Gas Hydrate Accumulation Mechanism of the Clayey Silt Reservoir in the Shenhu Area, South China Sea

The basic pore structure characteristics and poro-perm properties of the clayey silt reservoirs play an important role in understanding the accumulation mechanism of gas hydrates in the Shenhu area, South China Sea (SCS). In this work, the nonhydrate and hydrate-bearing reservoir samples from depths of 97.32 to 194.46 m in the Shenhu area, SCS, were comprehensively analyzed using total organic carbon (TOC) testing, Rock-Eval analysis, X-ray diffraction, porous-perm capacities, nitrogen (N2) adsorption, and focused ion beam-scanning electron microscopy (FIB-SEM). The experimental results suggest that the hydrate-bearing reservoirs contain relatively lower quartz and higher clay contents, indicative of an abundant plate-like pore network system. In addition, the hydrate-bearing reservoirs tend to have more meso- and macropores, suggesting that gas hydrates can easily occur in those large pores, especially the foraminifera-rich pore network system. Permeabilities of the nonhydrate reservoirs are much higher than that of the hydrate-bearing reservoirs. In addition, the total pore volumes of hydrate-bearing reservoirs are 27% higher than that of the nonhydrate reservoir, indicating a relatively higher original porosity, which can provide sufficient pore space for hydrate growth. A simple conceptual model for gas hydrate accumulation is proposed owing to the detailed research on those two reservoirs. The outcomes of this study, can shed more light on underlying mechanisms involved in the exploration and exploitation of the clayey silt gas hydrates, specifically in the Shenhu area, SCS.