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Assessing the quantitative reliability of solid-state 13C NMR spectra of kerogens across a gradient of thermal maturity |
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| Authors: | Smernik Ronald J Schwark Lorenz Schmidt Michael W I |
| Institution: | aSoil and Land Systems, School of Earth and Environmental Sciences, The University of Adelaide, Waite Campus, Urrbrae, SA 5064, Australia bGeological Institute, Cologne University, Zuelpicher Str. 49a, D-50674, Cologne, Germany cDepartment of Geography, University of Zürich, 8057 Zürich, Germany |
| Abstract: | Five type II kerogens, shown by elemental analysis and Rock-Eval pyrolysis to represent a gradient of thermal maturity, were further characterized using a range of solid-state 13C NMR spectroscopic techniques. 13C cross polarization (CP) NMR spectra of the kerogens confirmed the well-established pattern of increasing aromaticity with increasing thermal maturity. Spin counting showed that CP observability was around 50% for the immature kerogens, and only 14–25% for the mature kerogens. Spin counting also showed that the direct polarization (DP) observabilities were >80% for all but one of the kerogens. Despite the large differences in observability between the two techniques, aromaticities derived from corresponding CP and DP spectra differed by only 1–15%. The RESTORE technique showed that the low CP observability of the immature kerogens was due mostly to rapid T1ρH relaxation, whereas both rapid T1ρH relaxation and slow polarization transfer contributed to the low CP observability of the mature kerogens. |
| Keywords: | Solid-state 13C NMR Kerogen Quantitation Spin counting RESTORE |
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