A study conducted in the Surat Basin in southeast Queensland, Australia, which has been published in Scientific Reports and funded by the Australian Government’s Cotton Research and Development Corporation, has found there is hydraulic connectivity between the Walloon Coal Measures and the Condamine Alluvium but the extent is low.
The research included the development and testing of a new methodology to evaluate water connectivity, provided independent baseline information for those communities near Dalby using groundwater for irrigation in proximity to CBM developments.
Through analysing the geochemistry of groundwater from 30 boreholes throughout the Condamine Alluvium, the researchers were able to determine if there was a geochemical fingerprint that indicated there was movement between the Walloon Coal Measures (a stratified geological formation that contains coal and CBM), and the Condamine Alluvium groundwater system.
The authors noted that there are natural pathways of hydraulic connectivity through faults, fracture networks, and permeable sedimentary formations. But connectivity can also occur through abandoned exploration wells and faulty well casing.
The investigations also determined that there was a low concentration of methane measured throughout the Condamine Alluvium.
The study was undertaken in association with the University of NSW (UNSW) Connected Waters Initiative Research Centre, Australian Nuclear Science and Technology Organisation (ANSTO), Royal Holloway, University of London and the University of East Anglia.
ANSTO participated in the study, helping to evaluate the extent of natural groundwater connectivity between the Australian overlying aquifer and deep CBM resources.
In the study, ANSTO measured levels of tritium (3H), a naturally occurring radioactive isotope of hydrogen, to gain information about groundwater residence times, water recharge processes and potential groundwater mixing. The radioactive emissions of tritium can be counted using liquid scintillation.
“We were all expecting mixing of water sources, instead we found a gas diffusion process that has probably been operating for a long time,” stated ANSTO Environmental Researcher, Dr Dioni Cendón, who was involved in the organisation of the study, geochemistry analyses, field sampling and the interpretation of results.
“ANSTO brings considerable expertise in the use of tools and techniques to measure changes in water isotopes that enable us to characterise water masses and to trace water and its interaction above and below the earth,” he continued.
Sulfate and nitrate anions were also measured at ANSTO using ion chromatography to provide insight into anaerobic process deep within an aquifer.
“Our measurements of the carbon-13 of dissolved inorganic carbon using mass spectrometry, told us something about the source of inorganic carbon in the groundwater,” indicated Cendón.
A continuous mobile methane survey adjacent to CBM developments led by Associate Professor Bryce Kelly at UNSW was also used to determine the source of the methane. The chemical signature at four isolated sites indicated it was probably sourced from the Western Coal Measures.
“Methane gas can migrate upwards into other aquifers but that does not involve mixing of waters, just the gas migrating. The water from the alluvium, which is used by irrigators, and the gas production water are chemically very different, therefore any mixing will be quite evident,” explained Cendón.
“It was important to show the growers and other involved parties how hydrogeochemical studies with different natural radioactive traces and stable isotopes can provide valuable baseline studies and/or separate natural and anthropogenic processes,” he continued.
The information is also being shared more widely with government and the scientific community.
Edited from press release by Harleigh Hobbs
Read the article online at: https://www.worldcoal.com/cbm/26112015/enhancing-research-into-water-connectivity-between-cbm-and-aquifers-3211/