Abstract
The effect of particle shape and heterogeneity on hydraulic anisotropy of unconsolidated granular packs is hereby investigated. Direct simulation was carried out on synthetically generated spherical, aspherical, ellipsoidal (aspect ratio of 2 and 3) and lenticular samples. Single phase Stokes equation was solved on models discretised on finite element geometries and hydraulic permeability computed in the horizontal and vertical directions to estimate the degree of anisotropy. The spherical and aspherical packs with varying degrees of particle shapes and heterogeneities are virtually isotropic. Ellipses with aspect ratios 2 and 3 have higher anisotropy ratios compared to the spherical and aspherical geometries while the lenticular geometry is the most anisotropic. This is attributable to the preferential alignment of the grains in the horizontal flow direction during random dynamic settling under gravity.
Highlights
Anisotropy (Kh/Kv) is a measure of the directional change in permeability of a rock sample
The porosities of the resulting packs depend on the particle shape and the friction coefficient used for the grain-grain interaction
As the aspect ratio increases, the preferential alignment increases resulting in higher hydraulic anisotropy
Summary
Anisotropy (Kh/Kv) is a measure of the directional change in permeability of a rock sample. Anisotropy controls single and multi-phase fluid flow effective mobility through porous systems. Small scale anisotropy in geologic formations may occur due to: stratification, directional rock fractures or orientation of non-spherical grains. The hydraulic anisotropy of soils and sedimentary rocks has a great effect on fluid flow and contaminant transport. An understanding of the anisotropy ratio is important for many subsurface fluid-associated problems such as the design of oil or water well fields, underflow beneath dams and dykes, internal erosion in soil masses or settlement rates of consolidating clays. Small scale anisotropy may occur from stratification due to the process of formation of the rock [9], directional rock fractures [10] or orientation of non-spherical grain particles during deposition [11]
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