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The risks of exploring for oil under Lake Kivu

Tuesday June 06 2017
EAKivuWatt

Gas exploration on Lake Kivu. Experts warn that it could trigger a hazardous explosion. PHOTO | CYRIL NDEGEYA

Rwanda and the Democratic Republic of the Congo in April signed a five-year joint exploration agreement for oil under Lake Kivu. But there are extraordinary risks: The lake has a huge amount of gas in its deep waters and could explode, with devastating consequences.

With a surface area of 2,370km² – almost the size of Mauritius – and a maximum depth of 480 metres, Lake Kivu is one of the Great Lakes of Africa. It is the third deepest in Africa, after Lakes Malawi and Tanganyika, all located in East Africa’s Western Rift Valley.

Kivu lies on the border between Rwanda and DRC. While other lakes in the Western Rift Valley are rich in fish species, Kivu is not. There are only 28, compared with over 400 in downstream Lake Tanganyika. Nevertheless, the lake supports an important fisheries industry — based on an introduced sardine native to Lake Tanganyika – yielding over 20,000 tonnes per year.

The Kivu basin is home to two million people, with more than 400 inhabitants per square kilometre. This is one of the highest population densities in the area surrounding the Great Lakes, with several large refugee camps near the shores.

Kivu is an important transport corridor for the informal economic exchange between Rwanda and DR Congo, with steady traffic in produce, fish and domestic goods. It is also a major reservoir providing water for power production downstream on the Ruzizi river.

Density stratification

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Although it has a mean depth of 240 metres, oxygen does not penetrate below 60 metres. This means that only bacteria grow through most of the volume of the lake while fish and other large organisms are restricted to the surface layer.

In common with all deep lakes, Kivu has density stratification: The densest water is found at the bottom and the least dense at the top. Density is a function of temperature and salinity. Cooler and more saline waters are denser.

Unlike most other lakes, Kivu gets warm, saline inflows into the water, enforcing a strong density gradation from bottom to top results in layers of different density and an uncommon temperature structure, where the warmest waters occur at the deepest ends.

Temperatures are affected by inflowing deep springs heated by the active volcanoes that form its northern watershed. But these warm springs are also rich in volcanogenic carbon dioxide and other salts. Because of the salt inputs, there is a very strong and permanent density gradient, with the water deep in the lake trapping dissolved gases such as carbon dioxide and methane.

There are over 60 cubic metres of methane dissolved in the depths of the lake, and it would degas spontaneously if the deep water were significantly displaced upward.

A simple example is the bubbling that occurs when you shake bottle of soda and remove its cap. The cap on Lake Kivu is the density gradient that prevents water from moving upward rapidly and de-gassing into the atmosphere.

READ: Symbion Power to produce 50MW from methane

Rapid de-gassing

But the potential for rapid de-gassing is real, especially in a geologically active region such as the Kivu basin. Volcanoes and earthquakes are common in the Rift Valley.

An example of the risk is illustrated by the 1986 tragedy at Lake Nyos in Cameroon, which released a gas cloud as a result of a landslide, killing more than 1,700 people.

Because of its much greater size and gas content, Kivu has the potential for a cataclysmic gas release. Its peculiar characteristics have led to the creation of a commercial scale methane gas reserve, which Rwanda is beginning to extract to produce electricity for its national grid.

This extraction has the dual benefit of producing electricity and reducing the risk of spontaneous degassing, as it will release the gas from the deep water in a controlled way and gradually reduce the gas pressure over time.

But currently, exploration drilling or commercial extraction of oil would add the risk of an uncontrolled gas release from the gas-rich deep water.

Because the Kivu basin is the highest in altitude of the lakes in the Western Rift Valley, the sediment thicknesses may not be as deep and oil-rich as in the Albert basin or the Lake Tanganyika basin. Nevertheless, there is still interest, as is evident in the recent Rwanda and DRC oil exploration agreement. If seismic exploration identifies positive signs of oil in the sediments under the lake, then exploratory drilling is likely to follow.

Possible explosion

Drilling would be hazardous because it could lead to rapid upwelling of deep water. If a blowout were to occur, the upwelling of oil or gas would displace the currently stable gas rich layers upward until the gas pressure exceeded the hydrostatic pressure at shallower depths, allowing spontaneous de-gassing.

This could release a powerful explosion, due to gas expansion, such as happened on Nyos — but potentially much larger. As elsewhere, oil extraction runs the risk of contamination. This would affect people who depend on the lake for their livelihoods.

These concerns were highlighted at the recent African Great Lakes Conference in Entebbe, but they extend beyond contamination, because Kivu carries much bigger risks than other lakes. These include the potential loss of human life in the surrounding catchment due to the release of carbon dioxide and the destruction of infrastructure by large waves due to the gas expansion.

Of course, oil would bring positive benefits if it is exploited carefully, is well regulated and the economic benefits equitably distributed.

I would advise the exploration teams not to do drill in the lake itself. Shore or land-based drilling would eliminate the risk of disturbing the lake’s density structure. But, even then, care must be taken to avoid possible contamination.

Companies and governments should ensure that there is good baseline data before drilling starts. But eliminating all risks will not be possible in such a geologically active area. Insurance should be sought or bonds posted to guarantee that funds would be available if anything goes wrong.

ALSO READ: Oil boom a threat to region’s wildlife

Robert Hecky is an Emeritus at the Biology Department and Large Lakes Observatory, University of Minnesota, Duluth.

-The Conversation

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