4c resistivity cpl
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DC Resistivity Method
cplin@mail.nctu.edu.tw
DC Resistivity Method
Resistivity Basics
Resistivity Surveys and Geology
Resistivity Equipment and FieldProcedures
Interpretation of Resistivity Measurements
Case Study
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Resistivity Basics
Current flow and Ohms law
Resistivity vs. Resistance
Resistivity for common earth materials
Current density and electrical field
Measurement of resistivity
DC resistivity basics
Current Flow and Ohms Law
DC resistivity basics
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Resistivity vs. Resistance
DC resistivity basics
Resistivity of Earth MaterialsMaterial Resistivity (Ohm-meter)
Air Infinite
Pyrite 3 x 10^-1
Galena 2 x 10^-3
Quartz 4 x 10^10 - 2 x 10^14
Calcite 1 x 10^12 - 1 x 10^13
Rock Salt 30 - 1 x 10^13Mica 9 x 10^12 - 1 x 10^14
Granite 100 - 1 x 10^6
Gabbro 1 x 10^3 - 1 x 10^6
Basalt 10 - 1 x 10^7
Limestones 50 - 1 x 10^7
Sandstones 1 - 1 x 10^8
Shales 20 - 2 x 10^3
Dolomite 100 - 10,000
Sand 1 - 1,000
Clay 1 - 100
Ground Water 0.5 - 300
Sea Water 0.2
Archies Law
=aw-m
DC resistivity basics
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Current Densities and Equipotential
DC resistivity basics
A First Estimate of Resistivity
DC resistivity basics
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Two closely spread electrodes
Current Path % of Total Current
1 17
2 32
3 43
4 49
5 51
6 57
DC resistivity basics
A practical way of measuring resistivity
DC resistivity basics
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A practical way of measuring resistivity
I
VK
rrrr
I
VV pPa
=
+
=
4
1
3
1
2
1
1
1
221
DC resistivity basics
Resistivity Survey and Geology
Sources of Noise
Depth of Current Penetration vs. CurrentElectrode Spacing
Current Flow in Layered Media
Variation in Apparent Resistivity: Layeredvs. Homogeneous Media
Resistivity survey and geology
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Sources of Noise
Electrode polarization
Use nonpolarizing electrodes
Use a slowly varying AC current
Telluric currents
Presence of nearby conductors
Low resistivity at the near surface
Near-electrode geology and topography
Current induction in measurement cables.
Resistivity survey and geology
Depth of current penetration vs.current electrode spacing
Resistivity survey and geology
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Current flow in two layer media
1
2
2
1
2
1
tan
tan
==
Resistivity survey and geology
Current flow in two layer media
Resistivity survey and geology
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Current distribution
Resistivity survey and geology
Layered vs. Homogeneous Media
IVK
rrrr
I
VVpP
a
=
+
=
4
1
3
1
2
1
1
1
221
Resistivity survey and geology
ApparentResistivity
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Current flow in layered media-Case 1
Resistivity survey and geology
Resistivity Surveys and GeologyCurrent flow in layered media-Case 1
Resistivity survey and geology
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Resistivity Surveys and GeologyCurrent flow in layered media-Case 2
Resistivity survey and geology
Resistivity Surveys and GeologyCurrent flow in layered media-Case 2
Resistivity survey and geology
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Resistivity Equipment and Field Procedure
Equipment
Survey Types Overview
Soundings
Profiles
Tomography
Choice of Best Array
Field Work
Resistivity equipment and field procedure
DC Resistivity Equipment
Current source
Ammeter
Voltmeter
Electrodes
Cables
Resistivity equipment and field procedure
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Survey Types Overview
Resistivity Soundings
To look for variations in resistivity with depth
Resistivity Profiles
To detect lateral variations in resistivity
Resistivity Tomography
2-D resistivity tomogram
Resistivity equipment and field procedure
Resistivity Soundings-Pole-Pole Array
Pole-Pole sounding data is plotted as
apparent resistivity vs. a
Resistivity equipment and field procedure
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Resistivity Soundings-Pole-Dipole Array
Pole-Dipole sounding data is plotted asapparent resistivity vs. a
Resistivity equipment and field procedure
Resistivity SoundingsWenner Array
Wenner sounding data is plotted asapparent resistivity vs. a on a log-log plot
Resistivity equipment and field procedure
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Resistivity SoundingsSchlumberger Array
Schlumberger sounding data is plotted asapparent resistivity vs. s (AB/2) on a log-log plot
Resistivity equipment and field procedure
Resistivity SoundingsDipole-Dipole Array
Dipole-Dipole sounding data is plotted asapparent resistivity vs. s (AB/2) on a log-log plot
Resistivity equipment and field procedure
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Resistivity SoundingsElectrode Spacings and Apparent Resistivity Plots
Resistivity equipment and field procedure
Resistivity Profiles
Resistivity equipment and field procedure
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Resistivity Tomography
Resistivity equipment and field procedure
Resistivity Tomography
Resistivity equipment and field procedure
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Resistivity Tomography
Pseudosection
Resistivity equipment and field procedure
CHOICE OF THE BEST ARRAY
Depends on:1) type of structure to be mapped
2) sensitivity of the resistivity meter3) background noise level
Things to be considered:
1) depth of investigation2) sensitivity of the array to vertical and horizontal structures3) horizontal data coverage
4) signal strength.
Resistivity equipment and field procedure
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Field Work
Resistivity equipment and field procedure
Interpretation of Resistivity Measurements
Apparent resistivity curves for soundingsover one-layered media
Apparent resistivity curves in two-layeredmedia
Resistivity Modeling and Inversion
Interpretation of resistivity measurements
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Apparent Resistivity CurveOne-layered media case 1
Interpretation of resistivity measurements
Apparent Resistivity CurveOne-layered media case 2
Interpretation of resistivity measurements
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Apparent Resistivity CurveTwo-layered media
Interpretation of resistivity measurements
Apparent Resistivity CurveTwo-layered media
Interpretation of resistivity measurements
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1D inversion
1D inversion
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Resistivity Modeling
Interpretation of resistivity measurements
Resistivity Modeling and Inversion
Interpretation of resistivity measurements
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Resistivity Modeling and Inversion
Interpretation of resistivity measurements
2D inversion
Interpretation of resistivity measurements
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Seismic and Electrical Tomography
Case Study 1
Case Study 1
ERT - along tunnel axis(Pole-Pole Array)
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ERT Simulation
Case Study 1
ERT Simulation
Case Study 1
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ERT Simulation
Case Study 1
Site condition
199
1
Case Study 2
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Logging Data
Case Study 2
DH5 DH1 DH2 DH4 DH3
Line1
Line2
Line3
Line3
cross
Measurement array
Wenner-Schlumberger
Case Study 2
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Inversion Result
Case Study 2
DH3
Line3 CrossLine3
Line2Line1
DH1 DH5
DH2DH4
Forward Model
Case Study 2
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Forward Model
Case Study 2
Interpretation
In-situ measurement data
Logging
Forward model
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