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Rocks of the Devonian, possible source of hydrocarbon reserves in the face of future scarceness

Given their location, and exploration in other potential regions, such as the basin of the eastern Colombian plains, they may be an alternative for the production of hydrocarbons that, according to the Colombian Ministry of Mines, would be enough to cover the internal demand up to the year 2029.

Although Colombia is progressing towards an energy transition with renewable sources, it is still a country that depends on energy-mining resources with conventional extraction forms.

One of these resources is hydrocarbons, which come from layers of organic matter, resulting from the decantation on the ocean floor of plant, animal, bacteria, and sand material for millions of years.

When oil companies drill looking for hydrocarbons they are generally inside the bedrock where they need to assess different elements, such as if in effect that are in oil-generating rocks, that the temperatures allow hydrocarbons to move easily through them, if the rock is porous and permeable, and if the product may be sealed and trapped to avoid it from being lost.

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Despite this, in July of 2021, the Ministry of Mines deemed that the oil reserves would only last until 2026, and the gas reserves to 2029, meaning that after this time, we would need to import more oil and gas to cover our internal demand.

Currently, much of the geology in Colombia has been around exploiting mining and oil resources, and exploration has been focused mainly on Mesozoic rock–known as the dinosaur era– that ended 66 million years ago.

Although there are other periods, such as the Paleozoic, which precedes the Mesozoic, characterized for being an era where invertebrates diversified in the oceans and the plants, amphibians and reptiles moved to the land, this period has not been studied as much, or has the records of oil exploration of its rocks, as the following eras.

One of the main reasons is that these rocks are generally found in such deep ocean floors that it is a great risk and large economic investment, compared to rocks nearer to the surface belonging to other periods. However, the volume of hydrocarbons that may be generated with Paleozoic rock is important, taking into account the need to incorporate reserves for the internal demand.

In face of this Universidad Nacional de Colombia (UNal) Researcher andM. Sc. in Sciences - Geology Andrés Felipe Pastor Chacón, set out to discover if in Colombia he could find Devonian era hydrocarbon generating rocks –when there are records of the appearance of the first forests– belonging to the Paleozoic era, that could be used to include them in future reserves of this product for the country.

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“Then the idea came up. If hydrocarbons were generated in areas close to Colombia, such as in Bolivia and Brazil, where there are rocks of similar age, why not assess the possibility of finding hydrocarbons in the rock of this era in Colombia?” said Pastor.

The problem of depending on resources

After the predictions of the Ministry of Mines, the country needs to cover the internal hydrocarbon demand, so the Government is implementing a strategy that goes in four directions. The first one is directed toward exploring and producing hydrocarbons in offshore and northern basins of the country, especially Cartagena, Montería, and the Caribbean to find new resources. A second strategy is related to boosting reservoirs in hydrocarbon-generating rock that would require non-conventional extraction techniques such as fracking. The third one is promoting and strengthening research to develop technologies of improved recovery, and the fourth strategy (already in progress and in which Pastor is working towards his M.Sc.) is related to increasing the number of reserves in continental basins of several geographic locations in Colombia which are in advanced exploitation status, i.e. that have been historically drilled.

“After a statistical modeling that allowed us to go back in time and imagine how this place would be if the rock would comply with all the conditions, their research showed that all the rock from the Devonian, had the potential in their time to be hydrocarbon generating rocks, although at this time this rock is becoming depleted,” said Pastor.

According to the researcher, although the rock of study does not show any current records as a generating rock, that does not mean that in the past or another part of the country there aren’t rocks with this potential.

According to Pastor, close to 8.3% of the oil generated in the world comes from these types of rocks from producing basins of countries such as the United States, Peru, Bolivia, and the Arabian Peninsula.

Province of Boyacá, the study area

The project was focused at the Floresta Massif, in the municipalities of Floresta and Busbanzá in the Province of Boyacá, with Devonian period rock outcrops, known as the Floresta Formation, where different types of direct, and indirect techniques were used to assess its potential as hydrocarbon generators.

“The indirect technique is a sedimentological description, where the geologist visits the field and takes echelons of rocks, measuring meter by meter and describing the features and comparing with other records to describe how the rock was formed. For instance, making these observations and measurements, they can interpret if a rock is deposited in a marine or continental environment,” said the researcher.

Pastor says that the direct measurement technique consists of applying analytical techniques to rock samples to assess their potential and measuring the total organic carbon, while other techniques also direct, and known as pyrolysis, consists of measuring the number of free hydrocarbons and potential hydrocarbons after submitting them to temperatures above 400° C.

“The research project allows us to contribute information, not only in terms of direct measurements that can be applied, for instance of paleontological museums of the area and that will show better preservation and identification of new species for science. This, given the paleontological tradition and wealth of the municipality of Floresta, where the first paleontological research goes back 90 years and there are important fossils for science that allow speaking of continental and ocean positions during the Devonian period”.

Consejo Editorial