Abstract: In combination with geological background, the genetic types and origin of the found gases in the Liaodong Bay, Bohai Bay basin was studied based on the analysis data about their components, carbon isotope and light hydrocarbon. The results showed that the found gas in Liaodong Bay is mainly wet gas, and could be classified into two genetic types, which are petroliferous gas and humic-prone gas, based on δ¹³C₂. The two genetic types are correspond to organic materials of type Ⅱ₁ and type Ⅱ₂. The petroliferous gas distributes in hydrocarbon fields of JZ21-1、JZ25-1 and JZ25-1S. And the humic-prone gas distributes in JZ20-2 hydrocarbon field. The petroliferous gas mainly comes from the source rocks with 0.6%~1.1% (R_o), and for the humic-prone gas comes from the ones with 1.1%~1.3% (R_o). It is concluded that the source rocks with bigger than 0.6% (R_o) in Liaodong Bay area could serve as effective gas source rocks, which suggests an optimistic prospect for gas exploration.

Key words: Liaodong Bay, natural gas, genetic type, origin