板桥凹陷深层及奥陶系潜山均钻遇乙烷以上具异常重碳同位素的天然气。使用轻烃族组成、C7轻烃组成、环烷指数及苯、甲苯碳同位素证实 ,气源主要为板桥凹陷下第三系偏腐殖型烃源岩。进而从石炭―二叠系地层分布和二次成烃条件等方面 ,进一步否定了煤成气作为烃源的可能性。应用 δ¹³C₂ 与 δ¹³C_2-1相关关系图解判断 ,板桥凹陷异常重碳同位素天然气可以分为成熟阶段早期和中期腐殖型天然气、高成熟阶段早期腐殖型天然气和过成熟阶段天然气。根据天然气碳同位素特征 ,结合其它研究成果 ,认为千米桥潜山具多阶复合成藏特点。

Natural gas whose heavy hydrocarbon components are with abnormal heavy carbon isotope was obtained when drilling both Ordovician buried hill and deep beds in Banqiao Sag The analysis of light hydrocarbon group composition, C₇ light hydrocarbon composition, naphthene index, benzene and toluene carbon isotope proved that the gas mainly sourced from the Lower Tertiary kerogen Ⅱ₂ source rocks Moreover, the author further denied the possibility of coal|formed gas to be the hydrocarbon source on the basis of Carboniferous and Permian distribution and the secondary hydrocarbon generation condition. Applying the δ¹³C₂ and δ¹³C_2-1 correlation chart analysis, the author finds out that the nature gas with abnormal heavy carbon isotope in Banqiao Sag can be classified into three types, i e. humic gas in early and medium mature stage, humic gas in early high mature stage, and over matured gas Thus according to nature gas carbon isotope characteristics, combined with other corresponding research achievements, the author reveals that Qianmiqiao buried hill gas pool is specially characterized by its multistage, composite hydrocarbon accumulation.