Patent ID: 7036580
Filing Date: 2006-05-02
Classification: E21B

Abstract:
1. Downhole apparatus for limiting rotation of a rotor for transmitting torque to a downhole tool relative to a stator associated with the said rotor, the downhole apparatus comprising a body within a bore of which a locking member is located so as to be movable between a first axial position relative to the body, in which the locking member is disengaged from a rotor so as to allow rotation of said rotor relative to said locking member, and a second axial position relative to the body, in which the locking member is engaged with said rotor so as to limit rotation of said rotor relative to said locking member, the apparatus further comprising means for limiting rotational movement of the locking member relative to the body when said locking member is located in said second axial position, wherein said locking member is movable from said first axial position to said second axial position by the application of a static fluid pressure to a differential area of said locking member, and means for selectively applying static fluid pressure to said differential area of said locking member.