As such, in most cases, the spontaneous potential measured is only related to the electrochemical potential.
2.
Some measure spontaneous potential, a potential that arises in the ground because of man-made or natural disturbances.
3.
This led to the discovery of the spontaneous potential ( SP ) which was as important as the ability to measure resistivity.
4.
Spontaneous potentials occur when two aqueous solutions with different ionic concentrations are placed in contact through a porous, semi-permeable membrane.
5.
In 1940, Schlumberger invented the spontaneous potential dipmeter; this instrument allowed the calculation of the dip and direction of the dip of a layer.
6.
The SP log, known variously as a " Spontaneous Potential ", " Self Potential " or " Shale Potential " log is a voltmeter measurement of the voltage or electrical potential difference between the mud in the hole at a particular depth and a copper ground stake driven into the surface of the earth a short distance from the borehole.
7.
Since spontaneous potential is a measure of electrochemical potential and the ionic activity of a solution is inversely proportional to its resistivity, the above equation can be simplified as SP = " E " " C " = " K " log 10 ( " R " mfe / " R " we ), where " R " mfe and " R " we are equivalent mud filtrate resistivity and equivalent formation water resistivity respectively.
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