Heat Flow and Geothermal Resources in Egypt

日本地熱学会誌 J. Geotherm. 第 31 巻第 3 号（2009） Res.Soc.Japan 155 頁～166 頁総説 Vol.31. No.3(2009) P.155～P.166 Heat Flow and Geothermal Resources in Egypt Mohamed Abdel ZAHER* and Sachio EHARA** (Received 22 January 2009, Accepted 21 May 2009) Abstract Although Egypt is not characterized by abundant Cenozoic igneous activity, its location in the northeastern corner of the African plate suggests that it may possess geothermal resources, especially along its eastern margin. The Eastern Desert of Egypt characterizes by some geothermal potential fields particularly adjacent to the Red Sea. Although the western part of Egypt (Western Desert) has low regional temperature gradients, there are many wells with deep artesian aquifers which represent a low-temperature geothermal resource (35–40°C). In addition, the eastern shore of the Gulf of Suez consists of the hottest springs, including Ain Sokhna, Ayun Musa, Ain Hammam Faraun and Hammam Musa. These areas along both shores of the Gulf of Suez are the most promising for geothermal development. Many geothermal explorations were carried out in Egypt using geophysical and geochemical techniques. Recently obtained data indicates a temperature of 120°C or higher may be found in the reservoir located adjacent to the Gulf of Suez and Red Sea coastal zone. A conceptual model was constructed for the Hammam Faraun hot spring on the eastern side of the Gulf of Suez, which is the hottest spring in Egypt. The model shows the heat source of the hot spring is probably derived from high terrestrial heat flow and deep fluid circulation controlled by faults associated with the opening of the Red Sea and Gulf of Suez rifts. Keywords: heat flow, temperature gradient, geothermal resource, hot spring, Hammam Faraun , Egypt 1. Introduction compression in the northeastern Mediterranean and Anatolia Egypt occupies the northeastern corner of the African (McKenzie, 1972) and characterized by low heat flow, which continent (Fig. 1). The approximate land area of Egypt is suggests that northern Egypt is an unlikely area for geothermal 997,738 km2 and it is 1,085 km from north to south and 1,255 resources exploration. In contrast Egypt is bounded to the east km from east to west. It is bounded to the north by a zone of by what has been interpreted as a median spreading center in ✽✽ Graduate School of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan ✽✽ Faculty of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan Ⓒ The Geothermal Research Society of Japan, 2009 ― 155 ― Fig. 1 Map of locations in Egypt. the Red Sea and Gulf of Suez (McKenzie et al., 1970) and may and the Sinai area (Said, 1962). reflect the importance of these areas for geothermal development. The Red Sea occupies part of a large rift valley in the Therefore, the greatest areas of geothermal potential in Egypt continental crust of Africa and Arabia. This break in the crust is are close to the coasts of the Red Sea and Gulf of Suez. part of a complex rift system that includes the East African Rift Recently, geochemical and geophysical techniques have been System. The Red Sea bifurcates into the Gulfs of Suez and applied intensively in geothermal studies especially in the area Aqaba, with the Sinai Peninsula in between. The geology of around the Gulf of Suez and Red Sea due to geothermal the Sinai Peninsula is more complicated than that of any other resource exploration and enhancement of the geothermal location in Egypt and represents all geologic time. During the development activities in Egypt. The purpose of this paper is to Tertiary period at the opening of the Red Sea rift, there was briefly discuss the geological and structural setting of Egypt as volcanic activity in the western and central Sinai and there are well as its geothermal resources. Additionally, we many basaltic bodies, mostly doleritic, such as sills, plugs and summarize the geochemical and geophysical explorations of flows (Meneisy, 1990). The Western Desert of Egypt includes the geothermal resources in Egypt. These explorations show a famous series of depressions such as the Baharia, Farafra, that the most important geothermal resources in Egypt are Dakhla, and Kharga oases, which represent important located in the eastern and western sides of Gulf of Suez and the geomorphological features and most are probably structurally hottest one is Hammam Faraun hot spring. Accordingly, a controlled. The area of the Nile Delta, as part of northern conceptual model was made for Hammam Faraun hot spring Egypt, had been subjected to the same geologic events that depending on the previous geothermal, geochemical and affected the whole region during its pre-Miocene geologic geophysical studies. history. Seven major fault systems were established at the end of Pan-African consolidation of the Proterozoic craton: NW 2. Geological setting (Red Sea or Suez trend), NNE (Aqaba trend), E-W (Tethyan Much of northeastern Africa is mantled by thick trend), N-S (East African trend), W-NW (Darag trend), E-NE sedimentary strata of the Phanerozoic Eon, which form a (Syrian Arc trend), and NE (Aualitic or Tibesti trend) generally un-deformed cover to a deep crystalline basement. representing major transcontinental and regional shear zones The older rocks are well exposed in eastern Egypt and Sudan, that originated during different episodes of crustal deformation where they comprise part of the Arabian-Nubian Shield. in the Proterozoic (Youssef, 1968) (Fig. 2). Most late Cenozoic Geologically, Egypt is divided into four main geological and volcanic activities have been closed to the seismically active structural areas: Western Desert, Eastern Desert, Nile Delta, boundaries of the moving segments of the lithosphere defined ― 156 ― 1- NW 2- NNE 3- E – W 4- N-S 5- W - NW 6- E– NE 7- NE Fig. 2 Main tectonic trends and structural elements in Egypt (modified and simplified from the figure presented by Youssef (1968)). by the plate tectonic model of the earth. Therefore, it would the high temperature gradients. These high temperature seem reasonable to extend the geothermal resources gradients are due to oxidative heating of pyrite in the exploration for seismically active but non-volcanic plate phosphate deposit at the depth of about 80–150 m. Mining has boundaries. the overall effect of dramatically increasing the oxidation rates by creating greater surface area exposure through blasting, 3. Temperature gradient and heat flow data grinding, and crushing, and by concentrating sulfides in Morgan et al. (1976) reported subsurface temperature data tailings. The temperature data measured in eastern Egypt were from oil wells in northern Egypt, the Nile Delta and the Gulf of all in Precambrian basement outcrops that generally have a Suez (Fig. 3). On the basis of these data, temperature gradients higher thermal conductivity than the sediments in western were computed for the linear sections of the temperature- Egypt. A high temperature gradient was measured in the versus-depth and plotted by least squares regression analysis Hammam Faraun hot spring (48 mKm-1). The temperature technique (Table 1). The temperatures were measured in the gradients from these sites are generally higher towards the east, boreholes at 5 m intervals to a precision of 0.01°C using an and when the thermal conductivity is taken into account, they electrical resistance (thermistor) thermometer. Examples of define a high heat flow zone along the Red Sea coast. Sea floor these temperature data are shown in Fig. 4. temperatures measured in the Red Sea have abnormally high The data from the Western Desert reflect low temperature values and sharp increases toward the central axis. This gradients between 15 and 19 mKm-1, which were measured in regional high heat flow anomaly indicates the potential for sediments of low thermal conductivity and therefore low heat geothermal resources along the Red Sea margin. flow is indicated. In the Abu Tarture area, characterized by the presence of phosphate deposit, the temperature gradients 4. Hot spring distributions in Egypt averaged 74 mKm-1 although these holes were only a few A hot spring is produced by the emergence of geothermally kilometers from holes having regionally normal low heated groundwater from the Earth's crust. Before discussing temperature gradients. The rapid lateral transition from low to hot springs in Egypt we must take into account the prevailing high temperature gradients indicates a shallow heat source for mean ground temperature of the area in question. The mean ― 157 ― 4 Fig. 3 Map showing sites of existing boreholes in which temperature was measured and four thermal gradient boreholes (Morgan et al., 1983). Fig. 4 Examples of subsurface temperature data from existing boreholes at sites 2 and 8 shown in Fig. 3 (Morgan et al. 1976). annual ground temperature in Egypt is typically in the range the above definition of a hot spring, many of these reported hot 22–26°C (Morgan et al., 1983). If one accepts Waring's (1965) springs cannot strictly be classified as thermal, even though definition of a hot spring as a spring being 8.3°C (15°F) above their temperatures are slightly high (25–35°C). Fig. 5 shows all mean ground temperature, then the temperatures of Egyptian the springs and wells in Egypt identified as being thermal. All springs need to exceed 30–34°C to be classified as thermal. El the thermal springs in Egypt are located along the shores of the Ramly (1969) compiled a list of hot springs in Egypt, but using Gulf of Suez and Red Sea. These springs are probably of ― 158 ― Table 1 Existing temperature gradient and depth data from boreholes, especially drilled regional temperature gradient boreholes, in Egypt (from the work by Morgan et al.

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