Modeling of CO2 transport and pressure buildup in reservoirs during CO2 storage in saline aquifers: a case in Dongying Depression in China

Overuse of fossil fuels in industrial production and human life has increased greenhouse gas emissions. CO2 geological storage in deep saline aquifer can effectively control the extensive emission of CO2 and promote the smart cities performance of sustainability in economic, environmental, and social matters. The study area was set in the Dongying Depression, a structural unit of Bohai Bay. In this paper, four sets of reservoir and caprock layers suitable for CO2 geological storage were selected for the analysis of the properties of saline aquifers and caprocks, from the Shahejie Formation layers, the Es2, the upper and middle Es3 layers at depths between 1464 and 3102 m,. In order to assess the suitability and safety of CO2 storage during and after the injection period in these four saline reservoirs, the simulation software TOUGHREACT was selected to simulate the CO2 fluid migration process and pressure evolution in different conditions. The simulation results show that in the four reservoirs, the CO2 plume migrated about 1000–1200 m, and the pressure increased in the whole reservoirs with the largest pressure increment of 0.552–1.749 MPa near the injection well during the CO2 injection period; the CO2 gradually dissolved in the reservoir water, and the pressure was quickly restored to the original pressure after the CO2 injection period. The reservoir thickness, the porosity, and the permeability have an effect on the CO2 migration movement, and the pressure evolution in the reservoir, the shallower, and thicker reservoir is comparatively more suitable for CO2 geological storage. The sensitivity analysis proved the significant effect of the porosity and permeability on the CO2 transport and reservoir pressure. The results will be helpful to guide the development of CO2 geological storage projects and provide the theoretical basis for CO2 storage risk monitoring.