Using environmental tracers and modelling to identify natural and gas well-induced emissions of methane into streams
Using environmental tracers and modelling to identify natural and gas well-induced emissions of methane into streams
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DOI：
10.1016/j.apgeochem.2017.12.022
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发表时间：
2018-04-01
影响因子：
3.4
通讯作者：
Brantley, S. L.
中科院分区：
文献类型：
--
作者：
Grieve, P. L.;Hynek, S. A.;Brantley, S. L.
页岩气井的开发有时会导致甲烷(CH4)从钻孔运移到含水层。泄漏的识别依赖于对单个地下水样本中甲烷的分析，这些样本通常来自水井；然而，收集点数据成本很高，而且容易出现假象。河流甲烷分析是发现甲烷向地下水潜在渗漏的一种新方法。在宾夕法尼亚州(PA)页岩气井密度较高的集水区，在基流期间对溪流中的溶解碳氢化合物和地球化学示踪剂进行了测量，以确定与气井泄漏相关的特征。调查了三条未发现来自气井的污染的溪流，以及之前报告的一口气井附近的一条溪流，这些溪流正在泄漏甲烷。在可能发生泄漏的气井附近的溪流中观察到的区别于没有泄漏的溪流的特征包括：河岸地下水中CH4浓度较高(高达4600和206mug/L)，较高的天然气流入河道(>；70vs<；10mgm(-2)d(-1))，与中泥盆世马赛卢斯组页岩一致的碳氢同位素特征和放射性成因锶，以及地下水中现代大气年龄示踪剂的较高浓度。这些示踪剂浓度可能表明碳氢化合物作为单独的气相而不是在溶液中向上输送。此外，假定泄漏井附近的溪流并不位于与断层相关的地形线条上，而具有大量自然产热甲烷流入的溪流往往与潜在的地质结构对齐。STREAM方法是估算流域尺度地下水组成和CH4通量的有效技术，揭示了甲烷排放的自然和人为来源。
Development of shale gas wells sometimes results in migration of methane (CH4) from boreholes into aquifers. Identification of leakage has relied on analysis of CH4 in individual groundwater samples, usually from water wells; however, collection of point data is expensive and prone to artefacts. Methane analysis in streams is a novel way to find potential leakage of CH4 to groundwater. Here, dissolved hydrocarbons and geochemical tracers were measured in streams during base flow in watersheds with high densities of shale gas wells in Pennsylvania (PA) to identify characteristics related to leaking gas wells. Three streams with no known contamination from gas wells and one stream near a gas well previously reported to be leaking CH4 were investigated. The characteristics observed in the stream near the putatively leaking gas well that distinguish it from the streams without leaks include higher CH4 concentrations in riparian groundwater (as high as 4600 versus 206 mu g/L), a relatively high gas influx to the stream channel (> 70 versus< 10 mg m(-2) d(-1)), hydrocarbon isotopic signatures and radiogenic strontium consistent with Middle Devonian Marcellus Formation shale, and higher concentrations of modern atmospheric age tracers in groundwater. These tracer concentrations may indicate upward transport of hydrocarbons as a separate gas phase rather than in solution. In addition, the stream near the putatively leaking well was not located along a fault-related topographic lineament whereas streams with substantial natural thermogenic CH4 influxes tend to be aligned with potential geologic structures. The stream approach is an efficient technique to estimate watershed-scale groundwater compositions and fluxes of CH4 that reveal natural and anthropogenic sources of methane emissions.