Electromagnetic technology (EM)


EM  is a broad term and refers to a number of different things. When we use the term, we refer to a specific methodology called CSEM (controlled source electromagnetic sounding) which is a remote surveying technique that enables measurements of resistivity contrasts in the subsurface. 


In relation to oil and gas exploration, hydrocarbons are resistive while surrounding rocks are typically, but not always, conductive. This creates a resistivity contrast that can be mapped using CSEM techniques. EM data are complementary to seismic data. Whereas seismic data can identify structures that may contain hydrocarbons, EM data tell us something about the fluids within the structures.

In marine settings, EM receivers containing electric antennae and magnetic coils are placed on the seabed. A source is towed above the receivers, emitting electromagnetic energy with low frequency. Energy from the source propagates (diffuses) into the subsurface. If there are no resistivity contrasts present, the energy will gradually be attenuated and disappear. If resistivity contrasts are present (such as that caused by an oil-filled sandstone), EM energy will propagate back to the sea floor where it is recorded by receivers. The recorded information can be processed to create detailed charts of subsurface resistivity distribution. (Source: Rocksource).

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