An inversion of reservoir properties based on a concurrent modeling approach: the case of a West African reservoir

Abstract

Deterministic rock physics models were applied in a shale-sand environment located in the West African lower Congo basin, with the aim of estimating total porosity and clay content from P-wave acoustic impedance. Assuming that the only minerals within the target reservoir are quartz and clay, Han et al. model was used to determine the clay content which is referred herein as model-based C, while Krief et al. model was applied to solve the P-wave impedance for total porosity and clay content. The latter operation is a challenging task because of the nature of the actual rock physics equation that relates the known acoustic impedance to three unknown reservoir properties. This inherent difficulty is circumvented by making use of an additional linear equation, which is derived from the petrophysical link between porosity and clay content. To achieve this goal, firstly, a rock physics model was established, and then the reservoir was delineated through a combination of P-wave impedance and Poisson’s ratio. In the reservoir, total porosity and clay content were inverted based on P-wave impedance by applying the rock physics model of Krief et al. that related P-wave impedance to total porosity and clay content, alongside the established petrophysical link between the two reservoir properties. The result was found to be consistent on the well log scale. Uniquely, a good match was obtained when the methodology was repeated on the real seismic data.