Injection of supercritical CO₂ in brine saturated sandstone: Pattern formation during salt precipitation

In the present paper we report on the consequences of formation dry-out due to the injection of dry or under-saturated supercritical CO2 into geological formations. The reported findings are relevant for CO2 sequestration and acid-gas injection operations in the near well-bore environment. By injecting dry supercritical CO2 into brine-saturated sandstone, we investigated the drying process and the associated precipitation of salt in a capillary-pressure-dominated flow regime. Patterns of precipitated salt along the flow direction, as well as cross sectional patterns, were observed by means of mu;CT scanning. The experiments show that at a certain condition the locally precipitated amount of salt can be substantially higher than the amount of salt initially present in the same volume in the brine. A substantial impairment of the absolute permeability was found but, despite high local salt accumulation, the effective CO2 permeability increased during the experiments, which is likely a result of the observed cross sectional precipitation pattern.