STUDY OF COMPRESSIONAL WAVE VELOCITY-CLAY VOLUME RELATIONSHIP

Abstract

One of the methods of studying subsurface lithology is by studying the variation of compressional wave velocity. The Porosity of reservoir rocks in boreholes is obtained from measurement of transit times in sonic logs. Empirical relations between velocity and porosity enable determination of porosity. However, in practice, determinations of porosity from velocity have not always been accurate because of the inherent scatter in the porosity-compressional velocity and the porosity-permeability relationships. Empirical fits do not account for the scatter in the porosity-compressional velocity cross plots. Many studies in rock physics have been devoted to explaining the source of this scatter. Experimental data suggests that much of the scatter in the porosity compressional velocities cross plots can be attributed to clay content V 1 . In the present work it has been proposed to to study the variation of compressional wave velocity- clay volume relationship by using various models. It has been observed that there is an initial increase in compressional velocity (Vp) with the increase in clay particle until a critical-clay-volume fraction (normally between 20% and 40%) was reached, after which, Vp decreased with clay content. Such a result is sought along with the other relationships.