In one of our most detailed collaborations, Geo Energy Marketing is proud to share our latest Geothermal Country Overview, featuring Ethiopia. A very special thank you goes out to Jason Fisher, Geothermal Consultant and the man behind Isleofrocks as well as Kieran Boyd with TM Geothermal Plc (Tulu Moye Geothermal) for collaborating with Patrick Hanson to create this deep dive into Ethiopia’s great geothermal story.
Ethiopia is located in the Horn of Africa and is one of several countries in the East African Rift System (EARS). Along with the majority of the EARS, there is great geothermal potential for power generation. While Ethiopia is known for a number of key archaeological and paleontological finds (human and animal fossils), it has vast untapped potential for geothermal energy. Geothermal exploration began in 1969 and has identified twenty-four geothermal prospects. To date, only one geothermal power plant has been developed and has been through a number of production challenges. In the most recent energy plan, geothermal is slated to contribute 5,000 MW towards the 25,000 MW goal by 2037.
Geologically, Ethiopia is complex and is divided into three main geomorphological sections; the Afar depression, Main Ethiopian Rift (MER), and Ethiopian plateaus. The Afar region (referred to as the Afar, Afar Triangle or Afar Depression) is the triangular-shaped surface expression of the Red Sea –Gulf of Aden-East African rift system crossing through the African continent and covers Djibouti, Ethiopia, and Eritrea. It is said to be a section of seafloor uplifted by high heat flow from a plume directly beneath it. It is dominated by NNW transform faults and transverse fractures (think San Andreas, California). Some key structures include the Erta Ale, Alayta and Manda Harraro active volcanic ranges. The presence of a rift system indicates the presence of heat sources and transverse faults indicate fractured reservoirs; an ideal situation for the creation of high-temperature geothermal resources.
The MER is the northernmost of the EARS and extends from the Ethiopia-Kenya border to the Red Sea in a North-Northeast direction separating the uplifted western (Ethiopian) and eastern (Somalian) plateaus. The major fault systems recognized in the MER have an overall NE- SW trend, the most prominent being the Wonji Fault. The MER is dominated by a series of diagonal rift basins and has been differentiated into the north, central and south sections. The Northern MER is considered to extend from the Afar depression up to the Lake Koka region following the middle course of the Awash River valley with faults trending N50°. The Central MER encompasses most of the Lakes Region, up to the Lake Awasa (Hawassa) area with faults trending N30°–35°. The Southern MER extends south of Lake Awasa (Hawassa) beyond Lake Chamo into a region considered the overlapping area between the Ethiopian and Kenya Rifts. Faults in the Southern MER show a dominant N‐S to N20° trend.
IMAGE 1: Morphology of the Main Ethiopian Rift. From Corti, G., 2019.
IMAGE 2: Tectonic map of the Main Ethiopian Rift. The Abaya geothermal area is located within the black rectangle. From Cervantes et al. 2020
Twenty four geothermal prospects have been identified throughout Ethiopia. The following are the key geothermal areas that have been explored are reviewed.
Tendaho geothermal field: the Tendaho geothermal field is one of the best prospects located in the Afar depression. Surface manifestations include hot grounds, mud pools, and fumaroles.
Reconnaissance in this area began 1979 and 1980 with detailed exploration and drilling occurring from the 1980s-1990s. Between 1993 and 1998, three deep (reaching depths of ~2200m) and three shallow (reaching ~500m) wells were drilled. These wells proved the existence of high temperatures with downhole temperatures reaching 278°C.
Remnants of magma injected along rift zones are said to serve as heat sources for the geothermal system. Coarse sedimentary formations (fine to medium-grained sandstone) are assumed to be potential reservoir rocks of the system. Siltstone and claystone are considered as cap rocks of the geothermal system in the region
The system is water dominated and reservoir temperatures exceed 230°C. The tested waters of the shallow resource are characterized by relatively low total dissolved solids and low gas content. This makes it suitable for commercial applications having little environmental impact.
Geophysical surveys (magnetotelluric- MT and transient electromagnetic- TEM) identified a number of important layers and two potential localities for deep drilling with high-resolution MT surveys needed to verify the second. The layers are:
Dallol geothermal field: The field is named after the Dallol Mountain (domed structure) in the northern Afar region close to the Ethiopia–Eritrea border. It is located in the Dagad Salt plain, in the Danakil Depression. The area is dominated by sedimentary rocks and is filled with salt concretions (varying colors) and a variety of geothermal manifestations including, altered rocks, boiling hypersaline, hyper-acidic and mineral enriched hot springs and pools, fumaroles and geysers. The waters are said to reach temperatures of up to 128ºC. Due to the mineral enrichment of these waters, the area was the site a potash mine in the past.
A UNDP study concluded that Dallol was unsuitable for geothermal development on the basis of the geochemical content of the hot springs. However, it has been suggested based on studies of the phreatic explosions (steam-driven explosions that occur when water beneath the ground or on the surface is heated) in the area, that a deep, chemically suitable aquifer (in sedimentary rocks including limestone and sandstone) exists.
Boina geothermal area: The geothermal area is in close proximity to the Dabbahu volcanic center which has a number of surface manifestations dominated by fumaroles and hot springs. Silica deposits are frequently observed on these hydrothermal sites, indicating high-temperature at depth. Boina translates to fumaroles or steam vents in the Afar language, and the abundance of them gives this area its name. These have been a source of water through the use of small artisanal steam-condensing units. Unlike Dallol in the north, Boina in the NW area is characterized by faulted igneous rocks (basalts), has higher rainfall and is in close proximity to the Teru Plain (a very fertile area) and a higher population density. This makes the area favorable for the future development of geothermal resources.
South Manda Harraro Geothermal area: Manda Harraro is one of the active volcanic ranges in the Afar and is surrounded by numerous thermal manifestations including fumaroles, hot grounds, and hot-springs. In 2005 it experienced a significant volcano-tectonic event. Here a fissure opened over a period of 6 years, allowing the injection large volumes of magma (basaltic). To the south of this structure, intense faulting exists indicating the potential of high permeability. This southern section also has favorable hydro-geologic conditions as it is fed by the Awash and Mille river basins. This provides an ideal situation for geothermal resources having all the necessary components (heat source, water/steam, and a permeable reservoir).
Dofan-Fantale geothermal prospect area: The Dofan-Fantale geothermal prospect is located where the rift starts funneling into the Afar triangle. The main structures and features of the area are:
Water chemistry in the area points to the existence of NaHCO3, CaHCO3, and Na/ClHCO3 water types. Based on geothermometry studies (SIO2 and Na-K) from thermal manifestations (hot springs) the reservoir temperature is ~224-252ºC.
Aluto–Langano Geothermal area: This field is the most explored geothermal field in Ethiopia and is associated with the Aluto volcano complex. Exploration ran from 1981-1986 and resulted in the drilling of 6 deep exploratory wells. The maximum depth achieved was 2500m with temperatures up to 335° C. Aluto Langano hosts the only producing power plant in Ethiopia.
Aluto-Langano is a water-dominated geothermal field with alkali-chloride-bicarbonate water. The reservoir/feed zones in the wells are fractured basalts. Three alteration zones (smectite; illite/chlorite; and illite/chlorite/epidote zone), an unaltered zone and an abundance of calcite and pyrite have been identified in a number of wells.
Geophysical studies carried out include MT, Audio magnetotelluric (AMT) and gravity surveys. These studies identified potential drilling at depths ranging from 1,000-2000 m in the central and southern sections of the field. A caldera within a caldera was identified along with a number of vents, craters, and domes. A number of faults were identified ranging in depth from 80 and 2100 m.
Tulu Moye geothermal area: this area is located north of the Aluto Langano geothermal power plant. It is characterized by NNE-SSW aligned normal faults of the Wonji Fault Belt, the most tectonically active segment of the MER. The Salen Volcanic Ridge (SVR) is also a key structure in this area. Geothermal manifestations are characterized by large areas of altered ground associated with weak steam activity (fumaroles) and hot/steaming grounds (40–100 °C @50cm depth). The manifestations are closely associated with the structural features in the area. Due to its high altitude and depth to groundwater, there is an absence of hot springs.
Integrated geological, geochemical and geophysical studies (1998-200) including shallow temperature gradient surveys (150-200m), confirmed the existence of potential geothermal reservoirs with a temperature of about 200°C and delineated target areas for further deep exploration wells. Five temperature gradient wells were drilled in 2002 by the Geological Survey of Ethiopia, reaching 90 – 120 m depth and > 90 °C. Geothermometry based on gas samples from fumaroles and the steam from temperature gradient wells suggests reservoir temperatures of > 250 °C.
Geophysical work carried out includes resistivity surveys and seismic studies. The resistivity survey suggests a clay cap in the south section of the area. The is estimated to be 500-1000 m thick, possibly covering >200 km. Under the southern part of the Salen Volcanic Ridge, a shallow low resistivity anomaly was identified. This anomaly is assumed to be a magma chamber at shallow depth and the heat source of the geothermal system in Tulu Moye.
Seismic studies (2018) identified a series of low magnitude (less than 2.5) earthquakes in the southern region of the prospect. This possibly reflects the hydrothermal fluid flow in the area and suggests that subsurface permeability is present.
Corbetti geothermal area: The Corbetti geothermal area is part of the southern Lakes District basin in the CMER. The Corbetti geothermal area is named after the prominent structure in the area, the Corbetti Caldera. Other important structures include a volcanic belt hosting Mt. Urji and Mt. Chebi. It is a silicic (high silica) volcano system within a 12 km wide caldera that contains widespread manifestations such as fumaroles and steam vents.
Eight shallow exploration wells were completed (1987) with depths ranging from 93-178 m. Geothermal waters encountered averaged temperatures of 96 ºC in the northern section of the caldera and are of a bicarbonate –sodium type.
Geothermometers from the shallow exploration wells indicate a resource temperature of ~ 140 °C. Other geochemical studies focused on the analysis of steam, as no surface water (hot springs etc) was found within or near the caldera. Based on CO2 geothermometry analysis, it is suggested that this area hosts a high-enthalpy reservoir with temperatures => 300°C.
MT and TEM surveys were carried out identifying a number of structures described below:
Abaya geothermal area: The Abaya area is in the western half of the SMER. Main structures identified in the area include the northwest Abaya Fault; Lake Abaya; Obitcha Caldera; and three grabens associated with NNE-SSW trending faults.
Surface exploration has been carried focusing around the Abaya Fault and one of the three grabens, Salewa Dore –Hako. Boiling mud pools, abundant fumaroles (both ranging from 50 –100 ̊C), several springs (40 ̊C to close to 100 ̊C) and altered surface rocks are associated with the Abaya Fault. While steaming/hot grounds (30-45 ̊C) areas are associated with Salewa Dore –Hako.
Waters collected from the springs show high concentrations of SiO2, CO2, and a lack of H2S. Geothermometers estimate reservoir temperatures of >140 ºC and 243 ºC (silica) and 252 ºC- 260 ºC (cation). Analysis of the waters shows the existence of NaCl-HCO3 and NaHCO3 geothermal water. Anomalies identified in soil gas surveys match temperature anomalies in the area. The most obvious is with high-temperature manifestations and boiling thermal waters (shallow) along the Abaya Fault.
Geophysical studies identified two key subsurface layers (low resistivity): a layer starting at a few hundred meters depth to ~2000 m depth, interpreted as thermally altered zone (temperatures up to 230°C); and a second layer at ~8000 m interpreted as a heat source for the active geothermal system in Abaya.
Ethiopia currently has two geothermal power production projects underway (Tulu Moye & Corbetti). The most advanced of these is the Tulu Moye geothermal prospect, found 150Km South of Addis Ababa. Tulu Moye is being developed by TM Geothermal Plc (TMGO), an SPV of the global investment firm, Meridiam, and Icelandic firm Reykjavik Geothermal. Through meeting stringent international requirements, grant funding has also been secured from multiple international bodies such as the Geothermal Risk Mitigation Facility (GRMF), which is funded by the UK, Germany and the EU, and the United States Trade and Development Association (USTDA).
IMAGE 3: Drilling Rig set up onsite at Tulu Moye in Ethiopia
TMGO was founded in 2017 as one of the first independent power production projects in Ethiopia and has since begun groundwork on the development of a 50MW (1st phase) power plant. The company is fortunate enough to benefit from the experience of two employees, including the CEO, who worked on Ethiopia’s first Geothermal plant at Aluto Langano, completed in 1998. TMGO is currently in its drilling phase, with KenGen (Kenya’s state utility) contracted to drill an initial 12 exploratory, production, and injection wells, following the completion of civil works in late 2019. The site is expected to begin power production after the completion of phase 1 in 2022, with current plans to expand the project to 150MW in phase 2, depending on the geothermal resource confirmation.
IMAGE 4: TMGO CEO Darrell Boyd and KenGen CEO Rebecca Miano at contract signing
TMGO has been actively involved in the geothermal sector in Ethiopia, providing the driving force behind the revival of the Ethiopian Geothermal Association and co-organizing and sponsoring events such as the first Ethiopian Symposium on Geothermal Energy, where delegates from various institutions with ties to geothermal were able to come and present, network and learn more about the geothermal potential of Ethiopia.
Moreover, TMGO is pursuing an ambitious social investment program aimed at improving the water supply system and electrification of the population of the project area and surrounding Kebeles. This is alongside numerous smaller projects such as funding the training of 40 local young people to attend technical and vocational training courses with a view to future employment opportunities with TMGO and associates for those that excel.
IMAGE 5: Representatives at the first Ethiopian symposium on geothermal
TMGO has so far created 320 jobs linked to the project, with more on the way in 2020 as drilling and construction efforts expand.
IMAGE 6: KenGen and local Ethiopian workers on-site as the project moves to the drilling phase
The future looks bright for the Geothermal Sector in Ethiopia. As the government pushes to reach its goal of lower-middle-income status by 2025, it is looking ever deeper into geothermal resources alongside Ethiopia’s traditionally dominant renewable energy source, hydropower. You can expect to see plenty more geothermal developments emerging as the country expands its electrification and industrial programs in line with this goal, which forms a part of the country’s 2nd Growth and Transformation Plan. Ethiopia’s vast geothermal potential will be realized over the next decade or two, as the country seeks to become a net energy exporter to the region.
This concludes our most comprehensive Geothermal Country Overview to date. This series highlights countries around the world, showcasing geothermal potential, development, and energy independence. For more Geothermal Country Overview’s scroll throughout our blog or click here.
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