Application of Nuclear Magnetic Resonance (NMR) Spectroscopy to Lacustrine Kerogen Geochemistry: Paleogene Dongpu Sag, China

Solid-state nuclear magnetic resonance (NMR) spectroscopy has been widely used in organic geochemistry because of its utility in examining the chemical structures present in sedimentary organic matter (kerogen). Here, we present such an investigation of kerogens from the Paleogene Shahejie Formation in the Dongpu Sag, Bohai Bay Basin, eastern China. Results show that the NMR spectra and their parameters are sensitive to kerogen type as defined by elemental ratios. The NMR spectra of types I and II kerogens are similar and show that the dominant chemical structures are aliphatic functional groups (e.g., methylene and methyl carbons), followed by aromatic moieties, with relatively fewer structures containing heteroatoms. In contrast, type III kerogen is considerably different, having a much lower aliphatic than aromatic functional group content and a higher degree of aromaticity. Based on this, a formula is established in response to the source rock hydrogen index and hydrocarbon generation potential. Our data suggest that the chemical structural characteristics of lacustrine facies kerogens can be effectively studied by NMR in good response to hydrocarbon geochemistry. This implies that NMR is possibly a promising approach in lacustrine organic geochemistry and provides complements to the challenging study of paleoenvironment and organic matter accumulation in lacustrine systems due to the heterogeneity of source rock deposition.