Relationships between major ions in coal seam gas groundwaters: Examples from the Surat and Clarence-Moreton basins

Owen, Daniel D.R., Raiber, Matthias, & Cox, Malcolm E. (2015) Relationships between major ions in coal seam gas groundwaters: Examples from the Surat and Clarence-Moreton basins. International Journal of Coal Geology, 137, pp. 77-91.

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Using a combination of multivariate statistical techniques and the graphical assessment of major ion ratios, the influences on hydrochemical variability of coal seam gas (or coal bed methane) groundwaters from several sites in the Surat and Clarence-Moreton basins in Queensland, Australia, were investigated. Several characteristic relationships between major ions were observed:

1) strong positive linear correlation between the Na/Cl and alkalinity/Cl ratios;

2) an exponentially decaying trend between the Na/Cl and Na/alkalinity ratios;

3) inverse linear relationships between increasing chloride concentrations and decreasing pH for high salinity groundwaters, and;

4) high residual alkalinity for lower salinity waters, and an inverse relationship between decreasing residual alkalinity and increasing chloride concentrations for more saline waters.

The interpretation of the hydrochemical data provides invaluable insights into the hydrochemical evolution of coal seam gas (CSG) groundwaters that considers both the source of major ions in coals and the influence of microbial activity. Elevated chloride and sodium concentrations in more saline groundwaters appear to be influenced by organic-bound chlorine held in the coal matrix; a sodium and chloride ion source that has largely been neglected in previous CSG groundwater studies. However, contrastingly high concentrations of bicarbonate in low salinity waters could not be explained, and are possibly associated with a number of different factors such as coal degradation, methanogenic processes, the evolution of high-bicarbonate NaHCO3 water types earlier on in the evolutionary pathway, and variability in gas reservoir characteristics. Using recently published data for CSG groundwaters in different basins, the characteristic major ion relationships identified for new data presented in this study were also observed in other CSG groundwaters from Australia, as well as for those in the Illinois Basin in the USA. This observation suggests that where coal maceral content and the dominant methanogenic pathway are similar, and where organic-bound chlorine is relatively abundant, distinct hydrochemical responses may be observed. Comparisons with published data of other NaHCO3 water types in non-CSG environments suggest that these characteristic major ion relationships described here can: i) serve as an indicator of potential CSG groundwaters in certain coal-bearing aquifers that contain methane; and ii) help in the development of strategic sampling programmes for CSG exploration and to monitor potential impacts of CSG activities on groundwater resources.

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ID Code: 86468
Item Type: Journal Article
Refereed: Yes
Keywords: Coal seam gas (CSG), Coal bed methane (CBM), Hydrochemical indicator, Methanogenesis, Sodium–bicarbonate groundwater
DOI: 10.1016/j.coal.2014.11.004
ISSN: 0166-5162
Divisions: Current > Schools > School of Earth, Environmental & Biological Sciences
Current > QUT Faculties and Divisions > Science & Engineering Faculty
Copyright Owner: Copyright 2014 Elsevier B.V.
Copyright Statement: Licensed under the Creative Commons Attribution; Non-Commercial; No-Derivatives 4.0 International. DOI:
Deposited On: 06 Aug 2015 23:42
Last Modified: 13 Aug 2015 00:38

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