Hydrate-bearing sediment of the South China Sea: Microstructure and mechanical characteristics

The successful offshore hydrate production tests in the South China Sea proved the high productivity of clayey-silty hydrate reservoirs. However, the mechanical characteristics of these clayey-silty sediments have not been comprehensively investigated since the concerns about the productivity of such low-permeability reservoirs. In this study, based on the sediment matrix from the South China Sea, specimens were remolded with a porosity of 41% and hydrate saturation of 30% to perform a comprehensive mechanical investigation from micro to macro. Microcosmically, the hydrate in the clayey-silty sediment presents patchy distribution, being particle-displacive and particle-wrapped segregated hydrate morphology. Macroscopically, the compression and swelling indices of hydrate-bearing sediments in the South China Sea are obtained for the first time, which are larger than that of the hydrate reservoir in Krishna-Godavari Basin. The increasing effective confining pressure can slightly reduce the strain-softening and dilation characteristics of the hydrate-bearing sediments in the South China Sea. What's more, the failure strength and stiffness increase with an increasing effective confining pressure, while the failure volumetric strain firstly increases and subsequently decreases with an increasing effective confining pressure. These results are essential input parameters to establish a constitutive model and numerical simulations.