mineral physics tutorial 2 · digital rock physics i ´ obtain darcy velocity (q) ´ apply darcyʼs...
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Mineral Physics Tutorial 2Physical Properties of Composite Materials: Effective Medium Models
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Effective Elastic Moduli
´ Rocks are polymineralic, heterogeneous
´ To estimate effective elastic moduli of rocks, we need:´ Elastic moduli of each constituent (minerals, interstitial
fluid etc.)
´ Volume of each constituent
´ Distribution of all constituents
´ The geometric details of the distribution are the hardest to measure
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3-dimensional (3D) Imaging
Dvorkin et al., 2008
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Digital Rock Physics
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Digital Rock Physics I
´ Obtain Darcy velocity (q)
´ Apply Darcyʼs Law
´ Virtual permeability experiments (Miller, Zhu, Montesi, and Gaetani, 2014)
´ Mimics an actual permeability experiment.
´ Imposing pressures, P1 > P2, induces fluid flow.
´ Solve Stokes Equations for velocity (finite-volume method)
v : velocity [m s-1]µ : viscosity [Pa s-1]p : pressure [Pa]
q : Darcy velocity [m s-1]k : permeability [m2]L : length of sample [m]
€
∇⋅ v = 0µ∇2v −∇p = 0
⎧ ⎨ ⎩
€
q = −kµP1 − P2L
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Melt Transport
´ Miller, Zhu, Montesi and Gaetani, 2014
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Digital Rock Physics II
´ Apply Ohm’s Law for volume-averaged quantities:
´ Virtual direct current experiment (Miller, Montesi, and Zhu, 2015)
´ Assign conductivities to materials.
´ Melt: 7.53 S/m (ten Grotenhuis et al., 2005)
´ Olivine: 0.009 S/m (Constable, 2006)
´ Imposing voltage gradient, V1 > V2, induces electric current.
´ Solve Laplace Equation (in-house finite-difference code).
1Ωtotal
J|| dΩ =σ bulkV1 −V2L
J is current density [A m-2]σ is conductivity [S/m]V is voltage [V]
where,
Where Ω is volume
∇2V = 0J = −σ∇V
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Radius-dependence of fluid & current
´ Stronger radius-dependence of fluid flux.
´ Weaker radius-dependence of electric flux.
L = 70 μm
R =10 μm
P,Voutlet`
P,Vinlet
Schematic
Velocity
Electric Field
Φ = πR2 ΔVLElectric Flux:
Q = πR4
8µΔPLFluid Flux:
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Elastic Modulii
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State-of-the-Art
´ 3D-Atom Probe (LEAP 5000)´ Both 3D imaging
and chemical composition at atomic scale
´ Evaporate atoms by field effect (near 100% ionization), projected onto a position sensitive detector
(Madonna et al., 2012)
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Voigt-Reuss-Hill Average
´ Voigt bound (upper bond)
´ Reuss bound (lower bound)
´ Voigt-Reuss-Hill Average
KVoigt = f1K1 + f2K2 µVoigt = f1µ1 + f2µ2
KReuss = f1K1−1 + f2K2
−1−1( )−1
µReuss = f1µ1−1 + f2µ2
−1( )−1
KVoigt-Reuss-Hill =12KVoigt +KReuss( ) µVoigt-Reuss-Hill =
12µVoigt +µReuss( )
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Geometric Interpretations(From G. Mavko)
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Hashin-Shtrikman Bounds´ HS upper bound: Stiff material is shell, K1, µ1
´ HS lower bound: soft material is shell, K1, µ1
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Hashin-Shtrikman Bounds´ Shell: K1, µ1
´ Sphere: K2, µ2
KH-S 1 = K1 +f2
1K2 −K1
+f1
K1 + 43 µ1
µH-S 1 = µ1 +f2
1µ2 −µ1
+2 f1 K1 + 2µ1( )5µ1 K1 + 4
3 µ1( )
KH-S 2 = K2 +f1
1K1 −K2
+f2
K2 + 43 µ2
µH-S 2 = µ2 +f1
1µ1 −µ2
+2 f2 K2 + 2µ2( )5µ2 K2 + 4
3 µ2( )
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Transport properties
´ Permeability: k
´ Parallel connection (arithmetic mean): Upper Bound
´ Serial connection (harmonic mean): Lower Bound
´ Random connection (geometric mean): average
´ Hashin-Shtrikman bounds
kParallel = f1k1 + f2k2
kSerial = f1k1−1 + f2k2
−1−1( )−1
kRandom = k1f11 k2
f2
kH-S 1 = k1 +f2
1k2 − k1
+f1
3k11
kH-S 2 = k2 +f1
1k1 − k2
+f2
3k2
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Other elastic properties
´ Estimate bulk and shear moduli from Young’s modulus and Poisson’s ratio
´ Mixing theory on K or µ
´ Compute Young’s modulus, P-wave and S-wave velocity
E = 9K µ3K +µ
µ =E
2 1+ν( )K =
E3 1− 2ν( )
VP =K + 4
3 µρ
VS =µρ
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