Coal seam water quality and the impact upon management strategies

The rapidly developing coal seam gas industry produces significant volumes of associated brackish water which needs to be appropriately managed. The aim of this study was to determine the variability of water composition within and between multiple gas fields in a defined geographic area and to discover relationships between species present. Water quality from 150 coal seam gas production wells from the Surat Basin, Queensland has been analysed. Chemical analysis revealed the associated water to predominantly contain bicarbonate (< 2030 mg/L), chloride (< 5910 mg/L) and sodium (< 3700 mg/L) species. In several instances, water parameters such as fluoride, were above recommended limits for direct beneficial reuse. Principal component analysis revealed three groups of water quality parameters which described the data. Iron, manganese and aluminium were in one group; bromide, magnesium, strontium, potassium, hardness, calcium, chloride, electrical conductivity, total dissolved solids and sodium appeared as a second group and a third group comprised of fluoride, bicarbonate alkalinity as CaCO3, sodium adsorption ratio, pH, boron, silica, total organic carbon, and sulfate. The variability in water compositions may impact on water management technologies such as reverse osmosis as there may be a propensity for membrane fouling by alkaline earth ions or silica. This study suggested that the mineral quantities in coal such as clay, sulfide ores, oxide ores, quartz and phosphates may correlate with the water quality patterns. Through the use of multivariate analysis it was shown that depth of the CSG production well and the location of the CSG production well did not correlate with differing water quality patterns. The physical and chemical parameters that were analysed in this study will aid in the efficient management of associated water and provide information which allows better understanding of environmental impacts and the prospect for beneficial reuse.