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.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)[0001]This application claims priority to U.S. Provisional Application No. 61 / 405,066, filed Oct. 20, 2010, which is incorporated herein by reference.BACKGROUND[0002]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) for controlling weight-on-bit during drilling operations.[0003]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...

AI Technical Summary

Benefits of technology

[0014]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

Problems solved by technology

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 press

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