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Reservoir Lithology and Fluid Characterization Based on Extended Previous HitElasticNext Hit Previous HitImpedanceNext Hit Inversion: A Gulf of Mexico Case Study



Discrimination of lithology and fluid types within target reservoirs is the primary objective in reservoir characterization. This essentially constitutes a process of integrating different disciplinary knowledge, i.e. geophysics, geology and petrophysics etc., thus making a quantitative prediction about the spatial distribution of reservoir rock and fluid. Reliable reservoir characterization is of great significance to detect favorable sweet spots and hence to optimize drilling locations with reduced risk.

Extended Previous HitElasticNext Hit Previous HitImpedanceNext Hit (EEI) inversion has proven to be an effective framework to account for AVO effects while formulating the problem into a conventional full stack seismic inversion scheme. It has been demonstrated that through EEI the Previous HitelasticNext Hit properties such as P-Previous HitimpedanceNext Hit, S-Previous HitimpedanceNext Hit, Density, Vp/Vs ratio, and Poisson's Ratio, etc. can be derived from seismic partial stacks at optimal projection angles (c). Angle c can be determined at well locations, which maximizes the correlation between the property logs and corresponding EEI curves. The derived Previous HitelasticNext Hit properties can be further classified, calibrated by rock physics modeling at offset wells, to delineate reservoir litho/fluid facies.

In this study, an integrated EEI inversion workflow is applied on a dataset from a development project from the GOM. Seismic partial stacks are used to compute EEI reflectivity volumes. Multiple calibration wells are incorporated for rock physics feasibility analysis as well as for the determination of the optimal angle c. Interpreted horizons are also integrated to provide lateral constraints and therefore to ensure that inversion results conform to the structural framework. Rock physics feasibility study has demonstrated that density is a very important Previous HitelasticTop attribute and, along with Vp/Vs, provides an effective means to discriminate reservoir lithology and fluid. Great correlations between density, Vp/Vs and corresponding EEI logs are also observed, which validates that the EEI inversion workflow is applicable in this field. Inverted density and Vp/Vs are further classified into lithology and fluid volumes. Since multi-disciplinary data sets are integrated, the characterization result is expected to simultaneously honor all the constraints and, as a result, to be reliable to assist in development drilling optimization.