Effect of weathering of oil shale at Julia Creek (Australia) on kerogen, oil yields and oil properties

Differing degrees of oxidation, caused by weathering at the surface, are evident in the Julia Creek oil shale deposit. Weathering results in decreased oil yields and its extent is indicated by the oil/organic carbon ratio. In a series of carefully selected samples, this ratio (by weight) varies from 0.55 for ‘fresh’ shale to 0.38 for appreciably altered shale. Oxidation of kerogen is reflected in the elemental composition of kerogens obtained by demineralization of the samples. FT-i.r. spectra of kerogens show that CH concentrations decrease and COOH contents increase with in situ oxidation. Nuclear magnetic resonance spectroscopy gives clear evidence that, as well as oil quantity, oil quality progressively changes with shale weathering. Results are, in general, directly comparable with those for artificially weathered shales.