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The Leading Edge; November 2003; v. 22; no. 11; p. 1127-1129; DOI: 10.1190/1.1634917
© 2003 Society of Exploration Geophysicists
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Shallow electromagnetic exploration for hydrocarbons at Sergipe-Alagoas Basin, Brazil

Paulo de Tarso, L. Menezes and Eutair R. Morais

Universidade do Estado do Rio de Janeiro

Corresponding author: ptarso@uerj.br

The first 20% of the full text of this article appears below.

Brazil covers a large surface area and about 6 436 000 km2, including the continental margin, are covered by sediments. The onshore portion, 4 885 000 km2, is divided into more than 20 Proterozoic, Paleozoic, and Tertiary basins (Figure 1)—most being virtually unexplored or underexplored for oil and gas. Petroleum exploration began in 1954 with the creation of Petrobrás (Brazilian State Oil Company) and implementation of the state monopoly. Exploration has mainly focused on the offshore continental margin. Two major exceptions are Recôncavo and Sergipe-Alagoas basins which have been explored since the 1960s.


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  		Figure 1. Distribution of onshore sedimentary basins in Brazil.

 
In 1997 a new petroleum law opened the country to all segments of the oil industry and created a new government agency—ANP (Agência Nacional de Petróleo)—which is responsible, among other things, for awarding exploration and producing licenses. Since the end of the state monopoly, more than 34 companies have operated in Brazil. In 1999-2002, ANP held four licensing rounds that offered several areas for exploration in almost all onshore sedimentary basins.

The 1997 law requires that all submitted bids be preceded by geologic and geophysical studies. The high cost of onshore exploration justifies the use of shallow geophysical and geochemical methods to reduce the inherent risk and focus the exploration efforts. Recent work has shown that oil reservoirs can be overlain by alteration plumes that can be mapped with geochemistry and/or shallow geophysical surveys. Geochemical prospecting, which has been around since the 1930s, can provide evidence of migration of hydrocarbons because that migration often changed some physical properties of the capping rocks. These changes can, in some cases, be detected by geophysical methods.

The motivation for the work described in this article was to . . . [Full Text of this Article]






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