Electromagnetic survey methods, used for decades mainly for mining exploration on land, have burst upon the offshore hydrocarbon exploration scene over the past five years. This move, driven by the costs and challenges associated with the deepwater exploration environment, has left many companies scrambling to understand new and unfamiliar technologies, and has resulted in a sudden expansion of the portfolios of the few “nonseismic” geophysicists left in the oil industry. Of the two main methods, magnetotelluric (MT) surveys are at least somewhat familiar from their use on land as a reconnaissance tool and for problem-solving in areas of poor seismic performance, and to a large extent can be applied to the marine environment in a similar way to their terrestrial counterparts. The other dominant technology, controlled-source electromagnetic (CSEM) sounding, has featured much less in land exploration, but more importantly behaves so very differently in the deepwater marine environment that it might as well be considered a completely separate method. Indeed, this has resulted in the early advocates of its use in offshore exploration creating new (and more marketable) names, such as seabed logging by Statoil and remote reservoir resistivity mapping by ExxonMobil.

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