Quantitative characterization of synergistic effect in CO2 storage and enhanced recovery systems with considering CO2–water–salinity–rock reactions

CO2 geological utilization and storage (CGUS) is one of the crucial steps to achieve carbon neutrality goals. Partial and permanent mineralization of CO2 is seen as a secure means of storage. However, the quantitative characterization of essential geochemical processes involving in carbon sequestration under realistic system conditions, are yet to be considered fully. As a result, we developed an optional CGUS simulator: (1) detailed geochemical reactions and mineralization capabilities, (2) CO2 oil water rock interactions, and (3) synergistic CO2 storage and utilization. Using the methodologies and tools developed, we studied and quantitatively characterized the synergistic effects of CO2 sequestration and geological utilization during the critical 30 year period of carbon capture, utilization and storage (CCUS) demonstration sites in China. The results indicated that even depleted oil reservoirs can be the favorable sinks of CO2 sequestration as the remaining oil phase can enhance the migration of CO2. Dissolution of CO2 in the oil and water phases is not a mutually exclusive process, and there is inherent thermodynamic equilibrium that exists between the phases, while contributions by each phase can be optimized: the oil saturation at the startup of the injection, porosity, and injection rate has impact on incremental recovery and amount of carbon sequestered; the single injection slug size has a completely opposite effect on the geological utilization and sequestration, which needs to be optimized for more practical situations. Reservoirs rich in Mg-bearing minerals are favorable to CO2 mineralization and make storage more permanent as they lead to stable mineralization as a result of reactions with CO2. This study provides the important guidelines to achieve both efficient sequestration and geological utilization to increase the subsurface storage capabilities today and as well as the near future.