Abstract The Yuka depression is one of the most important energy production bases in the Qaindam Basin. Although shales in the 7th member of the Dameigou Formation (J2d7) are key members of Middle Jurassic Petroleum System, organic geochemistry and petrography of different rock facies have not been fully analyzed. In this study we evaluate hydrocarbon generation potential of the J2d7 by applying integrated petrographic, geochemical and mineralogical analyses. In addition, pore structure is characterized using field emission scanning electron microscopy (SEM), CO2 and N2 physisorption. Results indicate that mudstone, carbonaceous-mudstone and siltstone have total organic carbon (TOC) values of 2.64%, 5.61% and 0.48%, respectively, as well as variations in the hydrogen index (HI). Kerogen types are mainly Type Ⅲ, with maturity varying from marginally mature to mature. Notably, excess methane adsorption capacities were higher in the carbonaceous-mudstone sample (4.66 cm3/g) than in the mudstone sample (1.78 cm3/g). Primary minerals in the mudstone were quartz and clay; kaolinite, illite and illite/smectite (I/S) were the dominant clay minerals. Clay minerals and TOC content, as well as positive correlations between illite, I/S and mesopore SSA, were factors controlling pore structure development; in contrast, kaolinite contents were negatively correlated with SSA. Liptinite is the dominant maceral composition and a high content of C29 regular sterane in the carbonaceous-mudstones suggests primary higher-plant input, associated with a low gammacerane index (0.28–0.32) and a high pristane/phytane (Pr/Ph) ratio (3.02–3.96). Petrographic and geochemical results indicate an alternating depositional environment across suboxic semi-saline to oxic fresh water changes. Higher-plants were predominant and a small quantity of algae were preserved through in-situ accumulation and migration during shale development; an oxic water column with carbonaceous-mudstone was also present. Although organic matter was marginally mature to mature, the abundance of liptinite (average of 63%) was derived from higher-plants, possibly being the primary materials producing gaseous hydrocarbons.

中文翻译：

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柴达木盆地尤卡坳陷中侏罗统湖相烃源岩孔隙结构特征及生烃潜力：岩石学和有机地球化学分析的启示

摘要 尤卡坳陷是柴达木盆地最重要的能源生产基地之一。虽然大梅沟组七段（J2d7）页岩是中侏罗统石油系统的重要成员，但不同岩相的有机地球化学和岩相学尚未完全分析。在这项研究中，我们通过应用综合的岩石学、地球化学和矿物学分析来评估 J2d7 的生烃潜力。此外，使用场发射扫描电子显微镜 (SEM)、CO2 和 N2 物理吸附表征孔结构。结果表明，泥岩、碳质泥岩和粉砂岩的总有机碳 (TOC) 值分别为 2.64%、5.61% 和 0.48%，以及氢指数 (HI) 的变化。干酪根类型主要为Ⅲ型，成熟度从略成熟到成熟不等。值得注意的是，碳质泥岩样品（4.66 cm3/g）中的过量甲烷吸附能力高于泥岩样品（1.78 cm3/g）。泥岩中的主要矿物是石英和粘土；高岭石、伊利石和伊利石/蒙脱石（I/S）是主要的粘土矿物。粘土矿物和TOC含量以及伊利石、I/S和中孔SSA之间的正相关是控制孔隙结构发育的因素；相比之下，高岭石含量与 SSA 呈负相关。Liptinite 是主要的微晶成分，碳质泥岩中 C29 规则甾烷含量高表明初级高等植物输入，与低伽玛蜡烷指数 (0.28-0.32) 和高原始烷烃/植烷 (Pr/Ph) 比率相关。 3.02–3.96）。岩石学和地球化学结果表明，在低氧半咸水到含氧淡水变化之间存在交替的沉积环境。页岩发育过程中以高等植物为主，少量藻类通过原位积累和迁移得以保存；还存在含碳质泥岩的含氧水柱。虽然有机质稍微成熟到成熟，但丰富的 liptinite（平均 63%）来自高等植物，可能是产生气态烃的主要材料。还存在含碳质泥岩的含氧水柱。虽然有机质稍微成熟到成熟，但丰富的 liptinite（平均 63%）来自高等植物，可能是产生气态烃的主要材料。还存在含碳质泥岩的含氧水柱。虽然有机质稍微成熟到成熟，但丰富的 liptinite（平均 63%）来自高等植物，可能是产生气态烃的主要材料。