Tracer test to constrain CO2 residual trapping and plume evolution

Abstract

CO2 residual trapping, post-injection plume extent, and time for plume stabilization for CO2 geological storage highly depend on the hysteresis process which is the discrepancy between drainage and imbibition processes. CO2 flow in the injection zone during the injection period is mainly controlled by the drainage process during which the non-wetting CO2-rich phase replaces the wetting aqueous phase. Using data collected over the injection period may be insufficient in constraining the hysteresis parameters required to predict the post-closure plume evolution. Long-term data collection over the post-injection period to determine the residually trapped CO2 and to predict the CO2 plume evolution and stabilization can be very expensive. Here, we introduce a tracer test to enable the determination of the residually trapped CO2 and prediction of the CO2 plume evolution and stabilization in a temporal manner. The tracer test is introduced at the end of an injection period to obtain information on the residual trapping parameters including imbibition/drainage discrepancy (hysteresis) and critical CO2-rich phase saturation. The sensitivity of the proposed tracer test to residual trapping parameters is evaluated with respect to the tracers’ peak times at the injection well (which serves as observation well during post-injection period) as well as an offset location at an updip distance from the injection well. The effect of residual trapping on the plume evolution and tracer test response is studied considering reservoir properties representative of a real project.