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 predict the multiphase fluids distribution and production capacity of reservoirs. Hydrate saturation and effective stress present significant effect 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 shows that the variation paths of gas permeability in sediments during hydrate decomposition are completely different due to different effective stresses. Under unconsolidated and σ'=1MPa condition, the gas permeability increases gradually as the decomposition of hydrate, and the magnitude of permeability variation before and after decomposition increases with increasing hydrate saturation. When σ' is increased to 3MPa and 5MPa, the results are contrary, which is the result of the game between effective stress compression and hydrate decomposition. The effect of hydrate saturation on permeability dynamic change dominates at low effective stresses, while the effect of effective stress variation on gas permeability dynamic change dominates at higher effective stresses. In addition, with the increase in hydrate saturation from 23.37% to 48.7%, the effect of increasing effective stress on gas production changed from inhibition to facilitation.