Abstract

Oil and gas exploration started in the Santos Basin of Brazil during the 1970s. After almost 25 years of drilling 102 dry and subcommercial exploration wells, the exploration campaigns came to a near halt. With the opening of the Brazilian petroleum market in 1997, the National Agency of Petroleum, Natural Gas and Biofuels (ANP) was founded, and exploration in the basin resumed. The years between 1999 and 2004 saw an increase in the exploration effort of major oil companies, including ExxonMobil, Petrobras, Shell, British Gas, Galp, and Eni, among others. The new drilling campaign added 65 exploration wells in only six years. However, the oil discovery success ratio was below 5%. The lessons learned were significant, showing that the search for Tertiary and Upper Cretaceous turbidites of the Santos Basin would not be as successful as in the Campos Basin. Furthermore, the turbidite reservoir paradigm hindered the adoption of new and more productive paradigms—in particular, the directive to “Go Deep.”

With the advancement of molecular geochemistry and deep-water seismic and 3-D petroleum system modeling technology, the incredible journey from near failure changed the fate of the Santos Basin to a huge success. In 2006, the Tupi oil field which targeted a new pre-salt play concept, encountered good-quality oil sourced by lacustrine calcareous black shales of the rift-upper Barremian Itapema Formation source rock system that accumulated in more than 400 m, thick-net-pay microbialite reservoir in the sag-mid-to-late Aptian system.

In the following years, several giant oil fields, utilizing the same play concept, were discovered in the basin, including Sapinhoa, Búzios, and Mero. These fields showed similar reservoir performance to the Tupi Field, which had more than 30 wells producing more than 25,000 bbl/day, and some of them producing up to 45,000 bbl/day (e.g., 1-BRSA-1305-RJS). In December 2019, the Santos Basin pre-salt system contained more recoverable reserves than all other Brazilian sedimentary basins combined.

This chapter describes how the petroleum system approach using rock and oil samples from the Santos Basin supports the dismantling of previous paradigms and the creation of new ones that resulted in the immense success of Santos Basin exploration. This work is based on the application of the petroleum system concept from source to trap, integrated with 3-D modeling and recent results of oil and gas production data from the largest oil fields found to date in the Santos Basin.