Hundreds of thousands of documented and undocumented orphaned oil and gas wells exist in the United States (U.S.). These wells have the potential to contaminate water supplies, degrade ecosystems, and emit methane and other air pollutants. Thus, orphaned wells present risks to climate stability and to environmental and human health, which can be reduced by plugging. To quantify environmental risks and opportunities of well plugging at the national level, we analyze data on 81 857 documented orphaned wells across the U.S. We find that > 4.6 million people live within 1 km of a documented orphaned well. 35% of the documented orphaned wells are located within 1 km of a domestic groundwater well, yet only 8% of the wells have groundwater quality data within a 1 km radius. Methane emissions from the documented orphaned wells represent approximately 3%–6% of total U.S. methane emissions from abandoned oil and gas wells, but this estimate is based on measurements at < 0.03% of U.S. abandoned wells. 91% of the documented orphaned wells overlie formations favorable for geologic storage of carbon dioxide and hydrogen, meaning that orphaned well plugging can reduce leakage risks from future storage projects. Finally, we estimate plugging costs for documented orphaned wells to exceed the $4.7 billion federal funding by 30%–80%, emphasizing the importance of prioritizing federal spending on wells with large remediation benefits. Overall, environmental monitoring data are not extensive enough to quantify risks, especially those related to air and water quality and human health. Plugging orphaned wells can provide opportunities for geologic storage of carbon dioxide and hydrogen and geothermal energy development, thereby facilitating efforts to transition to net-zero energy systems. Our analysis on environmental risks and opportunities of orphaned wells provides a framework that can be used to manage the millions of documented and undocumented orphaned wells in the U.S. and abroad.

Extensive development of shale gas has generated some concerns about environmental impacts such as the migration of natural gas into water resources. We studied high gas concentrations in waters at a site near Marcellus Shale gas wells to determine the geological explanations and geochemical implications. The local geology may explain why methane has discharged for 7 years into groundwater, a stream, and the atmosphere. Gas may migrate easily near the gas wells in this location where the Marcellus Shale dips significantly, is shallow (∼1 km), and is more fractured. Methane and ethane concentrations in local water wells increased after gas development compared with predrilling concentrations reported in the region. Noble gas and isotopic evidence are consistent with the upward migration of gas from the Marcellus Formation in a free-gas phase. This upflow results in microbially mediated oxidation near the surface. Iron concentrations also increased following the increase of natural gas concentrations in domestic water wells. After several months, both iron and SO₄²⁻ concentrations dropped. These observations are attributed to iron and SO₄²⁻ reduction associated with newly elevated concentrations of methane. These temporal trends, as well as data from other areas with reported leaks, document a way to distinguish newly migrated methane from preexisting sources of gas. This study thus documents both geologically risky areas and geochemical signatures of iron and SO₄²⁻ that could distinguish newly leaked methane from older methane sources in aquifers. Significance Development of shale gas has changed the economics of global energy. However, methane sometimes escapes from shale gas wells into aquifers and the atmosphere. Although many researchers investigate leakage of this greenhouse gas, detection can be difficult where natural sources of methane are present. Here, methane was studied in water near gas wells previously cited for well integrity issues. We identify chemical clues that can distinguish methane migration related to shale gas development from methane that was preexisting. We also document a geological setting—the upper part of a large geological fold at shallow depth—that may be prone to methane migration. Knowledge gained from this study may lessen the chances for fugitive methane emissions into aquifers in the future.

This study places constraints on the source and transport mechanisms of methane found in groundwater within the Barnett Shale footprint in Texas using dissolved noble gases, with particular emphasis on ⁸⁴Kr and ¹³²Xe. Dissolved methane concentrations are positively correlated with crustal ⁴He, ²¹Ne, and ⁴⁰Ar and suggest that noble gases and methane originate from common sedimentary strata, likely the Strawn Group. In contrast to most samples, four water wells with the highest dissolved methane concentrations unequivocally show strong depletion of all atmospheric noble gases (²⁰Ne, ³⁶Ar, ⁸⁴Kr, ¹³²Xe) with respect to air-saturated water (ASW). This is consistent with predicted noble gas concentrations in a water phase in contact with a gas phase with initial ASW composition at 18 °C-25 °C and it suggests an in situ, highly localized gas source. All of these four water wells tap into the Strawn Group and it is likely that small gas accumulations known to be present in the shallow subsurface were reached. Additionally, lack of correlation of ⁸⁴Kr/³⁶Ar and ¹³²Xe/³⁶Ar fractionation levels along with ⁴He/²⁰Ne with distance to the nearest gas production wells does not support the notion that methane present in these groundwaters migrated from nearby production wells either conventional or using hydraulic fracturing techniques.

Extraction of unconventional oil and gas using high-volume hydraulic fracturing (HVHF)—“fracking”—is a “wicked” problem: Science and policymaking are complex and opaque; problems are unstructured, cross areas of policy jurisdiction, require coordinated action among various stakeholders who disagree about values, and tend to result in limited solutions with complex consequences ( 1 ). Public participation in decision-making about hydrocarbon extraction is limited by the largely private nature of transactions among mineral rights owners and industry and the narrow opportunity for public input into procedures. Likewise, obstacles to accessing water-quality data and the dearth and diversity of such data limit shared understanding. We found, however, that, although data alone do not resolve wicked problems, shared interest in gathering, discussing, and improving water-quality data can lead to productive discussions among scientists, citizens with local knowledge, regulators, and industry practitioners. Such opportunities to “pull back the curtain” on science, funded and facilitated by honest brokers, could build trust and develop procedural fairness as foundations for social license.