Theoretical Study of Tool-Face Disorientation Mechanisms During Slide Drilling and Correction by Surface-Rotation Pulses

Abstract

Summary Tool-face control is an important issue when drilling directional wells with steerable motors. Although extensive knowledge about tool-face orientation is available, the mechanisms of tool-face disorientation during slide drilling are not completely understood. Surface-rotation pulses can correct tool-face orientation (Maidla and Haci 2004), but the underlying mechanism, in our view, remains unclear. This paper proposes a drillstring model to analyze the mechanisms underlying tool-face disorientation and correction. Our drillstring model is based on the finite rigid-body assumption with a mixed friction model that incorporates Stribeck's friction curve. The simulation results indicate that tool-face hysteresis caused by the difference in the higher loading rate and lower unloading rate of reactive torque is an essential factor in tool-face disorientation. In addition, a harder formation is more prone to inducing tool-face disorder. The process of tool-face correction can be divided into three stages, and the position of the vanishing point of reactive torque determines the effectiveness of the surface-rotation pulse. The tool face turns clockwise only if the applied rotation pulse drives the vanishing point of reactive torque downward to the bit. The simulation results and analysis are useful for understanding drillstring behavior during slide drilling and further improving the efficiency of tool-face control.