Supercritical CO2 and brine displacement in geological carbon sequestration: Micromodel and pore network simulation studies

The competence of geological carbon sequestration to a large extent relies on the short-term injection efficiency and the long-term capillary trapping and geological stability. This study uses a high-pressure micromodel and pore network simulation to investigate pore-scale displacement phenomena during the injection of supercritical carbon dioxide (scCO2) into brine-saturated reservoirs. Results show that the brine displacement can be enhanced by increasing the scCO2 injection rate, but hindered by brine salinity which alters the interfacial contact properties and displacement patterns. The scCO2-brine displacement ratio increases with the capillary number Nc, increasing which by adding viscosifiers or surfactants would enhance the overall scCO2 injection efficiency in microscopic flows. Results also suggest that better injection efficiency and capillary trapping capacity can be achieved in reservoirs with more widely-distributed pore sizes. It is not evident that mutual solubility and upscaling using the Leverett-J function readily allow to expand the injection efficiency results of microscopic flows to reservoirs; yet, the effects of salinity and pore size distribution on the scCO2-brine displacement process remain pertinent in both microscopic and macroscopic flows through porous media.