Injecting an acidic aqueous solution into a carbonate-rich permeable medium can cause the formation of a mobile gas phase through mineral dissolution. The flowing gas can cause significant changes in mineral identities through interaction with the initially present mineral and aqueous species. We have developed a solution to such transport problems based on a finite difference implicit-pressure/explicit-saturation formulation for two-phase flow, using the local equilibrium assumption as calculated with the Villars-Cruise-Smith stoichiometric chemical equilibrium algorithm.
We illustrate the changes that occur to a calcite/iron (II) hydroxide medium upon injection of hydrochloric acid and the stripping of hydrogen sulfide gas from carbon dioxide gas injected into a siderite-rich medium. The examples demonstrate that the formation and/or presence of a gas phase can alter resident minerals and that minerals can remove impurities from a gas phase.