有机质中三联苯成熟度参数及其化学机理:基于地球化学数据和量子化学计算

Maturity indicators and its mechanism of triphenyls in sedimentary organic matter:Based on geochemical data and quantum chemical calculation

三联苯(TrP)广泛分布于石油和沉积有机质中,是重要的多环芳烃化合物。本文采用标样共注,对鄂尔多斯盆地和准噶尔盆地25件煤样中三联苯系列化合物进行了准确鉴定,确定了该系列在HP-5MS色谱柱上的出峰顺序为邻位三联苯(o-TrP)、间位三联苯(m-TrP)、对位三联苯(p-TrP),并精确计算了各异构体在色谱柱上的标准保留指数。采用量子化学计算方法,对各异构体结构进行了优化,并获得一系列的热力学参数,确定了其热稳定性顺序:p-TrP>m-TrP>o-TrP,厘定了分子结构变形的程度大小:o-TrP>m-TrP>p-TrP,认为各异构体之间的热稳定性差异是由空间位阻效应大小不同导致的。初步建立了三联苯相关成熟度参数TrP1(TrP1=p-TrP/o-TrP)和TrP2(TrP2=(m-TrP+p-TrP)/o-TrP)与镜质组反射率(Ro)的换算关系式:Rc(%)=1.52×(TrP1/100)+0.53(Ro>0.4%)和Rc(%)=0.64×TrP2/100+0.52(Ro>0.4%)。本研究还发现沉积环境的氧化还原性对沉积有机质中的TrP1和TrP2参数值的影响很小,因而该参数能够评价低熟-高熟煤系烃源岩成熟度。与化学结构相似的甲基联苯(MBP)相比,TrP1和TrP2作为地球化学参数在成熟度评价方面比3-MBP/2-MBP(3-甲基联苯/2-甲基联苯)更具优越性。

Terphenyls(TrP)are important polycyclic aromatic hydrocarbons that occur ubiquitously in petroleum and sedimentary organic matter.In this study,terphenyls were analyzed by GC-MS and unambiguously identified in 25 coal samples from the Junggar Basin and Ordos Basin by using the co-injection of authentic standards.The elution order of three terphenyl isomers in an HP-5MS chromatographic column was as follows:o-TrP,m-TrP,and p-TrP.The standard retention indices of terphenyls were also calculated based on the retention index system.The thermodynamic properties and optimized geometries of terphenyl isomers were determined by quantum chemical calculation.The thermodynamic stability of the terphenyl isomers was ranked as:p-TrP>m-TrP>o-TrP,and the degree of their molecular structural deformation was ranked as:o-TrP>m-TrP>p-TrP.It is suggested that the difference in the thermal stability of the terphenyl isomers is mainly controlled by the effect of steric hindrance.The quantitative relationship between TrP1(TrP1=p-TrP/o-TrP)and TrP2(TrP2=(m-TrP+p-TrP)/o-TrP),the maturity parameters relative to terphenyls,and vitrinite reflectance(Ro)were preliminarily established as follows:Rc(%)=1.52×(TrP1/100)+0.53(Ro>0.4%)and Rc(%)=0.64×(TrP2/100)+0.52(Ro>0.4%).In addition,the redox condition of a sedimentary environment has been proven to have no significant effect on the TrP1 and TrP2 values.Therefore,TrP1 and TrP2 can be applied as effective maturity indicators to quantitatively assess the thermal maturity of coal-measure source rocks with low to high maturation levels.The comparisons of the distribution and thermodynamic stability of terphenyls and methylbiphenyls(MBP)suggest that TrP1 and TrP2 as geochemical parameters have an advantage over 3-MBP/2-MBP ratios in the assessment of maturity.