Abstract: An apparatus for selectively activating a downhole Measurement While Drilling (MWD) tool, so as to prolong the life of the MWD battery and improve function of the MWD flow restrictor pilot valve assembly, includes a switch actuator responsive to pressure differential disposed incorporated within a fluid sealed pressure chamber which also incorporates a pilot valve assembly for activating the flow restrictor for causing mud pulse signals. The switch actuator comprises upstream and downstream bellows sealing a fluid filled reservoir, with a push-action switch within the upstream bellows, isolated from the drilling fluid. Ports expose the upstream and downstream bellows to longitudinally spaced points in the flowstream, the upstream ports providing flow-through cleaning of the upstream bellows.

Abstract: An oil-field tool for use in combination with a MWD tool, for deployment and retrieval of a MWD tool through a drill string, and, for rigid continuously self-adjusting, centralization of the MWD tool during drilling, includes: housing having a tapering nose; slidable shaft having a flared portion; extendable fingers pivotably attached to the slidable shaft; means for releasable attachment to a workstring; and, means for attachment to a MWD tool.Typically, the housing of the invention is attached to a MWD tool while at the surface and the combined apparatus is lowered through the drill string by wireline releasably attached to the slidable shaft. During lowering, the weight of the housing and MWD tool extends the slidable shaft, positioning the extendable fingers above the tapering nose of the housing, thereby retracting the fingers.

Abstract: A downhole signal generating mud pulser has a poppet and orifice signal valve to variably resist the drilling fluid stream. The poppet is upstream of the orifice and is moved by a piston in fluid communication with opposite flow related sides of the signal valve such that more pressure drop across the valve applies more piston force to open the valve. The poppet is spring biased toward the orifice and the piston force and spring balance when a preselected operating pressure exists. A servo valve controls flow in a by-pass loop to apply additional pressure to the piston to create a signal pulse when open. The servo valve is urged closed by flow in the servo loop and the closing is retarded by a dashpot to determine signal duration. The servo valve is spring biased to open and is automatically latched closed by a latch that responds to a solenoid actuated to release the servo valve.