--> Rock Physics Driven Seismic Modeling of CO<sub>2</sub> Injection in a Carbonate Reservoir From Canada

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Rock Physics Driven Seismic Modeling of CO2 Injection in a Carbonate Reservoir From Canada

Abstract

Monitoring CO2 injection for enhanced hydrocarbon recovery in carbonate reservoirs poses a technical challenge interpreting changes in pressure & fluid saturations away from wells. The present study focuses on quantitative rock physics modeling of time-lapse (4D) changes in reservoir pressure and multi-fluid saturations in a carbonate reservoir from southern Canada. The field is currently under WAG (Water Alternate Gas) injection, and both pressure and CO2 saturation change during the CO2 flooding process. The goal of the dynamic reservoir modeling is to understand and predict CO2 saturations over the reservoir. To achieve this goal, we modeled reservoir properties at different fluid saturations with various effective pressure regimes. 4D rock physics analysis provides the link between dynamic reservoir properties and 4D seismic responses. We calculated elastic properties of fluid mixtures (brine, oil, and CO2) at different pressures, based on a constant reservoir temperature of 600C, as the WAG injection does not significantly alter temperatures in the reservoir. Initially, effective properties of the brine saturated reservoir are measured at the original pressure (15MPa). Then, we replace the brine fluid with different mixture of fluids and calculate effective properties of the reservoir at different expected pressure values. These elastic properties (incompressibility and rigidity) are affected by changes in the pressure for the same fluid saturation. Modeling results show a significant change (around 30–40% decrease) in the impedance for fluid saturation when the reservoir is saturated with CO2 compared to the brine-saturated case. 4D rock physics models demonstrated that, at reservoir level, Lambda-Rho highly correlate with changes in fluid saturation, with lowest values when the reservoir is saturated with CO2. Likewise, Mu-Rho, highly correlated with reservoir pressure, is higher as the effective pressure increases. During WAG injection, it is expected that changes in CO2 saturation are more prominent compared to changes in effective pressure away from injection wells.