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Geosciences 2017, 7(2), 43; doi:10.3390/geosciences7020043

Stable Isotope Systematics of Coalbed Gas during Desorption and Production

1
Statoil ASA, Martin Linges Vei 33, 1330 Fornebu, Norway
2
School of Earth and Ocean Sciences, University of Victoria, P.O. Box 3050, Victoria, BC V8W 2Y2, Canada
*
Author to whom correspondence should be addressed.
Academic Editors: Alexei V. Milkov, Giuseppe Etiope and Jesús Martínez Frías
Received: 2 May 2017 / Revised: 8 June 2017 / Accepted: 10 June 2017 / Published: 14 June 2017
(This article belongs to the Special Issue Natural Gas Origin, Migration, Alteration and Seepage)
View Full-Text   |   Download PDF [9041 KB, uploaded 14 June 2017]   |  

Abstract

The stable carbon isotope ratios of coalbed methane (CBM) demonstrate diagnostic changes that systematically vary with production and desorption times. These shifts can provide decisive, predictive information on the behaviour and potential performance of CBM operations. Samples from producing CBM wells show a general depletion in 13C-methane with increasing production times and corresponding shifts in δ13C-CH4 up to 35.8‰. Samples from canister desorption experiments show mostly enrichment in 13C for methane with increasing desorption time and isotope shifts of up to 43.4‰. Also, 13C-depletion was observed in some samples with isotope shifts of up to 32.1‰. Overall, the magnitudes of the observed isotope shifts vary considerably between different sample sets, but also within samples from the same source. The δ13C-CH4 values do not have the anticipated signature of methane generated from coal. This indicates that secondary processes, including desorption and diffusion, can influence the values. It is also challenging to deconvolute these various secondary processes because their molecular and isotope effects can have similar directions and/or magnitudes. In some instances, significant alteration of CBM gases has to be considered as a combination of secondary alteration effects. View Full-Text
Keywords: coal; coalbed methane; coal seam gas; coal seam methane; shale gas; canister desorption; production; gas composition; stable carbon isotopes; stable hydrogen isotopes; geochemistry coal; coalbed methane; coal seam gas; coal seam methane; shale gas; canister desorption; production; gas composition; stable carbon isotopes; stable hydrogen isotopes; geochemistry
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Niemann, M.; Whiticar, M.J. Stable Isotope Systematics of Coalbed Gas during Desorption and Production. Geosciences 2017, 7, 43.

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