油源对比微量元素地球化学研究进展

原油中的微量元素地球化学组成可以应用于油源对比,指标可以归纳为3类:①所含元素的聚类分析及其所反映的元素分布总体特征;②不同族、不同类型元素的组成,特别是过渡族金属元素;③稀土元素。但对于哪些微量元素可以应用于油源对比,哪些具有普遍意义,在不同地区是否具有适用性,影响其油源对比应用有效性的因素有哪些,主控因素是什么,仍然不甚清楚,由此导致很多方面的认识还不甚成熟,成功应用的实例相对常规的有机地球化学研究不多。原油中的微量元素主要来源于外部成油和运聚环境,在原油生成和运聚过程中,通过烃—水—岩之间的复杂有机—无机相互作用以金属卟啉螯合物、有机络合物或吸附态的形式聚集于原油中,并且沥青质是原油中微量元素的主要载体,元素组成在此过程中发生分异。此外,原油在自身形成与演化过程中也会发生元素组成的分异,影响因素包括油源母质类型、成熟度、次生变化等。在这些过程中,元素地球化学性质的不同会使原油中的元素组成出现差异,基本不发生/少发生变化的元素即可能是好的油源对比指标,这是应用微量元素进行油源对比的原理和理论基础。

Advances in Research of Using Trace Elements of Crude Oil in Oil-Source Correlation

Trace element geochemistry of crude oil can be used in oil-source correlation. The correlation parameters can be mainly divided into three categories: ①cluster analysis of trace elements and its indicated general distribution of the elements; ②composition of different families and types of elements, metal elements of transition family in particular; ③rare earth elements. However, there are many uncertainties in this research field. For instance, which elements can be used in oil source correlation? Which elements have general implications and can be applied to different areas? What factors controlling the effectiveness of the application and how about the main controlling factors? As a consequence, many understandings are preliminary and the successful applications are relatively less in comparison with the application of conventional organic geochemical studies. Trace elements of crude oil are mainly derived from external environment of oil formation and migration and accumulation. In the process of oil generation, migration and accumulation, the trace elements accumulate in oil by various ways, e.g., metalloporphyrin chelate compound, organic complex compound and adsorbed matters. This takes place through complex organic-inorganic interactions between reservoir hydrocarbons and water and rocks, with the elements dominantly accumulating in asphaltene. In these processes, trace elements of oil differentiate. Moreover, the elements can also differentiate in the formation and evolution of oil, being influenced by the primary organic matter type and maturity and secondary alterations of oil source. These all lead to the heterogeneity of element composition of oil due to different geochemical natures of the elements. The elements that have no or few changes are good parameters for oil-source correlation. This is the principle and theoretical foundation of the application of trace elements of crude oil to oil-source correlation.