Study on Gas Hydrate Accumulation Mechanism and Favorable Zones in Qiongdongnan Basin

As an important oil and gas basin in the northern South China Sea, the Qiongdongnan Basin has huge gas hydrate resource potential. However, there are still many deficiencies in the research on its occurrence characteristics and accumulation laws: the hydrate identification methods is limited, mostly relying on single geophysical anomalies; the comprehensive analysis of reservoir characteristics and transport channels in the migration and accumulation system is insufficient; the main controlling factors of accumulation and enrichment laws are unclear, and the research on the accumulation mechanism of super-enriched hydrates is weak. To address the above issues, taking the Quaternary gas hydrates in the Qiongdongnan Basin as the research object, through the combination of geological, geophysical and geochemical methods, a “five-in-one” comprehensive identification method of “water body - seabed - stable zone - reservoir - gas source” has been established; it is clarified that the reservoir is mainly composed of clayey silt, and its high porosity and medium saturation provide favorable conditions for hydrate occurrence; it is revealed that the transport system is composed of multiple gas sources, fault - gas chimney networks and sand bodies, ensuring efficient gas migration; three accumulation models are divided: lower generation and upper storage, self-generation and self-storage, and composite mixed type, and it is proposed that the accumulation of super-enriched hydrates requires the coupling of long-term stable zones, multi-stage thermogenic gas charging and favorable reservoirs; four favorable zones such as the Lingnan Slope are optimized. The research results improve the gas hydrate accumulation theory in the Qiongdongnan Basin and have important economic and strategic significance for promoting China’s marine energy development and ensuring national energy security.