dc resistivity method - chihping lin （林志平）resistivity vs. resistance resistivity for...

DC Resistivity Method

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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


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


A practical way of measuring resistivity


A practical way of measuring resistivity

IVK

rrrrIVV pP

a

=+

=

41

31

21

11

221


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.


Depth of current penetration vs. current electrode spacing


Current flow in two layer media

1

2

2

1

2

1

tantan

==


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


ApparentResistivity

Current flow in layered media-Case 1Resistivity survey and geology

Resistivity Surveys and GeologyCurrent flow in layered media-Case 1


Resistivity Equipment and Field Procedure

EquipmentSurvey Types Overview

SoundingsProfilesTomography

Choice of Best ArrayField Work

Resistivity equipment and field procedure

DC Resistivity EquipmentCurrent sourceAmmeterVoltmeterElectrodesCables


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 Soundings-Pole-Pole Array

Pole-Pole sounding data is plotted asapparent resistivity vs. a


Resistivity Soundings-Pole-Dipole Array

Pole-Dipole sounding data is plotted asapparent resistivity vs. a


Resistivity SoundingsWenner Array

Wenner sounding data is plotted asapparent resistivity vs. a on a log-log plot


Resistivity SoundingsSchlumberger Array

Schlumberger sounding data is plotted asapparent resistivity vs. s (AB/2) on a log-log plot


Resistivity SoundingsDipole-Dipole Array

Dipole-Dipole sounding data is plotted asapparent resistivity vs. s (AB/2) on a log-log plot


Resistivity SoundingsElectrode Spacings and Apparent Resistivity Plots


Resistivity ProfilesResistivity equipment and field procedure

Resistivity TomographyResistivity equipment and field procedure

Resistivity TomographyResistivity equipment and field procedure

Resistivity Tomography

Pseudosection


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.


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


Apparent Resistivity CurveOne-layered media case 2


Apparent Resistivity CurveTwo-layered media


Apparent Resistivity CurveTwo-layered media


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

dc resistivity method - chihping lin （林志平）resistivity vs. resistance resistivity for...

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