Natural Earth Currents and Electric Logging

CIM Bulletin1962
The influence of natural electric currents, induced in the earth by changes in the earth's magnetic field, on the electric logging of boreholes has not always been recognized. Measurements made with fixed electrodes of changes in the vertical potential gradient in a hole near Calmar, Alberta, have indicated the effect of earth currents related to magnetic disturbances. It is found that appreciable errors in self-potential logging could arise during periods of magnetic storms, but the precise pattern of disturbance in any area seems to depend on the local structural conditions. As the amplitude of the natural earth currents increases toward the a'.lroral zone, it is suggest ed that periods of magnetic disturbance be avoided, if possible, when electric logs are taken in the northern part of the western sedimentary basin.
Keywords: Calmar, earth magnetic field, potential gradient, sedimentary basin, telluric current, Canadian, Conductivity, Electrical, Electrodes, exploration, flow, Logging, Logs, North
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