The Renaissance of the Magnetotelluric Method: Focus on Land Exploration in Brazil

The 10th Bid Round of the National Petroleum Agency (ANP) for oil and gas exploration in Brazil offered only blocks on onshore basins, most of them still of frontier character and very large. The need to explore these areas also renewed interest in non-seismic methods which are able to survey these large areas quickly and provide important information on the interesting areas to design and undergo further exploration. These methods are also less expensive, noninvasive and the methodologies pose little or no<br>environmental impact. These are important features, if we consider that most of the operators of onshore blocks are small independent companies and that the environmental agency (IBAMA) imposes severe restrictions to methods that cause potential impacts.<br>The Magnetotelluric (MT) method is a powerful frequencydomain electromagnetic technique that provides a resistivity model of the subsurface of the earth at depth. MT data acquisition is fast, environmentally friendly and provides the structural and stratigraphic information needed to explore these large onshore basins. For these reasons, we recently experienced renewed interest in the use of the MT method in Brazil. In this paper, we show real data and modeling examples for different basins in Brazil and explain how these data can help improve the knowledge of Brazilian basins. This improved knowledge complements other geophysical data, indicates interesting areas and allow a better design of a high resolution survey, such as seismic data acquisition.