Department of Civil and Environmental Engineering, Parsons Laboratory, Massachusetts Institute of Technology, 15 Vassar Street, Cambridge, Massachusetts 02139, United States.
Civil and Environmental Engineering, The University of Washington, 3760 East Stevens Way Northeast, Seattle, Washington 98195, United States.
Environ Sci Technol. 2021 Dec 21;55(24):16413-16422. doi: 10.1021/acs.est.1c05272. Epub 2021 Dec 7.
Conflicting evidence exists as to whether or not unconventional oil and gas (UOG) development has enhanced methane transport into groundwater aquifers over the past 15 years. In this study, recent groundwater samples were collected from 90 domestic wells and 4 springs in Northeastern Pennsylvania located above the Marcellus Shale after more than a decade of UOG development. No statistically significant correlations were observed between the groundwater methane level and various UOG geospatial metrics, including proximity to UOG wells and well violations, as well as the number of UOG wells and violations within particular radii. The δC and methane-to-higher chain hydrocarbon signatures suggested that the elevated methane levels were not attributable to UOG development nor could they be explained by using simple biogenic-thermogenic end-member mixing models. Instead, groundwater methane levels were significantly correlated with geochemical water type and topographical location. Comparing a subset of contemporary methane measurements to their co-located pre-drilling records ( = 64 at 49 distinct locations) did not indicate systematic increases in methane concentration but did reveal several cases of elevated concentration ( = 12) across a spectrum of topographies. Multiple lines of evidence suggested that the high-concentration groundwater methane could have originated from shallow thermogenic methane that migrated upward into groundwater aquifers with Appalachian Basin brine.
关于非常规油气（UOG）开发在过去 15 年中是否增强了甲烷向地下水含水层的迁移，目前存在相互矛盾的证据。在这项研究中，在 UOG 开发十多年后，从宾夕法尼亚州东北部的 90 口国内水井和 4 处泉水采集了最近的地下水样本，这些水井和泉水都位于马塞勒斯页岩上方。地下水甲烷水平与各种 UOG 地理空间指标之间没有观察到统计学上的显著相关性，包括与 UOG 井和井违规的接近程度，以及特定半径内的 UOG 井和违规数量。δC 和甲烷与更高链烃的特征表明，甲烷水平的升高不是由 UOG 开发引起的，也不能用简单的生物成因-热成因端元混合模型来解释。相反，地下水甲烷水平与地球化学水类型和地形位置显著相关。将一组当代甲烷测量值与它们的共定位钻井前记录进行比较（= 64 个，位于 49 个不同位置），并没有表明甲烷浓度有系统的增加，但确实揭示了在不同地形范围内存在几个浓度升高的情况（= 12）。多种证据表明，高浓度的地下水甲烷可能来自浅层热成因甲烷，这些甲烷向上迁移到与阿巴拉契亚盆地卤水一起存在的地下水含水层中。
