Petrophysical Analysis of Open-Hole Geophysical Logs Acquired In Bosso Field, Offshore Niger Delta Basin, Nigeria

Abstract

Shaly sands constitute hydrocarbon reservoirs in Bosso Field of Niger Delta basin. Its In-house petrophysical estimations based correction for shaliness effect on linear estimation of reservoirs’ shale content (VSh) from gamma ray logs. The approach often results in wrong estimates of hydrocarbon saturation (Sh), bulk hydrocarbon volume per unit reservoir volume (BVH) and hydrocarbon reserve. Since Niger Delta basin consists of Tertiary sediments, this work employed Larinov’s empirical formula for correcting shaliness effect in Tertiary sandstones, and thereafter estimated Sh using Indonessian formula for shaly sands. The petrophysical estimations were performed using Geographix® Discovery™ 5000.0.0.0. The data employed comprise gamma ray log, resistivity log, neutron and density porosity logs obtained in six wells (BO-1, BO-2, BO-4, BO-5, BO-6, BO-7). The wells penetrated Benin and Agbada Formations. Three hydrocarbon sands (Sands A, B, C) were identified within the Agbada Formation. VSh values range from 0.03 to 0.200. Sand B’s VSh is 0.03 in BO-6 and 0.038 in BO-5, indicating that the sand is clean. The sand’s net-to-gross pay ratio is 1.00 in BO-6 and 0.956 in BO-5. Effective porosity (Փe ) ranges from 0.164 to 0.253, with Sand B having the highest Փe of 0.253. Sh ranges from 0.620 to 0.773 in the field. BVH values range from 69.09 to 591.21. The petrophysical attributes of each of the reservoirs vary spatially in the field. Sands A and B have better petrophysical attributes than Sand C.