The influence of macroscopic texture on biogenically-derived coalbed methane, Huntly coalfield, New Zealand

Mares, Tennille E. and Moore, Tim A. (2008) The influence of macroscopic texture on biogenically-derived coalbed methane, Huntly coalfield, New Zealand. International Journal of Coal Geology, 76 1-2: 175-185. doi:10.1016/j.coal.2008.05.013

Author Mares, Tennille E.
Moore, Tim A.
Title The influence of macroscopic texture on biogenically-derived coalbed methane, Huntly coalfield, New Zealand
Journal name International Journal of Coal Geology   Check publisher's open access policy
ISSN 0166-5162
Publication date 2008-10-02
Sub-type Article (original research)
DOI 10.1016/j.coal.2008.05.013
Volume 76
Issue 1-2
Start page 175
End page 185
Total pages 11
Editor Romeo M. Flores
Place of publication Amsterdam, Netherlands
Publisher Elsevier
Language eng
Formatted abstract
Secondary biogenic gas content can be related to textural characteristics in Eocene age subbituminous coals from the Huntly coalfield, New Zealand. However, the relationships between the two major coal seams in the basin are considerably different despite their close stratigraphic proximity (less than 25 m).

In this study, 163 coal samples were collected and desorbed from eight drill holes. Gas adsorption capacity and proximate analyses were conducted as well as macroscopic logging for coal type and vitrain banding characteristics. Vitrain bands were quantitatively point counted and the longest dimension of the shortest axis measured. Three coal types were recognized: bright luster non-banded, bright moderately banded and bright highly banded. Vitrain band thickness, converted to the phi (− log2) scale, was found to increase across the coal types with the thickest bands being associated with the most banded coal type. Overall, when normalized by seam and location, the dataset reveals a relationship between coal type and gas content with the non-banded coal type having the highest gas contents and conversely, the coal types with the most vitrain bands having the lowest gas contents.

However, when the seams are considered separately, it can be seen that in the stratigraphically higher Renown coal seam, gas has an indirect association with increasing band thickness, in agreement with the overall trend, while the stratigraphically lower Kupakupa coal seam appears to have a direct relationship. Interestingly the Renown seam, which has a greater percentage of non-banded material, generally has a greater methane adsorption capacity as well as a greater gas content compared to the Kupakupa seam. It is believed these differences are related to macroscopic texture and that the differing proportions of the coal types between the two seams has a fundamental effect on microporosity, ultimately controlling the available surface area for gas adsorption.
Keyword Secondary biogenic gas
Vitrain bands
New Zealand
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ
Additional Notes Special Issue: "Microbes, Methanogenesis, and Microbial Gas in Coal": This issue is the "Selected Proceedings of the Coal Geology Division session on 'Microbial Origin of Hydrocarbon Gases and Sedimentary Basins', Annual Meeting of the Geological Society of America, 28-31 October 2007, Denver, Colorado, U.S.A.". This paper was not presented at that conference: "Eight additional papers ...were included to broaden the scope of the Special Issue".

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Earth Sciences Publications
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