New Developments in Acoustic Borehole Imaging
David S. Epps, Robert W. Garland, Brian White
Geologists want to be able to "see" the formation in order to improve interpretations of depositional environment, net pay thickness, textural characteristics, as well as other desirable features. Many techniques have been employed to provide an image of the borehole, with varying levels of acceptance. Borehole imaging techniques may be classified by method of investigation--eyes of resistivity, eyes of video, or eyes of acoustics. This work addresses the acoustic method of borehole imaging, usually called the borehole televiewer (BHTV). The acoustic borehole televiewer, incorporating improved transducers, electronics, recording sensors, and well-site computers, provides for the reliable identification of textural features, vugs, fractures, dipping formations, and very th n beds.
Improvements in transducer design and construction enable the BHTV to generate stronger acoustic signals, producing higher reflected amplitudes. The BHTV eliminates the need for a protective window, allowing the transducer to be exposed to the mud and eliminating an acoustic impedance boundary, which further improves signal strength. It is now possible to log BHTV in weighted muds, oil emulsions, and larger diameter boreholes.
Continuous sampling around the borehole provides a more complete record for identifying formation features. Automatic gain control allows acquisition of borehole images even in out-of-round boreholes or when the tool is eccentered. Digital signal recording allows playback of tool signals in one of several formats. A scrolling video monitor and continuous hard-copy recorder permit realtime image presentation for review and quality control.
AAPG Search and Discovery Article #91031©1988 AAPG Eastern Section, Charleston, West Virginia, 13-16 September 1988.