Utilizing impressed cathodic corrosion protection currents to determine the electrical conductivity in the upper few kilometers of the earth (PipelineEM)

Basic data for this project

Description

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 a cathodic protection system. For pipeline integrity tests, the DC 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 propose 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. We concentrate on a test site in the Sauerland, where we combine electric field array measurements of the induced electromagnetic field with detailed studies of the current distribution in the pipeline, i.e. the source current. Our cooperation partners from the RWE Westfalen-Weser-Ems Netzservice GmbH will provide results from pipeline integrity surveys conducted recently in the test area, as well as access to the technical installations of the cathodic protection system. In combination with additional DC electrical and magnetostatic measurements, this will allow us to determine the source current. For an interpretation of the array measurements, we will consider the transient time domain as well as the frequency domain response of the earth to the current injected into a pipeline structure and leaking inductively and, at grounding points and coating defects, galvanically into the ground. This approach is closely related to controlled source electromagnetics, and 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.