Patent ID: 6089332
Filing Date: 2000-07-18
Classification: E21B

Abstract:
A method of operating a steerable rotary drilling system having a bottom hole assembly which includes a drill bit, a modulated bias unit and a control unit, the bias unit comprising a number of hydraulic actuators at the periphery of the unit for engagement with the formation of the borehole being drilled, each hydraulic actuator including a movable thrust member which is hydraulically displaceable, and each movable thrust member having an inlet passage for connection to a source of pressurised fluid, the pressure of fluid supplied to the movable thrust members from said source being controlled by valve means and the operation of the valve means being controlled by the control unit so as to modulate the fluid pressure supplied to the actuators as the bias unit rotates, the method including the step of deriving data signals from sensors in the bottom hole assembly, causing the control unit to control the bias unit in a manner dependent on said data signals from the sensors, detecting pulses transmitted through the fluid as a result of the consequent operation of the bias unit, and interpreting said pulses to derive therefrom data corresponding to said data signals from said sensors.