Lake Kivu - Gas Blocks

Location

Lake Kivu is located on the West Branch of the East African Rift, in the gap that separates Rwanda and the DRC; it is between 1° 34' 00'' and 2° 30'00'' South latitude and between 28°50'00'' and 29°23'00'' East longitude with an altitude of 1,463m, a surface area of 2,430 km² of which 55% of the lake is occupied by the DRC, i.e. 1,336 km², an overall volume of water of 580 km³ and a maximum depth of approximately 500 m.

Structural and Geological Context

Lake Kivu was formed from the growth of the Virunga volcanic chain which cut through the valley of the Nile flowing north. The dam created by the repeated deposits of the effusive rocks of this chain retained the waters of the river and resulted in the formation of Lake Kivu. The latter finds an outlet to the south through the current valley of the Ruzizi.

Studies carried out in 1959 by Olson and Broecker, in 1973 by Degens et al., in 1977 by Guibert and in 1982 by Hamilton showed that the Precambrian crystalline basement of Lake Kivu is covered under the lake by more than 500 meters thick. sediments of late Upper Pleistocene age in its northern part with a water depth of 485m.

Lake Kivu is unique in the world by the simultaneous presence of dissolved gases and the stratification of its waters in layers or zones. It is :

1. Biozone (0-60): Layer between 0-60 m deep where zooplankton and fish live.

2. Intermediate Zone, ZI (120-180): Layer between 120-180 m deep where traces of methane gas can be found.

3. Potential Resource Zone, ZPR (200-250):: Layer at approximately 200-250m depth.

4. Resource Zones, ZR (270-500): Layer between 300-500 m depth where the exploitable quantity of methane gas is found. It is subdivided into the Upper Resource Zone, ZSR (270-300m) and the Lower Resource Zone, ZIR (320-500m).

The areas are separated from each other by a layer called the density gradient. The density gradient prevents the rapid rise of gas to the surface. Density gradients are important parameters for maintaining lake stability.

Origin and Accumulation of Dissolved Gasses in the Waters of Lake Kivu

Studies by Degens (1971 -1972) and Jannasch (1975) recognized the origin of methane gas as coming from the anaerobic decomposition of plant waste such as phytoplankton and algae that grow in the surface layers of the lake. The accumulation of gas and its stagnation in the waters of Lake Kivu can be explained by the presence between approximately 250 and 300 m in depth, of a sufficiently intense density gradient called Principal Density Gradient to create a real "demarcation stage". between the waters of low concentration and those of high gas concentration called the Resource Zone.

Gas Dissolved in the Waters of Lake Kivu

According to studies carried out over the past decade, Lake Kivu is full of large quantities of gas estimated at 66 billion Nm³ of methane, i.e. the equivalent of 59.4 million tonnes of oil equivalent (toe) and 300 billion Nm³ of CO2. This volume of methane gas and CO2 evolves as these gases regenerate, hence the need for exploration studies to redefine the exact volume concentrated in the blocks.

Regarding the capacity of the methane contained in the blocks, the studies carried out do not give the real estimate for each block, but depending on the depth and the layers, the following can be distinguished:

Studies and Work Carried Out

The discovery of methane gas in the deep waters of Lake Kivu dates back to around 1935 by the Union Chimique Belge during . Since then, the lake and its precious resource have been the subject of numerous studies by many national and international scientists. Thus, the vast body of available research, a few exploitation attempts and the Management Prescriptions for the development of gas resources in Lake Kivu or "Management Prescriptions, MPs in acronym" constitute the basis of the technical information used by certain operators who have acquired concessions for the exploitation of dissolved gas in Lake Kivu.