The Viscoplastic Behavior of Natural Hydrate-Bearing Sandy-Silts Under Uniaxial Strain Compression (K0 Loading)

The in-situ stress state and geomechanical properties of hydrate-bearing sediments impact hydrate formation and gas production strategies. We explore the uniaxial strain compression and stress evolution of natural hydrate-bearing sandy-silts from Green Canyon Block 955 in the deep-water Gulf of Mexico. We performed constant rate of strain uniaxial strain experiments, interrupted by periods where we held the axial stress constant, to explore the vertical deformation and the evolution of the ratio of lateral to axial effective stress (K-0) with time. The hydrate-bearing sandy-silt is stiffer and has a larger K-0 than the equivalent hydrate-free sediment upon loading. During stress holds, the void ratio decreases sigmoidally with the log of time, and K-0 converges to isotropic conditions. We interpret that during loading, the hydrate bears the load and deforms. With time, the hydrate redistributes the load and K-0 increases. We used a viscoelastic model to describe the behavior. The model accurately captures deformation and K-0 trends but does not reproduce all the complex interactions of the hydrate with the porous skeleton. We anticipate that viscous effects within hydrate sediments will impact reservoir compression and stresses during production (hours to days), result in isotropic stress state over geological timescales, and explain the creeping movement in submarine landslides.