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DC Resistivity Method
DC Resistivity MethodResistivity BasicsResistivity Surveys and GeologyResistivity Equipment and Field ProceduresInterpretation of Resistivity MeasurementsCase Study
Resistivity BasicsCurrent flow and Ohms lawResistivity vs. ResistanceResistivity for common earth materialsCurrent density and electrical fieldMeasurement of resistivity
DC resistivity basics
Current Flow and Ohms LawDC resistivity basics
Resistivity vs. ResistanceDC 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 10^13 Mica 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
Current Densities and EquipotentialDC resistivity basics
A First Estimate of ResistivityDC resistivity basics
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
A practical way of measuring resistivity
IVK
rrrrIVV pP
a
=+
=
41
31
21
11
221
DC resistivity basics
Resistivity Survey and GeologySources of NoiseDepth of Current Penetration vs. Current Electrode SpacingCurrent Flow in Layered MediaVariation in Apparent Resistivity: Layered vs. Homogeneous Media
Resistivity survey and geology
Sources of NoiseElectrode polarization
Use nonpolarizing electrodesUse a slowly varying AC current
Telluric currentsPresence of nearby conductorsLow resistivity at the near surfaceNear-electrode geology and topographyCurrent induction in measurement cables.
Resistivity survey and geology
Depth of current penetration vs. current electrode spacing
Resistivity survey and geology
Current flow in two layer media
1
2
2
1
2
1
tantan
==
Resistivity survey and geology
Current flow in two layer mediaResistivity survey and geology
Current distributionResistivity survey and geology
Layered vs. Homogeneous Media
IVK
rrrrIVV pP
a
=+
=
41
31
21
11
221
Resistivity survey and geology
ApparentResistivity
Current flow in layered media-Case 1Resistivity survey and geology
Resistivity Surveys and GeologyCurrent flow in layered media-Case 1
Resistivity survey and geology
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
Resistivity Equipment and Field Procedure
EquipmentSurvey Types Overview
SoundingsProfilesTomography
Choice of Best ArrayField Work
Resistivity equipment and field procedure
DC Resistivity EquipmentCurrent sourceAmmeterVoltmeterElectrodesCables
Resistivity equipment and field procedure
Survey Types OverviewResistivity Soundings
To look for variations in resistivity with depth
Resistivity ProfilesTo detect lateral variations in resistivity
Resistivity Tomography2-D resistivity tomogram
Resistivity equipment and field procedure
Resistivity Soundings-Pole-Pole Array
Pole-Pole sounding data is plotted asapparent resistivity vs. a
Resistivity equipment and field procedure
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
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
Resistivity SoundingsElectrode Spacings and Apparent Resistivity Plots
Resistivity equipment and field procedure
Resistivity ProfilesResistivity equipment and field procedure
Resistivity TomographyResistivity equipment and field procedure
Resistivity TomographyResistivity equipment and field procedure
Resistivity Tomography
Pseudosection
Resistivity equipment and field procedure
CHOICE OF THE BEST ARRAY
Depends on:1) type of structure to be mapped2) sensitivity of the resistivity meter 3) background noise level
Things to be considered:1) depth of investigation2) sensitivity of the array to vertical and horizontal structures 3) horizontal data coverage4) signal strength.
Resistivity equipment and field procedure
Field WorkResistivity equipment and field procedure
Interpretation of Resistivity Measurements
Apparent resistivity curves for soundings over one-layered media
Apparent resistivity curves in two-layered media
Resistivity Modeling and Inversion
Interpretation of resistivity measurements
Apparent Resistivity CurveOne-layered media case 1
Interpretation of resistivity measurements
Apparent Resistivity CurveOne-layered media case 2
Interpretation of resistivity measurements
Apparent Resistivity CurveTwo-layered media
Interpretation of resistivity measurements
Apparent Resistivity CurveTwo-layered media
Interpretation of resistivity measurements
1D inversion
1D inversion
Resistivity ModelingInterpretation of resistivity measurements
Resistivity Modeling and InversionInterpretation of resistivity measurements
Resistivity Modeling and InversionInterpretation of resistivity measurements
2D inversionInterpretation of resistivity measurements
Seismic and Electrical TomographyCase Study 1
Case Study 1
ERT - along tunnel axis(Pole-Pole Array)
ERT Simulation
Case Study 1
ERT Simulation
Case Study 1
ERT Simulation
Case Study 1
Site condition1991
Case Study 2
Logging DataCase Study 2
DH5 DH1 DH2 DH4 DH3
Line1
Line2
Line3
Line3 cross
Measurement array
Wenner-Schlumberger
Case Study 2
Inversion ResultCase Study 2
DH3
Line3 CrossLine3
Line2Line1
DH1 DH5
DH2DH4
Forward ModelCase Study 2
Forward ModelCase Study 2
InterpretationIn-situ measurement dataLoggingForward model