Gas permeability variation during methane hydrate dissociation by depressurization in marine sediments

Accurate acquisition of permeability change in hydrate-bearing sediments (HBSs) is the key to predicting reservoirs' multiphase fluids distribution and production capacity. Hydrate saturation and effective stress present significant effects on reservoir permeability. Thus, the influence of hydrate saturation and effective stress on gas permeability change of remolded core during decompression was studied. The results showed that effective stress compression and hydrate decomposition determine the flow channel structure within hydrate sediments. Under unconsolidated and low effective stress(σ' = 1.2 MPa) conditions, the gas permeability increased gradually as the decomposition of hydrate, and the magnitude of permeability variation before and after decomposition increased with increasing hydrate saturation, indicating that the effect of hydrate saturation on permeability dynamic change dominated at low effective stresses. When σ′ was increased to 3.2 MPa and 5.2 MPa, the results were contrary, indicating that the effective stress variation on gas permeability dynamic change dominated at higher effective stresses. In addition, it was found that compression led to higher heat transfer efficiency in high-saturation samples. When hydrate saturation was increased from 23.37% to 48.7%, the effect of increasing effective stress on gas production changed from inhibition to facilitation.