Improving estimates of groundwater velocity in a fractured rock borehole using hydraulic and tracer dilution methods

Maldaner, Carlos Henrique; Quinn, Patrick M.; Cherry, John A.; Parker, Beth L.

doi:10.1016/j.jconhyd.2018.05.003

Cited by 25 publications

(25 citation statements)

References 28 publications

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“…In contrast, the combination of an acoustic televiewer and fluid logging with hydraulic conductivity from falling or rising head tests shows much lower values (~ 10 −4 ) of effective porosity in fractured rocks (Quinn et al 2011; Ren et al 2018). Values of effective porosity in the same order of magnitude have been found by Maldaner et al (2018) in a fractured dolostone combining an acoustic televiewer and well dilution tests with falling and rising head and pumping test data. Similar results were obtained for our case study aquifer by Medici et al (2019a) in the fractured dolomitic limestones of the UK Magnesian Limestone aquifer which is the subject of this paper.…”

Section: Introductionsupporting

confidence: 79%

Prediction of contaminant transport in fractured carbonate aquifer types: a case study of the Permian Magnesian Limestone Group (NE England, UK)

Medici

West

Chapman

et al. 2019

Environ Sci Pollut Res

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Viruses and bacteria which are characterized by finite lives in the subsurface are rapidly transported via fractures and cavities in fractured and karst aquifers. Here, we demonstrate how the coupling of a robust outcrop characterization and hydrogeophysical borehole testing is essential for prediction of contaminant velocities and hence wellhead protection areas. To show this, we use the dolostones of the Permian Magnesian Limestone aquifer in NE England, where we incorporated such information in a groundwater flow and particle tracking model. Within this aquifer, flow in relatively narrow (mechanical aperture of~10 −1-1 mm) fractures is coupled with that in pipe cavities (~0.20-m diameter) following normal faults. Karstic cavities and narrow fractures are hydraulically very different. Thus, the solutional features are represented within the model by a pipe network (which accounts for turbulence) embedded within an equivalent porous medium representing Darcian flowing fractures. Incorporation of fault conduits in a groundwater model shows that they strongly influence particle tracking results. Despite this, away from faulted areas, the effective flow porosity of the equivalent porous medium remains a crucial parameter. Here, we recommend as most appropriate a relatively low value of effective porosity (of 2.8 × 10 −4) based on borehole hydrogeophysical testing. This contrasts with earlier studies using particle tracking analyses on analogous carbonate aquifers, which used much higher values of effective porosity, typically~10 2 times higher than our value, resulting in highly non-conservative estimates of aquifer vulnerability. Low values of effective flow porosities yield modelled flow velocities ranging from~100 up to~500 m/day in un-faulted areas. However, the high fracturing density and presence of karstic cavities yield modelled flow velocities up to~9000 m/day in fault zones. The combination of such flow velocities along particle traces results in 400-day particle traces up to 8-km length, implying the need for large well protection areas and high aquifer vulnerability to slowly degrading contaminants.

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Section: Introductionsupporting

confidence: 79%

Prediction of contaminant transport in fractured carbonate aquifer types: a case study of the Permian Magnesian Limestone Group (NE England, UK)

Medici

West

Chapman

et al. 2019

Environ Sci Pollut Res

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“…In rock with low matrix permeability, the flow area would be equal to the fracture aperture multiplied by a transverse fracture width. Cubic law apertures could be estimated from hydraulic tests to estimate the hydraulic transmissivity of the intervals with evidence of active groundwater flow such as packer testing (Maldaner et al, ; Quinn et al, , ) and FLUTe T profiling (Keller et al, ; Quinn et al, ), and an estimation of number of fractures, that is, from acoustic and optical televiewer logs. However, most of the time fracture apertures are unknown and groundwater velocity can therefore not be calculated.…”

Section: Resultsmentioning

confidence: 99%

“…The Q flow values derived from the A‐DTS tests are compared with the values obtained from tracer dilution experiments (Maldaner et al, ), which helps to affirm the validity of the A‐DTS flow rate estimation approach. The tracer dilution experiments in selected intervals consisted of injecting a small volume of a concentrated tracer solution in continuously mixed test intervals, for example, isolated by straddle packers, and monitoring the tracer concentration over time.…”

Section: Methodsmentioning

confidence: 93%

“…Matrix porosity was measured for 24 rock core samples selected from the different lithologies in GDC‐05 providing values ranging from 0.002 to 0.1. Matrix hydraulic conductivity was measured for 20 rock core samples collected from an adjacent borehole at the research facility with values varying from 2 ×10 −7 to 2 ×10 −11 m/s, which are 2–3 orders of magnitude lower than the values obtained from hydraulic tests performed in 1.5‐m straddle packer intervals (Maldaner et al, ; Quinn et al, ). This indicates that groundwater flow occurs primarily through fractures, dissolution enhanced channels developed along horizontal bedding planes and high fossil‐content horizons.…”

Section: Methodsmentioning

confidence: 97%

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Groundwater Flow Quantification in Fractured Rock Boreholes Using Active Distributed Temperature Sensing Under Natural Gradient Conditions

Maldaner

Munn

Coleman³

et al. 2019

Water Resources Research

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Detection and quantification of groundwater flow in fractures is challenging due to its irregular distribution and fine scale, requiring intensive and depth‐discrete field data collection along boreholes. This study presents a new method using fiber optic active distributed temperature sensing (A‐DTS) in sealed boreholes to efficiently quantify depth‐discrete flow rates along the full length of a bedrock borehole. The method combines field data and numerical modeling to quantify groundwater flow rates under natural gradient conditions, which is important for assessing groundwater flow and contaminant transport. An empirical relationship between enhanced heat dissipation and groundwater flow rates is determined using a numerical model of groundwater flow and heat transport for a system of idealized parallel plate fractures in a homogeneous porous rock with negligible flow through the rock matrix. The empirical relationship is applied to a detailed profile of apparent thermal conductivity measured using A‐DTS that combines the effect of rock thermal properties and groundwater flow. In zones with no flow, the A‐DTS‐derived apparent thermal conductivity matches the laboratory effective rock thermal conductivity values measured independently. Local increases of A‐DTS apparent thermal conductivity relative to the rock matrix thermal conductivity can be used to estimate groundwater flow rates using the empirical relationship. The results are in reasonable agreement with straddle pacer tracer dilution tests in the same borehole, which helps to validate the approach. This new approach allows identification of active flow zones and quantification of flow rates and can be efficiently applied in single or multiple boreholes.

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“…Characterizing the flow regime and hydrogeological parameters for these fractured bedrock aquifers poses particular challenges due to their heterogeneous and anisotropic nature across varying scales of observation (Clauser 1992;Bonnet et al 2001;Oxtobee & Novakowski 2002). A variety of characterization and monitoring techniques find their application in fractured bedrock environments, ranging from traditional hydrogeological techniques, such as well hydrograph monitoring and time-series analysis (Molénat et al 1999;Chae et al 2010;Jimenez-Martinez et al 2013), hydraulic well testing (Marechal et al 2004;Neuman 2005), active tracer experiments (Gelhar et al 1992;McKenna et al 2001;Maldaner et al 2018), and hydrochemical/ geochemical and environmental isotope studies (Ofterdinger et al 2004;Ayraud et al 2008), to multiscale geophysical surveying techniques, such as well logging, ground-based and airborne geophysical surveys (Rubin & Hubbard 2005;Vereecken et al 2006;Cassidy et al 2014;Binley et al 2015), and other air-and satellite-borne remote sensing techniques (Becker 2006;Meijerink et al 2007).…”

mentioning

confidence: 99%

Groundwater in fractured bedrock environments: managing catchment and subsurface resources – an introduction

Ofterdinger

MacDonald

Comte

et al. 2019

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Improving estimates of groundwater velocity in a fractured rock borehole using hydraulic and tracer dilution methods

Cited by 25 publications

References 28 publications

Prediction of contaminant transport in fractured carbonate aquifer types: a case study of the Permian Magnesian Limestone Group (NE England, UK)

Prediction of contaminant transport in fractured carbonate aquifer types: a case study of the Permian Magnesian Limestone Group (NE England, UK)

Groundwater Flow Quantification in Fractured Rock Boreholes Using Active Distributed Temperature Sensing Under Natural Gradient Conditions

Groundwater in fractured bedrock environments: managing catchment and subsurface resources – an introduction

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