Effects of geologic heterogeneity on migration of gaseous CO2 using laboratory and modeling investigations

Abstract

There is a concern that underground stored CO2 may potentially escape and intrude shallow aquifers that may lead to degradation of the water quality and possible mobilization of metals. Moreover migrating CO2 gas may invade buildings causing lethal conditions for humans. A better understanding of gaseous CO2 migration in heterogeneous aquifer systems at low pressure will help in risk assessment of Carbon Capture and Storage (CCS). We performed complementary 1D column and 2D tank experiments by injecting gaseous CO2 at three different rates into constructed heterogeneous porous media in laboratory setups. Soil moisture sensors were installed in the test systems to monitor the movement of the gaseous phase. The generated experimental data was analyzed using the numerical multiphase modeling code T2VOC. The results confirmed that large-scale heterogeneity controls overall gaseous CO2 migration in porous media while processes occurring at smaller scale are of significance for gas saturations. Monitoring the exact gaseous movement and concentrations is difficult even in a constructed heterogeneous medium and point measurements are not always capturing the full dynamics of the system. The numerical model provided good estimates of the general flow of the gaseous phase around larger heterogeneous features and estimated the total amount of gaseous CO2 in the test system to a good approximation. However, the numerical model was not able to adequately describe the processes occurring at smaller scale including unstable gaseous movement at low flow rates and dissolution of CO2.