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Gondwana's Oil

If you look at a map of the world, the coastlines of Africa and South America seem to fit together perfectly, like pieces of a jigsaw puzzle, a fact that illustrates their geological history. Around 120 million years ago both continents were part of a super continent called Gondwana, which was split by the Atlantic Ocean, leaving very similar coastal sediment on both sides of the ocean. This has led geologists to believe that the oil deposits found in the Brazilian pre-salt layer could be mirrored on the other side of the ocean.
The concept of Gondwana was first suggested by palaeontologists, who found fossils of species such as Mesosaurus, a fresh water reptile, on both sides of the South Atlantic, the only possible explanation being that both continents had at some time been joined. Geologists also found the same types of rock and structural patterns, but no one was yet able to explain how South America and Africa broke apart.

Earth dynamics

It was not until the 60s that a scientific explanation was put forward, as Marcos Mozetic, geologist and Repsol's Executive Director for Exploration, explains Marcos Mozetic, "It was based on plate tectonics, a theory that was as revolutionary for geologists as Darwin's theory was for biologists."
Plate tectonics explains why the earth's crust moves. The crust, which lies on a flexible layer, called the mantle, is more rigid and is divided into tectonic plates, and these are in constant motion. When it was first introduced, the theory met with strong opposition. "We all want to live on stable ground, and we don't want to hear that the place where we live is moving every day", jokes Mozetic. Tectonic plates move at a rate of about 2.5 cm a year, about the same length your fingernails grow in the same time.

"Suddenly, everything fell into place, and we understood how mountains and oceans came into existence, and what caused volcanoes and earthquakes. And one aspect of particular interest to those of us involved in oil exploration: why sedimentary basins exist, which is where hydrocarbons are found".

Gondwana breaks up

Around 128 million years ago, in the Early Cretaceous, the African and South American plates started to drift apart. We now know that between what is now Brazil and East Africa a gigantic salt water lake formed in which conditions were ideal for creating and conserving oil: enclosed, anoxic waters, deposits of organic matter, and salt to preserve the formula.
"The next event was the opening up of the Atlantic Ocean", continues Mozetic, "but the salt had already been deposited on the ocean bed. Salt is completely waterproof, and the best medium for preserving oil."

Salt, oil's best ally

"Until recently, the question was: what's the difference between the Near East and other oil-rich countries? Today we know it is salt. Iran, Iraq, Saudi Arabia… all have a large mantle of salt that preserved much of their oil deposits, preventing them from degrading and draining away. And the same is true here. The pre-salt layer is interesting because all the oil created lies below it. The problem is finding it and bringing it to the surface."
Repsol geologists now want to take what they have learnt in the ocean depths of Brazil to the east coast of Africa, where in recent years the company has made some of the most important oil and gas finds in the world. The technological challenge is enormous. Take as an example Repsol's latest important discovery in the Brazilian pre-salt layer, where the oil lies under more than 2,000 metres of water.

There, the geologists' hypotheses have been confirmed: "Technology has been decisive in Brazil - the possibility of exploring far out to sea, but also the certainty that the right conditions were to be found there". Until the 70s, the centres of marine basins were not thought to be prospective. But then, the way in which good oil-storing sediment is taken from the coast to the seabed was discovered "And that is what really changed oil prospection in Brazil".

East Africa also has its pre-salt layer

Now, all eyes are on the African coast. "Why are we there? We know that large deposits have been discovered in Brazil, and there are also large deposits in the Niger delta and in Angola. However, the outlook has changed with the discoveries made in the last 10 years, with the advent of deep sea pre-salt layer exploration".
The answer lies out to sea, on continental shelves. Prospection is focussed on the areas of Africa situated opposite the Santos and Campos basins (Brazil) before Gondwana broke up. Today, this is Angola and the south coast of Gabon. "There are strong similarities between the seismic images of South America and Africa, and that is why we think that a volume similar to the 45 billion barrels found in Brazil could be found there".

Repsol has already won three of the eleven pre-salt blocks awarded by Angola. All three are situated in the Kwanza basin, an area that geologists see as a prolongation of its oil-rich twin, the Santos basin in Brazil. The US geological service has estimated that Angola could hold at least 30 billion barrels of oil, equivalent to the resources of Nigeria or Qatar. In the words of Marcos Mozetic, "We have tested our subsaline model in Brazil, and we got great results. So this is obviously a concept that merits further development".

Finding tomorrow's oil

The era of easy oil is over, and now we have to find our oil in increasingly obscure, deep and inaccessible areas. Exploration is based on calculations made by geologists, and studying the earth’s history helps them know what to look for and where to find it. "We try to use geology to add to our knowledge, although we cannot give complete assurances, because the risks are always there". Thanks to this knowledge, the oil industry has made enormous progress in recent years. 
Theories such as plate tectonics are still being used to an advantage. Geologists know that Africa is splitting into two, and that the eastern side is slowly separating from the main continent around the area of the great lakes. A new fracture is already opening up, giving rise to the same conditions that produced oil in other parts of the earth. "We are at a stage where "bedrock" can easily be accumulated, and this can produce oil. There are large lakes, anoxic environment, and preservation of organic matter at a deep enough level for oil to be created. This is why Uganda has oil".

"This is an interesting time", concludes Mozetic, "when a theory that was still under discussion in the 60s has now been proved, and all the initial hypotheses have been borne out in places such as Uganda". Gondwana will take millions of years to split apart again, but the oil is already being produced.
Last updated: June 2011