Abstract: A while drilling system and method for determining downhole parameters is provided. The system includes a retrievable while drilling tool positionable in a downhole drilling tool, a sensor chassis and at least one sensor. The while drilling tool is positionable in the downhole drilling tool and has a first communication coupler at an end thereof. The sensor chassis is supported in the drilling tool. The sensor chassis has a second communication coupler at an end thereof for operative connection with the first communication coupler. The sensor is positioned in the chassis and is adapted to measure internal and/or external parameters of the drilling tool. The sensor is operatively connected to the while drilling tool via the communication coupler for communication therebetween. The sensor may be positioned in the while drilling tool and retrievable with the drilling tool. Preferably, the system is operable in high temperature and high pressure conditions.

Abstract: A choke device for controlling fluid flow, particularly in a modulated bias unit, drill bit or other item downhole drilling component, comprises a passage for the flow of fluid, a choke aperture separating an upstream portion of the passage from a downstream portion thereof, and an impingement surface located in the downstream portion of the passage opposite and spaced from the choke aperture, so that fluid flowing through the choke aperture impinges on the impingement surface. The impingement surface is formed from superhard material, such as polycrystalline diamond, and may comprise the front facing table of a two-layer polycrystalline diamond compact of the kind used as cutting elements in drag-type drill bits.

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.