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Molecular Transformation of Crude Oil in Confined Pyrolysis System and Its Impact on Migration and Maturity Geochemical Parameters

Zhang, Yahe, Liao, Yuhong, Guo, Shaohui, Xu, Chunming, Shi, Quan
Energy & Fuels 2016 v.30 no.9 pp. 6923-6932
carbon, catalytic cracking, gas chromatography-mass spectrometry, oils, petroleum, polycyclic aromatic hydrocarbons, pyrolysis, reflectance, sulfur, temperature
The compositions of crude oils can vary significantly during thermal maturation through cracking and aromatization. In this study, an immature high sulfur crude oil was pyrolyzed in a closed gold-tube system with heating rates of 20 °C/h and 2 °C/h, respectively, to simulate the thermal maturation process of crude oil. The molecular compositions of heteroatom-containing compounds in crude oil were investigated by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) while the impact of thermal maturation on migration and maturity geochemical parameters were investigated by gas chromatography–mass spectrometry (GC-MS). Based on the analysis of pyrolysis products, the compositional variations of heteroatom-containing aromatic compounds and the validity of the aromatic geochemical parameters during thermal maturation were investigated. When the equivalent vitrinite reflectance value (Easy %Ro) was greater than ca. 0.85, alkyl chain cracking was the major reaction and led to the producing of a large amount of <C₁₅ hydrocarbons. The yields of these <C₁₅ cracking products decreased at high pyrolysis temperature (corresponding to Ro > ca. 1.18) due to further secondary cracking. Polycyclic aromatic compounds (PAHs) gradually became the dominant compounds in pyrolysis products; the carbon number of alkyl chains attached to aromatic core decreased while the aromaticity increased. Simultaneously, polar heteroatom-containing species became more dealkylated and aromatic with the increasing of maturity. The valid maturity range of geochemical parameters relevant to oil migration and maturity based on heteroatom-containing aromatic compounds were also discussed.