摘要
盐湖环境对油气生成具有重要的地质意义。国内外有诸多含油气盆地发育咸湖相烃源岩。自新生代以来，在青藏高原的隆升作用下，柴达木盆地的海拔升高、湖盆逐渐封闭、持续的干寒气候及盐源的充分供应，使得柴达木盆地逐渐变成了一个典型的高原咸化湖盆，其中，下干柴沟组为柴达木盆地西部英西地区的主力烃源岩层系。文中通过有机岩石学、有机地球化学及生物标志物地球化学研究，对英西地区下干柴沟组上段进行了烃源岩评价，并探讨了其沉积环境及生烃母质类型。研究结果表明：英西地区下干柴沟组上段烃源岩总有机碳质量分数在0.31%～1.49%，平均值为0.82%；氯仿沥青“A”质量分数在562.16×10-6～2 999.65×10-6，平均值为1 619.59×10-6。烃源岩生烃母质为藻类、细菌和高等植物，以低等水生生物为主。有机质类型主要为Ⅱ型，其次为Ⅲ型，烃源岩成熟度介于低成熟—成熟。英西地区下干柴沟组烃源岩综合评价为好的烃源岩。生物标志化合物特征表明，下干柴沟组上段烃源岩沉积于水体盐度较高、还原性较强的湖相环境之中。
Abstract
Salt lake environment has important geological significance for oil and gas generation. There are many oil-bearing basins containing salt lake facies source rocks at home and abroad. Since Cenozoic era, with the uplift of the Tibetan Plateau, the Qaidam Basin has gradually become a typical plateau salt lake basin because of the altitude rise, the lake basin gradually closed, the persistent dry and cold climate, and the adequate supply of salt. In the basin, the Xiaganchaigou Formation is the main source rock series in the Yingxi region which located in the western part of Qaidam Basin. Based on study of organic petrology, organic geochemistry and biomarker geochemistry, the source rocks of the upper member of Xiaganchaigou Formation in the Yingxi region were evaluated, and their sedimentary environment and the types of hydrocarbon generating parent material were discussed. The results show that the total organic carbon content of source rocks in the upper member of Xiaganchaigou Formation in the Yingxi region is 0.31% to 1.49%, with an average value of 0.82%. The value range of chloroform bitumen "A" is 562.16×10-6 to 2,999.65×10-6, with an average of 1,619.59×10-6.The source rocks are mainly composed of algae, bacteria and higher plants, mainly low aquatic organisms. The organic matter type is mainly type Ⅱ, followed by type Ⅲ. The maturity of source rock is between low maturity and maturity. Comprehensive evaluation shows that the source rocks of the Xiaganchaigou Formation in the Yingxi region are good source rocks. The characteristics of biomarkers indicate that the source rocks of upper member of Xiaganchaigou Formation are deposited in the lacustrine environment which has high salinity and strong reducibility.
Keywords:
School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, China;
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