Natural core-based laboratory analysis and comparisons of the mechanical and hydraulic characteristics of the soil skeleton of hydrate reservoirs in the South China Sea

Safe and efficient hydrate production relies on an in-depth understanding of the geotechnical characteristics of hydrate reservoirs. However, the role of the fundamental soil skeleton has not received sufficient attention. Using natural samples cored from the W01/W02 sites of GMGS4 in the Shenhu area of the South China Sea, we pri-marily performed classical geotechnical tests on their soil skeletons. Our analysis and comparisons indicate that these natural samples are clay-dominated soils with a low liquid limit. Clay-induced complex fluid-solid migration and water-induced bearing capacity decline should be considered. The absolute gas permeability, under confining stress range of 2-2.5 MPa, mainly varies between 0.05 and 1.5 mD with partial closed pores inside. The natural samples exhibit strain-hardening and two-stage stiffness characteristics. Based on other published data, the modulus-strength ratios of the natural soil samples in hydrate reservoirs of the South China Sea seem to be independent of the confining stress, and vary from 24 to 107. In addition, their recommended cohesion and friction angle are 70 kPa and 28.2 degrees, respectively. These findings are expected to provide a fundamental and valuable supplement for parameter selection in numerical simulations and response evaluation of field hydrate productions.

Automated summary

An analysis of natural soil samples from the Shenhu area of the South China Sea revealed that the samples are clay-dominated soils with a low liquid limit. The presence of clay induces complex fluid-solid migration and water-induced bearing capacity decline. The samples exhibit strain-hardening and two-stage stiffness characteristics, with an absolute gas permeability varying from 0.05 to 1.5 mD and partial closed pores. The modulus-strength ratios of the natural soil samples in hydrate reservoirs of the South China Sea are independent of the confining stress, ranging from 24 to 107, and have recommended cohesion and friction angle values of 70 kPa and 28.2 degrees, respectively. These findings are important for parameter selection in numerical simulations and response evaluation of field hydrate productions.