Reduction of molecular motion of polymethylene in oil shales by mineral matter

Kerogen from the Stuart deposit, Queensland, Australia has been isolated from its oil shale by a number of methods and studied by solid-state C-13 nuclear magnetic resonance spectroscopy (NMR). The kerogen is unusual, since there is clear evidence of a resolved polymethylene peak in the NMR spectrum rather than the broad resonance at about the same chemical shift normally obtained for highly aliphatic kerogens with aromaticities less than 0.25. X-ray diffraction data also indicate some ordered material in the kerogen. This polymethylene peak is not present in the NMR spectrum of the original oil shale and is absent in spectra of both oil shales and kerogens of similar deposits (e.g., Condor, Queensland, Australia). The mineral-matter components of Stuart oil shale do not differ significantly from oil shales with conventional kerogen NMR spectra. It may be concluded that precursor biopolymers in Stuart kerogen are not as cross-linked as other aliphatic kerogens such as Condor. This could be due to a higher concentration of Pediastrum species in the kerogen-forming biomass.