Undrained triaxial tests on water-saturated methane hydrate–bearing clayey-silty sediments of the South China Sea

Abstract

Approximately 90% of gas hydrates are buried in fine-grained sediments on earth, especially in the South China Sea. The potential instability of the fine-grained sediments induced by hydrate dissociation requires us to investigate the shear strength and pore pressure response of the sediments during the hydrate recovery. To date, most of studies focused on the undrained mechanical behavior of gas hydrate-bearing sand or gas hydrate-free clay, and few studies examined gas hydrate-bearing fine-grained sediments. According to the low-permeability and water-saturated characteristics of the sediments in the South China Sea, we performed a series of undrained triaxial shear tests on water-saturated methane hydrate-bearing clayey-silty sediments in this area. The experiment results show that the failure strength of methane hydrate-bearing sediments (MHBSs) increases with the increase in hydrate saturation and initial effective mean stress. The excess pore water pressure of MHBSs remains positive during shear. The cohesion in Mohr-Coulomb model increases with the increase in hydrate saturation, while the internal friction angle in Mohr-Coulomb model has little dependence on the hydrate saturation.

Influence of Particle Size Distribution on the Physical Characteristics of Pore-Filling Hydrate-Bearing Sediment

“…This is because the proportion of gas phase with lower thermal conductivity in pores gradually decreases. Moreover, the larger the particle sizes are, the higher the apparent thermal conductivity will be (7) As hydrate saturations increase, hydrate-bearing sediment's apparent electrical conductivity gradually decreases, while the resistivity index is opposite. 11 Geofluids…”

“…The physical characteristics of the hydrate-bearing sediment (HBS) are important to develop a reasonable exploitation plan [6,7], which mainly include the permeability [8], the thermal conductivity [9], and the electrical conductivity. In terms of HBSs' permeability research, Li et al [10] measured the permeability of unconsolidated quartz sands with different particle sizes before and after hydrate formation and found that the larger the particle sizes of the quartz sands, the higher the absolute permeability will be.…”

Seepage Force and Its Direct Mechanical Effects in Hydrate-Bearing Porous Media

“…Compared with the cementing hydrates, the pore-filling hydrates are believed to have a relatively small influence on the shear strength and stiffness of HBPM, but they can still restrict the movement of surrounding particles [37,39]; the loadbearing hydrates evolving from the pore-filling hydrates bond particles together into a cluster structure when hydrate saturation is beyond 40% [40]. In particular, the hydrate saturation can be higher than 80% in some local regions where the hydrates may directly bear loads [41,42]. Although hydrates with different pore-scale habits have different contributions to the shear strength and stiffness of HBPM, all of them can be regarded as a structure to bear and transfer loads.…”

Mechanical behaviors of hydrate-bearing sediment with different cementation spatial distributions at microscales

“…However, the hydrate reservoir existing in the excess gas is thought to have greater development potential since the free gas can be jointly exploited for increasing the natural gas production ( Yoneda et al., 2019 ). Generally, the current development of NGHs is in an important stage of progressing from field trials to commercial exploitation ( Wang et al., 2021 ; Zhou et al., 2018 ).…”