Problematic Methane Mining in Lake Kivu
Wednesday, 16. September 2009, 08:22:30
In a post two years ago I featured methane in Lake Kivu.
Lake Kivu contains approximately 55 km3 of dissolved methane gas at a depth of 300 m. Previously, the methane concentration was assumed to be in steady state. However, recent analysis indicates that the methane concentration has increased significantly by 15 to 20% since the 1970s’ measurements. For carbon dioxide, the observed concentration increase was on the order of 10%, but was not statistically significant. The main hypothesis for this increased production of methane is a rise of the nutrient inputs caused by the fast-growing population in the catchment of Lake Kivu. Until 2004, extraction of the gas was done on a small scale, with the extracted gas being used to run boilers at a brewery. As far as large-scale exploitation of this resource is concerned, the Rwandan government is in negotiations with a number of parties to produce methane from the lake. Extraction is said to be cost effective and simple because once the gas rich water is pumped up the dissolved gases (primarily carbon dioxide, hydrogen sulphide and methane) begin to bubble out as the water pressure gets lower. This project is expected to increase Rwanda's energy generation capability by as much as 20 times and will enable Rwanda to sell electricity to neighboring African countries.
So far so well.
Extracting valuable methane from the lake's depths might, however, trigger an outburst of gas that could wash a deadly, suffocating blanket over the 2 million people who live around Kivu's shores.
A group of biochemists warns that if unregulated extraction continues unabated, it could trigger a catastrophic outgassing of carbon dioxide - another dissolved gas abundant in the lake's depths. Such a disaster occurred at Lake Nyos in Cameroon in 1986, killing 1700 people. Kivu contains 300 times more CO2 than Nyos did.
Like Nyos, Lake Kivu is permanently stratified: a deep layer of dense water laden with CO2, methane, salt and nutrients is locked away beneath a surface layer of fresh water. Methane is generated by lake-bed bacteria that feed on a stream of dead algae sinking from the surface. The CO2 enters through volcanic seeps.
The most dangerous practice is pumping waste water into the lake's shallows. If degassed water is dumped at the surface, it sinks, mixing water and salts between the lake's layers. Enough mixing would disrupt the density stratification of the lake, and could bring huge volumes of CO2-rich water to the surface. The pressure reduction would cause the CO2 to bubble out of solution.
Another question is of course “what could happen if the methane is NOT exploited?". Indeed the Government of Rwanda is working with experts to mitigate an imminent explosion of the gases trapped under the surface of Lake Kivu that could cause a serious human catastrophe. Recent reports suggest that the huge amounts of carbon dioxide and highly combustible methane gas trapped under the surface of Lake Kivu could explode soon if not exploited, leading to disastrous effects on the surrounding population. In an interview with the Rwandan newspaper The New Times, Charles Nyirahuku, the Head of Oil and Gas Unit in the Ministry of Infrastructure and Energy, confirmed that indeed the alarm is there but the Ministry is working round the clock with experts to ensure that the fears are mitigated. "Indeed much has been said about the danger and all this time we have been discussing possible mitigating measures. We carried out a comprehensive study and found out that one way to mitigate the danger is to extract the gas. For the moment that is what we are focusing on." (He may be biased of course?)
It is in any case evident that a strict set of rules and regulations has to be followed to ensure that the whole process of extraction is secure so that no explosion is triggered - and the possibility of one is completely eliminated.
Lake Kivu contains approximately 55 km3 of dissolved methane gas at a depth of 300 m. Previously, the methane concentration was assumed to be in steady state. However, recent analysis indicates that the methane concentration has increased significantly by 15 to 20% since the 1970s’ measurements. For carbon dioxide, the observed concentration increase was on the order of 10%, but was not statistically significant. The main hypothesis for this increased production of methane is a rise of the nutrient inputs caused by the fast-growing population in the catchment of Lake Kivu. Until 2004, extraction of the gas was done on a small scale, with the extracted gas being used to run boilers at a brewery. As far as large-scale exploitation of this resource is concerned, the Rwandan government is in negotiations with a number of parties to produce methane from the lake. Extraction is said to be cost effective and simple because once the gas rich water is pumped up the dissolved gases (primarily carbon dioxide, hydrogen sulphide and methane) begin to bubble out as the water pressure gets lower. This project is expected to increase Rwanda's energy generation capability by as much as 20 times and will enable Rwanda to sell electricity to neighboring African countries.So far so well.
Extracting valuable methane from the lake's depths might, however, trigger an outburst of gas that could wash a deadly, suffocating blanket over the 2 million people who live around Kivu's shores.
A group of biochemists warns that if unregulated extraction continues unabated, it could trigger a catastrophic outgassing of carbon dioxide - another dissolved gas abundant in the lake's depths. Such a disaster occurred at Lake Nyos in Cameroon in 1986, killing 1700 people. Kivu contains 300 times more CO2 than Nyos did.
Like Nyos, Lake Kivu is permanently stratified: a deep layer of dense water laden with CO2, methane, salt and nutrients is locked away beneath a surface layer of fresh water. Methane is generated by lake-bed bacteria that feed on a stream of dead algae sinking from the surface. The CO2 enters through volcanic seeps.
The most dangerous practice is pumping waste water into the lake's shallows. If degassed water is dumped at the surface, it sinks, mixing water and salts between the lake's layers. Enough mixing would disrupt the density stratification of the lake, and could bring huge volumes of CO2-rich water to the surface. The pressure reduction would cause the CO2 to bubble out of solution.
Another question is of course “what could happen if the methane is NOT exploited?". Indeed the Government of Rwanda is working with experts to mitigate an imminent explosion of the gases trapped under the surface of Lake Kivu that could cause a serious human catastrophe. Recent reports suggest that the huge amounts of carbon dioxide and highly combustible methane gas trapped under the surface of Lake Kivu could explode soon if not exploited, leading to disastrous effects on the surrounding population. In an interview with the Rwandan newspaper The New Times, Charles Nyirahuku, the Head of Oil and Gas Unit in the Ministry of Infrastructure and Energy, confirmed that indeed the alarm is there but the Ministry is working round the clock with experts to ensure that the fears are mitigated. "Indeed much has been said about the danger and all this time we have been discussing possible mitigating measures. We carried out a comprehensive study and found out that one way to mitigate the danger is to extract the gas. For the moment that is what we are focusing on." (He may be biased of course?)
It is in any case evident that a strict set of rules and regulations has to be followed to ensure that the whole process of extraction is secure so that no explosion is triggered - and the possibility of one is completely eliminated.
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http://www.newscientist.com/article/mg20327254.500-methane-mining-could-trigger-killer-gas-cloud.html?DCMP=OTC-rss&nsref=online-news
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http://allafrica.com/stories/200908280047.html
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http://allafrica.com/stories/200811210816.html
WIDGETIZE
divalent2 # 16. September 2009, 02:42
I could see it possible if there was a gaseous eruption, but it sounds like if that happens, it's all over anyway.
nielsol # 16. September 2009, 08:21
Scientists hypothesize that sufficient volcanic interaction with the lake's bottom water that has high gas concentrations would heat water, force the methane out of the water, spark a methane explosion, and trigger a nearly simultaneous release of carbon dioxide.
I guess that the release of carbon dioxide would kill more people than the methane explosion