基于全二维气相色谱的原油C_8轻烃新参数

New C_8 light hydrocarbons parameters based on comprehensive two-dimensional gas chromatography

C_5—C_(13)轻烃馏分是原油的重要组分,对于C_8以上轻烃组分的研究一直处于比较薄弱的状态。对塔里木盆地哈拉哈塘凹陷11件典型的奥陶系海相原油样品及北部湾盆地福山凹陷流沙港组流三段8件典型的古近系陆相原油样品进行了全二维气相色谱(GC×GC)和色谱/质谱(GC-MS)对比分析。借助标准样品并结合相关文献资料,对原油C_8轻烃组分中31个化合物进行了定性定量分析,发现原油C_8轻烃馏分中三甲基环己烷和三甲基环戊烷丰度较高。其中:顺-1,3-二甲基环己烷(c,1,3-DMCYC_6)、反-1,4-二甲基环己烷(t,1,4-DMCYC_6)和1,1-二甲基环己烷(1,1-DMCYC_6)相对丰度始终保持固定的比例,比值接近4∶2∶1;顺-1,反-2,顺-4-三甲基环戊烷(ctc,1,2,4-TMCYC_5)和顺-1,反-2,顺-3-三甲基环戊烷(ctc,1,2,3-TMCYC_5)也保持着1∶1的近似比值。并推测二甲基环己烷与甲基环己烷、三甲基环戊烷与二甲基环戊烷可能有着相似的母源输入。在此基础之上,针对C_8中的单体化合物建立了C_8轻烃新参数——轻烃比LHR。LHR为反-1,4-二甲基环己烷+顺-1,3-二甲基环己烷+1,1-二甲基环己烷与顺-1,反-2,顺-4-三甲基环戊烷+顺-1,反-2,顺-3-三甲基环戊烷的丰度比值,即(t,1,4-+c,1,3-+1,1-)DMCYC_6/(ctc,1,2,4-+1,2,3-)TMCYC_5。研究表明,LHR与经典沉积环境参数Pr/Ph,C_(21)/C_(23)TT及DBT/P线性关系良好,可以有效地用于表征原油或源岩有机质来源。

C5-C13 light hydrocarbons play an important role in crude oil, but the research about C8＋ has been very poor for a long time. Based on the GC×GC and GC-MS, geochemical characteristics of light hydrocarbons for 11 typical marine oils from Halahatang Depression and 8 lacustrine oils from Fushan Depression were investigated and correlated. According to the standard samples and related literatures, 31 compounds of C8 light hydrocarbons were qualified and quantified, and it is found that the content of trimethylcyclohexane and trimethylcyclopentane in C8 light hydrocarbon fraction is higher. The relative abundance of cis-1,3-dimethylcyclohexane, trans-1,4-dimethylcyclohexane and 1,1-dimethylcyclohexane remains constant and the ratio is close to 4∶2∶1. Cis-1,trans-2,cis-4-trimethylcyclopentane and cis-1,trans-2,cis-3-trimethylcyclopentane also maintain an approximate ratio of 1∶1. It is presumed that dimethylcyclohexane and methylcyclohexane, trimethylcyclopentane and dimethylcyclopentane may have similar maternal input. Thus one C8 light hydrocarbon ratio（t,1,4-＋c,1,3-＋1,1-） DMCYC6/（ctc,1,2,4-＋1,2-3-） TMCYC5（LHR） was proposed. The results suggest that LHR correlates well with Pr/Ph, C21/C23TT and DBT/P and verifies the source input of crude oil.