辽河坳陷西部凹陷天然气成因类型与成藏模式

Origin of Nature Gas and Gas Filling Pattern in West Sag,Liaohe Depression

通过组分、同位素特征划分天然气成因类型,结合成藏条件对典型气藏进行解剖,探讨辽河西部凹陷不同成因天然气藏的成藏模式。研究认为,西部凹陷天然气以低熟煤成气和原油菌解气为主,分别以双台子地区和高升地区为典型。双台子地区原生气藏主要为东营期(35Ma)以来,沙三段中上部泥岩热解的煤成气从原油中出溶,或直接经断层运移至浅部聚集而成。高升地区菌解气藏分布于稠油层上方,主要为东营末期(24Ma)以来,原油在生物降解稠化过程中形成的生物气,经短距离运移后就近成藏。

Natural gas origin is classified by chemical and isotopic compositions of natural gas in the west sag of Liaohe depression.We discuss the gas filling pattern by means of conditions of gas accumulation.The low-mature coal-type gas and oil-biodegraded gas are dominant in the west sag,such as Shuangtaizi area and Gaosheng as typical case.The primary gas pool of Shuangtaizi was formed since the Dongying Phase,and the coal type gas sourced from the middle-upper part mudstone in three member of Sha Formation was resolved from oil and accumulated in shallow strata series or migrated into gas trap along faults.The oil-biodegraded gas was formed before 24Ma and accumulated at top of heavy oil layers by short distance migration in the Gaosheng area.