Meng Bingkun, Zhou Shixin, Li Jing
School of Petroleum Engineering and Environmental Engineering, Yan'an University, Yan'an, Shaanxi 716000, China.
Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China.
ACS Omega. 2024 Oct 1;9(41):42361-42374. doi: 10.1021/acsomega.4c05687. eCollection 2024 Oct 15.
The western Qaidam Basin is rich in oil and gas resources, constituting over 90% of the total oil and gas resources in the whole basin. However, the regional distribution characteristics of molecular markers of crude oil and the petroleum system elements relevant to the distribution of oil and gas in the northwest Qaidam Basin are still unclear, which restricts further exploration of oil and gas reservoirs. A total of 38 crude oils were collected from the Xiaoliangshan Sag and Mangya Sag in the northwest Qaidam Basin and analyzed by gas chromatography-mass spectrometry (GC-MS). The indicators of sedimentary environment, organic matter source, and thermal maturity show regular changes from the west to the east in the Xiaoliangshan Sag and Mangya Sag. The C /C , (C + C)/(C + C), and C-C-C regular sterane distribution characteristics indicate that the input proportion of lower aquatic organisms in source rocks (E-N) gradually increases, while the input proportion of terrigenous organic matter gradually decreases. The triaromatic dinosterane index (TDSI) and methyltriaromatic steroid index (MTDSI) indicate that the input proportion of dinoflagellates gradually increases. The gradual increase in the Pr/Ph ratio indicates a decrease in the reducibility of the sedimentary environment of source rocks. The gammacerane index (Ga/CH) and methylated-2-methyltrimethyltride-cylchromans (MTTCs) indicate that the degree of stratification and salinity of water body gradually decrease. A total of 23 thermal maturity parameters indicate that crude oil is in a mature evolution stage, and the thermal maturity of crude oil increases with depth, indicating that there are the characteristics of hydrocarbon accumulation close to source rocks. The variation features of sedimentary environment, organic matter origin, and thermal maturity indicators from the west to the east in the Xiaoliangshan Sag and Mangya Sag are controlled by the sedimentary structure characteristics of the study area.
柴达木盆地西部油气资源丰富，占全盆地油气资源总量的90%以上。然而，柴达木盆地西北部原油分子标志物及与油气分布相关的含油气系统要素的区域分布特征仍不明确，这制约了油气藏的进一步勘探。从柴达木盆地西北部的小梁山凹陷和茫崖凹陷共采集了38个原油样品，并采用气相色谱 - 质谱联用仪（GC - MS）进行分析。小梁山凹陷和茫崖凹陷的沉积环境、有机质来源和热成熟度指标自西向东呈现出规律性变化。C /C 、(C + C)/(C + C)以及C - C - C规则甾烷分布特征表明，烃源岩（E - N）中低等水生生物的输入比例逐渐增加，而陆源有机质的输入比例逐渐降低。三芳基甲藻甾烷指数（TDSI）和甲基三芳基甾烷指数（MTDSI）表明甲藻的输入比例逐渐增加。Pr/Ph比值的逐渐增大表明烃源岩沉积环境的还原性降低。伽马蜡烷指数（Ga/CH）和甲基化 - 2 - 甲基三甲基十三烷基色满（MTTCs）表明水体的分层程度和盐度逐渐降低。23个热成熟度参数表明原油处于成熟演化阶段，且原油热成熟度随深度增加，表明存在近源成藏特征。小梁山凹陷和茫崖凹陷自西向东沉积环境、有机质来源及热成熟度指标的变化特征受研究区沉积构造特征控制。
