Petro-electric modeling for CSEM reservoir characterization and monitoring

Abstract

The controlled-source electromagnetic (CSEM) method has been successfully applied to petroleum exploration; however, less effort has been made to highlight the applicability of this technique for reservoir monitoring. This work appraises the ability of time-lapse CSEM data to detect the changes in fluid saturation during water flooding into an oil reservoir. We simulated a poorly consolidated shaly sandstone reservoir based on a prograding near-shore depositional environment. Starting with an effective porosity model simulated by Gaussian geostatistics, dispersed clay and dual water models were efficiently combined with other well-known theoretical and experimental petrophysical correlations to consistently simulate reservoir properties. The constructed reservoir model was subjected to numerical simulation of multiphase fluid flow to predict the spatial distributions of fluid pressure and saturation. A geologically consistent rock physics model and a modified Archie’s equation for shaly sandstones were then used to simulate the electrical resistivity, showing up to 60% decreases in electrical resistivity due to changes in water saturation during 10 years of production. Time-lapse CSEM data were simulated at three production time steps (zero, five, and ten years) using a 2.5D parallel adaptive finite element algorithm. Analysis of the time-lapse signal in the simulated multicomponent and multifrequency data set demonstrates that a detectable time-lapse signal after five years and a strong time-lapse signal after ten years of water flooding are attainable using current CSEM technology.