Yaxin Shang, Keyu Liu, Jianliang Liu, School of Geosciences, China University of Petroleum (East China), Qingdao; Leilei Yang, Enhanced Oil Recovery Research Institute, China University of Petroleum, Beijing
Sequestering CO₂ in deep geological formations has been demonstrated to be a safe and effective option for large-scale CO₂ emission reduction worldwide. However, screening and assessing suitable geologic sites (reservoirs), and estimating storage capacity requires some robust subsurface reservoir characterization, which is often hampered by a lack of fine-scale data. Data such as porosity, permeability and thickness used in CO₂ storage capacity calculation are traditionally based on homogeneous layer-cake reservoir models constructed from seismic and well log data, which can cause significant deviations from the actual storage capacity due to strong sedimentary heterogeneities. The reservoir quality and its mineral constituents may also exert a strong effect on the CO₂ storage efficiency due to CO₂-water-rock reactions (diagenesis) after the CO₂ injection. To address such a key technical challenge, determine the effect of both the reservoir sedimentary and compositional heterogeneities on CO₂ storage efficiency, we coupled a hydrodynamics-based stratigraphic forward modeling program, SEDSIM, with the non-isothermal reactive transport simulation program, TOUGHREACT, to screen potential CCUS sites in some depleted reservoirs in the Dongying Sag, Bohai Bay Basin. SEDSIM was used to create a 3D sedimentary model conditioned by seismic and limited well data, providing a 3D sedimentary facies and lithological model containing fine heterogeneities with known storage capacity (total porosity). TOUGHREACT was then employed to simulate the CO₂-water-rock reactions after CO₂ injection using the 3D model generated from SEDSIM to assess the changes of reservoir petrophysical properties (Φ and K) and mineral species over time. Our preliminary work indicates that CO₂ would cause the dissolution of carbonate, feldspar and chlorite minerals, while precipitate dawsonite, ankerite and quartz. After 10,000 years, a carbonate crust would be formed at the top of the reservoir immediately below the seal rock. It is also found that CO₂ injection would exacerbate the sedimentary heterogeneities, enhancing permeability of the porous zones while cementing the low poroperm zones. Our initial work has demonstrated that the coupled modeling workflow can be quite effective for site screening and assessment for CCUS.