First Assessment of Geothermal Ressources in Morocco

FIRST ASSESSMENT OF GEOTHERMAL RESSOURCES IN MOROCCO

Abdelkrim Rimi

Department of Earth’s Physics Scientific Institute Ibn Battouta Avenue, B.P. 703 RABAT 10106 Morocco Tel: 212-7-774543, Fax: 212-7-774540 Email: [email protected]

Key Words: Heat Flow, low grade energy, springs, Morocco increasing HFD from the northern Middle Atlas, the Rif and the northeastern Morocco toward the Alboran Sea, the Southeast of ABSTRACT Spain and western Algeria. These two main geothermal structures could be the result of the same phenomenon of The Moroccan underground contain geothermal potentialities, increasing the mantle heat flow in relation with an extensional mainly low grade energy. The maps of heat flow density and tectonic regime over northwest Africa and the Betic-Rif the temperatures distribution down to 3000 m depth, are drawn orocline, since the Cretaceous rifting and the Alpine and area of geothermal resources are defined by the estimation orogenesis. of the heat in place. The more promising regions are northeastern Morocco and the sedimentary basins in the Sahara. 2.2. Subsurface temperatures INTRODUCTION

Being entirely dependant as regards energy, an effort is made The heat flow calculation procedure also provides a posteriori by Moroccan authorities, since 1970, to develop geothermal temperatures, interpolated at 500, 1000, 2000, 3000 and 4000 research. The purpose of this work is the first reliable m depth with their standard deviations. Thus the influence of assessement, of the geothermal potential covering the whole the variations of thermal conductivity, due to lithological country. Results are obtained on the base of sub-surface contrasts on the thermal gradient are taken into account. The temperatures determinations, and the hydrogeological figure 2 presents the computed results as contour maps characteristics of the aquifers containing hot water and which can constitute objectives in geothermics. 2.3. Thermal springs

1. BASIC DATA Among the inventoried hot springs in Morocco, those of northeast are clearly related to the recent volcanic and tectonic activities with a rise in mantellic flow (Rimi, 1999). In Western The study of the geothermal field components in Morocco (heat Rif, the hot temperature and the Artesian rise of thermal springs flow density, thermal gradient and subsurface temperatures) are ascribed to deep circulation along fracture systems in the was performed using, on the one hand thermal profiles and area. In central Morocco, the Lalla Haya spring (T=42 °C) is measured conductivities in shallow equilibrium boreholes, and from a structural point of view related to the granit on the other hand by a simultaneous inversion method (Vasseur emplacement in the region. The Eastern High Atlas conceals et al. 1984) of corrected BHT and estimated thermal thermomineral springs feeding in calcareous Lias. The hottest conductivities in deep oil wells (Rimi, 1999). one (T>52 °C with a flow rate of 5 litres/s) is located at Foum The hydrogeoligical information and the physico-chemical Zaâbel in the eastern High Atlas. Finally the two springs the composition of springs are collected, after a significant work more hot in the Southern provinces, Abeino (T=42 °C) and of analysis and checking, in the published technical reports. Timoulay (T=40 °C) are located in the hyperthermale zone extending between the Canary Islands and the Tindouf basin 2. GEOTHERAL FIELD 3. MAP OF THE GEOTHERMAL AREA 2.1 Heat flow density trends and geologicla framework The Precambrian Anti Atlas, belonging to the The variety of the tectonic and lithostratigraphic Northwest African shield is characterized by a flow of 40 ± structures in Morocco created various hydrogeothermal 5mWm-2 and a gradient of 13.5 ± 2 °Ckm-1, which are systems whose physical and lithological properties are comparable to those observed in the shield itself and the heterogeneous. For a preliminary description of the Moroccan Precambrian rocks worldwide; the stable Mesetas, with geothermal zones, two criteria are considered: 1- structural, Paleozoic and Mesozoic basement, are characterized by an lithological and hydrogeological context of the rocks to average flow and gradient of about 61 mWm-2 and 29 °Ckm-1 establish the existence or the absence of aquifers. 2- the water respectively; the northeast of Morocco from the northern temperature up to 3 km. Middle Atlas, the eastern Rif until Algeria show a high thermal Regional studies (Lahrach, 1994; Benabidate, 1994; anomaly with a heat flow and thermal gradients ranges of 80- Boukdir, 1994; Zaghloule, 1994 and Bahaj, 1997) gather basic 110 mWm-2 and 30-45 °Ckm-1 respectively. In the Saharan information on the aquifers: lithology, extent, depth, porosity, provinces, the coastal basins present a thermal gradient of 29 ± mode of feeding, gradient and water flow rate. However 7 °Ckm-1 and a heat flow of 81 ± 14 mWm-2 ; finally the characteristics such as the permeability, the transmissivity and Tindouf basin is abnormally hot with a flow and a gradient of the salinity are often lacking. According to theses works, the 84 ± 17 mWm-2 and 32 ± 10 ° Ckm-1 respectively. aquifers being able to constitute a geothermal resource in Morocco are of two types: 1) In the Tertiary and Quaternary Two major tendencies are therefore defined on each side of the deposits, the driven back water of porous spaces during the “south Atlas fault” (figure 1). In the north we observe an

397 compaction could constitute, up to 700 m of depth, good margin consists of mesozoïco-tertiary " post-rift "carbonated aquifers of low temperature (50-60 °C). 2) the typical water sediments, of which the thickness exceeds 10 km. The long circulation system for the pre-tertiary aquifers, 1000-4000 m wavelength HFD anomalies and the temperatures up to 3000 m depth, remains that guided by the topographic variations. depth, from the Canary Islands to the Tindouf basin, show that Meteoric water percolates in the topographic heights and these Saharan basins are abnormally hot. Oil wells had met hot discharges in the zones of low piezometric level, principally in water and vapor in the liasic aquifer (Hilali and Bouhaouli, carbonates of the major mesozoïc basins. If the permeabilities 1977). On the other hand, the sub-surface presence in the are favorable, water can penetrate rather deeply and to be Moroccan Sahara, of the lower Cretaceous sandy aquifer however gradually heated (the average temperature is 100°C). known as the" Continental intercalaire" (Guiraud, 1988), The map in Figure 3 synthesizes the levels of Moroccan encourages the exploration of this thick (> 1000 m) resource of geothermal potential as follows: class A characterizes the zone good hydraulic properties. extending since the southern Rif and northern Middle Atlas to eastern Morocco. The temperature of the aquifers existing up to 3000 m of depth can reach 120 °C. The zones of class B are of Western Meseta an average geothermal vocation, the temperature of the aquifers may exceed 100 °C but the aquifers are of moderate The western Meseta is a vast basin of 16000 km² consisted of importance. In this category, we have the Saharan basins and schisto-quartzitic paleozoic series. Hercynien granit and the southern Rif. The zones of class C are sedimentary basins Quaternary basaltic volcanism are reheating lithospheric of great extents where the temperature varies between 30 and processes in this zone. Indeed in two wells in the north of this 90 °C, the depth to which one can obtain hot water can be so area (Rimi et al, 1998), which attain granitic basement, at 530 great that this class C cannot be considered like potential to 790 m depth the temperature is of 50 to 60 °C, giving an resource in the immediate future. Finally the class D shows average thermal gradient of 48 °C.km-1. On the other hand, the areas without geothermal possibilities. heat production could constitute a good resource in this field, however we do not yet know the contents nor the in-depth 3.1. Major hydrogeothermal fields in Morocco distribution of these natural radioelements (U, Th, K). Eastern Rif and Eastern Morocco 3.2. Heat in place in the two hot basins By the number and the importance of the superficial thermal Two basins are chosen in the main geothermal area to give an shows (hot springs, recent volcanic and tectonic activities), in idea on their potetial energy. Available heat in the selected this region is the domain which the most drew the attention. A basins (Table 1), is evaluated by (Muffer & Cataldi, 1978) : study of french BRGM (Alsac et al. 1969) concluded that north-eastern Morocco does not constitute really a zone with H0 = ((1-ϕ)ρmcm + ϕρwcw).(Tt – T0)A.∆z significant potential. Thereafter a second study entrusted again where H = heat of place (J), ϕ = effective porosity to the BRGM (Cornet et al, 1974) underestimated the 0 (dimensionless), ρ = average density of rock column (kg/m3), possibilities of Eastern Rif. These two studies could not be m c = mean specific heat capacity (J/(kg/K)), Tt = temperature at conclusive because their thermometries carried out in the first the top of the aquifer (°C), T = temperature at the earth’s 60 meters of piezometers are strongly disturbed and the HFD 0 surface (°C), A = surface of considered area (m2), ∆z = could not be measured without thermal conductivity data, in thickness of the aquifer (m), m = rock matrix, w = water. addition their analyses had not integrated deep geophysical data (seismicity, focal mechanisms, electrical conductivity, volcanic The porosity values ϕ are deduced from a compaction law of xenoliths,...). The positive HFD anomaly in Rif and Eastern limestones, established in the coastal mesozoïc basin in Morocco is linked to a lithospheric tectono-magmatic process southern Morocco (Medina & Rimi, 1992): ϕ = 0.64 exp (-1.2 (Rimi et al, 1998). The sedimentary formations in Eastern Z), Z in km. Morocco, especially Liasic carbonates which can reach a thickness of 500 m, constitute the most significant aquifer in the area with a low to middle grade geothermal potential. The 4. CONCLUSION isobaths of Lias vary from few meters in the south to 1000 m northwards. The salinity of varies with the sense of water The use of heat flow data has indicated promising geothermal movement, 0.5-1% in the south to almost 3% in north. The potentialities in the northeastern Morocco and the sedimentary temperatures of about 60 °C can be reached at 600 m and one basins of the Sahara. The hot water may be recovered could obtain 100 °C at 1000 to 1500 m depth. The first essentially in Lias series, for geothermal purposes such as argument which cancelled the conclusions of the BRGM in space heating. However, the problem with the Liasic aquifers, Eastern Rif was reported by a geothermal anomaly met in a is that they are formed by intrinsically compact limestones and mining borehole drilled in rhyolitic and andesitic series (Kariat dolomites, but which can contain water in fractures and even of Arekman, 35.11N, 2.74W); figure 4). The well, of 680 m depth, karsts systems. In some regions such the Rif (Ostapenko, revealed from 450 m depth a salted artesian water (20 to 25 g/l 1985), the reservoirs are located in fractured rocks. The and a flow rate of 1.4 to 2 l/s) with a temperature of 42 °C at formations are thus transmissives but not very accumulatives. the discharge and more than 90 °C at the bottom (Demble & On the other hand, continuous shallow aquifers, even if they Lopez, 1977). The estimated HFD exceeds 200 mW.m-2 (Rimi are not as hot as Lias, considering their good hydraulic & Lucazeau, 1991). properties such as consolidated sandstone may furnish temperatures less than 50°C which be appropriate for soil Coastal basins in the Sahara heating in greenhouses or fish ponds. The quantitative use of chimical geothermometers (whose Belonging to the continental Atlantic margin, these Saharan SiO2 silica is the most significant) requires precautions: a basins represent a very wide hyperthermal field. The Moroccan

398 water-rock equilibrium within the geothermal system, and no Rimi A., Chalouan A. and Bahi L. (1998). Heat flow in the precipitation of silica, no mixture with nonthermal water during westernmost part of the Alpine Mediterranean system the migration of water towards surface. The temperature – (the Rif, Morocco), Tectonophysics, 285: 135-146 depth profiles, are a diagnosis of the heat transfer processes in Vasseur, G., Lucazeau, F. and Bayer, R. (1985). The problem subsurface. Therefore, detailed surveys, with a spacing of 2-3 of heat flow density determination from km, are necessary for a fine investigation of the local thermal inaccurate data. Tectonophysics, 121: 25-34. field. The assessment of these resources could be better Zarhloule, Y. (1994). Potentialités hydrogéothèrmiques du bassin specified by combining with other geophysical (geoelectricity d’Essaouira – Agadir (Maroc), Doctorat de spécialité, and magnetotellury), geological and geochemical Université de Sfax, Tunisie. (geothermometry and isotopes) determinations.

Aknowledgements This work has beneficiated partially of the support of the PARS project n° SDU 26 ‘Les Sources thermales du nord du Maroc- Contrôle structural et géothermique-Application pour la recherche de l’eau’. References Alsac C., Cornet G., Destombes J. P., Hentinger R., and Llavigne J. (1969). Etude géothermique du Maroc oriental. Rapport inédit, BRGM 69 SGL 264 GTM, ORLEANS, France, 97p., 16fig. Bahaj S. (1997). Studio geochimico delle acque termali del Marocco Centro- Sttentrionale (Rif e Massif Central), Dottorato di Ricerca, Universita Cagliari. Benabidate, L., (1994). Contribution à l’étude hydrogéothermique du Maroc Nord-occidental (Rharb, Rides et Saïs) Thèse Univ. Sfax Tunisie. Boukdir A. (1994). Contribution à l’étude géothermique du bassin du Tadla, Plateau des phosphates et Tassaout aval. Application au réservoir calcaire du Turonien (Crétacé). D.E.S. Université Cadi Ayad, Marrakech. Cornet G., Demange J., Ducroux J., and Lopoukhine M. (1974)- Etude géothermique du Rif (Maroc). Rapport inédit, BRGM 74 SGN 087 GTH, France, 53p. Demble, H. and Lopez N. (1977). Sondage de Kariat Arekman – région de Nador. Etude hydrogéolgique et géothermique préliminaire. Rapport BRPM, inédit. Guiraud, R. (1988). L'hydrogéologie de l'Afrique, J. Afr. Sc. Terre, 7:519-543. Hilali E. A. and Bouhaouli A. (1977). Recherches géothermiques au Maroc et perspectives d’avenir. Mines, Géologie & Energie, n°44 : 131-135. Lahrach, A. (1994). Potentialités hydrogéothermiques du Maroc oriental. Doctorat de spécialité, Université de Sfax, Tunisie. Medina, F. and Rimi, A. (1992). Détermination des coefficients de compaction pour les calcaires et les argiles du bassin côtier mésozoïque marocain, Bull. Inst. Sci., Rabat, 16 :60-64. Muffler, L. J. P. and Cataldi, R. (1978). Methods for regional assessment of of geothermal ressources, Geothermics, 7 : 53-89. Ostapenko, S. V. (1985). Conditions hydrogéologiques et perspectives pétrolières du bassin du Gharb-Prérif. Rapport inédit, No 31389. Office National de la Recherche et d’Exploration Pétrolière, Rabat, Maroc. Rimi, A. (1999). Variations régionales du flux géothermique au Maoc – Applications. Doctorat es sciences thesis Univ. MV. Rabat. Rimi, A. and Lucazeau, F. (1991). Geothermal Atlas of Europe - Morocco. In : Geothermal Atlas of Europe, Hurtig E., Cermak V., Haenel R. and Zui V. (eds), Hermann Haack Verlag, Gotha, 60-62.

399 -16 -14 -12 -10 -8 -6 -4 -2

34 -16 -14 -12 -10 -8 -6 -4 -2 32 Heat Flow Density

in Morocco Rif 30 34 (mW/m²) le d Meseta id 28 M 32 Atlas

n High ea 26 Oc Anti Atlas 30 c ti 24 lan (c) Temperature t at 2000 m depth A s 28 in 22 (°C) s Tindouf Bassin a B n a ra eri -16 -14 -12 -10 -8 -6 -4 -2 26 a g h a Al S l ta s 34 a 24 o C

32 22 Mauritania 30

130 110 90 70 50 30 mW/m² 28

Figure 1 : Heat flow density contours surimposed on the 24 (d) Temperature structural sketch of Morocco at 3000 m depth 22 (°C) -16 -14 -12 -10 -8 -6 -4 -2

Figure 2: Temperature contours (°C) at 0.5 km beneath the 34 surface (a), at 1 km depth (b), at 2 km depth (c) and at 3 km depth (d). 32

24 (a) Temperature 22 at 500 m depth (°C)

-16 -14 -12 -10 -8 -6 -4 -2

24 (b) Temperature at 1000 m depth 22 (°C)

400 Figure 3: zones with geothermal resources potential in Morocco.

401

Temperature (°C)

40 60 80 100Stratigraphy Hydrogeology

0 <--- saturation level

Dry residue.: 2 to 16g/l

a cold and salted water rn

100

n <--- Confined water

silty clay ia

h c n

a cold and salted water fr

la il

V e

200 Kariat Arekman borehole n sandy clay e c

(35.11N; 2.74W) o

-p to

marl, sand P

300

n ia

s e

marl M Depth (m) 400

re 500 P

marl and marl tuff volcanic

n 600 ia <--- hot and artesian water in s salt content: 20 to 25g/l

rhyolite s e PH: 6.5 M flow rate: 1 à 2l/s

700 0 100 200 300 Geothermal gradient (°C/km)

Figure 4: Thermal and lithological profils of Kariat Arekman borehole

Table 1 : Heat in place in the two main geothermal potential area of Morocco; O-T b: Oujda Taourirt basin represents a N45 furrow between the Middle Atlas and eastern Rif (north eastern Morocco) ; Tarfaya basin belongs to the Coastal Saharan Basins

Region O-T b Tarfaya basin Reservoir Lias Lias Lithology Limestone-dolomite Limestone-dolomite Depth (m) 10003687-4091 Salinity (g/l) 0.1-4l NaCl/ 7,5 Gradient (°C/km) 30-40 20-30 φφφ 0,3 0,1 ρ (kg/m3) 2,6 2,6 Cw (J/kg/K) 4186 4186 Tt (°C) 50-60 100-140 z (m) 500 400 Α (Α ( m²) 2600 32000

ΗΗΗ000(J) 1.3e+17 3.2e+18

402