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对我国4个盆地典型煤型气和油型气的209个样品轻烃组成和53个样品轻烃单体碳同位素进行了分析,提出或完善了我国煤型气和油型气的鉴别指标.在天然气轻烃单体碳同位素指标系列中,煤型气具有δ13C苯>-24‰,δ13C甲苯>-23‰,δ13C环己烷>-24‰,δ13C甲基环己烷>-24‰的分布特点,油型气具有δ13C苯<-24‰,δ13C甲苯<-24‰,δ13C环己烷<-24‰和δ13C甲基环己烷<-24‰的分布特点.在正庚烷(nC7)、甲基环己烷(MCH)、二甲基环戊烷(ΣDMCP)等C7轻烃化合物组成中,nC7相对含量和MCH相对含量受影响因素少,能够较好地反映天然气的成因类型.因此,提出nC7相对含量大于30%,MCH相对含量小于70%,为油型气;nC7相对含量小于35%,MCH相对含量大于50%,为煤型气;在C5-7脂肪族组成中,C5-7正构烷烃含量大于30%的区域为油型气,而C5-7正构烷烃含量小于30%的区域为煤型气.这些指标范围具有相对较好的适用性,可作为鉴别煤型气和油型气的重要指标.
The light hydrocarbon composition of 209 samples and the carbon isotopes of 53 light hydrocarbon monomers of the typical coal gas and oil gas in 4 basins of China were analyzed, and the discrimination index of coal gas and oil gas in China was proposed or perfected. In the carbon isotope index series of natural gas light hydrocarbon monomer, the coal gas has the following characteristics: δ13C benzene> -24 ‰, δ13C toluene> -23 ‰, δ13C cyclohexane> -24 ‰, δ13C methylcyclohexane> -24 ‰ Distribution characteristics of oil gas with δ13C benzene <-24 ‰, δ13C toluene <-24 ‰, δ13C cyclohexane <-24 ‰ and δ13C methylcyclohexane <-24 ‰ distribution characteristics in n-heptane (nC7 ), Methylcyclohexane (MCH) and dimethylcyclopentane (ΣDMCP), the relative content of nC7 and the relative content of MCH are affected by less factors, which can well reflect the type of natural gas. Therefore, it is proposed that the relative content of nC7 is greater than 30% and the relative content of MCH is less than 70%, which is oil-type gas; the relative content of nC7 is less than 35% and the relative content of MCH is greater than 50% The area where the content of C5-7 n-paraffins is more than 30% is oil-type gas and the area where the content of C5-7-n-paraffins is less than 30% is coal-type gas These ranges have relatively good applicability and can be used as An important indicator to identify coal-type gas and oil-gas.