Proceedings World Geothermal Congress 2005 Antalya, Turkey, 24-29 April 2005

1

Hydrostratigraphical Study, Geochemistry of Thermal Springs, Shallow and Deep Geothermal Exploration in Morocco: Hydrogeothermal Potentialities

Yassine Zarhloule1, Salem Bouri2, Abderahim Lahrach3 , Mimoun Boughriba1 ,Abdenbi El Mandour1 and Hamed Ben Dhia2.

1: Faculty of Sciences, Department of Geology, Laboratory of hydrogeology & environement, Oujda, Morocco.

2: ENISfax, Department of Geology, Laboratory of water, energy & environment, Sfax, Tunisia.

3: Faculty of Sciences, Department of Geology, Fès, Morocco.

yassine@sciences.univ-oujda.ac.ma, Zarhloule@yahoo.fr

Keywords: aquifers, thermal springs, geochemistry, temperatures, oil wells, shallow wells, hydrodynamism, geothermal gradient, thermal anomalies, conceptual model, Morocco.

ABSTRACT

The aim of this paper is to obtain a first reliable evaluation of the geothermal potential of the country. It’s caracterised by more than 70 hot springs, several deep hot aquifers, more than 1000 petroleum exploration wells and various existing geological, geophysical and hydrogeological data. So, its was possible to distinguish the mains geothermal features if the country, by evaluating both the underground temperature and the potential reservoirs.

The hydrostratigraphical study of each basin revealed several potentiel reservoir layers in which the carbonate aquifer of Turonian (Tadla basin and Agadir basin) and Liasic (North-western basin of Morocco and North-Eastern basin) are the most important hot water reservoirs in Morocco. this study made it possible to identify the main aquifers, their temperatures, depth and extension.

A shallow geothermal prospecting has been performed in four zones in Morocco for wich few deep thermal data are available (North-western basin of Morocco, North-Eastern basin of Morocco, Tadla basin and Agadir basin). These areas are different geologically and hydrogeologically. The shallow temperature measurements program has been launched to estimate the natural geothermal gradient in these areas, to determine the principal thermal anomalies, to identify the main thermal indices, and to characterize the recharge, discharge and potential mixing limits of the aquifers.The main thermals clues and the principal thermal anomalies that coincide with zone of artesianism of Turonian and Liasic aquifers have been identified, as well as the potential mixing limit of the aquifers systems. Also,for each basin a conceptual model is presented to interpret the relation between temperature, hydrodynamism and topography within the sedimentary basins .

The chimical of several thermal springs, in the north part of Morocco, has been investigated. Measured temperature ranges from 21 to 54°C, discharges rates range from 2.5 to 40l/s and TDS range 132 mg/l to 3g/l. The waters are mainly HCO3-Ca-Mg type, resulting from the great influence of carbonate rocks, and the Na-Cl type, resulting from the interaction of water with marine sediments.The geochimical prospecting using geothermometers(silica, Na/K, Na-K-Ca,

Na-K-Ca-Mg, Mg/Li and Na/Li) has been applied and only the silica geothermometrs seem to give plausible values.

Alkaline geothermometers used for the thermal springs are not reliable for prospecting, inasmuch as the chemical composition is greatly affected by the enormous dilution with the shallow cold water and probably affected by interaction with the evaporitic rocks that are ubiquitous in the basin.The application of Giggenbach method to springs revealed that the waters result from mixing of deep water with shallow cold water. In this case the reservoir deep temperature is given by the mixing model.

The deep geothermal study is based on the petroleum well data which present 1126 BHT and 78 DST. A statistical method is used to process these temperature indications and gives a geothermal gradient ranging from 16 to 41°C/Km. In order to establish the first geothermal gradient map for the whole of Morocco , the country is subdivided to five hydrogeothermal basins. Each basin is characterized by its geodynamical evolution and its specific reservoirs and hydrodynamism. Also, The data were treated separately and five maps of geothermal gradient were realized. The resulting map of Morocco shows that the geothermal anomalies are related to deeper hydrodynamic, recent tectonic, volcanism or to elevation of the Moho.

1. INTRODUCTION

For Morocco, the oil crises and the decrease in local energy ressources, gave impetus to geothermal energy, for potential assessment, exploration and utilisation. The evaluation of hydrogeothermal resources of Morocco is mainly done by the knowledge of the temperature, the chemical characteristics of water, the hydrodynamics of the reservoirs containing hot water. The research undertaken showed a country with real potentialities either by its important deep aquifers or by the relatively high values of geothermal gradient. It is expected that these efforts of geothermal investigation will continue in the future.

2. GEOLOGICAL SETTING

Morocco is located in a strategic area at the interaction of several plates (Africa, European, Mediterranean and Atlantic). The structural framework is characterized by transition from the African domain in the southern part of Morocco to Alpin foldeed structures (Atlasic domain and Rif troughs). Four main structural units are defined from South to North (Fig. 1): Anti-Atlas and Saharian domain corresponds to the Precambrian basement, Atlas corresponds to an Alpine intracontinental range, Mesetas corresponds to stable Paleozoic-Mesozoic basement, Rif represents the Alpine belt around the Western Mediterranean .

Morocco was subdivided into five hydrogeothermal basins (Fig. 1), distinguished by specific geological and hydrogeological feautres (North-Western basin, North-

Zarhloule et al.

2

Eastern basin, South-Western basin, Tadla basin, Errachidia-Ourzazate-Boudnib basin and Tarfaya. Laayoune-Moroccan Sahara basin).

200 km

Tadla

N

1

QS

Tr

C

H-Be

Pr-K

Ox

D

L

TsPz

43

2

ReservoirHydrogeothermal

Reservoir

Aquiclude

65

5

6

Rifdomain

Essaouira

Agadir

Errachidia

OujdaFes

Sahariandomain

Mediterraean Sea

Atlantic Ocean

Rabat

Sebta

Tarfaya

Laayoune

Q

S

Tr

C

IC

BB

AToDo

TsPz

QSTrC

H-B

Pr-K

Ox

D

L

Ts

Pz

Q

M

Og

STrCP-K

Cal-Ox

Ba-To

L

TsPz

Pl-Q

Mp

Npr

MpPlC

D

L

TsPz

Q

Ms-Eo

S

C-Tr

IC TsPz

1

2

34

Meseta

areas studies: 1:South-Western basin, 2:Tadla basin, 3:North-Western basin (Saïss), 4:North-Easternbasin, 5:Tarfaya-Laayoune-Moroccan Sahara basin, 6:Errachidia-Ourazazate-Boudnib basin.1.2.3.4.5.6:Deep geothermal exploration, 1.2.3.4:shallow geothermal exploration, 3.4:Geochimicalinvestigation. Q:Quaternary, M:Miocene, Og:Oligocene, S:Senonian, Tr:Turonian, C:Cenomanian,Pr:Portlandian, K:Kimmeridgian, Cal:Callovian, Ox:Oxfordian, Ba-To:Bathonian-Toarcien, L:Lias,Ts:Triasic, Pz:Paleozoïc, A:Aalenian, Do:Domerian, P-N:Paleogene-Neogene, H-Be:Hauterivian-Berriasian, D:Dogger, Ms-Eo:Maastrichtian-Eocene, Pl:Pliocene, IC:Infra-Cenomanian, Mp:Miocenepost-nappe, Npr: Nappe pre-rifain

Mor

occa

n Sah

ara

Atlasic domain

Anti-Atlas domain

Meseta

Figure 1: Simplified geological map of Morocco with the study zones and their hydrostratigraphical logs.

3. HYDROSTRATIGRAPHICAL STUDY

The basic data were mainly obtained from final well reports, from both oil and hydrogeologic research. Also some data have been acquired on the land (piezometrical level, chemical analysis of water, measure of temperature). These data proved useful for characterising the hot aquifers of Morocco.

The hydrostratigraphical study (Fig.1) of each basin revealed several potential reservoir layers in which the carbonate aquifer of Turonian (South-Western and Tadla basin) and Liasic (North-Western and North-Eastern basin) are the most important hot water reservoirs in Morocco (Zarhloule, 1999, Zarhloule et al.2001). These areas are different geologically and hydrogeologically.

3.1 Hydrogeological characterstics of the Turonian aquifers

3.1.1 South-Western basin

In the Agadir basin the aquifer is mainly limestone. The outcrops are limited to High-Atlas, Haffaia, Sidi-bourja, Ouled bou Rbia, El Aaricha and Tagtrannat zones. The aquifer thickness ranges from 10m in the East to 120m in the West. The depth of the aquifer varies from the outcrops in the south of the basin to 500 m in the East (Fig. 2a). The hydrodynamic flow is from the Est (outcrops zone) to the West of the basin, where the reservoir is deep and artesien (Ouled Teima, El-Klea and El gouna zones) (Fig. 2b). The aquifer temperature and the salinity varies respectively from 22°C to 32°C and from 330 mg/l to 750 mg/l.

Turonian visible fault Fault from electric Hydrogeological wellOil wellSouth limit of Turonian deposit 200 Structural curve of Turonian aquifers

High-AtlasAtlantic

-1000

-800

-600-400

-200

00

-400

10 km

N

El Goun

a

El Kléa

Bou Rbia

El Haffaia

Od Teima

Biougra

0

-200

+200

0

+400

Sidi Bourja

Tagatrant

Agadir

Anti-Atlas

Ocean-200

-200

-400

-400

Figure 2a: Structural map of Turonian aquifer.

140

230170

200

110

High-Atlas

10 km

NAnti-Atlas

Atlantic

OceanEl Gouna

Bou RbiaEl Haffaia

Od Teima

Biougra

Sidi Bourja

Tagatrant

Agadir

El Klea

Turonian visible fault Fault from electric Hydrogeological wellOil wellSouth limit of Turonian deposit 200 Piezometric curve of Turonian aquifers

Figure 2b: Piezometric map of Turonian aquifer.

3.1.2 Tadla basin

In the Tadla basin the aquifer is represented by the carbonate. The outcrops are limited to the Nord of Kasbat Tadla-El Borouj. The tickness varies from 20m to 100m. The depth of the reservoir ranges from the outcrops to 500m (Fig. 3a ). In the north part of Kasbat Tadla-El Borouj, the hydrodynamic flow is from the North to the South of the basin and to South-Ouest, but in the South of this limit the aquifer is deep and the groundwater flow is toward ENE-WSW . The discharge zone is in the South-Ouest of El Brouj (Fig. 3b). The aquifer temperature and the salinity varies respectively from 21°C to 47°C and from 530mg/l to 2530mg/l

+200

KT: Kasba Tadla, EB: El Borouj, FBS: Fkih Ben Salah, BM: Beni Mellal, OZ, Ouled Zidouh.

-600

FBS

OZ

BM

KT

-2000

EB

+200

Atlasic

Domain

Turonian

PaleozoïcHydrogeological well

15 km

+400

0-200

-400

+600

Figure. 3a. Structural map of Turonian aquifer.

OZ

BM TuronianPaleozoïc

Hydrogeological well

FBSE.B

KT

Piezometric curve

KT: Kasba Tadla, EB: El Borouj, FBS: Fkih Ben Salah, BM: Beni Mellal, OZ, Ouled Zidouh.

560

640

720

480

400320

460

720

400 400

15 km

N

Figure. 3b. Piezometric map of Turonian aquifer.

Zarhloule et al.

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3.2 Hydrogeological characterstics of the Liasic aquifers

3.2.1 North-Western part of Morocco

In this zone, the aquifer is mainly limestone. The outcrops are limited to the South of the basin. The tickness varies from 14 m to 370m. The deep of the aquifer ranges from outcrops to 1000m (Fig. 4a). The hydrodynamic flow is from the South to the North in the Eastern part of the basin and to the West in the Western zone of the basin (Fig. 4b). The aquifer temperature and the salinity varies respectively from 22°C to 55°C and from 132mg/l to 2334mg/l.

Structural curve Hydrogeological well (Liasic) Oil well Thermal spring

Liasic hiatus

Paleozoïc

Liasic

Permo-Triasic

Fault 4 km

N

0

Fès

Meknès

South rifain-rides

-200

-1000

-200

-400

200 400

600 800

1000

0

200

-200

200400

800

600

0

0

-200

Midle Atlas

Figure 4a: Structural map of Liasic aquifer.

700

300 Fès

Meknes

South rifain-rides

4 km

NLiasic hiatus

Paleozoïc

Liasic

Permo-Triasic

Fault

Piezometric curveHydrogeological well (Liasic) Oil well Thermal spring

Midle Atlas

400

450500

800 900

1000

650

600

600500

600 400

700

300

300

Figure 4b: Piezometric map of Liasic aquifer.

3.2.2 North-Eastern part of Morocco

In this zone, the aquifer is mainly limestone. The outcrops are limited to Beni Snassen, High-Atlas, Midle-Atlas and the South of the basin. The tickness varies from 50 m to 1140m. The deep of the aquifer ranges from outcrops to 1370m. The hydrodynamic flow is from the South to the North of basin (Fig. 5). The aquifer temperature and the salinity varies respectively from 20°C to 52°C and from 130mg/l to 3000mg/l.

500

6 km

Beni Drar

Oujda

Aïn Sfa

N

400450

550

600

650700

750

Liasic-DoggerPermo-TriasicHydrogeological well

(Liasic)Piezometric curve

Horst Mountains

500

Figure 5b: Piezometric map of Liasic aquifer.

4. SHALLOW GEOTHERMAL PROSPECTION IN MOROCCO

The shallow geothermal methods has ben used in many locations and has met with considerable succes in the past (Leshack and lewis 1983; Smith 1983; Sass et al., 1984; Ben Dhia et al., 1992).The shallow temperature measurements program has been undertaken in four zones in Morocco (Fig.

1) for which few deep thermal data are avaible (North-Western basin, North-Eastern basin, South-Western basin, Tadla basin). It has been launched to estimate the natural geothermal gradient in these areas, to determine the principal thermal anomalies, to identify the main thermal indices, and to characterize the recharge, discharge and potential mixing limits of the turonian and liasic aquifers (Zarhloule et al., 1998, 2001).

The temperature data from depths between 15 and 500m of 250 wells have been analysed. The temperature measurements were made at 5m depth intervals using portable thermistor probe equipment with 0.01°C resolution. The shallow temperature data allowed to establish a thermal profile for each investigated well, assumed to be in thermal equilibrium (Fig. 6).

53 : Apparent shallow geothermal gradient (C°/km), WT : Water table (m)T0i: Interception temperature(°C)

23 25

20

60

100

140

12

26 28 30 32

59

T(°C) 10

30

50

7090

24 25T0i

110

10

26 272524 24 25 2624 24 26

WT

53 4 19 22

Z (m)

T(°C)

Z (m)

Figure 6: Example of thermal profile.

Thermal behaviour is changing from an area to an another, from a well to another as well as within the same well. These differences in the Lateral and vertical temperature assessment depend on several factors: geological and structural homogeneity within the same region, the lithology and its degree of homogeneity within each well, the depth of water table and its temperature and the well location within the hydrodynamic frame. The temperature values of water range from 18 to 55.5°C.

From a well to another, several main types of profiles have been distinguished depending on whether the evolution V.S depth is increasing (Fig. 7a), steady (Fig. 7c) or decreasing (Fig. 7b). In the same well three main slope breaks in the termal profile have been noticed that are (Fig. 7d): G0 is the thermal gradient between the surface and the limit of influence of surface effects (10m), G1 is the thermal gradient between the groundwater level and he bottom of the limit of influence of surface effects, G2 is the thermal gradient between the groundwater level and the bottom of the well and GGSA is apparent shallow geothermal gradient. Also an another gradient has been defined Gwater that corresponds to the thermal gradient between the groundwater level and the interception temperature (T0i).

The cartography of some parametrizes (water temperatures and GGSA) for each basin show that the recharge outcrops zones of the turonian and lisaic aquifers are characterised by the high topography, high water potential, shallow cold water, low geothermal gradient and negative anomalies (Fig.8a-d). The disharge zones are characterised by low topography, low piezometric level, high geothermal gradient, high water temeprature with hot spring and positive anomalies (Fig. 9a-d).

Zarhloule et al.

4

0 40 80 12026

28

30

32T(°C)

Z(m)

a

0 20 40 6010 30 50 70

30

24

26

28

Z(m)

T(°C)

20 60 100015

25

35T(°C)

Z(m)

0 20 40 60 80 10010

20

30 T(°C)

Z(m)

G0 G1

G2GGSA

T0i

b

c

d

Water table

Figure 7: Different types of geothermal gradient: a) positive gradient; b) negative gradient; c) no gradient; d) main slope breaks in the thermal profile.

30 < Te < 32°C28 < Te < 30°C26 < Te < 28°C 24 < Te < 26°C 20<Te< 24°CTuronian

:Fault:Plio-Quaternary well :Turonian well

Agadir

26

0 10 km

:South Limit of Turonian deposit

El GounaBou Rbia

El HaffaiaOd Teima

Biougra

N

High-Atlas

Anti-Atlas

Atlantic

Ocean

a

30

28

30 24 24

24

26

26 24

El Kléa

Figure 8a: Temperature distribution map of water of the Turonian and Plio-Quaternary aquifers (Agadir basin).

Fes

Meknes

Hydrogeological well Southern limit of the RifThermal spring

25

40

25N

Te > 4035 < Te < 40

25 < Te < 35Te < 25

5 km

Pre-rifainb

35

Midle Atlas

Figure 8b: Temperature distribution map of water of the Liasic aquifer (South-Western basin: Saïss).

30

6 km

25

30

Beni Drar

Oujda

Aïn Sfa

Plio-quaternary well Permo-TriasicLiasic well Liasic- Dogger

Te > 3025 < Te < 30Te < 25

NNNNN

25

Mountain Horst

Algeria

c

Figure 8c: Temperature distribution map of water of the Liasic aquifer (South-Eastern basin: Oujda).

15 km

N

E.B FBS

BM

KT

OZ

Paleozoïc TuronianHydrogeological well KT: Kasba Tadla, EB: El Borouj, FBS: Fkih Ben Salah, BM: Beni Mellal, OZ:Ouled Zidouh.

3035

40 35

40

25

25

Te > 4035 < Te < 40 30 < Te < 35

25 < Te < 30

Te < 25

Atlasic Domain

d

30

Figure 8d: Temperature distribution map of water of the Turonian aquifer (Tadla basin).

GGSA > 35 °C/Km 25 < GGSA < 35 °C/Km 0 < GGSA < 25 °C/Km

Turonian

: Fault

: Hydrogeologica well (Turonian) : Hydrogeological well (Plio-Quaternary)

GGSA < 0

0 10Km

High-Atlas

Anti-Atlas

Atlantic

Ocean

Agadir

:South Limit of Turonian deposit

35

25

25 35

25

0

0

0

25

a

Figure 9a: Isovalue map of apparent shallow geothermal gradient (°C/km) (Agadir basin).

0

Fes

Meknes

N

5 km

GGSA > 40 C°/km

0 < GGSA < 20

GGSA < 0

20 < GGSA < 40

Hydrogeological well Southern limit of the RifThermal spring

Midle Atlas

Pre-rifain

b 40

20

0

2040

Figure 9b: Isovalue map of apparent shallow geothermal gradient (°C/km) (South-Western basin: Saïss).

6 km

Beni Drar

Oujda

Aïn Sfa

NGGSA > 50 C°/km

30 < GGSA < 50

0 < GGSA < 30

Algeria

Plio-quaternary well Permo-TriasicLiasic well Liasic- Dogger

c

30 30

30

30

50

50

50

Mountain Horst

Figure 9c: Isovalue map of apparent shallow geothermal gradient (°C/km) (South-Eastern basin: Oujda).

Zarhloule et al.

5

d

20

15 km

N

E.B

KT

GGSA > 40

20 <GGSA< 30 GGSA < 20

30 <GGSA< 40

Paleozoïc TuronianHydrogeological well KT: Kasba Tadla, EB: El Borouj, FBS: Fkih Ben Salah, BM: Beni Mellal, OZ:Ouled Zidouh.

20 30

4040

4040

30

OZ

FBS

BM

Figure 9d: Isovalue map of apparent shallow geothermal gradient (°C/km) (Tadla basin).

The bottom shallow wells temperatures values are plotted against depth (Fig. 10) showing a rather important disturbed points either for highs or lows. Giving the fact that normal temperature can be considered, at a given depth, as the one in agreement with the regional geothermal gradient, noticible higher and lower values at the same depth, should be considered as anomalous. Negative anomalies correspond to the recharge zone of each aquifer with topographic highs and infiltration meteoric cold water, whereas positive anomalies correspond to the shallow upcoming hot water and to the more or less well defined disharge zones.

15

20

25

30

35

40

0 100 200 300 400 500

Temperature (°C)

Depth (m)

30 °C/K

m

Figure 10: Bottom shallow hydrogeological wells temperture V.S depth

The main thermal indices (Fig. 11) and the principal thermal anomalies coincide with the zones of turonian and Liasic aquifers. Also the water temperatures of the shallow aquifer is higher to the neighborhood of the artesianisme zones of the deep aquifers that in the rest of the basins. What explians the existence of a groundwater flow from deep aquifer to shallow one favoured by an abandant fracturation.

5. GEOCHEMISTRY OF THERMAL SPRINGS IN NORTHERN MOROCCO

The Northern Morocco basin is constituted by a lithological succession from paleozoïc to Quaternary (Fig.1) and only the Liasic limestone aquifer is an importante hydrogeothermic unit. The Numerous hot springs are know in the North part of Morocco (Fig. 12a-b) (Lahrach et al.1998, Zarhloule, 1999).

The outcrops are limited to the Middle-Atlas (Saïss), the Northern and the Southern areas of Oujda. The aquiclude consists of the Cretaceous to Tertiary sediments (schale). The hot springs emanating from the limestone liasic aquifer, have been inventoried and analysed in order to characterize

the origin-reservoir, to evaluate undergroud temperature and to determined the mixing shallow cold water with deep hot water.

a

b

c

Mediterranean Sea

SebtaTanger

Rabat

Fès

300 KmNNNNN

Hauts Plateaux

Saïss

Rif

mio-plio-quaternaryvolcanism

a Termal anomalies

Oujda

Nouthern part of Morocco

10KmN

High-atlas

Anti-Atlas

E.BFBS

BMAfDOZ

NNNNN15 KmTadla basin

DOZ, Daouar Ouled Zidouh. EB: El Borouj, FBS: Fkih Ben Salah,

15Km

Termal anomaliesb

c Termal anomalies

Agadir basin

Figure 11: Map of shallow geothermal anomalies in Morocco.

Fes

Meknes

14

9104

16

12

118

1510 km

South rifin zones

Liasic Permo-TriasicPaleozoïc

Thermal water

N

Rharb

Rifan zoneRides South-rifan limit

Mio - Plio - Quaternary

Saïss

23

7

213

5 1

Midlle Atlas

Plain of

Figure 12a: Geological skech map of the North western of Morocco (Saïs basin) with location of simpling sites.

5.1 Water chemistry

Major (Na, K, Ca, Mg, HCO3, SO4 and CL) and minor (SiO2, Li) components in solution (mg/l) are reporeted in Table 1.

We retained all the analysed springs with good ionic balance. From Table I it can be seen that PH varies from 6.9 to 7.9, temperature ranges from 22 to 54°C, salinity from 0.13 to 27.6 g/l. From the North Western to the North Eastern part of Morocco, there are wide variations in these parametrs because for the same aquifer system there may be heterogeneity within a given reservoir and /or variation in the upflow routes linking the reservoir to the surface (Zarhloule 1999, Lahrach et al.1998).

Based on the relative amount of major ions, The water classification has been made in Figure.13, using the Langelier and Ludwing diagram (1996).

Zarhloule et al.

6

5 m

Beni Methar

41

424344

45

47

NNNNN

46

Taourirt32

10 km

N

1817

19

20 21

22

23

24

25

27

5 Km 262829

3031N

Oujda

Alge

ria

Oujda

25 km

Melilla

Ahfir

Taourirt

Mio-plio-quaternary volcanism Mediterranean Sea

N

Berkane

Beni Mathar

5 km

Ahfir

Berkane

33 3435

36

37

38

3940

N AlgeriaEastern Beni Snassen

GuercifBasin Horst z

ones

Ben Snassen Montain

Gareb M

ontainKebdana

Thermal waters

Neogen and QuaternaryRifan unitCarbonate rocks (Mesozoic)

Algeria

Oujda

Figure 12b: Geological skech map of the North Eastern of Morocco with location of simpling sites.

Ca

+ M

g

Na

+ K

HCO3 + CO3

SO4 + Cl

113

2

3

4

5

6

78

9

10

11

12

14

1516

17

1819

20

2122

23

24

25

26

27

28

29

3031

32

33

34

35 3637

38

39

40

4142

4344

4546

47

0 5050

0050

50

0

C

B

A

Figure 13: Langelier-Ludwing diagram for the water samples investigated.

The hot waters can be grouped into Ca (Mg)-SO4 (Cl) (A) type waters with moderate salinity (<3g/l), Ca(Mg)-HCO3 (B) type waters with low salinity (<700mg), and Na-Cl (C) type waters with a salinity that varied from 0.61mg/l to 27.6g/l. The C type waters showed a chemical composition nearby to the Ca-Mg with the exception of springs N° 5,11,13 and 32 who have a high salinity. This can be due to the interaction of water with the different rocks principally evaporitic one.

Table 1: Chemical composition of thermal waters from northern Morocco

30 2311/ 12 28 7.1 580 1.7 74 76 56 142 366 33 12

N°

1 A.H.du Zalagh 35.5 7.1 3850 32 1325 88 42 2066.1244 184.3 17.1 5

Name T (°C) pH TDSK

+Na

+Ca

2+Mg

2+Cl

-HCO

3-

2 A. Anseur 24 7.3 510 9 70 68 21 78.1 280.6 111.9 10.3 1.23 A.Maaser 25 7 610 2 125 73 18 177.5 256.2 62.5

Ben Kachour18 51 7.2 2680 14 899 70 51 1391 311 181 26.4 0.1

5 M. Y. Outita 39 7.4 6230 37.8 1704.7 349.2 122.4 3735.9292.8 1139 24.8 76 A. El Beida 22 7.6 460 8.5 65 84 18 92.3 219.6 64.27 A. Es-Skhoun 25 7.5 440 1.9 51.1 74.8 24.8 87.3 283.6 34.5 188 A. H. My. Idriss31 7.2 2850 6.2 282.2 465 106.1 476.4 283.6 1379 12.8 5.29 A. Skhinat 33 7.1 1020 6 244 66 38 440.2 292.8 59 11.1 1.3

10 S. Harazem 35 7.3 710 3.8 150 62 36 312.4 256.2 14 9.4 1.711 My. Yacoub Fès54 7.2 23430 320 7900 1150 260 13668 219.6 28 30.8 6012 A. Allah 45 7 450 1.3 50 50 48 71 335 67 11.1 0.413 M. Y. Tiouka 24 7.8 27610 143 10230 775 400 15365 756 328 16.3 5.314 A. S. Metmata 31 7.6 1120 3 300 50 36 525.4 317.2 36.2 1015 A. H .Bou Draa 22.5 7.3

39016 2527/15 38 7 2 57 41 22 149.1 170.8 37.8 11.1 0.43.1 75 87.4 29.9 120 271.4 89.7 13

17 Camp. Rose

20 2843 / 12 28 7.6 1010 2.3 53 61 55 220 154 90.5 10.21225 / 1219 26 7.4 1040 13 335 14 34 362 133 102.8 13 0.1

21 2899 / 1227

7.6 620 2.7 80 60 52 230 135 57.6 11.222 2933 / 1223 2952/ 12 46.5 7.1 2960 18 920 114 52 1508 372 192 25.7 0.224 2431 / 12 30 6.9 695 1.8 72 70 59 181 353 48 1525 2364 / 12 26.5 7.4 615 1.6 117 72 58 106 378 172 13.826 2363 / 12 28 7.4 700 2.1 69 76 58 135 402 52 12.327 Oued Nachef IV33 7.1 870 3 149 66 60 305 378 96 18 0.228 Champ de tir 29 7.5 2880 9.8 869 80 50 1363 323 96 16 0.229 1255 / 12 29 7.2 640 3.2 179 64 54 255 323 139 12.8 0.1

31 1125/ 12 28 7.3 715 1.7 71 74 58 156 347 67 12.432 S. Gouttitir 49 7.3 9700 24.7 2472 870 169.2 4110.9 199 2146.1 34.6133 Tercha 28 7.3 360 1.5 30 37 38 35 268 67.5 12.334 Fezzouane 37 7.9 340 1.1 22 70 36 28 292 19.5 15.335 Sidi Rahmoune 29 7.4 500 1.7 43 66 44 106 353 24.3 13.236 Aichoun 29 7.8 130 1.7 32 74 33 60 341 33.4 12.8

37 S. Aoulout 20.5 7.4 320 2.6 32 55 49 60 341 55.9 12.238 S. Kiss 27 7.1 780 45 330 104 52 610 281 176 17.339 1292 / 7 24 7.2 755 1.9 94 60 50 184 341 33 12

40 1267 / 7 34.5 7.9 395 0.7 18 60 44 24 378 33 20 0.141 22 / 18 26 7.1 870 2.3 162 86 49 273 286 124 13.6

42 62 / 18 27.5 7.2 630 2.8 135 56 62 266 274 76 12.643 159 / 18 26.5 7.7 860 2.5 142 56 44 220 268 48 1344 170 / 18 27.5 7.1 1020 39.9 135 58 68 248 280 187 12.145 171 / 18 25 7.9 1740 5.9 219 170 94 433 225 470 12

188 / 1846 26 7.3 1710 4.1 175 160 94 426 237 350 1447 35 / 18 29 7.3 625 3 144 56 65 266 274 144 15

4 A. S. Trhat 26 6.9 840 4.6 198 34 28 277.2 305 139.9 15.4 1.7

SO42- SIO2

28

25.5

7.6

7.6

540

1005

650

2.6

3.3

37

55

60

85

66

53

152

230

329

130

62

117.7

13.2

14.3

Limg/l mg/lmg/l

Zarhloule et al.

7

Table 2: Chemical geothermometry. Application in Northern of Morocco.

30 2311/ 12 28 45 31.5 13 17 81 122 70 115 117 237 17

N°

1 A.H.du ZalaghName T (°C)Qz Rof Qz ArnCal RofCal Arn

Na/Li L S

Na/LiH S

2 A. Anseur3 A.Maaser 25 61 91 49 91 98 88 67

Ben Kachour18 51 74 61.5 43 46 7 60 10341 48 89 97 270 27 28

5 M. Y. Outita6 A. El Beida 22 224 218300 300 241 165 677 A. Es-Skhoun 25 59.5 46 27 31 114 155.5 103 155.5 146 108 478 A. H. My. Idriss 31 48 34 15 19 353 112254 79 67 112 115 98 67.5 529 A. Skhinat 33 43 29 10 15 195 244 85 120 73 120 120 112 26 45

10 S. Harazem 35 37 23 4.5 9 280 306 87 122 76 122 122 108 27 51.511 My. Yacoub Fès 54 80.5 68 49 52 538 161 107272 118 161 150 165 69 8812 A. Allah 45 43 28 10 15 237 124 77276 89 124 123.5 96 1913 M. Y. Tiouka 24 56 42 23 27.5 456 54.5 82 42242 82 91.5 123 29 74.514 A. S. Metmata 31 39 25 6.5 11 39 63 26 63 76 8415 A. H .Bou Draa 22.5 48 34 15 20 120 163 109 163 152 116 4516 2527/15 38 42 29 10 15 223 108 148265 97 148 141 110 28 3317 Camp. Rose 28 49 35 16 20 162 189 152 217 188 310 27.5

20 2843 / 12 28 40 26 7 12 123 158 112 167 155 279 221225 / 1219 26 48 34 16 20 45 115 151 10481 157 147 346 36 32

21 2899 / 12 25.5 43 29 10 105 14315 94 145 139 270 2022 2933 / 12 27 51 38 19 23 148 178 138 199 177 302 3923 2952/ 12 46.5 73 60 41 45 31 72 11467 60 104 108 283 49 4124 2431 / 12 30 53 39 21 25 86 126 75 121 121 243 1525 2364 / 12 26.5 50 36 17 22 53 97 41 81 90 214 11.526 2363 / 12 28 46 32 14 18 99 137 87 136 133 255 2027 Oued Nachef IV33 60 46 27 31 128 74 115166 62 106 110 246 14 3928 Champ de tir 29 55 42 23 27 34 44 89 3269 70 82 244 25 4129 1255 / 12 29 47 34 15 19 75 67 109.5 55112 98 103 242 15 28

31 1125/ 12 28 46 33 14 18 84 124 72 118 119 239 1632 S. Gouttitir 49 85 73 54 57 59 95 39 26 63 76 232 84 628333 Tercha 28 46 32 14 18 134 166.5 123 181 164 281.5 2034 Fezzouane 37 54 40 21 25 134 166.5 123 181 164 265 3535 Sidi Rahmoune 29 49 35 16 20 116 152 105 159 148.5 265 2636 Aichoun 29 48 34 15 19 138 170 128 187 168 279 4537 S. Aoulout 20.5 46 32 13 18 175 200 166 234 200 320 3538 S. Kiss 27 58 45 26 30 229 241 223.5 307 245 455 13139 1292 / 7 24 45 31.5 13 13 74 116 62 106 110 207 1040 1267 / 7 34.5 63 50 31 35 260 115 151294 104 157 147.5 243 18 2941 22 / 1842 62 / 18 27.5 47 33 14 19 75 117 64 108 111 247 1243 159 / 18 26.5 48 34 15 20 66 109 54 97 103 237 1644 170 / 18 27.5 46 32 13 17 340 319 344 465 332 545 14745 171 / 18 25 45 31.5 13 17 90.9 130 79 127 125.5 265 32

188 / 1846 26 51 37 18 22 82.5 123 71 116.5 118 250 2647 35 / 18 29 53 39 21 25 75.7 117 64 108 111 249 11

4 A. S. Trhat 26 54 40 21.5 25 245 282 82 116 70 115.9 117 112 57

Na/KArn1

35.5 58 44 25 2924

39

26

40

72

50

26

59

36

7

40

17

12

43

21

164341

171

347 222

55

119298

113

99

73216

68

43

Na/KArn2

Na/KTr

Na/KMi

Na/K Rof

Na-K-Ca Na-K-CaMg Mg/Li

220

226

84

79

119298

113

83

119239.5

115

92

133167.5

123

221

3447

44

22

7255.5

56

The application of the IIRG diagram (D’Amore et al.1983) (Fig.14 ), show the same results gotten by the Langelier and Ludwing diagram.

100

50

0

-50

-100A B D EC F

N°.12 100

50

0

-50

-100A B D EC F

N°.15, 16

100

50

0

-50

-100A B D EC F

N°. 14100

50

0

-50

-100A B D EC F

N°. 2, 6, 7, 10 100

50

0

-50

-100 A B D EC F

N°. 8

100

50

0

-50

-100A B C D E F

N°.1, 3, 4, 5, 9, 11, 13

% INDICES

INDICES

100

50

0

-50

-100 A B C D E F

N°. 17, 19, 20, 25, 26, 30.

N°. 18, 19, 23, 27, 28, 29. 100

50

0

-50

-100A B C D E F

100

50

0

-50

-100 A B C D E F

N°. 32.100

50

0

-50

-100 A B C D E F

N°. 21, 24, 22.

100

50

0

-50

-100A B C D E F

N°. 45, 46.100

50

0

-50

-100A B C D E F

N°.41, 42, 43, 44, 47.

100

50

0

-50

-100A B C D E F

N°. 38, 39. 100

50

0

-50

A B C D E F-100

N°. 33, 34, 35, 36, 37, 40. A: anhydritic rocks, B: Limestonecirculation, C: Deep circulation prowithin the cristalline basement,D: Marl-clay sediments, E: circulatlimestone or sulphate reservoir, F: the increasing of cencentration of K

Figure 14: IIRG diagram for the water samples

investigated.

The thermal waters are mainly Cl or HCO3-Ca and Mg. The parameterize calculated (A, B, C, D, E, F) are reported in Figure and Table . That shows that the thermal springs (1, 3, 4, 5, 9, 10, 11, 13, 14, 18, 19, 23, 27, 28, 29, 38, 41 and 42) have a deep circulation in detrital layers , what shows the influence of the evaporitic rock of the Triasic on the chemical composition of the water. The springs and a borholes (2, 6, 7, 12, 15, 16, 17, 20, 24, 25, 26, 30, 31, 33, 33, 34, 35, 36, 37, 39, 40 and 43) have a limestone origin also revelead by the local geology near of the emergence zones (36, 37 and 2). The points (21, 22, 44, 45, 46 and 47) show that the waters circulated in the limestone resrvoir in contact with a evaporitic rock of the Triasic. The thermal springs N°32 and 8 have a deep circulation with influence of gypseous layers.

5.2 Geothermometry

The following geothermometers were applied to estimate subsurface temperatures and the depth of the thermal aquifers by using the geothermal gradient (Zarhloule, 1999, Lahlou Mimi et al 1999): silica (Fournier et Rowe, 1966, Arnorson et al., 1983), Na/K (Fournier, 1979, Truesdell, 1976, Michard, 1979, Arnorson et al., 1983, Arnorson, 1983), Na-K-Ca ( Fournier and Truesdell, 1973), Na-K-Ca-Mg ( Fournier and Potter, 1979), Mg/Li (Kharaka and Mariner, 1986) and Na/Li (Fouillac and Michard, 1981). Table 2, shows the temperature estimates from the above geothermometers. Extreme values revealed by each are: 37

Zarhloule et al.

8

to 85°C (QzRof), 23° to 73°C (Qz Arn), 7 to 54°C (cal Rof) and from 12 to 57°C (cal Arn). The mesaured températures are ranges from 20°C to 54°C.

In order to evaluate the applicability of those geothermometers (Lahrach et al.1998, Zarhloule, 1999), the estimated values are plotted against the measured values(Tm). Figures 15a-i, show the plots of Tm versus alkaline geothermometers (TNa/K-Arn2, TNa/K-Tr, TNa/K-Mi, TNa/K-Rof, TNa-K-Ca, TNa-K-Ca-Mg, TMg/Li, TNa/Li high salinity and TNa/K low salinity).

0

50

100

150

200

250

300

350

20 25 30 35 40 45 50 55

Na/K Tr

b

y= -2x + 156R=0.25N=47

0

100

200

300

400

500

20 25 30 35 40 45 50 55

Na/K Mi

c

y= -2x + 221R=0.25N=47

0

100

200

300

400

500

600

20 25 30 35 40 45 50

Na-K-Ca

e

y= -2x + 274R=0.14N=47

0

100

200

300

400

500

600

20 25 30 35 40 45 50 55

Na/Li low salinity

i

y= -1.6x + 259R=0.1N19

0

50

100

150

200

250

300

350

20 25 30 35 40 45 50 55

Na/Li high salinityh

y= 1.4x + 79R=0.5N=19

10

20

30

40

50

60

70

80

90

20 25 30 35 40 45 50 55

Mg/Li

g

y= 0.1x + 44R=0.05N=19

50

100

150

200

250

300

350

20 25 30 35 40 45 50 55

Na/K Arn 2

a

y= -1.8x + 200R=0.26N=47

50

100

150

200

250

300

350

20 25 30 35 40 45 50 55

Na/K Rof

dy= -2x + 189R=0.26N=47

0

50

100

150

20 25 30 35 40 45 50 55

Na-K-Ca-Mg

f

y= 0.5x + 22R=0.13N=44

Figure 15a-i: Plot of Tm Vs alkaline geothermometers.

The wide spread of the geothermometer values reveal that these temperatures can not be considered reliable. This could be explained by a strong possibility of a mixing between fresh and deep waters during upflow from the reservoir to surface such mixing could greatly affect all the geothermometry. Also the water composition is greatly affected by the interaction with the evaporitic rocks that are ubiquitous in the region.

The silica geothermometers have been applied: quartz Rof (TQRof ), quartz Arnorsson (TQArn), chalcedony-Rof (Tcal-Rof) and chalcedony-Arnorsson (Tcal-Arn). Figure 16a-d, shows the plot of TQRof, TQArn, Tcal-Rof and Tcal-Arn against Tm, with the correlation coefficients of 67%.

30

40

50

60

70

80

90

20 25 30 35 40 45 50 55

y = 22.76 + 0.94x R= 0.67 N=47

Tm (°C)

TQz Rof (°C)

20

30

40

50

60

70

80

20 25 30 35 40 45 50 55

y = 8.12+ 0.97x R= 0.67 N=47

T Qz Arn (°C)

T m (°C)

0

10

20

30

40

50

60

20 25 30 35 40 45 50 55

y = -5.05+ 0.92x R= 0.67 N=47

Tm (°C)

Tcal Arn (°C)

(d)

0

10

20

30

40

50

60

20 25 30 35 40 45 50 55

y = -10.7+ 0.97x R= 0.67 N=47

T Cal Rof (°C)

Tm (°C)

(c)

(b)(a)

Figure 16a-d: Plot of Tm Vs silica geothermometers.

Temperature estimated by QRof are systematically higher than for the other three. It ranges from 37 to 85°C for Qrof, 23 to 73°C for QArn, 7 to 54°C for Cal-Rof, 12 to 57°C for Qcal-Arn. The mesured temperatures ranges from 20 to

54°C. Also the gap between the measured and estimated temperatures (TQRof) are all positive (except N°12) and it ranges from 2.4°C (n°10) to 36.4°C (n°32). On the other hand, several Tcal-Rof and Tcal-Arn are lower than Tm, for which silica equilibrium seems to be in correspondence with Quartz (Fig. 17).

20

40

60

0 20 40 60 80

Tm (°C)

5

32

38713

SIO2 (mg/l)

12

Figure 17: Application of the silica gheothermometer.

While the other springs especially for n°5, 7, 13, 32 and 38 show a good tendency to ward the chalcedony curve. The deep reservoir temperatures cannot be lower than the spring discharge temperatures, so the chalcedony temperatures appear to be in error for the other springs. So, only the silica geothermometers quartz Rof and quartz Arnorsson seem to give plausible values, except for the springs n° n°5, 7, 13, 32 and 38 whose temperature is estimated better by chalcedony. The silica geothermometer used for the thermal waters in North part of Morocco gave 81°C as a maximum value (n°11). Similar estimates have also been obtained through application of the K-Na-Mg technique (Giggenbach, 1988) summarized in the K/100-Na/1000-Mg1/2 ternary diagram of Figure 18. where the most of thermal springs are aligned towards the Mg corner, suggesting very low K2/Mg deep temperatures that varying between 60 and 100°C, what could be to explaine by the enormous dilution with the waters of shallow aquifers in the

*

*

*

*

**

****

**

**

**

Na / 1000

K / 100 Mg1/2

50 %

50 %

300°

2x4x

10x

200°100°

dilution

240° 16

0°

1113

5

132

Partial equilibrium dilution

immaturewaters

fullequilibrium line

Figure 18: Application of ternary diagram (Giggenbach, 1988) showing relative cation concentrations for thermal springs.

Zarhloule et al.

9

The depth of the thermal aquifers in the North part of Morocco is gotten by the use of the deep geothermal gradient calculated from the petroleum well that ranges from 19 to 42°C/km (Zarhloule, 1999) and the deep temperatures estimated from the geothermometers. The depth of thermal aquifers ranges from 524m to 1700m.

5.3 Schematic and idealized hydrogeological model of thermal waters in Northern Morocco.

As shown in Figure 19, the outcropings zones of the Liasic aquifer are characterized by shallow cold water and both from cold spring and hydrogeological wells are mainly Ca(Mg)-HCO3 type, resulting from great influence of carbonate rocks. The discharge zones are characterized by shallow hot water. The hot springs are generaly Ca(Mg)-SO4(Cl) or Na-Cl, resulting from infleunce of evaporitic rocks. The midle of the basin shows a communication between the deep and the shallow aquifers and the waters are Ca(Mg)-SO4(Cl) or Ca(Mg)-HCO3. In this zone there is a high dilution of thermal water by the shallow aquifers.

Thermal springs, high temparatureMedium temperature water Cold water

Ca (Mg)-HCO3Ca (Mg)-SO4 (Cl) ou Na-Cl

Hihg mixing waterLow mixing water Ca (Mg)-SO4 (Cl) ou Ca (Mg)-HCO3

Limestone (deep aquifer)

Marl-ClayEvaporitic rocksBasalteEvaporitic rocks

Paleozoïc Basement

AlluvionsCalcareous

Marl

Tufs and clayPlio-Quternary(shallow aquifer)

Permo-Triasic

Cretaceaous

Jurasic

Tertiary

Source froide

Source chaude

Forage artésien d'eau chaude

water flow

SN

Disharge zoneRecharge areaTranstition area

Deep of the reservoir 1700m as maxumumTemperature estimated by geothermometer 80°C-100°C

Figure 19: Conceptuel model: relation between topography, temperature, geochimestry and hydrodynamics.

6. DEEP GEOTHERMAL GRADIENT OF MOROCCO: PETROLEUM DATA

The aim of this study is to establish a geothermal gradient map for the whole of Morocco, by using thermal data obtained from petroleum exploration wells. Both the corrected bottom-hole temperatures (BHT) and the drill-stem test temperature (DST) were used to elaborate the geothermal gradient map. A total of 410 wells provided 1204 temperature values (1126 BHT and 78 DST) (Fig. 20).

100 km

Oujda

MelillaTanger

RabatCasablanca Fès

Taza

Tadla

Colomb Bechar

Errachidia

OuarzazateAgadir

Bir LahlouSmaraBoukraa

Boujdour

Tarfaya

Laayoune

Guelta Zemmour

Bir Enzaran

10 km

10 km

Mediterranean sea

Atlantic ocean

N

Essaouira

Iles canaries

ZL1AZ1

Smara2-17

TW561

TW521

IFNI1

E1

MO4

AF4

OZ101

KAT1

IZA1

LARA1ANS1

DHT1

MAO1

TAT1RH1 à 9

NDK

DIR

ESS1

RR1

ATM1

BHL1

RJK1

MO8

TGA1

Corc1

TW7-1

EAN1

4°6°8°10°12° 2°14°16°

34°

32°

30°

28°

26°

24°

Figure 20: Location of petroleum wells used.

BHT were systematically corrected for mud circulation cooling effects either by Horner technique when several temperature records are available at a given depth or by the

comparison of all BHT with test temperatures (DST) that are representive of the actual formation temperatures. In order to establish the geothermal gradient of Morocco , the area was subdivided into five hydrogeothermal basins (Fig. 1): north-eastern basin, north-western basin, Errachidia-Boudnib basin, south-western basin and the tarfaya-laayoune-sahara basin. Each basin presents the same geodynamical evolution and is characterised by its specific reservoirs and hydrodynamism. For each basin the petroleum well data have been processed. The objective was to set a regional geothermal gradient map, and then to compilate a geothermal gradient map of Morocco.

6.1 Processing of temperature values

Temperature behaviour with depth is studied both for the rough BHT (Fig. 21a-g) and DST (Fig.22)..

20

40

60

80

100

120

140

160

0 1000 2000 3000 4000 5000

Tbht = 23z + 23r = 0.79N = 53

BHT (°C)

Depth (m)

a

20

40

60

80

100

120

140

160

0 1000 2000 3000 4000 5000

Tbht = 23z + 29r = 0.92N= 555

BHT (°C)

Depth (m)

b

20

60

100

0 2000 4000

Tbht = 18z + 29r = 0.91N = 298

BHT (°C)

Depth (m)

c

30

50

70

90

0 500 1500 2500

Tbht = 19z + 32r = 0.95N = 16

BHT (°C)

Depth(m)

dTadla basin

20

60

100

0 500 1500 2500 3500

Tbht = 25z + 17 r = 0.97N= 49

BHT (°C)

Depth(m)

Errachidia-Boudnib-Ouarzazatebasin

e

20

60

100

140

0 2000 4000

Tbht = 19z + 29r = 0.92N= 155

BHT (°C)

Depth (m)

Tarfaya-Laayoune-Sahara basin

f

0

20

60

100

140

0 2000 4000

Tbht = 20z + 29r = 0.90N = 1126

BHT (°C)

Depth (m)

Morocco

g

Northeastern basin of Morocco Northwestern basin of Morocco Southwestern basin of Morocco

BHT: Bottum hole temperature (°C)r: correlation coefficientN: number of temperture BHTz: depth (m)

Figure 21: BHT vs depth for each basin

The least squares fitted straight line gave: For BHT(Fig. 21), T= az+Ts, where a is the slope of the straight line and the average geothermal gradient measured in the mud, Ts is the BHT at the surface and T is the BHT (°C) at any given depth z(m). For Morocco the average geothermal gradient is 20°C/km. For the DST (Fig. 22), T=az+Ts, where a is the averge geothermal gradient of DST, which could be the value nearest the true geothermal gradient, and Ts is the surface temperature, representing the mean annual temperature as indicated by climatic surveys. For Morocco the geothermal gradient from DST is 24°C/km

40

60

80

100

120

140

0 1000 2000 3000 4000

Tdst = 25z + 22.5r = 0.98N = 14

Errachidia-Boudnib-Ouarzazatebasin

Depth (m)

DST (°C) b

0

20

40

60

80

100

120

0 500 1500 2500 3500

Tdst = 23z + 21r = 0.97N = 48

DST (°C)

Depth (m)

Southeastern basinof Morocco

20

40

60

80

100

120

140

0 1000 2000 3000 4000 5000

Tarfaya-Laayoune-Sahara basin

Tdst=26z + 21r = 0.93N = 16

DST (°C)

depth (m)

c

20

40

60

80

100

120

140160

0 1000 2000 3000 4000 5000

Tdst = 24z + 23r = 0.92N = 78

DST (°C)

Depth (m)

Morocco

d

a

Figure 22: DST vs depth for each basin

With DST values as references, it was possible to calculate the difference (∆T) beween DST and BHT at the same depth for each value. Plotting the ∆T values with depth (Fig. 23a)

Zarhloule et al.

10

gave a curve wich is used a correction abacus. Also, for the Northern part of Morocco, there is no DST values, the application of the Horner plot method’s allowed us to correct the BHT tempertures in this area (Fig. 23b).

0

2

4

6

8

10

12

14

0 1000 2000 3000 4000 5000

∆(t)= 0.003z - 0.86r = 0.98N= 33

∆t (°C)

z (m)

Southwestern basin

2

3

4

5

6

7

8

1000 2000 3000 4000

∆(t)= 8.6*logz - 23r = 0.95N= 9

∆(t)

z (m)

Errachidia-Boudnib-Ouarzazate basin

0

1

2

3

4

0 1000 3000 5000

Tarfaya-Laayoune-Sahara basin

∆(t) = 3.5logz-8.5r = 0.93N = 18

∆(t) (°C)

z(m)

0

2

4

6

8

10

12

14

0 1000 2000 3000 4000 5000

∆(t)= 0.002z + 0.062r = 0.85N = 60

∆(t) (°C)

z(m)

Morocco

Figure 23a: ∆T vs depth

0

40

80

120

160

BHTc = 0.035z + 4r = 0.9N = 15

BHT corrected (°C)

Depth (m)

Extrapolated temperatures values

0 500 1500 2500 35000

40

80

120

160

0 500 1500 2500 3500

BHT = 0.03z + 8.6r = 0.86N = 15

BHT (°C)

Depth (m)

Measured tempertures values

Figure 23b: Application of Horner plot method’s.

Thus, after correcting all the BHT values, we plotted coorected BHT and DST with depth (Fig. 24a-g). The least squares fitted straight line gave: T= az + Ts, where T is the undergroud temperature at any given depth z, a is the slope, representing the average geothermal gradient in the region (28°C/k for north-eastern basin, 27°C/km for north-western basin, 28°C/km for Errachidia-ouarzazat-Boudnib basin, 21°C/km for the south-western basin, 21°C/km for the tarfaya-laayoune-sahara basin, 22°C/km for Tadla basin and 23°C/km for the whole of Morocco) and Ts is the surface temperture.

BHTc (°C)DST(°C)

0

20

60

100

140

0 2000 4000

z (m)

T = 21z + 28r = 0.95N = 346

South westernbasin

c

30

50

70

90

0 1000 2000 3000

T = 22z + 31r = 0.96N = 16

BHTc (°C)

z(m)

Tadla basin dBHTc (°C)DST (°C)

0

20

60

100

140

0 1000 2000 3000 4000

T= 28z + 16r = 0.98N = 63

z (m)

Errachidia-Boudnib-Ouarzazate basin

eDST (°C)BHTc (°C)

0

20

60

100

140

0 2000 4000

T = 21z + 28r = 0.93N = 171

Tarfaya-Laayoune-Sahara basin z (m)

f

50

100

150

200

1000 3000 5000

T = 23z + 28r = 0.92N = 1205

Morocco

BHTc and DST (°C)

z (m)

g

0

80

160

0 2000 4000

T = 28z + 19r = 0.85N = 54

BHTc (°C)

z (m)

Northeastern basin a

0

50

100

150

200

0 1000 2000 3000 4000 5000

T = 27z + 25r = 0.94N = 556

BHTc(°C)

z (m)

bNorth western basin

0

BHTc: corrected BHT(°C)DST: drill steam temperaturez: depth (m)r: correlation coefficientN: number of temperaturesT: Temperture

Figure 24: Corrected temperature vs de

6.2 Geothermal gradient map of each basin

Corrected BHT and DST values for each well will be used to estimate theaverge geothermal grdaient to selected wells and thus to construct the geothermal gradient map for each hydrogeothermal basin and the compilation of the regional maps allowed us to establish he geothermal gradient for the whole of Morocco.

In the North-Western part of Morocco (Fig. 24a) the deep geothermal gradient ranges from 26°C/km to 35°C/km . Zones of relatively high geothermal gradient seem to correspond to zones proved or supposed faults. Also the anomalies are related to deep hydrodynamic activities (Zarhloule, 1999).

The spatial distribution of geothermal gradients in the North-Eastern Morocco (Fig. 24b) could be related to the hydrodynamic effects and the neotectonic associated to the recent volcanim. It ragnes from 15 to 42°C/km (Zarhloule, 1999).

FesRabat

TangerSebta

OC

EA

N

AT

LA

NT

IC

100 km

Larache

SPAIN

28 geothermal isogradient curve (°C/km), petroleum borhole

N 6° 5°

35°

34°

26

28

3230

32

2826

28

30

34

Mediterranean Sea

Figure 24a: Geothermal gradient map of the North-western basin of Morocco.

100 km

18

22

26

26

30

30

34

38

42

MelillaEl Hoceima

Oujda

Taza

Mediterranean seaN

18 geothermal isogradient curve (°C/km), Petroleum well

N 3°4°

33°

34°

35°

Figure 24b: Geothermal gradient map of the North-Eastern basin of Morocco.

In the South-Western basin (Fig. 24c), the higher geothermal gradient observed in the center could be the consequence of proximity to the Tidsi diapir, given the high thermal conductivity of evaporitic rocks (Zarhloule et al., 1998). Also the anormal geothermal gradient is related to

Zarhloule et al.

11

the deep hydodynamic effects (oxfordian reservoirs) (Zarhloule, 1994). In the South of the basin, the geothermal gradient is related to the basement faulting.

27

2123

25

27

29 29

21

23

25

2723

25

27

21

25

isogradient curve (°C/ km)25

Essaouira

FaultFault

21

17

23Safi

Kourati Mountain's

Hadid Mountain's

Ihchech Mountain'sAmsitene Mountain's

N

21

23

N

32°

Atlantic

Oean

JurassicTriasic (diapir)Permian

Petroleum well

10 km

3329

31

25

25

29

31

Agadir

Anti-Atlas

21

27

27

Turonian

9°10°

31°

21

19

Figure 24c: Geothermal gradient map of the South-Western basin of Morocco.

The Tarfaya-Laayoune-Sahara basin (Fig. 24d) presents two domains with a relative high geothermal gradient: the on-shore domain characterized by a great fault basement of N65 to N70 direction revealed by geophysics, and the off shore domain where the Miocene volcanoes of the Canary Islands contribute to increased geothermal gradients (Zarhloule, 1999).

100 km NPetroleum borehole

geothermal isogradient curve (°C/km)

32 3028

2624

2628

32

26

2022

24

26

30

32

24

24

26

Tarfaya

Laayoune

Boujdour

Dakhla

Samara

Tindouf

ATLANTIC

OCEAN

CANARIAS

MAURITANIE

34

N 22

20

29°

25°

16° 10°

24

Figure 24d: Geothermal gradient map of Tarfaya-Laayoune-Sahara basin.

The regional distribution of geothermal gradients in the Errachidia-Ouarzazate-Boudenib basin (Fig. 24e) shows that the relatively high geothermal gradients could be related to subsidence and the basement proximity, respectively, in the south-eastern and southern sectors in the basin (Zarhloule, 1999).

30 km

High-atlas

Errachidia

Senonian

PaleozoïcSouth-atlasic fault

N

30

2220

2426

28

2628

30geothermal isogradientcurve (°C /km)

N

31°

5° 3°

30°

Petroleum borehole

Figure 24e: Geothermal gradient map of the Errachidia-Ouarzazate-Boudnibe basin.

For the whole of Morocco (Fig. 25) the geothermal gradient varies from 15 to 42°C/km. A distinction can easily be made between zones of high geothermal gradient (>30°C/km) and others of low geothermal gradient (<30°C/km). The major part of the region is characterized by low gradient ranging from 20 to 30°C/km. The areas of high gradient marked in the regional maps (Fig. 24a-e) are in the geothermal gradient map of Morocco (Fig. 25). The isogradient curves dispaly several main directions where the geothermal anomalies are related to deeper hydrodynamic, recent tectonic, volcanism or to elevation of the Moho (Zarhloule, 1999, 2003).

0 100 km

Oujda

Melilla

Tanger Sebta

Kénitra

Fès

Azrou

Tadla

Errachidia

Ouarzazat

Marrakech

Boujdour

Laayoun

Guelta Zemmour

DakhlaBir Enzaran

MIDITERRANEAN SEA

ATLANTIC OCEAN

Alg

eria

LAR.A1

N

Essaouira

Azemmour

Agadir

30

25

Tarfaya

Deep Geothermal gradient GG. (°C/km)GG > 3530 < GG < 3525 < GG < 302 0 < GG < 252 0 < GG

Deep geothermal anomalies

2°

34°

4°6°8°10°12°14°16°

32°

30°

28°

26°

30

20

25

35

30

30

30

3030

25

25

25

2030

30

30

30

20

20

25

25

25

Figure 25: Geothermal gradient map of Morocco.

7. SYNTHETIC GEOTHERMAL APPROACH AND CONCLUSION.

Geothermal studies of sedimentary basin have revealed lateral as well as vertical variations in the temperature fields. These variations are commonly interpreted as resulting from thermal conductivity heterogeneities or local variations in basement heat flow. Variations many also result from groundwater flow systems. The movement of water in deep aquifers can significantly perturb the local underground temperature distribution in sedimentary basins (Zarhloule, 1994).

Zarhloule et al.

12

In sedimentary basins of Morocco, the treatment and the compilation of geological, geophysical and hydro-geothermal data allowed the construction of a conceptual model showing the relationships between topography, hydrodynamism, chemistry and temperature of the all hot aquifers in Morocco (Fig. 26).

T(°c)

Z(m)

T(°c)

Z (m)

+*

Recharge zoneDischarge zone

High Tm (30-54°C)

Low dilution of the thermal waters

Potential mixing zone

Meduim Apparent shallow geothermal gradient (GGSA)Medium mesured temperature of water (Tm) (24-29°C)

High dilution of thermal waters

Low to negative GGSA Low Tm (< 23°C)

Zone of thermal anomalies and shallow indices

Only the silica geothermometrs seem togive a plausible values.

High temperature of the reservoir. It's depend

Infiltration of meteoric Water

Aquiclude

Plio-quaternary aquifer

Aquiclude

Deep aquifer (hot water)

+Well in the artesia zones

* Plio-quaternary well Thermal spring

T(°c)

Z(m)

of deep geothermal gradient

Hot area

Cold area

Transition area

Cold areaAlimentation

"mixing"

Higher GGSA

T(°c)

Z(m) shallow thermal profil

Alimentation

Figure 26.Conceptual model of circulation of hot water of the different aquifers in Morocco: relationship between hydrodynamism, temperature, chemistry and topography (schematic section).

The recharge zones are characterized by shallow cold water, low apparent geothermal gradient, negative anomalies and high topography. The waters are mainly HCO3-Ca-Mg type, resulting from the great influence of carbonate rocks.

The discharge zones are characterized by shallow hot water, high apparent geothermal gradient, positive anomalies and low topography. The hot springs are generaly Ca (Mg)-SO4 (Cl) or Ca (Mg)-HCO3 type, resulting from the main influence of evaporitic rocks.

The middle of the basin shows a low apparent geothermal gradient. However, the communication between the deep and the shallow aquifers found expression in a potentiel mixing zone, with a hot water and a high apparent geothermal gradient.

In general the shallow geothermal gradient is high near hot springs. Hot springs represent discharge from deep reservoir, and upward moving growndwater flow. The upward moving water may come from the centre of the basin and the discharge zone may be related to the hydrologic limit of the aquifer or to the existence of faults or fractures.

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