Exploring with Controlled Source Electro-Magnetic (CSEM) methods: from 2D profiling to 3D multi-azimuth surveying

Subsurface resistivity mapping based on Controlled Source Electromagnetic (CSEM) measurements is an attractive technology for exploration as it offers the possibility to distinguish between hydrocarbon and brine bearing prospects where conventional seismic methods prove inconclusive. In Shell, we have applied the CSEM method on a worldwide scale since 2003 to both de-risking and portfolio polarization. Early on in the development of the CSEM technique some compelling results were obtained with single 2D profiles over prospects. Unfortunately, the lack of subsurface coverage of this type of acquisition often leads to ambiguous results because the Earth rarely satisfies the 2D assumption at the scale of the CSEM experiment. To reduce such ambiguities, we have focused efforts on the development of 3D processing and inversion capabilities as well as interpretation workflows that take the complexity of the Earth into account. In this paper, we share some of our motivations behind our approach and illustrate its effectiveness with both real and synthetic data examples.