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Infrared Spectroscopy and Chemometrics: What Can They Tell Us About Petroleum Systems?


Infrared spectroscopy is utilized to study important properties of refinery and petrochemical products, such as octane number and viscosity, and for the prediction of crude oil geochemical parameters, including API gravity, percent sulfur, and saturate/aromatic ratios. This technique can also be used to assess source-rock kerogen properties such as thermal maturity and hydrogen richness. In this study, Fourier transform infrared spectroscopy (FTIR, 400 to 4000 cm-1), coupled with chemometric analysis, is applied to oil-source rock correlations in petroleum systems. Immature kerogen, oil, and extractable organic matter samples from the Green River Formation (Utah, USA), New Albany Shale (Illinois, USA), Ghareb Formation (Jordan), and Bakken Shale (North Dakota, USA) were thermally matured via hydrous pyrolysis (HP) experiments, and naturally matured shales and oils from the Bakken Shale were characterized using attenuated total reflectance (ATR) FTIR. These data were sorted by applying cluster and principal component analysis (PCA) to examine oil-oil and source rock-oil correlations. Results show that free-oil pyrolyzates, generated from various source rocks subjected to the same degree of thermal stress via HP, are readily sorted using chemometric tools applied to infrared spectra. These results indicate that it may be possible to correlate oils to source rocks across a basin using FTIR and chemometric analyses. Initial examination of kerogens subjected to increasing thermal stress, both in HP and natural systems, cluster based on source rock and plot in PCA space primarily according to hydrogen content. Asphaltenes may also prove useful in direct oil-source rock correlations as they generally retain geochemical features similar to the source kerogen and are readily amenable to characterization by FTIR.