Impact of Clay on the Decompositional Mechanical Properties of Clayey Silt Hydrate Sediments
Qiongqiong Tang, Chengqi Sun, Yuanbo Chen, Wei Guo, Rui Jia, Huicai Gao, Yu Zhou, Weiqiang Chen, Guansheng Han, Xiangyang Xu
Abstract
For sustainable and safe gas production, it is crucial to correctly understand the mechanical properties of clayey silt hydrate reservoirs. To investigate the impact of clay on the decompositional mechanical behavior of clayey silt hydrate sediments during gas production, artificial hydrate samples with illite or montmorillonite were first prepared according to the survey data in the South China Sea. Then, depressurized decomposition was used to simulate the real gas production process. Finally, axial loads at different confining pressures were applied to samples with different residual hydrate saturations in multistage triaxial tests. Results show that clays considerably impact the decompositional mechanical properties of clayey silt hydrate sediments. Although both sediment types exhibit strain hardening and shear shrinkage during gas production, illite-containing clayey silt hydrate samples have a lower stiffness to resist deformation but a higher strength to resist failure than montmorillonite-containing clayey silt hydrate samples at similar residual hydrate saturations. The stress–strain curves of completely decomposed montmorillonite-containing clayey silt hydrate samples almost coincide with those of hydrate-free samples, while those of completely decomposed iIllite-containing samples are slightly higher than those of hydrate-free samples. Furthermore, a modified Mohr–Coulomb strength criterion was established for clayey silt hydrate sediments with different clays during hydrate dissociation. This study guides the future commercial extraction of hydrates from clayey silt reservoirs.