Abstract: A pressure compensation system for a wellbore instrument coupled to a drill string includes a shaft rotatably mounted with respect to an instrument housing. A lubrication chamber included in the instrument has at least one bearing for rotatably supporting the shaft. The lubrication chamber includes a face seal coupled on one face to the shaft and on another face to the housing. A pressure compensator establishes hydraulic communication between the lubrication chamber and the interior of the drill string. The compensator includes a barrier to fluid movement between the lubrication chamber and the interior of the drill string. The barrier enables pressure communication therebetween. The compensator includes a pressure communication port extending between the barrier and a portion of the shaft exposed to the interior of the drill string.

Abstract: A pressure compensation system for a wellbore instrument coupled to a drill string includes a shaft rotatably mounted with respect to an instrument housing. A lubrication chamber included in the instrument has at least one bearing for rotatably supporting the shaft. The lubrication chamber includes a face seal coupled on one face to the shaft and on another face to the housing. A pressure compensator establishes hydraulic communication between the lubrication chamber and the interior of the drill string. The compensator includes a barrier to fluid movement between the lubrication chamber and the interior of the drill string. The barrier enables pressure communication therebetween. The compensator includes a pressure communication port extending between the barrier and a portion of the shaft exposed to the interior of the drill string.

Abstract: A modulated bias unit, for controlling the direction of drilling of a rotary drill bit when drilling boreholes in subsurface formations, comprises a number of hydraulic actuators spaced apart around the periphery of the unit. Each actuator comprises a movable thrust member which is hydraulically displaceable outwardly and a pivotally mounted formation-engaging pad which overlies the thrust member. An inlet passage supplies fluid under pressure to the chamber, and an outlet passage delivers fluid from the chamber to a lower pressure zone. A selector control valve modulates the fluid pressure supplied to each actuator in synchronism with rotation of the drill bit so that, as the drill bit rotates, each pad is displaced outwardly at the same selected rotational position so as to bias the drill bit laterally and thus control the direction of drilling.

Abstract: A modulated bias unit, for controlling the direction of drilling of a rotary drill bit when drilling boreholes in subsurface formations, comprises a number of hydraulic actuators spaced apart 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. A selector control valve modulates the fluid pressure supplied to each actuator in synchronism with rotation of the drill bit so that, as the drill bit rotates, each movable thrust member is displaced outwardly at the same selected rotational position so as to bias the drill bit laterally and thus control the direction of drilling. The control valve is a disc valve comprising two relatively rotating elements having contiguous surfaces formed of polycrystalline diamond.