METHOD AND APPARATUS FOR DETERMINING A GRANULARITY PROPERTY OF A SUBSURFACE FORMATION AROUND A BOREHOLE

摘要

Techniques for a broad band high frequency acoustic investigation of a subsurface formation around a borehole are described utilizing a range of acoustic frequencies selected to produce detectable acoustic backscatter from grains within the subsurface formation. The acoustic backscatter is detected and a spectrum thereof is produced and averaged over adjacent subsurface formation regions. A subsurface formation parameter such as the frequency dependency of the attenuation of the backscatter is determined from an analysis of the spectrum to provide an indication of the granularity property of the subsurface formation. Use of a broad range of frequencies enables a determination of the subsurface formation parameter over a large range of grain sizes. In another technique the spectrum of the detected backscatter is modified to remove the effect of the frequency response of the system with which the investigation is made. The modified spectrum may then be used to derive an indication of the granularity property of the subsurface earth formation such as its mean grain size or grain size distribution.