STEERABLE ROTARY DRILLING SYSTEMS

摘要

A system for maintaining a downhole instrumentation package in a roll stabilised orientation with respect to a drill string comprises an instrument carrier which is mounted within a drill collar for rotation about the longitudinal axis of the collar. An impeller is mounted on the instrument carrier so as to rotate the carrier relatively to the drill collar as a result of the flow of drilling fluid along the drill collar during drilling. The torque transmitted to the instrument carrier is controlled, in response to signals from sensors in the carrier which respond to the rotational orientation of the carrier, and input signals indicating the required roll angle of the carrier, so as to rotate the carrier in the opposite direction to the drill collar and at the same speed, so as to maintain the carrier non-rotating in space and hence roll stabilised. The torque may be controlled by controlling a variable coupling between the impeller and the carrier and/or by controlling a brake between the carrier and the drill collar.