Evaluation of Lithological Influence on Seismic Wave Velocity in Part of Niger Delta, Nigeria

Abstract

This study is aimed at evaluating the influence of lithology on seismic wave velocity in part of Niger Delta. A suite of geophysical well log comprising of gamma ray, sonic and density logs in Log Ascii Standard (LAS) format from two exploratory wells (OKO 5 and OKO 7) within the study area was used for this study. Gamma ray log was used to identity and delineate the lithology into shale and sand units, seismic wave velocity was categorized into compressional wave velocity Vp and shear wave velocity Vs. The former was computed from interval transit time while the later from compressional wave velocity. The results of this study show that seismic wave velocity is very much affected by difference in the lithology of formation. Compressional wave velocity (Vp) is higher than shear wave velocity (Vs) in shale and sand lithologies in the two wells. The values of the compressional wave velocity, shear wave velocity, percentage volume of shale and percentage volume of sand ranges from 3485 to 6620m/s, 2159 to 3932m/s, 2682 to 5323m/s, 1736 to 3161m/s, 11 to 60%, 13 to 59%, 40 to 89% and 29 to 87% for the two wells respectively. The knowledge of this study can be applied in civil engineering and engineering geophysics activities like foundation for high rise buildings, dams, bridges and road construction.