Load-bearing characteristic of methane hydrate within coarse-grained sediments - Insights from isotropic consolidation

FF Gas hydrate, as a solid pore constituent, can potentially share external load with sediment matrix, and critically impact geological evolution of its hosting sediments, well integration and sediment settlement during gas production depending on its contribution to support external loading. We aim to address the question of whether hydrate shares the load with the soil skeleton through isotropic consolidation experiments. Our results highlight the formation of methane hydrate does not affect the integrity of sediment skeletons if the effective stress previously applied on the skeleton remains constant, which indicates that methane hydrate would not actively support the load. Subsequent external load applied to the sediments after hydrate formation can be supported by hydrate. Secondly, hydrate as well as hydrate-bearing sediments exhibit creep behavior. As hydrate creeps, the load transfers to the sediment skeleton with time and hydrate gradually retreats from the status of load-bearing. When hydrate saturation is low and the coexisting pore fluid can percolate through sediments, the local deformation of hydrate due to sediment consolidation induces excess pore pressure, which dissipates by pushing out the pore fluid. When the coexisting pore fluid is enclosed in hydrate mass in high hydrate saturation environments, the dissipation of excess pore pressure relies on the viscous flow of hydrate. This pressure dissipation could last for millions of years according to analytical analysis based on Terzaghi's consolidation theory, during which hydrate cannot completely escape the status of load-bearing. These observations conclude that load bearing is a dynamic status rather than a stagnant pore habit, countering conventional thinking that load bearing joins grain-coating, cementing and pore-filling as a pore habit of gas hydrate.