Abstract: A downhole circulation tool includes: a housing having an axially extending delivery bore for conveying a drilling mud flow therethrough, the housing having a circulation port for discharging drilling mud; and a valve member rotatably disposed within the housing, the valve member comprising a through-flow channel and a circulation channel. The valve member is rotatable between a through-flow position in which the through-flow channel is arranged to convey drilling mud flow from an upstream portion of the delivery bore to the downstream portion of the delivery bore, and a circulation position in which the circulation channel is arranged to convey drilling mud from the upstream portion of the delivery bore to the circulation port to discharge drilling mud from the housing. There is also disclosed a downhole tool comprising a unidirectional drive mechanism, an actuation element for a downhole tool, and a method of operating a downhole tool.

Abstract: A downhole circulation tool includes: a housing having an axially extending delivery bore for conveying a drilling mud flow therethrough, the housing having a circulation port for discharging drilling mud; and a valve member rotatably disposed within the housing, the valve member comprising a through-flow channel and a circulation channel. The valve member is rotatable between a through-flow position in which the through-flow channel is arranged to convey drilling mud flow from an upstream portion of the delivery bore to the downstream portion of the delivery bore, and a circulation position in which the circulation channel is arranged to convey drilling mud from the upstream portion of the delivery bore to the circulation port to discharge drilling mud from the housing. There is also disclosed a downhole tool comprising a unidirectional drive mechanism, an actuation element for a downhole tool, and a method of operating a downhole tool.

Abstract: Within a longitudinally-extending main housing having a longitudinally-extending duct, an indexing mechanism comprises a mandrel within the duct and capable of longitudinal movement relative to the main housing; a cam sleeve rotatable with respect to the mandrel but constrained in terms of longitudinal movement with respect to the mandrel, the cam sleeve having an external surface provided with a groove in the form of a closed loop; a cam follower resiliently urged into the groove of the cam sleeve; a main spring tending to urge the mandrel in a first direction along the duct; and a fluid abutment face, on which, in use, fluid under pressure can act to tend to urge the mandrel in a second direction opposite to the first direction; the groove having ramps and associated steps thereby restricting relative movement of the cam follower with respect to the groove, to one direction progressively around the closed loop; the groove having a plurality of rest positions at which the cam follower can rest, depending on