School of Earth, Environmental and Biological Sciences, Queensland University of Technology, 2 George St, GPO Box 2434, Brisbane, Queensland 4001, Australia.
Water Res. 2013 Mar 1;47(3):1021-34. doi: 10.1016/j.watres.2012.11.003. Epub 2012 Nov 8.
A pilot study has produced 31 groundwater samples from a coal seam gas (CSG) exploration well located in Maramarua, New Zealand. This paper describes sources of CSG water chemistry variations, and makes sampling and analytical recommendations to minimize these variations. The hydrochemical character of these samples is studied using factor analysis, geochemical modelling, and a sparging experiment. Factor analysis unveils carbon dioxide (CO(2)) degassing as the principal cause of sample variation (about 33%). Geochemical modelling corroborates these results and identifies minor precipitation of carbonate minerals with degassing. The sparging experiment confirms the effect of CO(2) degassing by showing a steady rise in pH while maintaining constant alkalinity. Factor analysis correlates variations in the major ion composition (about 17%) to changes in the pumping regime and to aquifer chemistry variations due to cation exchange reactions with argillaceous minerals. An effective CSG water sampling program can be put into practice by measuring pH at the wellhead and alkalinity at the laboratory; these data can later be used to calculate the carbonate speciation at the time the sample was collected. In addition, TDS variations can be reduced considerably if a correct drying temperature of 180 °C is consistently implemented.
一项初步研究从位于新西兰马马鲁瓦的一个煤层气（CSG）勘探井中采集了 31 个地下水样本。本文描述了 CSG 水样化学变化的来源，并提出了采样和分析建议，以最大限度地减少这些变化。利用因子分析、地球化学模拟和曝气实验研究了这些样品的水化学特征。因子分析揭示了二氧化碳（CO(2)）的脱气是导致样品变化的主要原因（约 33%）。地球化学模拟证实了这些结果，并确定了脱气过程中碳酸盐矿物的少量沉淀。曝气实验通过在保持恒碱度的同时显示 pH 值的稳定上升，证实了 CO(2)脱气的影响。因子分析将主要离子组成的变化（约 17%）与抽汲制度的变化以及与泥质矿物的阳离子交换反应引起的含水层化学变化相关联。通过在井口测量 pH 值和在实验室测量碱度，可以实施有效的 CSG 水样采集方案；这些数据以后可用于计算采集样品时的碳酸盐形态。此外，如果始终如一地执行 180°C 的正确干燥温度，则可以大大降低 TDS 的变化。
