Patent ID: 7719439
Filing Date: 2010-05-18
Classification: E21B

Abstract:
1. A downhole measurement-while-drilling rotary pulser comprising: a windowed restrictor movable between an open position which permits mud flow through a fixed housing having a flow passage and a restricted position which restricts mud flow through the fixed housing having the flow passage, the windowed restrictor powered between the open position and the restricted position by a reversible electric motor, wherein the windowed restrictor is movable between the open position and the restricted position in a reciprocating rotary motion relative to the fixed housing, and wherein the fixed housing is held stationary and the windowed restrictor is rotatable, driven in rotation by the motor; and a controller to control the reversible electric motor and to sense the position of the windowed restrictor relative to the fixed housing, wherein the position of the windowed restrictor is adapted to be sensed when the mud flow through the flow passage is restricted, and wherein an amount and direction of rotations of the motor from the position are counted and stored by the controller, wherein the controller senses the position of the windowed restrictor by sensing whether movement of the windowed restrictor is impeded, wherein the controller counts a number of rotations of the motor until the windowed restrictor is impeded and compares the number of rotations to an expected number of rotations to determine the position of the windowed restrictor with respect to the fixed housing, and wherein the expected number of rotations is preset to allow a predetermined rate of mud flow past the windowed restrictor when the windowed restrictor is moved away from the fixed housing by the preset expected number of rotations and wherein the sensed position of the windowed restrictor is calibrated as a fully closed position of the windowed restrictor in controlling the windowed restrictor's travel during operation to avoid excess collision or frictional wear between the windowed restrictor and the windowed restrictor stop.