Active CO ₂ reservoir management for CO ₂ capture, utilization, and storage: An approach to improve CO ₂ storage capacity and to reduce risk

CO ₂ capture, utilization, and storage (CCUS) in deep geological formations is regarded as a promising means of lowering the amount of CO ₂ emitted to the atmosphere and thereby mitigating global climate change. For commercial-scale CO ₂ injection in saline formations, pressure buildup can limit CO ₂ storage capacity and security. Issues of interest include the potential for CO ₂ leakage to the atmosphere, brine migration to overlying potable aquifers, and pore-space competition with neighboring subsurface activities. Active CO ₂ Reservoir Management (ACRM) combines brine production with CO ₂ injection to relieve pressure buildup, increase injectivity, spatially and temporally constrain brine migration, and enable beneficial utilization of produced brine. Useful products may include freshwater, cooling water, make-up water for oil, gas, and geothermal reservoirs, and electricity generated from extracted geothermal energy. By controlling pressure buildup and fluid migration, ACRM can limit interactions with neighboring subsurface activities, reduce pore-space competition, and allow independent assessment and permitting. ACRM provides benefits to reservoir management at the cost of extracting brine. The added cost must be offset by the added benefits to the storage operation and/or by creating new, valuable uses that reduce the total added cost. We review potential uses of produced brine and conduct a numerical study of potential reservoir benefits. Using the NUFT code, we investigate CO ₂-injector/ brine-producer strategies to improve CO ₂ storage capacity and minimize interference with neighboring subsurface activities. Performance measures considered in this study include magnitude of vertical brine migration and areal extent and duration of pressure buildup. We consider ranges of CO ₂-storage-formation thickness and permeability and caprock-seal thickness and permeability, comparing injection-only cases with ACRM cases with a volumetric production-to-injection ratio of one. The results of our study demonstrate the potential benefits of brine production to CO ₂-storage operations. The economic value of these benefits will require more detailed, site-specific analyses in future studies.