The rock physics basis for 4D seismic monitoring of CO2 fate: Are we there yet?

Abstract

Monitoring, verification, and accounting (MVA) of CO2 fate which are the three fundamental needs in geological sequestration are discussed. The primary objective of MVA protocols is to identify and quantify the injected CO2 stream within the injection/storage horizon and any leakage of sequestered gas from the injection horizon, providing public assurance. Changes in the elastic properties of the reservoir induced by the injection of CO2 can be various, affecting the properties of the fluid, those of the rock frame, or both. Seismic reservoir monitoring has traditionally treated the changes in the reservoir rock as a physical-mechanical problem, that is changes in seismic signatures are mostly modeled as functions of saturation and stress variations and/or intrinsic rock properties. To enhance the effectiveness of time-lapse seismic studies, CO2-optimized physical-chemical models involving frame substitution schemes must be developed to account for the type and magnitude of reductions caused by rock-fluid interactions at the grain/pore scale.