A new breakthrough pressure model for coal considering effective stress and water saturation

Gas breakthrough pressure is a key parameter governing gas migration in reservoirs and plays a critical role in assessing the safety of geological storage of gases such as CO₂ and H₂. However, existing breakthrough pressure prediction methods largely rely on empirical correlations fitted to experimental data, which lack a solid physical basis and are unable to simultaneously account for the coupled effects of water saturation and effective stress. In this study, a series of gas breakthrough pressure experiments were conducted on coal samples from Bowen Basin under varying effective stress and water saturation conditions. The experimental results demonstrate that cleat networks, effective stress, and water saturation jointly control breakthrough behavior in coal reservoirs. Based on these observations, a new physics–informed gas breakthrough pressure model for coal was developed by incorporating effective stress, water saturation, cleat compressibility, porosity, and initial permeability within a unified theoretical framework. The proposed model enables direct prediction of breakthrough pressure curves using sample-specific physical parameters and improves prediction accuracy compared with existing models, particularly for low-permeability samples. Compared with the J-function and the exponential model, it reduces the overall mean absolute error across the five samples from 36.8 kPa and 18.7 kPa to 12.1 kPa, corresponding to reductions of 67.1% and 35.3%, respectively. This study provides a robust approach for predicting gas breakthrough pressure in coal reservoirs and offers insights into underground gas storage assessment.