Estimation of Shear Wave Velocity for Lithological Variation in the North-Western Part of the Niger Delta Basin of Nigeria

摘要

This paper presents the estimation of Shear wave velocity analysis for the prediction of lithological discrimination of the subsurface geology from two petroleum wells AK-1 and AK-2 located in the North-Western part of the Niger Delta. Gamma ray log was used for the lithological differentiation. Sonic log was used for computation of compressional wave velocity. Shear wave velocity was determined from compressional wave velocity. The analysis of shear and compressional wave velocity shows a general conventional trend of increase in velocity with depth but varies at some depth due to lithological variation, heterogeneity and anisotropic nature of the earth. Compressional wave velocity V_p is higher than shear wave velocity V_s in both sandy and shaly formations for the two wells under consideration. The compressional wave velocity values of shale beds of well AK-1, and well AK-2 varies from 3485 to 4830m/s, and 2339 to 3167m/s respectively while compressional wave velocity values of sand beds for the same wells varies from 3304 to 6767m/s, and 2093 to 3932m/s and respectively. The shear wave velocity values of shale beds of well AK-1, and well AK-2 varies from 2682 to 3717m/s, and 1799 to 2437m/s respectively while shear wave velocity values of sand beds for the same wells varies from 2656 to 5441m/s, 1682 to 3161m/s and 1826 to 2809m/s respectively. This implies that the shear wave velocity is slower than the compressional wave velocity.