Pore morphology and permeability evolution of hydrate-bearing sediments during dissociation process

Abstract

Accurate permeability prediction in hydrate-bearing sediments (HBS) is crucial for efficient hydrate exploitation and production control. However, hydrate dissociation processes exhibit significant heterogeneity and discontinuity. Traditional methods, which phenomenologically study seepage behavior by only considering saturation and effective pore changes, often fail to effectively describe the coupled influence of complex pore structure evolution and permeability under hydrate phase transition and in-situ stress. This study utilized an X-ray computed tomography triaxial system to conduct micro-visualization tests of HBS depressurization and thermal stimulation dissociation under constant axial load and identical supercooling conditions. We found that thermal stimulation significantly accelerated the dissociation rate by approximately 75% compared to depressurization. Quantitative digital volume correlation analysis revealed thermal stimulation led to more intense, randomly distributed pore-scale damage, with the maximum vertical displacement increment being 20% higher than depressurization. The complex pore structure change profoundly impacts fluid transport and production potential. Therefore, from the perspective of pore fractal structure evolution, we proposed a permeability model based on fractal parameter and established an upscaling framework for accurately predicting heterogeneous core permeability. This framework achieved a 33.93% improvement in root mean square error compared to homogeneous assumptions. Leveraging its enhanced accuracy, this study provides critical guidance for optimizing oil and gas exploitation, improving recovery efficiency, and reducing risks in complex geological environments.