Stratification in poured granular heaps

Baxter, John; Tüzün, U.; Heyes, D. M.; Hayati, Igan; Fredlund, P

doi:10.1038/34328

Cited by 81 publications

(68 citation statements)

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“…Similar deposition mechanisms are responsible for the formation of stratification and segregation patterns in heaps and silos (Williams 1968, Makse et al 1997, Gray & Hutter 1997, Baxter et al 1998, which are as equally familiar to those handling bulk solids in industry as they are to geologists (Fineberg 1997).…”

Section: Introductionmentioning

confidence: 99%

A theory for particle size segregation in shallow granular free-surface flows

2005

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Granular materials composed of a mixture of grain sizes are notoriously prone to segregation during shaking or transport. In this paper a binary mixture theory is used to formulate a model for kinetic sieving of large and small particles in thin rapidly flowing avalanches, which occur in many industrial and geophysical free-surface flows. The model is based on a simple percolation idea, in which the small particles preferentially fall into underlying void space and lever large particles upwards. Exact steady-state solutions have been constructed for general steady uniform velocity fields, as well as time-dependent solutions for plug-flow, that exploit the decoupling of material columns in the avalanche. All the solutions indicate the development of concentration shocks, which are frequently observed in experiments. A shock-capturing numerical algorithm is formulated to solve general problems and is used to investigate segregation in flows with weak shear.

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Section: Introductionmentioning

confidence: 99%

A theory for particle size segregation in shallow granular free-surface flows

2005

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“…We found that the fine-grained samples showed natural stratification, with roughly horizontal layers. This natural stratification has been seen in mixtures of (a) large rounded grains and small rough grains (Makse et al, 1997; Cizeau et al, 1999), and (b) various grain sizes with similar grain shapes (Baxter et al, 1998). Our coarse-grained samples did not show natural stratification.…”

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confidence: 65%

“…The effect of gravity settling on natural stratification in granular materials has been shown through lab tests and theoretical simulations (Makse et al, 1997;Baxter et al, 1998;Cizeau et al, 1999). This textural anisotropy influences the anisotropy of mechanical properties (Wong and Arthur, 1985;Jiang et al, 1997;Hoque and Tatsuoka, 1998).…”

Section: Introductionmentioning

confidence: 99%

Seismic and Rock Physics Diagnostics of Multiscale Reservoir Textures

Mavko¹

2003

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As part of our study on "Relationships between seismic properties and rock microstructure", we have studied 1. Methods for detection of stress-induced velocity anisotropy in sands.2. We have initiated efforts for velocity upscaling to quantify long-wavelength and short-wavelength velocity behavior and the scale-dependent dispersion caused by sediment variability in different depositional environments. INTRODUCTIONIn this quarter, we submit results of our research on: pore textural mapping and its relation to centimeter-scale core measurements of impedance and measurements of seismic properties of unconsolidated sediments at very low effective pressures. The special effect of stress anisotropy on velocity anisotropy is investigated. Two papers have been submitted for publication. This report presents preprints of our research relevant to this project on impedance mapping, soft-sediment measurements, stress anisotropy, and scale effects. PAPER 1Vega, S., Prasad, M., Mavko, G., and Nur, A., Detection of stress-induced velocity anisotropy in sands. Submitted to GRL In this paper, we present a preliminary study on stress-induced velocity anisotropy in two different sands. We describe the method used for sample preparation, and the polyaxial apparatus used for velocity, strain, and stress measurements. Furthermore, we examine the velocity response as a function of stress in different directions of applying uniaxial strain test to the samples. The strains and velocities of the two sands are also compared. We show that stress-induced velocity anisotropy exists and is detectable in sands. A stress anisotropy of 87% corresponds to a velocity anisotropy of 29%-34%, and there is a linear dependency of velocity anisotropy on stress anisotropy in the sands. We apply different statistical methods for characterizing heterogeneity and textures from scanning acoustic microscope (SAM) images of shale microstructures. Characterizing and understanding the microgeometry, their textures, scales, and textural anisotropy is important for better understanding the role of microgeometry on effective elastic properties. We analyzed SAM images from Bakken shale, Bazhenov shale, and Woodford shale. Our analysis, based on spatial autocorrelation functions shows that there is a small positive correlation between the degree of heterogeneity and the mean spatial correlation length of the microstructure. The textural anisotropy ranges from 10% to 80%. There is considerable variability within each image, as well as from one image to another. A singular value decomposition (SVD) spectral analysis showed that the shale microstructures have characteristics in common with fractal stochastic images. We also obtain a correlation between maturity and textural heterogeneity. The textural heterogeneity increases with increasing maturity (decreasing kerogen content), while there is a general decrease in textural anisotropy with maturity. The accompanying paper A4 in this volume relates the textural characteristics obtained from image processing ...

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“…This sand shows natural stratification when it is poured (Figure 1a). Natural stratification has also been observed in different mixtures of granular materials (Makse et al, 1997;Baxter et al, 1998;.…”

Section: Samples and Sample Preparationmentioning

confidence: 79%

“…Makse et al, 1997 and have shown that natural stratification occurs in poured granular mixtures of large rounded and small rough grains. However, Baxter et al, 1998 reported that natural stratification also occurs in mixtures of same grain shape and various grain sizes for a relatively low deposition speed.…”

Section: Introductionmentioning

confidence: 99%

Seismic and Rock Physics Diagnostics of Multiscale Reservoir Textures

Mavko¹

2003

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As part of our study on "Relationships between seismic properties and rock microstructure", we have 1. Studied relationships between velocity and permeability. 2. Used independent experimental methods to measure the elastic moduli of clay minerals as functions of pressure and saturation. 3. Applied different statistical methods for characterizing heterogeneity and textures from scanning acoustic microscope (SAM) images of shale microstructures. 4. Analyzed the directional dependence of velocity and attenuation in different reservoir rocks 5. Compared Vp measured under hydrostatic and non-hydrostatic stress conditions in sands. 6. Studied stratification as a source of intrinsic anisotropy in sediments using Vp and statistical methods for characterizing textures in sands.4 INTRODUCTIONIn this quarter, we submit results of our research on: impedance mapping on a micrometer scale and its relation to centimeter-scale core measurements of impedance, measurements of clay mineral modulus and the seismic properties of unconsolidated sediments at very low effective pressures. We have also begun work on analyzing the effects of scales on textural, impedance and velocity anisotropy and heterogeneity in consolidated and in unconsolidated materials. Six papers have been published on the work done in this year of the project. This report presents reprints of our publications relevant to this project on impedance mapping, acoustic measurements, and scales analyses. 9 PAPER 1Prasad, M., Velocity-permeability relations within hydraulic units. Velocity-permeability relations within hydraulic unitsManika Prasad * ABSTRACTRelationships between seismic velocity and permeability have been difficult to establish. I show that by grouping and sorting rocks into hydraulic units, we can establish relationships between velocity and permeability. The hydraulic units are calculated from measured porosity and permeability values. Correlation between velocity and permeability is significant within each hydraulic unit (the correlation coefficient, R 2 , lies in the range 0.65-0.87). This correlation is an extension of the match between porosity and permeability within a hydraulic unit. I show how the compaction and cementation history of a sediment can have effects on its physical properties such as porosity and permeability and on its seismic properties. The measured velocity data are further approximated with the Biot model. The velocitypermeability relation and modeling results are demonstrated for a large data set of laboratory measurements. The good match between calculated and measured data demonstrates that this relation can be used to predict permeability from velocity in well logs by zoning the data from training wells into hydraulic units. One possible application is shown where, by using site-specific data, the velocity-permeability relation is vastly improved with a correlation coefficient R 2 of 0.9.

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Stratification in poured granular heaps

Cited by 81 publications

References 1 publication

A theory for particle size segregation in shallow granular free-surface flows

A theory for particle size segregation in shallow granular free-surface flows

Seismic and Rock Physics Diagnostics of Multiscale Reservoir Textures

Seismic and Rock Physics Diagnostics of Multiscale Reservoir Textures

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