Spontaneous potential log, commonly called the self potential log or SP log, is a passive measurement taken by oil industry well loggers to characterise rock formation properties. The log works by measuring small electric potentials (measured in millivolts) between depths with in the borehole and a grounded electrode at the surface.

The spontaneous potential log (SP) measures the natural or spontaneous potential difference (sometimes called self-potential) that exists between the borehole and the surface in the absence of any artificially applied current. It is a very simple log that requires only an electrode in the borehole and a reference electrode at the surface.

Feb 22, 2013 · The spontaneous potential (SP) log measures the natural potential difference between the borehole and surface without any applied current. It arises from differences in salinity and fluid access between borehole fluid and formation fluid.

Jul 28, 2016 · The spontaneous potential (SP) log was developed next and was presented along with resistivity logs. It is a measurement of the voltage difference between a movable electrode in the wellbore and a fixed electrode at the surface.

Jan 29, 2025 · The SP log is typically scaled at 100 mV per log track. If the resistivities of the mud filtrate and formation water are similar, the SP deflections are small and the curve is rather featureless. An SP curve cannot be recorded in holes filled with nonconductive muds, such as oil-based muds (OBMs).

Apr 5, 2022 · Water resistivity or R w, is a critical component of log analysis in calculating water saturation using the Archie equation. R w can be measured from a sample of formation water taken from the zone of interest at the well site or a nearby well, or it can be calculated using spontaneous potential (SP) log data.

Jan 22, 2025 · Self-potential (SP) borehole logging is an electrical wireline method that passively measures naturally occurring voltage anomalies along the length of an open, fluid-filled borehole.

Sep 7, 2018 · SP log is one of the first tools used for formation evaluation. It measures the difference in potential or DC voltage between two points. One point is the electrode on the surface. Second point is the electrode taken downhole by wireline (Fig.1.)

Spontaneous potentials (SP) are usually caused by charge separation in clay or other minerals, due to presence of semi-permeable interface impeding the diffusion of ions through the pore space of rocks, or by natural flow of a conducting fluid through the rocks.

Oct 15, 2016 · The document discusses the spontaneous potential (SP) well log. It describes how the SP log can be used to identify permeable zones, define bed boundaries, and compute shale content. It provides examples of calculating shale volume from the SP response.