Modeling Water Retention Curve of Hydrate-Bearing Sediment

The water retention curve is an important constitutive relation routinely incorporated into numerical stimulations of production from gas hydrate reservoirs. It has significant influences on the physical and mechanical behaviors of unsaturated sediments. In most existing simulators, the water retention curve models are assumed to be independent of hydrate saturation, or coefficients are incorporated that consider the influence of hydrate, which may not accurately and fully characterize the water retention curves of hydrate-bearing sediments. This paper proposes a new model that can be used to determine water retention curves for hydrate-bearing sediments. The model was developed based on the original van Genuchten model, introducing a gas-entry pressure and residual water saturation as a function of hydrate saturation. The proposed model was calibrated against several experimental and numerical data sets. Good agreement between the experimental data and simulated results indicates that the proposed model captures the essential water retention curve characteristics of hydrate-bearing sediments, such as the residual water saturation and gas-entry pressure.