SPWLA Glossary

A curve recorded as a result ot simultaneous SP measurements from two electrodes located downhole, each serving as a reference potential for the other. The purpose of a differential SP is to minimize or eliminate unwanted effects induced on the SP measuring circuitry (i.e., electrode and survey conductor). The “twin” circuitry allows spurious efforts induced simultaneously on each segment of the circuit to negate each other at the recording galvanometer. The two downhole electrodes selected for this purpose should be separated by enough distance that their equal and opposite responses do not cancel the valid SP signals produced by different segments of the formation. See SP, downhole ground, and telluric currents.