Wang Youzhi, Mao Cui, Duan Xinguo
College of Energy Resources, Chengdu University of Technology, Chengdu, Sichuan 610059, China.
Exploration and Development Research Institute of Daqing Oilfield Company Ltd., Daqing, Heilongjiang 163712, China.
ACS Omega. 2024 Jun 17;9(26):28237-28252. doi: 10.1021/acsomega.4c01542. eCollection 2024 Jul 2.
The sedimentary environment is paramount in dictating depositional processes, ecological settings, and hydrodynamic conditions, all of which are pivotal to the aggregation of organic-rich sediments. A synergistic interplay is observed among the paleosedimentary environment, lithofacies, and enrichment of shale oil. Utilizing an analysis of elemental geochemistry and organic geochemical parameters-such as total organic carbon (TOC) content-this study endeavors to identify the predominant factors that govern the enrichment of organic matter (OM). It reconstructs the evolutionary trajectory of the paleosedimentary environment and introduces a dynamic model for shale oil enrichment within the Jurassic Lianggaoshan Formation of the Sichuan Basin. The results indicate that the Lianggaoshan Formation shale can be categorized into five lithological types, including high TOC felsic-rich shale (A), moderate TOC felsic-rich shale (B), moderate TOC felsic-rich mudstone (C), low TOC felsic-rich shale (D), and low TOC felsic-rich mudstone (E), and high TOC felsic-rich shale has the highest TOC and oil content. The shales of the Lianggaoshan Formation were deposited in an environment characterized by abundant terrestrial input, humid climate, freshwater conditions, reduced oxygen levels, and thriving primary productivity. OM enrichment is mainly controlled by the combination of a humid paleoclimate, high primary productivity, and other factors. The paleoenvironment deposited by lithofacies A coincides with the paleoenvironment conducive to OM enrichment, which makes lithofacies A become the dominant lithofacies for shale oil enrichment. Additionally, the sedimentary environment evolution characteristics and shale oil enrichment model of the Lianggaoshan Formation were established based on geochemical parameters. The paleosedimentary environment of the Lianggaoshan Formation from bottom to top is more and more unfavorable. The No.1 submember of the Lianggaoshan Formation is the most potential shale submember for shale oil exploration due to the paleosedimentary environment that promoted the deposition of lithofacies A and OM enrichment.
沉积环境在决定沉积过程、生态环境和水动力条件方面至关重要，所有这些对于富含有机质沉积物的聚集都至关重要。在古沉积环境、岩相和页岩油富集之间观察到一种协同相互作用。本研究利用元素地球化学和有机地球化学参数（如总有机碳（TOC）含量）分析，努力确定控制有机质（OM）富集的主要因素。它重建了古沉积环境的演化轨迹，并引入了四川盆地侏罗系凉高山组页岩油富集的动态模型。结果表明，凉高山组页岩可分为五种岩性类型，包括高TOC富长英质页岩（A）、中等TOC富长英质页岩（B）、中等TOC富长英质泥岩（C）、低TOC富长英质页岩（D）和低TOC富长英质泥岩（E），高TOC富长英质页岩的TOC和含油率最高。凉高山组页岩沉积于陆源输入丰富、气候湿润、淡水条件、氧含量降低和初级生产力旺盛的环境中。OM富集主要受湿润古气候、高初级生产力等因素的综合控制。岩相A所沉积的古环境与有利于OM富集的古环境相吻合，这使得岩相A成为页岩油富集的主导岩相。此外，基于地球化学参数建立了凉高山组沉积环境演化特征和页岩油富集模型。凉高山组从下到上古沉积环境越来越不利。凉高山组一段是页岩油勘探最具潜力的页岩段，因为其古沉积环境促进了岩相A的沉积和OM富集。
