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WS0708

Dr. Laurent Marescot

Electrical Surveying

Part II: Induced polarization method

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Introduction

Electrical surveying

Resistivity method

Induced polarization method (IP) Self-potential (SP) method

Higher frequency methods (electromagnetic surveys):

Electromagnetic induction methods

Ground penetrating radar (GPR)

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Application

Exploration of metalliferous mineral deposits

Clay location for hydrogeological surveys

Mapping electrochemical reactions for pollutants in the

ground

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Structure of the lecture

1. Basic IP theory and units

2. IP properties of rocks

3. Survey strategies and interpretation

4. Conclusions

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1. Basic IP theory and units

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Basic theory

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Membrane polarization

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Electrode polarization

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10Note that membrane and electrode polarizations cannot be

separately identified!

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Time-domain IP

=2

1

)(1

0

t

t

a dttV

VM

Ma

is the apparent chargeability in

milliseconds (ms)

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Frequency-domain IP

aAC

aACDCaFE

=100

FE is the percent frequency effect (in %)

aDC

is the apparent resistivity mesured at

low frequency (0.05-0.5 Hz)aAC

is the apparent resistivity mesured at

higher frequency (1-10 Hz)

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Frequency-domain IP

( )aDCaACaDC

aACaDC FEMF

55 102102 ==

MF is the metal factor in Siemens per meters (S/m)

This normalization removes to a certain effect thevariation of IP effect with the effective resistivity of

the host rock (aDC

)

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2. IP properties of rocks

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IP versus resistivity

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Chargeability of minerals

Concentration 1 %, current injection time 3 s, integration time 1 s

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IP effect

is higher for disseminated than massive clay and

metallic particles

depends on the concentration of clay and metallic

particles

increases if water in the ground has a low conductivity

increases with decreasing porosity

varies with the amount of water in the ground depends on the current intensity and the current

frequency

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3. Survey strategies and interpretation

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Interpretation

Mainly qualitative, more complex than for resistivity

Inversion using iterative algorithms (similar to resistivity)

For SIP, getting information on material structures (e.g.

size of pores) using the Cole-Cole model

Mi i h i

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Mining geophysics

G th

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Geothermy

Hydrogeology

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Hydrogeology

Geology

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Geology

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4. Conclusions

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Advantages

Detection of disseminated mineral (difficult with

resistivity)

Method sensitive to clay in aquifers

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