Uganda
Microearthquake Survey at the Buranga Geothermal Prospect
Electricity sector
Power generation in Uganda is dominated by hydropower. Uganda has a total electricity generating capacity of 529 MW, mainly generated by Jinja and Bujagali stations on the River Nile. Around 80% of power is generated by hydropower. The electrification rate is very low, with grid access of only 12% of the population for the whole country and 6% in rural areas. Additional 1% of the population provides itself with electricity by using generators, car batteries and solar photo voltaic systems. The electricity demand is estimated to be growing at an average rate of 10% per annum resulting in a need for an increase in power generation.
The growing demand for electricity and the lack of public and private investments in power infrastructure projects are major reasons. Droughts and increased discharges lower the water level and lead to significant power losses. To address the power crisis, the Government of Uganda has introduced a number of measures, including load shedding and increased lease and import of thermal energy. Since expensive thermal energy is replacing cheaper hydropower, tariffs have been increased significantly. The industrial and business sectors have been hit particularly hard by these measures.
Uganda continues to explore and to build new hydroelectric facilities at other locations. It is estimated that the hydroelectric potential is 2,000 MW, nearly six-fold the current maximum capacity. However, environmentalists raised numerous concerns, including the loss of famous falls, impacts on tourism and fisheries and secondary impacts from the people displaced by the project.
Burganga hot spring
Geothermal potential
Uganda’s potential for geothermal power generation is estimated at about 450 MW. The geothermal potential of Uganda has been explored since early 1950s but has not been used by now. To reach a further step on the way to utilisation of the geothermal resources, the Ugandan Ministry of Energy and Mineral Development (MEMD) through the Department of Geological Survey and Mines (DGSM) and the Federal Institute for Geosciences and Natural Resources (BGR), Germany, initiated a project with the title “Detailed surface analysis of the Buranga geothermal prospect, West-Uganda”, which started at the end of 2004.
A 3-dimensional view of the Rwenzori Massif from space as seen from the north overlain by a lineament pattern and integrated conceptual model (vertical section along the Bwamba fault) of the Buranga geothermal prospect (not to scale).
Project description
The Buranga hot springs are situated in the Albertine Rift (western branch of the East African Rift) within the Semliki National Park in Bundibugyo district between Semliki River to the west (borderline to the Democratic Republic of Congo) and Rwenzori Massif to the east. In the region of the Albertine Rift, where Buranga is located, no geological surface indications for volcanic activity or intrusive dikes have been found so far which could act as a heat source for the thermal water. However, geochemical findings prove that a still hot actively degassing magma body exists in the subsurface of the Buranga area. This magmatic body serves most likely as a heat source of the hot springs.
Geophysical methods were assigned to detect and delineate this magmatic intrusion. The known high seismicity suggests that Buranga provides excellent requirements to apply seismology in order to delineate an assumed magmatic intrusion. 4.185 earthquakes were localised in the period January to August 2006. The majority of the localised events exhibit a focal depth between 10 and 30 km; the deepest events occur at depths of about 55 km.
A tomographic inversion unfold the strongest P-wave velocity anomaly (-9%) in 10 km depth directly south of the Buranga hot springs. The low velocity anomaly coincides with the aseismic region within the northern Rwenzori block which could be a further indication that the reduction in velocity is caused by temperature effects in the subsurface of this region. High temperatures would not allow rocks to develop stress levels that are high enough to be released as earthquakes (ductile behaviour).
The results of the tomography clearly reveal definite low velocity anomalies. Taking the findings of geochemistry into account, the most plausible conclusion for the observed velocity reductions are high temperature anomalies. Meanwhile, the existence of intrusive magmatic bodies has also been proven by reflection seismics in the vicinity of the Buranga hot springs.
By combining all findings a conceptual model for the Buranga geothermal prospect was developed which is presented in the figure below. The four major components of the geothermal system addressed in the conceptual model are:
a) recharge,
b) sufficient permeability allowing fluid flow,
c) a heat source and
d) a seal on top of the geothermal reservoir.
On the basis of the presented conceptual model a possible drilling location was suggested. The deep exploration well should reach down to about 2,000 m where high flow rates and reservoir temperatures of up to 160°C are expected. A 10 MWe binary power plant might be feasible which could allocate a local (decentralised) electricity supply in Bundibugyo district for more than 200,000 people.
Cooperation partners:
Department of Geological Survey and Mines (DGSM)