流体压力对原油裂解气态烃碳同位素分馏效应的影响  

The influence of fluid pressure on the carbon isotope composition of gaseous hydrocarbons derived from the thermal cracking of crude oil

作　　者：石军 蒋文敏 李芸[1,2] SHI Jun;JIANG Wenming;LI Yun(State Key Laboratory of Deep Earth Processes and Resources,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;CAS Center for Excellence in Deep Earth Science,Guangzhou 510640,Guangdong,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院广州地球化学研究所,深地过程与战略矿产资源全国重点实验室,广东广州510640 [2]中国科学院深地科学卓越创新中心,广东广州510640 [3]中国科学院大学,北京100049

出　　处：《地球化学》2025年第2期213-223,共11页Geochimica

基　　金：国家自然科学基金项目(41773034)资助。

摘　　要：压力是影响有机质热演化的基本地质条件之一,受制于压力变化及相关模拟实验的局限性,目前缺乏关于封闭体系内部流体组成及含量变化引起的流体压力变化,以及流体压力对有机质热演化过程的影响研究。本文通过改造金管热解体系和控制样品质量,使金管内部的流体压力逐渐增大,结合气态烃(甲烷、乙烷和丙烷)产率、C同位素组成与样品质量的关系,探究流体压力对原油热演化过程中(Easy R_(o)=1.0%~2.1%)气态烃C同位素分馏作用的影响,揭示原油裂解过程中区别于其他类型压力对气态烃C同位素组成分馏效应的影响,并完善热模拟实验对压力作用影响的研究。结果表明:在生油窗早期(Easy R_(o)=1.0%),由于气态烃主要来源于大分子及杂原子团,C同位素组成差异明显,并不能体现流体压力作用;在湿气阶段早期(Easy R_(o)=1.5%),由于甲烷转化率较低及瑞利分馏作用影响,甲烷C同位素组成较轻;在湿气阶段晚期(Easy R_(o)=2.1%),流体压力引起甲烷和丙烷C同位素组成发生正偏。结合温度、压力范围、加压介质特征和高温流体相态演化的讨论,流体压力对气态烃C同位素组成的影响相对复杂,控制因素多样。Pressure is one of the basic geological factors influencing the thermal evolution of organic matter;however,considering the variation of pressure itself and the limitation of the relevant simulation experiments,there is an obvious lack of study on changes in the fluid pressure caused by the composition and concentration of fluids,and the effects of fluid pressure on the changes in the constitution and carbon isotope composition of pyrolysates in sealed pyrolysis systems.Therefore,this study implements increasing fluid pressure by modifying the gold pyrolysis system and controlling the sample mass,and then combining the evolution path of yields and carbon isotope compositions of gaseous hydrocarbons(methane,ethane and propane)with increasing sample mass,respectively,to explore the effects of the fluid pressure on C_(1)-C_(3) hydrocarbons carbon isotope fractionation during organic matter evolution(Easy R_(o)=1.0%-2.1%),and to distinguish the influence of other types of pressure on carbon isotope fractionation of the gaseous hydrocarbons as well as to supplement thermal simulation experiments researching on pressure influences.Results indicate that in the early stage of oil window(Easy R_(o)=1.0%),the differences for a certain hydrocarbon are significant on account of the sources of gaseous hydrocarbon,which cannot magnify fluid pressure influences;in the early stage of wet gas(Easy R_(o)=1.5%),because of the lower conversion rate and Rayleigh fractionation,the carbon isotope composition of methane is lighter,while that of methane and propane increases caused by fluid pressure at the late stage of wet gas(Easy R_(o)=2.1%).Combining with discussions about the setting range of temperature-pressure,characters of pressure media,and phase evolution of fluids at high temperature,the effects of fluid pressure on the carbon isotope fractionation of gaseous hydrocarbons are complex,and the controlling factors are diverse.

关 键 词：流体压力 C同位素分馏 金管热解体系 压力作用 

分 类 号：P618.13[天文地球—矿床学]