中国陆相烃源岩氮同位素组成与有机质聚集

Nitrogen isotope compositions and organic matter accumulation in terrestrial hydrocarbon source rocks in China

曹剑 夏刘文 胡文瑄 STÜEKENEva E 支东明 唐勇 向宝力 何文军

CAO Jian XIA Liuwen HU Wenxuan STÜEKEN Eva E ZHI Dongming TANG Yong XIANG Baoli HE Wenjun

南京大学 地球科学与工程学院, 南京 210023 School of Earth and Environmental Sciences, University of St Andrews, St Andrews, Scotland, KY16 9AL, UK 中国石油 吐哈油田分公司, 新疆 哈密 839009 中国石油 新疆油田分公司, 新疆 克拉玛依 834000

School of Earth Science and Engineering, Nanjing University, Nanjing, Jiangsu 210023, China School of Earth and Environmental Sciences, University of St Andrews, St Andrews, Scotland, KY16 9A, UK PetroChina Tuha Oilfield Company, Hami, Xingjiang 839009, China PetroChina Xinjiang Oilfield Company, Karamay, Xinjiang 834000, China

氮作为重要的生命元素与有机质聚集之间具有成因联系，但尚未形成系统性、规律性认识。以中国广泛发育的二叠系—古近系陆(湖)相烃源岩为例，对此进行了探讨。结果表明，根据氮同位素(δ15N)组成，结合盐度和蒸发性碱类矿物特征，可将中国陆相烃源岩分为3组：近中性组1(δ15N平均值为4.0‰±1.5‰)、近中性组2(δ15N平均值为7.1‰±1.6‰)和碱性组(δ15N平均值为18.4‰±3.3‰)。在δ15N < 10‰的近中性组中，烃源岩的δ15N与有机质丰度、类型、生烃能力和页岩油潜力呈正相关，原因在于较高的δ15N值指征了生烃母质组成的变化。在δ15N>10‰的碱性组中，有机质类型都较好，页岩油潜力都较高，但烃源岩的δ15N与有机质聚集的响应关系不如中性组，反映有机质聚集受非δ15N其他综合因素的影响与控制。据此建立了基于δ15N划分出的3类湖相烃源岩的有机质聚集模式(< 5‰、5‰~10‰、>10‰)。δ15N具有示踪有机质聚集和烃源岩质量的潜力，以湖相烃源岩为例，低δ15N型(δ15N < 5‰)质量差，中—高δ15N型(δ15N>5‰)质量好。从氮同位素组成和氮循环这一新角度探讨了烃源岩有机质聚集，丰富了氮的生物地球化学与烃源岩地球化学研究。

As an important biological element, nitrogen is causally linked with organic matter accumulation, but a systematic and regular understanding has not been developed. This paper discusses this issue by taking the widely developed Permian-Paleogene terrestrial (lacustrine) hydrocarbon source rocks in China as an example. The results show that the terrestrial source rocks in China can be classified into three groups according to the nitrogen isotope (δ15N) compositions and combined with the salinity and evaporative alkali mineral characteristics: the circum-neutral group 1 (average δ15N=4.0‰±1.5‰), the circum-neutral group 2 (average δ15N=7.1‰±1.6‰), and the alkaline group (average δ15N=18.4‰±3.3‰). In the circum-neutral group with δ15N < 10‰, the δ15N of the source rocks is positively correlated with organic matter abundance, type, hydrocarbon generating capacity and shale oil potential due to the fact that higher δ15N characterizes changes in the composition of the hydrocarbon generating bio-precursors. In the alkaline group with δ15N>10‰, the organic matter types are good and shale oil potentials are higher, but the response relationship between δ15N of source rocks and organic matter accumulation is not as good as that of the circum-neutral group, reflecting that the organic matter accumulation in alkaline group is influenced by other comprehensive factors other than δ15N. Accordingly, the organic matter accumulation models of three types of lacustrine source rocks (< 5‰, 5‰-10‰, and >10‰) classified on the basis of δ15N were established. The δ15N has the potential to trace organic matter accumulation and quality of source rocks. For example, low δ15N type (δ15N < 5‰) is of poor quality and medium-high δ15N type (δ15N>5‰) is of good qualityin lacustrine source rocks. This paper enriches the biogeochemical and hydrocarbon source rock geochemical studies of nitrogen by exploring organic matter accumulation in source rocks from the new perspective of nitrogen isotope composition and nitrogen cycling.

国家自然科学基金 42230808;国家自然科学基金 42203055;中国石油科技重大专项 2021DJ0108

https://doi.org/10.11781/sysydz202305912