原油热裂解过程中的红外光谱演化特征及其主控因素

原油的红外光谱能够反映原油中各种分子基团的信息，对于简单、快速识别原油的成因类型和热演化程度有很大的应用潜力。通过对两个不同有机相来源的原油样品开展热解实验，初步研究了原油热解过程中红外光谱的演化特征及其主控因素。结果表明，随着原油热解程度的增加，不同类型原油的红外光谱具有相似的演化模式，可近似划分为两个阶段。在早期阶段(实验温度<370℃)，热解油中甲基/亚甲基吸光度比值(A_CH3/A_CH2)变化不明显，而芳环分子基团吸光度(A_aro)及其与烷基分子基团吸光度比值(A_aro/A_sat)减小，这主要是由于原油中部分热稳定性低的化合物发生脱支链作用，形成了饱和烃组分，降低了芳烃/饱和烃比值。在晚期阶段(实验温度>370℃)，热解油中A_CH3/A_CH2,A_aro和A_aro/A_sat

Infrared spectra evolution of crude oil under pyrolysis and its controlling factors

Infrared spectra of crude oils can indicate information of various molecular groups， which is of great potential to identifying the genetic type and thermal evolution degree of crude oil. In this study， pyrolysis experiments are performed on two immature crude oil samples from different organic facies， to preliminarily investigate the infrared spectra evolution of crude oils under pyrolysis and its controlling factors. The results indicate that the infrared spectra evolutions are similar for the two oil samples and can be approximately divided into two stages with the increase in oil cracking extent. At the early stage with experiment temperatures of lower than 370 ℃， the A_{\mathrm{C}{\mathrm{H}}_{\mathrm{3}}}/A_{\mathrm{C}{\mathrm{H}}_{\mathrm{2}}} value of cracking oil varies slightly， while the A_aro and A_aro/A_sat values progressively decrease. This is due to some compounds with a weak thermal stability undergoing debranching during this stage， which results in an increase in saturated hydrocarbon content and decrease in the ratio of aromatic/saturated hydrocarbons. At the later stage with experiment temperatures of over 370 ℃， the A_{\mathrm{C}{\mathrm{H}}_{\mathrm{3}}}/A_{\mathrm{C}{\mathrm{H}}_{\mathrm{2}}}， A_aro and A_aro/A_sat values of oil samples significantly increase mainly due to the compounds with long molecular chain structures significantly cracked into compounds with short molecular chain structures， causing an increase in the A_{\mathrm{C}{\mathrm{H}}_{\mathrm{3}}} content. Meanwhile， the aromatization degree of the compounds is significantly enhanced at this stage， which results in an increase in aromatic hydrocarbon content as well as the ratio of aromatic/saturated hydrocarbons. There are still some differences in the infrared spectral parameters between the two oil samples during the oil cracking process， especially at the early stage. Therefore， cross plots of infrared spectral parameters， such as the plot of A_CH3/A_CH2-A_aro/A_sat， can be used to classify the types of crude oils and identify their thermal maturity.