A Two‐Phase Layered Model for Simulating Leakage Along Faults Considering the Blocking Effect of CO2 Exsolution

CO2 geological storage is associated with the risk of faults activation and CO2 leakage along the activated faults. During the leakage, pressure decline along the fault causes CO2 to exsolve from formation water, forming a lower aqueous phase with dissolved CO2 and an upper two‐phase zone with CO2 bubbles dispersed in water. The CO2 bubbles in this zone significantly reduce fluid mobility, lowering leakage rates. Existing leakage models neglecting such CO2 exsolution effect overestimate leakage rates and risks. To address this limitation, this study improves the calculation method for CO2 gas‐phase exsolution location by establishing a pressure distribution equation within faults and deriving an analytical solution for the exsolution location using monitorable fault inlet pressure; a two‐phase layered flow model is then developed by incorporating two‐phase relative permeability which can reflect the flow resistance effects after CO2 exsolution. The application of the developed model to a CO2 leakage case in an oil field located at Ordos Basin, China, demonstrates that the model can reflect the effect of gas‐phase CO2 exsolution along faults. Quantitative analysis shows a 67%–75% reduction in CO2 leakage rate simulated by the layered model compared to non‐layered models, indicating that the developed model can address the influence of CO2 exsolution on blocking leakage fluid flow and thus calculate the leakage amount more accurately. 2025 Society of Chemical Industry and John Wiley & Sons, Ltd.