A mechanistic model for permeability in deformable gas hydrate-bearing sediments

Abstract

Accurate characterization of permeability behavior in hydrate-bearing sediments (HBS) is crucial for sustainable gas production. During gas exaction from HBS, permeability is strongly affected by the geomechanical conditions, which change pore structure of HBS. Moreover, hydrate dissociation will also change pore structure and geomechanical behavior of HBS. Therefore, the predictive modeling of permeability behavior in HBS under stress condition poses great challenges. In this work, a new analytical model is derived to study the effect of hydrate saturation on stress-dependent permeability behavior of HBS. The proposed permeability model solves the steady-state Navier-Stokes equations for fluid flow in HBS with hydrates. It considers hydrate saturation, retained water and hydrate-growth pattern, and is adequately validated with the experimental results in existing literatures. The model demonstrates that the permeability in wall coating (WC) hydrates is larger than that in pore filling (PF) hydrates. Pore habits of gas hydrates transfer from WC pore habit to PF pore habit when hydrate saturation increases. This work constitutes a comprehensive investigation of stress-dependent permeability in deformable HBS, which is a key issue for sustainable gas production. It not only provides theoretical foundations for quantifying permeability in HBS, but also can be used to estimate pore-scale parameters and other relevant parameters (e.g., rock lithology) of HBS using inverse modeling.