ULTRASONIC STAND-OFF GAUGE

摘要

An ultrasonic stand-off gauge for use in measuring the instantaneous stand-off distance between the drill stem and the borehole wall while drilling. A primary transducer mounted on the drill collar sends and receives ultrasonic pulses between the drill collar and the borehole wall. A second, reference transducer mounted on the pressure barrel within the drill collar measures the sound speed of the drilling fluid. The drilling fluid flows through a conduit within the drill collar, where the reference transducer transmits a pulse through the drilling fluid in the conduit. The pulse from the reference transducer is reflected off an internal reflector mounted on the internal surface of the drill collar. Since the distance between the reference transducer and the reflector is known and constant, the sound speed of the drilling fluid is determined accurately. Electronic circuitry uses the sound speed measurement of the drilling fluid as determined by the reference transducer to calculate accurate values of stand-off distance. The electronic circuitry also compensates for the variations of pressure, temperature and other characteristics of the drilling fluid, as well as for variances in the standoff distance.