The deep geothermal potential of East Africa is a huge, under-exploited resource that has so far failed to attract investors from the oil and gas world.
The East Africa Rift System (EARS), with its western and eastern branches, could generate 20 gigawatts of geothermal power, according to Darren Jones, petroleum geologist at the British Geological Survey.
This is equivalent to 10 Hoover Dams in the US supplying 10 million people, he said, stressing that full exploitation of the rift system’s geothermal resource could provide power to perhaps 40 million people, given East Africa’s much lower per-capita demand for power.
To date, only 10% of electricity generated in the region comes from geothermal, but this is likely to increase because the EARS has high heat flows and temperatures of up to 400 degrees Celsius, conditions ideal for viable geothermal reservoirs.
Hive of activity
Kenya is in the vanguard, with geothermal supplying 40% of domestic electricity demand — about 880 megawatts. Ethiopia also hosts significant projects.
Production is growing at 17% per year, Jones told listeners at an Africa E&P event organised by PESGB-HGS last month.
The region’s first geothermal project was a plant in the Democratic Republic of the Congo that ran for 18 years from 1952 as part of a mining operation.
Kenya kicked off its Olkaria project in 1981. The multi-field complex west of Nairobi now generates 600MW of power.
A Zambia pilot plant ran in the mid-1980s, with Ethiopia joining the party in the late 1990s and new plants built in Kenya in the early 2000s.
Studies and small pilot projects are under way in all these countries, plus Djibouti, Uganda, Rwanda and Tanzania.
Jones suggested to Upstream that the lack of oil and gas company interest in East Africa's geothermal sector is due to financial and policy issues.
He said many East African projects rely on public funds, at least in their costly early stages.
“We really need more private investors to really get the exploration going, because it is the initial capital cost that turns people away.”
Jones suggested “risk-mitigation schemes or insurance schemes may attract private investors” who would help accelerate exploration and project development.
Despite these obstacles, upstream companies have been eyeing direct or indirect investments in East Africa’s geothermal potential.
For example, Tullow Oil may power its planned Lokichar oil project in northern Kenya through geothermal power, while BP has been assessing Africa’s geothermal potential.
On the policy front, Jones said there are “no structured licensing procedures” as in the oil and gas sector, which is a barrier to upstream players.
Geothermal energy is seen as an attractive resource in the region, he said, because it has a low levelised cost for producing electricity of $0.07 to $0.10 per kilowatt hour.
Its other advantage is that it runs 24/7, while field life ranges from 30 to 50 years.
However, Jones acknowledged that it is not plain sailing. As with oil and gas projects, geology will always throw up challenges.
Some Ethiopian fields have problems with salinity and gases such as carbon dioxide, which is why “a lot of these systems are being looked at in terms of their CO2 storage potential”.
Well integrity can also be a problem. Key issues include degeneration of cement and corrosion of equipment associated with hydrogen sulphide as well as CO2.
The geothermal potential differs between the EARS eastern branch, running through Eritrea, Djibouti, Ethiopia, Kenya and northern Tanzania, and the western branch that traverses Uganda, the Democratic Republic of the Congo, Rwanda, Burundi, Tanzania, Zambia and Malawi to Mozambique.
Jones said the eastern branch is better understood and exploited. It hosts volcanic reservoirs expressing themselves as calderas or hot springs, with temperatures greater than 100 degrees Celsius, two-phase flow (water and water vapour) and often associated with a focused heat source.
Temperatures higher than 150 degrees Celsius are generally needed to produce power.
An advantage of reservoirs in the eastern branch is their lack of permeability, which acts as a caprock to prevent hot water rising and as an insulator to prevent heat escaping.
The best flow rates are along reworked or fractured volcanic zones close to caldera walls.
These eastern branch resources are more suited to generate electricity — according to Jones, who previously worked for Africa-focused junior Surestream Petroleum — compared with the less-understood western branch, a much younger system characterised by narrow, deep lakes such as Albert, Tanganyika and Malawi.
Here, the geothermal play generates temperatures of less than 100 degrees Celsius, with water flowing through fractures, making it more suitable for direct heating and cooling uses. The heat is generated mainly by deep-seated magma features rather than large volcanoes.
This play “is relatively new and has been underexplored”, with reservoirs likely to be in basement rocks such as granite or associated with particular prospects in sedimentary basins.
Further field work is needed, but Jones said understanding heat flow and temperature variations would be vital to assessing geothermal potential and identifying optimum areas for hydrocarbon generation.
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