Analytical model of CO2 storage efficiency in saline aquifer with vertical heterogeneity

• Established a multi-layer supercritical CO2–brine two-phase displacement model.
• Larger heterogeneity coefficient or larger porosity would result in smaller percolating resistance.
• Higher injection rate or higher radial extent would result in greater percolating resistance.
• Heterogeneity coefficient has most significant effect on sweep efficiency.

CO2 injection into saline aquifers for storage is the most effective way to reduce greenhouse gas emissions. However, the storage layers are heterogeneous because of millions of years of tectono-sedimentary evolution. A multilayer supercritical CO2–brine two-phase displacement model with vertical heterogeneity was established to make clear the impact of heterogeneity on storage efficiency. The analytical solutions were obtained after simplifying the mathematical model. The results show that, the percolating resistance increased with the increase of injection rate and radial extent, with the decrease of heterogeneity coefficient and porosity. Larger heterogeneity coefficient or higher injection rate will result in lower sweep efficiency, and is not conducive to CO2 storage. Larger radial extent or larger porosity will result in higher sweep efficiency, and is conducive to CO2 storage. Calculation showed that heterogeneity coefficient has much more significant effect on storage efficiency than other influencing factors such as injection rate, radial extent and porosity. The analytical solutions of supercritical CO2–brine two-phase displacement model considering vertical heterogeneity provide an easy and accurate method for the evaluation of CO2 storage.