Conceptual Model of the Geometry and Physics of Water Flow in a Fractured Basalt Vadose Zone: Box Canyon Site, Idaho

“…Box Canyon was chosen for a multidisciplinary study by Lawrence Berkeley National Laboratory, INEEL, and Stanford researchers for hydrologic characterization of the fractured basalt [Faybishenko et al, 1999a[Faybishenko et al, , 1999b. The overall study integrates in situ infiltration tests for unsaturated flow, geophysical investigations, hydrological modeling, and geological characterization of the fracture system.…”

Section: Introductionmentioning

confidence: 99%

A deterministic methodology for prediction of fracture distribution in basaltic multiflows

Lore¹,

Aydin²,

Goodson³

2001

J. Geophys. Res.

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Abstract. The fracture distribution in basalt flows is a direct result of thermal processes. Thus basalt flows present a unique opportunity to characterize a nearly perfect deterministic system with its fundamental physical parameters. Fracture distribution data collected on cliff exposures of basalt flows near the Idaho National Engineering and Environmental Laboratory (INEEL) are combined with calculations of cooling rate and temperature distribution from a finite element model to construct a predictive methodology for fracture spacing. The methodology is based on an empirical power law relationship between inverse cooling rate and fracture spacing. The methodology may be applied to unexposed basalt flows of approximately elliptical cross section whose thickness and width are constrained only by geophysical or borehole data if sufficient fracture data on nearby exposed flows are available. The methodology aids waste remediation efforts at sites involving contaminant transport through fractured basalt, such as the INEEL and the Hanford site in Washington, as well as involving transport and fluid flow through volcanic or intrusive rocks where thermal processes are responsible for fracturing. IntroductionColumnar tensile fractures in basalt flows are driven by thermal elastic strain due to differential cooling of the basalt, as opposed to regional tectonic extension. Given the low matrix permeability of basalt, characterizing the spatial distribution of thermal contraction fractures is the key to understanding the overall permeability structure of multiple basalt flows. The goal of the geological portion of the integrated study, and the subject of this paper, is the development of a methodology to predict fracture distribution in basalt flows when only limited knowledge of the flow geometry is available. Obtaining fracture information on basalt flows not exposed at the surface is challenging, as geophysical methods have resolution falling below that required to image the fractures directly and core fracture measurements sample a very small volume. The We integrate field data on basalt flow geometry and fracture spacing with numerical constraints on the thermal history during fracturing. The result provides a methodology to estimate fracture spacing as a function of cooling rate, controlled by flow thickness and geometry. Although this work is part of a study for hazardous waste containment, aspects are directly applicable to water, oil, or gas reservoirs in thermally fractured volcanic or intrusive rocks.

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“…With this in mind, we examined hydrogeological data collected by Faybishenko et al (1998aFaybishenko et al ( , 1999 for the 96-1 and 97-1 to 97-4 infiltration tests to determine whether fractures that actively conducted water could be observed as they intersected the boreholes shown on Figure 2a. These features were inferred from bromide samples, lysimeter, tensiometer, time domain reflectometry (TDR) probe and electrical resistivity (ER) probe data collected during the 96-1 infiltration test as well as additional ER probe and bromide sample data collected during the 97-1 to 97-4 infiltration tests.…”

Section: Geological Model Conceptualizationmentioning

confidence: 99%

Simulating Infiltration Tests in Fractured Basalt at the Box Canyon Site, Idaho

Unger

Faybishenko

Bodvarsson

et al. 2004

Vadose Zone Journal

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The results of a series of ponded infiltration tests in variably saturated fractured basalt at Box Canyon, Idaho, were used to build confidence in conceptual and numerical modeling approaches used to simulate infiltration in fractured rock. Specifically, we constructed a dual-permeability model using TOUGH2 to represent both the matrix and fracture continua of the upper basalt flow at the Box Canyon site. A consistent set of hydrogeological parameters was obtained by calibrating the model to infiltration front arrival times in the fracture continuum as inferred from bromide samples collected from fracture/borehole intersections observed during the infiltrating tests. These parameters included the permeability of the fracture and matrix continua, the interfacial area between the fracture and matrix continua, and the porosity of the fracture continuum. To calibrate the model, we multiplied the fracture-matrix interfacial area by a factor between 0.1 and 0.01 to reduce imbibition of water from the fracture continuum into the matrix continuum during the infiltration tests. Furthermore, the porosity of the fracture continuum, as calculated using the fracture aperture inferred from pneumatic-test permeabilities, was increased by a factor of 50 yielding porosity values for the upper basalt flow in the range of 0.01 to 0.02.The fracture-continuum porosity was a highly sensitive parameter controlling the arrival times of the simulated infiltration fronts. Porosity values are consistent with those determined during the Large-Scale Aquifer Pumping and Infiltration Test at the Idaho National Engineering and Environmental Laboratory.2

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Conceptual Model of the Geometry and Physics of Water Flow in a Fractured Basalt Vadose Zone: Box Canyon Site, Idaho

Cited by 10 publications

References 28 publications

Viscoelastic thermal stress in cooling basalt flows

Viscoelastic thermal stress in cooling basalt flows

A deterministic methodology for prediction of fracture distribution in basaltic multiflows

Simulating Infiltration Tests in Fractured Basalt at the Box Canyon Site, Idaho

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