Center on Global Change, Nicholas School of the Environment, Duke University, Durham, NC 27708, USA.
Proc Natl Acad Sci U S A. 2011 May 17;108(20):8172-6. doi: 10.1073/pnas.1100682108. Epub 2011 May 9.
Directional drilling and hydraulic-fracturing technologies are dramatically increasing natural-gas extraction. In aquifers overlying the Marcellus and Utica shale formations of northeastern Pennsylvania and upstate New York, we document systematic evidence for methane contamination of drinking water associated with shale-gas extraction. In active gas-extraction areas (one or more gas wells within 1 km), average and maximum methane concentrations in drinking-water wells increased with proximity to the nearest gas well and were 19.2 and 64 mg CH(4) L(-1) (n = 26), a potential explosion hazard; in contrast, dissolved methane samples in neighboring nonextraction sites (no gas wells within 1 km) within similar geologic formations and hydrogeologic regimes averaged only 1.1 mg L(-1) (P < 0.05; n = 34). Average δ(13)C-CH(4) values of dissolved methane in shallow groundwater were significantly less negative for active than for nonactive sites (-37 ± 7‰ and -54 ± 11‰, respectively; P < 0.0001). These δ(13)C-CH(4) data, coupled with the ratios of methane-to-higher-chain hydrocarbons, and δ(2)H-CH(4) values, are consistent with deeper thermogenic methane sources such as the Marcellus and Utica shales at the active sites and matched gas geochemistry from gas wells nearby. In contrast, lower-concentration samples from shallow groundwater at nonactive sites had isotopic signatures reflecting a more biogenic or mixed biogenic/thermogenic methane source. We found no evidence for contamination of drinking-water samples with deep saline brines or fracturing fluids. We conclude that greater stewardship, data, and-possibly-regulation are needed to ensure the sustainable future of shale-gas extraction and to improve public confidence in its use.
定向钻井和水力压裂技术极大地增加了天然气的开采量。在宾夕法尼亚州东北部和纽约州北部的马塞勒斯和尤蒂卡页岩地层的含水层中，我们记录了与页岩气开采有关的饮用水中甲烷污染的系统证据。在活跃的天然气开采区（一公里内有一个或多个气井），饮用水井中甲烷的平均和最大浓度随与最近的气井的距离而增加，分别为 19.2 和 64 毫克/升（n = 26），这是潜在的爆炸危险；相比之下，在相邻的非开采区（一公里内无气井）中，类似地质构造和水文地质条件下的溶解甲烷样本的平均值仅为 1.1 毫克/升（P < 0.05；n = 34）。浅层地下水中溶解甲烷的平均 δ13C-CH4 值对于活跃区比非活跃区明显更负（分别为-37 ± 7‰和-54 ± 11‰；P < 0.0001）。这些 δ13C-CH4 数据，加上甲烷与高链烃的比值以及 δ2H-CH4 值，与马塞勒斯和尤蒂卡页岩等更深的热成因甲烷来源一致，与附近气井的气体地球化学相匹配。相比之下，非活跃区浅层地下水中浓度较低的样本具有反映更生物成因或混合生物成因/热成因甲烷来源的同位素特征。我们没有发现饮用水样本受到深层盐水或压裂液污染的证据。我们得出的结论是，需要加强管理、提供更多的数据，并可能进行监管，以确保页岩气开采的可持续未来，并提高公众对其使用的信心。
