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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 (K0) with time. The hydrate‐bearing sandy‐silt is stiffer and has a larger K0 than the equivalent hydrate‐free sediment upon loading. During stress holds, the void ratio decreases sigmoidally with the log of time, and K0 converges to isotropic conditions. We interpret that during loading, the hydrate bears the load and deforms. With time, the hydrate redistributes the load and K0 increases. We used a viscoelastic model to describe the behavior. The model accurately captures deformation and K0 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. Plain Language Summary: Natural methane hydrates are ice‐like crystalline solids, typically found within and beneath permafrost regions and near the seafloor in the deep ocean. They host large amounts of methane and are envisioned as a potential energy resource, a potential geo‐hazard, and an active component in the Earth's carbon cycle. We studied the geomechanical behavior of natural and intact hydrate‐bearing sandy‐silts recovered from the deep‐water Gulf of Mexico. We performed all the experiments at a high pressure and low temperature to maintain the hydrate stable during testing. This study demonstrates that these hydrate‐bearing sandy‐silts are viscoplastic; deformation and stresses are rate‐dependent. Under sustained vertical load, while allowing no lateral deformation, the lateral stress rises with time. This process is known as stress relaxation. Simultaneously, the material undergoes vertical compression with time, a process known as creep. We interpret that these systems deform by hydrate "flowing" and displacing the pore water within the sediment. The hydrate distributes the load in all directions, and stress relaxation takes place. This viscoplastic behavior has important implications for gas hydrate production models, drilling and completing wellbores safely, and may elucidate the mechanisms for submarine landslides. Key Points: Hydrate‐bearing sandy‐silts are viscoplastic materials with a relaxation time scale on the order of hoursThe in‐situ stress state in hydrate‐bearing sandy‐silts undergoing burial may be isotropicLoad‐bearing hydrate flow viscously and redistributes the load. A spring‐dashpot model captures this behavior [ABSTRACT FROM AUTHOR] |
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