DYNAMIC MIGRATION OF GAS HYDRATE STABILITY ZONE IN THE DEEP WATER AREAS OF THE QIONGDONGNAN BASIN SINCE PLIOCENE AND ITS DISTRIBUTION PATTERN

The deepwater area of the Qiongdongnan Basin is beneficial to the enrichment of natural gas hydrate, where great potential occurs for commercial exploration and development of the hydrate. Utilizing the key parameters obtained in recent years, the dynamic migration of gas hydrate stability zone in the deepwater area of the basin since Pliocene (approximate 5 Ma) is carefully studied in this paper. The results suggest that the gas hydrate stability zone in the Qiongdongnan Basin currently occurs under the seafloor with a water depth >600 m and the maximum thickness may approach 190 m in the area with water depths around 800～2 400 m. Sea level falling during the glacial period might drive the gas hydrate stability zone migrating toward the abyssal plain, and there was an approximately 80 m reduction of gas hydrate stability zone in the transitional zone between the continental slope and abyssal plain. Thickness of the gas hydrate stability zone in the abyssal plain was thinned by approximately 50 m due to magmatic thermal events, and hydrate decomposition may cause the formation of polygonal faults.