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Geological History of the Campos Basin

The Campos Basin – with its area of around 100,000 square kilometers located on the northern coast of Rio de Janeiro state and southern coast of Espírito Santo – is a geologically rich and strategic region for oil exploration. Over the years, several oil fields have been discovered and operated in this area, each one with its own geological history and distinct characteristics.

The history of the formation of the Campos Basin is part of the context of the fragmentation of the supercontinent known as Gondwana, when the African and South American continents began to move apart around 130 million years ago. In the first stages of this continental rupture, a major magmatic event occurred that formed thick layers of volcanic rock which, added to the pre-existing crystalline shield, is known as basement (in dark gray).

As the continents separated, large lakes formed. In the deep regions, clay and organic remains sedimented, resulting in the formation of shales abundant in organic matter. Over millions of years, under conditions of high pressure and temperature, these shales underwent physical–chemical transformations, resulting in the creation of hydrocarbons. In the shallow regions of the lakes, carbonate rocks were formed, which would later become the pre-salt reservoir rocks (in blue). The migration of oil occurred through faults and fractures, to the traps located under the salt, forming the pre‑salt reservoirs (in black), as found in the Albacora Leste, Itaipu and Wahoo fields.

With the continued break-up of Gondwana, there were marine incursions that introduced salts into the region, transforming the lakes into saline environments. During periods of aridity, these lakes repeatedly evaporated, resulting in the formation of the salt layer that later sealed off the pre-salt petroleum system. With the deposition of the overlapping layers, the salt (in white) underwent deformations, due to its plastic behavior across geological time, until reaching its current structural configuration of domes and diapirs.

In the first stage of formation of the Atlantic Ocean, in a shallow marine environment, several types of sediments close to the coast were deposited in the Campos Basin. This period was marked by the formation of carbonate platforms (in blue‑green), such as those found in the Polvo and Tubarão Martelo reservoirs.

In periods of high sediment input or low sea level, deposition of continental sediments occurred in deep waters. The deposition of turbidite sandstones (in yellow) occurs through submarine channels that carry sediments from the continental shelf to abyssal portions of the oceans. The reservoirs found in the Albacora Leste, Frade and Polvo fields are the result of this sedimentation process that took place from the end of the Cretaceous period (in green) and Paleocene epoch (in light gray) up to the Miocene epoch (in dark brown). From the Pliocene epoch (in light brown) to the present day, mainly clay and turbidite sedimentation has occurred.

The PRIO fields, with their distinct geological ages and reservoir characteristics, represent the complexity and geological richness of the Campos Basin. By developing and understanding their geology, we can better take advantage of the oil resources of these fields, thus contributing to the economic and energy development of the region and the nation.