Towards a de-carbonized energy system in North-Eastern Morocco: Prospective Geothermal Resource

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ContentslistsavailableatSciVerseScienceDirect

Renewable

and

Sustainable

Energy

Reviews

jo u r n al hom e p a g e :w w w . e l s e v i e r . c o m / l o c a t e / r s e r

Towards

a

de-carbonized

energy

system

in

north-eastern

Morocco:

Prospective

geothermal

resource

Abdelkrim

Rimi

a,∗

_,

_Yassine

_Zarhloule

b

_,

_Alae

_Eddine

_Barkaoui

b

_,

_Antonio

_Correia

c

_,

Julio

Carneiro

c

_,

_Massimo

_Verdoya

d

_,

_Francis

_Lucazeau

e

a_Institut_{Scientiﬁque,}_Université_Mohammed_V-Agdal,_Avenue_Ibn_Battouta,_B.P.₇₀₃_Rabat,₁₀₁₀₆_Morocco b_Université_Mohammed_1er,_Oujda,_Morocco

c_Geophysical_Centre_of_Evora_(CGE),_University_of_Evora,_Portugal

d_Dipartimento_per_lo_Studio_del_Territorio_e_delle_sue_Risorse,_Università_di_Genova,_Italy e_Institut_de_Physique_du_Globe_de_Paris,_France

a

r

t

i

c

l

e

i

n

f

o

Articlehistory: Received22April2011 Accepted19December2011 Keywords: Geothermalgradient Heatﬂow Thermalspring Geothermometer Geothermalpotential Morocco

a

b

s

t

r

a

c

t

Geothermaldatahasbeenindicatingpromisingpotentialitiesinthenorth-easternMorocco.Thispaper presentsnewtemperaturedata,recentlyrecordedinwaterboreholeslocatedintheBerkaneandOujda areas.Generally,theobservedtemperaturegradientsareratherhigh.OneholenearBerkane,revealedan averagegeothermalgradientofmorethan110◦C/kmatdepthsgreaterthan300m.Thisresultconﬁrms thegeothermalgradientestimatedinaminingboreholelocatedabout30kmwestoftheBerkane bore-hole,inwhichwatertemperatureof96◦_C_is_reached_at_a_depth_of_about₇₀₀_m._Such_a_high_geothermal gradient,exceedingbyfartheonesalreadydeterminedfornortheasternMorocco,couldactasastimulus toprogramsaimedatthegeothermalexploitationofhightemperatureaquifers.

Contents

1. Introduction... 2207

2. Geologicalbackground... 2208

2.1. Recentvolcanism... 2208

3. Hydrogeologicalandgeochemicalfeatures... 2209

4. Geothermalpatternandnewboreholethermallogs ... 2210

4.1. Heatﬂow... 2212

4.2. SomeresultsfortheBerkanewell... 2212

4.3. PresentdaythermalwatersdirectuseinnortheasternMorocco... 2214

5. Discussion... 2215

6. Conclusion ... 2215

Acknowledgements... 2215

References... 2215 1. Introduction

Since2009,Moroccohasbeenengagedinasustainable develop-mentandrenewableenergystrategy.WithnooilreservesMorocco hasthe necessary assets toachieve thesegoals, particularlyof developingfreecarbonenergies,mainlysolar,windand geother-mal.Owing to its special geographical and geological position, NorthEastpartofMorocco,whichisendowedbyanaturalbounty

∗ Correspondingauthor.

E-mailaddresses:rimikrimo@gmail.com,rimi@israbat.ac.ma(A.Rimi).

ofsunshineandgeothermalresources,hasseenanumberof start-ingprojectsincludingthatofthesolarthermal plantofAin Bni Mathar.Thispaperwewillfocusparticularlyonitsgeothermal potential,whichmayreinforceitsdevelopmentasanemerging economicregion.

SinceRimiandLucazeau[1]havebeenpointedouttheregional thermalphenomena(volcanism,hotsprings,extensivetectonics and seismicactivity) inNorth-eastern Morocco,mostadvanced temperatureandgeochemicalsamplinghavebeendoneinthispart ofMorocco[2,3].Workaccomplishedinthisregionhashighlighted theopportunityforlarge-scalegeothermalanomalyfromdeep[4],

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whileseveralsouthernMoroccosedimentarybasinssuchasthe SoussCoastalBasinsarenowbeingexploredforlowerenthalpy. Bothsubsectorshavebeeninferredtocontainenormous quanti-tiesofstoredheat[5,6].Duetothelargenumberandsizeofsurface thermalmanifestations(hotsprings,recentvolcanismand neotec-tonicactivity),north-easternMoroccoisaregionthathasattracted theattentionofgeothermalexpertssincethe1960s[7–9]. 2. Geologicalbackground

EasternMoroccoisasystemofplains,plateausandmountain rangesextendingon theeastern parts of theMeseta-Atlas and Rifdomains.It is represented bytheEastern Middle Atlasthat continuesthroughtheGuercifbasintoBeniSnassen,thevalley ofMoulouya,theOujda-Tazacorridor,the“PaysdesHorsts”and acrustalblockwithoutnotable alpinedeformation, which con-stitutestheHighPlateaus.ThreeENE–WSWstructuralunitsare deﬁnedinEasternMoroccoregionFig.1:

-Theeastern-riﬁanforelandcomposedofGarebchaoticunitnear theactiveRifchainandalittledeformedtectonicforeland(Terni Masgout,BeniBou Yahi,BeniMamouand BeniSnassen), pro-longedtowardstheeast(inAlgeria)bytheTrarasmounts. -TheGuercifandTaourirt-Oujdabasinswhichshowsedimentsof

middleMiocenetoQuaternaryage,andareconnectedtotheTafna basintotheeast(Algeria).

- TheTaourirt-Oujdamountswhich show sub-horizontal Juras-sicsedimentsaffectedbyfaultsystemswhosedevelopmentand geometryarestronglydependentonthepre-existingstructures inhercynianbasement.Theyareprolongedtotheeastbythe pre-tellianforelandofTlemcen.

TheRifdomain,locatednorthwards,belongstotheBetic-Rifbelt andispartoftheperi-Mediterraneanalpinechain.WiththeAtlas, thesemorpho-structuralzonesresult fromthesuperpositionof severaltectonic,compressiveandextensionalphasesofalpineage. ThesephaseshaveoccurredsincetheLateCretaceous.Mostof thesezonesareENE–WSWtoE–Wdirected(e.g.,“PaysdesHorsts”) andNE–SW(MiddleAtlas,valleyofMoulouya),reﬂectingpartofthe alpinegeologicalevolution.

From Landsat image analysis, El Hammichi et al. [10] had depictedfourfaultssystems:

(a)Theﬁrstsystem,NE–SWoriented,iswelldevelopedand rep-resented by several faults with regional importance. Along thisfault,structuresareveryclearandindicateprevailingleft strike-slipmovement;

(b)NW–SE(N135◦EtoN160◦E)trendingfaultsare oftenlonger than15kmandextendthesouthernsector;

(c) The third system in this sector is represented by arcuate ENE–WSWtoE–Wtrendingfaults;

(d) Thelastfaultsystem,affectingespeciallythewesternsideof thestudiedarea,isrepresentedbyfaultstrendingN–S.These faultsareclearandlonglineaments.Kinematicindicatorsand verticaloffsetstestifynormalmovements.

2.1. Recentvolcanism

OnthescaleofMorocco,thevolcaniccentersextendroughly alongaNE–SWdirectionsincetheMediterraneancoasttothe Anti-AtlasandtheCanaryIslands.

InNorth eastern Morocco,lateMiocene toPliocenevolcanic activitiescorrespondtoashoshoniticediﬁces intheGuillizand

Fig.1.SimplifiedstructuralsketchmapandvolcanisminnortheasternMorocco(modifiedafterHernandez[29];Hervouet[30]).Heatflowdensityvaluesaresuperimposed onthismap;numbersincirclerepresentspringtemperaturevalues,K:miningboreholeatKariatArekman,B:boreholeatBerkaneandF:boreholeatFezouanesite.

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KoudiatHamra(nearTaourirt)(Fig.1)withagerangingfrom8to 4.5My[11]andcalcalkalinecentersintheOujdaarea(Fig.1)with agerangingfrom6.2to4.8My[12].

Regionally,thestudyareaislocatedeastofGibraltarArc,which iscurrentlythesubjectofmanygeological,geophysicaland geo-dynamicalinvestigations.ThishasshownthattheGibraltarArcis characterizedbythinnedcrustandlithosphere,withafast thick-eningtowardstheBeticsandtheRifmountainranges.

IneasternMorocco,magmatismdevelopedduringtheMiocene. Amorerecentepisodeconsistingofalkalinevolcanicactivityhas takenplacefrom6to0.8Ma,andoccurredalonga NE-trending beltextendingfromtheTrans-AlboranzonetotheMiddle Atlas domainandtotheAnti-Atlas(J.Sirouavolcano).Their geochemi-calsignatureissimilartothatofintra-oceanicislandbasalts,and suggeststheroleofanasthenospheric“hotlineament”[13].Such interpretationisconsistentwithgravimetricandgeodetic model-ingofthelithosphere[14–16].ThisMHLcouldextendfromthe CanaryIslandstosoutheastSpainatleast.

Lithosphericthinning under theAlboran Seaand thickening undertworidgesoftheadjacentGibraltarArcisofbasic impor-tancefor geodynamicmodelswhich invokeconvective removal andorogeneticcollapse,a mantellicdelaminationandanactive subduction[17–21].TheAlboranSeacontinueseastwardwiththe Algerianoceaniccrustbasin[22].

3. Hydrogeologicalandgeochemicalfeatures

A sub-surface reservoir is suitable for extracting heat, if its porosity,permeability,thickness,lateralextensionand tempera-turesare sufﬁcientlylarge. Fora preliminarydescriptionofthe geothermalareasofMorocco,twocriteriaareconsidered:

-Thestructural,lithologicalandhydrogeologicalcontextto estab-lishtheexistenceortheabsenceofaquifers;

-Temperaturesofaquifers,orimpermeableformationsupto3km deep.

ThevarietyoftectonicandlithostratigraphicinMoroccohas created various hydrogeothermal systems with heterogeneous lithologicalandphysicalproperties.RegionalstudiesinPrerif[23], easternMorocco[24],theplateauofphosphates[25], Essaouira-Agadir Basin [26,27] and the central Morocco [28] have been gathering backgroundinformation onaquifers fromarchivesof piezometersandoilBoreholes:structure,depth,porosity,modﬂow andgroundwatervelocity.

Butfeaturessuchaspermeability,transmissivityandsalinityare oftenlacking.Accordingtothesestudies,thepotentialgeothermal aquifersresourcesinMoroccoareoftwotypes:

(1)InthelatestTertiaryandQuaternarydeposits,waterpumped outfromporespacesduringcompactioncouldconstituteupto 700mdepth,aquifersofgoodlowtemperature(50–60◦C). (2)Thetypicalsystemofwatercirculationforpre-Tertiaryaquifers,

1000–4000mdepth,isguidedbydifferencesinhydraulicload associatedwithformationchanges.Themeteoricwater inﬁl-tratesintothehillsandtopographicreliefanddischargesin areasof lowgroundwaterlevel, mainlyinMesozoic carbon-atesofthemajorbasins.Ifthepermeabilitiesarefavorable,the watercanpenetratedeepenoughandwarmupgradually (aver-agetemperatureis 100◦C).However,thelithologicalnature mayleadtotheformationoflocalorevenregionalconvective systems.Thedescentofcoldwaterandtheriseofhotwatercan disturbthethermalﬁeld.

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Table1

Thermaldatafromhydrogeologicalandpetroleumboreholes.

Descriptivescodes Latitude Longitude Elevation (m) Maximumdepth (m) Geothermalgradient (◦C/Km) Heatﬂow (mW/m2₎ Fezouane2 34.927 −2.213 252 49.0 140 1624/7Berkane 34.93 −2.3 160 127.0 510* 2952/12 34.693 −1.818 560 500 49.0 111 2362/12 34.647 −1.930 215 43.0 87 1199/12 34.645 −1.964 641 125 34.0 90 1225/12 34.782 −1.930 75 49.0 98 2899/12 34.642 −1.847 620 128 14.0 89 186/16 34.015 −1.913 385 255 32.0 60 A4 34.305 −2.227 1068 260 39.0 81 A13 34.311 −2.232 1095 170 30.0 119 A14 34.309 −2.238 1068 350 34.0 100 A7 34.299 −2.222 216 36.0 89 P3 34.308 −2.232 240 33.0 68 BR41W 34.45 −1.802 1058 170 45.0 144 TEFADIS 34.507 −1.780 1125 100 45.0 112 BN38NW 34.452 −1.81 1053 100 43.0 105 BN30 34.443 −1.792 1050 120 37.0 108 BS38N 34.450 −1.804 120 36.0 84 BR41S 34.448 −1.807 120 35.0 91 NADOR1 35.326 −2.662 2703 41.8 86 AREKMAN 35.109 −2.739 678.7 124.0 192 YADIM 35.093 −2.475 70 40 57 Grf1 34.279 −3.424 36.3 92 Tafrata1x 34.22 −3.106 34.6 76 Msd1 34.245 −3.47 37.0 90

* _This_value_is_still_a_rough_estimate_since_we_have_no_real_{determination}_of_thermal_conductivity_and_porosity._Ranging_from_3.7_to_5.5_W/m◦_C,_the_thermal_conductivity

ofthedolomitedecreasesastheporosityandtemperatureincrease.

For an areatobe prospectivefor high enthalpygeothermal resourcetheremustexist highaveragegeothermalgradientsto createhightemperaturesatdepthsoverasigniﬁcantareawhich canbeeconomicallydrilled.Inadditiontothistheheatmustbe abletobeeconomicallyexploited.Thisrequirestheexistenceof suitablereservoirrockswitheitherhighnaturalporosityand per-meabilityortheconditionsthatallowpermeabilitytobeartiﬁcially enhancedbyreservoirengineering.

Thesedimentary formationsin north-eastern Morocco units containhotreservoirs;inparticularLiassiccarbonatesupto500m thickwhichisthemostimportantaquiferintheregion(Fig.2).The mainaquiferisfedintotheHorstsareaanddischargesintheplainof Oujda-Angad,andiscomposedofcarbonaterocks(limestonesand dolomites)fromthelowerCretaceous,theLias(Fig.2).Theisobaths ofLiasvaryfromafewmeterssouthto1000mtowardsthenorth. Hydrostratigraphicstudiesbasedongeologicaland hydrogeologi-caldatafromboreholesshowtheLiassiccarbonatetobethemain hydrogeothermalreservoirofthehotspringsintheregion.

TheLiassicreservoirofEasternMoroccobelongs totheAtlas domain,whichischaracterizedbyasuccessionofNE–SWhorst andgrabenof pre-Miocene ageandby Plio-quaternarybasaltic volcanics,associatedwithcrustalthinning(Table1).

Thisreservoirisattheoriginoftwenty-fourthermalsprings. Table2whosetemperaturerangesfrom20to54◦Candtheﬂow ratecanreach40l/satcertainpoints.Salinityvariesfrom0.28to 29.6g/l.Someofthesehotspringsplayanimportantroleinthe economyofthearea(e.g.,Fezouane,nearBerkaneandHammam BenKachour,atOujda[3,4].

Fig.2showstheLiassicaquiferinbothOujdaandBerkaneregion. ThepiezometricalmapshowsthatﬂowdirectionisfromSEtoNW. Therechargeareaoftheconﬁnedaquiferislocalisedinthesouth, wheretheLiassicoutcrops.IntheFezouaneregion,theaquiferis artesian.

IntheOujdaregion,theLiassiclimestoneformsthemainaquifer. LimestoneoutcropsinBeniSnassen,High-Atlas,Middle-Atlasand thesouthernpartofthebasin.Thethicknessvariesfrom50mto 1140m,andthemaximumdepthis1370m.Thegroundwaterﬂow isfromsouthtonorthofbasinFig.2.Theaquifertemperatureand

salinityvaryfrom20◦Cto52◦Candfrom130mg/lto3000mg/l, respectively.

AccordingtoZarhloule[3],thehottemperatureandthe arte-sianriseofmostofthethermalspringsinnorth-easternMorocco originatefromdeepcirculationinrelationtoasystemofbasement activefaults,individuatinghorstsandgrabens,inarecentvolcanic area.

Winckel[28]performedathoroughgeochemicalanalysisofthe mainhotspringsinMoroccoandfoundthatelevenofthoselocated alongtheMHL(MoroccanHotLine)releaseCO2thatispartially

ofdeeporigin.Recently,Tassietal.[31]conﬁrmedthatCO2-rich

thermalspringswith3Heanomaliesarelikelyrelatedtothishot line.TheyaremainlydistributedalongaNE–SWtrendfromNador toTaza,and fromFes(MoulayYacoub) toOulmessouthofthe Riffrontalthrust.Thecontemporary presenceof3Heanomalies andminorrecentbasaltoutcropsindicatethatCO2originatesfrom

mantledegassingordeephydrothermalsystemsinthesethermal discharges

Thegeochemicalanalysesandwaterclassiﬁcationbymeansof thediagramofLangelierandLudwiggavethefollowing hydrogeo-chemicalfaciesCa(Mg)–HCO3),NaClandCa–Mg[6].

Theestimated temperaturesbysilica geothermometersvary between37and85◦C(quartzofFournier), 23and73◦C(quartz of Arnorsson), 54◦C (chalcedony of Fournier) and 57◦C (chal-cedonyofArnorsson).Themeasuredemergencetemperaturesvary between20and54◦C.Thecorrectionofthewaterestimated reser-voirtemperaturesbythemixturegeothermometerrevealsthatthe temperatureintheoriginalreservoirmayexceed110◦C,witha rel-ativelylowrateofmixturebetweenhotdeepwaterandcoldsurface water.

4. Geothermalpatternandnewboreholethermallogs Hydrogeothermal structure was impulsed by a geothermal anomalymeasuredinaminingboreholedrilledinrhyoliticand andesiticseriesatKariatArekman(35.11◦N,2.74◦W;Fig.3).The well,680mdeep,revealedfrom450mdepthsaltartesianwater (20–25g/l and a ﬂow rate of 1.4–2l/s) with a temperature of

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Table2

Thermalspringsproperties.

Name Latitude Longitude T(◦c) Rate (l/s)

Gas ChimicalFacies Reservoir Use Project

Sidichafﬁ Midar 34.9 −3.61 32 4 CO2 Na–HCO3 Marl-limestone cretaceous Drink,therapeutic bathing,irrigation Hammam AinMessouda 35.03 −3.25 17–21 3 Chloride,sodium,

sulfate, calcic-magnesian

Gastricandurinary diseases Botling manufactory projectin1959 AinHammam BeniSidel

35.17 −3.19 32–35 1 H2S,CO2 Na–Cl Miocenerhyolite

postnappe,Tuffset breccias interbedded Dermatological bathings Hammam Hammam Chaabi

35.17 −3.09 34 2 Na–Cl Massivelimestone

andgrayslateof Jurassicof Taliouîne

Dermatological bathings

Hammam

HajraSafra 34.26 −3.56 2 CO2 Na–Cl Marl-limestone

cretaceous miocene Dermatological bathings Hammam AinHaddouOu Hamma

35.14 −3.09 29 1 H2S,CO2 Na–Cl Massivelimestone

andgrayslateof Jurassicof Taliouîne

Dermatological bathings

Hammam

AinGoutitir 34.35 −3.06 44–49 12 Cl–Ca

Limestone-dolomiticlower lias-Domerian

Hydrotherapy Hammam

GufaitSprings 34.24 −2.38 26 10–15 SO4–Ca

Limestone-dolomitic Lias

Bathing,drinkand irrigation

AinBourachad 33.86 −3.60 32 2 Na–Cl

Limestone-dolomitic Lias-Dogger

Dermatology Twopools

AinElHamra 34.61 −3.91 24–26 6–15 CO2 HCO3–Ca Marl-limestone

andsandstone Miocene

Reputeforkidney diseases

Hammam

42◦Catthesurface,andmorethan90◦Catthebottom[32].This

good result infirmedtheearlier studies [8,9], which concluded on the base on 60 meters deep thermal profiles, that north-easternMoroccodoesnotconstitutereallyazonewithsignificant geothermalpotential.Carriedoutintheveryshallowboreholes, suchworkscannot beconsideredconclusive, becausethe ther-malstateisstronglydisturbedbywatermovementatthisdepth. Inaddition,morerecentdeepgeophysicalinvestigations (seismo-logical,gravityandmagnetic)claimthatthepositivegeothermal anomalyintheRifandEasternMoroccoisexplainableasasurface manifestationofadeepandwidetectono-magmaticlithospheric process[33].

Thesurfaceheatflowandbroadthermalconductivitystructure (andthusthetemperaturefield)ofnortheasternMoroccohasbeen estimatedsince1987,[1,3,4,6]providedbroadapproximationsof northeasternMoroccocontinent temperaturefield, butsuffered fromasparsegeographic distributionofheatflow and thermal conductivitydata.

The analysis of the long wavelength anomalieshighlights a heatﬂuxincreasingnortheastward:80–110mW/m2 _in_the

east-ernRif,northeasternMorocco,AlboranSea(eastofthemeridian line4◦W),southeasternSpainandnorthwesternAlgeria.In east-ernMorocco,thecrustisthinnedto15–20km.Thehighestheat ﬂow(80–140mW/m2₎_and_geothermal_gradient_(35–50◦_C/km)_are

observedinthenorth-easternpartofthecountry(MiddleAtlasand EasternRif),whichischaracterizedbyintensiveQuaternary volcan-ism,highresidualmagneticanomaliesandshallowCuriedepths [34].TheGibraltarArcregionischaracterizedbyaradialheatflow patternwithincreasingvaluesfromtheouterrangestowardsthe centerandeasternpartofthebasin[2,35](Fig.4).Themost strik-inggeothermalfeatureistheabnormallyhotzoneobservedeastof 4◦WandtheheatflowincreasetowardstheAlgerianbasin,where wefindvolcanicenvironmentsandhighvaluestypicalofayoung oceaniclithosphere[2,36].

Fig.5showsasetoftemperaturedatarecordedinboreholesof thestudyareain1986[1].Itshowsthatthegeothermalgradientis generallylargerthan30◦C/km.Newthermallogswereperformed in2007and2009atsomeboreholes(seeFig.1fortheirlocation). Fig.6pointsoutabnormallyhotdeepgeothermsbeneathEastern RifandAlboranbasin[37].

Withtheobjectiveof improvingthegeothermaldatasetand gainingabetterinsight intothegeothermalpotentialofeastern Morocco,anexploratorygeothermalsurveywasconductedin2007 and 2009;intheregionofOujda(Fig.6)tologsomehydraulic boreholes.Inparticular,twowellsintheregionofBerkaneshow highgeothermalgradientsandcouldprovevalidforhighenthalpy geothermalpurposes.Thispaperisasummary oftheresultsof theserecentinvestigationsanddiscussesthenewdatainthelight ofpreviouslycollectedinformationindeepandshallowboreholes (Fig.7).

The borehole 2952/12. Fig. 8a shows a good concordance betweenthethermalproﬁlesmeasuredafter20years.At600m depth(correspondingtothelithologicalchangefrommarlto car-bonate),theboreholemaybeinvadedwithbyawarmwaterarrival. This resultsin a sharp decreasesand even aninversion of the geothermalgradient.Thethermallogofthewelllocated30kmwest ofBerkane.Fig.8bischaracterizedbyanincreaseofthe geother-malgradientat300mdepth.Noticethattheincreaseofgeothermal gradientcannot,toacertainextent,beexplainedbyachangein lithology.Inthatcase,asdolomiteshouldhavethermal conduc-tivityhigherthanclay,thegeothermalgradientshoulddecrease. Forthemoment,nothermalconductivitymeasurementisavailable andnoheatﬂowdensityestimatecanbedone.

ThethermallogoftheFezouanehole(Fig.8c)exhibitsa ther-malgradient,which apparentlyvariedwithdepth. Thethermal gradientis42◦C/kmintheuppermost60–120msection,andthen decreasesto14◦C/kmbetween120and150m,toincreaseagain toabout70◦C/kminthedeeperpartofthehole.Noticethatthis

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Fig.3.ObservedtemperatureintheKariatArekmanhole[32].Localestimatedheatﬂowdensityexceeding200mW/m2_[1].

Fig.4.TerrestrialheatﬂowdensityinMoroccoandneighboringregions[34].

logissignificantlyaffectedbywaterflowingwithinthehole,since itcrossesaconfined,artesianaquifer.

4.1. Heatﬂow

Ifweassumethattheconductionisthemainmodeofheat trans-ferinthecrust,averageverticalheatﬂow,attheearth’ssurfacecan bedeterminedby:

QS=zgradz+

H

where(zisthethermalconductivity(W/mK)atdepthzandgradz

thegeothermalgradient(K/m)atdepthz,(Histheadditive radioac-tiveheatproductionbetweenthesurfaceandthedepthz. 4.2. SomeresultsfortheBerkanewell

Thischange in the geothermal gradient is not a result of a thermal conductivity change. A simple calculation shows that theaveragegeothermalgradientabove300misabout29◦C/km (0.0293◦C/m)whilethegeothermalgradientbelow300misabout 127◦C/km(0.1275◦C/m).Atadepthofabout470mthe tempera-tureis50◦C,andassumingthatthesameformationreachesdepths of700m(seelithologiclog)thismeansthatanestimated temper-atureofabout78◦Cisattainedatabout700m.

Ifweassumeathermalconductivityof1.5W/mKfortheclay above 300m and a thermal conductivity of 4.0W/mK for the

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Fig.5.ThermalproﬁlesinminingandwaterboreholesdoneinOujda–Berkane region.

dolomitesbelow300mwecanconcludethattheheatﬂowdensity (HFD)alongthewellisnotconstantandthereforethereis geother-malenergytrappedforlevelsbelow300mdeep.Theestimated HFDabove300mis43mW/m2_,_and_below₃₀₀_m_is₅₁₀_mW/m2_.

Ifweassume thatthewellisrepresentativeof thegeologic, hydrogeologic,andthermalstatusforarelativelylargeare(let’s saytensofsquarekm),wecantrytoestimatetheheatinplace(H0)

withintheaquiferusingthefollowingequation: H0=[(1−˚)mCm+˚wCw]·(Tt−T0)·A·z

Fig.6. CrustalgeothermsbeneathEasternRif(RF)andAlBoranbasin(AB)[37].

Fig.7.Geothermalgradient(a)andHeatﬂowdensity(b)distributioninthestudy area.

˚istheeffectiveporosity,Cisthemeanspeciﬁccapacity(j/KgK), isthemeandensityoftherockcolumn(kg/m3_),_T

tisthe

tem-perature at thetopof theaquifer (◦C),T0 theaverage regional

temperatureatthesurfaceoftheearth(◦C),aistheareaofthe aquifer,andzisthethicknessoftheaquifer;thesubscriptsm

andwrefertorockmatrixandwater,respectively.

For the Berkane well if we assume that: ˚=0.1, T0=20◦C,

Tt=30◦C, w=1000kg/m3, m=2600kg/m3, Cw=4190J/kgK,

Cm=840J/kgkm the heat in place per square meter is about

9.5×109J/m2_(9.5_G_J/m2_).

Itmustbesaidthatwewereabletogowiththetemperature dataloggerasdeepas900minthewell;however,wewerenot countingthatsuchhightemperatureswerereachedatdepthsof about500mandsothetemperature dataloggersaturated just above50◦C.Thenexttemperaturelogmustthenbeobtainedwith

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Fig.8.(a)Thermalproﬁlemeasuredinthewell2952/12(34.4◦_N,_1.5◦_W)_in₁₉₈₆_and_2007._(b)_Temperature_log_of_the_well_1624-7_in_the_region_of_Berkane._(c)_Temperature

loginthewellFezouane2intheregionofBerkane.

a temperaturedata loggerthat allows measuringtemperatures higherthan50◦Corwithanothertemperaturemeasuringdevice thatcanmeasuretemperatureshigherthan50◦C.

4.3. Presentdaythermalwatersdirectuseinnortheastern Morocco

ToughgeothermalenergyresearchinMoroccoisrelativelymore thanfortyyearsold[38],theutilizationofgeothermalresources hasnotyetbeenenoughdevelopedandstillrestrictedtosparse lowenthalpydirectuses.Amongthegeothermalpotentialitiesof Morocco,numeroushotspringsoccurandaremostlyconcentrated inthenortherncountry:CentralMorocco,Prerif,andnortheastern Moroccowherehighgeothermalgradientsareobserved.Because ofthelowtointermediateenthalpylevelofthesegeothermalhot springs,thedirectuseofthewarmspringsisstillfortherapeutic orfortheirchemicalcontents.Howeverexceptforthespringof

MoulayYacoubofFezwheremoderntherapeuticbathingexists,the thermalwatersinMoroccoremainstillprimitivelyused.Inspiteof thewholeenergydependenceofMoroccoandthedevelopmentof thegeothermalstudies,theMoroccanauthoritiesarenotdecided yettopromotetheuseofthegeothermalenergycontainedinthe undergroundofthecountrywhichcouldmakeprimarilyproﬁtit’s agriculturalandﬁshingvocation.

Foraﬂowrateof5l/sandanaverageof3l/sandatemperature changeof10◦Candatotalof12naturalspringbaths(Benkachour, MyYacoub,etc.).

Installedcapacity(MWt)=peakuse×“T”×0.004184 ×numberofbaths=10l/s×10◦C×0.004184×12=2.51MWt Annualenergyuse (TJ/year)=averageuser“T”×0.1319 ×numberofbaths=3l/s×10◦C×0.1319×12=47.48TJ/year

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Thereforegeothermalannualusedonlybythenaturalhotbaths inMorocco,remainslessthan50TJ/yearwhichcorrespondstoa capacityof3MWt.

5. Discussion

Thenewthermallogsrecentlyrecorded showpossible ther-malperturbationduetogroundwatereffectsand/orwaterﬂowing withintheholes.Theacquireddataneedfurtherprocessingand carefulanalysesbeforetheiruseforgeothermalmodeling. How-ever,somegeneralconclusionscanbedrawnfromtheobserved temperatures.

Achangeinthegeothermalgradientdoesnotappearasaresult ofachangeinthermalconductivity.Asimplecalculationforthe Berkanewell.Fig.8bshows thattheaveragegeothermal gradi-entabove300misabout29◦C/kmwhilethegeothermalgradient below300misabout127◦C/km.Atadepthofabout470mthe tem-peratureis50◦C,andassumingthatthesameformationreaches depthsof700m(seelithologiclog)thismeansthatanestimated temperatureofabout78◦Cisattainedatabout700m.

Ifweassumeathermalconductivityof1.5W/mKfortheclay above 300m and a thermal conductivity of 4.0W/mK for the dolomitesbelow300mwecanconcludethattheheatﬂowdensity alongthewellisnotconstantandthereforethereisheattrapped atdepthbelow300m.

The hot water may be recovered essentially in Lias series, forgeothermalpurposes.However,theproblemwiththeLiasic aquifersisthattheyareformedbyintrinsicallycompactlimestones anddolomites,butwhichcancontainwaterinfracturesandevenof karstssystems.Theformationsmaybethustransmissivesbutnot veryaccumulativeswhichmakeshardlythedeﬁnitionofthe thick-nessoftheaquifer,theporosityandthetransmissibility.Further investigationsmustbedeservedforagoodestimationofthe thick-nessandtheporosityoftheaquiferwhichremainkeyparameters foranyattemptofgeothermalspringassessment[39,40].

TheboreholeofBerkanemaynotbeconsideredas represen-tative of the geologic, hydrogeologic, and thermal status for a relativelylargearea,owingprobablytocomplexupwardor down-ward groundwater ﬂow. We remark the difference in thermal gradientbetweenthetwoboreholes,Berkane(Fig.6)andFezouane (Fig.8c),between150and200mdepth.

Noticethatwewereabletogowiththetemperaturedatalogger asdeepas900minthewell;however,atdepthsofabout500mand sothetemperaturedataloggerhasreacheditsmaximumoperation limit(50◦C).Futureinvestigationsshouldthenuseatemperature dataloggerthatallowstomeasuretemperatureshigherthan50◦C. 6. Conclusion

Itwashypothesizedfromgeologicalandgeophysicalthermal spring datathat NortheasternMorocco is likely to bea region of highaverage geothermalgradients and thus prospective for geothermalenergy.

Theheatﬂowmeasurementsinhydraulic,miningandoil bore-holesreturnedresultsthathavevalidatedthishypothesis.

Thesedimentsinthestudyareahavemoderatethermal conduc-tivity,andhavebeensampledforsomelaboratorymeasurements andestimatedbygeometricmodelstobebetween2.5and7kmin totalthickness.Withthisamountofmoderateconductivity sed-imentsoverlyinga thinnedcrust,plus itsproximity toexisting powerinfrastructure,theNortheasternMoroccoisnowconsidered prospectiveforeconomicgeothermalenergydevelopment.

Thestudyareaispartofalarger,elongate,geographicalregion extendingfromMoroccotoAlboranSeaandSouth-easternSpain.

These largeresources of geothermal energy in northeastern Moroccowouldnotbeunnoticed.Itcanbebelievedtheywillattract

interestofpotentialinvestorsandwillbeproﬁtablealsoforthose wholeareas.

HighgeothermalgradientsareobservedinNEMoroccoInthe regionofBerkane,temperatureshigherthan50◦Cweremeasured inawaterwellatdepthsofabout470mwhilethistemperature wasalmostreachedat600minanotherwellofOujdaregion.

Thislargegeothermalanomaliesoccurringatdepthand this alreadyobservedinaminingboreholeatArekmanarea(Eastern Rif)indicatethatmediumtohighenthalpyusesarenotdiscarded. OtherwellsareavailableinnortheasternMoroccofor tempera-turelogging,sothatthegeothermalpotentialcanbeestimated. For a valuable assessment of the potentialgeothermal springs, detailed geophysical surveys have to be carried out in the Oujda–Berkane–Arekmanarea.

Acknowledgements

This work was supported by the Moroccan-French project “CNRST-CNRSSDU02/07,theMoroccan-PortugueseCNRTS-GRICES project SDT/09, the Moroccan-Italian MAE project and 7PCRD Project:“COMET”no241400.

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