在系统分析柴达木盆地西部南区第三系大量岩心和岩屑样品的基础上,确定了该区有效烃源岩有机碳含量下限值为0.4%,并依此厘定了红狮凹陷、扎哈泉凹陷和狮子沟地区E23和E13上部应为柴西南区第三系有效烃源岩。同时还选取了24块上述有效烃源岩进行了抽提物的饱和烃生物标志物分析,针对其典型的咸水湖相沉积环境进行了烃源岩的地球化学特征研究。结果表明:柴西南区第三系烃源岩总体呈现正构烷烃的偶奇优势,Pr/Ph<0.6,较高伽玛蜡烷和升藿烷的翘尾巴特征,但不同地区与凹陷的上述特征略有差异;Pr/Ph 、C35藿烷/C3藿烷与伽玛蜡烷/C30藿烷等一系列沉积环境参数指标的差异揭示出扎哈泉凹陷第三系烃源岩自成一体,特征迥异,应该处于微咸水—弱还原沉积环境,而红狮凹陷、跃进地区和狮子沟地区第三系烃源岩处于高盐度—强还原沉积环境,只是狮子沟地区相对较弱一些。认为柴西南区2类差异较大的第三系烃源岩分布区域特征可能预示柴西南区的原油也存在2类,因而在该区可能存在2大独立的油气系统。
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Based on analyses of source rocks in the Tertiary system in the south area of the western Qaidam basin, the low limit value of TOC is fixed on 0.4%. On this basis, the upper part of Xiagancaigou Formation(E2 3) and the lower part of Xiagancaigou Formation(E1 3) in the Hongshi sag, Zhahaquan sag and Shizigou zone are considered as effective source rocks. By the biomarkers analyses of 24 effective source rocks, we examined the sediment characteristics of the saline lacustrine environment to investigate the Geochemical characteristics. The results show: the Tertiary source rocks in the area are characterized by even over odd preference of n\|Alkanes, Pr/Ph<0.6 and high abundance of gammaceranes and C35 homohopanes, but these characteristics are different in all sags or zones. Different values of Pr/Ph, C35 homohopane/C34 homohopane and gammacerane /C30 hopane reveal that the sediment environment of Tertiary source rocks in the Hongshi sag, Yuejing zone and Shizigou zone is a high saline lacustrine and strong reduction environment and that of Shizigou zone is relatively inferior, while that of Zhahaquan sag is a low\|saline lacustrine and low reduction environment. The two types of oils in the south area of the western Qaidam basin, further, two independent hydrocarbon systems may be indicated by the two patterns of Tertiary source rocks in the same area.