Applications of sonics and ultrasonics in geophysical prospecting

This paper describes some of the applications of acoustic techniques that are used in the exploration and production of hydrocarbons from underground reservoirs. Borehole sonic measurements (0.5 to 20 kHz) probe rock formations with depths of investigation extending up to a few meters, whereas ultrasonic measurements (80 kHz to 2.5 MHz) provide images of the borehole wall, casing corrosion monitoring, and evaluation of the annulus between casing and borehole. Newer applications of sonic measurements are in the estimation of formation anisotropy that may be caused by intrinsic microlayerings or thin beddings, aligned fractures, and tectonic stresses transverse to the borehole axis. The section on ultrasonic measurements covers open-hole imaging of breakouts and fractures intersecting the borehole, casing integrity inspection, and evaluation of cement sheath placed to support the casing and ensure isolation of hydrocarbon-bearing from water-bearing zones. These measurements are today carried out with pulse-echo techniques using travel time and amplitude processing for the first two applications and amplitude decay estimation of a casing resonance for the latter. Recent research topics include improvements in interpretation methodologies to extract more value from existing measurements as well as use of new transducer designs to remedy to the limitations of current cement evaluation techniques.