stall device tool piston area which can be verified during assembly and centerline pressure of the drilling system as realized at the anti-stall tool location. As seen on the surface, the result is a rapid decrease in weight-on-bit and centerline pressure which provides a signal that current surface operating settings have exceeded downhole operating limits.
The methods can be applied to the entire range of typical drilling assembly sizes from 2⅛ inch to 17½ inch diameters. The methods of the present invention can be incorporated into all drilling control methods including both manual and automatic driller type rigs. This is to include control by rate of penetration, weight-on-bit, mechanical specific energy as well as combinations of the above and other methods of control.
The benefits of the present invention include fast rate of penetration and cost reduction. Great financial benefit of the system is the direct increase in drilling efficiency which results in lower cost per foot of drilling, a common measurement of normalizing drilling costs. For example, a twenty percent increase in average rate of penetration could result in a ten percent cost reduction for drilling the well. A second benefit is the reduction of stick-slip. Reduction in stick-slip reduces vibration damage to other bottom hole assembly elements such as rotary steerable tools, thereby producing potentially large savings. Another benefit is field adjustability wherein the system specifically allows for the programming while in the field. The system has access ports to allow input of specific tool parameters related to the particular well and bottom hole assembly. The methods provide compatibility with existing drilling methods and equipment wherein no significant changes in typical drilling operations are required, thereby allowing prompt and efficient use of the anti-stall device and technology. Further reduction requirements for expert advice for drilling when empirically verified, the optimized drilling conditions for a well or a field, the optimum drilling parameters can be included in the control algorithms thereby reducing the number of drilling conditions that require expert help for the field personnel and thereby reducing cost per well. The method of the present invention provides increased drilling efficiency. Weight is controlled immediately at the drill bit thereby providing greater efficiency than systems controlled entirely at the surface. Parasitic losses from the surface are up to seventy-five to ninety percent of the drilling energy, but the invention herein virtually delivers ninety-five to one hundred percent of its energy directly to the drill bit.
These and other aspects of the invention, including additional embodiments, will be more fully understood by referring to the following detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a downhole assembly containing an anti-stall tool according to principles of this invention;

FIG. 2 shows a cross-sectional view of one embodiment of a hydraulic-operated anti-stall tool;

FIG. 3 is an elevational view showing a further embodiment of an anti-stall tool;

FIG. 4 is a cross-sectional view showing the anti-stall tool of FIG. 3 along with a schematic view of an improved controller;

FIG. 5 shows a cross-sectional view of another alternative embodiment spring-operated anti-stall tool;

FIG. 6 is a cross-sectional view of an electrically controlled anti-stall tool which includes a 2-position, 4-way pilot valve with a pressure control valve according to principles of this invention;

FIG. 7 shows an alternative embodiment electrically controlled anti-stall tool which includes a 3-position, 4-way valve;

FIG. 8 shows a cross-sectional view of the electrically controlled AST, which includes an electronics package and electrical downhole motor contained in the AST; and

FIG. 9 shows a cross-sectional view of another electrically controlled AST.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram illustrating a coiled tubing drilling system 10 for drilling a well bore in an underground formation 12. The coiled tubing drilling system can include a coiled tubing reel 14, a gooseneck tubing guide 16, a tubing injector 18, a coiled tubing 20, a coiled tubing connector 21, and a drill bit 22 at the bottom of the well bore. FIG. 1 also shows a control cab 24, a power pack 26, and an alignment of other BHA tools at 27. A tractor (not shown), such as that described in U.S. Pat. No. 7,343,982, may be used to move downhole equipment within the bore. The '982 patent is incorporated herein in its entirety by this reference. During drilling, the downhole equipment includes a downhole motor 28, such as a positive displacement motor (PDM), for rotating the drill bit. An anti-stall tool (AST) 30, according to principles of this invention, is positioned near the bottom of the coiled tubing, upstream from the downhole motor and the drill bit. In one embodiment, hydraulic back pressure produced within the coiled tubing is measured at the surface. Torque produced at the drill bit during drilling operations is directly related to back-pressure. As a result, hydraulic back-pressure measurements can be sensed and used as inputs to a hydraulic control valve system contained in the anti-stall tool.
The anti-stall tool 30 incorporates use of a series of hydraulic cylinders and as few as three pressure-actuated valves to control the applied weight-on-bit (WOB) while drilling. This tool will virtually create a real time, downhole motor pressure sensor that will alter the WOB to maintain a relatively constant drilling rate of penetration and provide feedback to the coiled tubing operator to adjust coiled tubing injector rates to match the PDM pressure.
The invention uses the working pressure range of the downhole positive displacement motor 28 to alter the WOB if the downhole pressure surpasses either end of the working range. During drilling operations, the AST controls WOB through the use of three distinct operations: active WOB, passive WOB and reverse.
FIG. 2 illustrates one embodiment of the anti-stall tool 30 which includes a series of axially aligned hydraulic cylinders with separate pistons that define piston areas A1 and A2, A3A and A3B, and A3C and A3D. The torque section of the tool is shown at 35. FIG. 2 also schematically shows a hydraulic controller 34 contained in the anti-stall tool. The controller includes a pressure reducing valve 36, a reverser valve 38, and a vent valve 40. Hydraulic control fluid passes through a filter 42.
In the description to follow, specific operating pressure set points or values are related to operative ranges for coiled tubing equipment. Use of the anti-stall tool in rotary drilling operations, for example, would involve use of different operating pressure ranges or control valve set points.
The first stage of the hydraulic anti-stall tool is activated when the unloaded PDM produces low downhole pressures. For example, if the PDM creates a back pressure of 200 psi (adjustable to specific motor requirements), the anti-stall tool will be in the active WOB stage. This causes pressure to be supplied to all pistons that will produce a force in the downhole direction (A1, A3A and possibly A3C). As the WOB is applied, the normal reaction is for the PDM to generate more pressure. As the anti-stall tool senses the increase in pressure to 250 psi (adjustable to specific motor requirements), the pressure reducing valve 36 will shut off additional flow to the pistons and hydraulically lock the pistons in the passive WOB stage.
In the passive WOB stage, the anti-stall tool transfers the force from the tubing to the bit. The tool is acting as a rigid member and is monitoring the PDM back-pressure. The pressure reducing valve 36 is closed and is sealing the fluid in the pistons (A3A and possibly A3C) that produce a force in the downhole direction. All of the resultant pressure from the WOB will be contained in the sealed piston volumes.
During the final stage of the anti-stall tool, the back pressure due to high torque in the PDM triggers the reverser valve 38 and vent valve 40 to reduce WOB. Once the back pressure reaches 1,000 psi (adjustable to specific motor requirements), the reverser valve 38 switches the flow of fluid to the pistons that produce force in the uphole direction (A2, A3B, A3D). At the same time, the vent valve 40 vents the opposite side of those pistons. This allows the tool to travel uphole, reducing WOB and thereby reducing the PDM back pressure. As the PDM back pressure falls below the reverser valve setting (including hysteresis) the reverser valve 38 will switch back to its original position.
The anti-stall tool is designed to be in the fully expanded position at low pressures. This bias allows the tool to have the full length of stroke available to retract as much as needed until the PDM back-pressure reduces below the lower limit of the vent valve. The anti-stall tool will then try to fully expand, but the pressure may rise to the pressure control valve setting or higher and limit the expansion. Therefore, the long stroke length will allow several retraction steps before the stroke length is used up. The coiled tubing operator can adjust the input speed of the coiled tubing into the hole to prevent the anti-stall tool from fully retracting. The operator will see a change in pump pressure with each retraction to signal the need to reduce the coiled tubing input speed.
The anti-stall tool operates as an open loop system. Drilling fluid from the surface is pumped down the bore in the tubing through the tool, to the motor for rotating the drill bit. Most of the fluid flow in the system is used for driving the drill bit. A small amount of the fluid is used for the controller and is jetted out to the sides and into the annulus during use.
The anti-stall tool includes splines in a torque section 44 which contains an outer spline housing and splines contained internally on the piston housing. The splines allow the BHA to maintain its orientation relative to the motor and drill bit, without undesired twisting. The splines allow the tool to be used with a steerable BHA. Steerable BHAs can be controlled to drill the hole to a desired location, while changing the direction of the hole while drilling to achieve this goal. The splines allow the PDM and bit to maintain alignment with the orienting tools that would be uphole of the anti-stall tool. The torque load is transferred from the PDM across the outermost housings and across the spline of the anti-stall tool to the tools uphole of the anti-stall tool. The inner shafts do not see direct loading due to torque. The spline section functions in both the expansion and retraction of the anti-stall tool.
FIGS. 3 and 4 show an improved anti-stall tool 30′ which produces a three-stage controlled translational motion to the drill bit that increases drilling efficiency.
This illustrated embodiment includes a series of axially aligned hydraulic cylinders with pistons that cooperate to form piston areas S1, A1 and A2, and A3A and A3B. The torque section of the tool is shown at 44 along with a hydraulic controller contained in the anti-stall tool and shown schematically at 46. The controller includes a pressure control valve 48, a pilot valve 50, a sequence valve 52, and a vent valve 54. A filter for the hydraulic controller is shown at 56.
In one embodiment, the controller has the three stages of operation: (1) active, (2) passive, and (3) retraction. The control valves contained in the controller area of the tool are shown schematically in FIG. 4: pressure lines are shown as solid lines, pilot lines are shown as dashed lines, and exhaust lines are shown in dotted lines. In the following description, the pressure ranges are used as examples only; they are adjustable to specific motor requirements.
The active stage applies downward force to the drill bit based on motor back-pressure from the positive displacement motor. If pressure is less than 400 psi, for example, the hydraulic pistons apply a downward force which generates more PDM back-pressure. The vent valve 54 of the controller is open and supplies a pilot signal to the pilot valve 50. If pressure reaches 400 psi, the vent valve 54 closes and vents the pilot line for the pilot valve 50. But the vented pilot valve stays in position, and the PDM back-pressure is sensed by the pressure control valve 48. The pistons apply the downward force until sensed downhole pressure reaches 650 psi, for example, which represents a desired working pressure.
The pressure control valve then switches the anti-stall tool to the passive mode when sensed pressure reaches the desired drilling pressure of 650 psi, for example. Here the pressure control valve 48 shuts off flow to the pistons and hydraulically locks the pistons in the passive WOB mode. The pressure control valve 48 is closed and no pressure is sent to the pistons. The pistons are sealed, and existing force is transferred to the drill bit. Motor pressure is not increased. Downhole pressure continues to be monitored in the passive mode via the vent valve 54 and sequence valve 52, which monitor pressure change in the coiled tubing. The passive state continues until sensed back-pressure reaches 800 psi, for example.
Once downhole pressure reaches the 800 psi level, the anti-stall tool switches to the reverse mode. That is, if torque in the PDM increases, it causes an increase in back-pressure. Motor stall is prevented by sensing and reacting to back pressure at a level below motor stall, e.g., 800 psi, or other pressure below that at which stall can occur.
When sensed pressure reaches 800 psi, the normally-closed sequence valve 52 is opened, sending a pilot signal to the pilot valve 50 which reverses flow of hydraulic fluid to the pistons to produce a force in the uphole direction, to reduce WOB.
As back pressure falls below 800 psi, the pilot signal from the sequence valve 52 to the pilot valve 50 is closed. The sequence valve 52 vents the pilot signal, and this continues until sensed PDM pressure falls to 400 psi, where the vent valve 54 opens and sends a pilot signal to the pilot valve 50 to shift back to the active mode, by supplying fluid pressure to the pistons to expand and to apply downward force to increase WOB.
Thus, in this embodiment, the tool is normally controlled to apply WOE when drilling at pressures within a desired wide range of pressures. These can be from 400 to 800 psi, for example. When reaching a preset anti-stall pressure, such as 800 psi, which would be a safe level below the pressure at which stall actually occurs, the tool is reversed and does not resume applying WOB over a preset wide range of pressure drop, before resuming active WOB operations. This wide range of pressure drop can be from about 200 to about 2,000 psi. In the illustrated embodiment, the range of pressure drop is 400 psi (from 800 to 400 psi), before WOB is resumed.
The tool applies WOB during the desired wide range of operating pressures via two stages, one stage where pressure is increasing up to a set desired operating pressure, for example 650 psi, and then switches to a second-stage locked position at that pressure and higher up until an anti-stall limit, of say 800 psi is reached, before reversing flow to the pistons and lifting the drill bit.
A key feature of the anti-stall tool is the single input necessary for the tool to operate. The tool need only sense and respond to the back-pressure created by the PDM. Stated another way, the anti-stall tool operates on constant (although adjustable) working pressure set points. The fixed set points can be fine-tuned to control the thresholds at which the control valves open and close, and as a result, drill bit penetration rate is more uniform.
An alternate embodiment of the invention comprises a two-phase anti-stall method for controlling drilling operations in a downhole assembly, which includes the tubing that extends downhole, the drill bit carried on the tubing, the positive displacement motor (PDM) for rotating the drill bit, and the anti-stall tool adjacent the PDM. This method comprises sensing pressure in the PDM, providing a range of operating pressures for the PDM defined by high and low limits of operating pressures, and operating the anti-stall tool in: (1) an active stage increasing WOB forces in the downhole direction when the low limit of operating pressure is sensed, and (2) a reverse stage providing a force in the reverse direction, reducing the WOB, when the high limit of operating pressure is sensed.
This two-phase anti-stall method can be accomplished by adjusting the setting of the sequence valve 52 equal to or lower than the pressure control valve 48, but still above the setting of the vent valve 54.
The anti-stall tool also can be operated by the two-phase method, combined with a passive range that operates (as described above) between a small range of pressure settings.
Different orifice adjustments can be used to control the speed at which the tool responds. In FIG. 2, the orifice is not shown. The orifice can be on the exhaust of the reverser valve 38.
Although the schematic in FIG. 4 depicts a single orifice 55, those skilled in the art would understand that the two-position/four-way valve contains two exhaust ports. Each of the ports vents a different piston area, either the piston area to produce downhole force (expand) or uphole force (retract). Using the high and low limits of the operating pressures, the orifice sizes can be calculated to restrict the volumetric flow rate of fluid exhausted through the valve and thereby control the speed at which the tool expands or retracts. The expansion and retraction of the tool can be controlled individually by different orifice sizes.
As an alternative, WOB can be controlled by a combination of control valve settings and adjustments to orifice sizes.

EXAMPLE

The following specifications illustrate one embodiment of the anti-stall tool:


	Description	Characteristic

Tool OD	3.00	in
Tool ID	.75	in
Length - Expanded	8.1	ft
Length - Collapsed	7.4	ft
Stroke	9	in
Max Temp	300°	F.
Tensile Strength	50,000	lbs
Max Motor Torque	2,000	ft-lbs
Max Dog Leg	25°/100	ft
Tool Joint	2⅜	PAC

The design is flexible in that the pressure settings and orifice size may be changed to fine-tune the tool. If a much larger WOB change is needed, then the shaft can be replaced to allow installation of additional pistons.


	Total Downhole	Pressure Control	Max WOB from
# of Pistons	Area (sq. in.)	Valve Setting (psi)	AST (lbs)

1	4.8	650	3,055
2	7.9	650	5,135
3	11.0	650	7,150

The anti-stall tool cylinders and valves may be manufactured from various corrosion-resistant materials including tungsten carbide, Inconel, high strength nickel alloyed steel such as MP35, beryllium-copper, and the like.
Examples of improvements provided by the anti-stall tool are:

(1) Active WOB: The tool will attempt reset into the fully extended position when the pressure falls below 650 psi. If a motor stall has occurred and the AST has pulled the bit off bottom, the Active WOB stage will produce a minimum WOB and thrust the bit downhole until the PDM pressure exceeds 650 psi.
(2) Passive WOB: Shuts off the Active WOB stage and allows the coiled tubing to transfer WOB to the bit. Prevents excessive WOB that can be developed as PDM pressure rises and acts on the pistons producing force downhole.
(3) Reverse: Reduces WOB to prevent motor stalls.
(4) Torque section will transfer torque through the AST into the coiled tubing.

A downhole tool that monitors motor pressure and sharply reduces the occurrence of motor stalls will increase the overall drilling efficiency by:

(1) Increasing the average rate of penetration. This is achieved reducing the occurrences of pulling off bottom for motor stalls.
(2) Decreasing the damage to PDMs through repeated motor stalls, thereby decreasing occurrence of downhole failure.
(3) Decreasing the fatigue cycles on the coiled tubing. The increases the number of wells a coiled tubing string can service.

FIG. 5 illustrates a spring-operated anti-stall tool 130 according to this invention. In the description to follow, motor pressure values are examples only; they are dependent upon and adjustable to specific motor requirements.
The FIG. 5 embodiment includes a series of axially aligned hydraulic cylinders with separate pistons that define piston areas A1 and A2, A3A and A3B, and A3C and A3D. The torque section of the tool is shown at 35. The piston area A3B contains a compression spring that applies a spring force F1 and a piston area A3D which contains a compression spring that applies a spring force F2. FIG. 2 also schematically shows a controller 34 contained in the anti-stall tool. The controller includes a pressure reducing valve 136 and a vent valve 138. Hydraulic fluid passes through a filter 140.
In the description to follow, specific operating pressure set points or values are related to operative ranges for coiled tubing equipment. Use of the anti-stall tool in rotary drilling operations, for example, would involve use of different operating pressure ranges or control valve set points.
The first stage of the spring operated anti-stall tool 130 is activated when the unloaded PDM produces low downhole pressures. For example, if the PDM 20 creates a back pressure of 200 psi, the spring-operated tool will be in the active WOB stage. This causes pressure to be supplied to all pistons that will produce a force in the downhole direction (A1, A3A and possibly A3C). This will compress and load the springs with a spring force F1 and F2. As the WOB is applied, the normal reaction is for the PDM to generate more pressure. As the tool senses the increase in pressure to 250 psi (adjustable to specific motor requirements), the pressure reducing valve 136 will shut off additional flow to the pistons and hydraulically lock the pistons in the passive WOB stage.
In the passive WOB stage, the spring-operated tool transfers the force from the coil to the bit. The tool is acting as a rigid member and is monitoring the PDM back-pressure. The pressure reducing valve 136 is closed and is sealing the fluid in the pistons (A3A and possibly A3C) that produce a force in the downhole direction. All of the resultant pressure from the WOB is contained in the sealed piston volumes.
During the final stage of the spring-operated tool, the back pressure due to high torque in the PDM triggers the vent valve 138 to pull the bit off-bottom. Once the back pressure reaches 1,000 psi (adjustable to specific motor requirements), the vent valve 138 vents piston volumes A3A and A3C. The resultant force F1 and F2 of the compressed springs will push the tool uphole, reducing WOB and thereby reducing the PDM back-pressure. As the PDM back-pressure falls below the vent valve setting (including hysteresis), the tool will switch back to one of its other stages of operation.
FIGS. 1-5 illustrate two AST designs having hydraulic controllers, however FIG. 6 shows an alternative embodiment electrically controlled AST 58 having a 2-position, 4-way pilot valve 60 with pressure control valve 62. An electrical controller could be incorporated into the AST embodiments shown in FIGS. 1-5. The embodiment, as shown in FIG. 6, is based on using the working pressure range of a downhole positive displacement motor (PDM) 28 to alter the weight-on-bit (WOB) if the downhole pressure surpasses either end of the PDM's working range. Alternatively, this embodiment can use the working power range of an electric downhole motor 64 to alter the WOB if the power consumption surpasses either end of the motor's working range. During drilling operations, the anti-stall tool (AST) 58 will control the WOB through the use of three distinct operations; active WOB, passive WOB, and Off Bottom.
The first stage of the AST is activated when the unloaded PDM produces low downhole pressures. For example, if the PDM and drill bit jets create a back pressure of 300 psi, the AST will be in the active WOB stage. This means that pressure will be supplied to all pistons in the AST that will produce a force in the downhole direction (A1, A3A). As the WOB is applied, the normal reaction is for the PDM to generate more pressure. When the pressure reaches 400 psi, for example, the electronics package 66, which receives a pressure-related input from a pressure transducer (P) 68, will signal the motor 64 to shift the pilot valve (PV) 60. The PV is a motor-driven, two position, four way spool valve. The PV controls whether the AST will expand or contract. As the AST senses the increase in pressure to 650 psi (adjustable to specific motor requirements), the pressure control valve (PCV) 62 will shut off additional flow to the pistons and hydraulically lock the pistons in the AST in the passive WOB stage.
In the passive WOB stage, the AST simply transfers the force from the coil tubing to the drill bit. The AST is acting as a rigid member and is simply monitoring the PDM back pressure. The PCV is closed and is sealing the fluid in the pistons (A1, A3A) that produce a force in the downhole direction. All of the resultant pressure from the WOB will be contained in the sealed piston volumes.
During the final stage of the AST, the back pressure due to high torque in the PDM signals the electronics package 66 via the pressure transducer 68 to shift the pilot valve 60 and pull the bit off bottom. Once the back pressure reaches 800 psi (off bottom setting, adjustable to specific motor requirements), the pressure transducer/electronics package will signal the electric downhole motor 64 to shift the PV's position. This switches the flow of fluid to the AST pistons that produce force in the uphole direction (A2, A3B). This allows the tool to travel uphole, reducing WOB and thereby reducing the PDM back pressure. When the pressure falls below the active WOB setting (400 psi), the pressure transducer/electronics package will signal the electric downhole motor to shift the PV's positions. Once the PV switches back to its original position, the AST will return to the active WOB stage. The electronics package 74 receives a pressure input from pressure transducer (P) 76 and signals motor 72 to shift pilot valve 70.
FIG. 7 shows a 3-position, 4-way pilot valve 70. The alternative embodiment, shown in FIG. 7, is based on using a single valve to control the AST. The pilot valve 70 is a motor 72 driven, three-position, four-way spool valve. The center position of the pilot valve generates the hydraulic lock necessary for the passive WOB stage.
FIG. 8 illustrates a cross sectional view of the electrically controlled AST 58 which includes a torque transducer 78 (or alternative sensing method), electronics package 66 and the electric motor 64 driven pilot valve 60 within the housing.

EXAMPLE

Specifications for One Embodiment AST illustrated in FIGS. 6-8:


	Description	Characteristic

The design of an electrically controlled AST is flexible in that the pressure settings may be changed to fine tune the AST. Programmable pressure settings may be changed on surface or while in operation. Current available communication techniques include mud pulse telemetry, fiber optic and wireline.
If a large increase in WOB is needed, then the shaft of the AST can be replaced to allow the installation of additional pistons.


	Total Downhole	Pressure Control	Max WOB from
# of Piston	Area (sq. in)	Valve Setting (psi)	AST (lbs)

1	4.8	650	3,055
2	7.9	650	5,135
3	11.0	650	7,150

Features and Benefits:
The following illustrates features of an electrically controlled AST:

Active WOB: The tool will attempt reset into the fully extended position when the pressure falls below 650 psi. If a motor stall has occurred and the AST has pulled the bit off bottom, the Active WOB stage will produce a minimum WOB and thrust the bit downhole until the PDM pressure exceeds 650 psi.
Passive WOB: Shuts off the Active WOB stage and allows the coiled tubing to transfer WOB to the bit. Prevents excessive WOB that can be developed as PDM pressure rises and acts on the pistons producing force downhole.
Off Bottom: Pulls the bit off bottom to prevent motor stalls.
Torque section will transfer torque through the AST into the coiled tubing.

The downhole tool monitors motor pressure and sharply reduces the occurrence of motor stalls to thereby increase the overall drilling efficiency by:

Increasing the average Rate of Penetration (ROP). This is achieved reducing the occurrences of pulling off bottom for motor stalls.
Decreasing the damage to PDMs through repeated motor stalls, thereby decreasing occurrence of downhole failure.
Decreasing the fatigue cycles on the coiled tubing. This increases the number of wells a coiled tubing string can service.

By achieving a more efficient drilling operation, the operators can substantially increase the cost savings of drilling a well.
Alternative Methods of Operations:
Instead of an absolute pressure transducer, the AST may sense:

Differential Pressure between annulus and bore using a Differential Pressure Transducer
Load transferred through the tool or Weight on Bit (WOB) using a Load Cell
Torque transferred through the tool using a Torque Transducer
Rotational deceleration using a Torsional Accelerometer

If the system is connected to an electric motor instead of a hydraulic motor, the AST may sense:

Change in voltage
Change in electric current

The AST system itself may be hydraulically powered, electrically powered, battery powered, mechanically assisted, or any combination.
FIG. 9 illustrates a self-contained, automatic feed-back, real-time AST 80 for use in a downhole assembly that provides optimization of the rate of penetration via the manipulation of weight-on-bit while preventing the downhole parameters from exceeding the operational limitations. The AST 80 includes an electrical controller 82 which when placed in a downhole drilling assembly having a minimum bottom hole assembly including drill pipe, a motor and a drill bit, enables the AST to be responsive to real-time input information received from onboard sensors 84 to adjust the weight on the drill bit to maximize rate of penetration of the drill bit. The AST further includes a computerized downhole computation capability (microprocessor) within the electronics section 82 and a controlled downhole weight modification section 86 comprised of motors and valves, a piston extension section 90, a piston retraction section 92, and a torque section 94.
The drilling method for use with the AST consists of at least one initial threshold or thresholds set-up based on known drilling parameters when the AST is run downhole. The AST may be tuned to new thresholds after the initial run once on surface or during the downhole drilling process. The range of adjustments may vary from minor adjustments known as trimming to major adjustments.
The sensor section 84 can receive inputs such as torque, weight-on-bit, vibration, differential pressure, revolutions per minute, logging while drilling input or measurement while drilling inputs. Sensors are positioned on the AST to collect the information.
Along with the evolutions of bottom hole assemblies, downhole communication has evolved beyond the typical mud pulse telemetry system. Recent advancements have allowed drill pipe to have a continuous conduit from surface to bit, allowing “real-time” downhole data to be transferred at the surface. These systems may incorporate the AST activation into the overall system feedback loop to maximize drilling efficiency. Wi-Fi communication between tools has recently been introduced to downhole bottom hole assemblies. This form of communication allows tools to talk when not adjacent in the bottom hole assembly. The AST may be fitted with Wi-Fi communications loop or RFID communication system to optimize drilling effectiveness. A communication system of the AST 80 is an open loop to surface however, the AST is applicable to and compatible with a number of communication systems including bottom hole assembly, closed loop, surface closed loop, memory tool, mud pulse telemetry, wired pipe, as well as the Wi-Fi and RFID previously mentioned.
The methods of operation to be described herein are applicable to wells that are balanced, that is pressure from the formations equal to the pressure from the fluid column used while drilling, underbalanced, that is pressure from the mud column that is less than the formation, or over balanced, pressure from the mud column is greater than the formation. The downhole environment requires the use of fluids and pressure balance to prevent the flow of fluids into or out of the formation being drilled. Additional techniques require a rotating head at the surface to prevent the downhole fluids from flowing up the wellbore. This allows for a reduced pressure on the formation to prevent damage. In this method, utilizing the AST shown in FIG. 9, differential pressure from the centerline flow to the annulus to power the hydraulic cylinders 96 in the extension area 90 and retraction area 92 produces movement of the AST.
The method of using the AST includes the driller running the bottom hole assembly with the AST into the hole and start drilling with a preferred set of drilling parameters including weight-on-bit, drilling fluid circulation rate, drill string torque and rotation rate (rpm) of the drill string. The sensors 84 monitors these conditions and signals to the electronics 82 to actuate the assembly to manipulate weight-on-bit. The AST receives real-time measured drilling parameters which may include weight-on-bit, torque, rpm, differential pressure or other parameters such as formation changes. With the instantaneous input computed within the electronics through a series of pre-programmed algorithms, the time averaged input is updated and compared to recent drilling history inputs or pre-programmed thresholds. The comparison of the updated input to the previous time averaged input determines if the weight-on-bit is appropriate (unchanged, increasing, or decreasing). A command is then sent to adjust the weight-on-bit appropriately thus optimizing the rate of penetration for the current drilling conditions. The drilling process then adjusts via the drill string to the new conditions of altered weight-on-bit. This feedback loop continues throughout the drilling of the hole section and may require little or no intervention of the driller.
The AST 80 operates using the several pre-programmed thresholds that define an optimal drilling envelope. The envelope demarcates an upper limit and a lower limit at which the tool will response to maintain the optimal drilling envelope. For example, a torque sensor is positioned within the sensor section sensing torque as the trigger and the tool responds by extending, locking or retracting as described herein. As drilling conditions change and the motor torque exceeds the optimal operating range, the AST's upper torque threshold is exceeded and the AST retracts and reduces weight-on-bit. On surface, an increase then rapid decrease in pressure signals the driller or the AST has functioned to reduce rate of penetration. The AST continues to retract until torque drops below the lower threshold setting. At this point the AST will extend until the torque increase to above the lower threshold, or inside the optimal drilling envelope. The tool locks and monitors the, current drilling input. During normal drilling conditions, when the torque input is inside the envelope or between the thresholds, the AST is hydraulically locked and structurally rigid to prevent the AST from applying excessive weight-on-bit and pushing the motor outside of the optimal operating range.
As another example, the AST can contain sensors to measure vibration, weight-on-bit or differential pressure. The electronics 82 and the AST are capable of processing multiple inputs and have the ability to compute complex algorithms based upon these inputs. The use of electronics allows the AST to be scalable into the advancement in downhole communications. The AST may utilize one or more sensor inputs and multiple threshold settings to maintain the optimal drilling envelope for maximum drilling efficiency. The sensor inputs may be physically installed on the AST or communicated to the AST through a variety of other methods or tools located within the bottom hole assembly. The processor contained within the electronics can include algorithms for establishing the optimal drilling envelope through the inputs of the one or more sensors.
By incorporating the AST 80 of FIG. 9 into a bottom hole assembly provides for a self-contained, automatic feedback, real-time downhole assembly method of operation that provides optimization of the rate of penetration via the manipulation of weight-on-bit while preventing the downhole parameters from exceeding the operational limitations of the bottom hole assembly components. Similarly, the method eliminates stick-slip to reduce drilling cost.
The method includes the initial step of setting up the AST which includes the upper threshold limit and the lower threshold limit to enhance the operating envelope of the mud motor or drilling system. Set-up includes programming the processor in the AST by inputting the upper torque threshold, lower torque threshold and pause duration from event to tool reaction. Determination of the set points is established by other bottom hole assembly and operating parameters such as downhole motor performance and bottom hole assembly elements. Next, the tool monitors torque. The drill string torque below the AST to the bit is continuously monitored by the AST torque sensor and the sensor has been designed to eliminate the effects of bending, differential pressure and weight-on-bit. In this step the sensor continuously monitors and processes the torque and in a second step determines if the threshold limits have been exceeded for a specified duration which requires intervention. The processor uses a sophisticated algorithm to determine the tool actions based on pre-programmed threshold limits, values and set points. Enhanced firmware requires advance analog and digital filtering to negate the effects of high frequency sensor spikes derived from the drilling environment. In a third step the sensor algorithm determines the appropriate action, the processor communicates to the electrical motor 86 to position the valves 88 in the precise location for the required hydro-mechanical tool response. In a fourth step a communications loop to the electric motors provides feedback to resolve the motor actuation and verify position. In a fifth step all sensor information and motor actuations are recorded, including accurate downhole torque measurements to optimize the AST set-up and enhance future drilling operations.
Based upon this information the AST can be operated in one of three operating modes. First a method for operating the AST in a downhole extension mode occurs when downhole torque decreases below the lower threshold limit beyond the specified time duration. In a second step, the AST signals a motor sequence to place the tool in extend mode, a communication loop to the electric motors is fed back to resolve the motor actuation, verify position and record movement. In a third step, the two position, four-way valve directs pressurized fluid flow into the hydraulic cylinder volumes resulting in the regulated telescopic extension of the AST. In a fourth step, the valve position vents the volume of fluid retained in the retraction side of the pistons. In a fifth step, the extension results in weight-on-bit decrease of the drill string by generating a force vector in the downhole direction. The AST tool will extend until it reaches the end of stroke or a threshold limit is exceeded. The magnitude of the vector is a function of the AST tool piston area and centerline pressure of the drilling system as realized at the AST tool locations. As seen on surface, the result is an increase in weight-on-bit and centerline pressure.
Operating in a second mode of operation for the AST which is a downhole hydraulic lock, in a first step, the downhole torque is within the range of the lower threshold limit and the upper threshold limit for a specified time duration. In a second step, the AST signals a motor sequence to place the tool in lock mode, a communication loop to the electric motors is fed back to resolve the motor actuation, verify position and record movement. In a third step, the two position, four-way valve is positioned to prevent pressurized fluid flow into or out of the hydraulic cylinder volumes, resulting in the hydraulic lock of the AST. This condition results in a complete weight-on-bit transfer from the drill string to the bit. As seen on surface, the result shows normal drilling parameters and that current surface operating settings have not exceeded downhole operating limits.
In a third mode of operation, which is downhole retraction for the ASD, in a first step the downhole torque increases above the upper threshold limit beyond the specified time duration. In a second step, the AST signals a motor sequence to place the tool in retract mode, a communications loop to the electric motors is fed back to resolve the motor actuation, verify position and record movement. In a third step, the two positon, four-way valve directs pressurized fluid flow into the hydraulic cylinder volumes resulting in the telescopic collapse of the AST. In a fourth step, the valve vents the volume of fluid retained in the extension side of the pistons. In a fifth step, the collapse results in weight-on-bit reduction of the drill string by generating a force vector in the uphole direction. The AST will retract until it reaches the end of stroke or a threshold limit is exceeded. The magnitude of this vector is a function of the AST piston area and centerline pressure of the drilling system as realized at the AST location. As seen on surface, the result is a rapid decrease in weight-on-bit and centerline pressure which provides a signal that current surface operating settings have exceeded downhole operating limits.
Although the invention has been described in connection with oil well drilling and use with a coiled tubing, the invention has other applications, including jointed pipe, or rotary drilling; in operations besides drilling where it is useful to retract a tool at high pressures; or where adjustments to the drill bit are made to keep contact with the formation or to pick up the bit completely off the formation. The invention also may be used with other pressure-inducing tools such as high pressure jetting tools.
The anti-stall tool cylinders and valves may be manufactured from various corrosion-resistant materials including tungsten carbide, Inconel, high strength nickel alloyed steel such as MP35, beryllium-copper, and the like.
This method can be incorporated into multiple drilling control methods including both manual and automatic driller type rigs. This is to include control by rate of penetration, weight on bit, mechanical specific energy as well as combinations thereof.

Claims

what is claimed is:

1. A method of operating a bottom hole assembly in real-time including a drill pipe, an anti-stall tool, a motor and a drill bit comprising the steps of:

entering an upper torque threshold and a lower torque threshold as operating parameters for the bottom hole assembly into the anti-stall tool;

continuously sensing torque of the bottom hole assembly by a torque sensor in the bottom hole assembly,

electronically determining if the sensed torque has exceeded the upper torque threshold or the lower torque threshold for a specified duration of time requiring intervention by the anti-stall tool; and

communicating instructions to the anti-stall tool for proper hydro-mechanical adjustment of the anti-stall tool.

2. The method of claim 1 further comprising the step of adjusting weight on the drill bit to maximize a rate of penetration of the drill bit or reduce stick-slip.

3. The method of claim 1 further comprising the step of:

monitoring torque in a communications loop until the sensed torque has not exceeded the upper torque threshold or the lower torque threshold; and

recording the sensed torque and hydro-mechanical adjustments of the anti-stall tool.

4. The method of claim 1 wherein when the sensed torque decreases below the lower threshold limit for the specified duration of time, the step of communicating instructions to the anti-stall tool for proper hydro-mechanical adjustment includes signaling a motor sequence of the anti-stall tool to place the anti-stall tool in an extend mode.

5. The method of claim 4 further comprising the step of initiating a communications loop to feed back to a processor in the anti-stall tool to resolve motor actuation, verify position and record movement.

6. The method of claim 4 wherein the step of communicating instructions includes signaling a valve in the anti-stall tool to direct pressurized fluid flow into hydraulic cylinder volumes of the anti-stall tool to extend telescopic pistons.

7. The method of claim 1 wherein when the sensed torque remains within a range of the upper torque threshold and the lower torque threshold for the specified duration of time, the step of communicating instructions to the anti-stall tool for proper hydro-mechanical adjustment includes signaling a motor sequence for the anti-stall tool to place the anti-stall tool in a lock mode.

8. The method of claim 7 further comprising the step of initiating a communications loop to feedback to a processor in the anti-stall tool to resolve motor actuation, verify position and record movement.

9. The method of claim 7 wherein the step of communicating instructions include signaling to a valve to prevent pressurized fluid into or out of hydraulic cylinder volumes of the anti-stall tool to hydraulically lock the anti-stall tool.

10. The method of claim 1 wherein when the sensed torque increases above the upper torque threshold for the specified duration of time, the step of communicating instructions to the anti-stall tool for proper hydro-mechanical adjustment includes signaling a motor sequence of the anti-stall tool to place the anti-stall tool in a retract mode.

11. The method of claim 10 further comprising the step of initiating a communications loop to feedback to a processor in the anti-stall toll to resolve motor actuation, verify position and record movement.

12. The method of claim 10 wherein the step of communicating instructions include signaling a valve in the anti-stall tool to direct pressurized fluid into hydraulic cylinder volumes of the anti-stall tool to retract telescopic pistons.

13. A method of operating a bottom hole assembly to provide optimization of rate of penetration by manipulation of weight on a drill bit to prevent the bottom hole assembly from exceeding operational limits comprising the steps of

operating a self-contained, automatic feedback, real-time downhole tool to sense at least one of torque, weight-on-bit, vibration, differential pressure or rpms of the bottom hole assembly to generate a sensed signal;

operating a computerized downhole computation device within the downhole tool to determine whether the sensed signal is within a pre-programmed operating range; and

adjusting a controlled downhole weight modification section of the downhole tool depending on the determination of the computerized downhole computation device.

14. The method of claim 13 wherein the downhole tool is an anti-stall tool.

15. The method of claim 13 wherein the computerized downhole computation device is a pre-programmed processor on the anti-stall tool.

16. The method of claim 13 wherein the step of adjusting the control downhole weight modification section includes at least one of a tool extension mode, to a lock mode and to a retraction mode.

17. The method of claim 13 wherein the downhole tool is pre-programmed with upper and lower operating thresholds.