Abstract:

Based on research of origin and filled periods of  CO₂   and development characteristics of diapirs, the distribution rules of  CO₂    in different types of diapirs and relevant causes are analyzed. The result shows that CO₂  of shallow gas reservoirs is mainly originated from pyrolysis of the crustal carbonate rocks, and the major causes of distribution diversity are differences of fluid components and filled periods, and difference of diapiric activity intensity. In low amplitude and weak energy diapirs,  CO₂   has mainly accumulated in underside of hydrocarbonriched reservoir. In high amplitude and middle energy diapirs, the distribution of  CO₂   shows apparent characteristics of blocksubregion: hydrocarbon gas rich is in shallow reservoir but  CO₂   is rich in deep reservoir on the same side of fault, and hydrocarbon gas is relatively  rich in reservoirs on hanging wall of fault but  CO₂  is rich in reservoir on footwall of fault, and CO2 hydrocarbon gas is relatively rich nearby fault but  is rich far away from fault. In eruptiontyped high energy diapirs, the distribution rule of  CO₂    is not apparent. Distribution depth of  CO₂   is relevant to its solubility in water:   CO₂  is relatively large in deep formation water, so the possibility of forming free  CO₂   gas reservoir is very small.

Key words: natural gas, distribution rule of CO₂, fluid diaper, shallow gas reservoir, Yinggehai basin