The pre-salt
Located in an area of approximately 800 km in length and 200 km in width in the territorial sea between the states of Santa Catarina and Espírito Santo, the Pre-salt Polygon is among the most important discoveries of oil and natural gas in recent years.
The total depth – distance between sea surface and the oil reservoirs below the salt layer – can reach up to 7,000 meters. Reserves are composed of large accumulations of high-quality light oil featuring high commercial value.
Pre-salt oilfield production rates are substantial. Daily production rates have increased from 41,000 barrels per day (bpd) in 2010 to 1.41 million bpd in 2018, or about 34-fold.
Brazil’s pre-salt oilfields are today among the largest producers globally (see chart below).
In the current pricing environment, a major challenge facing pre-salt operators is to reconcile cost reduction and increased oil well productivity on the one hand, with operational and environmental safety on the other.
The pre-salt discoveries have further established Brazil as a leading player in the global energy industry, and are providing important inputs for Brazil’s economic development.
The origin of the pre-salt
The pre-salt is a sequence of sedimentary rocks formed more than 100 million years ago, following the break-up of the old continent Gondwana, generating the regions currently identified as South America and Africa.
Great depressions were formed between the two currently existing continents, originating great lakes, which accumulated large amounts of organic matter in their deeper regions, mainly from microscopic algae. Such organic matter combined with sediments to make up the pre-salt oil and gas generating rocks. After a process featuring high temperatures and pressure, the organic matter was converted into oil and gas, in a process called “generation”.
In the shallower parts of the lakes, in large lacustrine islands, calcareous shells (the coquinas) and, later, stromatolites – which are a type of seaweed that originates calcareous rocks – were accumulated. These two types of deposits constitute the main pre-salt reservoirs.
Following the above described process, the great lakes, originally lacustrine systems, were connected to the oceans, becoming a restricted marine system and leading to the formation of an extensive gulf. Due to the period’s prevailing arid climate (the Aptian), intense seawater evaporation, which invaded these lake depressions, resulted in the accumulation of a thick layer of salt that worked as a seal to prevent the oil from escaping to the surface.