Offshore electromagnetic methods have proven to be a useful addition to seismic exploration. But next to the need to be imbedded in a seismic analysis, the main restriction was its limited penetration depth. To change this limit and its restriction to certain geological settings, we set out to improve the existing system a hundred-fold. To achieve this goal the positioning of the multi-component seabed receivers and their noise floor was improved 10-fold. Additionally, the source system was completely redesigned to allow for amplitudes up to 10 000 amperes. The system is designed to record beyond 3 km water depth and can reach targets down to 4.5 km beneath the seabed. We have tested the new system together with the standard CSEM equipment in several field tests in the Norwegian Sea and the results shown here confirm the envisioned improvements, which open most areas worldwide for CSEM exploration.

This presentation discusses the inversion of controlled source electromagnetic data in complex geological settings. The inversion is based on a fast 3D modeling method combined with local optimization techniques and a least-squares misfit. The method can further be characterized by its decoupling of inversion and computational grids, allowing multiple frequencies to be inverted simultaneously without additional computational effort. This decoupling also proves beneficial in identifying the depth of anomalies. Finally, a simple exponential depth weighting is used to improve on the rate of convergence. To demonstrate the capabilities of the method, inversions of synthetic data is shown that represents a realistic, fairly complex geology.

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