A Two‐Phase Layered Model for Simulating Leakage Along Faults Considering the Blocking Effect of CO ₂ Exsolution

ABSTRACT CO 2 geological storage is associated with the risk of faults activation and CO 2 leakage along the activated faults. During the leakage, pressure decline along the fault causes CO 2 to exsolve from formation water, forming a lower aqueous phase with dissolved CO 2 and an upper two‐phase zone with CO 2 bubbles dispersed in water. The CO 2 bubbles in this zone significantly reduce fluid mobility, lowering leakage rates. Existing leakage models neglecting such CO 2 exsolution effect overestimate leakage rates and risks. To address this limitation, this study improves the calculation method for CO 2 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 CO 2 exsolution. The application of the developed model to a CO 2 leakage case in an oil field located at Ordos Basin, China, demonstrates that the model can reflect the effect of gas‐phase CO 2 exsolution along faults. Quantitative analysis shows a 67%–75% reduction in CO 2 leakage rate simulated by the layered model compared to non‐layered models, indicating that the developed model can address the influence of CO 2 exsolution on blocking leakage fluid flow and thus calculate the leakage amount more accurately. 2025 Society of Chemical Industry and John Wiley & Sons, Ltd.