A major challenge in managing coal seam gas (CSG) water is predicting how much water will be produced as the industry develops. Klohn Crippen Berger Ltd (KCB) was commissioned by the Queensland Department of Natural Resources and Mines (DNRM) to develop a tool to forecast where, when, and how much CSG water will be produced in the Surat and Southern Bowen Basins under various industry expansion scenarios.
The Water Production Tool (WPT) uses the Theis equation, a non-equilibrium groundwater flow equation that accounts for the effect of pumping time on well yield in confined aquifers, to predict water production volumes. Where multiple pumping wells are in close proximity, the required pumping rates for coal seam depressurisation are reduced. Therefore, pumping effects are projected spatially to assess interference effects between wells. Water production is then up-scaled to the projected scale of the CSG industry within the Surat and Southern Bowen Basins.
Two modifications were made to address the dual phase nature of CSG extraction (a transmissivity reduction factor) and the impact of weathering at the eastern margin of the Surat Basin (a ?near edge effect? factor). These factors modify relevant hydrogeological parameters in a consistent and defensible manner to more closely match observed water production. The WPT was verified by comparing results to equivalent Theis equation calculations and to type curves provided by CSG proponents. Calibration was achieved by varying the spatial distribution and intensity of the near edge effect factor in conjunction with a chi-squared analysis of residuals.
The tool, which is now being maintained and further developed by the Centre for Water in the Minerals Industry (CWiMI), was built to balance numerical complexity against relative flexibility and simulation speed. The result is a tool that can produce statistically relevant results of prescribed scenarios to plan water handling and treatment requirements in discrete zones of operation.
Strand, R., L. Reading and G. Keir. 2013. “Water Production Simulation Tool for Coal Seam Gas Operations in Bowen and Surat Basins,” in: Water in Mining 2013, Brisbane, Australia, November 26-28, 2013. Carlton, Victoria: Australasian Institute of Mining and Metallurgy.
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