准噶尔盆地车排子隆起西南部原油地球化学特征及油源分析

Petroleum Geochemistry and Oil-source Analysis in the Southwest of Chepaizi Uplift,Junggar Basin

车排子隆起毗邻昌吉凹陷和四棵树凹陷,油源丰富,构造条件良好,具备比较有利的油气聚集条件。近年来已在车排子隆起的侏罗系、白垩系、古近系和新近系获高产工业油气流。分析了车排子隆起西南部原油(或油砂抽提物)的地球化学特征,并对其油源作初步分析。结果表明研究区具有两类地球化学性质存在明显差别的原油。第一类原油遭受了不同程度的生物降解,并存在二次充注现象,推测早期充注原油来自昌吉凹陷二叠系,并遭受了不同程度的生物降解,后期混入了来自侏罗系烃源岩生成的原油。第二类原油具有侏罗系煤系烃源岩与白垩系湖相泥质烃源岩混源的特点,这类原油的碳同位素组成、正构烷烃分布特征和姥植比等均表现出煤成油的特征,但甾、萜烷烃类化合物组成与白垩系烃源岩接近,推测是由于侏罗系煤成油在向上运移成藏过程中,受到成熟度相对较低、生物标志物相对丰富的白垩系烃源岩的浸析作用所致。

Chepaizi uplift lies between Changji sag and Sikeshu sag, which is a favorable area for oil accumulation with abundance oil sources and favorable structures. During recent years, many new oil fields were found in the southwest of Chepaizi uplift. By 2004, the oils had been discovered from the Jurassic, Cretaceous and Tertiary in the study area. Geochemical features of oils or core extracts are analyzed from these reservoirs. It is concluded that these oils can be divided into two groups. The first group is subjected to biodegraded heavily and two stages of hydrocarbon accumulation are predicted. In the first stage oils from Permian were biodegraded, and in the second stage oils were derived from Jurassic. The second group are the mixtures of Jurassic coal-formed oils and Cretaceous-derived oils. The carbon isotope, n-alkanes and isoprenoids compositions of these oils are similar to core extracts from Jurassic coal measures. However, sterane and terpane compositions of these oils show affinity to Cretaceous source rocks. It is deduced that coal-formed oils dissolved the biomarker-rich Cretaceous bitumen of relatively low thermal maturity, and overprinting occurs during oil migration.