淡水和咸水湖相泥质烃源岩不同赋存态有机质的地球化学特征

Geochemical investigation of organic matter of various occurrences released via sequential treatments of two argillaceous source rock samples from fresh and saline lacustrine environments

赵悦 蔡进功 谢奥博 董哲 周祺盛 雷天柱 杨燕

ZHAO Yue CAI Jingong XIE Aobo DONG Zhe ZHOU Qisheng LEI Tianzhu YANG Yan

1. 中国石油勘探开发研究院, 北京 100083; 2. 同济大学 海洋地质国家重点实验室, 上海 200092; 3. 甘肃省油气资源研究重点实验室/中国科学院 油气资源研究重点实验室, 兰州 730000; 4. 中国石油 冀东油田分公司, 河北 唐山 063004

1. Research Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083, China; 2. State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China; 3. Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Science, Lanzhou, Gansu 730000, China; 4. Jidong Oil Company, PetroChina, Tangshan, Hebei 063004, China

泥质烃源岩中的有机质存在多种赋存形式，其中与无机矿物结合形成有机—无机复合体是有机质保存的重要方式之一。为了对比研究泥质烃源岩中不同赋存态有机质的地球化学特征，选取东营凹陷沙三下亚段（淡水湖相）和沙四上亚段（咸水湖相）优质烃源岩为研究对象，采用“溶剂抽提—皂化—HCl酸解—HF/HCl酸解”的连续处理实验方法，依次得到烃源岩中的游离态有机质、黏土矿物层间吸附有机质、碳酸盐矿物结合有机质和黏土矿物表面化学吸附有机质。结果表明，烃源岩中的矿物结合态有机质约占可溶有机质总量的10%，矿物结合态有机质与游离态有机质表现出显著的地化特征差异：矿物结合态有机质以非烃、沥青质等极性组分为主要组成，饱和烃中轻烃比例较高；矿物结合态有机质可以补充保存具有生源指示意义的分子标志物，如指示Botryococcus braunii生源的两环倍半萜类分子标志物仅在碳酸盐矿物结合有机质中检出，指示古菌生源的角鲨烷仅在HF/HCl酸解有机质中检出；此外，矿物结合态有机质亦可对沉积环境的差异做出分子响应。因此，在对游离态有机质地化特征分析基础上，如能综合分析不同矿物结合态有机质的地化特征，可以获得更为全面的地质分析结果。

Organic matter (OM) in argillaceous source rocks occurs in various forms, and it is common for OM be bounded to minerals forming OM-mineral complexes. In order to geochemically characterize OM of different occurrences, some high quality source rocks were sampled from the lower third member (Es3) and the upper fourth member (Es4) of the Shahejie Formation in the Dongying Sag, and were subjected to sequential treatments as follows:solvent extraction-saponification-hydrochloric acid hydrolysis-hydrofluoric acid hydrolysis. The free, clay interlayer absorbed, carbonate-bound, and clay surface-bound OM were successively released and GC-MS analyzed. Results indicated that the mineral-bound OM accounted for approximately 10% of the total soluble OM in source rocks, and there exists distinct geochemical differences between the free and mineral-bound OM, with the latter dominated by polar fractions such as nonhydrocarbons and asphaltene. The former comprised higher proportions of light hydrocarbons, and selectively preserved biomarkers indicative of biogenic origin, like the bicyclic sesquiterpenoids in the carbonate-bound OM, indicative of input from Botryococcus braunii, and squalane in the clay surface-bound OM, indicative of input from archaea. The mineral-bound OM was also sensitive to environmental changes, and exhibited molecular differences between fresh Es3 and saline Es4 samples. Thus, it was concluded that comprehensive geochemical investigation of the free and mineral-bound OM in argillaceous source rocks could achieve more authentic geological interpretations. Besides, molecular characterization of hydrocarbons of various occurrences could help further elucidate OM preservation mechanisms, as well as better evaluate source rock potential.

国家自然基金项目“泥页岩中不同赋存态烃的分离及特征研究”（41372130）、“泥页岩中有机质的存在对蒙脱石伊利石化进程影响的研究”（41672115）和国家重大科技专项“济阳坳陷古近系烃源岩有机—无机协同演化及其资源潜力评价”（2016ZX05006-001-003）联合资助。

https://doi.org/10.11781/sysydz201805705