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

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

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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

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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

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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. (1983, 1985)). * Numbers refer to numbers in Fig. 4. Values in parentheses after gradients are the numbers of boreholes used in the site gradient calculation.

**Depth range of temperature measurements used for temperature gradient calculation.

* ** Map Location Temperature gradients Depth Key (mKm-1) (m) (A) Northern and Western Egypt 1 Northern Egypt oil wells 20.6 ± 2.9 (128) 114-4656 2 Abu Tartur 18.7 ± 1.0 (4) 10-235 2 Abu Tartur (phosphate) 74 ± 6 (8) 25-145 3 West Kharga 15.2 (1) 100-430

(B) Eastern Egypt (existing data and boreholes) 4 Gulf of Suez oil wells 26.9 ± 5.7 (105) 457-5198 (Hammam Faraun hot spring) 48 (1) 5-80 5 Abu Shegala 30–50 (1) 20-200 6 Abu Dabbab 28.9 ± 2.9 (8) 20-200 7 Neweibi 20.3 ± 2.6 (10) 30-190 8 Sukkeri 18.9 (3) 60-240 9 Abu Ghalaga 18.8 (5) 100-225 10 Umm Samiuki 19.1 (2) 25-140 11 Barramiya 16.7 (1) 50-300 12 Genina 12.0 (1) 30-60 13 Homr Akarem 17.6 (2) 45-120 14 Gabbro Akarem 8.2 (3) 30-70

(C) Eastern Egypt (especially drilled regional gradient boreholes) 15 Wadi Ghadir 55.0 (1) 20-150 16 Aswan 13.9 (1) 20-100 17 Wadi Higlig 23.4 (1) 20-100 18 Berenice 21.5 (1) 35-100

tectonic or non-volcanic origin associated with the opening of solute sources and geothermal potential. Silica, Na-K-Ca the Red Sea–Gulf of Suez rifts. The only other possible (sodium-potassium-calcium) and Na-K-Ca-Mg (sodium- thermal spring is the Helwan sulfur spring located 25 km south potassium-calcium-magnesium) geothermometers are used to of Cairo and it is reported as having a temperature range estimate the temperature of a geothermal reservoir at between 23 - 32°C (El Ramly, 1969). In the Western Desert, equilibrium. Unfortunately none of these techniques indicate there are no springs that can be classified strictly as thermal, very high subsurface temperature, even for the thermal springs and all occurrences of thermal water are from deep wells, around the Gulf of Suez. Ain Hammam Faraun, the hottest many of which are artesian. spring in Egypt at 70°C (El Ramly, 1969), gives a Na-K-Ca geothermometer of 129°C, but it is suspected there is mixing 5. Hot water chemistry and geothermometry of geothermal fluids with sea water. Swanberg and Morgan Thermal waters, discharged at several locations in Egypt, (1979, 1980) used the silica content of groundwater for were sampled for chemical analysis to evaluate their origin, estimating regional heat flow. The appropriate equation to use

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Fig. 5 Map showing locations of thermal springs and wells in Egypt and their temperatures (El Ramly, 1969).

is q = (TSiO2 – T0) / m, where TSiO2 is the quartz conductive per liter based on the chemical analysis in Table 3. The solute silica geotemperature (°C), T0 is the mean annual ground concentration being below the seawater dilution line in the plot temperature (°C), m is 0.67°C m2(mW)-1 and q is heat flow reflects that some Na may have been lost owing to water–rock (mWm-2). Table 2 shows the silica heat flow data for different interaction within the reservoir. The thermal waters are also areas in Egypt. Application of the silica/heat flow technique to enriched in SO4 relative to the water dilution line except the silica data suggests regionally higher subsurface Hammam Faraun hot water (Fig. 7B). This may be due to the temperatures in eastern Egypt than in western and northern derivation of Ca from the dissolution of gypsum in these areas. Egypt. Details of chemical and isotopic studies in the areas Fig. 7(C) shows the enrichment of all thermal waters and the around the Gulf of Suez were made by Sturchio et al. (1996). maximum percentage of Ca is recorded in the Hammam The studied areas including Ain Sokhna, Ayun Musa, Faraun hot spring. This implies dissolution of Ca minerals such Hammam Faraun, and Hammam Musa are considered the as calcite and gypsum from surrounding and overlain upper main hot springs in Egypt (Fig. 6). Results of chemical and isotopic analyses of thermal waters are presented in Table 3. We find the most abundant solutes in all thermal waters are Na and Cl, while Mg, Ca, and SO4 are also prominent. The pH values are near neutral. The total dissolved solids range from 2600 to 14,000 mg/l. Chemical compositions indicate derivation of solutes mainly from regional marine sedimentary rocks and windblown deposits (marine aerosol and evaporate dust). Chloride variation diagrams for Gulf of Suez thermal waters (Hammam Faraun, Hammam Musa, Ayoun Musa and Ain Sokhna) were made and compared with the sea water dilution line. The comparison may help us in discussing the origin of these thermal waters. Fig. 7(A) shows the relation Fig. 6 Location of the studied areas around the Gulf of Suez for between Na concentration and Cl concentration in milligrams geochemical analysis.

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Fig. 7 Chloride variation diagrams for the Gulf of Suez thermal waters with the seawater dilution (dashed) line shown for comparison (Sturchio et al., 1996).

Cretaceous and Eocene carbonate rocks. concentration of boron and this depletion may argue against Most of the thermal waters are enriched in Br relative to the direct sea water mixing in these areas. However, boron can seawater dilution line (Fig. 7D), which indicates dissolution adsorb from groundwater onto clay minerals (Palmer et al., and an evaporate concentration of marine aerosols in the 1987). recharge area. Almost all thermal waters have a low

― 161 ― Table 2 Heat flow at various locations in Egypt based on the was also applied. The 2D resistivity cross section clearly silica heat flow technique (Morgan et al., 1980). elaborates the subsurface structure in the spring area and explains the hot water source in the area. From the 2D Location Number of TSio2 T0 q Samples (°C) (°C) (mWm-2) interpretation of these geoelectric data, a promising area for Eastern Desert 44 75.4 ± 15.3 27.9 72.2 geothermal drilling is found around the hot spring where there Kharga Oasis 13 47.5 ± 2.4 26.0 32.1 is considerable aquifer thickness. Salem et al. (2000) analyzed Bahariya Oasis 12 54.8 ± 2.8 26.0 43.0 the aeromagnetic anomalies of the Quseir area and the possible Dakhla Oasis 18 55.7 ± 4.2 14.4 46.7 relationship of these anomalies to the thermal sources of the Mediterranean Coast 21 55.4 ± 17.3 21.2 51.0 Red Sea geothermal system. Depths to the bottom of the Siwa Oasis 22 60.3 ± 13.7 26.4 50.6 Wadi Natrun 7 74.7 ± 19.4 26.0 72.7 magnetic sources indicate a general increase in the temperature -1 Cairo Area 4 89.2 ± 13.4 24.9 96.0 gradient of 64°C km toward the Red Sea (Fig. 8). Thus there Sinai (West Coast) 4 73.8 ± 14.6 25.0 72.8 is a source of geothermal energy, with temperatures greater than 100°C being reached at depths of less than 2 km. 6. Geophysical exploration of geothermal resources in Consequently, north Quseir is a promising area for further Egypt geothermal exploration. High temperatures and hot thermal fluid circulation in Microearthquake monitoring and gravity data in the area geothermal systems strongly influence the physical properties between the Nile River and Red Sea indicate that the high heat of geologic formations; therefore, geophysical (gravitational, flow is associated with the opening of the Red Sea (Morgan et magnetic, geoelectric, and seismic) tools play an important role al, 1979). Mekkawi and Ebohoty (2007) studied hot springs in in the exploration of geothermal resources. El-Qady (2006) central Sinai to illustrate the role of magnetotelluric (MT) and delineated the geothermal reservoir at the Hammam Musa hot magnetic interpretation in the detection of major subsurface spring in Sinai using geoelectric techniques. The geoelectric tectonic structural elements affecting both the sedimentary survey comprised 19 vertical electric sounding (VES) section and the underlying basement complex. The results of measurements and used the Schlumberger array with AB/2 up magnetic interpretation revealed the Abou Swira hot spring is to 1000 m. A two-dimensional (2D) inversion based on the tectonically controlled by faulting having a major NW–SE Akaike Bayesian information criterion least-squares method alignment and extends to a depth of about 1.60 km. The strong

Table 3 Chemical data for the Gulf of Suez thermal waters, with concentrations in units of milligrams per liter. Samples were collected in January 1993 except for Ayun Musa (March 1994) (Sturchio et al., 1996). Ain Ayun Hammam Hammam Sokhna Musa Faraoun Musa T (°C) 32 37 70 48 pH 7.74 6.02 7.44 7.59 SiO2 19.1 17.8 51.1 21.6 B 0.04 0.90 0.18 0.04 Li 0.11 0.09 0.32 0.12

Na 1946 652 3642 1586 K 72.2 38.9 127 64.2 Mg 258 52.2 270 330 Ca 413 224 966 523 Sr 16.3 4.85 21.9 10.1 HCO 200 243 109 116 3 SO4 1320 378 780 1130 F 2.4 6.6 2.5 1.6 Cl 3710 983 8050 3870 Br 14 6.3 46 31 T.D.S 7960 2600 14030 7670 87 86 Sr/ Sr 0.70803 0.70776 0.70795 0.70795

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Fig. 8 (A) Temperature gradient contour map of the Quseir area (contour interval of 5°C km-1); (B) surface heat flow contour map of the Quseir area (contour interval of 10 mWm-2) measured by Salem 2000.

Fig. 9 Geoelectric cross section constructed by El-Qady (2000), with the topographic map of the study area showing the locations of VES measurements. magnetic anomalies surrounding the hot spring can be profile; this correlates with sea water intrusion in that area. In attributed to the occurrence of basic subsurface intrusion of the southern part, below the hot spring, a highly resistive body high magnetic content. El-Qady et al. (2000) used the was recognized and may be due to the presence of uplift in geoelectric resistivity method for detecting and delineating a basement rock; consequently, this explains the origin of hot geothermal reservoir and groundwater aquifer in the Hammam water at the Hammam Faraun hot spring. From the section, we Faraun area using a Schlumberger array comprising 17 VES note two structure-faulting systems in NNW–SSE and EW measurements with a maximum AB/2 of 1000 m. From the directions affecting the area. results obtained through inversion processes, El-Qady constructed a 2D geoelectrical cross section for a profile 7. Conceptual thermal model for the hottest spring in parallel to the Gulf coast and passing through the hot spring Egypt (Fig. 9). The general feature of the inverted section is a huge Among the previous study areas, the most interesting for and thick body with low resistivity in the northern part of the geothermal study is the area around the Gulf of Suez and the

― 163 ― Red Sea coast, and the hottest spring is located in the relative to the seawater dilution suggests the presence of Ca Hammam Faraun area. The Hammam Faraun area is one of minerals such as calcite or gypsum; their possible sources are the main fault blocks in the central dip province of the Suez the upper Cretaceous and Eocene carbonate rocks overlying rift, which began during the late Oligocene to early Miocene the Nubian sandstone, windblown deposits in the recharge with the NE–SW separation of the African and Arabian plates area, and gypsum from Miocene evaporates and marine (Patton et al., 1994). The geological setting of the Hammam aerosols. The enrichment of chlorite may derive from sea

Faraun fault block shows it has a half-graben geometry water intrusion in that area. In addition, the abundance of SO4 dipping moderately to the east and is up to 25 km wide and 40 may indicate excess Ca was derived from the dissolution of km long, being bounded to the east and west by the Thal and gypsum. Hammam Faraun normal fault zones, respectively. Therefore, Temperature measurements made by Morgan et al. (1985) the major geological structure of this area is a well defined in the study area show that the temperature in the Hammam fault block oriented NNW–SSE, which is tilted strongly Faraun area increases with depth by 48 mKm-1. From previous eastward on its western side. The shallow geological geological, geochemical, and geophysical information, we try successions of Hammam Faraun are sand, conglomerate, to construct an initial conceptual model for the Hammam sandy limestone, lagoonal gypsum limestone and chalk with Faraun hot spring (Fig. 10). The conceptual model reflects that flinty limestone. the Hammam Faraun hydrothermal system is considered to be The results of chemical and isotopic analysis of thermal dynamic and the source of the hot spring is due to the tectonic water in Hammam Faraun are presented in Table 3. Chemical uplift of hotter rocks and residual heat from intruding pluton compositions indicate derivation of solutes mainly from causing deep fluid circulation through faults. regional marine sedimentary rocks. The abundance of Ca

Fig. 10 Schematic conceptual model showing the origin of the Hammam Faraun hot

spring.

― 164 ― 8. Conclusion deduced from magnetotelluric and magnetic data, Geophysical Temperature gradient and heat flow data indicate low heat Research Abstracts, 9, 05014. flow in western Egypt, which is consistent with the Meneisy, M.Y., (1990) Volcanicity, Chapt.9 In Geology of Egypt, Precambrian platform tectonic setting and extends the low heat (Said, R., Ed.), Balkema Pub. Rotterdam, Netherlands, 157-172. flow province of the eastern Mediterranean south into Morgan, P., Black'well, D. D., Fanis, T. G., Boulos, F. K. and Salib, P. northeastern Africa. High heat flow values, up to 72 mWm-2, G. (1976) Preliminary temperature gradient and heat flow values have been measured in eastern Egypt, and the heat flow for northern Egypt and the Gulf of Suez from Oil well data, appears to increase towards the Red Sea coast. Regional Proceedings International Congress on Thermal Waters. geothermal exploration was conducted in Egypt using thermal Geothermal Energy and Volcanism of Mediterranean area, Vol. 1, gradient/heat flow and groundwater temperature/chemistry Geothermal Energy, 424-438. techniques as well as geophysical tools. All of these techniques Morgan, P., Boulos. K., Hennin, S.F., Elerif, A.A., El-Sayed, A.A., suggested that the greatest areas of geothermal potential in Basta, N.Z., and Melek, Y.S. (1985) Heat flow in Eastern Egypt: Egypt are close to the coasts of the Red Sea and the Gulf of The thermal signature of a continental breakup, J. of Suez. This indicates the potential for development of Geodynamics, 4, 107-131. geothermal resources along the Red Sea and Gulf of Suez Morgan, P., Boulos. K. and Swanberg, C. A. (1983) Regional coasts. Conceptual modeling of the Hammam Faraun hot geothermal exploration in Egypt, EAEG, 31, 361-376. spring, which is the hottest spring in Egypt, shows that the heat Morgan, P. and Swanberg, C.A., (1979) Heat flow and the geothermal source of the hot spring is probably derived from high heat potential of Egypt. Pageoph, 117, 213-225. flow and deep fluid circulation. Morgan, P., Swanberg, C.A., Boulos, F.K., Hennis, S.F., El-Sayed, D.A., and Basta, N.Z. (1980) Geothermal studies in northeast Acknowledgment Africa, Ann, Geol. Surv. Egypt, X: 971-987. Appreciation is expressed to all staff at the Laboratory of Palmer M. R., Spivack A. J. and Edmond J. M. (1987) Temperature Geothermics, Department of Earth Resources Engineering, and pH controls over isotopic fractionation during adsorption of Faculty of Engineering, Kyushu University, Japan, for their boron on marine clay, Geochim. Cosmochim. Acta, 51, 2319- guidance and support. In addition, I would like to express our 2323 gratitude to all staff at the National Research Institute of Patton, T.L., Moustafa, A.R., Nelson, R.A., Abdine, S.A., (1994) Astronomy and Geophysics (NRIAG), Egypt, for their Tectonic evolution and structural setting of the Suez Rift, In assistance and especially to Dr. Gad El-Qady, an Assistant Landon, S.M. (Ed.), Interior Rift Basin. American Association Professor at NRIAG, for his continuous support. Petroleum Geologists Memoir, 59, 7-55. Said, R. (1962) The Geology of Egypt. Elsevier, Amsterdam, 377 pp. References Salem A., Ushijima, K., Elsirafi, A. and Mizunaga, H. (2000) Spectral El-Qady G., Ushijima K and El-Sayed A. (2000) Delineation of a analysis of aeromagnetic data for geothermal reconnaissance of geothermal reservoir by 2D inversion of resistivity data at Quseir area, Northern Red Sea, Egypt, Proceedings World Hammam Faraun area, Sinai, Egypt, Proc. World Geothermal Geothermal Congress 2000, Kyushu - Tohoku, Japan,1669-1674. Congress 2005, 1103–1108. Sturchio N. C., Arehart G. B., Sultan M., Sano Y., AboKamar Y., and El-Qady G. (2006) Exploration of a geothermal reservoir using Sayed M. (1996) Composition and origin of thermal waters in geoelectrical resistivity inversion: case study at Hammam Musa, the Gulf of Suez area, Egypt, Applied Geochemistry, 11, 471- Sinai, Egypt, J. Geophys. Eng., 3, 114-121. 479. El Ramly, M. F. (1969) Recent review of investigations on the thermal Swanberg, C.A. and Morgan, P. (1979) The linear relation between and mineral springs in the U. A. R., XXIII Int. Geol. Cong., 19, temperatures based on the silica content of groundwater and 201-213. regional heat flow: a new heat flow map of the United States, McKenzie D. P., Davies D., Molnar P. (1970) Plate tectonics of the Pure and Applied Geophysics, 117, 227-241. Red Sea and East Africa, Nature, 226, 243 – 248. Swanberg, C.A. and Morgan, P. (1980) The silica heat flow McKenzie, D. P. (1972) Active tectonics of the Mediterranean region, interpretation technique: assumptions and applications, Journal Geophys. J. R. Astr. Soc., 30, 109-185. of Geophysical Research, 85, 7206-7214. Mekkawi M. and Ebohoty M. (2007) Delineation of subsurface Waring, G. A. (1965) Thermal springs of the United States and other structures and tectonics of hot spring, central Sinai, Egypt as countries of the world-a summary, U.S. Geol. Surv., Prof. Pap.,

― 165 ― 492:383 pp. Youssef, M. I. (1968) Structural pattern of Egypt and its interpretation, Bull. Ann. Assoc. Petrol. Geol., 52, 601-614.

総説

エジプトの地殻熱流量と地熱活動

モハメドアブデルザヘール・江原幸雄（平成 21 年 1 月 22 日受付, 平成 21 年 5 月 21 日受理）

概要エジプトでは新生代の火成活動は多くはないが, アフリカプレートの北東端に位置することから, 特にその東縁に沿って, 地熱資源の存在が推定される。エジプト西部（西砂漠地域）の大規模なオアシス（カルガ, ダクラ, ファラフラ, そして, バハリア地域）では低地温勾配であるが, 多くの井戸があり, 深部被圧帯水層は温度 35-40℃の低温地熱資源となっている一方,東砂漠地域, 特に紅海近傍地域では地熱資源が有望な地域が知られている。さらに, スエズ湾の東海岸地域にはソクナ, ムサ, ハマム・ファラウン及びハマム・ムサ等の高温温泉がある。スエズ湾岸に沿うこれらの温泉地域は, エジプトにおける最も有望な地熱地域である。エジプトでは, 地球物理学的および地球化学的手法を使った地熱探査が多く行われてきた。最近のデータは, スエズ湾及び紅海の海岸地域の地熱貯留層の温度が 120℃あるいはそれ以上であることを示している。エジプトで最も高温を示す, スエズ湾東岸のハマム・ファラウン温泉地域の地熱系概念モデルが構築された。この温泉の熱源はおそらく高い地殻熱流量と紅海及びスエズ湾のリフト拡大に伴って形成された断層によって規制された深部循環水によると考えられる。

キーワード：地殻熱流量, 地温勾配, 地熱資源, 温泉, ハマムファウラン, エジプト

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