Experience with CSEM offshore southeast Brazil

During 2004 and 2005, Shell Brasil (SBEP) purchased on a spec basis controlled source electromagnetic (CSEM or EM) datasets in the Campos, Santos, and Espirito Santo Basins of southeast Brazil (Figure 1). PGS acquired the 2004 dataset (~1600 km), while Electromagnetic Geoservices (emgs) acquired the 2005 dataset (~1200 km). Shell evaluated the CSEM data over a number of field analogues and prospects, including Shell’s 2002 O-North discovery in the Campos Basin. In the process, we obtained calibration of the technology and a successful pre-drill EM prediction prior to Shell’s Nautilus discovery. In interpreting these large surveys, we also encountered situations where CSEM technology was ineffective. With this experience, we now have a more realistic view of the technique’s strengths and limitations. As a result, we can often use CSEM in an integrated approach to influence prospect portfolio decisions. We are also evaluating new technology to increase the resolving power of EM.