Deformation behaviors of hydrate-bearing silty sediment induced by depressurization and thermal recovery

Abstract

Hydrate dissociation during gas production would lead to severe deformation of hydrate-bearing sediments and further induce the damage of the production well and possible reservoir instability. Predicting the deformation response of hydrate-bearing silty sediments during hydrate dissociation enable appropriate design and anticipate risk due to extraction process of gas from silty reservoirs which exist widely and stores large amounts of hydrates. To that end, this paper designs a series of triaxial tests, which were followed by thermal injection or depressurization, on artificial hydrate-bearing silty sediments. Deformation response of silty sediments during gas production is analyzed, and the respective effect of hydrate dissociation and pore-pressure-drop on the volume deformation of hydrate-bearing silty sediments is predicted. The results suggest that hydrate-bearing silty sediments are not broken during the depressurization process; instead, severe deformations occur. The axial and volume deformations of hydrate-bearing silty sediments are governed mainly by the effective stress, the effective stress ratio and the hydrate saturation. The mean effective stress plays the main role in the volume deformation induced by pore-pressure-drop, and the effective stress and effective stress ratio both plays important role in the volume deformation induced by hydrate dissociation. In contrast, collapse occurs for all hydrate-bearing silty sediments with various hydrate saturations when the thermal recovery method is applied.