Impacts of relative permeability on CO2 phase behavior, phase distribution, and trapping mechanisms

Abstract:

A critical aspect of geologic carbon storage, a carbon-emissions reduction method under extensive review and testing, is effective multiphase CO₂ flow and transport simulation. Relative permeability is a flow parameter particularly critical for accurate forecasting of multiphase behavior of CO₂ in the subsurface. The relative per­meability relationship assumed and especially the irreducible saturation of the gas phase greatly impacts predicted CO₂ trapping mechanisms and long-term plume migration behavior.

A primary goal of this study was to evaluate the impact of relative permeability on efficacy of regional-scale CO₂ sequestration models. To accomplish this we built a 2-D vertical cross-section of the San Rafael Swell area of East-central Utah. This model simulated injection of CO₂ into a brine aquifer for 30 years. The well was then shut-in and the CO₂ plume behavior monitored for another 970 years. We evaluated five different relative permeability relationships to quantify their relative impacts on forecasted flow results of the model, with all other parameters maintained uniform and constant.

Results of this analysis suggest that CO₂ plume movement and behavior are significantly dependent on the specific relative permeability formulation assigned, including the assumed irreducible saturation values of CO₂ and brine. More specifically, different relative permea­bility relationships translate to significant differences in CO₂ plume behavior and corresponding trapping mechanisms.