Fluid and Lithology Discrimination Using Rock Physics Modelling and LambdaMuRho Inversion: An Example from Onshore Niger Delta, Nigeria

Ekwe, Amobi C.¹; Onuoha, Mosto K.²; Osayande, Nedo ³
(1)Geology, University of Nigeria, Nsukka, Nsukka, Nigeria. (2) Geology, University of Nigeria, Nsukka, Nsukka, Nigeria. (3) Exploration, Shell Petroleum Development Company Limited, Port-Harcourt, Nigeria.

Rock physics modelling and LambdaMuRho seismic inversion have been applied in an integrated approach to identify and delineate hydrocarbon charged reservoirs in an old producing field in the Niger Delta basin. Shear wave logs were generated empirically from the Castagna mud rock line relationship while fluid substitution was used to obtain correct log values over hydrocarbon bearing intervals. Common depth point (CDP) super gathers were generated to improve fidelity of pre-stack seismic data while cross-plots of elastic rock properties were generated to determine which of them constitute better pore fill and lithology indicators. Volumes of P-impedance, S-impedance, Vp/Vs, LambdaRho (λρ), MuRho (μρ) and density(ρ) were calculated through a LambdaMuRho (LMR) inversion process while data slices of LambdaRho, MuRho, Vp/Vs and Lambda/Mu were generated to capture, delineate and validate a known prospect located on a structural high and containing five wells within a four way dip closure. The cross-plot of LambdaRho versus MuRho from wells successfully distinguished between fluids and lithology in the area while a similar cross-plot from the inverted seismic volume validated the results from wells. A combination of LambdaRho and MuRho data slices was used to delineate hydrocarbon charged sand compartments in the study area. The results show that high values of MuRho (μρ) were indicative of clean sands and lower values of LambdaRho (λρ) correlated well with areas containing hydrocarbons. Using similar capture technique as applied to the known prospect, three other zones of exploration interest were identified.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.