Geochemical reactions and their effect on CO2 storage efficiency during the whole process of CO2 EOR and subsequent storage

CO2-formation water-rock geochemical reactions can occur, affecting the reservoir physical properties and CO2 trapping forms during the CO2 enhanced oil recovery (CO2-EOR) process. In this paper, based on the properties of the reservoir and fluids in a high-temperature oil reservoir, a comprehensive model, including formation water evaporation, dissolution, diffusion of CO2 in water, CO2-water-rock geochemical reactions, and relation of porosity and permeability, is established to simulate the CO2 EOR process and subsequent geological storage. The geochemical reactions and CO2 trapping forms in these two stages are analyzed using this model, and the influences of reservoir heterogeneity and different CO2 injection schemes on EOR and CO2 geological storage are studied. The results show that the geochemical reactions can change reservoir porosity and permeability, but their effect is little, and most of the injected CO2 is trapped as the supercritical gas during the CO2 EOR process. During the stage of CO2 geological storage, the supercritical CO2 continuously converts into mineral form under the action of geochemical reactions, which results in the reservoir pressure decreasing. Whether the reservoir is heterogeneous or homogenous, the water-alternating-gas (WAG) scheme should be the first choice because it can enhance both oil recovery and CO2 storage efficiency in the EOR process. The injection of CO2 after the CO2 EOR process can improve the CO2 storage capacity and simultaneously maintain the reservoir pressure stabilization.

Automated summary

The study reveals that geochemical reactions have slight effects on reservoir properties during the CO2 enhanced oil recovery process, with most injected CO2 trapped as supercritical gas. In the stage of CO2 geological storage, supercritical CO2 converts into mineral form under the action of geochemical reactions, leading to reservoir pressure decrease. The water-alternating-gas (WAG) scheme is recommended for optimizing oil recovery and CO2 storage efficiency in the EOR process, while post-CO2 EOR injection can enhance storage capacity and maintain reservoir pressure stability.