Rapid Resistivity Imaging Using a Transient Marine CSEM Survey with Two Transmitter Polarizations

The marine electromagnetics group at GEOMAR has recently developed a novel transient marine controlled-source electromagnetic experiment suitable for surveys of small seafloor targets such as mud volcanoes, fluid flow features, gas-hydrate reservoirs and submarine massive sulphide deposits. An electric dipole transmitter is set down by an ROV on the seafloor sequentially in two perpendicular orientations for each transmission station. Two orthogonal horizontal electric field components are recorded on the seafloor by an array of independently deployed nodal receivers. The unique acquisition geometry of the system provides a very rich dataset with two transmitter polarizations. On the other hand, most conventional interpretation schemes are no longer suitable. This paper describes a simple imaging technique, which can be used for a rapid, first-step mapping of seafloor resistivity with this system before resorting to more complicated interpretation methods. The robustness of the approach is demonstrated using a synthetic dataset as well as a real dataset acquired from a mud volcano in the West Nile Delta.