Schlumberger

Land Magnetotellurics (MT)

Magnetotellurics is a broad-band electromagnetic geophysical technique which uses natural time-dependant variations in the Earth’s magnetic field as the source, and electric fields induced in the earth as output. These data are used to determine (usually via 2D or 3D inversion) the resistivity distribution within the earth to depths of many kilometers. This is then interpreted in terms of lithology.

Under some geological conditions, it is impossible or prohibitively expensive to acquire useful seismic data. These conditions include subthrust plays, areas of volcanic cover, and beneath shallow salt bodies. To MT, the conditions which cause problems to seismic data are largely transparent, and thus the method readily images the subsurface in terms of resistivity. Ideal targets include resistive carbonate reservoirs below shale or flysch, clastic reservoirs below salt bodies. Exploration environments we have worked in include the Alpine thrust belts of Europe and the Middle East; subvolcanic areas in North Africa, the Middle East, and the United States; and subsalt zones in Europe, the Middle East, and the Gulf of Mexico.

The results of an MT survey carried out in Greece are shown on the right, in an area where seismic data obtained and processed with modern techniques gave almost no useful results. The objective was to map the 3D structure of multiple-thrusted carbonate and anhydrite units and the underlying autochthon. This region is an active petroleum exploration area where carbonates can represent both source and reservoir rocks.

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WesternGeco

MT Proves Successful in Problematic Geological Areas

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