Glossary

Acoustic borehole image (borehole televiewer)

A class of borehole imaging devices that work on the principle of acoustic signal return sourced from a rotating sonde; in effect, a down hole ultrasound device. A rotating transducer, within a centralised assembly, emits and records a high frequency acoustic signal, and as the tool is drawn up the borehole collects a spiral of data from around the entire borehole wall.

The tool gathers measurements of travel time and return signal amplitude. Travel time is the period from the emission to collection at the sonde of the signal and is a function of drilling mud properties and hole size. Amplitude is the reflected signal amplitude that is a function of drilling mud, hole size, wall microrugosity and wellbore acoustic impedance contrasts.

These data can be converted to images and oriented, allowing interpretation. Amplitude data usually provides better quality images than the travel time data which reveals detailed borehole shape. The major advantage of televiewers is that they function in resistive (oil-based) drilling muds, unlike many dipmeters and resistivity imaging tools, and through sections that would often be resistivity saturated e.g. evaporites.

PRENSKY, S. E. 1999. Advances in borehole imaging technology and applications. In: LOVELL, M. A., WILLIAMSON, G and HARVEY, P. K. (eds.). Borehole Imaging: Applications and Case Histories. Geological Society Special Publication No. 159, 1-43.

LUTHI, S. M. 2000. Geological Well Logs. Springer, Berlin, p373.

RIDER, M., 1996. The Geological Interpretation of Well Logs, Whittles Publishing, Caithness, p280.

PAILLET, F., BARTON, C., LUTHI, S., RANBOW, F. and ZEMANEWK, J. 1990 (eds.). Borehole Imaging, SPWLA Reprint Volume, Houston Texas, p472.

Acoustic image principles.