Reply to Engelder: Potential for fluid migration from the Marcellus Formation remains possible

Warner, Nathaniel R.; Jackson, Robert B.; Darrah, Thomas H.; Osborn, Stephen G.; Down, Adrian; Zhao, Kaiguang; White, Alissa; Vengosh, Avner

doi:10.1073/pnas.1217974110

Cited by 20 publications

(24 citation statements)

References 5 publications

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“…Warner et al . [] replied providing various lines of potential evidence for the existence of hydraulic connections, and Llewellyn [] describes the mechanisms by which brines could migrate to shallow aquifers in the Appalachian basin. This debate about the existence and frequency of permeable pathways continues today [e.g., U.S. Environmental Protection Agency , ; Lange et al ., ; Gassiat et al ., ; Ingraffea et al ., ; Flewelling and Sharma , ; Lefebvre et al ., ].…”

Section: Factors Controlling Vertical Migration Of Hf Fluidsmentioning

confidence: 99%

Hydraulic fracturing fluid migration in the subsurface: A review and expanded modeling results

et al. 2015

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Understanding the transport of hydraulic fracturing (HF) fluid that is injected into the deep subsurface for shale gas extraction is important to ensure that shallow drinking water aquifers are not contaminated. Topographically driven flow, overpressured shale reservoirs, permeable pathways such as faults or leaky wellbores, the increased formation pressure due to HF fluid injection, and the density contrast of the HF fluid to the surrounding brine can encourage upward HF fluid migration. In contrast, the very low shale permeability and capillary imbibition of water into partially saturated shale may sequester much of the HF fluid, and well production will remove HF fluid from the subsurface. We review the literature on important aspects of HF fluid migration. Single-phase flow and transport simulations are performed to quantify how much HF fluid is removed via the wellbore with flowback and produced water, how much reaches overlying aquifers, and how much is permanently sequestered by capillary imbibition, which is treated as a sink term based on a semianalytical, one-dimensional solution for two-phase flow. These simulations include all of the important aspects of HF fluid migration identified in the literature review and are performed in five stages to faithfully represent the typical operation of a hydraulically fractured well. No fracturing fluid reaches the aquifer without a permeable pathway. In the presence of a permeable pathway, 10 times more fracturing fluid reaches the aquifer if well production and capillary imbibition are not included in the model.

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Section: Factors Controlling Vertical Migration Of Hf Fluidsmentioning

confidence: 99%

Hydraulic fracturing fluid migration in the subsurface: A review and expanded modeling results

et al. 2015

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“…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).…”

Section: Introductionmentioning

confidence: 99%

“…Such advances are essential in order to distinguish between natural and anthropogenic sources of hydrocarbons in shallow aquifers and for source attribution in instances where contamination of groundwater by anthropogenic gas has occurred. The shallow bedrock aquifers overlying the Marcellus and Barnett formations are good examples of these fine-grained clastic rocks, characterized by an inherently low matrix permeability (Warner et al 2012a(Warner et al , 2012bDarrah et al 2015a;Nicot et al 2017b). For example, aquifers rarely can be characterized as homogenous porous media (Gorody 2012;Darrah et al 2015a;Nicot et al 2017aNicot et al , 2017b.…”

Section: Introductionmentioning

confidence: 99%

“…Modeling gas transport in shallow aquifers overlying unconventional hydrocarbon reservoirs is complicated by complexities in the physical setting. Yet, localized lithological heterogeneity or secondary porosity provided by open tectonic and neotectonic fractures, joints, and faults can enhance the hydraulic conductivity and serve as the dominant pathways for groundwater flow (Engelder et al 2009;Warner et al 2012aWarner et al , 2012bNicot et al 2013;Darrah et al 2015a). Instead, they are fractured and porous rock units that have been deformed through multiple tectonic and glacial cycles.…”

Section: Introductionmentioning

confidence: 99%

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

Moortgat¹,

Schwartz

Darrah

2018

Groundwater

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Horizontal drilling and hydraulic fracturing have enabled hydrocarbon recovery from unconventional reservoirs, but led to natural gas contamination of shallow groundwaters. We describe and apply numerical models of gas-phase migration associated with leaking natural gas wells. Three leakage scenarios are simulated: (1) high-pressure natural gas pulse released into a fractured aquifer; (2) continuous slow leakage into a tilted fractured formation; and (3) continuous slow leakage into an unfractured aquifer with fluvial channels, to facilitate a generalized evaluation of natural gas transport from faulty natural gas wells. High-pressure pulses of gas leakage into sparsely fractured media are needed to produce the extensive and rapid lateral spreading of free gas previously observed in field studies. Transport in fractures explains how methane can travel vastly different distances and directions laterally away from a leaking well, which leads to variable levels of methane contamination in nearby groundwater wells. Lower rates of methane leakage (≤1 Mcf/day) produce shorter length scales of gas transport than determined by the high-pressure scenario or field studies, unless aquifers have low vertical permeabilities (≤1 millidarcy) and fractures and bedding planes have sufficient tilt (∼10°) to allow a lateral buoyancy component. Similarly, in fractured rock aquifers or where permeability is controlled by channelized fluvial deposits, lateral flow is not sufficiently developed to explain fast-developing gas contamination (0-3 months) or large length scales (∼1 km) documented in field studies. Thus, current efforts to evaluate the frequency, mechanism, and impacts of natural gas leakage from faulty natural gas wells likely underestimate contributions from small-volume, low-pressure leakage events.

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“…Others also linked water contamination to shale gas extraction. [18][19][20][21] Several studies have considered the GHG emissions from shale gas used for electricity generation in the USA. One of the most cited, but also most controversial, studies found electricity generation from shale gas to have a higher global warming potential (GWP) than coal, ranging from 834-2225 g CO 2 Eq.…”

Section: Introductionmentioning

confidence: 99%

Environmental Impacts of Shale Gas in the UK: Current Situation and Future Scenarios

2014

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This paper presents life cycle environmental impacts of UK shale gas used for electricity generation, in comparison with other fossil, nuclear and renewable options. Per kWh of electricity generated, shale gas has higher environmental impacts than the other options, except for coal. Thus, if it were to replace coal, most impacts would be reduced, including the global warming potential (GWP; by 2.3 times). However, if it were to compete with nuclear or some renewables most impacts would rise, with the GWP increasing by 5–123 times. Within a future UK electricity mix up to 2030, shale gas would make little difference to the environmental impacts of electricity generation, including the GWP, even for the most optimistic assumptions for its domestic production. This suggests that, in the medium term, shale gas cannot help towards meeting UK climate change targets and that certain renewables and nuclear power should be prioritized instead.

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Reply to Engelder: Potential for fluid migration from the Marcellus Formation remains possible

Cited by 20 publications

References 5 publications

Hydraulic fracturing fluid migration in the subsurface: A review and expanded modeling results

Hydraulic fracturing fluid migration in the subsurface: A review and expanded modeling results

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

Environmental Impacts of Shale Gas in the UK: Current Situation and Future Scenarios

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