Electro magnetic (EM)

Marine Electromagnetic seabed surveys are used to map subsurface resistivity in order to locate hydrocarbon reservoirs which are normally highly resistive.

The controlled source (CSEM) technique employs a powerful low frequency (typically 0.1-10Hz) source close to the seafloor with an array of detectors lying on the seabed, to map subsurface resistive layers.

In resistive layers, such as a hydrocarbon reservoir, the magnetic and electric field attenuation is lower than in the surrounding water saturated sediments. Electromagnetic surveys can therefore potentially distinguish between water filled and hydrocarbon filled reservoirs, and can also be used to detect Basalt, Carbonates and Salt. EM complements information derived from seismic methods. Water depth has a strong influence on the measured signal due to the airwave effect generated at the sea-air interface.

New acquisition and processing methods are being developed for shallow water applications and also to improve the vertical and lateral resolution of the EM method.

back to top