In a hydrocarbon exploration workflow, marine controlled-source electromagnetic (mCSEM) data are usually acquired after seismic interpretation for prospect identification and close-to-the-drilling decision making. Therefore, the mCSEM interpreter must provide quick answers to the asset teams in a way that the EM interpretation can add value to that decision. To achieve that goal, Petrobras developed a fast-track mCSEM interpretation workflow that consists in identifying anomalies in the mCSEM data set by frequency normalization, and then performing 1D CMP inversions followed by 2.5D polygonal inversions. The proposed workflow was successfully applied to several mCSEM surveys offshore Brazil. We evaluated an application in a complex geologic setting where the reservoir dips toward allochthonous salt. The reservoir appears as a flat spot in the seismic section, but with no significant amplitude variation with offset response. The mCSEM analysis confirmed the seismic anomaly and extended it northward. Two drilled wells corroborated the mCSEM interpretation.

Marine-controlled source electromagnetics (CSEM) have been extensively applied to various exploration scenarios worldwide. However, its perceived value and cost relative to seismic and the scarcity of realistic case studies have limited the industry’s interest in time-lapse reservoir-monitoring (4D) applications. A feasible way to make demand for CSEM for 4D-monitoring programs would be to increase the value of information and reduce survey costs by performing joint operations where seismic and CSEM data are acquired during the same survey and at equivalent spatial densities. To this end, we propose a new multiphysics ocean-bottom nodes (OBN) concept and show the industry that CSEM can be a cost efficient and effective integrators to 4D seismic projects. To this end, we conducted a feasibility study demonstrating that horizontal magnetic field components have the required sensitivities and can be used instead of horizontal electric field components in mapping the 3D resistivity distribution and 4D fluid change responses in a given reservoir. This makes engineering a new OBN class simpler and cheaper, as various miniaturized magnetic field sensors are available off-the-shelf or readily working along with packaging and coupling solutions.

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The controlled source electromagnetic (CSEM) method is frequently used as a risk reduction tool in hydrocarbon exploration. This paper aims to provide a comprehensive historical review of the CSEM method’s twenty-year history in the Brazilian continental margin. Since 2003, we have significantly improved our understanding of CSEM resistivity data across various geological scenarios. This review presents a roadmap of the technical advancements in acquisition design and interpretation techniques. As a result, our understanding of the methodology has broadened from traditional to more general use, such as salt imaging, gas hydrates, geohazard mapping, and reservoir characterization. Finally, we indicate the potential upcoming CSEM applications in new energy resources and carbon capture and storage.