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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.