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A mechanical oscillator driven by drilling fluid flow pumped down a drill string bore is combined with sensors and controls to produce a downhole drilling fluid pressure pulse generator for use in drill strings for Measurement While Drilling (MWD) pipe bore telemetry. A fluid flow responsive valve d

A mechanical oscillator driven by drilling fluid flow pumped down a drill string bore is combined with sensors and controls to produce a downhole drilling fluid pressure pulse generator for use in drill strings for Measurement While Drilling (MWD) pipe bore telemetry. A fluid flow responsive valve designed to be put in continual motion by fluid flow is associated with a motion stop lock so that, on release, a discrete digital fluid pressure change is generated. A downhole instrument package controls the lock release in a timed sequence, so that a series of pressure changes represent information to be decoded at the earth surface to determine downhole parameters sensed by the instrument package. The active elements of the downhole system may be installed in the drill string or lowered as a shuttle package down the drill bore. The fluid pressure pulse generating apparatus can be classified as a fluid flow excited oscillator or an auto-cycling pulse generator. Controls are provided to enable the auto-cycling valve to respond to electric signals from downhole instruments to generate code messages by digital pulse, change-of-state in valved flow resistance and frequency change in standing wave pressure pulses.

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A fluid flow resistance change signal generator for transmitting signals along a moving fluid column in a drill string bore from a downhole location in a well, the signal generator comprising: (a) a body adapted to function as a length of drill string, having means at each end to attach with fluid t

A fluid flow resistance change signal generator for transmitting signals along a moving fluid column in a drill string bore from a downhole location in a well, the signal generator comprising: (a) a body adapted to function as a length of drill string, having means at each end to attach with fluid tight engagement to a continuing drill string, and a drilling fluid channel extending therethrough; (b) a resonant signal valve in said body, adapted to change resistance to the flow of drilling fluid in said drilling fluid channel, said signal valve adapted to oscillate between a first position corresponding to less flow resistance and a second position corresponding to more flow resistance in response to fluid flow rate oscillations of fluid flowing in said drilling fluid channel, the movement of said signal valve responsive to bias force arranged to urge said signal valve toward said second position and responsive to piston force arranged to urge said signal valve toward said first position, said piston force produced by a piston operatively connected to move said valve and arranged to respond to fluid pressure differential across said signal valve; and (c) restraint means arranged to restrain said signal valve in said first position and to release said valve from said first position in response to signals from a downhole instrument.