孝泉-丰谷构造带须家河组天然气烷烃碳同位素特征及气源对比

Carbon Isotope Features of Alkane Gases of Xujiahe Formation in Xiaoquan-Fenggu Structural Belt and Their Gas-source Correlation

孝泉-丰谷构造带天然气资源非常丰富。"须上盆"、"须下盆"天然气组成差异明显,"须上盆"天然气干/湿混合现象明显,具有差异运聚特征,整体表现为构造气藏;"须下盆"主要为干气,热成熟作用较强。63个样品烷烃碳同位素资料统计表明,须家河组绝大多数为正碳同位素系列,即δ13 C1<δ13 C2<δ13 C3<δ13 C4,其中δ13 C1明显重于川中和川西地区,热演化程度异常高。须家河组烃源岩以腐殖型为主,天然气主要为干酪根初次裂解气。"须上盆"和"须下盆"自成藏特征明显,"须上盆"天然气δ13 C1一般小于-32.2‰、δ13 C2大于-25‰,"须下盆"天然气δ13 C1一般大于-32.2‰,δ13 C2一般小于-27‰。"须下盆"气藏母源主要来自须二段或须一段,为下生上储和自生自储气藏,合兴场地区有来自须三段倒灌气源充注;"须上盆"气源主要来自须三段烃源岩,为下生上储。

There were abundant natural gases in Xiaoquan-Fenggu tectonic belt.Gas composition was significantly different in the upper and lower natural gas systems,natural gas in the upper system was obvious mixture of dry and wet gases,the reservoir was structural gas reservoir.Compared with upper system,the gas in lower system was dry gas the strong thermogenics.The most of carbon isotopes of Xujihe Formation were positive(δ13C1<δ13C2<δ13C3<δ13C4),its δ13C1 value was heavy in contrast to the central and eastern Sichuan Basin with high degree of thermal evolution.Based on the 63 analysis samples,the organic matter of source rocks are dominated by huminite,mostly the gas is the primary cracking of the kerogen.Hydrocarbon accumulation characteristics are obvious,δ13C1 value is typically lighter than-32.2‰,δ13C2 value is more than-25‰ in the upper system,but in the lower system,δ13C1 value is typically more than-32.2‰ and δ13C2 is lighter than-27‰.According the research of gas-source correlation,the gas in the lower system is originated from the second member of Xujihe Formation and Ma'antang-Xiaotangzi Formation and the third member of Xujiahe Formation is the source rock of the upper system.