Method of and apparatus for making near-bit measurements while drilling

Apparatus for use in making downhole measurements during the drilling of a well bore with a drill string having a motor included therein that rotates a drill bit, said motor having a power section that drives an output shaft that is coupled to the bit, comprising:

• sensor housing means including a tubular housing and a mandrel mounted inside said housing, said mandrel having a central bore through which a portion of said shaft extends;
• annular chamber means between said housing and said mandrel;
• sensor means mounted in said chamber means for making said downhole measurements and producing signals which are representative thereof;
• and acoustic means for transmitting bursts of acoustic waves which are representative of said signals upward along the drill string to a receiver that is located above said motor, each of said bursts having a predetermined member of oscillations and being time-spaced in a manner such that no oscillation appears between bursts.

A method of transmitting signals representing downhole measurements from a measurement sub positioned near the bit in a drill string that includes a mud motor assembly and a measuring and telemetry tool in the drill string above the mud motor assembly, comprising the steps of:

• making measurements with said measurement sub and producing a telemetry frame of encoded signals to drive a transmitter that produces bursts of sonic vibrations and couples said vibrations into the walls of the drill string, each of said bursts having a predetermined number of vibrations and being time-spaced in a manner such that no vibration appears between bursts;
• transmitting said vibrations up through the walls of the drill string to a receiver that is associated with said measuring and telemetry tool;
• sensing said vibrations with said receiver and producing output signals representative thereof;
• decoding said output signals to provide noise-avoidance;
• processing said output signals to convert them into digital signals;
• feeding said digital signals to said measuring and telemetry tool;
• and using said measuring and telemetry tool to transmit to the surface pressure pulses in the drilling mud that represent said digital signals, so that said pressure pulses can be detected and decoded at the surface to reproduce the said measurements for display and analysis.