A Novel Approach to Enhancing the CO2 Sequestration Volumetric Capacity for CCS Project by Re-Injection of Produced Brine

Abstract Objectives/Scope Reducing anthropogenic carbon dioxide (CO2) in the atmosphere is crucial for mitigating climate change. CO2 Capture and Sequestration (CCS) is considered one of the most promising options for carbon reduction. It involves the injection of CO2 into the structural reservoirs in deep, permeable geologic formations. The effectiveness of CCS relies heavily on the geological and petrophysical properties of the storage reservoir. It has been studied that some percentage of injected supercritical CO2 is securely trapped underground via two major trapping mechanisms: physical trapping, and geochemical trapping. Physical trapping mechanisms include structural (hydrostratigraphic) trapping, residual (capillary) trapping, and sorption trapping. The physical trapping is relatively fixed for a given storage reservoir due to its geological parameters. The geochemical trapping mechanism occurs through solubility trapping and mineral trapping. It is very well known that solubility trapping includes slow diffusion in the aqueous phase and convective processes. In the case of mineral trapping, the process is over a much longer period, and it is one of the slowest mechanisms. Methods, Procedures, and Process This study employed a novel approach to enhance CO2 sequestration rates by injecting CO2 and brine produced from the same reservoir simultaneously. The solubility trapping occurs because of the dissolution of CO2 in the brine, leading to dense CO2-saturated brine. The main rate-limiting step in solubility trapping is the CO2 migration in brine which happens through diffusion and is very well known to be a slow process. To address this, the study proposed enhancing the mixing between injected CO2 and brine during the injection phase while maintaining reservoir pressure. Results, Observations, Conclusions Utilizing a systematic numerical model, the study identified an optimal approach involving a combination of CO2 and brine injection with brine production based on reservoir pressure transients. This strategy significantly enhanced CO2 injection rates, leading to a potential increase in CO2 sequestration capacity throughout the injection and storage campaign. Thus, with this innovative approach and with the use of existing CCS reservoir and existing facilities we achieved 10% to 30% more CO2 sequestration capacity through enhanced solubility trapping as well as some increment in mineral trapping. Novel/Additive Information A novel approach was employed to enhance CO2 sequestration rates by injecting CO2 and brine produced from the same reservoir simultaneously. This simulation exercise provides guidelines on enhanced reservoir management to increase CO2 sequestration rates and therefore volumes in a reservoir by managing the production and disposal of water. These novel guidelines enable operators to increase the economic value and ROI (Return on Investment) on such CSS projects.