Campos Basin

The Campos Basin is a massive sedimentary basin located along the coast of Brazil. It is one of twelve such basins in the country. The basin covers a vast area of the South Atlantic Ocean. A small part of it sits on land near Rio de Janeiro. It is named after the city of Campos dos Goytacazes. Geographically, the basin is defined by two specific boundaries. To the south, the Cabo Frio High separates it from the Santos Basin. To the north, the Vitória High marks the boundary with the Espírito Santo Basin.

The formation of this basin is tied to the breakup of the supercontinent Gondwana. This process began during the Neocomian stage of the Cretaceous period. This occurred between 145 and 130 million years ago. As Gondwana broke apart, it created a sequence of rift basins. These basins eventually became the modern South Atlantic Ocean. The seafloor spreading process moved north toward the Campos Basin during the Early Albian. This happened approximately 112 million years ago.

Geologists have identified five distinct tectonic stages in the Brazilian basins. The first is the pre-rift stage, which lasted from the Jurassic to the Valanginian. Next is the syn-rift stage, occurring from the Hauterivian to the Late Barremian. The third is the sag stage, spanning the Late Barremian to the Late Aptian. This was followed by the post-rift stage during the Early to Middle Albian. Finally, the drift stage began in the Late Albian and continues into the Holocene.

The layers of rock, or stratigraphy, in the basin are very complex. It begins with basalt flows that are about 120 million years old. These are followed by the Lagoa Feia Group. This group includes organic-rich lacustrine green shales, limestones, and sandstones. As the environment changed, marine sediments like evaporites and limestones formed. The Macaé Formation consists of shallow marine limestones. Below the Campos Formation, you can find Namorado turbidite sandstones. Turbidites are deposits that move down slopes in the deep ocean.

Humans began exploring the Campos Basin for oil in 1968. The first exploratory well was drilled in 1971. Discovery of oil fields happened steadily over the following decades. The Garoupa field was found in 1974 in shallow water. The Namorado field was discovered in 1975 at a depth of 150 meters. In 1977, the Enchova Field began its first oil production. The Marlim field, discovered in 1985, is one of the largest. It is located in the northeast in water depths between 300 and 1,000 meters.

The economic scale of the basin is quite large. By the year 2003, there were 41 discovered oil and gas fields. These fields were located at various distances from the coast. They also sat at different water depths. In 2003, daily oil production reached 1.21 million barrels. The total cumulative production by that year was 3.9 billion barrels of oil. There were also 8.5 billion barrels of reserves remaining at that time. In 2010, Petrobras made a new discovery of 65 million barrels near the Barracuda field.

Energy extraction in the basin relies on many different types of reservoirs. These reservoirs include siliciclastic turbidites and fractured basalts. They also include coquinas and calcarenites, which are types of limestone. The Namorado Field is a good example of how these work. Its reservoirs are marine turbidite deposits that cross over the Albian limestone shelf. This field is located at a depth of about 2,500 meters. Understanding these different rock types is essential for finding and reaching the oil.