US Patent 7152696 Method and control system for directional drilling

A method and control system for directional drilling are described. A drill string motor is commanded to rotate at a constant speed in a forward direction and the constant speed in a reverse direction for a first duration and a second duration, respectively, for at least one oscillation cycle. The difference between an averaged absolute angle of the drill string and a target rotation angle for the drill string is maintained near zero by adjusting the length of the durations as necessary. The target rotation angle can be changed based on measurement while drilling data obtained during drilling operations. Advantageously, friction between the drill string and bore hole is reduced, leading to an increase in the drilling penetration rate.