Integration of Rock Physics and Seismic Inversion for Net-To-Gross Estimation: Implication for Reservoir Modelling and Field Development in Offshore Niger Delta

Abstract

This study highlights a technique adopted for predicting and mapping net-to-gross (NTG) away from well locations through a combination of rock physics and seismic inversion applied in the Baza Field. The Baza field is located offshore Nigeria, with reservoirs poorly to mildly consolidated that were originally deposited in a deep-water submarine canyon system. The field is a partially appraised green field with three well penetrations encountereing amalgamated channels and lobes within the canyon system of tuiditic origin. Of the three wells drilled to date, only one well penetrated the key reservoir of interest- the B4 sands. The paucity of well penetration posses a challenge for accurate reservoir property assessment, particularly net-to-gross that has direct impact on hydrocarbon volume computation and ultimately on field development. Net-to-gross was predicted from seismic data based on a linear relationship observed from log derived P-impedance-AI (density × compressional velocity logs) and S-impedance-SI (density × shear velocity). Both properties when integrated can descrimate between sands and shales, and therefore serves as a proxy for calculating NTG. The linear relationship was applied to AI and SI seismic volumes built from simultaneous inversion of three sub-stack seismic data – the near (0-18), median (12-24) and far (24-45). The seismically derived net-to gross computed from simultaneous inversion compares favorably with log derived net-to-gross at well locations. The net-to-gross model resulted in a robust static and dynamic model that ultimately formed the basis for selecting optimal locations for future development wells for the B4 reservoir.