浅表沉积有机质生烃特征研究现状及发展趋势

An overview of hydrocarbon generation from shallow sedimentary organic matter: Current status and future prospects

油气成因理论一直在不断发展,尽管目前以干酪根晚期热降解为主导的生烃理论已被大多数学者所接受,但是对于有机质在未熟—低熟情况下能否向油气转化及其转化的能力,一直没有形成系统的认识。本文系统查阅了国内外对第四系沉积物和现代生物生烃特征相关研究文献,总结了浅表沉积有机质来源、生烃潜力、生烃模式等方面的认识,并提出浅表沉积有机质生烃发展趋势和建议。现代沉积物中存在丰富的可溶有机质,仅有0.1%~2%的初级生产有机质进入到成岩后期阶段,其中脂肪酸是未熟—低成熟阶段向液态烃转化的重要物质,藻类、树脂、孢粉的热模拟实验显示特殊有机质的类脂物在低温催化作用下不需要经历干酪根阶段就可以向液态产物转化,热解产物显示为沥青质和胶质含量远高于总烃含量的特征,并且极性组分不断向总烃组分转化,生烃路径表现为生物原生有机质向可溶有机质转化、可溶有机质脱杂原子官能团向烃类演化,现代生物生烃总结为4个阶段,即原始状态、早期成烃、成烃高峰、成烃后期。总体而言,对于现代沉积有机质生烃机理、模式和能力的研究相对薄弱,目前研究主要针对某一种单一或多种原始生命体,缺少对原始生命体自沉积开始进入到生烃门限阶段的演化过程与生烃转化的机理性认识,并且研究手段仍依赖于有机质热模拟,以温度为主控因素,忽略了可溶有机质受到的综合地质作用,建议未来立足于现代海洋或湖盆沉积,发展成岩过程实验与生烃过程等检测技术,完善原始生命体自沉积后到进入生烃门限过程的生烃演化机理,加强现代沉积有机质生烃过程的系统模拟和生成产物的后期演化分析,以完善有机质生烃理论,为油气资源评价提供更有力的理论支撑。

The understanding of hydrocarbon generation has been continuously developed. Although hydrocarbon generation through kerogen late thermal degradation has been widely accepted by most scholars, there has been no systematic understanding of whether organic matter can be converted to oil and gas under immature conditions. This paper systematically reviewed hydrocarbon generation characteristics of Quaternary sediments and modern biology in China and abroad, and summarized the understanding of organic matter sources of shallow sediments, hydrocarbon generation potentials, and hydrocarbon generation models, investigating the development trends and suggestions of shallow sediment hydrocarbon generation characteristics. There is abundant soluble organic matter in modern sediments, and only 0.1%~2% of primary organic matter is preserved into the late diagenetic stage, among which fatty acids are an important material to transform into liquid hydrocarbon in an immature stage. The thermal simulation experiments of algae, resin and sporopollen show that lipids of special organic matter can be transformed into liquid product without undergoing a kerogen stage under low temperature catalysis. The pyrolysis products show that the content of asphaltene and resin is much higher than that of total hydrocarbon, and polar fractions are continuously transformed into total hydrocarbon fractions. The hydrocarbon generation path is the transformation of primary organic matter into soluble organic matter, and evolution of soluble organic matter into hydrocarbon by removing the heteroatom functional groups. Furthermore, the hydrocarbon generation of modern organisms can be divided into four stages, i.e., original stage, early hydrocarbon generation, hydrocarbon generation peak and late hydrocarbon generation. However, the research into the mechanism, model and ability of hydrocarbon generation of modern sediments is relatively weak. At present, the research mainly focuses on single or multiple primitive organisms and lacks the mechanism recognition of evolutionary process and hydrocarbon generation transformation of primitive organisms from the beginning of sedimentation to the hydrocarbon generation threshold, and research methods still rely on the thermal simulation of organic matter, with temperature as the main controlling factor, but ignore the comprehensive geological process of soluble organic matter. It is suggested to develop diagenetic process experiments and isochronous detection technologies for hydrocarbon generation processes based on modern marine or lake deposition in the future, and improve the hydrocarbon generation mechanism from deposition to hydrocarbon generation threshold, strengthening the systematic simulation of the hydrocarbon generation process of modern sediments and the late evolution analysis of the products, in order to improve the understanding of hydrocarbon generation and provide more powerful theoretical support for the evaluation of oil and gas resources.