Impact of hydrate spatial heterogeneity on gas permeability in hydrate-bearing sediments

Abstract

The permeability characteristic of hydrate-bearing sediments (HBSs) is an essential factor for assessing the exploiting potential of target area. The two trial tests in the South China Sea have demonstrated the production feasibility of clayey hydrate reservoirs, and further clarifying main controlling factors of the permeability characteristic is an essential prerequisite for commercial development. However, the current studies mainly focus on homogeneous HBSs with different saturations and porosities, ignoring the natural spatial heterogeneity of hydrate since the sedimentary and accumulation history. In this study, spatial heterogeneous hydrate (0–23.1%) was generated in montmorillonite specimens, and effective stress (1–5 MPa) was applied. The results show that 1) HBSs permeability with heterogeneity hydrate occurrence presents an exponential-like relationship with saturation. 2) Heterogeneous hydrate occurrence would reduce the permeability sensitivity to saturation. 3) The permeability of heterogeneous HBSs decreases in a power function trend with increasing effective stress. 4) The heterogeneity reduces compression effect and decreases permeability damage rate. 5) Increasing hydrate spatial heterogeneity would decrease HBSs permeability.