Self-potential measurements are one of the oldest of the geophysical techniques. The earth can sometimes act as a small voltage source due to electro-chemistry variations. Oxidation-reduction reactions near metal ore-bodies has been used to help explore for new deposits. Oil spills in the shallow subsurface of the earth also cause electrical changes in the subsurface and an example is shown below.
Figure 1. Equipment used to perform Self Potential surveys. This survey is quite simple and the equipment needed is relatively inexpensive.
Figure 2. Data comparison from Line 1, collected from a portion of a landfill.
Figure 3. Data comparison from Line 2, collected from a portion of a landfill.
Figure 4. Model that tries to explain the origin of the Self Potential effect around a buried metal object.
An oil spill in soil will also create an SP effect. This is shown in the figures below.
Figure 5. Here's what the oil spill looked like on the driveway. A small grid was set out over the area.
Figure 6. Data collected from the Self Potential survey over an oil spill on a gravel driveway.
Figure 7. Data from the Self Potential survey shown as a contoured image.
Figure 8. Here is the approximate area of the oil spill superimposed over the contoured data from the Self Potential survey.