An alternative approach to understanding groundwater flow in sparse channel networks supported by evidence from ‘background’ fractured crystalline rocks

Black, J. H.; Barker, John A.

doi:10.1007/s10040-018-1823-1

Cited by 8 publications

(9 citation statements)

References 26 publications

(48 reference statements)

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“…This is an important consideration in bedrock aquifers because it may be unclear whether to assume that an aquifer behaves as a porous medium and use Darcy's law, or whether to use the cubic law for fracture flow or else a pipe flow equation for flow in channels, using the Hagen‐Poiseuille equation for laminar flow or the Darcy‐Weisbach equation for turbulent flow. Furthermore, the assumption that a single fracture has a constant aperture is a simplification, and all fractures have variability in their apertures, which leads to channeling of flow (Tsang et al 2015; Black and Barker 2018). Positive feedback processes associated with weathering, especially by solution, then preferentially enlarge the channels, enhancing fracture connectivity and increasing groundwater velocities.…”

Section: Methods Of Determining Effective Porositymentioning

confidence: 99%

Estimating Effective Porosity in Bedrock Aquifers

Worthington¹

2022

Groundwater

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Flow in many bedrock aquifers is through fracture networks. Point to point tracer tests using applied tracers provide a direct measure of time of travel and are most useful for determining effective porosity. Calculated values from these tests are typically between 10 −4 and 10 −2 (0.01% to 1%), with these low values indicating preferential flow through fracture and channel networks. Tracer tests are not commonly used in site investigations, and specific yield is often used as a proxy for effective porosity. The most popular methods have used centrifuge measurements, water table fluctuations, pumping tests, and packer tests. Specific yield varies substantially with the testing method. No method is as reliable as tracer testing for providing estimates of effective porosity, but all methods provide complementary insights on aquifer structure. Temporal and spatial scaling effects suggest that bedrock aquifers have hierarchical structures, with a network of more permeable fractures and channels, which are connected to less permeable fractures and to the matrix. Consequences of the low effective porosities include groundwater velocities that often exceed 100 m/d and more frequent microbial contamination than in aquifers in unconsolidated sediments. The large uncertainty over the magnitude of effective porosity in bedrock aquifers makes it an important parameter to determine in studies where time of travel is of interest.

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Section: Methods Of Determining Effective Porositymentioning

confidence: 99%

Estimating Effective Porosity in Bedrock Aquifers

Worthington¹

2022

Groundwater

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“…Many of the early DFN models can be considered channel/pipe‐networks (CN) (Black & Barker, 2018; Cacas et al., 1990; Long et al., 1982; Moreno & Neretnieks, 1993; Tsang et al., 1988). CN models may be viewed as a precursor to modern DFN models in that they represent the fracture network as one‐dimensional pipe‐like elements.…”

Section: Models Of T‐h‐m‐c Coupled Processes In Fractured Rockmentioning

confidence: 99%

From Fluid Flow to Coupled Processes in Fractured Rock: Recent Advances and New Frontiers

Viswanathan

Ajo‐Franklin

Birkhölzer

et al. 2022

Reviews of Geophysics

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Quantitative predictions of natural and induced phenomena in fractured rock is one of the great challenges in the Earth and Energy Sciences with far‐reaching economic and environmental impacts. Fractures occupy a very small volume of a subsurface formation but often dominate fluid flow, solute transport and mechanical deformation behavior. They play a central role in CO2 sequestration, nuclear waste disposal, hydrogen storage, geothermal energy production, nuclear nonproliferation, and hydrocarbon extraction. These applications require predictions of fracture‐dependent quantities of interest such as CO2 leakage rate, hydrocarbon production, radionuclide plume migration, and seismicity; to be useful, these predictions must account for uncertainty inherent in subsurface systems. Here, we review recent advances in fractured rock research covering field‐ and laboratory‐scale experimentation, numerical simulations, and uncertainty quantification. We discuss how these have greatly improved the fundamental understanding of fractures and one's ability to predict flow and transport in fractured systems. Dedicated field sites provide quantitative measurements of fracture flow that can be used to identify dominant coupled processes and to validate models. Laboratory‐scale experiments fill critical knowledge gaps by providing direct observations and measurements of fracture geometry and flow under controlled conditions that cannot be obtained in the field. Physics‐based simulation of flow and transport provide a bridge in understanding between controlled simple laboratory experiments and the massively complex field‐scale fracture systems. Finally, we review the use of machine learning‐based emulators to rapidly investigate different fracture property scenarios and accelerate physics‐based models by orders of magnitude to enable uncertainty quantification and near real‐time analysis.

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“…Many of the early DFN models can be considered channel/pipe-networks (CN) (Black & Barker, 2018;Cacas et al, 1990;Long et al, 1982;Moreno & Neretnieks, 1993;Tsang et al, 1988). CN models may be viewed as a precursor to modern DFN models in that they represent the fracture network as one-dimensional pipe-like elements.…”

Section: Discrete Models (Dfn Dfm and Cn)mentioning

confidence: 99%