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Sources of hydrochemical variability and implications associated with CSG water extraction

Taulis, Mauricio (2012) Sources of hydrochemical variability and implications associated with CSG water extraction. In 34th International Geological Congress : Unearthing our Past and Future, 5-10th August, 2012, Brisbane Convention & Exhibition Centre, Brisbane, Australia. (Unpublished)

Abstract

Coal Seam Gas (CSG) production is achieved by extracting groundwater to depressurize coal seam aquifers in order to promote methane gas desorption from coal micropores. CSG waters are characteristically alkaline, have a neutral pH (~7), are of the Na-HCO3-Cl type, and exhibit brackish salinity. In 2004, a CSG exploration company carried out a gas flow test in an exploration well located in Maramarua (Waikato Region, New Zealand). This resulted in 33 water samples exhibiting noteworthy chemical variations induced by pumping. This research identifies the main causes of hydrochemical variations in CSG water, makes recommendations to manage this effect, and discusses potential environmental implications.

Hydrochemical variations were studied using Factor Analysis and this was supported with hydrochemical modelling and a laboratory experiment. This reveals carbon dioxide (CO2) degassing as the principal source of hydrochemical variability (about 33%). Factor Analysis also shows that major ion variations could also reflect changes in hydrochemical composition induced by different pumping regimes. Subsequent chloride, calcium, and TDS variations could be a consequence of analytical errors potentially committed during laboratory determinations.

CSG water chemical variations due to degassing during pumping can be minimized with good completion and production techniques; variations due to sample degassing can be controlled by taking precautions during sampling, transit, storage and analysis. In addition, the degassing effect observed in CSG waters can lead to an underestimation of their potential environmental effect. Calcium precipitation due to exposure to normal atmospheric pressure results in a 23% increase in SAR values from Maramarua CSG water samples.

Impact and interest:

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ID Code: 55155
Item Type: Conference Item (Presentation)
Keywords: Coal Seam Gas, Groundwater, Hydrochemistry
Subjects: Australian and New Zealand Standard Research Classification > EARTH SCIENCES (040000) > GEOCHEMISTRY (040200)
Australian and New Zealand Standard Research Classification > EARTH SCIENCES (040000) > GEOCHEMISTRY (040200) > Inorganic Geochemistry (040202)
Australian and New Zealand Standard Research Classification > EARTH SCIENCES (040000) > GEOLOGY (040300) > Basin Analysis (040301)
Australian and New Zealand Standard Research Classification > EARTH SCIENCES (040000) > OTHER EARTH SCIENCES (049900) > Earth Sciences not elsewhere classified (049999)
Australian and New Zealand Standard Research Classification > ENGINEERING (090000) > ENVIRONMENTAL ENGINEERING (090700) > Environmental Engineering Modelling (090702)
Divisions: Current > Schools > School of Earth, Environmental & Biological Sciences
Past > QUT Faculties & Divisions > Faculty of Science and Technology
Past > Institutes > Institute for Sustainable Resources
Deposited On: 28 Nov 2012 09:39
Last Modified: 28 Nov 2012 09:39

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