Lake Kivu Gas Extraction Report on Lake Stability July 2006 Lake Kivu Gas Extraction Report on Lake Stability July 2006 Report no. 62721-0001 Issue no. 0 Date of issue July 12, 2006 Prepared By an expert committee consisting of: George Kling, University of Michigan, USA, [email protected] Sally MacInty re, University of California, Santa Barbara, USA, [email protected] Jørgen S. Steenfelt, COWI, Denmark, [email protected] Finn Hirslund, COWI, Denmark, [email protected] Lake Kivu Gas Extraction 1 Table of Contents 0 Reader's guide 4 1 Executive Summary 5 2 Charge of Expert Committee 8 3 Summary and Recommendations 10 3.1 Background 11 3.2 Potential risks 12 3.3 Gas Reserves and Method of Extraction 15 3.4 Environmental impact 20 3.5 Monitoring programme 21 3.5.1 Rationale and components 21 3.6 Oversight and Responsibilities for the Monitoring Programme 23 4 Density, Stratification and Stability 25 4.1 Background for gas accumulation in lakes 25 4.2 Factors that influence water density 26 4.3 Normal Mixing and Transport Mechanisms 27 4.3.1 Movements and Transport on Molecular Scale 27 4.3.2 Temperature Induced Turbulent Mixing 28 4.3.3 Effects of external forces 28 4.3.4 Effects of internal waves 29 4.4 Lake Kivu 29 4.4.1 Lake Kivu density structure 30 4.4.2 Details of mixing and stratification 33 4.5 Gas Production and Gas Accumulation 35 4.6 Measurements of gas concentrations 36 5 Risks 39 5.1 Nature of Risks 39 J:\OS 25 Projecten\O72 Advice on Lake Ki vu Stability Monitoring\Documentati e wg works hop Lac Ki vu\Expert Committee Report Final version.doc . Lake Kivu Gas Extraction 2 5.2 Monitoring the lake stability and hazard risk 41 5.2.1 Density Gradient 41 5.2.2 Saturation Distance 41 5.2.3 E* stability 41 5.2.4 Buoyancy Frequency 43 5.2.5 The Wedderburn number 44 5.2.6 Double Diffusive Convection 46 5.3 Classification of eruptions 46 5.4 Role of methane and carbon dioxide 48 5.4.1 Other Basins of Lake Kivu 49 5.5 Other Lakes, Nyos and Monoun 49 5.6 Triggering events 52 5.6.1 Gas Accumulation in Sediment 54 5.6.2 Volcanic Activity 54 5.6.3 Earthquakes 55 5.7 Potential Consequences 56 5.8 Conclusion for Lake Kivu 59 6 Gas Reserves and Method of Extraction 61 6.1 Experience from Lake Monoun 61 6.2 Present Gas Extraction Concept 63 6.3 Water re-injection constraints 65 6.4 Gas reserves at present 66 6.5 Long term gas reserves 68 6.6 Alternative Gas Extraction Scheme? 71 6.7 Improving fish yields? 72 6.8 Conclusions regarding reserves and production method 73 7 Environmental Observations 75 7.1 Emissions to atmosphere 75 7.1.1 From Lake Kivu 75 7.1.2 From Nyiragongo 76 7.2 Ecological changes within the lake 76 7.2.1 Observations helpful for assessing ecological change: 78 7.2.2 Flux calculations: 78 7.3 Conclusions on Environmental Observations 79 8 Required and Recommended Activities 82 8.1 Pilot plant feasibility 82 8.2 Elements of the recommended action plan 83 J:\OS 25 Projecten\O72 Advice on Lake Ki vu Stability Monitoring\Documentati e wg works hop Lac Ki vu\Expert Committee Report Final version.doc . Lake Kivu Gas Extraction 3 9 Monitoring Programmes 85 9.1 Monitoring strategy 85 9.2 Background for the monitoring programmes 87 9.3 Developer's monitoring programme 89 9.3.1 Monitoring onboard platform 89 9.3.2 Monitoring in lake 89 9.4 Baseline studies 90 9.4.1 Modelling 92 9.5 Continuous lake monitoring programme 93 9.6 Improvement in the lake fishery 94 9.7 Specifications and requirements for monitoring and instruments 95 10 References 98 11 Index 101 J:\OS 25 Projecten\O72 Advice on Lake Ki vu Stability Monitoring\Documentati e wg works hop Lac Ki vu\Expert Committee Report Final version.doc . Lake Kivu Gas Extraction 4 0 Reader's guide The present report is prepared by an Expert Committee with a charge as de- scribed in Section 2. Sections 4 through 9 report on the work carried out and outline the opinions and recommendations by the Expert Committee. To aid the reader an extended Section 3 summarizes the conclusions and rec- ommendations with a minimum of scientific explanations. Section 1 is the very brief version of the report in the form of an Executive Summary. J:\OS 25 Projecten\O72 Advice on Lake Ki vu Stability Monitoring\Documentati e wg works hop Lac Ki vu\Expert Committee Report Final version.doc . Lake Kivu Gas Extraction 5 1 Executive Summary In Lake Kivu on the border between the Republic of Rwanda and the Democ- ratic Republic of Congo some 300 km3 of dissolved carbon dioxide and 55-60 km3 of methane gas is accumulated and trapped at significant depth in the lake. The lake is 485 m deep with a surface area of 2400 km2 at an altitude of 1462 m. A natural concern is that Lake Kivu could erupt, as occurred in Cameroon at Lake Nyos in 1986 and at Lake Monoun in 1984. These two gas eruptions from the lakes themselves suffocated more than 1700 people. For these lakes the re- medial measures consist of venting the remaining gas to the atmosphere in or- der to eliminate the eruption risk. In all three lakes gases are continuously ac- cumulating, and they will erupt eventually if nothing is done. For Lake Kivu the gas content is still below saturation, and the risk of an erup- tion is not imminent. However, if nothing is done the accumulating gas will cause a catastrophic eruption in all likelihood within the time span of 100-200 years. An eruption may take place with the current level of gas accumulation, but this requires a very strong earthquake, a very significant lava inflow or a volcanic eruption at the lake bottom. The probability of these triggering events is low, but the consequences of a major eruption are very dire as hundreds of thousands to millions of people living around Lake Kivu and the northern part of Lake Tanganyika could be affected. To reduce or eliminate the risk of eruption the gas in the lake could be vented to the atmosphere. However, a large part of the methane gas in Lake Kivu is extractable and may be used to fuel power plants to supply electricity at a very competitive price rather than being vented and lost to the atmosphere. The first phase in the harvesting of methane gas consists of a project developed by the "Kibuye Stage 1 Power Limited", KP1. This is a public-private partner- ship between the Government of Rwanda (GoR) and Dane Associates Limited. The project consists initially of a Pilot Plant placed one kilometre off shore from Gisenyi and a 35 MW power plant at Kibuye powered by gas extracted nine kilometres offshore. The project is being reviewed by an Independent Engineer on behalf of the lenders, and as part of this assignment the Independent Engineer has assembled J:\OS 25 Projecten\O72 Advice on Lake Ki vu Stability Monitoring\Documentati e wg works hop Lac Ki vu\Expert Committee Report Final version.doc . Lake Kivu Gas Extraction 6 an Expert Committee to produce an opinion on the impact of the project on lake stability and the risk of an uncontrolled gas release. The Expert Committee has critically assessed the available information on the gas reserves in the lake, the conditions of the lake facilitating the accumula t ion of gas, the risks associated with the gas in the lake, the environmental observa- tions pertaining to the lake ecology and environment, and the requirements for the gas extraction project with regard to maintaining lake stability. The unanimous results and recommendations of the Expert Committee work may be summarized as follows: 1. Lake Kivu is a stratified lake with several gradient layers (density varia- tion of the water with depth) which serve as “flexible lids” ensuring both a resistance to mixing (which could cause a gas release), and a bar- rier which allows for the accumulation of methane gas (and carbon di- oxide) in the lake. Notably there are two gradient layers at about 80 and 260 m depth, respectively, where the upper layer protects the overlying biozone and the lower layer confines and protects the major part of the gas deposit. 2. Measurements in the lake from 1975 to 2004 indicate that the amount of methane gas has increased by 10-15 %, and that saturation and ac- companying eruption may be reached in 100 to 200 years without hu- man intervention. 3. Due to the inherent dangers of the large gas deposit in Lake Kivu, liv- ing around the lake means accepting a higher risk than living elsewhere in the region. Extraction of gas from the lake must occur to reduce the risks and avoid a major disaster with loss of lives in the hundreds of thousands to millions around the lake. 4. If the extraction projects are properly regulated and monitored, they will decrease this risk for the population. In the course of the methane extraction it is possible that errors or accidents would increase the risk temporarily, which is why continuous monitoring and regulation is mandatory. 5. The Expert Committee recommends an action plan based on monitoring programmes at three levels: (i) the Pilot Plant at Gisenyi, (ii) The main KP1 Production facilities, and (iii) a baseline study of Lake Kivu at large.