塔里木盆地柯克亚地区侏罗系湖相烃源岩地球化学特征——对古环境和有机质富集的指示意义

Geochemical characteristics of Jurassic lacustrine source rocks in Kekeya area, Tarim Basin: implications for paleoenvironments and organic matter enrichment

孙迪 谢小敏 屈洋 肖七林 黎立 陈才 王张虎

SUN Di XIE Xiaomin QU Yang XIAO Qilin LI Li CHEN Cai WANG Zhanghu

中国石油 塔里木油田分公司 勘探开发研究院, 新疆 库尔勒 841000 长江大学 资源与环境学院 油气地球化学与环境湖北省重点实验室, 武汉 430100

Research Institute of Exploration and Development, PetroChina Tarim Oilfield Company, Korla, Xinjiang 841000, China Hubei Key Laboratory of Petroleum Geochemistry and Environment, College of Resources and Environment, Yangtze University, Wuhan, Hubei 430100, China

为进一步揭示塔里木盆地塔西南坳陷侏罗系烃源岩发育特征及其记录的古环境，更好地指导下一步页岩油气勘探开发，综合岩石热解、显微组分、无机地球化学、生物标志化合物和碳同位素等分析，明确了塔西南坳陷柯克亚地区下侏罗统康苏组煤系泥岩与中侏罗统杨叶组泥岩、粉砂质泥岩发育特征及有机质富集规律。康苏组与杨叶组烃源岩总有机碳(TOC)含量较高，分别为1.7%~63.5%(平均值为24.4%)和0.6%~6.9%(平均值为2.1%)，为好至优质烃源岩。两套烃源岩成熟度均较低，处于低成熟—成熟阶段。干酪根碳同位素、岩石薄片与生物标志化合物等均指示康苏组煤系泥岩和杨叶组下段泥岩有机质母质主要以高等陆源植物为主，而杨叶组上段粉砂质泥岩含较多的浮游藻类。康苏组沉积时期古气候相对温暖湿润，水体环境为淡水、贫氧偏氧化环境；杨叶组沉积早期气候相对炎热潮湿，沉积环境与康苏组沉积时期类似，同样为淡水、贫氧偏氧化环境，随着杨叶组沉积晚期湖平面的逐步上升，古环境逐渐转变为半咸水、贫氧环境。炎热潮湿的气候与咸化的水体有利于浮游藻类等水生生物的繁衍，从而影响了杨叶组上段粉砂质泥岩中有机质的供给。此外，该时期水体还原性的增强同样有利于有机质的保存。综上，古气候、古盐度与沉积环境是影响柯克亚地区侏罗系湖相烃源岩中有机质富集的重要因素。

To further reveal the development characteristics of Jurassic source rocks in the southwest depression of the Tarim Basin and their paleoenvironments, with the aim of guiding future shale oil exploration and development, the study integrated rock pyrolysis, maceral analysis, inorganic geochemistry, biomarker compounds, and carbon isotope analyzes.It explored the development characteristics and organic matter enrichment patterns of coal-bearing mudstones from the Lower Jurassic Kangsu Formation and mudstones and silty mudstones from the Middle Jurassic Yangye Formation in the Kekeya area of the southwest depression, Tarim Basin. The results showed that the total organic carbon (TOC) content in the source rocks of the Kangsu and Yangye formations was relatively higher, ranging from 1.7% to 63.5% (with an average of 24.4%), and 0.6% to 6.9% (with an average of 2.1%), respectively, indicating source rocks of good to excellent quality. Source rocks from both formations exhibited low maturity, being in the low-maturity to mature stage.In addition, carbon isotope analysis of kerogen, thin section observations, and biomarker compound analysis indicated that the parent material of the organic matter in the coal-bearing mudstones of the Kangsu Formation and the lower section of the Yangye Formation mainly derived from higher terrestrial plants, while the silty mudstones of the upper section of the Yangye Formation contained abundant planktonic algae. During the depositional period of the Kangsu Formation, the paleoclimate was warm and humid, and the water environment was freshwater, with suboxic and slightly oxidizing conditions. In the early depositional stages of the Yangye Formation, the paleoclimate was also hot and humid, and the depositional environment was similar to that of the Kangsu Formation, characterized by freshwater and suboxic conditions. With the gradual rise in lake level in the late depositional period of the Yangye Formation, the paleoenvironment transitioned to a brackish and suboxic environment. The hot and humid climate, coupled with increased salinity, was conducive to the reproduction of planktonic algae and other aquatic organisms, thereby affecting the organic matter supply in silty mudstones of the upper section of the Yangye Formation. Furthermore, the enhancement of water reducibility during this period was also beneficial for the preservation of organic matter. In summary, paleoclimate, paleosalinity, and depositional environment are important factors influencing the organic matter enrichment in the Jurassic lacustrine source rocks of the Kekeya area.

国家自然科学基金项目 42302159;湖北省自然科学基金项目 2022CFB642;中国石油塔里木油田分公司项目 041021090118

https://doi.org/10.11781/sysydz2024061312