Patent ID: 8146680
Filing Date: 2012-04-03
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, and a hydraulic controller contained in the outer housing, the 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 either the downhole direction or the reverse direction to adjust weight-on-bit (WOB) while drilling, 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: 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, in which the first set point is provided by a vent valve that monitors the working pressure in the tubing and is open when the working pressure is below an adjustable preset lower pressure limit, and in which the vent valve closes when the working pressure reaches the preset lower limit, sending a first hydraulic pilot signal to a pilot valve, and in which the second set point is provided by a sequence valve that monitors the working pressure in the tubing and is closed when the working pressure is below an adjustable preset upper limit but opens when the working pressure reaches the upper limit, sending a second hydraulic pilot signal to the pilot valve; 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, in which the active stage valve assembly includes the pilot valve which 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; 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 for maintaining WOB via the drilling fluid in the tubing, independent of the piston assembly, when the sensed working pressure is within the desired working pressure range of the drive motor, in which the passive stage valve assembly includes the pressure control valve which 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 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, in which the reverse stage valve assembly responds to the second pilot signal sent from the sequence valve to the pilot valve, to reverse 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.