Analysis of Straightening Behavior of the Electronic Automatic Vertical Drilling Tool

Automatic vertical drilling tools are the key technologies to achieve vertical drilling in deep & super-deep wells, and are also the core for deviation control and well straightening. Based on a self-development automatic vertical drilling tool with electronic closed loop control system (EVDT) designed by the research team, straightening behavior is analyzed in this paper. The mechanical analysis model of the BHA (bottom hole assembly) equipped with the EVDT is developed by using the beam-column theory. The formulas are deduced for calculating the bit lateral forces, bit tilt angle and trend angle of deviation. The influence laws of the push-out force, WOB (weight on bit), deviation angle and wellbore curvature on the straightening behavior of drilling tools are discussed. The results show that when the counterforce of the push-out force is pointing to the low side of borehole wall, the bit lateral force is inclination-drop force and the drilling tendency is straightening. The absolute values of bit lateral force and trend angle of deviation decrease with the increase of WOB but increase with the increase of push-out force, deviation angle and wellbore curvature. The push-out force and wellbore curvature have great influence on both bit lateral force and trend angle of deviation. WOB has major influence on trend angle of deviation, but minor influence on bit lateral force. The deviation angle has little influence on both bit lateral force and trend angle of deviation. This provides basis for predicting and controlling wellbore trajectory.