塔里木盆地塔东英南2气藏气源分析

英南2凝析气藏天然气属富氮湿气,烃类气体体积分数一般为78.86%~87.67%;甲烷68.92%~76.67%,重烃气体为9.17%~14.01%,非烃气体氮气为13.89%~21.07%,甲烷和乙烷的碳同位素分别为-38.6‰~-36.2‰和-30.9‰~-34.7‰.根据天然气组分、天然气碳同位素的特征,认为英南2凝析气藏的天然气来源于高过成熟的下古生界海相寒武系—下奥陶统腐泥型干酪根形成的原油裂解气,同时应用ln(C2/C3)-ln(C1/C2)及δ13C2-δ13C3与ln(C2/C3)判识模式也印证了英南2气藏气源为原油裂解气,气藏凝析油中存在高含量的金刚烷,指示原油经历了裂解,裂解程度为80%~90%.

Gas source analysis of Yingnan-2 gas reservoir in the eastern part of Talimu Basin

The natural gas in Yingnan-2 condensate gas pool is wet gas and rich in nitrogen.The content of hydrocarbons ranges from 78.86% to 87.67%,of which,methane accounts for 68.92%～76.67%,heavy hydrocarbon accounts for 9.17%～14.01% and nitrogen gas accounts for 13.89%～21.07%.The carbon isotopes of methane and ethane compositions are in the range of-38.6‰～-36.2‰ and-30.9‰～-34.7‰ respectively.According to the components and carbon isotope characteristics of the gas,it is held that Yingnan-2 condensate gas is from the oil-cracked gas generated from hypemature Cambrian-Lower Ordovician sapropel kerogens.The identification modes of ln(C2/C3)-ln(C1/C2),δ13C2-δ13C3 and ln(C2/C3) verify also that Yingnan-2 gas is from oil-cracked gas.There is high content of adamantine in the condensate oil in the gas pool,which shows that the condensate oil is cracked.The cracking degree of the oil is 80%～90%.