GRC Transactions, Vol. 30, 2006

Yemen Geothermal Resources

Anis Abdallah Kamra UNEP Geothermal Consultant

ABSTRACT to 2500-2000 m (a.s.l) in the central part, and to 2000-1000 m (a.s.l) in the southern part, presents a number of high, medium and low III.) Hadramawt-Mahra Uplands (well dissected plateau enthalpy geothermal zones of interest. Some low enthalpy and highlands): highest elevation in this province ranges from resources are exploited by the private sector in tourism activi- about 1500 m (a.s.l) in the west to 1000 m (a.s.l) in the east, ties: hotels, recreation and therapeutic applications. The present and study is clearly high enthalpy geothermal energy, with a view IV.a,) and IVb.) Rub Al-Khali and Ramlat Al-Saba’tayn to electricity generation, in response to the priority accorded (desert and sand seas): elevations in these inland desert areas to establishing whether geothermal power generation in Ye- range from about 900-500 m. men would be feasible. The evaluation of the high enthalpy geothermal resources of the country and the selection of a site of prime interest were the main objectives of the study carried Energy Context out recently by the author as a consultant of UNEP, comple- Yemen’s state-owned Public Electricity Corporation (PEC), mented by field work for the Yemeni authorities. The present under the Ministry of Electricity and Water, operates an esti- article integrates all pertinent geothermal information available and new scientific data recently collected and shows that Yemen represents a good prospect for geothermal resource exploration and feasibility and selects Dhamar area as a high geothermal target.

Geographical Setting Yemen is located at the South-west- ern edge of the Arabian Peninsula. The country is bordered by Saudi Arabia in the North, Oman in the East, the Arabian Sea and the Gulf of in the south, and the Red Sea in the West (Figure 1). We can distinguish four principal physio- graphic provinces as listed below (Figure 2, overleaf). I) Coastal Plains of the Red Sea (Tihama) and Gulf of Aden, II.a) and IIb). Yemen Highlands and High Plateaus (highly and poorly dis- sected mountainous area and uplands): they may attain 3666 m (a.s.l) in the north Figure 1. Location, urban centres, and communication.

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less than 5 MW, and the sale of generators of 5 MW-20 MW through public offerings. However, plans to privatize the power actions have been delayed indefinitely. Currently, Yemen’s two largest power plants are the 165-MW power station at Ra’s Kanatib, near , and the 160-MW station in Al Mukha, south of Al Hudaydah. Long term development of Yemen’s power sector includes a reduction in oil dependence, thus maximizing oil for export. Yemen’s plans include the con- struction of several gas-fired power stations, expansion of the national power grid, and the introduction of renewable energy, such as geothermal energy and solar energy. In the immediate term, the government is promoting large-scale IPPs in order to increase generation capacity by an additional 1,400 MW in near future.

Figure 2. Simplified physiographic Map. Geothermal Energy Resources A series of preliminary geothermal investigations have mated 80% of the country’s generating capacity as part of the been carried out over the past three decades both in the national grid. The remainder of Yemen’s electricity is generated Southern and Northern part of the country. National and by small off-grid suppliers and privately-owned generators International groups contributed in these activities. This in rural areas. The PEC distributes electricity in the national led to the definition of preliminary working hypotheses, to grid through two 132Kv transmission systems, one serving the the selection of one or more preferential areas, and to the northern region of -Hudaydah -Aden, the other serv- proposal of work programs of surface explorations and fea- ing and Hadramawt region (Figure 1). Coverage is sibility studies. All studies presented geological descriptions, reportedly sporadic and inefficient. In 2003, the Government geochemical and hydrological data of the regions concerned. of Yemen estimated that 25% of electricity capacity is lost in The division of the country in two parts in the past did not generation. According to the World Bank, Yemen’s electricity allow the professionals to coordinate their conclusions and shortage is one of the major restraints on economic growth recommendations. In that context, different authors tried, - limiting industrial production and depressing standards of separately, to conclude by a selection of one or more areas living. Traditionally, consumer electricity in Yemen has been as a high priority geothermal zones. highly subsidized. In accordance with IMF reforms, the gov- ernment of Yemen has recently increased electricity tariffs. The General Geological 2002 reduction in subsidization allowed the PEC to break even Setting for the first time ever. The geology of Yemen Electricity Sector Republic is dominated by the major structures of the In 2002, Yemen’s oil-fired power plants generated 3.1 bil- region: the Red Sea and lion kilowatt-hours of electricity. According to Yemen’s Public the Gulf of Aden. In early Corporation for Electricity (PCE), the country’s generating Miocene times (30 to 25 mil- capacity (810 MW) and electricity distribution network is lions years) the Arabo-Afri- inadequate. Currently, it is estimated that less than one-third can continental crust made of households in Yemen have access to electricity from the of Precambrian crystalline national power grid. Even for those connected to the grid, basement, ruptured along electricity supply is intermittent, with rolling blackout sched- N.NW trending faults in ules maintained in most cities. According to the PCE, Yemen’s the Red Sea region and E-W generation capacity must increase by 1000 MW by 2010, in trending faults in the Gulf order to meet growing demand (up 4.8% over 2001) and to avert of Aden region. Contem- an energy crisis in the medium term. Over the past decade, the poraneously, the basement government has taken steps toward alleviating Yemen’s electric- was uplifted and basaltic ity shortage, including reform, expansion and integration of and rhyolitic intense activ- the country’s power sector through small-scale privatization ity took place building the and independent (private) power projects (IPPs). Plans to Ethiopian and Yemenite restructure the electricity sector were formally laid out in the plateaus (Figure 3). In the Figure 3. General Topographic 1997 Power Sector Strategy, which included a restructuring tertiary, the Red Sea graben Context Red-Sea, Gulf of Aden and of the PCE, planned for 2001. The reform package originally was formed with erosion Rift Valley Yemenite and Ethiopian including the privatization of generators having a capacity of terraces and evaporites and Plateaus.

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exact location and date of occurrence, tectonic effect, international studies based on regional observations suggest that three major seismic zones occur in Yemen: 1. The Red Sea coastal region, north of Ho- deida. 2. The axis Yarim-Dhamar-Sana’a 3. The Transverse structure with respect to Red Sea axis NW-SE to E-W trends.

It hence appears that Yemen is far from being a stable continental zone, but is charac- terised by several signs of endogenous activities, with occurrence of both magmatic and thermal convective systems in relation with deep crustal fracturation.

Selection of Potential Figure 4. General Geological Map of Yemen. Geothermal Sites coral reef deposition. The General Geological Map of Yemen The most favourable site should benefit of the superposi- (Figure 4) illustrates schematically the presence of Geological tion of all criteria: thermal, volcanic, seismic and tectonic Units. activities. In this report, three types of area (A, B, C) can be distinguished in Yemen: Present Activity Areas of Thermal Activity Only Quaternary (< one million year) and historic volcanic and Hot springs are observed in the basement, in the traps series sismo- tectonic activities occur in Yemen: at the favour of faults or at the contact of different geological formations. In this case, heat manifestation at the surface is Volcanic Activities simply linked with circulation of water towards the surface. Four major zones of recent volcanic activity are known in the country: 1. Sana’a – Amran 2. Dhamar – Rada’a / 3. Sirwah – 4. Aden Volcanic series: Shuqra, Bir Ali, East of Mukalla

Thermal Activities Hot springs are known to occur in the following sites: Is- bile, Ali Lissi, East of Dhamar, Hammam Ali, west Dhamar, Demt, Juban La Hammam and Ga’abada, to the south, Al Asurna and Belet Ata’am, east of Hodeida Hot springs are also reckoned to occur in Sukham (Tihama) and Beni Hawan (Sana’a). Seismic Activities Several earthquakes have been reported in Yemen in his- torical times. The most violent occurred in 1057 and partly destroyed towns from Aden to Sana’a. Other earthquakes occurred in 1064 and in 1878 in Dhamar. More recently, earthquakes have been reported in Al Amar (Sa’ada province), in 1975 in Beit Badr ( province) and in Hodeida. In 1983, important seismic events took place in Dhamar area. Although no systematic research was performed in ancient text in order Figure 5. Sana'a Amran Volcanic Field (after Grolier and Overstreet, 1975 to precisely determine the intensity of seismic major events, and Landsat Imagery).

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Area of Recent Volcanic Activity Only In both volcanic districts of Sana’a – Amran and Dhamar – Marib, basaltic flows and scoria cones are observed. They have been enclosed through fissures of roughly E-W direction, and produced basaltic flows only, with no associated silicic prod- ucts. In Sana’a—Amran also called Harra of Arhab—(Figure 5), historic eruptions occurred in the period 400 to 600 A.D.. The Arab geographers of middle ages called this eruption “Nar el Yemen” (“fire of Yemen”). Another eruption took place in the south-east around 200 A.D. But although very recent, and historically active, this area, at this stage of knowledge, should not be considered as a geothermal target of primary interest. Rapid uprising of basaltic magma through fissures, from deep in the mantle, did not enable shallow magmatic pockets to stay in the crust long enough to produce a heat anomaly. In fact, no thermal spring or fumerolitic activity is observed with this volcanic unit. Figure 7. The Dhamar–Rada'a Volcanic Area (after Grolier and Overstreet, Similar situation prevails in Shirwah – Marib volcanic 1975 Landsat Imagery). field (Figure 6). This is a 75 km long chain of basaltic spat- ter-cones from Djebel-el-Rebeke to Et-Tadawin. According to do occur. Fumeroles, steam vents and hot springs are associ- Geukens (1960), the final collapse of great Marib dam took ated with this volcanism. In addition, these signs of convective place between 543 A.D, and the life of Mohammed, as result of thermal activity occur in an area of recent tectonics, at the intersection of two grabens which display clear evidence of seismo-tectonic activity. The recent seismic activities of Dhamar (December 13th 1982 with a magnitude of 6.0) associated with tectonic evidence confirm the geodynamic context of the area. The hydrological context of the area is characterised by moderate precipitation with an annual rate of 400 to 500 mm. At this stage of knowledge, this area of “Dhamar – Rada” presents the main geothermal characteristics to be considered as a favourable geothermal target and interesting geothermal zone to be proposed for detailed surface exploration and probably for feasibility study. In the past, within a program of preliminary studies, BRGM (from France) has recommended this area as a high priority geothermal target and suggested other zones in Southern part of Yemen as medium and low enthalpy prospects. Electro- consult from Italy gave the same recommendation on Dhamar area and carried out preliminary Figure 6. The Mareb-Sirwah Volcanic Field (after Grolier and Overstreet, 1975 and Landsat surface investigations (geology, geochemistry and Imagery). vertical electric soundings). We confirm and sup- port this opinion in the case of “Dhamar–Rida volcanic eruption and earthquake located west Shirwah. These “area, on the bases of current regional geodynamic and geo- two volcanic districts, although recent and even historically thermal knowledge. This zone is situated one hour drive south active, can not be recommended as high priority geothermal of the capital Sana’a on the asphalted road Sana’a – Taëz which zones at this stage. is an important conomic axe today.

Area of Simultaneous Recent Magmatic, Thermal and Geothermal Specifications of Dhamar–Rada’a Area Seismo-Tectonic Activities Major Geological Units The superposition of these favourable criteria is observed in the region of Dhamar-Rada in Yemen (Figure 7), which ex- Five major geological units can be distinguished in the tends over 50 km long and 40 km large to the east of Dhamar. area. Two of them can be ascribed to the substratum of the Numerous recent volcanic centres, both basaltic and rhyolithic geothermal system, the other plio-quaternary.

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Precambrian Basement and its Mesozoic (Sandstone Tectonics and Limestone) Cover to the East Altogether, the quaternary unit corresponds structurally Strikes are generally oriented N.NE to N-S in this unit to a tectonic triple junction of distensive active zone systems, with major N-S, E-W and NW trending faults.The Mesozoic two of which (N.NE and N.NW ) are dominantly tectonic, sediments, with mainly sandstones, outcrop north and south the other being essentially volcanic. Being located in a high of Rada’a, in the area of contact basement and trap series. and crucial position of the Yemenite plateau, this displays all characteristics of a hot spot breaking the lithosphere in a three Miocene Trap Series - branches star like way. They are made of fissural basalts and rhyolite of Miocene age (30 to 20 millions years).This series is affected by faults Seismic Data of N.NW direction to the west (Red Sea) and E-W direction In the Annual Seismological Bulletin since 1994, the Na- to the south (Gulf of Aden) tional Seismological Network gives us a very good picture of the annual and frequent earthquakes in different parts of Pliocene Silicic Centre of Jebel Dhu Rakam Yemen, their locations, magnitudes and depths. Particularly It is characterised by a very large caldera (10 to 25 km in the seismic data of Dhamar area confirm the presence of high diameter), only the eastern side of which is presently visible. seismo-tectonic activities with numerous events at shallow This centre gave rise at least two very wide ignimbrite sheets, depths. which presently cover the wide Ma’bar- Dhamar plain, over 50 km long. Remnants of this eruption are found north, south Geochemistry and west at a distance over 50 km from the centre. Two grabens National and International scientific activities and publi- are well visible in the topography, north and south of Dhamar cations in this field associated with volcanic structures were and crossing each other in Dhu Rakam-Hayd al Isi area: the continuously developed since more than one decade. The southern Qa Shriah graben, oriented N.NE and the northern recent publications and updated results indicate the presence N.NW trending graben. of shallow heat sources in different areas and particularly in the North West of the country including Dhamar area. The Quaternary Sediments western Yemen volcanic province is characterized by several They are filling the two grabens and the lows located at hydrothermal features, such as thermal springs, condensates, the contact between quaternary volcanics and pre-pleistocene fumaroles and in many cases hot well waters. These thermal substratum. features are related to relatively shallow felsic magma chambers (Mattash, 2005). Quaternary Volcanic Flows and Pyroclastites of Al Lissi-Isbil Volcanic Zones Heat Source This is oriented along an east-west trending axis well visible Volcanic and structural evidence give us a preliminary from geological interpretations. It is made of silicic central indication of the presence of shallow magma chamber still volcanoes with calderas of and basaltic flows emitted from active underneath the central part of the volcano unit. This centres located on either radial or east-west fissures. heat source is overlain by a fractured basement, sediments and The Quaternery Volcanic Unit: AL LISSI- ISBIL – The trap series, block-faulted in three directions and covered by area of major interest is located in the quaternary volcanic of quaternary pyroclastics and flows which altogether certainly Al Lissi – Isbil: provide several geothermal reservoirs of great quality. Al Lissi – It is a flat strato-volcano with elliptic caldera (6X3 km) elongated in W.NW direction. Its pyroclastic products Hydrogeology and Thermal Manifestations mainly spread towards the southern graben. Caldera collapse Jebel Rakam and Jebel Isbil, over 3000 m high and made of was followed by a rhyolitic activity (mainly domes) within the interlayred rhyolithic flows and pyroclastites certainly consti- caldera and by basaltic activity. tute wide potential areas of hydraulic recharge to the system. Isbil – It is also a strato-volano with an elliptic caldera Although climate in Yemen is generally dry, the area is char- (9X3 km) oriented along an east-west direction. A basaltic acterised by moderate precipitation. The annual precipitation initial activity evolved towards rhyolites with the building is nearly 300 mm to 400 mm according to compiled reports of the strato-volcano. The caldera collapse resulted from the and the potential areas of recharge (over 200 Km²). Rate of eruption of important rhyolitic flows and minor pyroclasts, and infiltration is certainly very high in these porous fractured vol- was followed by basaltic flows which covered most pre-existing canic units and the numerous terraces and cultivation system reliefs inside and outside the caldera. A few rhyolitic domes reduces to null the surface flow. Heat manifestations are not also occurred during this very recent phase. The most recent very abundant but are very significant. Steam at a temperature rhyolitic domes and basaltic flows and scoria cones are as well up to 93° (2) and sulphuric fumaroles are observed along the preserved and non eroded that they must probably result from rims of two recent rhyolitic domes in Al Lissi and Isbil. Hot sub-historic act. springs occur in the crater of Al Lissi. At least two water drill-

641 Abdallah ings in this zone gave 43° to 45°C at 105 m deep at Al Lissi an References the other at Maram village. Geukens F. (1960). Contribution à la geologie du Yemen. Mém. Inst. Geol.Louvain, vol. 560B. Conclusions Geukens F. (1966). Geology of the Arabian Peninsula, Yemen. U.S. Geol. Surve prof.paper volc.geoth.Res.,4 307-314 Based on the results of preliminary surveys carried out over the past two decades and the actual knowledge of the De Saint Ours P.(1977). Seismic and volcanic risks in the Yemen Arab Republic UNRO/19/77, 53 p author on the regional geodynamic setting and the geothermal information gathered during recent field work, the conclusion Civetta L., Lavolpe L., Lires L. (1978). K-Ar ages of the Yemen plateau. J. 21 indicates the presence of four major zones of recent volcanism Civetta L., Defino M., Lavolpe L., and LIRER L. (1980). Recent associated with hydrothermal activity. Among these zones, volcanism of North Yemen : structural and genetic implications preprint. Dhamar volcanic and hydrothermal area is identified as the most attractive geothermal target where all favourable ele- Elc- Electroconsult, Milano, Italia (1982). Dhamar- Rada’ Geothermal prospect. Geology and Volcanology of the Dhamar- Rada’ Region. ments for an attractive high enthalpy geothermal field are 1-1 to 5-3. potentially superimposed: - a shallow magmatic heat-source - a Jac A. M Van Der Gun, Abdul Aziz Ahmed (1995). The Water Resources dense and active fracture system – several potential reservoirs of Yemen.TNO. Inst. Applied. Geoscience. The Netherlands. and covers- hydrothermal manifestations and a wide area of Mattach M (2005). Development of the Yemeni Cenezoïc Volcanic Group hydraulic recharge. in relation to Rift Formation.

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