A Strategy for Enhanced Carbon Storage: A Hybrid CO[sub.2] and Aqueous Formate Solution Injection to Control Buoyancy and Reduce Risk

Conventional Carbon Capture and Storage (CCS) operations use the direct injection of CO[sub.2] in a gaseous phase from the surface as a carbon carrier. Due to CO[sub.2] properties under reservoir conditions with lower density and viscosity than in situ brine, CO[sub.2] flux is mainly gravity-dominated. CO[sub.2] moves toward the top and accumulates below the top seal, thus reinforcing the risk of possible leakage to the surface through unexpected hydraulic paths (e.g., reactivated faults, fractures, and abandoned wells) or in sites without an effective sealing caprock. Considering the risks, the potential benefits of the interplay between CO[sub.2] and an aqueous solution of formate ions (HCOO¯) were evaluated when combined to control CO[sub.2] gravity segregation in porous media. Three combined strategies were evaluated and compared with those where either pure CO[sub.2] or a formate solution was injected. The first strategy consisted of a pre-flush of formate solution followed by continuous CO[sub.2] injection, and it was not effective in controlling the vertical propagation of the CO[sub.2] plume. However, the injection of a formate solution slug in a continuous or alternated way, simultaneously with the CO[sub.2] continuous injection, was effective in slowing down the vertical migration of the CO[sub.2] plume and keeping it permanently stationary deeper than the surface depth.