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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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