μ-CT analysis and numerical simulation of drying effects of CO₂ injection into brine-saturated porous media

CO2 injection in brine-saturated Bentheimer sandstone was studied experimentally to visualize and quantify salt precipitation in porous rock caused by evaporation of water into injected gaseous phase CO2. Gas and solid-salt saturation profiles were captured by μ-CT (micro computed tomography) and the pressure drop over the core was monitored continuously. The experimental results were compared with numerical simulations using the TOUGH2 reservoir simulator with the equation of state module ECO2N, and a numerical code that we have developed with an alternative approach on evaporation. Using the equilibrium phase partitioning model in TOUGH2, simulation results predict injectivity decline due to an accumulation of precipitated salt near the core inlet. This is in contradiction to our experimental observations, in which neither salt accumulation nor injectivity impairment was noticed. It appears that at near well injection velocities, local equilibrium phase partitioning used in the simulator overestimates evaporation of water into the CO2 gaseous phase. On the other hand, satisfying results were obtained from our model which uses a kinetic formulation for the evaporation. No injectivity impairment was found which is compatible with the experimental results.