Utilization of Carbon Dioxide for In-Situ Precipitation of Calcium Carbonate for Conformance Control in Heterogeneous Porous Media

Abstract Conformance control is a necessary part of enhanced oil recovery operations in heterogeneous oilfields. However, many techniques center on near-wellbore conformance or are not well suited for low matrix permeability formations. We propose the injection of calcium hydroxide and carbon dioxide as a novel conformance control strategy in reservoirs that experience poor sweep efficiency due to heterogeneity. These two chemical agents react to precipitate solid calcium carbonate, potentially blocking already-swept pores and directing injected fluids to unswept regions of the reservoir. Microfluidic devices (micromodels) were used to perform experiments to observe the fundamental behavior of this reaction in porous media. Precipitation grain size, location, and relative quantity were directly observed while changing injection order, CO2 state, and injection rate. It was found that the reaction took place in porous media for both states of CO2 (gaseous and dissolved in deionized water). Injecting at a lower rate (0.33 ft/day) resulted in less precipitate, but larger grains during single-phase (aqueous) experiments than injecting at a higher rate (1 ft/day). Additionally, more precipitate formed during experiments in which gaseous CO2 was used, compared to when CO2 was dissolved in water. Overall, precipitation occurred where the reactants both contacted each other and mixed, which did not have a preference for high or low permeability zones. Precipitation was also shown to block pore throats in a 2.5D micromodel, reducing the permeability by 92.6% at a 10 ft/day interstitial injection rate. Precipitation via this method can be controlled through CO2 placement in the reservoir and injection rate, as the reaction only occurs where CO2 and Ca(OH)2 are both present and have sufficient convective mixing.