摘要
Qikou sag is the most enrichment area of natural gas in the Huanghua Depression. Based on geochemical data, the authors consider that most of mature natural gas is of humic origin in the Qikou sag. According to thermal stage of natural gas, four types of natural gas are classified as follows: microbial gas, mixing gas of microbial-thermal gas, thermal biogenic gas and abiogenic gas. The thermal biogenic gas as a main component is the future exploration target. In comparison with light hydrocarbon absorbed in the rock gas and natural gas, the authors consider that natural gas in the Qikou sag would be mainly originated from the Es3 source rock, and a certain contribution of Es1 source rock and Es1 oil biodegraded play an important role. Thus, natural gas originated from the Es3 source rock is the main goal for future exploration as well as the Es1 source rock.