塔里木盆地古城墟隆起顺南1井古油藏热裂解过程的分子碳同位素地球化学记录

Molecular carbon isotopic geochemistry records of thermal cracking in the palaeo-reservoir of well Shunnan 1 in Guchengxu Uplift, Tarim Basin

孙永革 孔丽姝 路清华 顾忆

SUN Yongge KONG Lishu LU Qinghua GU Yi

中国石化 石油勘探开发研究院 无锡石油地质研究所, 江苏 无锡 214126 浙江大学 地球科学学院 有机地球化学研究组, 杭州 310027

Wuxi Research Institute of Petroleum Geology, SINOPEC, Wuxi, Jiangsu 214126, China Organic Geochemistry Unit, School of Earth Sciences, Zhejiang University, Hangzhou, Zhejiang 310027, China

塔里木盆地古城墟隆起顺南1井高成熟度轻质原油被认为是典型的热裂解残余油。研究揭示顺南1井原油中高丰度的苯系物和丰富的稠环芳烃，是其在地质历史上经历强烈热裂解的次生产物之一；苯系物应为热裂解、环化、芳构化过程的中间产物，而稠环芳烃可能指示了缩聚过程。烃类分子裂解—缩聚过程诱发的碳同位素分馏，不仅使顺南1井原油正构烷烃分子碳同位素较下古生界含油气系统中正常原油的重8‰~10‰，而且烷基萘系物分子碳同位素也比下古生界含油气系统中的正常原油重6‰~8‰。研究结果进一步实证了与裂解成因相关的芳烃分子及其稳定碳同位素组成是判识深层—超深层油藏是否经历热蚀变的有效手段，其对于准确评估深层—超深层油气相态与资源格局具有重要意义。

The highly mature light oil from well Shunnan 1 in the Guchengxu Uplift, Tarim Basin is considered to be a typical residual oil by thermal cracking. The study reveals that the abundant monoaromatic hydrocarbons and polynuclear aromatics in the crude oil of well Shunnan 1 are the by-products of severe in-reservoir oil-cracking during the geological history. The monoaromatic hydrocarbons are the intermediate products of thermal cracking, cyclization and aromatization, while the polynuclear aromatics are indicative of polycondensation reaction. The strong carbon isotopic fractionation induced by hydrocarbon molecule cracking and polycondensation makes the molecule carbon isotope of n-alkanes and the molecule carbon isotope of alkyl naphthalenes in the crude oil of well Shunnan 1 respectively 8‰-10‰ and 6‰-8‰ heavier compared to those from unaltered crude oils in Lower Paleozoic oil-bearing system. The results further proved that the aromatic molecules related to oil cracking and their stable carbon isotopic compositions could be a potentially powerful tool to identify whether thermal alteration occurred in deep and ultra-deep oil reservoirs, and further helps to effectively evaluate the oil and gas phase and resource pattern in the deep and ultra-deep reservoirs.

国家自然科学基金 42030803

https://doi.org/10.11781/sysydz202305904