Two-phase relative permeability of hydrate-bearing sediments: A theoretical model

The understanding of two-phase flow behavior inside hydrate-bearing sediments (HBSs) is vital for commercial and safe gas production. Existing relative permeability models usually treat hydrate as a part of a solid matrix, ignoring the existence of hydrates in the pores. Besides, several models present complicated forms. These drawbacks undermine reliable predictions, leading to restricted applicability in specific cases. To solve this problem, we proposed an innovative two-phase relative permeability model considering hydrate as an independent phase from solid soil particles. The proposed model is presented in a simple form with easily determined parameters. It is verified by 193 data points of relative permeability, and proved to be capable to capture the essence of the behavior of two-phase flow in HBSs. The average RMSE of the improved model by transformation and participation of empirical parameters is 0.045. Both water and gas relative permeability decrease with increasing hydrate saturation and total void ratio. The relative permeability in pore-filling HBSs is generally smaller than that in grain-coating HBSs. Different behavior of two-phase flow could be attributed to the viscosity ratio and the wettability. Ignoring residual gas and water may account for the remaining uncertainty in predictions.