Spontaneous potential or SP log based on natural electric field measurement. As well, it’s a part of the conventional open-hole logging suite to be registered in the wells.

Spontaneous potential logging solves the following tasks:

- lithology differentiation;

- correlation of well logs;

- reservoir rocks identification accompanied by other petrophysical methods.

The quality of SP registration decreases with mud salinity increasing. Consequently, it is recommended to drill the well with a water-based and low-salinity mud for a better log reading.