石油碳、氢同位素组成的研究

Study on Carbon and Hydrogen Isotopes Composition of Crude Oils

通过对我国１８个含油气区、３８５个石油样品进行碳、氢同位素和部分馏份碳同位素分析，将所获数据对两种不同性质的石油如正常原油和轻质（凝析）油分别研究其碳、氢同位素地球化学特征，提出轻质（凝析）油的碳同位素值（δ１３Ｃ为－３２．５‰～－２４．３‰）比正常原油δ１３Ｃ为－３４．４‰～－２４．６‰）相对偏高；石油馏份中芳烃碳同位素组成的变化受母质继承效应更为明显。因此，用芳烃碳同位值可以判识不同母质来源的石油。与海相有关的轻质（凝析）油的氢同位素值大于－１５０‰，而非海相轻质（凝析）油的δＤ值（δＤ为－２１０‰～－１０５‰）基本覆盖了海相轻质油的分布范围，从淡水－微咸水－半咸水和海水环境其氢同位素有明显变重趋势，表明氢同位素主要与沉积环境密切相关。

In this paper 385 crude oil samples from 18 oil bearing areas of China have been analysed for carbon and hydrogen isotopic compositions and part of their saturated and aromatic hydrocarbons have been analysed for carbon isotopic compositions.Based on the analytical data,the geochemical characteristics of carbon and hydrogen isotopes have been studied for two different types of oils,i.e.,normal oil and light oil (condensate)and the hydrocarbon generating organic sources and depositional environments have been discussed combined with local geological background.The author propose that the δ 13 C values of light oil (condensate)(δ 13 C -32.5‰～ -24.3‰) are higher than that of normal oil (δ 13 C -34.4‰～-24.6‰).The variation of carbon isotopic compositions of aromatic hydrocarbons of crude oils was obviously affected by the inheritance effect of organic sources, consequently the δ 13 C values of aromatic hydrocarbons could be used to identify crude oils generated from different organic sources. Light oils (condensates) related to marine facies have δD values higher than -150‰ ,whereas that related to nonmarine facies have δD values(-210‰～-105‰)which basicly cover the δD distribution range of marine light oils (condensates).With the depositional environments changes from fresh water to slightly salt water to brackish water to marine salt water,δD values of light oils (condensates)become obviously heavier, indicating that δD values mainly related to the depositional environment.