Processing and inversion of marine electromagnetic data

Marine electromagnetic (EM) exploration is a new geophysical tool for locating off-shore hydrocarbon reservoirs. The principle of electromagnetic seabed logging exploits the large resistivity contrast known to exist from standard borehole logging between oil or gas reservoirs and surrounding water-filled sediments. In the presence of hydrocarbons, signals are refracted back to the seabed where they are recorded. In shallow water, however, electromagnetic exploration is complicated by source-excited waves which have been reflected at the sea surface or have travelled in the air and been refracted down to the receivers. The project consists of three Ph.D.-projects focused on improved data processing, modeling and inversion: 1. Attenuation of sea-surface e ffects. Using techniques similar to surface-related multiple attenuation in seismics, the air wave and multiple reflections in the water layer can be attenuated. 2. Asymptotic modelling methods. New electromagnetic modeling tools that enable accurate det ection and identification of waves refracted in high resistive layers will be developed. Three-dimensional effects can be modelled using Kirchhoff-type surface integrals. 3. Joint inversion of seismic and EM data. By combining seismic (streamer or OBS) d ata with EM data we want to develop a method for the detection of high pressure and the presence of hydrocarbons. We may use both a controlled low-frequency source and the magneto-telluric signal in the inversion.