oa Utilizing Impressed Current Cathodic Protection as the Source for Electromagnetic Exploration

Central Europe is criss-crossed by pipelines to transport water, gas and oil. Metal pipelines are routinely protected against electrochemical corrosion with a coating supplemented with an impressed current cathodic protection (ICCP) system. For pipeline integrity tests, the rectified injection current is temporarily switched on and off. The switching scheme effectively generates time-varying electrical currents and induces secondary electric and magnetic fields in the subsurface, which decay spatially and temporally as a function of subsurface electrical resistivity. Here, we describe our first attempts to measure and to analyze the induced electromagnetic fields generated by switched cathodic protection currents in order to determine the subsurface electrical resistivity structure in the upper (few) kilometers depth range. This approach is closely related to controlled source electromagnetics. It may provide a cheap complement to existing electromagnetic geophysical sounding techniques, which is applicable in noisy environments without facing the logistical challenge of the installation a strong current source in the field. The methodology can aid in geophysical subsurface reconnaissance addressed in the exploration and monitoring of resources, reservoirs and geological storages.