Electrical controller for anti-stall tools for downhole drilling assemblies

Abstract

An anti-stall tool in an oil well drilling assembly that controls reciprocation of the drill bit by an electrical controller that alters weight-on-bit (WOB) depending upon measured downhole pressure or torque at the downhole motor. The electrical controller receives preset high and low working pressure limits for the downhole motor and activates a hydraulic valve system to keep the drill bit rotating by maintaining WOB during normal drilling operations, increasing WOB if sensed working pressure indicates that drill bit loading or torque is undesirably low, and reversing WOB by retracting the drill bit if excessive working pressure or torque is sensed.

1 . A spring-operated anti-stall tool adapted for use in a downhole assembly comprising a tubing for extending downhole; a drill bit carried on the tubing; and a drive motor adjacent the drill bit for rotating the drill bit during drilling operations; the spring-operated anti-stall tool carried on the tubing and positioned adjacent the motor for preventing stalling of the motor due to excessive loads on the drill bit, the anti-stall tool including at least one piston in a cylinder having a forward piston area and a reverse piston area, and an electrical controller which signals a hydraulic valve system for controlling operation of the piston, the forward piston area receiving hydraulic fluid to produce a force in the downhole direction, the reverse piston area containing a load spring adapted to apply an upward spring force on the piston, the electrical controller sensing operating pressure of the drive motor and setting a desired range of operating pressures for the motor, including an upper limit and a lower limit, the electrical controller adapted to: (1) supply hydraulic fluid to the forward piston area to increase force in the downhole direction to increase weight-on-bit (WOB) when operating pressure in the motor surpasses the lower limit, thereby compressing 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 can expand to push the tool uphole to retract the drill bit, to decrease WOB when operating pressure in the motor exceeds the upper limit; and (3) optionally lock the piston in a passive state when the motor is operating within its normal operating pressure range under the bias of the spring. 
     
     
         2 . Apparatus according to  claim 1  in which the electrical controller comprises an electronics package which receives a pressure-related input from a transducer to signal a motor to shift the hydraulic valve system. 
     
     
         3 . Apparatus according to  claim 1  in which the hydraulic valve system includes a pilot valve and a pressure control valve. 
     
     
         4 . Apparatus according to  claim 3  in which the pilot valve is a motor driven, two position, four way spool valve. 
     
     
         5 . Apparatus according to  claim 1  wherein the hydraulic valve system is a three position, four way pilot valve. 
     
     
         6 . Apparatus according to  claim 2  wherein the transducer is a torque transducer. 
     
     
         7 . Apparatus according to  claim 2  wherein the motor is an electric motor. 
     
     
         8 . Apparatus according to  claim 1  in which the electrical controller comprises an electronics package which receives a differential pressure input between a drilling annulus and a bore hole from a differential pressure transducer to signal a motor to shift the hydraulic valve system. 
     
     
         9 . Apparatus according to  claim 1  in which the electrical controller comprises an electronics package which receives a load transferred through the anti-stall tool input or a WOB input from a load cell to signal a motor to shift the hydraulic valve system. 
     
     
         10 . Apparatus according to  claim 1  in which the electrical controller comprises an electronics package which receives a rotational deceleration input from a torsional accelerometer to signal a motor to shift the hydraulic valve system. 
     
     
         11 . Apparatus according to  claim 1  in which the electrical controller comprises an electronics package which receives a change in voltage input to signal an electric motor to shift the hydraulic valve system. 
     
     
         12 . Apparatus according to  claim 1  in which the electrical controller comprises an electronics package which receives a change in electric current input to signal an electric motor to shift the hydraulic valve system. 
     
     
         13 . 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 drive motor for rotating the drill bit, and a spring-operated anti-stall tool adjacent the motor, the method comprising electrically sensing pressure in the motor, providing a range of operating pressures for the motor 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 by applying pressure to the anti-stall tool against the bias of a compression spring therein, when the low limit of operating pressure is sensed, (2) a reverse stage for providing a WOB force in the reverse direction via the compression spring bias, 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 drive motor is operating within the limits of its normal operating pressure range. 
     
     
         14 . The method according to  claim 13  in which electrically sensing pressure is by an electronics package receiving an input from a transducer. 
     
     
         15 . The method according to  claim 13  in which the anti-stall tool is operated in the active stage, reverse stage and passive stage by a hydraulic valve system responsive to a signal from an electrical controller. 
     
     
         16 . A downhole assembly adapted for anti-stall drilling operations, the downhole assembly including a drill bit, a drive motor for rotating the drill bit, a tubing for supplying drilling fluid to the drive motor, and an anti-stall tool positioned between the tubing and the drive motor for controlling the force applied to the drill bit during drilling operations, to thereby prevent the drill bit from stalling under load, the anti-stall tool comprising:
 an outer housing,   an internal passageway extending through the housing for transmitting drilling fluid from the tubing to the drive motor for rotating the drill bit,   an open loop controller contained in the outer housing, the open loop controller comprising:   a piston assembly slidably disposed in the outer housing, said internal passageway extending through the piston assembly,   the piston assembly comprising one or more hydraulic cylinders each having a piston therein for applying axial forces in the either the downhole direction or the reverse direction to adjust weight-on-bit (WOB) while drilling,   a hydraulic control valve system contained in the outer housing with an inlet for receiving a supply of hydraulic control fluid from the drilling fluid in the internal passageway, for supplying the hydraulic control fluid to the piston assembly to control WOB, and   an electronics package contained in the outer housing for controlling the hydraulic control valve system,   the hydraulic control valve system including:   an adjustable first set point for indicating a desired lower limit for hydraulic working pressure of the drilling fluid in the tubing, and an adjustable second set point for indicating a desired upper limit for hydraulic working pressure of the drilling fluid in the tubing, the first and second set points representing a desired working pressure range for the drive motor,   an active stage valve assembly for sensing the working pressure in the tubing and supplying the hydraulic control fluid to one or more of the cylinders contained in the piston assembly to apply an axial force in the downhole direction to increase WOB when the sensed working pressure is below the first set point,   a passive stage valve assembly for sensing the working pressure in the tubing and shutting off the hydraulic control fluid supplied to the piston assembly to hydraulically lock the piston assembly in a passive state for maintaining WOB when the sensed working pressure is within the desired working pressure range of the drive motor, and   a reverse stage valve assembly for sensing the working pressure in the tubing and reversing the flow of the hydraulic control fluid supplied to one or more of the cylinders contained in the piston assembly to apply an axial force in the reverse direction to retract the drill bit to decrease WOB when the sensed working pressure reaches or exceeds the second set point.   
     
     
         17 . The assembly according to  claim 16  in which the electronics package which receives a pressure-related input from a transducer in the outer housing to signal a valve motor in the outer housing to shift the hydraulic control valve system. 
     
     
         18 . The assembly according to  claim 16  in which the active stage valve assembly, the passive stage valve assembly and the reverse stage valve assembly comprises a pilot valve and a pressure control valve. 
     
     
         19 . The assembly according to  claim 18  in which the pilot valve is a two position, four way spool valve. 
     
     
         20 . The assembly according to  claim 18  in which the hydraulic control valve system is a three position, four way pilot valve. 
     
     
         21 . The assembly according to  claim 17  wherein the transducer is a torque transducer. 
     
     
         22 . The assembly according to  claim 17  wherein the valve motor is an electric motor. 
     
     
         23 . The assembly according to  claim 16  wherein the electronics package receives a differential pressure input between a drilling annulus and a bore hole from a differential pressure transducer to signal a motor to shift the hydraulic valve system. 
     
     
         24 . The assembly according to  claim 16  wherein the electronics package receives a load transferred through the anti-stall tool input or a WOB input from a load cell to signal a motor to shift the hydraulic valve system. 
     
     
         25 . The assembly according to  claim 16  wherein the electronics package receives a rotational deceleration input from a torsional accelerometer to signal a motor to shift the hydraulic valve system. 
     
     
         26 . The assembly according to  claim 16  wherein the electronics package receives a change in voltage input to signal an electric motor to shift the hydraulic valve system. 
     
     
         27 . The assembly according to  claim 16  wherein the electronics package receives a change in electric current input to signal an electric motor to shift the hydraulic valve system.