Brazil has an active offshore oil program and is seeing a dramatic increase in interest as demonstrated by the 11th round lease sale.
Challenges presented by deep water, salt and complex geology result in extremely high finding costs and drive innovative companies to new technologies. Starting in 2011, Petrobras and EMGS invested in the acquisition of over 15,000 km2 of 3D EM data across several basins.
EMGS acquired EM data over several prospects in the Sergipe Alagoas basin. The majority of the surveys were wide azimuth 3D and the initial results presented here are from unconstrained anisotropic 3D inversions. No seismic data or resistivity logs were included to allow for an unbiased evaluation.
The results from an early processing stage can be used to review seismically derived drilling locations, resulting in more informed drill-drop decisions or revised well locations. The absence of false negatives (non-resistive and commercial) in Brazil and around the world illustrates the potential of using 3D EM in drill-drop decisions. The resistive anomaly SSE of 1-SES-173 could indicate remaining exploration potential despite the negative well result. In these examples, 3D EM adds value to seismically derived prospects by decreasing exploration uncertainty and increasing the probability of success.
It should be noted that not all EM anomalies are associated with commercial hydrocarbon volumes. Therefore, further work is required to thoroughly explain all the observed features. An integrated interpretation study including geology, seismic and petrophysical data with 3D EM will help to discriminate commercial volumes from non-hydrocarbon events.