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Description
Saline formations predominantly comprise sandstone lithologies, with pronounced reservoir heterogeneity observed in Chinese sandstone formations. The spatial distribution of CO2 flow and occurrence in heterogeneous sandstone reservoirs is intrinsically linked to storage efficiency and displacement effectiveness. Consequently, investigating the flow process and characteristics of CO2-brine two-phase flow under varying influencing factors is imperative. Also, precise characterization of the dynamic evolution of the CO2-saline interface during unsealing procedures is essential to provide a theoretical foundation for accurately predicting the dynamic flow behavior of CO2-brine in porous media. This study provides experimental support by elucidating the gas-water flow characteristics during CO2 flooding of saline water, with the aid of computed tomography (CT). Utilizing micro-CT enables the measurement of relative permeability and saturation distribution of CO2 and brine in reservoir cores. This approach facilitates the prediction of CO2 migration pathways in reservoirs and plays a critical role in deciphering the migration laws of CO2 within geological formations. Using an experimental approach that combines micro-CT with in-situ two-phase flow techniques, CO2-brine displacement experiments were conducted on sandstone core samples from the Liujiagou formation of China’s Shenhua CCS project. The displacement process of CO2-brine two-phase flow within the core was quantitatively characterized. The influence of layered heterogeneity on the supercritical CO2-brine two-phase seepage under reservoir temperature and pressure conditions was revealed. The physical process of supercritical CO2 displacing brine within multi-scale pore structures was also characterized. The main conclusions and understanding obtained are as follows:
(1) The physical and chemical properties of CO2 in its supercritical state exhibit marked differences compared to those in gaseous and liquid CO2 phases, with further variations observed under diverse temperature-pressure conditions. Despite these variations, the migration behavior of supercritical CO2 within porous media predominantly follows gas-like transport mechanisms, characterized by an intermediate regime between the Klinkenberg effect and laminar flow principles.
(2) During CO2 injection, the CO2 initially infiltrates large-scale pores without immediate saturation. Within individual pores, the displacement mode of supercritical CO₂ aligns with the Klinkenberg effect, manifesting as laminar displacement rather than piston-like displacement.
(3) When CO2 is injected into heterogeneous formations, it preferentially flows through high-permeability strata before migrating into low-permeability layers. CO2 rapidly penetrates high-permeability lithological units, establishing preferential flow channels. Under continuous injection conditions, CO2 achieves rapid saturation of high-permeability zones, followed by gradual saturation of low-permeability regions.
| Country | China |
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