柴达木盆地西部咸化湖相优质烃源岩形成机理

古近系咸化湖相烃源岩是柴达木盆地西部地区主力油源。传统认为该地区烃源岩有机质丰度低、类型差、生油潜力有限，劣质的烃源条件与显著的勘探成效极不匹配。此前的研究首次证实了该地区发育优质烃源岩，对于重新认识柴达木盆地西部油气资源潜力、坚定寻找大中型油气田的信心具有重要的意义。本研究在烃源岩地球化学精细解剖基础上，应用岩石学、元素地球化学和有机地球化学等多种手段，探讨了优质烃源岩发育的条件，发现柴达木盆地西部地区咸化湖相沉积具有水体较浅且相对安静、盐度较高、营养物质相对贫乏的特点。受干旱寒冷气候影响，陆源淡水补给有限，水生生物发育程度相对较低。优越的保存条件有利于水生生物等生油母质的快速保存，形成富含氢元素的烃源岩，且可溶有机质含量较高；而较低的古生产力使得有机质丰度总体低于东部咸化湖盆。半深湖区水体盐度相对较低、营养物质较为丰富，是优质烃源岩形成最有利的地区；沉积凹陷区烃源岩厚度较大，但由于水体盐度高，远离物源区，水体分层明显，有机质丰度中等-好。

Formation mechanism of excellent saline lacustrine source rocks in western Q aidam Basin

The Paleogene saline lacustrine source rocks are the main sources of oil in western Qaidam Basin. It is traditionally believed that the source rocks in this area have low organic matter abundance, poor type and limited oil generating potential, and the inferior hydrocarbon source conditions are very inconsistent with significant exploration results. Previous study has confirmed the development of high-quality source rocks in the area, which is of great significance for re-recognizing the potential of oil and gas resources and consolidating the confidence of exploring large and medium-sized oil and gas fields in western Qaidam Basin. Based on the fine geochemical analysis of source rocks, the conditions for the development of high-quality source rocks are discussed by means of petrology, element geochemistry and organic geochemistry. It is found that the saline lacustrine deposits in western Qaidam Basin are characterized by relatively shallow and quite water, high salinity and poor nutrients. Affected by the drought and cold climate, the supply of fresh water is limited, and the development of aquatic organisms is relatively low. Favorable preservation conditions are conducive to the rapid preservation of oil generating biomass such as aquatic organisms, forming source rocks rich in H element with high soluble organic matter content. But lower paleo-productivity leads to the organic matter abundance overally lower than that of the eastern salinized lacustrine basins. The salinity of water in semi-deep lake is relatively low with rich nutrition, which is favorable to develop excellent source rocks. The source rocks are thick in the sedimentary depression, but due to high water salinity and far away from the source area, water stratification is obvious with moderate-high organic matter abundance.