Study of Steering Actuator of Static "point-the-bit" Rotary Steerable System

This paper describes a new steering actuator of static "point-the-bit" rotary steerable system (RSS). It works by controlling the bias unit to give the mandrel an offset to the original axis, so as to drive the drill bit deviation from the borehole axis. The bias force is provided by the hydraulic cylinder. The steering actuator introduces two universal joints, which effectively improved the conditions of bearing high alternating stress, and the build up rate of the system. Mandrel's static and kinematic equations were established on the basis of simplifying the mechanical structure model of the mandrel and bearing. Bending angle and deflection curve equation were derived and the position of the hydraulic cylinder was optimized. At last, the paper gives the control model of the bias unit.