Stream Measurements Locate Thermogenic Methane Fluxes in Groundwater Discharge in an Area of Shale-Gas Development

Abstract

The environmental impacts of shale-gas development on water resources, including methane migration to shallow groundwater, have been difficult to assess. Monitoring around gas wells is generally limited to domestic water-supply wells, which often are not situated along predominant groundwater flow paths. A new concept is tested here: combining stream hydrocarbon and noble-gas measurements with reach mass-balance modeling to estimate thermogenic methane concentrations and fluxes in groundwater discharging to streams and to constrain methane sources. In the Marcellus Formation shale-gas play of northern Pennsylvania (U.S.A.), we sampled methane in 15 streams as a reconnaissance tool to locate methane-laden groundwater discharge: concentrations up to 69 μg L(-1) were observed, with four streams ≥ 5 μg L(-1). Geochemical analyses of water from one stream with high methane (Sugar Run, Lycoming County) were consistent with Middle Devonian gases. After sampling was completed, we learned of a state regulator investigation of stray-gas migration from a nearby Marcellus Formation gas well. Modeling indicates a groundwater thermogenic methane flux of about 0.5 kg d(-1) discharging into Sugar Run, possibly from this fugitive gas source. Since flow paths often coalesce into gaining streams, stream methane monitoring provides the first watershed-scale method to assess groundwater contamination from shale-gas development.

Numerical Modeling of Methane Leakage from a Faulty Natural Gas Well into Fractured Tight Formations

“…Typically, once the pressure of a free-phase gas is dissipated, geysering and bubbling subside or even cease, which allows for re-entrainment of water and suppression of further gas release (Gorody 2012). These plumes of dissolved natural gases migrate advectively and can persist in shallow aquifers until they are mitigated by aerobic oxidation, biodegradation, or discharge to the surface (Van Stempvoort et al 2005;Etiope et al 2009;Molofsky et al 2013;Jackson et al 2013aJackson et al , 2013bDarrah et al 2014Darrah et al , 2015aHeilweil et al 2015Heilweil et al , 2016Wen et al 2016). These plumes of dissolved natural gases migrate advectively and can persist in shallow aquifers until they are mitigated by aerobic oxidation, biodegradation, or discharge to the surface (Van Stempvoort et al 2005;Etiope et al 2009;Molofsky et al 2013;Jackson et al 2013aJackson et al , 2013bDarrah et al 2014Darrah et al , 2015aHeilweil et al 2015Heilweil et al , 2016Wen et al 2016).…”

“…Nonetheless, in the absence of chemical or biological degradation, this methane would only be transported to other areas in the subsurface or discharge to the atmosphere through springs or hyporheic interactions (Heilweil et al 2015(Heilweil et al , 2016Kang et al 2016). The complexity arises from the dynamic interplay among buoyancy, capillary, and dispersive forces, as well as chemical and biological reactions, which are together hard to fully capture in numerical simulations.…”

“…Several studies have suggested that problems of natural gas well integrity associated with shale gas production lead to fugitive gas contamination of groundwater in a subset of drinking water wells near drilling sites (Osborn et al 2011;Jackson et al 2013a;Darrah et al 2014;Heilweil et al 2015;Sherwood et al 2016). Several studies have suggested that problems of natural gas well integrity associated with shale gas production lead to fugitive gas contamination of groundwater in a subset of drinking water wells near drilling sites (Osborn et al 2011;Jackson et al 2013a;Darrah et al 2014;Heilweil et al 2015;Sherwood et al 2016).…”

“…Significant progress has been made in collecting data in advance of drilling for shale gas and in developing more robust geochemical and hydrogeological approaches to evaluating the source and the occurrences of methane in shallow aquifers (Darrah et al 2015a(Darrah et al , 2015bHarkness et al 2017;Heilweil et al 2015Heilweil et al , 2016Humez et al 2016;Jackson et al 2013a;Moritz et al, 2015;Nicot et al, 2017aNicot et al, , 2017bSiegel et al 2015;Vengosh et al 2014;Warner et al 2012aWarner et al , 2012bWarner et al , 2014). Yet, there is a need for modeling approaches to constrain the pathways, timing, and mechanisms of hydrocarbon migration to and within shallow aquifers (Schwartz 2013).…”

Biogeochemical constraints on the origin of methane in an alluvial aquifer: evidence for the upward migration of methane from underlying coal measures

“…There is concern regarding the potential impacts of gas and fluid movement, as well as depressurisation, on groundwater quality and quantity in adjacent aquifers used to support other industries (Atkins et al, 2015;Heilweil et al, 2015;Iverach et al, 2015;Moritz et al, 2015;Owen et al, 2016;Zhang and Soeder, 2016).…”