Experimental study of kerogen maturation by solid-state 13C NMR spectroscopy

Chemical changes in the structure of kerogen during simulated thermal maturation were investigated by solid-state 13С NMR spectroscopy. The spin counting technique was used to evaluate the share of “observable” carbon atoms with increasing hydrous pyrolysis temperature. The obtained one-dimensional CP–MAS spectra showed that up to 50% of ether bonds were destroyed during the initial stages of sample heating. In spite of the loss of a significant part of alkyl chains, kerogen remained aliphatic. The aromatic structure of kerogen underwent considerable changes: two-dimensional 1H–13C heteronuclear solid-state NMR (HETCOR) spectra showed that in the process of hydrous pyrolysis, the redistribution of carbon atoms took place – branched aromatic carbons transform into bridgehead aromatic carbons.