Dynamics of dissolution trapping in geological carbon storage

Abstract

We report a quantitative study on the dynamics of dissolution trapping occurring during the injection of supercritical CO2 (scCO2) into a brine-filled heterogeneous porous medium, implying an application for the geological storage of CO2 in saline aquifers. We present volume-of-fluid (VOF)-based simulations of integrated two-phase flow and species mass transport at the pore-scale to capture transient dissolution of scCO2 in brine. It becomes evident that CO2 dissolution is not an instantaneous process, as the structural heterogeneity of the porous medium induces incomplete mixing leading to non-equilibrium dissolution. According to our observations, dissolution of scCO2 into brine occurs at an increasing rate at the early stage of the injection period, reaches a peak value, and follows by a declining trend at late stages. The observed trend in the dissolution rate is attributed to the evolution of interfacial area between percolated fingers of CO2 plume and brine. When the system reaches the steady-state, a stabilized interface between scCO2 and brine forms, undermining the scCO2 dissolution and dissolved CO2 mass transfer in brine. The pore-level analysis implies that injection rate and surface wettability are key factors influencing the evolution of the scCO2-brine interfacial area and consequently the mass transfer occurring at the interface during the dissolution trapping of scCO2. According to the results, scCO2 dissolution becomes more pronounced when the injection rate becomes higher and the medium is more wetting to the brine.