Enhancing hydrate-based CO2 storage security in muddy reservoirs: Quantitative analysis of permeability and breakthrough pressure

CO2 breakthrough pressure is a critical parameter for evaluating the storage security of muddy hydrate-bearing reservoirs. It is determined by the synergistic effects of fluid saturation and stress conditions on permeability. However, the quantitative coupling mechanisms between permeability and breakthrough pressure in muddy hydrate-bearing cores remain poorly understood. Therefore, this study remolded 18 muddy cores under different water saturation, hydrate saturation, and effective stress conditions. Permeability and breakthrough pressure were measured continuously using the pulse method and the gradient pressurization method, respectively. The maximum increase in the stress sensitivity coefficient of muddy cores is approximately 69.12%, and the maximum increase in the stress damage coefficient is approximately 23.08%. Increasing water saturation and effective stress can reduce core permeability, thereby significantly elevating the breakthrough pressure. In contrast, increasing hydrate saturation enhances the permeability stress sensitivity coefficient by up to 75.20%, while restricting the increase in the permeability stress damage coefficient to a maximum of 6.26%. Pearson correlation analysis reveals that among all parameters, effective stress exhibits the strongest influence on permeability. Comparative analysis demonstrates that the hydrate saturation's permeability effect is 1.16 times more pronounced than water saturation's impact. Furthermore, to our knowledge, this study presents the quantitative correlation between permeability and breakthrough pressure in CO2 hydrate-bearing muddy cores firstly. Their synergistic variation follows a power-exponential empirical relationship. These findings provide both theoretical foundations and practical guidance for safe and efficient CO2 storage in muddy reservoirs via the hydrate method.