Spontaneous potential survey

Traditionally, self-potential surveys have been carried out in mineral exploration to locate and delineate conductive mineral deposits. These surveys were most successful where a strong oxidation-reduction potential was present in the mineralized body. In addition to conductive mineral deposits, self-potential anomalies may also be attributed to the flow of subsurface fluid or heat.

In the geotechnical and engineering fields, self-potential surveys are carried out almost exclusively for the detection of seepage through earthen water retention structures such as dams, dikes, reservoir floors, unstable landslide areas and canals. In addition, surveys have been successfully completed to locate structures such as faults, to detect seepage through menbranes and to delineate flows around wells and in geothermal areas.

map-of-spontaneous-potential

                                      A map of spontaneous potential at earth dam

Self-potential or streaming potential anomalies in an earthen structure are caused by fluid flow through the porous medium and ion exchange between the fluid and soil particles within the zone. Measurement of these voltages provides information on the location, flow magnitude and the depths and geometries of subsurface flow paths. Negative anomalies occur where seepage enters a structure or flows horizontally with positive anomalies occurring where the flow is generally ascending and surface seepage occurs.

Streaming potential surveys have been successfully employed not only to detect anomalous seepage conditions but also to evaluate remedial measures emplaced to control seepage. Pre- and postgrouting surveys in an earthen dam for example, would reveal a change in the magnitude of streaming potentials and provide a means of assessing the effect of grouting operations.

Streaming potential surveys are generally carried out with a fixed base electrode and a roving measuring electrode with station locations determined by pre-surveyed grid. Streaming potential profiles or if data density permits, contours in millivolts are produced that are evaluated for anomalous conditions. The significance of streaming potential anomalies is greatly enhanced by comparison with the detailed geological and hydrogeological data provided by resistivity imaging surveying. Fieldwork, processing and interpretation of stray currentsurvey are carried out in accordance with Vietnamese standard 9417:2012.