Ultrasonic measurement apparatus

Abstract

Pulse echo apparatus and methods are disclosed for measuring characteristics of a borehole while it is being drilled. A component of a bottomhole assembly, preferably a drilling collar, is provided with one or more ultra-sonic transceivers. A pulse echo sensor of the transceiver is preferably placed in a stabilizer fin of the collar, but may also be placed in the wall of the collar, preferably close to a stabilizing fin. Electronic processing and control circuitry for the pulse-echo sensor is provided in an electronic module placed within such collar. Such pulse echo apparatus, which preferably includes two diametrically opposed transceivers, generates signals from which standoff from a borehole wall may be determined. A method and apparatus are provided for measuring standoff and borehole diameter in the presence of drilling cuttings entrained in the drilling fluid. In a preferred embodiment, such signals are assessed by the electronic processing and control circuity to determine if gas has entered borehole. Three methods and apparatus are provided for such gas entry determination. The first relies on measurement of sonic impedance of the drilling fluid by assessing the amplitude of an echo from an interface between the drilling fluid and a delay-line placed outwardly of a ceramic sensor. The second relies on measurement of drilling fluid attenuation of a borehole wall echo. The third relies on measurement of the phase of oscillations of echoes to identify large gas bubbles entries. The pulse-echo sensor includes a sensor stack including a backing element, a piezo-electric ceramic disk, and a delay-line.