Three-dimensional electromagnetic holographic imaging in active monitoring of sea-bottom geoelectrical structures

We consider an application of the ideas of electromagnetic (EM) holography/migration to the interpretation of a typical marine controlled-source EM (MCSEM) survey, which consists of a set of sea-bottom receivers and a moving electrical bipole transmitter. The three-dimensional interpretation of MCSEM data is a very challenging problem because of the enormous amount of computations required in the case of the multitransmitter and multireceiver data acquisition systems used in these surveys. At the same time, we show that the MCSEM surveys with their dense system of transmitters and receivers are extremely well suited for application of the holography/migration method. The combined EM signal in the receivers forms a broadband EM “hologram” of the sea-bottom geological target. As in optical and radiowave holography, we can reconstruct the volume image of the geological target by “illuminating” this EM hologram with the reference signal. The principles of holography/migration imaging formulated in this chapter are tested on typical models of a sea-bottom petroleum reservoir. We also apply this new technique to the interpretation of an MCSEM survey conducted in the Troll West gas province, offshore from Norway.