SPWLA Glossary

A technique, now obsolete, for determining the presence of a thin permeable bed enclosed in a thick highly resistive formation. The technique also permits the recording of an approximation to the static SP. The method involves the measurement of two curves by a sonde with a special electrode arrangement. An SP measuring electrode is placed between two potential-monitoring electrodes and two current electrodes in symmetrical array. One curve is recorded with the SP electrode while the potential-monitoring electrodes are maintained (by current electrodes) at the static SP of shales, and the other curve is recorded while the potentialmonitoring electrodes are maintained at the static SP of permeable beds. A comparison of the curves will reveal SP anomalies at the permeable beds, and means to derive static SP. See SP and SSP.