eeg electrical surveying ip
DESCRIPTION
yapTRANSCRIPT
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Introduction
Electrical surveying…
Resistivity method
Induced polarization method (IP)
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Self-potential (SP) method
Higher frequency methods (electromagnetic surv
Electromagnetic induction methods
Ground penetrating radar (GPR)
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Induced polarization me
The induced polarization method makes use o capacitive action of the subsurface to locate zo clay and conductive minerals are disseminated host rocks
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Application
Exploration of metalliferous mineral deposits
Clay location for hydrogeological surveys
Mapping electrochemical reactions for polluta ground
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Structure of the lectu
Basic IP theory and units
IP properties of rocks
Survey strategies and interpretation
Conclusions
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1. Basic IP theory and units
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Basic theory
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Membrane polarizatio
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Electrode polarizatio
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Note that membrane and electrode polarizations ca separately identified!
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Time-domain IP
1 t2
M a = V0 ∫t1 V
Ma is the apparent ch milliseconds (ms)
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Frequency-domain I
FE =100 ρa DC
ρ
FE is the percent frequ
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ρaDC is the apparent res low frequency (0.05-0.
ρaAC is the apparent resi higher frequency (1-10
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Frequency-domain I
MF = 2π ⋅105 (ρ
aDC −
ρ
aAC )= 2π ⋅105
ρaDC
ρaAC
MF is the metal factor in Siemens per meters (S/
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This normalization removes to a certain effect th variation of IP effect
with the effective resistivity the host rock (ρaDC )
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Spectral induced polarizatio
For a complete description of the IP phenomen frequencies are not enough.
The SIP technique frequency spectrum ranging from 10-2 to 104 H
The shift between the current and the potential discriminate between various metallic ores or
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2. IP properties of rocks
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IP versus resistivity
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Chargeability of miner
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Concentration 1 %, current injection time 3 s, int
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Chargeability of rock
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Current injection time 3 s, integration time 0.02 s
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IP effect…
… is higher for disseminated than massive cla metallic particles
… depends on the concentration of clay and m particles
…increases if water in the ground has a low co
… increases with decreasing porosity
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…varies with the amount of water in the groun
…depends on the current intensity and the cur frequency
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3. Survey strategies and interpretatio
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IP measurement
Different measurement devices for Time-dom Frequency-domain IP
Same electrode arrays (for mapping and sound conventional resistivity
Sensitive to telluric noise
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Sensitive to noise resulting from electromagne between adjacent wires (dipole-dipole array ve
Stability of potential measurements can be a p non polarizable electrodes, see lecture on SP s
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Interpretation
Mainly qualitative, more complex than for resi
Inversion using iterative algorithms (similar to
For SIP, getting information on material struct size of pores) using the Cole-Cole model
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Mi
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4. Conclusions
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Advantages
Detection of disseminated mineral (difficult w resistivity)
Method sensitive to clay in aquifers
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Drawbacks
Same disadvantages than resistivity method
Electrochemical phenomena are still not well u
IP surveys is slow and more expensive than re surveys