Effect of clay type and content on the mechanical properties of clayey silt hydrate sediments

Knowledge of the mechanical properties of natural gas hydrate reservoirs is fundamental to the safe and commercial extraction of natural gas hydrate. In our work, according to the characteristics of marine sediments in the South China Sea, gas hydrate samples with matrices containing 0%, 10%, 20%, and 30% montmorillonite or illite were prepared based on the saturated gas method. Under effective confining pressures of 2, 3 and 4 MPa, drained compression tests were performed on the samples. The results show that the clay type and clay content affect the failure strength and deformation of clayey silt hydrate sediments. The presence of clay causes the clayey silt hydrate samples to exhibit strain hardening behavior accompanied by shear shrinkage, and the failure strength and stiffness decrease with increasing clay content, as does the internal friction angle. The strength, stiffness, and Poisson's ratio of samples containing illite are generally greater than those containing montmorillonite. In addition, due to the strong bound water between particles, the cohesion of hydrate samples containing montmorillonite with similar hydrate saturations is higher than that of samples containing illite, while the internal friction angle is lower. These results are valuable for production well siting assessment in clayey silt hydrate reservoir and provide requisite theoretical basis for wellbore safety design.