Camco Drilling Group Ltd. of Hycalog

Camco International (uk) Limited

Camco Drilling Group Limited of Hycalog

William C Motion

John D Barr

John M Clegg

Michael King Russell

A steerable rotary drilling system has a bottom hole assembly which includes, in addition to the drill bit, a modulated bias unit and a control unit, the bias unit comprising a number of hydraulic actuators around the periphery of the unit, each having a movable thrust member which is hydraulically displaceable outwardly for engagement with the formation of the borehole being drilled. Each actuator may be connected, through a control valve, to a source of drilling fluid under pressure and the operation of the valve is controlled by the control unit so as to modulate the fluid pressure supplied to the actuators as the bias unit rotates. If the control valve is operated in synchronism with rotation of the bias unit the thrust members impart a lateral bias to the bias unit, and hence to the drill bit, to control the direction of drilling. Pulses transmitted through the drilling fluid as a result of operation of the bias unit are detected and interpreted at the surface, or at a different location downhole, to obtain information regarding the operation of the bias unit or other parts of the bottom hole assembly. Data signals from downhole sensors may be arranged to modify the control and operation of the bias unit in such manner that the data is encoded as pulses generated in the drilling fluid by the bias unit.

Steerable rotary drilling systems

Steerable rotary drilling systems and method of operating such systems

A system for controlling the rotation of a roll stabilizable 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 rotational 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 stabilized 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.

System and method of controlling rotation of a downhole instrument

A steerable rotary drilling system comprises a bottom hole assembly which includes, in addition to a drill bit, a modulated bias unit and a control unit including an instrument carrier which is rotatable relative to the bias unit. The bias unit comprises a number of hydraulic actuators spaced apart around the periphery of the unit, each having a movable thrust member which is displaceable outwardly for engagement with the formation. Each actuator can be connected, through a rotatable control valve, to a source of drilling fluid under pressure, the control valve comprising a first part, rotatable with the instrument carrier, which cooperates with a second part which is rotatable with the bias unit. Means are provided to roll stabilize the instrument carrier so that relative rotation between the bias unit and instrument carrier, as the bias unit rotates, causes the valve to operate the actuators in synchronism with rotation of the bias unit so as to apply a lateral bias thereto. In order to neutralize or reduce the net bias applied to the bias unit the instrument carrier may be rotated in various modes instead of being roll stabilized, e.g., it may be rotated at a constant slow speed relative to the bias unit, or at a significantly faster rate so that the actuators do not have time to operate fully. The angular velocity of the carrier may also be varied during its rotation, according to various formulae, in order to vary the net bias. The net bias may also be varied by alternating different modes of carrier rotation.

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Prestbury, United Kingdom

William C Motion