Department of Geology and Environmental Science, University of Pittsburgh, 200 SRCC 4107 O'Hara St., Pittsburgh, PA 15260, United States.
Department of Geology and Environmental Science, University of Pittsburgh, 200 SRCC 4107 O'Hara St., Pittsburgh, PA 15260, United States.
Sci Total Environ. 2019 Dec 10;695:133944. doi: 10.1016/j.scitotenv.2019.133944. Epub 2019 Aug 15.
The large increase in unconventional shale gas extraction has raised concerns about potential water contamination from leaks and spills. Shale gas produced water is challenging to detect in areas impacted by legacy contamination, particularly from conventional sources. Previous studies have proposed combinations of Br, SO, Ba, Cl, and other more specialized stable isotope systems to delineate shale gas produced water from 1) non-impacted waters and 2) other sources of water contamination. In general, the efforts that rely on relatively simple chemistry do not allow differentiation between conventional and unconventional brine chemistry. We examined variations in Ca/Mg and Ca/Sr ratios that seem to arise from variation in temperature with depth, to differentiate among conventional brines, unconventional brines, and non-impacted waters. This approach was applied to four sedimentary basins in the USGS produced water database: Williston, Michigan, Appalachian, and the Green River basin. In addition, the utility of the system was demonstrated with field samples taken during periods of known unconventional brine releases to surface waters. The Ca/Mg and Ca/Sr ratios allow distinction among these three water types in all basins, suggesting a relatively simple and direct way to evaluate water chemistries in landscapes dominated by unconventional shale gas extraction.
页岩气开采的大幅增加引发了人们对潜在的水污染问题的担忧，这些污染可能来自于泄漏和溢出。在受传统污染影响的地区，特别是受传统来源污染影响的地区，页岩气生产用水很难被检测到。先前的研究提出了 Br、SO、Ba、Cl 和其他更专业的稳定同位素系统的组合，以将页岩气生产用水与 1）未受影响的水和 2）其他水源的水污染区分开来。一般来说，那些依赖相对简单化学的研究并不能区分常规和非常规盐水化学。我们研究了 Ca/Mg 和 Ca/Sr 比值的变化，这些变化似乎是由于深度变化引起的温度变化，从而区分常规盐水、非常规盐水和未受影响的水。该方法应用于美国地质调查局生产用水数据库中的四个沉积盆地：威利斯顿、密歇根、阿巴拉契亚和绿河盆地。此外，该系统还通过在已知非常规盐水释放到地表水中的时期采集的野外样本进行了验证。Ca/Mg 和 Ca/Sr 比值可在所有盆地中区分这三种水类型，这表明在非常规页岩气开采为主的景观中评估水质的一种相对简单直接的方法。
