Elastic-wave and related properties of clastic rocks from a part of Niger Delta, Nigeria

Abstract

Elastic-wave velocities of drill-core specimens with mineral compositions and textures of elastic rocks at Niger Delta, Nigeria, can be useful for identifying large zones of high porosity or high clay content (such as some fault zones, or the clay-rich haloes surrounding known uranium ore bodies). The overall objective of this study is to identify zones of high porosity and high clay contents using elastic-wave velocities V_p and V_s, and the ratio V_p/V_s. Thin sections were studied, and measurement of V_p, V_s, and porosity were made from cylindrical core specimens representing the Niger Delta Agbada Formation. Multiple linear regression has been employed to determine 1\V_p and 1\V_s, and the ratio V_p/V_s as a function of porosity (Φ) and clay fraction (Fc) for all specimen from the study area. The seismic velocities V_p and V_s, and the ratio V_p/V_s for Agbada sediment are found to be influenced by changes in porosity more strongly than by changes in clay content by a factor of approximately four. For clay fractions less than 0.15, simple linear relationships appear to exist between the reciprocal velocities 1/V_p and 1/V_s, and the ratio V_p/V_s, and porosity.

Keywords: compressional, shear velocity, porosity, permeability, clastic rock

Nigeria Journal of Pure and Applied Physics Vol. 4(1) 2005: 82-89