Temperature Effect on Undrained Mechanical Properties of Hydrate-Bearing Clayey Silts in the South China Sea

Abstract

Nearly 90% of hydrate resources are found in low-permeability and fine-grained soils, which requires investigation on the undrained mechanical characteristics of hydrate-bearing fine-grained soils (HBFGSs) to accomplish safe and efficient hydrate exploitation. Additionally, factors such as hydrothermal and geothermal gradients of the marine sediments and hydrate extraction by heat injection method simultaneously require an understanding of the temperature effect on the stability of HBFGSs and overburden hydrate-free sediments. For these reasons, this study conducted consolidated undrained (CU) triaxial experiments on water-saturated hydrate-free and hydrate-bearing clayey silts in the South China Sea (SCS) at different temperatures and presented results of temperature effects on undrained mechanical properties. This paper reveals the following and analyzes the reasons accordingly: (1) the failure strength of the hydrate-free clayey silts increases with temperature, whereas the failure strength of hydrate-bearing clayey silts decreases with temperature; (2) the temperature has almost no effect on the fitting line of end-of-test data for undrained shear of hydrate-free clayey silts in p′–q space; and (3) the presence of hydrates has a considerable influence on the excess pore pressure response and effective stress paths of clayey silts. The results will contribute to the understanding of the influences of environmental changes and hydrate extraction by thermal injection on the stability of hydrate reservoirs in the SCS.

Undrained Mechanical Properties of Overlying Soils of Gas Hydrate Reservoirs in the South China Sea

“…Numerous scholars from various fields have conducted extensive research on the mechanical characteristics of NGH layers. Research has shown that factors such as hydrate saturation, effective stress, particle size distribution, strain rate, and temperature–pressure conditions all exert impacts on the mechanical characteristics of NGH reservoirs. − The higher the hydrate saturation, the greater the strength and modulus of NGH reservoirs, especially when hydrate saturation exceeds 50% . With an increase in effective stress, NGH reservoirs’ strength and stiffness undergo a significant increase, accompanied by a transition from strain-softening behavior to strain-hardening behavior; Miyazaki et al confirmed that hydrate-bearing sediments exhibited greater strength at higher strain rates .…”