Key Laboratory of Tectonics and Petroleum Resources, China University of Geosciences, Ministry of Education, Wuhan, 430074, China.
Faculty of Earth Resources, China University of Geosciences, Wuhan, 430074, China.
Environ Sci Pollut Res Int. 2019 Nov;26(31):31956-31980. doi: 10.1007/s11356-019-06350-0. Epub 2019 Sep 6.
The Southern Junggar Basin (SJB) in China is an emerging coalbed methane (CBM) development area with abundant low-rank CBM resources. CBM development is accomplished by pumping significant volumes of water from the aquifer, and this water is commonly termed as produced water, which has great utilization values for the water-deficient areas like SJB. Geochemistry signatures are prerequisites in the management of the produced water. Meanwhile, geochemistry surveys of this produced water could also help study the basin hydrogeology and then serve the CBM development. In this study, geochemical compositions of the produced waters, including major ions, stable isotopic compositions, trace elements, and rare earth elements, were analyzed. Results show that produced waters from CBM wells in the SJB are of Na-HCO type and have wide total dissolved solid (TDS) ranges from 963 to 11,916 mg/L (avg. 7417 mg/L). Cl, Na, and HCO are the principal determinates of the TDS contents of the produced waters, and their concentrations all increase with greater depth of the produced waters. Overall, the net results of groundwater-aquifer mineral-bacteria interactions with groundwater flowing along the flow path are to deplete Ca, Mg, and SO and increase Na, Cl, HCO, and TDS. Stable isotopic values of the CBM produced waters (δD and δO) cluster along or below the local meteoric water line (LMWL), and the shift of stable isotopic values to the right side of LMWL was affected by a joint effect of evaporation and mixing with near-surface water. Trace elements that exceed the regulated concentrations for drinking water of China include As, Fe, Mn, Ba, and Ni, among which Ba and Fe need to be most concerned because over 50% of the CBM produced waters exceed the regulated values. Through principal component analysis, the trace element associations in the CBM produced waters and their potential origins were analyzed. The ∑REY concentrations of the CBM produced waters increase exponentially with the increase of pH and present a certain correlation with TDS. The relationship between ∑REY concentrations and TDS reflects different water-rock reaction degrees and hydrogeological backgrounds.
中国南天山盆地（SJB）是一个新兴的煤层气（CBM）开发地区，拥有丰富的低阶 CBM 资源。CBM 的开发是通过从含水层中抽取大量的水来完成的，通常将这种水称为生产水，对于像 SJB 这样缺水的地区具有很大的利用价值。地球化学特征是生产水管理的前提。同时，对生产水进行地球化学调查也有助于研究盆地水文地质，进而为 CBM 开发服务。在本研究中，分析了生产水的地球化学组成，包括主要离子、稳定同位素组成、微量元素和稀土元素。结果表明，SJB 中 CBM 井的生产水属于 Na-HCO 型，总溶解固体（TDS）范围很宽，为 963 至 11916mg/L（平均值为 7417mg/L）。Cl、Na 和 HCO 是生产水中 TDS 含量的主要决定因素，其浓度随生产水深度的增加而增加。总体而言，地下水沿流动路径与含水层矿物-细菌相互作用的净结果是消耗 Ca、Mg 和 SO，增加 Na、Cl、HCO 和 TDS。CBM 生产水的稳定同位素值（δD 和 δO）沿或低于当地大气降水线（LMWL）聚集，稳定同位素值向 LMWL 右侧的偏移受到蒸发和与近地表水混合的共同影响。超过中国饮用水规定浓度的微量元素包括 As、Fe、Mn、Ba 和 Ni 等，其中 Ba 和 Fe 需要特别关注，因为超过 50%的 CBM 生产水超过规定值。通过主成分分析，分析了 CBM 生产水中微量元素的关联及其潜在来源。CBM 生产水的∑REY 浓度随 pH 值的增加呈指数增长，并与 TDS 呈一定相关性。∑REY 浓度与 TDS 的关系反映了不同的水岩反应程度和水文地质背景。
