Induced polarisation and self potential Flashcards
What is induced polarisation?
A current-stimulated electrical phenomenona observed as a delay voltage response in earth materials resulting from a capacitive behavior. The physical property measured is chargeability. The chargeability is significant for disseminated ores.
What is chargeability?
A measurement of how well a material holds charge
Two types of phenomena causes induced polarisation, which?
Electrode polarisation - current is normally conducted by positive and negative ions moving through the groundwater. Electrode polarization happens when grains causes a blockage of pore channels that causes build-up of ions. Negative ions will give away electrons through the grain to positive ions on the other side of the blockage but ions cannot pass through the blockage. This exchange is rather slow and a buildup of ions happens on each side, forming an accumulation of charge. When the current then is switched off these charges are dispersed through the pore water and briefly produces a small current. The potential difference does not reach zero immediately and that is what you measure.
Membrane polarisation - Clay particles on the sides of pores have negative charges on the surface and attract positive ions when electric current flows past. Gives unwanted noise when surveying.
What does polarisation depend on?
Type of electronic conductive material. Pores. Clay minerals. Temperature. Current intensity and current frequency.
Measurements of induced polarisation can be based on two different things, which?
Time domain measurements - Voltage decay is observed as a function of time after injected current is switched off.
Frequency domain measurements.
What is self-potential (SP)?
Self-potential is a spontaneous polarisation. A naturally occurring potential difference between points in the ground. Not certain how SP is generated.
