comparison of pore fabric based on high-resolution x-ray ... · comparison of pore fabric based on...
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Comparison of pore fabric based on high-resolution X-ray computed tomography and magnetic pore
fabric in sedimentary rocks Yi Zhou*, Michele Pugnetti*, Anneleen Foubert**, Christoph Neururer** & Andrea R. Biedermann* *Institute of Geological Sciences, University of Bern, Baltzerstrasse 1+3, CH-3012 Bern, Switzerland
**Department of Geosciences, University of Fribourg, Chemin du Musée 6, CH-1700 Fribourg, Switzerland
• The pore size and geometry, as well as their connectivity determine the permeability and preferred permeability direction.
• X-ray micro-tomography (XRCT) is a widely used technique to generate digital rock models, visualize and quantify pore shape and size distributions, and the connectivity of pores with a spatial resolution on the order of 10 microns.
• Magnetic pore fabrics (MPF), obtained by impregnating ferrofluid prior to measuring anisotropy of magnetic susceptibility could be complementary to existing techniques and capture smaller pores.
• This study is aimed at quantitatively analyzing relationships between pore fabric or permeability anisotropy and MPF.
• Plio-Pleistocene calcarenite (Apulia, Italy) with ~50% porosity, ~300 μm average equivalent diameter of pores and complex pore structure.
• Upper Marine Molasse sandstone (OMM, Belpberg, Switzerland) with 5-20% porosity, ~150 μm average equivalent diameter of pores and relatively homogeneous pore structure.
1. Introduction
2.1 Samples
2.3 Magnetic pore fabric method
• Impregnation by vacuum and fifteen-directions measurement scheme to determine the full susceptibility tensor.
2. Methods
2.2 XRCT• XRCT scanning and full-tensor permeability simulations in 6 directions
4. Summary
3.2 Sample: molasseAvizo 2019.4 pore network modellingUser Guide from www.fei.com
15-position measuring
3. Results
3.1 Sample: calcarenite• MI-1-Z3 (calcarenite)
Total pore shape ellipsoidMinimum pore dimensionMaximum pore dimension
Max
Min
Intermediate
• MI-1-Z3 (calcarenite)
• D1112Y (molasse)
Pore
s ≥4
×4×4
voxe
ls
• Orientation density functions of maximum and minimum pore axes are affected by resolution artefacts unless smaller pores are filtered out.
• Total shape ellipsoid reflects preferred orientation of pore shape, and is largely unaffected by artefacts related to unresolved pores.
• Permeabilities can be simulated from the XRCT data, but can be still improved in accuracy and need verification against measurements.
• The orientation of the MPF maximum axis correlates with the maximum dimension of the mean shape ellipsoid at 95% confidence.
• The MPF anisotropy degree is generally smaller than that of the total shape ellipsoid.
simulations in 6 directions
Impregnation
Orientations and orientation density functions of pore axes
All
mea
sure
d p
ore
sPo
res
≥4×4
×4vo
xels
Pore
s ≥1
6×1
6×1
6vo
xels
Minimum pore dimensionMaximum pore dimensionOrientations and orientation density functions of pore axes
Mu
ltiples o
f rand
om
d
istribu
tion
Max
Min
Intermediate
Upper Upper
Upper
Upper Upper
Upper
Upper Upper Upper
UpperUpper
Upper Upper Upper Upper
Mu
ltiples o
f rand
om
d
istribu
tion
Min
Intermediate
Total pore shape ellipsoid
Upper
0.5
Mu
ltiples o
f rand
om
d
istribu
tion
90
70
50
30
10
4.5
3.5
2.5
1.5
Mu
ltiples o
f rand
om
d
istribu
tion
Upper4.5
3.5
2.5
1.5
0.5
Upper
Max
Int
Min
90 (Y)
0 (X)• Max• Int• Min
90 (Z)
Upper
MeanIndividual data95% confidence
3.5
3
2.5
2
1.5
1
0.5
Max
Max
Min
Intermediate
Upper
Simulated permeability
Max
Int
Min90 (Y)
0 (X)
• Max• Int• Min
Upper
90 (Z)
Samples drilled in different directions
MI-1-Z3
Z
X
Y
MI-2-Y3
0 (X)
90 (Y)
• Max• Int• Min
90 (Z)
Upper
Max
IntMin
• MI-1-Z3• MI-2-Y3• MI-3-X15
Max
Min
Intermediate
Max
Min
Intermediate
Max
Min
Intermediate
Comparison ontotal shape ellipsoid
Max
Int
Min
0 (X) • Max• Int• Min
90 (Z)
Upper
90 (Y)
k1=max eigenvalue; k2=intermediate eigenvalue; k3=min eigenvalue;P = k1/k3, anisotropy degree;U = (2*k2-k1-k3)/(k1-k3), shape
• Checking for consistency of pore shape in three perpendicular cores
Simulated permeabilityMPF
P-U
Upper
Bootstrapped total shape ellipsoid
Max
Int
Min
90 (Y)
0 (X)
• Max• Int• Min
Upper
90 (Z)
MeanIndividual data95% confidence
Bootstrapped total shape ellipsoid
P-U
Upper