Abstract:

Analytic techniques of the light hydrocarbon and the carbon isotope of natural gases were employed to cast light on the natural gas origin of shallow gas reservoirs and the migration characteristics, and the origin of the gas hydrate proved in the north of the South China Sea, in combination with the regional geology and gas hydrate data. The result indicates that the natural gas from shallow reservoirs is a mixture of biogenic gas and thermal genetic gas. It reveals that the potential gas source for gas hydrate was not limited to biogenic gas, but the biodegradation gas and thermal genetic gas have great contribution to the gas hydrate. The thermal genetic gas in the mixture gases is from deep hydrocarbon reservoirs, which indicates that the gas hydrate maybe has a close relationship with the regular deep hydrocarbon reservoirs. It can be concluded that two types of gas hydrates originated from biogenic gas and mixture gas exit in Shenhu deep zone of continental margin in the north of the South China Sea. The deep zone of Baiyun Sag in Pearl River Mouth basin will be the most valuable target for gas hydrate exploration in this area.

Key words: gas hydrate, biogenic gas, biodegradation, mixture gas, Baiyun Sag