Mud operated pulser

Abstract

A poppet and orifice mud pulser assembly is disclosed for use in an MWD system. The mud pulser is capable of generating pressure pulses in the column of drilling mud of various amplitudes to increase the data rate of the mud pulse telemetry system. The mud pulser includes a piston assembly that positions the poppet with respect to the orifice. The piston assembly comprises part of a by-pass conduit which defines a mud flow path around the orifice. Mud flow in the piston assembly generates a force tending to shut the poppet, because the surface area of the piston A.sub.2 is greater than the surface area of the poppet A.sub.1. Mud flow through the conduit (and thus through the piston) tends to force the poppet into a closed position because the force on the piston is greater than the force on the poppet, because of the greater surface area of the piston. A pilot valve is provided to enable and disable flow through the conduit, thus allowing the poppet to open and close. Other amplitude level signals are generated by permitting the poppet to partially open through the implementation of a plurality of parallel pressure relief valves, each of which is set with a different pressure relief value. The pressure relief valves are selected by an associated selector valve. Selection of a pressure relief valve prevents pressure within the piston from exceeding the pressure relief valve, which causes the poppet to partially open, thereby changing the pressure pulse amplitude generated. Alternatively, a motor operated pressure control valve may be used to vary the amplitude of the pressure pulse, thereby permitting the generation of waveforms of any shape.