Effect of Capillary Induced Flow on CO2 Residual Trapping

Residual trapping is one of the main mechanisms for immobilizing CO2 after the injection phase of a geological sequestration project. Residual trapping results from capillary forces at the pore scale which lead to snap-off and bypass of CO2. For heterogeneous systems, there is, in addition to the capillary potential at the pore scale, a capillary potential at the scale of the heterogeneity which will result in capillary induced flows and trapping. We investigate the impact of capillary induced flow on multiphase flow behavior and its implications for residual trapping of CO2 by performing experimental and numerical core-flood tests. Results show that the magnitude and spatial extent of the heterogeneity impact the local capillary forces and, therefore, the capillary pressure and saturation distribution. In certain cases, even in the capillary dominated regime, local capillary disequilibrium was observed, leading to capillary induced flow when the system relaxed. This work shows that for layered rock with small variations in permeability, laminations direction has minimal impact on the local capillary forces and does not effect the residual trapping potential. Further research is needed to investigate if lamination direction impacts the residual trapping potential in the case of layered rocks with larger variations in permeability.