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AAPG Bulletin

Abstract

AAPG Bulletin, V. 97, No. 3 (March 2013), P. 421436.

Copyright copy2013. The American Association of Petroleum Geologists. All rights reserved.

DOI:10.1306/09101211189

Characterization of oil shale, isolated kerogen, and postpyrolysis residues using advanced 13C solid-state nuclear magnetic resonance spectroscopy

Xiaoyan Cao,1 Justin E. Birdwell,2 Mark A. Chappell,3 Yuan Li,4 Joseph J. Pignatello,5 Jingdong Mao6

1Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, Virginia; xcao@odu.edu
2U.S. Geological Survey, Denver Federal Center, Denver, Colorado; jbirdwell@usgs.gov
3Environmental Laboratory, U.S. Army Corps of Engineers, Vicksburg, Mississippi; mark.a.chappell@usace.army.mil
4Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, Virginia; yxxli001@odu.edu
5Department of Environmental Sciences, The Connecticut Agricultural Experiment Station, New Haven, Connecticut; joseph.pignatello@ct.gov
6Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, Virginia; jmao@odu.edu

ABSTRACT

Characterization of oil shale kerogen and organic residues remaining in postpyrolysis spent shale is critical to the understanding of the oil generation process and approaches to dealing with issues related to spent shale. The chemical structure of organic matter in raw oil shale and spent shale samples was examined in this study using advanced solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Oil shale was collected from Mahogany zone outcrops in the Piceance Basin. Five samples were analyzed: (1) raw oil shale, (2) isolated kerogen, (3) oil shale extracted with chloroform, (4) oil shale retorted in an open system at 500degC to mimic surface retorting, and (5) oil shale retorted in a closed system at 360degC to simulate in-situ retorting. The NMR methods applied included quantitative direct polarization with magic-angle spinning at 13 kHz, cross polarization with total sideband suppression, dipolar dephasing, CHn selection, 13C chemical shift anisotropy filtering, and 1H-13C long-range recoupled dipolar dephasing. The NMR results showed that, relative to the raw oil shale, (1) bitumen extraction and kerogen isolation by demineralization removed some oxygen-containing and alkyl moieties; (2) unpyrolyzed samples had low aromatic condensation; (3) oil shale pyrolysis removed aliphatic moieties, leaving behind residues enriched in aromatic carbon; and (4) oil shale retorted in an open system at 500degC contained larger aromatic clusters and more protonated aromatic moieties than oil shale retorted in a closed system at 360degC, which contained more total aromatic carbon with a wide range of cluster sizes.

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