ROCK/FLUID INTERACTION BY INJECTION OF SUPERCRITICAL CO2/H2S: INVESTIGATION OF DRY-ZONE FORMATION NEAR THE INJECTION WELL

摘要

In the present paper we report on two consequences of formation dry-out due to the injection of dry or under-saturated acid-forming fluids such as CO2 and H2S into geological formations.The reported findings are coupled to each other and are relevant in the surrounding well-bore environment for CO2 sequestration and acid-gas injection operations. By injecting supercritical(SC) CO2 into brine-saturated sandstone,we investigated salt precipitation due to drying in a capillary-pressure-dominated flow regime.Patterns of precipitated salt were observed along the flow direction as well as cross sectional patterns.A substantial impairment of the absolute permeability(K) was found but, despite high local salt accumulation,the effective CO2 permeability(K·k_(rel)) increased during the experiments. In the second part of the paper we address the question of whether a dry zone is necessarily chemically stable.We injected SC H2S into practically dry limestone. Substantial water production was observed as result of a dissolution reaction,which potentially prevents formation drying.The experiment demonstrates chemical rock/fluid interaction in the absence of an aqueous phase.