Mechanical Characteristics of Underconsolidated Methane Hydrate- Bearing Clayed-Silty Sediments

Natural gas hydrate reserves in the South China Sea are huge, and their commercial prospects have been proved by repeated trial production. It is essential to systematically clarify the mechanical properties of hydrate-bearing sediments for the safe drilling of hydrate reservoirs. To date, most research studies focus on the undrained mechanical behavior of hydrate-bearing sandy or clayed sediments under normal consolidation conditions, but there are few reports on underconsolidated-undrained triaxial shear experiments. In this study, the present research conducts undrained triaxial shear tests on hydrate-bearing clayed-silty sediments. The results show that underconsolidated hydrate-bearing sediments appear to show a strain-hardening phenomenon, which are different from hydrate bearing sands in Nankai Trough. The excess pore water pressure of hydrate-bearing sediments remains positive during shear. The increasing degree of consolidation will increase the failure strength and the Secant Young's modulus E50. According to the Mohr- Coulomb criterion, the corresponding predicting formulas are established, and the cohesion increases with the increase in the degree of consolidation, while the internal friction angle is not sensitive to the degree of consolidation. In addition, the failure strength and the Secant Young's modulus E50 increase with the increase in initial effective confining stress before shearing.

Automated summary

The huge reserves of natural gas hydrates in the South China Sea have been proven to have commercial prospects through repeated trial production. It is crucial to understand the mechanical properties of hydrate-bearing sediments to ensure safe drilling of hydrate reservoirs. This study focused on undrained triaxial shear tests on hydrate-bearing clayed-silty sediments, revealing a strain-hardening phenomenon and positive excess pore water pressure during shear. The research also established predicting formulas based on the Mohr-Coulomb criterion, showing that the degree of consolidation affects the failure strength and the Secant Young's modulus E50.