Coupled Effects of Capillary Pressure and Relative Permeability on Gas Production Behavior During Hydrate Depressurization

Capillary pressure and relative permeability are two key factors governing gas–water two-phase flow during hydrate depressurization; however, their relative contributions to gas production and the coupling mechanisms remain poorly understood. In this study, a unified and consistent framework has been developed to examine the coupled effects of capillary pressure and relative permeability for gas–water flow during hydrate depressurization. More specifically, an empirical relationship based on the van Genuchten (VG) model has been obtained for the entry pressure P0 and the shape parameter m, together with their representative ranges, by regressing the capillary pressure data from hydrate-bearing sediments collected from the public domain. Then, a numerical model was constructed to quantify the individual and coupled effects of capillary pressure and relative permeability on gas production in a target hydrate formation. The simulations employed fixed P0 values and prescribed relative permeability curves, without dynamically updating during hydrate dissociation. Across the compiled datasets, P0 is found to decrease inversely with pore radius and increase as a power-law function with hydrate saturation, whereas m exhibits considerable scatter in both sand-dominated (0.62–0.82) and silt-dominated (0.52–0.85) sediments. Within the tested VG model, parameter ranges, and Shenhu reservoir conditions, capillary pressure primarily suppresses local gas migration by enhancing water retention, with its limited impact on gas production, while cumulative gas production is overestimated without considering capillary pressure. In contrast, relative permeability plays a dominant role in hydrate production by directly controlling gas and water flow capacity and influencing pressure propagation. This study clarifies the relative roles and coupling mechanisms of capillary pressure and relative permeability during hydrate depressurization and provides a practical basis for selecting van Genuchten parameters and conducting flow-function sensitivity analyses in hydrate-bearing reservoirs.