Abstract:

The Qaidam Basin located in dry climatic zones of north latitude during the Tertiary Period.For the lack of continuous source of river and being surrounded by high mountains,it was only supplied by pluvial river temporarily and formed a perennial inland block saltwater basin.The issues of organic matter abundance for source rocks in salt lacustrine facies and evolutionary process of hydrocarbon generation play the significant roles in the assessment of hydrocarbon generation. Exploration indicated that the west region of Qaidam Basin is rich in oil and gas with source rocks of the Tertiary salt lacustrine facies. The source rocks are characterized by high salinity of 15 permillage to 60 permillage,high carbonate content over 20 percent,low average of total organic carbon content less than 0.5 percent,high percentage in conversion of hydrocarbon. The average ratio of chloroform bitumem "A" to the total organic carbon content(TOC) is 20 percent,and the highest ratio of "A" to TOC is 60 percent. The average ratio of hydrocarbon content(Hc) to TOC is 12 percent,and the highest Hc to TOC ratio is 40 percent. The evolution of source rocks has the characteristic of "two-stage hydrocarbon generation" of early stage and late stage. In the early stage when the vitrinite reflectance(R_o) was equal or less than 0.7 percent formed the immature to low-mature oil. In the late stage when R_o was larger than 0.7 percent formed the mature to high-mature oil.

Key words: Qaidam Basin, Tertiary salt lacustrine facies, source rock, geochemistry characteristic, hydrocarbon generation evolution

摘要：

柴达木盆地在第三纪时期位于北纬干燥气候带上,由于缺乏源远流长的河流,仅有短暂性洪水型河流补给水源,加上四周被高山环抱,所以形成了常年性内陆封闭咸水湖盆.咸水湖相中的烃源岩有机质丰度和成烃演化过程对生烃评价具有特殊意义.勘探证实柴达木盆地西部地区是以第三系盐湖相为烃源岩的油气富集区,烃源岩以含盐度高(15‰~60‰)、碳酸盐岩含量高(>20%)、有机碳含量低(一般低于0.5%)、烃转化率高(氯仿沥青"A"与有机碳含量之比一般为20%,最高可达60%;烃含量与有机碳含量之比一般为12%,最高可达40%)为其特征.同时,烃源岩的演化具有"两期成烃"的特点,即早期(R_o≤0.7%)形成未熟-低熟石油,晚期(R_o>0.7%)形成成熟-高成熟石油.

关键词: 柴达木盆地, 第三系盐湖相, 烃源岩, 地球化学特征, 成烃演化