Induced polarization

Induced polarization (IP) is a geophysical imaging technique used to identify the electrical chargeability of subsurface materials, such as ore.[1][2]

The polarization effect was originally discovered by Conrad Schlumberger when measuring the resistivity of rock.[3]

The survey method is similar to electrical resistivity tomography (ERT), in that an electric current is transmitted into the subsurface through two electrodes, and voltage is monitored through two other electrodes.

Induced polarization is a geophysical method used extensively in mineral exploration and mine operations. Resistivity and IP methods are often applied on the ground surface using multiple four-electrode sites. In an IP survey, in addition to resistivity measurement, capacitive properties of the subsurface materials are determined as well. As a result, IP surveys provide additional information about the spatial variation in lithology and grain-surface chemistry.

The IP survey can be made in time-domain and frequency-domain mode:

In the time-domain induced polarization method, the voltage response is observed as a function of time after the injected current is switched off or on. [4]

In the frequency-domain induced polarization mode, an alternating current is injected into the ground with variable frequencies. Voltage phase-shifts are measured to evaluate the impedance spectrum at different injection frequencies, which is commonly referred to as spectral IP.

The IP method is one of the most widely used techniques in mineral exploration and mining industry and it has other applications in hydrogeophysical surveys, environmental investigations and geotechnical engineering projects.[5]

Measurement methods

Time domain
Typical transmitted current waveform and potential response for time domain resistivity and induced polarization measurements.

Time-domain IP methods measure considers the resulting voltage following a change in the injected current. The time domain IP potential response can be evaluated by considering the mean value on the resulting voltage, known as integral chargeability[2] or by evaluating the spectral information and considering the shape of the potential response, for example describing the response with a Cole-Cole model.[6]

Frequency domain
Main article: Spectral induced polarisation

Frequency-domain IP methods uses alternating currents (AC) to induce electric charges in the subsurface, and the apparent resistivity is measured at different AC frequencies.

See also

References
  1. Bleil, David Franklin (July 1953). "Induced Polarisation: A Method of Geophysical Prospecting". Geophysics. 18 (3): 636–661. doi:10.1190/1.1437917. Retrieved 2018-05-15.
  2. Zonge, Ken; Wynn, Jeff; Urquhart, Scott (2005). "Chapter 9. Resistivity, Induced Polarization, and Complex Resistivity". In Butler, Dwain K. (ed.). Near-Surface Geophysics - Investigations in Geophysics. Society of Exploration Geophysicists (SEG). pp. 265–300. doi:10.1190/1.9781560801719.ch9. ISBN 978-1-56080-130-6.
  3. Allaud, Louis A.; Martin, Maurice H. (1977-10-01). Schlumberger - The History of a Technique. Translated by Schwob, Marcel. New York, USA: John Wiley & Sons, Inc. ISBN 978-047101667-0.
  4. Olsson, Per-Ivar; Dahlin, Torleif; Fiandaca, Gianluca; Auken, Esben (2015). "Measuring time-domain spectral induced polarization in the on-time: decreasing acquisition time and increasing signal-to-noise ratio" (PDF). Journal of Applied Geophysics. 123: 316–321. doi:10.1016/j.jappgeo.2015.08.009. ISSN 0926-9851.
  5. "Induced Polarization (IP) What Is It?". Surface Search Inc. 2018. Archived from the original on 2018-05-17. Retrieved 2018-05-06.
  6. Pelton, William H.; Ward, Stanley H.; Hallof, Philip G.; Sill, William R.; Nelson, Philip H. (1978-04-01). "Mineral discrimination and removal of inductive coupling with multifrequency IP". Geophysics. 43 (3): 588–609. doi:10.1190/1.1440839.

Further reading
  • Kearey, Philip; Brooks, Michael (1991). An Introduction to Geophysical Exploration (2 ed.). Blackwell Science. ISBN 978-0-632-02923-5.
  • Example IP equipment and image results
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