Integrated mCSEM Interpretation — Success Stories from the Brazilian Deepwaters

Zerilli, Andrea¹
 Buonora, Marco P.²
 Labruzzo, Tiziano¹
 Rodrigues, Luiz F.³

¹Brazil Technology Center, Schlumberger, Rio de Janeiro, Brazil.
²GEOF/MP, Petrobras E&P, Rio de Janeiro, Brazil.
³IABS/PN, Petrobras E&P, Rio de Janeiro, Brazil.

In recent years marine Controlled Source Electromagnetics (mCSEM) has driven the attention of an increasing number of operators due to its sensitivity to map resistive structures (such as hydrocarbon reservoirs) beneath the ocean bottom, and successful case studies have been reported.

An extensive mCSEM program was performed as part of a co-operation project between Petrobras and Schlumberger. The mCSEM data were acquired as a feasibility and calibration study; provide state of the art data that would lead to a realistic view of the technique’s strengths and limitations when applied to the Brazilian deep offshore and to bring new insights toward the development of novel and cost effective applications.

The mCSEM acquisition program covered distinct areas where water depths range from approximately 1000 to more than 2000 meters. The areas host producing oil reservoirs and a number of exploration prospects previously identified from 2D and 3D seismic. The areas are characterized by complex settings that challenge seismic interpretation. Accounting for the complex geology represents a technical challenge for mCSEM data interpretation.

To confront these interpretation difficulties, we applied an advanced processing and interpretation workflow based on: accurate 3D data processing and integrated interpretation.
Data interpretation proceeded in stages. Processed multi-component field data were normalized using modeled reference background fields. The reference background fields were computed by combining the detailed layering from available borehole measurements into reduced geoelectric sections and constrained by seismic depth models.

Multi-component E and H responses were computed for these complex models using fast multi-dimensional fully anisotropic finite-difference frequency domain approaches. The mCSEM data were also interpreted using a new fast 2.5D anisotropic inversion method where the model parameters are based on interfaces known from seismic interpretation in depth.

We show that the application of the new integrated interpretation workflow strengthens our understanding of the entire EM response and increase our confidence about the resistivity at the reservoir(s) level. The mCSEM response of the hydrocarbon reservoirs known to be present in the survey areas yield anomalies that can be clearly imaged and there are evident correlations between the anomalies and the reservoirs.