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.