塔里木盆地库车坳陷致密砂岩气地球化学特征

Geochemical characteristics of tight sandstone gas in Kuqa Depression,Tarim Basin

通过系统分析塔里木盆地库车坳陷不同区带致密气藏的天然气地球化学特征,探讨了库车坳陷深层致密砂岩气来源。库车坳陷中段天然气对应烃源岩热演化程度高,天然气主要为高—过成熟煤型气,可能存在三叠系湖相原油裂解气;库车坳陷东部和西部天然气对应热演化程度中等,现今发现的天然气来源于侏罗系煤系(迪那气田)、三叠系湖相泥岩(迪北、博孜气田),尚未发现湖相原油裂解气。根据库车坳陷不同区带天然气地球化学特征及来源的差异,结合烃源岩热演化差异性,指出大北—克深地区侏罗系—三叠系内有效圈闭有望成为三叠系湖相原油裂解气勘探新领域,秋里塔格构造中段—西段、阿瓦特—博孜古近系膏盐之下白垩系储层内构造圈闭、北部山前带东段侏罗系内构造—岩性圈闭为高—过成熟煤型气有利勘探区域。

Based on the systematic analysis of natural gas geochemical characteristics of gas reservoirs in different zones,this paper discusses the source of deep tight sandstone gas in Kuqa Depression,Tarim Basin.It is considered that the thermal evolution degree of source rocks corresponding to natural gas in the middle section of Kuqa Depression is high,and the natural gas is mainly the mixture of high-over mature coal-derived gas and Triassic lacustrine oil cracking gas.While the thermal evolution degree of source rocks corresponding to natural gas in the eastern and western Kuqa Depression is moderate.The discovered natural gas comes from Jurassic coal measures(Dina Gas Field)and Triassic lacustrine mudstone(Dibei and Bozi Gas Fields),no lacustrine oil cracking gas has been found.According to the differences of geochemical characteristics and sources of natural gas in different zones of Kuqa Depression,combined with the differences of thermal evolution of source rocks,it is pointed out that the effective traps in Jurassic strata in Dabei and Keshen areas are new exploration fields for Triassic lacustrine oil cracking gas;the structural traps in Cretaceous reservoirs under the Paleogene gypsum salt in the middle west section of Qiulitage structure and Awate and Bozi areas,and the Jurassic structural lithologic traps in the eastern part of northern piedmont belt are favorable exploration areas for high and over mature coal-derived gas.