Stability Analysis of Gas Hydrate in the Shenhu Survey, northern slope of South China Sea

Gas hydrate formated in submarine sediments under low temperature and high pressure condictions. The gas hydrate stability zone, which related to stability conditions, is widely identifitied around continental margine in the... [ view full abstract ]

Gas hydrate formated in submarine sediments under low temperature and high pressure condictions. The gas hydrate stability zone, which related to stability conditions, is widely identifitied around continental margine in the world, including South China Sea. In 2007, the China Geological Survey (CGS) carried out the first gas hydrate drilling expedition in the Shenhu Area, northern continental slope of South China Sea. A total of eight boreholes were drilled and gas hydrate was revealed in the core samples from 3 sites(SH2, SH3, SH7). Numerous gas hydrate-related data have been reported, including 2D and 3D seismic data, log well data, geochemical in situ test data and heat flow data. In this study, we modeled the gas hydrate stability zone (GHSZ) with the Tishchenko’s equation (2005) using methane gas composition, water temperature, seafloor temperature and geothermal gradient to see if it is consistent with the observed depth of the BSR. However, the background heat flow at northwest (where SH2 located) and southeast (where SH5 located) are different significantly. It is higher at southeast. According to the calculation, the depth of the BSR matches well with the base of GHSZ estimated from the background heat flow (geothermal gradient) at both northwest and southeast. We tried to discuss, under comparison of gas hydrate stability conditions and gas fluid flow at SH2 (which gain gas hydrate samples) and SH5 (which do not gain gas hydrate samples), especially the absence of gas hydrate at site SH5 even there is GHSZ absolutely, various factors about gas hydrate distribution in the northern slope of South China Sea. We infered that gas fluid flow and sediments may more effective than other factors.