Imageamento Bidimensional de IP-Resistividade Com Sistema EM Multifrequência na Exploração e Monitoramento de Reservatórios de Petróleo

In this work we discuss the results of two experiments, performed using a new prototype of the multi-frequency EM method proposed by Dias (1968), over on-shore know oil fields of Recôncavo and Espírito Santo basins. The processed EM results are presented as 2D images of apparent resistivity and induced polarization parameter using a consistent plotting procedure developed by Dias and Sato (1981) and improved by Machado et al. (2009). Four 3.5 km transects were surveyed across Araças area to delineate the extent of an oil occurrence within sandstones of São Sebastião Formation, containing fresh to saline ground waters. Eight 5.5 km transects were performed across São Mateus area to map its underground geological structure up to 2.4 km depth. The electrical images, controlled by seismic and well log data, allow to recognize the following features: (i) the interfaces between lithologies of strong electrical contrasts as shales, sandstones, limestones and salt rocks; (ii) an inferred oil-water contact in some São Sebastião sandstones; (iii) sub vertical zones of large resistivity and IP contrasts, representing faults and fracture zones filled with conducting minerals or hydrocarbon residues. These results stretchen the possibility to use the multi-frequency EM method in the direct detection of hydrocarbons, as well as for monitoring the performance of injection procedures for enhanced oil recovery.