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Use of stable carbon isotope compositions of pyrolytically derived methane as maturity indices for carbonaceous materials

Journal Article · · Geochim. Cosmochim. Acta; (United States)
Nineteen coals of varying ranks and twelve organic-solvent-extracted shales of different ages and maturities were subjected to a long-term, closed system, isothermal (500/sup 0/C) pyrolysis procedure until no additional methane or carbon oxide gases were generated. Three significant trends were observed: (1) for all of the samples, the stable carbon isotope difference between the total accumulated methane and parent carbon was linearly correlated with yield of methane with r = 0.88; (2) for a series of thirteen model compounds, two lipid-free shales and twelve coals, the H/C ratio of each was linearly correlated with the yield of methane with r = 0.93; (3) for a series of eleven coals samples, the O/C ratio of each was linearly correlated with the yield of carbon oxides with r = 0.97. The experimental relationships described above indicate that a simple pyrolysis procedure and measurements of the amounts of generated CH/sub 4/, CO/sub 2/, and CO relative to the carbon content of the sample and the stable isotopic compositions of the methane and parent organic carbon give: (a) an index of the maturity and (b) values which are directly related to the H/C and O/C ratios of the carbonaceous materials. 7 figures, 5 tables.
Research Organization:
Texas A and M Univ., College Station
OSTI ID:
5699595
Journal Information:
Geochim. Cosmochim. Acta; (United States), Journal Name: Geochim. Cosmochim. Acta; (United States) Vol. 43:12; ISSN GCACA
Country of Publication:
United States
Language:
English