Electrical Surveying Part II: Induced polarization

Dr. Laurent Marescot

laurent@tomoquest.com

Introduction

Electrical surveying…

Resistivity method

Induced polarization method (IP)

Self-potential (SP) method

Higher frequency methods (electromagnetic surv

Electromagnetic induction methods

Ground penetrating radar (GPR)

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

Application

Exploration of metalliferous mineral deposits

Clay location for hydrogeological surveys

Mapping electrochemical reactions for polluta ground

Structure of the lectu

Basic IP theory and units

IP properties of rocks

Survey strategies and interpretation

Conclusions

1. Basic IP theory and units

Basic theory

Membrane polarizatio

Electrode polarizatio

Note that membrane and electrode polarizations ca separately identified!

Time-domain IP

1 t2

M a = V0 ∫t1 V

Ma is the apparent ch milliseconds (ms)

Frequency-domain I

FE =100 ρa DC

ρ

FE is the percent frequ

ρaDC is the apparent res low frequency (0.05-0.

ρaAC is the apparent resi higher frequency (1-10

Frequency-domain I

MF = 2π ⋅105 (ρ

aDC −

ρ

aAC )= 2π ⋅105

ρaDC

ρaAC

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

This normalization removes to a certain effect th variation of IP effect

with the effective resistivity the host rock (ρaDC )

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

2. IP properties of rocks

IP versus resistivity

Chargeability of miner

Concentration 1 %, current injection time 3 s, int

Chargeability of rock

Current injection time 3 s, integration time 0.02 s

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

…varies with the amount of water in the groun

…depends on the current intensity and the cur frequency

3. Survey strategies and interpretatio

IP measurement

Different measurement devices for Time-dom Frequency-domain IP

Same electrode arrays (for mapping and sound conventional resistivity

Sensitive to telluric noise

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

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

Mi

4. Conclusions

Advantages

Detection of disseminated mineral (difficult w resistivity)

Method sensitive to clay in aquifers

Drawbacks

Same disadvantages than resistivity method

Electrochemical phenomena are still not well u

IP surveys is slow and more expensive than re surveys