摘要
油源对比微量元素地球化学示踪是油气地球化学领域的前沿科学问题.以准噶尔盆地二叠系风城组碱湖含油气系统为例,对此进行了探索研究.通过对烃源岩和原油样品的微量元素组成进行电感耦合等离子体质谱(inductively coupled plasma mass spectrometry,ICP-MS)分析和系统对比,发现检出的33个常见微量元素中,过渡族金属元素(Ti、V、Cr、Ni、Cu、Zn、Mn和Zr)、碱土金属元素(Sr和Ba)和非金属元素(B和As)在烃源岩与原油间具有较好的继承性,展示出油源对比和示踪意义,但由源到油,元素含量下降0.3~1141倍,差异富集特征显著,表明不能直接简单应用于油源对比.分析认为,微量元素从源到油的差异富集主要受控于微量元素以有机络(螯)合物或无机盐离子形式在有机质成烃演化与成藏过程中的动态分配.Ni和部分V以N–Ni/V键合于卟啉化合物,受油气运移影响小,相对稳定;大部分V以难溶矿物相赋存,油气初次运移时优先富集于烃源岩;Cr、Cu和Zn与有机酸中O/S原子络合,但在油气二次运移过程中化学键容易破裂;Mn、Zr、Ti、Sr和Ba主要以矿物相赋存于烃源岩中,在油气运移中以离子形式存在,易受油-岩相互作用发生离子交换;B以矿物相赋存于烃源岩中,但在初次运移时易与有机酸络合且受二次运移影响有限;As主要以砷化物或砷酸根离子赋存,受二次运移影响较大.据此,Ni、V、B、Cr、Cu、Zn和As具有较好的示踪意义,形成了4组参数:Ni含量进行油源对比、V/Ni和Ni/B示踪初次运移、Cr–Cu+Zn–As三端元图示踪二次运移.油气形成演化过程中的元素地球化学行为复杂,可在深入剖析后遴选有效参数应用于油气示踪,是经典有机地球化学方法的有效补充.
Trace element tracing of oil-source rock correlations in petroliferous basins is a cutting-edge area of research in the field of petroleum geochemistry,providing an important supplement for the traditionally used organic geochemistry approach.However,the specific proxies and mechanisms are not well understood,limiting the application of the trace element approach and theoretical geochemical behavior during the oil generation,migration and accumulation.To fill the knowledge gap,based on a case study in the lower Permian Fengcheng Formation alkaline-lacustrine petroleum system,located in the northwestern Junggar Basin,Northwest China,novel trace element proxies for oil-source rock correlations was evaluated with the geochemical behavior and mechanisms being explored.Trace elements and conventional geochemistry in twenty source rock and nineteen crude oil samples were analyzed by inductively coupled plasma–mass spectrometry(ICP-MS)and gas chromatography-mass spectrometry(GC-MS)to systematically compare.Analysis of 33 commonly-detected trace elements showed that the transition metals(Ti,V,Cr,Ni,Cu,Zn,Mn,and Zr),alkaline earth metals(Sr and Ba),and nonmetallic elements(B and As)exhibit good correlations between each source rock and crude oil.However,the contents of these 12 elements exhibit changes by a factor of 0.3–1141 times from source rock to crude oil.Elements Ni,Cu,Zn and Cr are relatively enriched in crude oils,elements V,Ti,Mn and Zr are relatively enriched in source rocks,and elements B,As,Sr and Ba are not apparently enriched.This indicates that the elements contents cannot be directly used for oil-source rock correlations.Understanding the geochemical behavior and mechanisms of the differential enrichment of trace elements from source rock to crude oil is prerequisite.It is argued that the differential enrichment is mainly controlled by the geochemical partition of these elements,in the form of organic complexes(and chelates)or inorganic ions during hydrocarbon generation and accumulation.In detail,Ni and some V are chelated to organic porphyrin compounds by strong N–Ni/V bonds,which are little affected by petroleum migration and are thus relatively stable.In addition,most of the V occurs in insoluble mineral phases,and thus is preferentially enriched in source rocks during primary hydrocarbon migration.Chromium,Cu,and Zn are mainly complexed with O or S atoms in organic acids in the form of Cr–O or Cu(Zn)–S bonds.These chemical bonds are readily broken during secondary petroleum migration.Manganese,Zr,Ti,Sr,and Ba occur mainly in mineral phases in the source rocks and as ions during petroleum migration,and thus are modified by oil-rock interactions.Boron occurs mainly in mineral phases in the source rocks,but is easily complexed with organic acids,and thus undergoes limited modification due to secondary hydrocarbon migration.Arsenic occurs mainly as arsenide or arsenate ions,which are strongly affected by secondary petroleum migration.As such,Ni,V,B,Cr,Cu,Zn,and As are more reliable for oil-source rock correlations and are incorporated into four new parameters established in this study:(1)Ni contents can be used for oil-source rock correlations;(2)V/Ni and Ni/B ratios can be used to trace primary petroleum migration;and(3)a Cr–(Cu+Zn)–As ternary diagram can be used to trace secondary petroleum migration.In conclusion,trace elements in petroleum systems exhibit complex geochemical behavior during hydrocarbon generation and primary(secondary)oil migration.However,robust trace element proxies for oil-source rock correlations can be established after consideration of the geochemical behavior of each element.The proposed method is an important addition to conventional oil-source rock correlations based on organic geochemistry.
作者
张景坤
曹剑
施春华
胡文瑄
王小林
姚素平
唐勇
向宝力
Jingkun Zhang;Jian Cao;Chunhua Shi;Wenxuan Hu;Xiaolin Wang;Suping Yao;Yong Tang;Baoli Xiang(School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China;College of Resources and Environmental Engineering,Guizhou University,Guiyang 550025,China;PetroChina Xinjiang Oilfield Company,Karamay 834000,China)
出处
《科学通报》
EI
CAS
CSCD
北大核心
2023年第10期1247-1265,共19页
Chinese Science Bulletin
基金
国家自然科学基金(42230808,42102148)
中国博士后科学基金(2021M691497)资助。
关键词
油气示踪
有机-无机相互作用
有机络(螯)合物
碱湖
风城组
准噶尔盆地
petroleum tracing
organic-inorganic interaction
organic complexation(and chelates)
alkaline lacustrine
Fengcheng Formation
Junggar Basin
