A novel geochemical approach for environmental risk assessment of stray gas contamination in shallow aquifers within active and prospective shale gas development zones

钻井技术和生产策略的进步，如水平钻井和水力压裂，大大提高了非常规油气藏的天然气和石油产量。虽然这些活动极大地改变了美国的能源格局，最近的研究结果表明，在宾夕法尼亚州东北部的一些活跃的页岩气威尔斯井附近的浅饮用水威尔斯井中存在甲烷污染的可能性。这些发现提出了关于钻井实践潜在安全性的重要问题。然而，其他工作人员强调，天然存在的甲烷发生在黑色页岩矿床上的浅层含水层中。这些相互竞争的解释引发了学术界、工业界和监管科学家关于水力压裂和水平钻井潜在环境影响的辩论。甲烷的稳定碳和氢同位素通常用于确定甲烷的来源。然而，美国和加拿大的一些产碳氢化合物的黑色页岩具有重叠的同位素比率，掩盖了人为污染和地下天然甲烷之间的潜在差异。因此，这一争议突出表明，需要开发独立和互补的地球化学工具，以限制天然气的来源和运输机制在浅水饮用沃茨，特别是那些可能受到杂散气体迁移污染。该项目旨在开发惰性气体地球化学，将其作为一种新的地球化学工具，与传统的化学和同位素测量相结合，用于划定阿巴拉契亚盆地页岩气勘探相关的浅层含水层中碳氢化合物的来源。特别是，该项目将建立更强有力的标准，以区分天然存在的甲烷和与钻井有关的污染。调查人员希望能够区分：1）浅层未受污染的地下水; 2）在地质时期内受天然烃气体沿沿着天然裂缝迁移影响的地下水;以及c）受故障/安装不足的威尔斯井中的烃气体迁移污染的地下水。鉴于水力压裂和天然气钻井在美国的重要性，预计这项研究会引起公众的重大兴趣。该项目的成果将为政策决策提供信息，以便在经济上可持续的页岩气开发和制定适当的保护环境法规之间建立适当的平衡。

Advances in drilling technologies and production strategies, such as horizontal drilling and hydraulic fracturing, have significantly improved the production of natural gas and oil from unconventional hydrocarbon deposits. While these activities have dramatically changed the energy landscape in the U.S., recent research results suggests the potential for methane contamination in shallow drinking water wells near some active shale gas wells in northeastern Pennsylvania. These findings raise important issues about the potential safety of drilling practices. However, other workers highlight that naturally occurring methane occurs within shallow aquifers that overlie black shale deposits. These competing interpretations provoke debate amongst academic, industry, and regulatory scientists regarding the potential environmental impacts of hydraulic fracturing and horizontal drilling. Stable carbon and hydrogen isotopes of methane are commonly used to determine the source of methane. However, some hydrocarbon producing black shales in the US and Canada have overlapping isotopic ratios that mask potential differences between anthropogenic contamination and the natural methane in the subsurface. Consequently, this controversy highlights the need to develop independent and complementary geochemical tools to constrain the source of natural gas and the mechanism of transport in shallow drinking waters, specifically those potentially contaminated by stray gas migration. This project aims to develop noble gas geochemistry as a new geochemical tool, integrated with traditional chemical and isotopic measurements, for delineating the sources of hydrocarbons in shallow aquifers associated with shale gas exploration in the Appalachian Basin. In particular, the project will establish more robust criteria for distinguishing naturally occurring methane from that sourced by drilling-related contamination. Investigators expect to be able to distinguish between: 1) shallow uncontaminated groundwater; 2) groundwater that was affected by natural hydrocarbon gas migration along natural fractures over geological time; and c) groundwater contaminated by hydrocarbon gas migration out of faulty/insufficiently installed wells. Given the importance of hydraulic fracturing and gas drilling in the U.S., significant public interest is expected from this study. Outcomes from this project will inform policy decisions toward establishing the appropriate balance between economically sustainable shale gas development and the development of adequate safeguard environmental regulations.