STEERABLE ROTARY DRILLING SYSTEMS

摘要

A system for controlling the rotation of a roll stabilisable control unit in a steerable rotary drilling assembly comprises an instrument carrier rotatably mounted on a support connected to the drill string. A first rotatable impeller is mounted for rotation by a flow of drilling fluid over the impeller and is coupled to the instrument carrier so as to transmit a torque to it. Sensors carried by the instrument carrier sense the relational orientation of the instrument carrier and produce a control signal indicative of its rotational orientation, and the torque applied to the instrument carrier by the impeller is controlled, at least partly in response to said signal, so that the instrument carrier can, for example, be roll stabilised if required. A second rotatable impeller is coupled to the instrument carrier for transmitting to it a second torque, which may also be controlled, in the opposite direction to the torque transmitted by the first impeller. The provision of two opposed impellers allows the rotation of the control unit to be controlled over a greater range than is possible with a single impeller.