Control of marine geothermal field on the occurrence of gas hydrates in Northern South China Sea

摘要

Marine geothermal fields play important roles in controlling the formation and occurrence of gas hydrate resources. Recent drillings show that the northern slope of the South China Sea is rich in gas hydrate resources. Gas hydrate samples were retrieved from many boreholes of the scientific drilling in the Shenhu deepwater area. However it has been a significant challenge to understand the fact that there is no presence of gas hydrates at drill site SH5, although the bottom simulating reflection (BSR) below this borehole is strong. In this report, we provide results from analysis of the seabed heat flow, in-situ temperature and thermal conductivity data collected in the Shenhu gas hydrate drilling area. The geological environment with low heat flow, such as the ridge of canyon, away from the fault, the middle fan subfacies, is more conducive to gas hydrate occurrence. Nevertheless in the vicinity of SH5, a mud diapir pierced into the gas hydrate stability zone. Consequently, it changed the temperature field of the region, which led to the hydrates decomposition.