Patent ID: 8439129
Filing Date: 2013-05-14
Classification: E21B

Abstract:
1. 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 hydraulically 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; a piston assembly slidably disposed in the outer housing for applying axial forces in either a downhole direction or a reverse direction to adjust weight-on-bit (WOB) while drilling, said internal passageway extending through the piston assembly; and 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; the hydraulic control valve system including: wherein the hydraulic control valve system operates in an active stage for sensing the working pressure in the tubing and supplying the hydraulic control fluid to the piston assembly to apply an axial force in the downhole direction to increase WOB when the sensed working pressure is below a first set point, in the active stage the pilot valve opens in response to receiving the first pilot signal to supply hydraulic control fluid to the piston assembly through a pressure control valve which, in an open position thereof, controls the flow of hydraulic control fluid to the piston assembly to increase WOB; wherein the hydraulic control valve system operates in a passive stage for sensing the working pressure in the tubing and shutting off the hydraulic control fluid supplied to the piston assembly for maintaining WOB via the drilling fluid in the tubing, independent of the piston assembly, when the sensed working pressure is within a desired working pressure range of the drive motor, in the passive stage the pressure control valve switches from the open position to a closed position when the sensed working pressure reaches a preset pressure value within the desired working pressure range, to stop the supply of hydraulic control fluid to the piston assembly and hydraulically lock the piston assembly in a passive state; and wherein the hydraulic control valve system operates in a reverse stage for sensing the working pressure in the tubing and reversing the flow of the hydraulic control fluid supplied to 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 a second set point, in the reverse stage the second pilot signal sent from the sequence valve to the pilot valve reverses the supply of hydraulic control fluid to the piston assembly to decrease WOB, in which the sequence valve closes when sensed working pressure diminishes to a level below the preset upper limit, and in which the vent valve is maintained in a closed position until the first pilot signal is sent to the pilot valve to initiate the active stage.