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  • 1
    Electronic Resource
    Electronic Resource
    Seismic wave attenuation in fluid-saturated porous media (1988)
    Springer
    Pure and applied geophysics 128 (1988), S. 423-432 
    Details
    ISSN: 1420-9136
    Keywords: Seismic attenuation ; porous media ; permeability ; local flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Contrary to the traditional view, seismic attenuation in Biot's theory of fluid-saturated porous media is due to viscous damping of local (not global) pore-fluid motion. Since substantial inhomogeneities in fluid permeability of porous geological materials are to be expected, the regions of highest local permeability contribute most to the wave energy dissipation while those of lowest permeability dominate the fluid flow rate if they are uniformly distributed. This dichotomy can explain some of the observed discrepancies between computed and measured attenuation of compressional and shear waves in porous earth. One unfortunate consequence of this result is the fact that measured seismic wave attenuation in fluid-filled geological materials cannot be used directly as a diagnostic of the global fluid-flow permeability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01772607
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  • 2
    Electronic Resource
    Electronic Resource
    Physical processes in an Indian Ocean atoll (1998)
    Springer
    Coral reefs 17 (1998), S. 155-168 
    Details
    ISSN: 1432-0975
    Keywords: Key words Atoll hydrodynamics ; Lagoon ciculation ; Wave transformation ; Currents ; Physical processes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract  Detailed measurements of water levels, and tide and wave-induced currents were undertaken to examine physical processes and their relationship with morphology in the Cocos (Keeling) Islands, a medium sized atoll in the Indian Ocean. Results indicate that the atoll structure controls both lagoon circulation and the spatial pattern of energy distribution. Lagoon circulation is tide dominated (currents 16–31 cms-1) with flushing (2–5 days) of the lagoon occurring through the deep leeward passages. Wave- and tide-driven unidirectional flows through shallow passages (26–65 cms-1) are important mechanisms of ocean to lagoon water exchange and contribute up to 24% of the lagoon neap tide prism. Reef flats are dominated by wave energy (maximum velocity 140 cms-1, east) with measurements of the attenuation of wave energy between reef flats and shallow lagoon (80–90%) conforming to measurements from fringing and barrier reefs. Spectral analysis shows that the characteristics of wave energy vary on different sectors of the atoll, with gravity wave energy dominating the east, and infragravity wave energy dominating the southern reef flat and passages. Wave setup at the reef crest is considered to be responsible for an identified 0.1 m higher water level in the southern as opposed to eastern and northern atoll, which promotes higher reef flat growth. Transmission of gravity waves across reef flats requires threshold water depths of 0.65 (east) and 0.70 m (south). The higher southern reef is an effective filter of gravity wave energy for most tidal elevations. Differences in the type and magnitude of physical processes within the atoll are discussed with relation to geomorphic development on Cocos.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003380050110
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  • 3
    Electronic Resource
    Electronic Resource
    Renormalization group analysis of permeability upscaling (1999)
    Springer
    Stochastic environmental research and risk assessment 13 (1999), S. 131-161 
    Details
    ISSN: 1436-3259
    Keywords: Key words: Renormalization ; random fields ; effective ; permeability ; preasymptotic.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The heterogeneity of the subsurface permeability is considered as the most influential factor in determining groundwater flow and the transport of toxic contaminants. Numerical simulators cannot handle the large grids required to represent the small-scale variability of permeability, and thus explicit estimates of the large-scale behavior in terms of coarse-grained parameters are often required. Perturbation formulations of the effective permeability are based on simplifying assumptions that are valid only for certain probability distributions and weak heterogeneity. A generalized perturbation ansatz that involves higher orders has been proposed (Gelhar and Axness, 1983), but to our knowledge its validity has not been rigorously proved before in three dimensions. In this work we propose a general upscaling formulation valid for strong heterogeneity, general permeability distributions, and media with impermeable zones. We show that the effective permeability is determined by the self-energy series of the permeability fluctuations at zero frequency. Using the diagrammatic representation, we obtain a Dyson equation that involves only irreducible diagrams of the proper self-energy series. We develop a renormalization group (RG) analysis for isotropic lognormal media that proves the generalized perturbation ansatz to all orders. We show that the RG result accurately estimates laboratory permeability measurements in limestone (strong heterogeneity) and sandstone (weak heterogeneity). We also propose an explicit RG estimate for the preasymptotic effective permeability. We compare our results with an approach based on a leading order Green's function expansion (Paleologos et al., 1996), which, however, requires intensive numerical computations. Finally, we investigate the relation between the RG expression and the algebraic means used in numerical upscaling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004770050036
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  • 4
    Electronic Resource
    Electronic Resource
    The effect of pressure on the electrical conductivity of KTB rocks (1995)
    Springer
    Surveys in geophysics 16 (1995), S. 63-81 
    Details
    ISSN: 1573-0956
    Keywords: Complex electrical resistivity ; ktb ; permeability ; pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Complex electrical resistivity and permeability were measured on two gneiss samples and nine amphibolites (originally located at a depth of 4150 m to 5012 m) from the main drilling of the German deep drilling project (KTB). Measurements were performed as a function of hydrostatic pressures up to 240 MPa on core samples (30 mm in diameter and 10–20 mm high). For each measurement, two samples were used, one being parallel, and one perpendicular to the borehole axis. At low pressures and again at maximum pressure the frequency dispersion (1 kHz up to 1 MHz) of the complex resistivity was measured using a two electrode device. An unusual pressure effect was detected on some of the samples and was established to be due to the oriented deposition of good conducting phases in the foliation. Rock fabric and the orientation of ore mineralization was measured on thin sections and polished sections prepared from the same samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00682713
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  • 5
    Electronic Resource
    Electronic Resource
    Scales of rock permeability (1996)
    Springer
    Surveys in geophysics 17 (1996), S. 245-263 
    Details
    ISSN: 1573-0956
    Keywords: Rocks ; crust ; permeability ; scale
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Permeability is a transport property which is currently measured in Darcy units. Although this unit is very convenient for most purposes, its use prevents from recognizing that permeability has units of length squared. Physically, the square root of permeability can thus be seen as a characteristic length or a characteristic pore size. At the laboratory scale, the identification of this characteristic length is a good example of how experimental measurements and theoretical modelling can be integrated. Three distinct identifications are of current use, relying on three different techniques: image analysis of thin sections, mercury porosimetry and nitrogen adsorption. In each case, one or several theoretical models allow us to derive permeability from the experimental data (equivalent channel models, statistical models, effective media models, percolation and network models). Permeability varies with pressure and temperature and this is a decisive point for any extrapolation to crustal conditions. As far as pressure is concerned, most of the effect is due to cracks and a model which does not incorporate this fact will miss its goal. Temperature induced modifications can be the result of several processes: thermal cracking (due to thermal expansion mismatch and anisotropy, or to fluid pressure build up), and pressure solution are the two main ones. Experimental data on pressure and temperature effects are difficult to obtain but they are urgently needed. Finally, an important issue is: up to which point are these small scale data and models relevant when considering formations at the oil reservoir scale, or at the crust scale? At larger scales the identification of the characteristic scale is also a major goal which is examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01904043
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  • 6
    Electronic Resource
    Electronic Resource
    The dependence of transport properties ofin situ rocks on pore fluid composition and temperature (1996)
    Springer
    Surveys in geophysics 17 (1996), S. 289-306 
    Details
    ISSN: 1573-0956
    Keywords: Effective properties ; pore fluids ; cracked rock ; permeability ; stress ; temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Fluids saturating cracked rocks within the crust can vary widely in composition and physical properties, which depend greatly on pressure and temperature. External non-hydrostatic stress applied to a cracked medium may result in a significant change of crack volume (and hence, for the undrained regime, pore-fluid pressure) due to the processes of crack closure (opening), and thus lead to a drastic change of the overall physical parameters of a rock. The purpose of the study is to estimate theoretically, using the effective-medium theory, the macroscopic seismic and transport parameters (such as permeability) of cracked rocks (granites) saturated with hydrocarbon gases, oils, brines and water. Variations of crack geometry and fluid parameters in the closed system (at constant fluid mass) under uniaxial compression are considered as well. The results show that composition of a saturating fluid as well as fluid temperature greatly influence the effective permeability and shear velocities of a rock mass, while thermal conductivity is not so sensitive to variations of fluid parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01904045
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  • 7
    Electronic Resource
    Electronic Resource
    Fractures: Finite-size scaling and multifractals (1992)
    Springer
    Pure and applied geophysics 138 (1992), S. 679-706 
    Details
    ISSN: 1420-9136
    Keywords: Fractures ; fractals ; multifractals ; scaling ; percolation ; geohydrology ; rock mechanics ; permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The distributions of contact area and void space in single fractures in granite rock have been determined experimentally by making metal casts of the void spaces between the fracture surfaces under normal loads. The resulting metal casts on 52 cm diameter core samples show a complex geometry for the flow paths through the fracture. This geometry is analyzed using finite-size scaling. The spanning probabilities and percolation probabilities of the metal casts are calculted as functions of observation scale. Under the highest stresses of 33 MPa and 85 MPa there is a significant size-dependence of the geometric flow properties for observation scales smaller than 2 mm. Based on this data, the macroscopic percolation properties of the extended fracture can be well represented by relatively small core samples, even under normal stresses larger than 33 MPa. The metal casts also have rich multifractal structure that changes with changing stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876344
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  • 8
    Electronic Resource
    Electronic Resource
    Radon anomalies on three kinds of faults in California (1993)
    Springer
    Pure and applied geophysics 141 (1993), S. 111-124 
    Details
    ISSN: 1420-9136
    Keywords: Radon emanation ; soil air ; active faults ; fault creep ; fault gouge ; fractures ; permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Radon emanation is known to be anomalously high along active faults in many parts of the world. We tested this relationship in California during July and early August 1992, using a portable radonmeter to conduct soil-air radon surveys at 5 sites across three kinds of faults: Creeping, locked, and freshly broken. Along a 350-m long survey line across a creeping segment of the San Andreas fault at Nyland Ranch in San Juan Bautista, we found anomalous radon concentrations not in the creep zone itself as determined by a creepmeter, but on the adjacent sides, 10 and 30 meters from the center line of the fault. The anomalous values were 5 times higher than the background values measured farther away from the fault. A similar radon anomaly was observed along a 420-m long survey line across a creeping segment of the Calaveras fault near 7th Street in Hollister. There, the anomalous values were about 6 to 11 times the background values and about 40 and 50 m from the center line of the fault. The double-peaked featire of the anomalies may be indicative of a relatively low gas permeability of the fault-gouge materials in the creeping zones and high permeability of fractured rocks in the adjacent shear zones. Along a 144-m survey line across the currently locked segment of the San Andreas fault at the Earthquake Trail near Olema, the radon concentration was indeed anomalously high in the fault zone, by a factor of two above background values. However, the maximum values (3 to 6 times background) again were recorded about 10 meters from the center line. Three weeks after the magnitude 7.5 Landers earthquake of 28 June 1992, we conducted a survey along a 300-m line across the earthquake fault alongside Encantado Road in the epicenter area. The radon values measured at the two main fault breaks were an order of magnitude higher than the background values. A similar result was found along a 420-m line alongside Reche Road about 1.7 km south of Encantado Road.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876238
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  • 9
    Electronic Resource
    Electronic Resource
    Experimental simulation of plagioclase diagenesis atP-T conditions of 3.5 km burial depth (1993)
    Springer
    Pure and applied geophysics 141 (1993), S. 221-247 
    Details
    ISSN: 1420-9136
    Keywords: Experimental ; plagioclase ; diagenesis ; porosity ; permeability ; dissolution ; precipitates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Dissolution of plagioclase under the physical conditions at shallow to intermediate burial depths is a prime candidate for secondary porosity generation in feldspathic siliciclastic sediments. The diagenetic behavior of granular aggregates of plagioclase feldspar and quartz has been investigated by experimentation performed in a Bridgeman-type pressure vessel. The experiments, each of two weeks duration, simulated pressure-temperature conditions approximating 3.5 km burial depth. By using a double-acting pore-fluid reservoir, solutions of various chemistries were cycled through samples composed of oligoclase or labradorite feldspar and quartz (90:10 wt% respectively). Scanning electron microscope analysis of the post-experiment samples reveals dissolution features and precipitated products. Dissolution voids of ∼10 microns occur typically in areas of maximum stress such as crack-tips and grain contacts. Dissolution on a larger scale is exemplified by topographical smoothing of grain su faces. The dissolved species are subsequently reprecipitated as Ca-enriched overgrowths (possibly zeolites) and clays. These precipitates are found individually on the scale of 10 microns and collectively as surface coatings on both feldspar and quartz grains. Atomic absorption spectroscopic analyses of the pore fluid suggest that the fluid chemistry is consistent with the observed experimental precipitates. These experiments show that clay coatings are unnecessary precursors to grain surface dissolution and that the diagenetic precipitation is not mineral selective. Also, the mass transfer of the dissolved species appears to be localized because grains displaying both dissolution and precipitation features are commonplace. Volume changes due to mineral transformation/alteration may increase secondary porosity if the dissolved species produced from dissolution are only partially involved in reprecipitation and the remaining dissolved material is flushed out by the pore fluids. However, if the mass transfer is primarily local then permeability would significantly decrease as precipitates may choke the pore throats.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00998330
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  • 10
    Electronic Resource
    Electronic Resource
    Petrophysical study of faults in sandstone using petrographic image analysis and X-ray computerized tomography (1994)
    Springer
    Pure and applied geophysics 143 (1994), S. 181-201 
    Details
    ISSN: 1420-9136
    Keywords: Cataclasis ; fluid flow ; fault ; video image analysis ; X-ray computerized tomography ; porosity ; permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Petrographic image analysis (PIA) and X-ray computerized tomography (CT) provide local determinations of porosity in sandstone. We have investigated small faults called deformation bands in porous sandstones using these techniques. Because the petrophysical properties of the fault rock vary at a small scale (mm scale), the ability of PIA and CT to determine porosity in small volumes of rock and to map porosity distribution in two and three dimensions is crucial. This information is used to recognize the processes involved in fault development and the different kinds of microstructures associated with dilatancy and compaction. The petrophysical study of fault rock in sandstone permits one to make predictions of the hydraulic properties of a fault and thereby evaluate the sealing or fluid transmitting characteristics of faulted reservoirs and aquifers. The results of this study indicate that faulting in sandstone alters the original porosity and permeability of the host rock: the porosity is reduced by an order of magnitude and the permeability is reduced by one to more than seven orders of magnitude for faults associated with compaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00874328
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  • 11
    Electronic Resource
    Electronic Resource
    The reflection of water waves by shear currents (1977)
    Springer
    Pure and applied geophysics 115 (1977), S. 937-949 
    Details
    ISSN: 1420-9136
    Keywords: Waves ; Currents ; Reflection ; Caustics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The refraction and reflection of linear water waves entering a following jet-type current is considered. A short-wave asymptotic solution is presented and the reflection coefficient found. This varies continuously from zero when the waves are normal to the current to unity when they are very oblique to it. The trapping of waves by an opposing current is also considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00881217
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  • 12
    Electronic Resource
    Electronic Resource
    Comparison of the effective pressure law for permeability and resistivity formation factor in Chelmsford granite (1988)
    Springer
    Pure and applied geophysics 127 (1988), S. 607-625 
    Details
    ISSN: 1420-9136
    Keywords: Physical properties of rocks ; permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Permeability, resistivity formation factor, and pore volume change were simultaneously measured on samples of Chelmsford granite subjected to confining pressure and pore pressure cycles. Using a technique described in a previous paper, the tangent coefficients of the effective pressure law for permeability α k and for formation factor α F were determined. α k and α F did not differ significantly from one another. They showed a strong stress history dependence as has already been observed for α k in several crystalline rocks. According to the definition of the effective pressure law used here, two physical properties with identical α's must be related through a one-to-one functional relationship. Hence, the observation above suggests that such a relationship may be empirically found between permeability and formation factor. Indeed, analysis of the data revealed that, to a good approximation, permeability was inversely proportional to the formation factor. The same relation has previously been observed in other crystalline rocks. This relationship was included in a recent version of the so-called equivalent channel model. Using this model, the specific surface area of the cracksA c/VS, the standard deviation of the distribution of asperities heightsh and the hydraulic radiusm o were evaluated. The following values were respectively found: 850 cm−1, 0.008 μm and 0.14 μm. The specific surface area of the cracks was independently estimated on micrographs of polished sections using a standard quantitative stereology method. The result was in good agreement with the values estimated from the transport properties data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00881747
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  • 13
    Electronic Resource
    Electronic Resource
    A Simple Model for the Variation of Permeability due to Partial Saturation in Dual Scale Porous Media (1997)
    Springer
    Transport in porous media 27 (1997), S. 243-264 
    Details
    ISSN: 1573-1634
    Keywords: permeability ; Darcy's law ; unsaturated flow ; dual scale ; resin transfer molding ; liquid injection molding.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The main focus of this work is to model macroscopically the effects of partial saturation upon the permeability of dual scale fibrous media made of fiber bundles when a Newtonian viscous fluid impregnates it. A new phenomenological model is proposed to explain the discrepancies between experimental pressure results and analytical predictions based on Darcy's law. This model incorporates the essential features of relative permeability but without the necessity of measuring saturation of the liquid for its prediction. The model is very relevant for the small scale industrial systems where a liquid is forced to flow through a fibrous porous medium. It requires four parameters. Two of them are the two permeability values based on the two length scales. One length scale is of the order of magnitude of the individual fiber radius and corresponds to the permeability of the completely staurated medium, the other is of the order of magnitude of the distance between the fiber bundles and corresponds to the permeability of the partially saturated medium. The other two parameters are the lengths of the two partially saturated regions of the flow domain. The two lengths of the partially saturated region and the permeability of the fully saturated flow domain can be directly measured from the experiments. The excellent agreement between the model and the experimental results of inlet pressure profile with respect to time suggests that this model may be used to describe the variation of the permeability behind a moving front in such porous media for correct pressure prediction. It may also be used to characterize the fibrous medium by determining the two different permeabilities and the relative importance of the unsaturated portion of the flow domain for a given architecture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006544107324
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  • 14
    Electronic Resource
    Electronic Resource
    The thermogravitational effect in porous media: A modelling approach (1992)
    Springer
    Transport in porous media 9 (1992), S. 223-240 
    Details
    ISSN: 1573-1634
    Keywords: Thermodiffusion ; Soret effect ; thermogravitational effect ; irreversible thermodynamics ; porous medium ; permeability ; transport model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The thermogravitational effect may induce large concentration contrasts, particularly in porous media. This phenomenon arises from a coupling of the Soret effect and convection currents in a temperature field. The present study of this phenomenon is motivated by the safety assessment of nuclear waste repositories, which are sources of thermal energy. Here, we present a modelling approach of laboratory experiments carried out at the University of Toulouse. The results of this model, though more adequate than the analytical solution to account for the influence of permeability, remain far from the experimental ones. In conclusion, it appears that the research must now focus on both a comprehensive phenomenology of the transport processes and experiments with new dimensional constraints.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00611968
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  • 15
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    Mean field calculation of effective permeability based on fractal pore space (1992)
    Springer
    Transport in porous media 8 (1992), S. 93-97 
    Details
    ISSN: 1573-1634
    Keywords: Porous rock ; permeability ; porosity ; fractal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Effective permeability for porous rocks is calculated using mean field theory. We make two simplifying assumptions about the internal conductances in a network representation of the porous rock: (i) Pore space is characterized by a uniform fractal scaling; (ii) the internal conductances depend only on the characteristic pore sizes. Within these approximations, it is possible to derive a simple probability density for the internal conductances which is used for calculating effective permeability. Good agreement between calculations and experimental data of permeability vs. porosity is achieved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00616894
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  • 16
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    Implication of fractal geometry for fluid flow properties of sedimentary rocks (1992)
    Springer
    Transport in porous media 8 (1992), S. 133-147 
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    ISSN: 1573-1634
    Keywords: Fractal ; multifractal ; sedimentary rocks ; permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract It is demonstrated that a certain amount of order can be extracted from an apparently random distribution of pores in sedimentary rocks by exploiting the scaling characteristics of the geometry of the porespace with the help of fractal statistics. A simple fractal model of a sedimentary rock is built, and is tested against both the Archie law for conductivity and the Carman-Kozeny equation for permeability. We demonstrate how multifractal scaling of pore-volume can be used as a tool for rock characterization by computing its experimentalf(α) spectrum, which can be modelled by a simple two-scale Cantor set.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00617114
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  • 17
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    Transport properties of rocks from statistics and percolation (1989)
    Springer
    Mathematical geology 21 (1989), S. 1-13 
    Details
    ISSN: 1573-8868
    Keywords: permeability ; electrical conductivity ; porosity ; microstructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Two simplified microstructural models that account for permeability and conductivity of low-porosity rocks are compared. Both models result from statistics and percolation theory. The first model assumes that transport results from the connection of 1D objects or “pipes”; the second model assumes that transport results from the connection of 2D objects or “cracks.” In both cases, statistical methods permit calculation of permeability k and conductivity σ, which are dependent on three independent microvariables: average pipe (crack) length, average pipe radius (crack aperture), and average pipe (crack) spacing. The degree of connection is one aspect of percolation theory. Results show that use of the mathematical concept of percolation and use of the rock physics concept of tortuosity are equivalent. Percolation is used to discuss k and σ near the threshold where these parameters vanish. Relations between bulk parameters (permeability, conductivity, porosity) are calculated and discussed in terms of microvariables.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00897237
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  • 18
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    A model of regional fluid flow: Sand concentration factors and effective lateral and vertical permeabilities (1985)
    Springer
    Mathematical geology 17 (1985), S. 297-315 
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    ISSN: 1573-8868
    Keywords: permeability ; sand ratio ; concentrations factors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Permeabilities of sand and shale differ by five to seven orders of magnitude. In the depositional pattern characteristic of the Gulf Coast, lenticular sand bodies occur randomly dispersed within a shale matrix, even though they can be grouped into stratigraphic sequences, contributing to net permeability of the sand-shale system and thus facilitating upward flow of pore water. In addition, a substantial lateral flow develops as fluid flow is directed toward sand bodies, thus concentrating fluid from a wide source area into sand bodies of limited lateral and vertical extent. Calculations reported here determine the effect of randomly distributed sands on both vertical and lateral permeabilities of composite sandshale systems. Effective permeabilities depend only on mean sand percent and local variance about the mean, because the effects of sand body shapes and their orientation and dip are not incorporated in the analysis. Results indicate that at a mean sand percentage of 20–50% a large lateral migration of fluid flow develops as sand bodies attract flow from a region two to seven times the radius of the sand body itself. For a mean sand percentage in excess of 50–60%, large vertical migration results and thus hydrocarbon trapping should not be expected for sand percentages in excess of 50–60%. Results of these calculations are in accord with observations that most larger oil accumulations on the Gulf Coast are found in regions having sandiness between about 20 and 50%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01034755
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  • 19
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    Effective-medium treatment of flow through anisotropic fracture system — Improved permeability estimates using a new lattice mapping (1992)
    Springer
    Transport in porous media 9 (1992), S. 287-295 
    Details
    ISSN: 1573-1634
    Keywords: Anisotropic fracture system ; effective medium theory ; permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The permeability tensor of a fractured reservoir, which will typically be anisotropic because of the presence of stress, is an important parameter to be taken into account when formulating a production strategy for the reservoir. Extensive computational effort is involved in calculating the permeabilities of model fracture systems by solving the fluid flow equations through finite realisations of the systems, and this renders a search for alternative techniques worthwhile. An attractive approach is to perform a rough mapping of the fracture system onto a lattice so that effective medium theory can be applied. For isotropic systems that are well-connected, this technique works well, but it gives increasingly poor results as the degree of anisotropy increases. In this contribution, a refinement of the lattice mapping is presented that incorporates an important aspect of the randomness present in the original system. This greatly increases the applicability of the technique.
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    URL: http://dx.doi.org/10.1007/BF00611972
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  • 20
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    Wavelet upscaling based on piecewise bilinear approximation of the permeability field (1996)
    Springer
    Transport in porous media 23 (1996), S. 125-134 
    Details
    ISSN: 1573-1634
    Keywords: permeability ; upscaling ; flow prediction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A method for upscaling of permeability in heterogeneous porous media is presented. The upscaled field takes the form K = e Y , where Y, in two dimensions, is a piecewise bilinear function. The method is tested on a number of random permeability fields, with different integral scale/correlation length and variance. The numerical results show that this method conserves much more of the heterogeneous fingering than classical block-based upscaling methods, e.g., geometric mean.
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    Permeability evolution induced by the precipitation of an advected solute: Effect of the microscopic and the macroscopic scales competition on the clogging mechanism (1996)
    Springer
    Transport in porous media 24 (1996), S. 341-375 
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    ISSN: 1573-1634
    Keywords: precipitation ; porous medium ; clogging ; feedback mechanism ; permeability
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    Notes: Abstract A model is proposed for coupling the one-dimensional transport of solute with surface precipitation kinetics which induces the clogging of an initially homogeneous porous medium. The aim is to focus the non-linear feedback effect between the transport and the chemical reaction through the permeability of the medium. A Lagrangian formulation, used to solve the coupled differential equations, gives semi-analytical expressions of the hydrodynamic quantities. A detailed analysis reveals that the competition between the microscopic and macroscopic scales controls the clogging mechanism, which differs depends on whether short or long times are considered. In order to illustrate this analysis, more quantitative results were obtained in the case of a second and zeroth order kinetic. It was necessary to circumvent the semi-analytic character of the solutions problem by successive approximation. A comparison with results obtained by simulations displays a good agreement during the most part of the clogging time.
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    URL: http://dx.doi.org/10.1007/BF00154097
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    Two-phase flow in heterogeneous porous media: The method of large-scale averaging (1988)
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    Transport in porous media 3 (1988), S. 357-413 
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    ISSN: 1573-1634
    Keywords: Two-phase flow ; heterogeneous porous media ; large-scale averaging ; permeability ; capillary pressure
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    Notes: Abstract The analysis of two-phase flow in porous media begins with the Stokes equations and an appropriate set of boundary conditions. Local volume averaging can then be used to produce the well known extension of Darcy's law for two-phase flow. In addition, a method of closure exists that can be used to predict the individual permeability tensors for each phase. For a heterogeneous porous medium, the local volume average closure problem becomes exceedingly complex and an alternate theoretical resolution of the problem is necessary. This is provided by the method of large-scale averaging which is used to average the Darcy-scale equations over a region that is large compared to the length scale of the heterogeneities. In this paper we present the derivation of the large-scale averaged continuity and momentum equations, and we develop a method of closure that can be used to predict the large-scale permeability tensors and the large-scale capillary pressure. The closure problem is limited by the principle of local mechanical equilibrium. This means that the local fluid distribution is determined by capillary pressure-saturation relations and is not constrained by the solution of an evolutionary transport equation. Special attention is given to the fact that both fluids can be trapped in regions where the saturation is equal to the irreducible saturation, in addition to being trapped in regions where the saturation is greater than the irreducible saturation. Theoretical results are given for stratified porous media and a two-dimensional model for a heterogeneous porous medium.
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    URL: http://dx.doi.org/10.1007/BF00233177
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    Effects of NAPL Contaminants on the Permeability of a Soil‐Bentonite Slurry Wall Material (2000)
    Springer
    Transport in porous media 38 (2000), S. 43-56 
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    ISSN: 1573-1634
    Keywords: NAPL ; hydraulic conductivity ; permeability ; slurry walls ; soil ; bentonite
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    Notes: Abstract Soil‐bentonite slurry walls are designed to inhibit the subsurface movement of contaminants from hazardous waste sites. Although it is generally accepted that high concentrations of organic compounds will adversely affect soil‐bentonite slurry walls and clay liners, previous research investigating the effects of NAPLs on the conductivity of clay wall materials has been inconclusive. In this study the effects of various organics (benzene, aniline, trichloroethylene, ethylene dichloride, methylene chloride) on the effective conductivity of a typical soil‐bentonite slurry wall material were studied under two effective stress conditions, 200 and 52 kPa. The hydraulic conductivity for the soil‐bentonite material permeated with water averaged 1.52×10-8 cm s-1. Compared to water, there was little change in conductivity when the sample was permeated with a solution containing a NAPL compound at its solubility limit, except for aniline. However, there was a one to two order of magnitude decrease in conductivity when the sample was permeated with a pure NAPL for all NAPLs tested. When the soil‐bentonite material was permeated with a water/NAPL/water/NAPL sequence, the conductivity decreased one to two orders of magnitude when a NAPL was introduced following water; however, when water was reintroduced after the NAPL, the conductivity increased to the initial hydraulic conductivity. The conductivity again decreased one to two orders of magnitude when the NAPL was reintroduced. This trend occurred for all NAPLs tested, and the fluid properties of the NAPL compounds alone did not account for the decrease in conductivity compared to water.
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    Data interpretation problems to be expected in the study of coupled fluid flow in porous media (1989)
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    Transport in porous media 4 (1989), S. 185-198 
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    ISSN: 1573-1634
    Keywords: Transport coefficients ; coupling ; fluid flow ; permeability
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    Notes: Abstract On the basis of recent work, it would appear that the transport coefficients descriptive of certain idealized cases of coupled flow of immiscible fluids in porous media, can be determined in principle by calculations employing well-defined experimental data. Other considerations show, however, that even small errors inherent in laboratory observations sometimes will have an enormously large effect on the accuracy of the calculated values. On the other hand, it often will be the case that values for the transport coefficients are not needed individually, as long as those particular functions which appear lumped together in the equations of motion, can be calculated from the same data but with less error. In any case, it will be clear that error problems will be, to some extent, mitigated when very accurate instrumentation is available to control and measure the fluxes and driving forces that give rise to the transport processes under study. Thus, the aim of this paper is to present an error analysis that will facilitate laboratory design in preparation for experimental work, and will also facilitate the interpretation of the data that eventually are to be obtained. Another aim is to underscore the risks taken by those who fail to take coupling effects into account just because the potential importance of them is not appreciated or not clearly revealed by existing data.
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    The effect of anisotropic permeability on free convective boundary layer flow in porous media (1995)
    Springer
    Transport in porous media 19 (1995), S. 79-92 
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    ISSN: 1573-1634
    Keywords: Porous medium ; convection ; boundary layer ; anisotropy ; permeability
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    Notes: Abstract The effect of an anisotropic permeability on thermal boundary layer flow in porous media is studied. The convective flow is induced by a vertical, uniformly heated surface embedded in a fluid-saturated medium. A leading-order boundary layer theory is presented. It is shown that the thickness of the resulting boundary layer flow is different from that obtained in an isotropic porous medium. In general, an anisotropic permeability induces a fluid drift in the spanwise direction, the strength of which depends on the precise nature of the anisotropy. Conditions are found which determine whether or not the boundary layer flow is three-dimensional.
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    Permeability of a random array of fractures of widely varying apertures (1987)
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    Transport in porous media 2 (1987), S. 31-43 
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    ISSN: 1573-1634
    Keywords: Homogenization ; permeability ; percolation
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    Notes: Abstract We modelize a fractured rock by a random array of plane cracks of finite extent having a very broad distribution of apertures (or of hydraulic conductances). If the rock is permeable, the flow will essentially take place along a ‘subnetwork’ made of the less resistant cracks. Using an analogy with the treatment of variable range transport in semiconductors, we evaluate the homogenization length and the permeability of this disordered network. This evaluation makes use of the notion of the critical bonds which are the weakest cracks among the good ones necessary for percolation; the remaining weaker bonds make a negligible contribution to the permeability. The method is applicable to other examples of transport in very heterogeneous macroscopic random materials.
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    Factorization of Transport Coefficients in Macroporous Media (2000)
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    Transport in porous media 41 (2000), S. 305-323 
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    Keywords: irreversible thermodynamics ; permeability ; transport coefficients ; linearization ; averaging
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    Notes: Abstract We prove the fundamental theorem about factorization of the phenomenological coefficients for transport in macroporous media. By factorization we mean the representation of the transport coefficients as products of geometric parameters of the porous medium and the parameters characteristic of the multicomponent fluid saturating the porous space. The two permeabilities of the porous medium, the convective and the diffusional ones, are separated. A similarity between the diffusional permeability and the porosity–tortuosity factor of the Kozeny–Carman theory is demonstrated. We do not make any specific assumption about stochastic or deterministic structure of the porous medium. The fluxes in fluid on the pore level are described by general relations of the non-equilibrium thermodynamics.
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    The Effect of Asphalt Precipitation on Flow Behavior and Production of a Fractured Carbonate Oil Reservoir During Gas Injection (2000)
    Springer
    Transport in porous media 41 (2000), S. 325-347 
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    ISSN: 1573-1634
    Keywords: fractured reservoir ; permeability ; injectivity index ; asphalt precipitation ; computer simulation
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    Notes: Abstract The first field data, collected over an 11 year period, are presented which indicate the possible effect of asphalt precipitation on the permeability and injectivity index of a fractured carbonate oil reservoir. The asphalt aggregates were formed during enhanced oil recovery by injection of a rich gas into the reservoir. The data indicate that, while at the initial stages of the operations the permeability and injectivity index decrease, at later times they appear to oscillate with the process time, with apparent oscillations' periods that depend on the heterogeneity of the reservoir. Two classes of plausible mechanisms that give rise to such oscillatory behavior are discussed. One relies on the changes in the structure of the reservoir's fractures, while the other one is based on asphalt precipitation in the reservoir. Computer simulations of flow and precipitation of asphalt aggregates in a pore network model of the reservoir are carried out. The results appear to support our proposition that asphalt formation and precipitation in the reservoir are the main mechanism for the observed behavior of the injectivity index. We also develop a stochastic continuum model that accurately predicts the time-dependence of the reservoir's permeability and injectivity index during the gas injection process.
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    URL: http://dx.doi.org/10.1023/A:1006759524127
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    Effective properties for flow calculations (1995)
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    Transport in porous media 20 (1995), S. 169-196 
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    ISSN: 1573-1634
    Keywords: effective flow properties ; reservoir geology ; permeability ; transmissibility
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    Notes: Abstract In this paper we discuss the background to the problems of finding effective flow properties when moving from a detailed representation of reservoir geology to a coarse gridded model required for reservoir performance simulation. In so doing we synthesize the pictures of permeability and transmissibility and show how they may be used to capture the effects of the boundary conditions on the upscaling. These same concepts are applied to the renormalization method of calculating permeability, to show its promise as an accurate, yet fast method.
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    Numerical and analytical study to estimate the effect of two length scales upon the permeability of a fibrous porous medium (1995)
    Springer
    Transport in porous media 21 (1995), S. 1-17 
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    ISSN: 1573-1634
    Keywords: Resin transfer molding ; permeability ; fibrous porous medium ; porous cylinders ; creeping flow ; length scales
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    Notes: Abstract A fibrous porous medium with two length scales is modeled as a bed of porous cylinders aligned perpendicular to the flow of viscous fluid. The flow behavior is described using Stokes and Darcy flow equations in the regions around (higher length scale) and within the cylinders (lower length scale) respectively. The typical ratio of higher and lower length-scale regions enable us to invoke lubrication approximation and simplify the equations to develop a closed form solution for the overall permeability of this dual-scale porous medium. A parametric analysis is performed to explore the dependence of permeability on factors such as the volumetric ratio of higher and lower length-scale regions, permeability and size of inclusions in the smaller length-scale region. The analytical model is compared with the numerical results and the trend is compared with the experiments.
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    A stochastic model for the permeability characteristics of saturated cemented porous media undergoing freezing (1996)
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    Transport in porous media 22 (1996), S. 345-357 
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    Keywords: permeability ; stochastic model ; freezing ; porous cemented materials
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    Notes: Abstract As the temperature of a saturated porous medium drops, the water in the pores starts to freeze. Since the temperature at which the phase change takes place is dependent on the pore size, the permeability of the medium changes continuously. Simultaneously, due to the expansion of water on freezing, it is forced to migrate through the pore body thus inducing stresses in material matrix. The stresses developed and the consequent frost damage are therefore dependent on the change in the permeability characteristics of the medium on freezing. This paper deals with the numerical prediction of permeability characteristics of porous cemented media saturated with water undergoing progressive freezing. A bond percolation model is used to generate the pore structure according to an assumed poresize distribution. Permeability of the medium at various temperatures is computed by solving the network problem. The computed results are compared with other analytical and experimental results. The proposed model predicts a threshold temperature below which permeability drops to zero. This phenomenon is crucial in developing a deeper understanding of the mechanism of frost damage to cemented porous materials such as bricks, stone, concrete, etc.
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    A Simple Model of a Two-Layered High-Temperature Liquid-Dominated Geothermal Reservoir as a Part of a Large-Scale Hydrothermal Convection System (1998)
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    Transport in porous media 33 (1998), S. 3-27 
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    ISSN: 1573-1634
    Keywords: geothermal reservoir ; high temperature ; Kakkonda ; natural convection ; numerical modeling ; permeability ; super-critical fluid
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    Notes: Abstract The Kakkonda geothermal reservoir, Japan, is a typical high-temperature liquid-dominated geothermal reservoir, except for its distinctive two-layered temperature structure. It has a shallow permeable reservoir of 230–260°, and a deep less permeable reservoir of 350–360°. Geology and hydrology indicate that the shallow reservoir is one to two orders of magnitude more permeable than the deep reservoir, but that the two reservoirs communicate. It has been widely assumed in engineering and scientific circles that the connection between the two reservoirs is a zero or low permeability barrier to fluid flow. We show that this hypothesis is untenable, based on both physical evidence and numerical simulation. We numerically model the evolution of the geothermal system as it heats after emplacement of an intrusion. The two-layered temperature structure is found to be a consequence of the permeability difference, i.e. the two-layered permeability structure.
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    Macroscale Properties of Porous Media from a Network Model of Biofilm Processes (1998)
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    Transport in porous media 31 (1998), S. 39-66 
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    ISSN: 1573-1634
    Keywords: network model ; biofilm ; biobarrier ; permeability ; Monod kinetics ; adsorption
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    Notes: Abstract We demonstrate how a network model can predict porosity and permeability changes in a porous medium as a result of biofilm buildup in the pore spaces. A biofilm consists of bacteria and extracellular polymeric substances (EPS) bonded together and attached to a surface. In this case, the surface consists of the walls of the porous medium, which we model as a random network of pipes. Our model contains five species. Four of these are bacteria and EPS in both fluid and adsorbed phases. The fifth species is nutrient, which we assume to reside in the fluid phase only. Bacteria and EPS transfer between the adsorbed and fluid phases through adsorption and erosion or sloughing. The adsorbed species influence the effective radii of the pipes in the network, which affect the porosity and permeability. We develop a technique for integrating the coupled system of ordinary and partial differential equations that govern transport of these species in the network. We examine ensemble averages of simulations using different arrays of pipe radii having identical statistics. These averages show how different rate parameters in the biofilm transport processes affect the concentration and permeability profiles.
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    Fractal porous media I: Longitudinal stokes flow in random carpets (1987)
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    Transport in porous media 2 (1987), S. 553-569 
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    Keywords: Porous media ; permeability ; random ; fractal
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    Notes: Abstract Two-dimensional porous media whose random cross-sections are derived from site percolation are constructed. The longitudinal flow of a Newtonian fluid in the Stokes approximation is then computed and the longitudinal permeability is obtained. Two methods are used and yield the same result when porosity is low. The Carman equation is shown to apply within ±7% when porosity is within the range from 0 to 0.75. Finally, random structures derived from stick percolation are investigated; results are qualitatively the same, but the Carman equation yields a poorer approximation.
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    Fractal porous media II: Geometry of porous geological structures (1987)
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    Transport in porous media 2 (1987), S. 571-596 
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    Keywords: Porous media ; fractal ; permeability ; transport
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    Notes: Abstract Some geological structures are analysed and found to be fractal. An interesting feature is the very large range of scales involved; the spreading dimension is also measured for some of them. The consequences of these measurements on the analysis of transport processes in porous media are presented - the existence of fractal structures multiplies the variety of actual porous media.
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    The statistical properties of immiscible fluid displacement in bond/site correlated network models of porous media (1991)
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    Mathematical geology 23 (1991), S. 87-110 
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    ISSN: 1573-8868
    Keywords: percolation ; lattice statistics ; permeability ; immiscible fluid flow
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    Notes: Abstract A statistical formulation is introduced which allows the determination of capillary pressure and relative permeability curves from lattice properties and, by extension, possibly core properties. Comparisons of statistical results to simulation results generally show good agreement for both drainage and imbibition. These processes turn out to be two different formulations of a single problem in one view presented here. Both agreement and disagreement between statistics and simulation results provide insight into the characteristics of the flow of immiscible fluids in porous media. A considerable amount of topological information on the fluids is also obtainable by these methods.
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    Use of the geometric average for effective permeability estimation (1991)
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    Mathematical geology 23 (1991), S. 833-840 
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    ISSN: 1573-8868
    Keywords: permeability ; geometric average ; geometric mean ; j th Winsorized mean ; robust estimation
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    Notes: Abstract The geometric average is often used to estimate the effective (large-scale) permeability from smaller-scale samples. In doing so, one assumes that the geometric average is a good estimator of the geometric mean. Problems with this estimator arise, however, when one or more of the samples has a very low value. The estimate obtained becomes very sensitive to the small values in the sample set, while the true effective permeability may be only weakly dependent on these small values. Several alternative methods of estimating the geometric mean are suggested. In particular, a more robust estimator of the geometric mean, the jth Winsorized mean, is proposed and several of its properties are compared with those of the geometric average.
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    Permeability semivariograms, geological structure, and flow performance (1996)
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    Mathematical geology 28 (1996), S. 419-435 
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    Keywords: semivariograms ; sedimentary structure ; permeability
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    Notes: Abstract Clastic sediments may have a strong deterministic component to their permeability variation. This structure may be seen in the experimental semivariogram, but published geostatislical studies have not always exploited this feature during data analysis and covariance modeling. In this paper, we describe sedimentary organization, its importance for flow modeling, and how the semivariogram can be used for identification of structure. Clastic sedimentary structure occurs at several scales and is linked to the conditions of deposition. Lamination, bed, and bedset scales show repetitive and trend features that should be sampled carefully to assess the degree of organization and levels of heterogeneity. Interpretation of semivariograms is undertaken best with an appreciation of these geological units und how their features relate to the sampling program. Sampling at inappropriate intervals or with instruments having a large measurement volume, for example, may give misleading semivariograms. Flow simulations for models which include and ignore structure show that the repetitive features in permeability can change anisotropy and recovery performance significantly. If systematic variation is present, careful design of the permeability fields therefore is important particularly to preserve the structure effects.
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    Flow Simulations To Evaluate Upscaling of Permeability (1998)
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    Mathematical geology 30 (1998), S. 717-731 
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    ISSN: 1573-8868
    Keywords: upscaling ; permeability ; flow simulation ; reservoir simulation ; homogenization
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    Topics: Geosciences , Mathematics
    Notes: Abstract We study upscaling of the permeability for porous media flow on a grid with one million blocks. The purpose is to illustrate how flow simulations can be used to evaluate upscaling methods.
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    Permeability Upscaling Measured on a Block of Berea Sandstone: Results and Interpretation (1999)
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    Mathematical geology 31 (1999), S. 749-769 
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    ISSN: 1573-8868
    Keywords: permeability ; upscaling ; Berea Sandstone ; minipermeameter ; nonuniform flow ; local-scale processes
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    Topics: Geosciences , Mathematics
    Notes: Abstract To physically investigate permeability upscaling, over 13,000 permeability values were measured with four different sample supports (i.e., sample volumes) on a block of Berea Sandstone. At each sample support, spatially exhaustive permeability datasets were measured, subject to consistent flow geometry and boundary conditions, with a specially adapted minipermeameter test system. Here, we present and analyze a subset of the data consisting of 2304 permeability values collected from a single block face oriented normal to stratification. Results reveal a number of distinct and consistent trends (i.e., upscaling) relating changes in key summary statistics to an increasing sample support. Examples include the sample mean and semivariogram range that increase with increasing sample support and the sample variance that decreases. To help interpret the measured mean upscaling, we compared it to theoretical models that are only available for somewhat different flow geometries. The comparison suggests that the nonuniform flow imposed by the minipermeameter coupled with permeability anisotropy at the scale of the local support (i.e., smallest sample support for which data is available) are the primary controls on the measured upscaling. This work demonstrates, experimentally, that it is not always appropriate to treat the local-support permeability as an intrinsic feature of the porous medium, that is, independent of its conditions of measurement.
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    Design of bentonite/crushed rock seals (1991)
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    Geotechnical and geological engineering 9 (1991), S. 63-72 
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    ISSN: 1573-1529
    Keywords: Bentonite ; crushed rock ; permeability ; piping ; plug design
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Summary The use of bentonite/crushed rock mixtures to form hydraulic barriers has greatly increased in recent years. To obtain an appropriate composition for such mixture sealants generally requires extensive laboratory work. Bentonite content and gradation of the crushed rock component are two key parameters in the seal design. This study investigates the effect of crushed rock gradation on the bulk porosity and permeability of systems of crushed tuff particles. Five different gradations are selected from the literature. The bulk porosity of systems of crushed tuff in the presence of bentonite is examined. The Fuller-Thompson gradations yield denser particle arrangements. For mixture samples containing 15% bentonite by weight, the amount of clay accounts for only 45 to 56% of the weight required to fill the interparticle pore space. The bentonite occupancy percentage amounts to 65 to 80% and 75 to 86.5% for samples having 25 and 35% bentonite by weight, respectively. The water content of bentonite at saturation is reduced and the resistance to piping and flow of bentonite is enhanced by the addition of clay. To reduce the bulk porosities of the mixtures containing 25% or more bentonite, a compaction energy higher than the standard Proctor compaction is necessary.
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    Water flow into undersea mine workings (1983)
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    Geotechnical and geological engineering 1 (1983), S. 237-251 
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    ISSN: 1573-1529
    Keywords: Aquifer ; geological structure ; ground water ; permeability ; subsidence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Summary Production at a number of mines operating off the North East coast has been seriously affected by the percolation of significant quantities of water onto working coal faces. A detailed study of factors affecting the incidence and distribution of water inflows has been undertaken, using operational, geological and hydrological data. Analysis indicates that major inflows are a consequence of dynamic strata deformations, which induce discontinuities within the overburden capable of transmitting water from overlying aquiferous formations into workings. Operations tend to encounter excessive water inflows when: (1) cover to the Permian aquifer is less than 100 m or major Coal Measure aquifers exist within about 45 m of workings; (2) tensile face strains induced at the base of the Permian exceed 6 mm m−1; (3) sandstone strata forms less than one third of the overburden, implying a lack of competence in the seam roof; (4) major strata ‘weights’ or ‘breaks’ occur; and (5) faults or other major discontinuities are present in the roof strata.
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    Utilizing computational neural networks for evaluating the permeability of compacted clay liners (1996)
    Springer
    Geotechnical and geological engineering 14 (1996), S. 193-212 
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    ISSN: 1573-1529
    Keywords: Clay liners ; neural networks ; error backpropagation algorithm ; permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The design of lined waste-storage facilities is significantly influenced by the permeability of the liner. The permeability of compacted clay liners, in turn, is influenced by factors such as clay type and composition, compaction type and effort, and operating conditions. The complexity of the permeation process makes it difficult to predict analytically the permeability from these factors. As a result, empirical regression models are frequently used to predict permeability. In this paper, permeability prediction models are developed using computational neural networks (CNNS). The developed CNN models are used to predict the permeability of compacted clay for a known set of soil properties and field and laboratory conditions. Moreover, the models are used to determine the relative importance of the various input parameters to the model output. Also, a comparison between regression models and neural networks for predicting permeability is presented and the advantages of utilizing CNN methodology over regression techniques in model development are highlighted.
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    URL: http://dx.doi.org/10.1007/BF00452947
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    Pressurized grout applications in fractured tuff for containment of radioactive wastes (1991)
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    Geotechnical and geological engineering 9 (1991), S. 53-62 
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    ISSN: 1573-1529
    Keywords: Grouting ; geologic repository ; rock mechanics ; fractured rock mass ; permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Summary Currently under study by the Department of Energy are the geologic and hydrologic characteristics of the ash-flow deposits under Yucca mountain at the Nevada test site. Of interest at this site is the potential for disposal of high-level radioactive wastes in the unsaturated zone of the densely welded portions of the tuffs. These studies include the preformance-assessment of barriers and seals for boreholes, ramps, drifts and shafts at the Yucca mountain site. In-situ tests on standard Type II Portland cement and microfine cement as grout materials have been performed on a similar rock type to Yucca Mountain's near Superior Arizona. The tests were performed in a vertical borehole drilled in highly fractured and densely welded tuff (brown unit of Apache Leap) through a series of pressurized grout applications. Packer flow tests prior to and after each grout application measure the effectiveness of the grout application in reducing the permeability of the rock surrounding the borehole. Overall the grout applications have reduced the permeability of the test hole by three orders of magnitude.
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    Numerical solution and sensitivity analysis of filter cake permeability and resistance to model parameters (1993)
    Springer
    Transport in porous media 10 (1993), S. 235-255 
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    ISSN: 1573-1634
    Keywords: Filter cakes ; permeability ; matrix compressibility modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The migration and capture of solid particles in porous media occur in fields as diverse as water and wastewater treatment, well drilling, and in various liquid-solid separation processes. Filter cakes are formed when a liquid containing solid particles is forced through a pervious surface which allows the liquid transport while retaining solid particles. Following a literature survey, a governing equation for the cake thickness is obtained by considering the instantaneous mass balance. Later, numerical solutions for the cake thickness, cake permeability, cake resistance, solid particle velocity (cake compression rate) and concentration of suspended particles are obtained and a sensitivity analysis is conducted. The sensitivity analysis shows that the cake permeability and cake resistance are more sensitive to the rate constant of cake erosion than they are to the rate constant of particle capture. However, the concentration of suspended solid particles, and the solid velocity are mostly sensitive to the slurry parameter and the rate constant of particle trapping. Moreover, cake permeability, compressibility, concentration of suspended particles, and the solid velocity are very sensitive to the concentration at the filter septum. Finally, as expected, with a thicker slurry, more particles are captured inside the cake, thus forming a thicker and more resistant cake. Also, as more particles are being filtered at the filter septum, a thinner cake is formed and a smaller effluent concentration is achieved.
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    URL: http://dx.doi.org/10.1007/BF00616811
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    Fractal porous media IV: Three-dimensional stokes flow through random media and regular fractals (1990)
    Springer
    Transport in porous media 5 (1990), S. 325-340 
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    ISSN: 1573-1634
    Keywords: Porous media ; three-dimensional ; permeability ; random ; fractal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The three-dimensional Stokes flow of a Newtonian fluid through random and/or fractal media is numerically determined. The permeability of these media is derived. Results relative to these structures are presented and discussed. The validity of the Carman equation and of a simple scaling argument is questioned.
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    URL: http://dx.doi.org/10.1007/BF01141990
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    Hydraulic radius and transport in reconstructed model three-dimensional porous media (1994)
    Springer
    Transport in porous media 17 (1994), S. 221-238 
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    ISSN: 1573-1634
    Keywords: building technology ; conductivity ; critical diameter ; hydraulic radius ; permeability ; porous media ; reconstruction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Methods for reconstructing three-dimensional porous media from two-dimensional cross sections are evaluated in terms of the transport properties of the reconstructed systems. Two-dimensional slices are selected at random from model three-dimensional microstructures, based on penetrable spheres, and processed to create a reconstructed representation of the original system. Permeability, conductivity, and a critial pore diameter are computed for the original and reconstructed microstructures to assess the validity of the reconstruction technique. A surface curvature algorithm is utilized to further modify the reconstructed systems by matching the hydraulic radius of the reconstructed three-dimensional system to that of the two-dimensional slice. While having only minor effects on conductivity, this modification significantly improves the agreement between permeabilities and critical diameters of the original and reconstructed systems for porosities in the range of 25–40%. For lower porosities, critical pore diameter is unaffected by the curvature modification so that little improvement between original and reconstructed permeabilities is obtained by matching hydraulic radii.
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    URL: http://dx.doi.org/10.1007/BF00613583
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    An equation of motion for an incompressible Newtonian fluid in a packed bed (1995)
    Springer
    Transport in porous media 18 (1995), S. 185-198 
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    ISSN: 1573-1634
    Keywords: Finite element ; permeability ; Navier-Stokes ; packed bed ; spherical particles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The application of a volume average Navier-Stokes equation for the prediction of pressure drop in packed beds consisting of uniform spherical particles is presented. The development of the bed permeability from an assumed porous microstructure model is given. The final model is quasi-empirical in nature, and is able to correlate a wide variety of literature data over a large Reynolds number range. In beds with wall effects present the model correlates experimental data with an error of less than 10%. Numerical solutions of the volume averaged equation are obtained using a penalty finite element method.
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    Network model evaluation of permeability and spatial correlation in a real random sphere packing (1993)
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    Transport in porous media 11 (1993), S. 53-70 
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    ISSN: 1573-1634
    Keywords: Correlation ; permeability ; network model ; sphere pack ; percolation ; tessellation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract In principle, network models can replicate exactly the microstructure of porous media. In practice, however, network models have been constructed using various assumptions concerning pore structure. This paper presents a network model of a real, disordered porous medium that invokes no assumptions regarding pore structure. The calculated permeability of the model agrees well with measured permeabilities, providing a new and more rigorous confirmation of the validity of the network approach. Several assumptions commonly used in constructing network models are found to be invalid for a random packing of equal spheres. In addition, the model permits quantification of the effect of pore-scale correlation (departure from randomness) upon permeability. The effect is comparable to reported discrepancies between measured permeabilities and predictions of other network models. The implications of this finding are twofold. First, a key assumption of several theories of transport in porous media, namely that pore dimensions are randomly distributed upon a network, may be invalid for real porous systems. Second, efforts both to model and to measure pore-scale correlations could yield more accurate predictions of permeability.
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    URL: http://dx.doi.org/10.1007/BF00614635
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    Nuclear magnetic resonance imaging of miscible fingering in porous media (1993)
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    Transport in porous media 12 (1993), S. 107-123 
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    ISSN: 1573-1634
    Keywords: Nuclear magnetic resonance imaging (MRI) ; miscible displacement ; buoyancy ; three-dimensional ; diffusion ; permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Nuclear Magnetic Resonance Imaging (MRI) can noninvasively map the spatial distribution of Nuclear Magnetic Resonance (NMR)-sensitive nuclei. This can be utilized to investigate the transport of fluids (and solute molecules) in three-dimensional model systems. In this study, MRI was applied to the buoyancy-driven transport of aqueous solutions, across an unstable interface in a three-dimensional box model in the limit of a small Péclet number (Pe〈0.4). It is demonstrated that MRI is capable of distinguishing between convective transport (‘fingering’) and molecular diffusion and is able to quantify these processes. The results indicate that for homogeneous porous media, the total fluid volume displaced through the interface and the amplitude of the fastest growing finger are linearly correlated with time. These linear relations yielded mean and maximal displacement velocities which are related by a constant dimensionless value (2.4±0.1). The mean displacement velocity (U) allows us to calculate the media permeability which was consistent between experiments (1.4±0.1×10−7cm2).U is linearly correlated with the initial density gradient, as predicted by theory. An extrapolation of the density gradient to zero velocity enables an approximate determination of the critical density gradient for the onset of instability in our system (0.9±0.3×10−3 g/cm3), a value consistent with the value predicted by a calculation based upon the modified Rayleigh number. These results suggest that MRI can be used to study complex fluid patterns in three-dimensional box models, offering a greater flexibility for the simulation of natural conditions than conventional experimental modelling methods.
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    Fractal porous media (1993)
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    Transport in porous media 13 (1993), S. 41-78 
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    ISSN: 1573-1634
    Keywords: Fractal ; permeability ; conductivity ; transports
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The transport properties of continuous deterministic fractals are reviewed. The method of construction, the fractal dimension, and the major features of transport are summarized. Then the major single-phase transports are addressed; attention is focused on the numerical results and on the analytical arguments which may be used to derive these results in a simple way, whenever it is possible.
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    URL: http://dx.doi.org/10.1007/BF00613270
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    An experimental investigation of dispersion in layered porous media (1994)
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    Transport in porous media 15 (1994), S. 15-30 
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    ISSN: 1573-1634
    Keywords: Experiment ; dispersion ; layered heterogeneity ; permeability ; averaging ; permutation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Experiments were run in three linear, homogeneous, nonuniform porous media constructed in lucite columns using spherical glass beads. The columns were also joined end to end to create an in series layered heterogeneous porous media. Each column, all combinations of columns and several permutations were studied with a factorial experimental design to determine the effects of porosity, permeability, velocity, length, and column order upon dispersion. Attempts to predict the heterogeneous results from the homogeneous results were made, and a statistical regression based on the factorial design was calculated. Results showed that no simple averaging procedure accurately predicted the heterogeneous results. The statistical regression showed permeability, velocity, viscosity, length and column order to be significant.
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    Flow characteristics of anisotropic structures constructed with porous layers (1994)
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    Transport in porous media 15 (1994), S. 151-173 
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    ISSN: 1573-1634
    Keywords: Anisotropic ; porous media ; flow characteristic ; permeability ; Forchheimer extension ; regression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Artificial structures, serving as the solid matrix of anisotropic porous media and satisfying the requirement needed for flow visualization, were constructed with the perforated Polypropylene plates in order to improve the understanding of transport phenomena occurring in anisotropic porous media. This paper reports the regressed correlations of the experimental pressure gradient and filtration velocity data of three anisotropic and one isotropic porous media measured along two mutually orthogonal directions, which correspond to the principal axes of the permeability tensor, for the filtration velocities ranging from 0.2 to 12 mm/s with water as the fluid. To reflect the observed data, the regression equation with two types of deviations was formulated, in which the pressure gradient is represented by the sum of the linear and nonlinear terms of the filtration velocity. The physical model developed for the linear term assumes the solid matrix as repeated circular orifices when the filtration velocity approaches zero. The exponent of the filtration velocity in the nonlinear term was determined to be that of the Forchheimer extension. Also, four models for the coefficient of the nonlinear term were examined and the results were compared. The distribution of the residuals (the differences between the observed and the correlated values) validated the suggested regression procedure and the resulting correlations.
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    The relative importance of convective and conductive effects in two-phase geothermal fields (1994)
    Springer
    Transport in porous media 16 (1994), S. 289-298 
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    ISSN: 1573-1634
    Keywords: Two-phase ; conduction ; theory ; permeability ; effective conductivities ; geothermal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Conductive and convective transport are related in two phase porous media, provided capillary effects are negligible. This paper shows that the role of conduction will be unimportant, relative to convective effects, for sufficiently high temperatures and sufficiently high permeabilities. An approximately linear relationship holds between temperature and the logarithm of permeability, above which conduction is unimportant relative to convection.
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    Network Model of Flow, Transport and Biofilm Effects in Porous Media (1998)
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    Transport in porous media 30 (1998), S. 1-23 
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    ISSN: 1573-1634
    Keywords: biofilm ; network model ; permeability ; transport ; numerical diffusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract In this paper, we develop a network model to determine porosity and permeability changes in a porous medium as a result of changes in the amount of biomass. The biomass is in the form of biofilms. Biofilms form when certain types of bacteria reproduce, bond to surfaces, and produce extracellular polymer (EPS) filaments that link together the bacteria. The pore spaces are modeled as a system of interconnected pipes in two and three dimensions. The radii of the pipes are given by a lognormal probability distribution. Volumetric flow rates through each of the pipes, and through the medium, are determined by solving a linear system of equations, with a symmetric and positive definite matrix. Transport through the medium is modeled by upwind, explicit finite difference approximations in the individual pipes. Methods for handling the boundary conditions between pipes and for visualizing the results of numerical simulations are developed. Increases in biomass, as a result of transport and reaction, decrease the pipe radii, which decreases the permeability of the medium. Relationships between biomass accumulation and permeability and porosity reduction are presented.
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    URL: http://dx.doi.org/10.1023/A:1006560705680
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    Hydrostatic pressure tests for the permeability - formation factor relation on crystalline rocks from the KTB drilling project (1995)
    Springer
    Surveys in geophysics 16 (1995), S. 47-62 
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    ISSN: 1573-0956
    Keywords: Crystalline rocks ; equivalent channel model ; hydrostatic pressure ; permeability ; resistivity formation factor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Transport properties (permeability and electrical conductivity) have been measured at different hydrostatic pressure runs on 7 crystalline rocks (gneisses and amphibolites) sampled from the KTB drilling project. The decrease of permeability by pressure are compared with the pressure-dependent data of the electrical conductivity (formation factor) resulting from complex impedance measurements. According to the equivalent-channel model (ECM), there exists a linear relationship between these parameters by representing both properties on logarithmic scales. The results show that it is possible to extrapolate high-pressure permeability from low-pressure (〈 60 MPa) permeability data by using the pressure-dependent electrical conductivity (up to 300 MPa).
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    Effects of serial and parallel pore nonuniformities: Results from two models of the porous structure (1996)
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    Transport in porous media 25 (1996), S. 335-350 
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    ISSN: 1573-1634
    Keywords: Cauchy-Schwarz-Bunjakovskij inequality ; computational fluid dynamics ; effective diffusivity ; permeability ; pore-size distribution ; specific surface area
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The effects of parallel-type and serial-type pore nonuniformities on the effective diffusivity and the permeability of a porous material were evaluated, constant porosity and constant specific surface area being assumed. Two structural models were considered. In the first model, the porous structure was described as a bundle of cylindrical capillaries penetrating the whole thickness of the material and in the other it was described instead as a collection of randomly distributed obstacles hindering transport. Both models predicted that parallel-type pore nonuniformities produce an increase in permeability compared with uniform structures having the same porosity and specific surface area. Both models also predicted that the increase in permeability due to parallel-type pore nonuniformities would be larger than the increase in effective diffusivity. Regarding serial-type pore nonuniformities, both models predicted a decrease in permeability and that this decrease would be greater than the decrease in effective diffusivity. The predicted changes in effective diffusivity due to nonuniformities of the sample differed for the two structural models.
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    Preferential Flow-Paths Detection for Heterogeneous Reservoirs Using a New Renormalization Technique (1997)
    Springer
    Transport in porous media 26 (1997), S. 1-23 
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    ISSN: 1573-1634
    Keywords: upscaling ; renormalization ; permeability ; local flux ; heterogeneity.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract We have devised a renormalization scheme which allows very fast determination of preferential flow-paths and of up-scaled permeabilities of 2D heterogeneous porous media. In the case of 2D log-normal and isotropically distributed permeability-fields, the resulting equivalent permeabilities are very close to the geometric mean, which is in good agreement with a rigorous result of Matheron. It is also found to work well for geostatistically anisotropic media when comparing the resulting equivalent permeabilities with a direct solution of the finite-difference equations. The method works exactly as King's does, although the renormalization scheme was modified to obtain tensorial equivalent permeabilities using periodic boundary conditions for the pressure gradient. To obtain an estimation of the local fluxes, the basic idea is that if at each renormalization iteration all the intermediate renormalized permeabilities are stored in memory, we are able to compute -- ad reversum -- an approximation of the small-scale flux map under a given macroscopic pressure gradient. The method is very rapid as it involves a number of calculations that vary linearly with the number of elementary grid blocks. In this sense, the renormalization algorithm can be viewed as a rapid approximate pressure solver. The ‘exact’ reference flow-rate map (for the finite-difference algorithm) was computed using a classical linear system inversion. It can be shown that the preferential flow paths are well detected by the approximate method, although errors may occur in the local flow direction.
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    Fractal porous media III: Transversal Stokes flow through random and Sierpinski carpets (1988)
    Springer
    Transport in porous media 3 (1988), S. 185-198 
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    ISSN: 1573-1634
    Keywords: Porous media ; permeability ; random ; fractal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The transversal Stokes flow of a Newtonian fluid through random and Sierpinski carpets is numerically calculated and the transversal permeability derived. In random carpets derived from site percolation, the average macroscopic permeability varies as (ε- ɛ c)3/2, close to the critical porosityɛ c. This exponent is found to be slightly different from the conductivity exponent. Results for Sierpinski carpets are presented up to the fourth generation. The Carman equation is not verified in these two model porous media.
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    Infiltration of Liquid Metals in Porous Compacts: Modeling of Permeabilities During Reactive Melt Infiltration (1999)
    Springer
    Transport in porous media 36 (1999), S. 43-68 
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    ISSN: 1573-1634
    Keywords: reactive melt infiltration ; ceramic ; composites ; porous compacts ; permeability ; modeling.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Reactive infiltration is a fast and cost-effective technique for manufacturing ceramic-matrix composites (CMCs). CMCs are used in elevated temperature applications like rocket engine casings, jet nozzles, gas turbine blades and nuclear cladding. There is an urgent need for minimizing experimental costs as well as optimizing process parameters during manufacture, so that we have minimized manufacturing costs and reduced infiltration times. Towards this end, the objective of this research was to develop an integrated micro-macro model of reactive flow of molten silicon in a porous preform consisting of carbon-coated silicon carbide fibers and then optimize process parameters computationally. The overall objective of the research was to arrive at a modified equation of Darcy's law for flow through a porous medium with the help of numerical/computational modeling. This paper deals with the flow of silicon through porous carbon at the macro level. The macro flow of silicon was integrated with an available micro model by determining the transient porosity from the micro model and using it in Darcy's law written for the macro flow of silicon. From the results of this study, we recommend suitable process parameters such as initial temperature of the solid reactant and the specific kind of reactants to be used for achieving complete infiltration. These conclusions are drawn after observation of the rate of decrease of permeability with more reaction.
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    URL: http://dx.doi.org/10.1023/A:1006574912165
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    Validation of the Slow Compressional Wave in Porous Media: Comparison of Experiments and Numerical Simulations (1999)
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    Transport in porous media 36 (1999), S. 149-160 
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    ISSN: 1573-1634
    Keywords: poroelasticity ; Biot's theory ; slow wave ; permeability ; acoustics.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract We perform numerical simulation of ultrasonic experiments on poroelastic samples, in which Biot's slow compressional wave had been observed. The simulation is performed using OASES modeling code, which allows to compute elastic wave fields in layered poroelastic media. Modeled were the experiments of Plona (1980), Rasolofosaon (1988), and our own measurements. In all the three situations, a good agreement between experiment and simulations has been observed. This further confirms the fact that Biot's theory of poroelasticity, on which the simulations were based, adequately describes the behavior of the porous materials under investigations at ultrasonic frequencies.
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    URL: http://dx.doi.org/10.1023/A:1006676801197
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    Ground water pressure relief wells in shaft sinking (1983)
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    Geotechnical and geological engineering 1 (1983), S. 229-236 
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    ISSN: 1573-1529
    Keywords: Shaft sinking ; ground water ; grouting ; wells ; permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Summary The pattern of pressure relief produced in a confined aquifer by a ring of vertical relief wells is conventionally evaluated by summation of simple contributions from individual wells. Where the wells surround an open excavation such as a shaft, the pattern is modified. This paper outlines the appropriate modifications. The resulting pattern of pressure relief and of shaft inflow is calculated for typical practical situations for an open circular shaft and also for a shaft protected by an annular zone of grouted ground. The examples show the influence of number and location of relief wells and the degree of permeability reduction in the annulus.
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    URL: http://dx.doi.org/10.1007/BF00881613
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