Geochemical characteristics and origin of natural gas in the Paleogene of northern Bohai Bay Basin, northeast China

As one of the most important proliferous basins in the northeast of China, the proven ration for natural gases in the Bohai Bay Basin is low. In order to figure out the genetic types and origins of natural gases in the Paleogene, a study on their geochemical characteristics (such as C₁₊, C₁/C₁₊, C₁/C₂₊₃, δ¹³C₁, δ¹³C₂) and kinetic behaviour of the lacustrine source rock have been carried out. The relationship between carbon isotopes and components of gases shows that oil-associated gas and coal-derived gas with low mature are the most important types in our research area. The gases were mainly generated from the lacustrine source rocks with type II₂-III kerogen. The pyrolysis experiment on the kerogen indicates that the Paleogene source rock entered the main gas window at the late Miocene. (paper)