The Earth’s magnetic field is constantly shifting, influenced by solar plasmas and the molten metals in its outer core. This magnetic field induces low voltage electric currents that flow around the Earth’s crust at and just below the surface, known as tellurics. As the earth spins they flow towards the sun, heading to the equator during the day and to the poles at night.
‘Transient pulses’ are discrete packets of electromagnetic energy which emanate from the earth along the vertical component of the Earth’s magnetic field, perpendicular to the ground. They are caused by passive seismic events underground, and the depth from which they originate is related to their frequency, generally in the range of 200-2200Hz. They occur randomly, but their likelihood is affected by certain conditions such as lightning and seismo-electric potentials within the earth. Critically they are also affected by by redox cells created by vertical hydrocarbon seepages.
ANE is planning a series of aerial Audio Frequency Electromagnetic (AFMAG) surveys to measure these transient pulses which are detectable at low altitudes. Studies carried out over proven producing and proven non-producing geological formations have shown that transient pulses are more frequent when hydrocarbons are present. Algorithms can be used to remove background pulses and identify the depths from which the pulses resulting from hydrocarbon seepage have emanated.
Much like conventional seismic surveying, measurements of how telluric flows behave in the crust can provide evidence of the subsurface architecture. Unlike seismic however, hydrocarbon bearing rock can be differentiated from other similar rocks due to their differing electrical resistivity. Based on the results of the aerial survey, ANE plans to undertake a ground telluric programme to gain more detailed data on interest areas identified.