Reply to comment by Flewelling and Sharma on “Hydraulic fracturing in faulted sedimentary basins: Numerical simulation of potential contamination of shallow aquifers over long time scales”

Lefebvre, René; Gleeson, Tom; McKenzie, Jeffrey M.; Gassiat, Claire

doi:10.1002/2014wr016698

Cited by 5 publications

(6 citation statements)

References 34 publications

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“…[] 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 ., ]. An additional consideration is whether induced hydraulic fractures can connect to natural permeable pathways or compromised wellbores.…”

Section: Factors Controlling Vertical Migration Of Hf Fluidsmentioning

confidence: 99%

“…In response, Gassiat et al . [] pointed out that simulated overpressure exists for long periods of time near the fault in the initialization stage of their simulation [ Lefebvre et al ., ].…”

Section: Summary Of Previous Modeling Studiesmentioning

confidence: 99%

“…This is a hypothetical generic permeable pathway that could represent a wellbore, a fault, a natural fracture, a joint, or some combination thereof. The likelihood of such permeable pathways has been debated (see sections 2.2 and 4) [ Engelder , ; U.S. Environmental Protection Agency , ; Warner et al ., , 2012b; Gassiat et al ., ; Ingraffea et al ., ; Flewelling and Sharma , ; Lefebvre et al ., ]. The inclusion of the permeable pathway in our model allows us to illustrate behavior in an extreme end‐member scenario, which is similar to the conservative assumptions employed in previous modeling studies.…”

Section: An Expanded Model Of Long‐term Hf Fluid Migrationmentioning

confidence: 99%

“…Flewelling and Sharma [2015] additionally pointed out that: (1) a fault which goes through the shale reservoir would likely release any overpressure that builds up in the shale reservoir; (2) fault orientation would become more horizontal at shallow depths, causing it to terminate below the aquifer; and (3) that overpressure in the gas phase within the reservoir may not translate into overpressure in the liquid phase above the reservoir (and thus no driving force would exist outside of the reservoir). In response, Gassiat et al [2013] pointed out that simulated overpressure exists for long periods of time near the fault in the initialization stage of their simulation [Lefebvre et al, 2015]. Reagan et al [2015] presented a full two-phase (gas and brine) model that focuses on short-term, $2 year, gas migration.…”

Section: 1002/2015wr017810mentioning

confidence: 99%

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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%

Section: Summary Of Previous Modeling Studiesmentioning

confidence: 99%

Section: An Expanded Model Of Long‐term Hf Fluid Migrationmentioning

confidence: 99%

Section: 1002/2015wr017810mentioning

confidence: 99%

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

et al. 2015

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“…Besides the simplification used for the simulations, Flewelling and Sharma identified other aspects of the study that they consider nonrepresentative or unlikely. The reply by Lefebvre et al stresses that Gassiat et al aimed to identify conditions needed for upward fluid migration, not their probability. Many authors consider that maintaining overpressured conditions after the production of a shale gas reservoir is extremely unlikely …”

Section: Fluid Migration Through Preferential Pathsmentioning

confidence: 99%

Mechanisms leading to potential impacts of shale gas development on groundwater quality

Lefebvre

2016

WIREs Water

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The development of shale gas resources was made possible by the combination of horizontal drilling and high‐volume hydraulic fracturing (fracking). Environmental concerns have been raised relative to shale gas production, especially potential impacts on groundwater. Fluids related to unconventional oil and gas (O&G) operations contain chemical compounds that can impact groundwater quality. Such impacts can occur due to (1) the infiltration of surface contaminant releases, (2) failures of the integrity of O&G wells, and (3) upward fluid migration from a shale/tight reservoir along preferential paths that can be natural (faults or fracture zone) or man‐made (O&G wells). Surface releases represent the most probable mechanism leading to groundwater contamination. Improvements in O&G drilling operations under stringent regulations can minimize this risk. Experts identify O&G well integrity as the most challenging issue that may lead to groundwater contamination. Failure of casing and cement can lead to upward fluid flow within or outside O&G wells, especially of methane. Integrity failures leading to fluid migration to shallow fresh water aquifers or to the surface are well understood and can be detected and repaired, but this can be complex and costly. A few regulators now impose groundwater monitoring to detect impacts from integrity failures. Occurrences of communication with existing O&G wells from fracking operations have also led some regulators to impose rules aiming to avoid such potential fluid migration paths. There is an ongoing scientific debate regarding the potential for fluids to migrate upward from exploited shale gas units to aquifers through natural preferential paths. WIREs Water 2017, 4:e1188. doi: 10.1002/wat2.1188 This article is categorized under: Engineering Water > Sustainable Engineering of Water Science of Water > Water Quality

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Understanding shallow and deep flow for assessing the risk of hydrocarbon development to groundwater quality

Raynauld

Peel

Lefebvre

et al. 2016

Marine and Petroleum Geology

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Reply to comment by Flewelling and Sharma on “Hydraulic fracturing in faulted sedimentary basins: Numerical simulation of potential contamination of shallow aquifers over long time scales”

Cited by 5 publications

References 34 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

Mechanisms leading to potential impacts of shale gas development on groundwater quality

Understanding shallow and deep flow for assessing the risk of hydrocarbon development to groundwater quality

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