Qu Yansheng, Qiao Jinqi, Zhong Ningning, Li Wei, Zhang Guanlong, Yu Hongzhou, Wang Gui, Yan Fangchao
Key Laboratory of Shale Gas Exploration, Ministry of Natural Resources, China University of Petroleum, Beijing 102249, China.
College of Geoscience, China University of Petroleum, Beijing 102249, China.
ACS Omega. 2025 Jan 15;10(3):2735-2761. doi: 10.1021/acsomega.4c08477. eCollection 2025 Jan 28.
Recently, there has been an increasing focus on deep and ultradeep oil and gas exploration and development. The Upper Jurassic Qigu Formation (Fm.) in the Yongjin region, located in the central area of the petroleum-bearing Junggar Basin, develops typically deep and ultradeep hydrocarbon reservoirs, but there is currently limited knowledge of the geochemical characteristics and origins of the oils in the reservoirs. A comprehensive analysis of the molecular characteristics and carbon isotopes of the oil and extractable organic matter (OM) samples from the Qigu reservoirs, as well as source rocks from the Middle Permian lower Wuerhe and Lower Permian Fengcheng Fm., was carried out to elucidate the thermal maturity, biological sources, and biodegradation scale of the OM, as well as the depositional environment of the related source rocks. The results suggest that the Qigu oils originated primarily from source rocks formed in a hypersaline lacustrine environment with paleoredox conditions of bottom water ranging from reducing to suboxic conditions. Furthermore, the biological sources of oils predominantly originated from bacteria, followed by algae. The degradation scales range between 3 and 4, and the thermal maturity is in the oil window for the samples examined. The OM of the Permian source rocks in the Yongjin region are in the high thermal maturity stage due to their ultradeep burial, thereby providing limited information to oil and source correlation. By combining more than 1000 published data from the entire basin, significant differences between the Jurassic and Permian source rocks, as well as minor differences between the lower Wuerhe (i.e., the ratios of Pr/C of <0.5, PhC of <0.5, Pr/Ph of >1.5, C/C sterane of >0.4, and hopanoids/steranes of >1 as well as the higher C/C Tri ratios) and Fengcheng source rocks (i.e., β-carotane/- ratios of >0.1 and some samples with C steranes concentrations of <10% in the normalized concentrations of C, C, and C steranes), were observed, and the origins of the oils were determined. The oil-source correlation suggests that the oils most likely originated from the lower Wuerhe Fm. without strictly excluding the possibility of a contribution from the Fengcheng Fm.
近年来，深部和超深部油气勘探开发日益受到关注。位于准噶尔含油盆地中部地区的永进地区上侏罗统齐古组发育典型的深部和超深部油气藏，但目前对该组油藏原油的地球化学特征及成因了解有限。通过对取自齐古组油藏以及中二叠统下乌尔禾组和下二叠统风城组烃源岩的原油和可提取有机质（OM）样品的分子特征和碳同位素进行综合分析，以阐明OM的热成熟度、生源以及生物降解程度，以及相关烃源岩的沉积环境。结果表明，齐古组原油主要来源于在高盐度湖相环境中形成的烃源岩，其底水的古氧化还原条件从还原到亚缺氧。此外，原油的生源主要来自细菌，其次是藻类。降解程度在3到4之间，所研究样品的热成熟度处于生油窗内。永进地区二叠系烃源岩由于埋深超深，处于高热成熟阶段，从而为油源对比提供的信息有限。通过整合全盆地1000多个已发表的数据，观察到侏罗系和二叠系烃源岩之间存在显著差异，下乌尔禾组（即Pr/C<0.5、PhC<0.5、Pr/Ph>1.5、C/C甾烷>0.4以及藿烷类/甾烷类>1，以及较高的C/C三环萜烷比值）和风城组烃源岩之间存在微小差异（即β-胡萝卜素/ - 比值>0.1，以及一些样品中C甾烷浓度在C、C和C甾烷归一化浓度中<10%），并确定了原油的成因。油源对比表明，这些原油最有可能源自下乌尔禾组，但并不完全排除风城组有贡献的可能性。
