封闭体系下烃源岩热模拟实验固体渣样总有机碳含量异常成因及意义

Causes and geochemical significance of total organic carbon anomaly in solid residue samples from source rock pyrolysis simulation experiments in a closed system

仓辉 陈治军 杨东 陈义国 韩长春 李子梁 陈玲玲

CANG Hui CHEN Zhijun YANG Dong CHEN Yiguo HAN Changchun LI Ziliang CHEN Lingling

陕西延长石油(集团)有限责任公司研究院, 西安 710075 长江大学 资源与环境学院, 武汉 430100 中国石油 渤海钻探工程有限公司 井下作业分公司, 河北 任丘 062552

Research Institute of Yanchang Petroleum (Group) Co., Ltd., Xi'an, Shaanxi 710075, China College of Resources and Environment, Yangtze University, Wuhan, Hubei 430100, China Downhole Services Company of CNPC Bohai Drilling Engineering Company Limited, Renqiu, Hebei 062552, China

自然演化条件下，烃源岩总有机碳(TOC)含量通常随着成熟度的增加而持续降低；但在封闭体系热模拟实验的晚期阶段，固体渣样的TOC呈现“不减反增”的异常现象。基于银根—额济纳旗盆地中生界湖相烃源岩样品的热模拟实验等相关测试资料，分析TOC异常变化成因，探讨了其地球化学意义。研究认为，造成这种异常现象的原因与原油二次裂解有关。由于热模拟为封闭体系，早期生成的原油因无法排出而滞留在反应釜内，随着热模拟温度的增加，原油开始大规模裂解，原油转化成气态烃的同时产生焦沥青，“不可溶”的焦沥青附着在固体渣样上导致TOC增大。该研究还建立了一种确定不同类型烃源岩所生油裂解气主生气门限的方法，即基于封闭热模拟实验固体渣样的TOC变化曲线来确定油裂解气主生气门限，因为焦沥青的大量生成会导致固体渣样TOC的增加，也是原油开始大规模裂解生气的重要标志。这种方法解决了现有方法的不足，如在厘定主生气门限时存在不可避免的人为误差、无法对混源油开展更为深入研究等。

Under natural evolution, the total organic carbon (TOC) content of source rocks typically decreases as maturity increases. However, in later stages of pyrolysis simulation experiments conducted in a closed system, the TOC content of solid residue samples would anomalously increase instead of decreasing. By analyzing data from pyrolysis simulation experiments on lacustrine source rock samples from the Mesozoic Yingen-Ejinaqi Basin, the causes of this TOC content anomaly were investigated, and its geochemical significance was explored. The results suggested that this anomaly was related to secondary cracking of crude oil. In the closed system of the experiments, early-formed crude oil was trapped in the reactor, unable to be discharged. As the temperature increased, large-scale oil cracking occurred, converting it into gaseous hydrocarbons and generating pyrobitumen. The insoluble pyrobitumen adhered to the solid residue samples, resulting in an increase of TOC content. Based on TOC variation curve of solid residue samples from the pyrolysis simulation experiments, a new method was established to determine the main gas generation threshold for oil cracking in different types of source rocks. The significant amount of pyrobitumen generated, accompanied by an increase in TOC content, indicated the onset of large-scale oil cracking and gas generation. This method overcomes the shortcomings of existing methods, such as inevitable human errors in determining the main gas generation threshold and the inability to conduct more in-depth study on mixed-source oils.

国家自然科学基金项目 42272160;国家自然科学基金项目 41872144;陕西延长石油(集团)有限责任公司科技攻关项目 ycsy2018ky-A-04;陕西延长石油(集团)有限责任公司科技攻关项目 ycsy2020jcyjB-03

https://doi.org/10.11781/sysydz2024061275