四川盆地高石梯-磨溪地区下二叠统气源示踪

以天然气、烃源岩及储层沥青的地球化学特征为主要依据,通过天然气-天然气、储层沥青-烃源岩、天然气-烃源岩3个方面对比,深入探讨四川盆地高石梯-磨溪地区下二叠统天然气来源。研究表明,四川盆地高石梯-磨溪地区下二叠统天然气主要来源于筇竹寺组泥岩。其5项证据分别为:下二叠统天然气乙烷碳同位素小于-30.5‰,甲、乙烷碳同位素倒转是由高演化程度烃源岩所致;多数下二叠统天然气与龙王庙组天然气特征最为相似;GS18,NC1井下二叠统天然气特征与寒武系相似,说明上下层气源一致;高石梯-磨溪地区下二叠统储层沥青地球化学特征与筇竹寺组泥岩最为相似;筇竹寺组泥岩主要为下二叠统供气,这一认识符合干酪根油气生成理论和同位素分馏规律。

Gas source tracing of Lower Permian in Gaoshiti-Moxi area,Sichuan Basin

Based on the geochemical characteristics of natural gas,source rock and reservoir asphalt,gas source of Lower Permian in Gaoshiti-Moxi area is deeply discussed according to gas-gas,reservoir asphalt-source rock and gas-source rock contrast.Research shows that gas source of Lower Permian in Gaoshiti-Moxi area in Sichuan Basin is mainly from Qiongzhusi mudstone.The five evidences are as follows.Ethane carbon isotope of Lower Permian gas in Gaoshiti-Moxi area is lighter than￣30.5‰and carbon isotope of methane and ethane reverses due to high evolution source rock.Gas of Lower Permian is most similar to that of Longwangmiao Formation.The natural gas characteristics of the Lower Permian and the Cambrian of well GS18 and NC1 are similar,which reveals that gas source of the upper and lower layers is similar.The geochemical characteristics of reservoir asphalt of the Lower Permian in Gaoshiti-Moxi area are most similar to those of the Qiongzhusi mudstone.The mudstone of Qiongzhusi Formation provides natural gas for the Lower Permian reservoir conforms the oil and gas generation theory and isotope fractionation rule.