An Analytical Model for the Permeability in Hydrate‐Bearing Sediments Considering the Dynamic Evolution of Hydrate Saturation and Pore Morphology

Hydrate‐saturation‐dependent permeability in sediments is largely affected by the pore morphology of hydrate. Hydrate pore morphology evolves from a single pore habit, which depends on its formation conditions, toward a sophisticated hybrid habit with increased hydrate saturation. Resulted permeability reduction curves in hydrate‐bearing sediments are diverse and lack universal models. By using a two‐parameter logistic function to link microscale hydrate pore habit evolution with macroscale permeability variations, this study establishes a pore‐morphology‐weighted permeability model that well captures the permeability evolution in hydrate‐bearing sediments at various conditions. The universality of this model is validated and the values of the two parameters in the model are calibrated using published laboratory and pressure core data. This newly proposed model offers a mechanistic understanding of the permeability in hydrate‐bearing sediments and an elegant expression that can be implemented in reservoir simulators for field‐scale gas production estimation. Plain Language Summary Permeability of hydrate‐bearing sediments governs the gas and water flow, and thus plays important roles in many energy, environment, and climate related processes including the formation and evolution of hydrate deposits, the recovery of hydrate resources, and the release of methane from hydrates into the ocean and the atmosphere. Existing models of permeability in hydrate‐bearing sediments assume single and simplified hydrate pore morphology, and thus, fail to capture the dynamic evolution of permeability in sediments with changing hydrate saturation. With recent advances of direct observations of hydrate crystallization in sediments using microfocus X‐ray computed tomography, much has been learned about the dynamic evolution of hydrate morphology in sediment pores, based on which we established a physical model to quantitatively correlate the dynamic evolution of hybrid hydrate pore morphology to the permeability variation in sediments in this study. The robustness and universality of this new model are validated using published data from both laboratory synthesized and naturally occurred hydrate‐bearing samples. The results of this study enhance the physical understandings of flow in hydrate‐bearing sediments and shed light to hydrate reservoir evolution. Key Points The evolution of hydrate pore morphology depends on hydrate formation conditions, exerting diverse controls ove