GEOLOGICAL CHARACTERS AND THE ORIGINS OF THE NATURAL GAS OF HUANGHUA DEPRESSION

The natural gases of Huanghua Depression are derived from various sources. On the basis of the geological characters of the natural gases in the studied area, the occurrence and the compositional features of the gas-pays and their associative relationship to crude oil are studied. The natural gases can be classified into five types, i.e. pure natural gas, gas-top gas, associated gas, condensate gas, and CO₂ gas. Based on the composition, dryness, and the features of carbon isotopic composition, the origins of the natural gas in the area have been analyzed. The hydrocarbon gases can be divided into biogenic gas, near-surface mixed gas, thermogenic gas and deep source mixed gas. The non-hydrocarbon gases can be classified into deep-sourced gas and thermogenic gas or/and the mixed gas.