柴达木盆地北缘中侏罗统大煤沟组七段烃源岩有机地球化学特征及生烃潜力

柴达木盆地北缘地区在中侏罗世晚期,即大煤沟组七段(J2d7)时演化至最大湖侵期,发育了一套湖相泥页岩。通过对区内鱼卡煤矿井下样品的实测分析,结合先前报道的研究成果,确认了这套湖相泥页岩为优质烃源岩,藻类体、角质体和孢子体是这套源岩的主要生烃显微组分,有机质类型最好可达II1型。热演化研究表明,该套源岩在不同构造单元处于差异热演化阶段,既可生油亦可生气。虽然J2d7段烃源岩在平面上不同凹陷区具有一定的非均质性,但其生烃潜力,特别是在赛什腾—鱼卡凹陷地区,完全可与我国西北地区其它侏罗系优质烃源岩相媲美。长期以来,下侏罗统烃源岩被认为是柴北缘地区的主要油气源,J2d7段优质烃源岩的确认,对于深化柴北缘地区的油气勘探和地质研究具有重要意义。

Organic Geochemical Features of Mudstone Source Rock from Member 7 Strata of Middle Jurassic Age in the Northern Margin of Qaidam Basin and Its Hydrocarbon-Generation Potential

It has been acknowledged for a long time that in the northern margin of Qaidam Basin,the Lower Jurassic mudstone source rock has a better hydrocarbon generation potential than the Middle Jurassic sequences.In this paper,the hydrocarbon generation potential of a set of lacustrine mudstone source rock sequences developed in the Middle Jurassic Member 7 was discussed comprehensively.Based on geochemical analyses on these source rocks collected from the Yuqia area,and in combination with analytical results reported in previous literature,it is indicated that the J2d7 mudstone belongs to organic-rich source rocks.Organic petrographical micro-observation shows that algae,cutinites and sporophytes mainly constitute organic maceral of these mudstone source rocks,with the type of organic matter reaching II1 as best.Additionally,according to information of maturation,it is suggested that this set of source sequences has undergone different histories in different depressions.This implies that it could generate not only oil,but also gas.Although the distribution and quality of the J2d7 mudstone source rocks are heterogeneous in different depressions,this set of source rocks has good hydrocarbon generation capabilities no worse than the Lower Jurassic ones and enough attention should be paid in the future petroleum geologic exploration and research.