| ABSTRACT
Petrographic and geochemical
studies of coal from the Almond Formation in the Greater Green River basin
demonstrate that the coal contains important volumes of stored liquid petroleum,
as well as methane. Modeling indicates that at the basin center, most of
the oil generated in the coal has been thermally cracked to gas, whereas
at the basin flank the oil-to-gas reaction has barely proceeded.
Several new concepts are presented about
the mechanism of petroleum generation in coal based on (1) natural maturation
trends gleaned from examination of Almond coal samples from different burial
depths and (2) similar maturation trends observed in hydrous pyrolysis
experiments using immature Almond coal samples. These new concepts show
that the oil in the coal was generated during the alteration of desmocollinite
and liptinite macerals to exsudatinite (waxy oil) and inertinite solid
residue; that the waxy oil was initially stored in porous structures and
subsequently in vesicles as the coal matured under increasing temperature;
that primary migration of the oil occurred as the generation of a sufficient
volume of exsudatinite microfractured the vitrinite-
semifusinite vesicles, interconnecting vesicles,
©Copyright
1996. The American Association of Petroleum Geologists. All rights reserved. 1Manuscript
received August 1, 1995; revised manuscript received April 23, 1996; final
acceptance July 15, 1996.
2Universidad
Industrial de Santander, P. O. Box 678, Bucaramanga, Colombia.
3University
of Wyoming, Laramie, Wyoming 82071.
4Brigham
Young University, Provo, Utah 84602.
We
wish to thank Donald McGowan for discussions that improved this paper,
Francis P. Miknis (Western Research Institute, University of Wyoming) for
the NMR analyses, Steven J. Butala (Department of Chemistry, Brigham Young
University) for the gas chromatography/mass spectrometry analyses, and
Steven Boese (Department of Geology and Geophysics, University of Wyoming)
for his analytical help. We would also like to acknowledge David Copeland
and Kathy Kirkaldie (Institute for Energy Research, University of Wyoming),
who greatly improved the manuscript with many suggestions.
This research
was supported under Gas Research Institute Contracts No. 5091-221-2146
and 5093-260-2764, U.S. Department of Energy Cooperative Agreement DE-FC21-86MC11076,
and NSF-EPSCoR-ADP Fossil Energy Contract EHR-910-8774. | 
