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Magnetotellurics (MT) and Controlled Source Electromagnetics (CSEM)


Magnetotellurics (MT)- the electrical method specialty of AOA measures the natural very low frequency electromagnetic energy field of the earth to determine subsurface resistivity features. The field components are influenced by the resistivity of the geologic formations beneath the measurement site, and the resistivity of the subsurface can be computed from the EM field measurements. AMT (Audio frequency MT) is an extension of MT to higher frequencies to investigate the shallow subsurface. MMT (Marine MT) is the extension of MT into the offshore environment.
Geologic structure and stratigraphy can be interpreted based on the knowledge of subsurface resistivity distribution. AOA is a specialist in the application of MT to complex exploration problems using sophisticated tools such as multidimensional modeling, inversion of realistic geologic structures, and full integration with seismic data to obtain MT derived velocity models. Applications emphasize exploration areas where seismic data is poor or ambiguous, or where a knowledge of subsurface resistivity is able to resolve seismic ambiguities.
Audio Frequency MT (AMT) is a higher frequency MT technology, often used for mining and engineering applications and in resolving special seismic statics problems coupled with advanced resistivity imaging, refraction tomography and high resolution seismic data. AMT is also used with conventional MT to provide shallow information where needed.

Marine MT and CSEM Receiver

Marine MT – The use of MT in the marine environment brought a new non-seismic imaging tool to the offshore oil industry. Beginning in 1995, surveys have been performed with support by AOA for research and development as part of an industry consortium led by the Scripps Institution for Oceanography, and by AOA for commercial exploration objectives on behalf of industry clients. Surveys have also been performed for non-exploration objectives such as near-seafloor anisotropy, fluid-filled fractures in shallow hard-rock areas, and variations in shallow resistivity that may relate to changes in sediment lithology. The identification and characterization of methane hydrate, an important geohazard and a potential energy resource, is a current area of study at AOA.

Marine Controlled Source Electromagnetics (CSEM) - Marine CSEM is an active-source electrical method whereby, in the marine environment, an array of autonomous EM receivers are deployed on the sea floor and an EM energy source, usually an electric dipole, is towed in the vicinity of the receiver array. The method is sensitive to relatively resistive formations and features, and can be used to characterize the section below the mudline based on resistivity and resistivity variations.  Targets may include shallow methane hydrate, fresh water outflows and sediments of varying composition.  CSEM may assist in characterizing reservoir fluids.
Let AOA assist you with your exploration objectives.