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INTERNATIONAL SUMMER SCHOOLon Direct Application of Geothermal Energy

Under the auspice of theDivision of Earth Sciences

ENERGY DEVELOPMENT PROBLEMATICSIN THE MEDITERRANEAN. THE AEOLIAN

AND AEGEAN ISLANDS. THE GEOTHERMALENERGY CASE

Pierre UNGEMACHGeoproduction Consultants (GPC)

ZI Paris Nord II – 14, rue de la Perdrix, Lot 109BP 50030 – 95946 ROISSY CDG CEDEX France

pierre.ungemach@geoproduction.fr

ABSTRACT

This paper aims at discussing thereasons why, despite a most favourablegeothermal energy environment, theislands of the southern and southeasternMediterranean stick to conventionalenergy processes and not to reclamationof alternative/renewable energy sourcesinstead, indeed a delicate exercise.

As a result the following headings areanalysed :(i) geodynamic settings which address

the Aeolian and Aegean volcanic is-lands arcs occurring at lithospheric platesubduction zones and, at a lesser extentthough, selected nearby active rifting andgraben structures, whose distinctive tec-tonic, magmatic and geohydrological attri-butes are known to host attractive hydro-thermal reservoir environments,(ii) present resource/reservoir evaluation

and development status related to pre-vious geophysical/geochemical surveys,direct drilling/testing assessments andearly pilot development projects,(iii) sensitive problem areas assumed to

restrict the harnessing of provengeothermal resources in the light of theMediterranean Insularity background andprevailing tourism oriented economics,and(iv) overcoming past errors and present/

future uncertainties by implementingrelevant, challenging, geothermal energydevelopment strategies securing feasible

development and reconciling island com-munities, often skeptic, if not hostile withgeothermal energy undertakings

In so exercising the following prioritydevelopment targets are suggested, ac-counting for specific insular conditions.(i) desalination from either stream con-

densates, high temperature flash or,preferably, low temperature evaporationcycles in order to meet island critical freshwater demands,(ii) direct uses encompassing cooling/

freezing, process heat, thermal/me-dicinal, space heating applications, and(iii) power generation, once a priority

objective, rated first at domestic and,optionally, at foreign requirements.

FOREWORD

While discussing with the organisersof the IGD 2002 event the author issuedthe following straight forward, if notprovocative, statement (Ungemach, 2002).

“The Mediterranean enjoys a mostattractive, proven, geothermal potential inparticular (but not only) in the Aeolian andAegean Volcanic Island Arcs, often directlyassessed via drillings in Italy (Vulcano andPantelleria) and Greece (Milos – Cyc-lades, Nisyros – Dodecanese). Althoughexploration benefitted from massive public(UN, EU, domestic) funding support no orvery limited development was achieved sofar.

Why ? Is there a structural impossibi-

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lity, is it still worth spending public moneyin, beforehand, aborted projects ?

Are most of these Islands bound tostick to diesel fired turbines, tank suppliedfresh water, fruit/vegetable/fish imports, totourism as the sole development route ?To Government and European subsidiesfor survival ?

Are the lobbies, conservative policies,insular archaism so strong, overwhelming,that the presently bleak outlook cannot bedefeated ?

Or, instead, can other alternativedevelopment scenarios be realisticallycontemplated ? The geothermal potentialis there, the technology/knowhow existsnot mentioning submarine power trans-mission – island to island, island tocontinent – practiced by the utility in theAegean and desalinisation from steamcondensates and flash/evaporation pro-cesses.

How can they be best implemented ?We are not speaking here of

Archeology”This is what this paper is all about.

BACKGROUND AND SCOPE

The islands of the southern andsoutheastern Mediterranean face theparadox of utilising, in many instances,conventional energy processes whereasthey enjoy among the most attractive rene-wable energy potential of which geother-mal sources take an important share.

Such in the case of the Aeolian andAegean volcanic island arcs of Italy andGreece which, owing to a favourablegeodynamic setting –lithospheric platesubduction zones – and related tectonic,magmatic and geohydrological featuresare likely to host dependable hydrothermalreservoir environments.

As a matter of fact, volcanological,geophysical and geochemical explorationconducted since the investigationspioneered in the early 1950s in Vulcano(Sommaruga, 1984), in these areas aswell as in nearby active rifting and grabenstructures, has evidenced promisingshows. Those could be further validatedvia direct drilling asessments in theVulcano, Pantelleria (Italy), Milos andNisyros (Greece) island localities.

However, in spite of these promisingpremices, insignificant or very limiteddevelopment was achieved so far.

The geothermal potential of theseislands, whose main chracteristics arefeatured in table 1, will be analysed in thelight of their remakable geodynamicsettings and geothermal/magmatic attribu-tes, and of their present resource/reservoirpresent exploration and developementstatus.

To date development of the geother-mal resources has been limited to a pilot2Mwe power plant on Milos, abandoned inthe early 1990s, and to a pilot desalinationunit, fed by low temperature geofluids inthe Kimolos island (Cyclades).

The problem areas, deemed criticalvis-à-vis geothermal development open-ings, will be reviewed with respect to

mining/geological risks . Those,examplified on several exploratory drillingventures (Vulcano, Pantelleria, Nisyros),address the variability of reservoirproperties, in both vertical and horizontaldirections. It affects reservoir continuity asa result of hydrothermal alteration / selfsealing, sharp lateral changes in lithology,water influx/mixing, depending chiefly onlocations respective of the governing heatsource and magma differentiationstructure (magma chamber / calderaassembly).

exploitation risks . They relate to :- the thermochemistry of the geothermalfluids and to dominantely scaling(carbonate, silica, heavy metal sulfidespecies) shortcomings and subsequentplugging of (production/injection) wells,surface facilities and, ocasionally, thereservoir proper,- reservoir life, (re)injection. Geothermalreservoirs of the type encountered in theAeolian and Aegean arcs are of limitedareal extent conforming to a fracturedominated porosity/permeability pattern.This signature renders these reservoirs, ifnot adequately assessed and managed,sensitive to early pressure and tempe-rature depletion. This bearing in mind that(re)injection of the heat depleted, wastebrine is an environmental prerequesitewhich, if not carefully designed, could leadto production/injection well shortcircuitingand premature cooling.

environmental hazards. Besides anormal volcanic activity, island arcs aresubjected to paroxismic outbursts as wit-nessed by, historically recorded, magmaticeruptions (Vulcano, Santorini) and phreaticexplosions (Milos, Nisyros). The advent,

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though unpredictible yet, of such eventswill occur sooner or later, illustrating theseismic/volcanic risk any local develop-ment and undertaking has to cope with.The seismicity induced by the (re)injectionof the waste brine may be regarded as asecondary risk, which could eventually beturned into an asset (stress release).

last, but not least, insularity. With thenotable exception of Lesvos (NorthAegean) the islands addressed to here(see characteristics in table 1), arerepresentative of the insular context.Summing up :(i) they are limited in size (from 20 to 300km2),(ii) their topography is uneven and theiresthetics outstanding,

(iii) their native population barely exceedsa few thousands inhabitants,(iv) their economy has become whollytourism addicted which causes thepopulation to increase up to one order ofmagnitude during peak summer months. Ithas also profundly modified the traditionalsocio-economical panorama, devoted tosea and agriculture, by moving to aservice dominated economy, stronglydepending on imported –food, energy,fresh water, labour force- supplies, and(v) the islanders have shown in severaloccasions to be skeptic if not hostile to-wards promoting geothermal energy. Thisreluctance to changes, often perceived asmere conservatism, complicates socialacceptance of geothermal developments.

Locality Country RegionArea

(km2)Population

Permanent Peaktouristic

Aeolian Italy SicilyVulcano 21 450 15,000 est.

Lipari 38 11,000 35,000 estPantelleria 112 7,500 n.a.

Aegean Greece AegeanMilos Cyclades 151 4,800 15,000

Santorini Cyclades 76 9,600 90,000Nisyros Dodecanese 37 950 2,000

Kos Dodecanese 290 18,000 108,000Lesvos North Aegean 2133 93,000 n.a.

Table 1. Island highlights

From present resource assessmentsand expectations and island energyrequirements the following developmenttargets have first been selected (i) powergeneration, (ii) fresh water supply/desalination, (iii) cooling/freezing, (iv)process heat, and (v) thermalism/spaceheating.

Their implementation will be discussedin view of reconciling development objec-tives with insular specificity by (i) adaptingproductive capacities to highly variable,season wise, loads, (ii) favouring modulardesign, (iii) small pilot units anddemonstrative trials prior to full scale com-missioning, (iv) environmental mitigationpolicies while accomodating seismichazards, landscape esthetics, waste dis-posal, clean air and gas abatementconcerns, and (v) improved communi-cation in informing, lobbying, management

and decision making thus avoiding pastredhibitory mistakes.

GEODYNAMIC SETTINGS ANDRESERVOIR OCCURRENCE

Most of the islands discussed herebelong to the Aeolian and Aegean Islandarcs which occur at lithospheric subduc-tion zones (fig.1) where both the over-ridden and overriding plates consist ofoceanic crust (Reeder, 1987).

In such zones magma often reachesthe surface giving rise to active volcanicisland arcs as is the case of the Aeolianand Aegean archipelagos.

Actually subduction zones volcanicarcs represent 62 % of the activevolcanoes of the world although theysupply less than 13 % of the magmaerupted yearly (Reeder, 1987). If the

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forearc and backarc regions reflect meanheat flow values of 30 and 90 mWm-2

respectively (as compared to the 60 mWm-

2 continental average) heat flows as highas 600 mWm-2 (i.e. tentimes thecontinental average) have been measuredin volcanic island arcs.

More over such zones exhibit dis-tinctive tectonic, magmatic, geological andhydrogeological features favouring thedevelopment of potentially exploitablehydrothermal reservoirs.

In fact 70 % of all electricity producedworldwide from water dominated (asopposed to dry steam) sources originatesfrom subduction zone volcanic arcs(Reeder, 1987). They are associated withquaternary igneous systems and magmadifferenciation processes taking place incompressional stress environments, gene-rating prevailing silicic calc-alkaline melts.

Reservoir occurrence is governed byfracturing and self sealing processes. Mostof the geothermal reservoirs consist ofhost rocks fractured at depth as a result ofintense magmatic, phreatomagmatic andregional tectonic stresses typical of thevolcanism of these zones which oftencombine caldera structures, phreaticexplosion craters and active faultingsystems. Owing to their high sourcetemperatures, two phase water dominatedsystems have a high self sealing potentialin the form of mineral (silica for instance)deposition during the fluid cooling process.Self sealing is beneficial as long as itfavours the formation of confiningcaprocks. However the risk exists ofhaving the reservoir entirely self sealed tothe point no permeable zone would nolonger exist, would there not be fracturingto defeat this fatal ending.

Geothermal fluids are generally a mixresulting from the influx of meteoric, seaand connate (of marine origin) waters andof magmatic gases. A classical model of avolcanic island arc geothermal reservoirwould consist of a dual aquifer systemcombining (i) a shallow hot water / or evensaturating steam bearing horizon, withpredominant meteoric recharge, and (ii) adeeper seated, hotter, hydrothermal reser-voir with likely sea water (not necessarily)and connate/magmatic liquid and gasintakes. Geochemistry, chiefly isotopegeochemistry, proved useful tools in dis-criminating water and gas origins andmixing in such reservoirs.

The Pantelleria (Sicilian channel) andLesvos (North Aegean) islands belong totwo different volcanic and tectonic set-tings.

Pantelleria is a volcanic island locatedin an active continental rift between Sicilyand Tunisia.

Lesvos, located in the very NorthAegean is a remnant of a tertiary volcanicisland arc whose volcanism is extinct butheat flows high owing to distensionaltectonics and an active graben structure.

PRESENT EXPLORATION ANDDEVELOPMENT STATUS

Aeolian island arc and Pantelleria

The Aeolian island arc (fig. 2) wasformed during Miocene and Pliocene, as aconsequence of the fragmenting, disper-sion ans subsidence of a formerly con-tinuous lithospheric plate leading to theformation of the Western MediterraneanBasin whose peri-Tyrrhenian margin hostsactive volcanoes (Stromboli, Vulcano,Lipari) (Bruno et al , 2000).

. VulcanoVulcano is an active volcanic island

whose last erruption dates back to the late1880's. Since then it has been the site ofintense fumarolic and gas ventingmanifestations (Todesco, 1995).

The geothermal interest of the islandwas recognised by AGIP who, in the early1950s, initiated exploration by drilling twoshallow drill holes (Sommaruga, 1984,AGIP SpA, 1987 and Todesco, 1995) VU1

and VU2bis (see characteristics in table 2,and well locations in fig. 3). Well drilled in1983/1984 turned out dry.

Besides exploratory drillholes, thereare numerous shallow wells drilled fordomestic use and irrigation and naturalgaseous manifestations (fumaroles, gasand steam vents) which have been sam-pled for the purpose of geochemical andisotopic investigations (Panichi et Noto,1992, Bolognesi et D'Amore, 1993, Cor-tecci et al, 2001) Studies of hydrothermalalterations and fluid inclusions have beenperformed to appraise rock water inter-actions, fluid origins and the systemthermal history (Gioncada et al, 1995).

Fumarole discharge (mainly CO2 andH2O), which can be in excess of 1,000t/day with temperatures ranging from 100to 600°C (during paroxismic crises), has

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evidenced the presence of, shallowseated, boiling aquifers intersectedactually by the early exploratory drillings.

Summing up, the foregoing enab-led to assess the hydrothermal reservoirconceptual model depicted in fig. 4. Accor-ding to this model hydrothermal fluids

represent a mix of meteoric, connate (ofmarine origin) and magmatic water andgases, with superficial steam heatedboiling ground water. Isotopic analysesreflect a geothermal water dilution bymagmatic vapour and no direct sea waterinflux.

Well Name Year Depth (m) Productivity Max Temp (°C) Observations

VU1 1952 2362400 t/daydry steam

2003 productive horizons(100,136,200°C)

VU2bis 1953 236168 t/daydry steam

150

IV1 1983/1984 2050 None 400

Well IV1 divsidetracked div. at980 mSelf sealingdownhole Totalcirculation losses 0-900m

VP1 1984 1000 None 200Total circulationlosses 0-900 m

Table 2. Vulcano well characteristics

LipariIn contrast with the Stromboli and

Vulcano settings , active Volcanism showsare limited to hot springs and tepid fuma-roles. It has been inferred volcanism ishere associated to a tectonic theme underthe form of a pull a part structure (Bruno etal, 2000). The volcano-tectonic faultsbounding the main Lipari depressionsfollow the same strike as that of thetectonic structure. It is further assumedthat the abscence of a caldera collapse isa consequence of the disconnection bet-ween the formation of volcano-tectonicdepressions and volcanic processes.

At Lipari an integrated geophysicalcampaign combining microgravity, 2Dgeoelectrics, seismic reflection/refractionprofiling surveys aimed at delineating alow enthalpy geothermal reservoir whosedevelopment could support thermal andbalneological applications. Geophysiscalsurveys were carried out in compliancewith the following rationale.(i) seismic profiling matches subsurface

seismic discontinuities (layering,faults),(ii) gravity constrains seismics in terms of

densities vs velocities and acousticimpedances, and(iii) geoelectric soundings pinpoint con-

ductive anomalies.As a result a relevant structural model

could be derived over the thermal springsarea which might reflect the presence of alow enthalpy geothermal reservoir within apermeable pyroclastics / lava sequenceintensely tectonised via subvertical faultinglikely to enhance hot fluid upwelling (Brunoet al, 2000).

PantelleriaThe island is the emerging part of a

submarine dormant volcano, trending pa-rallel to the active Sicilian channel conti-nental rift (Chierici et al, 1995, Grassi et al,1995, Squarci et al, 1994) (see fig. 5). Itinvolves most of the attributes of centralvolcanic settings –caldeira structure,numerous hot springs, fumaroles and gasvents- with shallow water temperatures ashigh as 98°C (Gianelli et Grassi, 2001).

Geothermal exploration started in1969 with the drilling of four shallow bore-holes. It resumed in 1990 with the drillingof four medium depth wells (depthsranging between 180 and 400 m) locatedin the areas deemed the most promising.Finally two deep exploratory wells, PT1and PT2, were drilled in 1992 and 1994 atdepths of 1100 m and 1200 mrespectively.

Well PT2 turned dry and cold (130°Cbottomhole temperature).

Well PT1 exhibited moderate reservoirperformance with a 270°C bottomholetemperature and a productive interval

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struck between 600 and 700 m facing apermeable brecciated horizon which, afteracid stimulation, delivered a 4t/hr drysteam flowrate.

Temperatures profiles (fig. 6) monito-red on six wells show a convective shift inthe upper 200 meters indicative of ashallow hot water aquifer resupplied bymeteorics waters.

The analysis of hydrothermal mineraland water samples collected on wells PT1and PT2 (Fulignati et al, 1997, Gianelli etGrassi, 2001) made it possible to assess arelevant conceptual model of the hydro-thermal reservoir shown in fig. 7. Accord-ingly the ground water circulation systeminvolves :(i) a shallow thermal aquifer consisting of

a mixture of meteoric recharge andsea water intake,(ii) an intermediate saline, dominantely

colder, sea water influx interactingwith mixing meteoric waters, and(iii) a deeper seated system fed by

upwelling geothermal fluids.Here undoubledy, and contrary to the

Vulcano model, the major inflow originatesfrom sea water.

Aegean island arc and Lesvos

The Aegean arc is typical of a plateconvergence environment as a result ofthe European (overriding) and African(overridden) plate subduction processtaking place in the South Aegean whichled to the fragmentation of the southernedge of the Eurasian lithospheric plate andto the associated structural features

sketched in fig. 8. The volcanic beltextends from the gulf of Saronikos to Kosand includes the active centers of Milos,Thira (Santorini) and Nisyros (Fytikas,1980).

Milos (Cyclades)

The island diplays the most importantvolcanism of the Aegean are with respectto quantity, products (calc-alkaline typicalof island arc suites) and activity (Fytikas,1989). Evidence of an intense magmatic,tectonic and geo-thermal activity isbrought by surface shows such as fumaro-les, hot springs, phreatic ) explosioncraters, hydrothermal alteration depositsnumerous throughout the island andsubsurface temperatures as high as200°C monitored at 250 m depth (fig. 9).

Exploration began in the early 1970'swith geophysics (geoelectric soundings,gravity survey) and the drilling of a firstexploratory borehole. It was followed in1975, 1976 by the drilling of two deepwells MZ1 and MA1 wich proved pro-ductive thus confirming the presence of ahigh enthalpy water dominated reservoir(Fytikas 1980 and 1989, Vrouzi, 1985).Field delineation and reservoir evaluationresumed in 1981-1982 with the drilling ofthree step out wells, MI-1, MI-2 and MI-3,all three productive (Cataldi et al, 1982,Vrouzi, 1985, Fytikas 1989).

Well lithological sequences andtemperature profiles are depicted in fig. 10and their main characteristics listed intable 3.

Well name MZ1 MA1 MI-1 MI-2 MI-3Year completed 1975 1976 1981 1981 1982Total depth (m) 1100 1165 1100 1380 1000Productive interval (m) 810-1100 750-1165 900-1100 940-1380 900-1000BHT (°C) 300 250 323 282 300BHP (Mpa) n.a. n.a. 11.7 11.9 n.a.WHP (Mpa) 0.6 0.74 1.2 1.2 n.a.Total flow (t/h) 22 51 120 50 125Steam / water ratio (1 MPa) 0.64 0.22 0.35 0.71 0.42Specific enthalpy (kj/kg) 2010 1170 1460 2200 1600TDS (ppm) > 100,000 > 100,000 120,000 140,000 130,000

Table 3. Milos wells summary sheet (after Cataldi et al, 1982 and Vrouzi, 1985)

Hence the features of a dependablegeothermal reservoir, conforming to theconceptual model illustrated in fig. 11,could be reliably assessed. According tothis model there is no occurrence of a

significant, shallow seated, reservoir themain resource, most likely supplied by seawater, being hosted by fractured cryst-alline rocks below 700 m depth.

Projected geoelectric designs targeted

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a 40MWe installed capacity (i.e. a ca 400t/h steam rate and a dual flash condensingcycle) deemed a realistic developmentobjective (Cataldi et al, 1982).

In 1987, after several preliminary trialand error runs, a pilot, 2MWe rated, powerplant was put on line by PPC, the Greekutility and concession owner, according tothe design (dual flash condensing)displayed in fig. 12, utilising MI-2 and MI-1as producer and injector wells respectively(Delliou, 1989). The plant could not beoperated continously due to severe scalingproblems affecting the surface facilities(turbine, separated brine piping, injectionpumps, valves etc…) reported by Delliou(1989). Scaling shortcomings have beenthoroughly investigated by Andritsos et al(1989) who identified heavy metal sulfidesand silicates/amorphous silica as themajor scale, forming at primary flash anddownstrem brine transmission stagesrespectiveley. Not overlooking the impactof, flashing induced, thermodynamicchanges (pressure and temperaturedecrease) they pinpointed pH increase asthe dominant factor controlling thesupersaturation/precipitation processes ofsensitive crystal species. Therefore theysuggest careful pH control as an effectivemeans for defeating scaling. It is theauthor's opinion that scale inhibition couldbe better and more economically masteredby enhancing precipitation undersuspended particulate form by means offlash crystalliser, brine reactor clarifier andbrine filtration units, a statementsubstantiated by the considerableexperience acquired in the Imperial Valleyof California (Cioppi et al, 1982).

Noteworthy is the hostility raisedamong the population by the environ-mental consequences (soil pollution) ofpower plant operation and, delicate euphe-mism, by repeated communication / publicrelation misunderstandings, leaving a poorimage of geothermal energy whose powergeneration segment is henceforth blacklisted.

The island however has to face grow-ing demands in fresh water supply, coolingand process heat to meet boomingtouristic and ore (bentonite, perlite, kaolinsilica deposits) processing (drying) needs.Renewed efforts have enabled to com-mission a low to medium enthalpy deve-lopemnt prospect, based on the drilling /completion of ten shallow depth wells in

order to drive a desalination plant of thetype (MED process) implemented in theneighbouring Kimolos island. Thereforegeothermal heat has a chance to reenterthe island energy scene.

Thira/Santorini (Cyclades)

Thira is a mythic site, recurrently asso-ciated with the legend of the lost Atlantis,and the birthplace of one the most brilliantcivilisations of the ancient Mediterranean,dating back to 2,000 BC.

It goes without saying its volcanismand seismicity are active as witnessed bynumerous, historically recorded, eruptionsand earthquakes. The huge caldera dep-ression which shaped the island uniquelandscape was created further to the 1,500BC great eruption. In 236 BC an earth-quake broke the northern part of the islandthus separating Thira from Thirassia. La-ter, from 197 BC till 1928, several conesemerged in the caldera, ultimately mergingto form the Neakaméni islet. The last ear-thquake in 1956 showed devastating as tohouse destructions and human casualties.

Hot springs, fumaroles and high heatflows inferred from temperature gradientslimholes were shows indicative of asubstantial geothermal potential (Fytikas),1980). Further exploration combining geo-chemical sampling, deeper drilling (250 to460 m) and geophysical surveys (micro-gravity, electrical soundings) were carriedout in the mid 1980s- According to Fytikaset al (1990 they provided strong expec-tations on the existence of a deep (800 to1000 m) geothermal reservoir, at sourcetemperatures nearing 160 °C, developingin fractured and tectonised metamorphicbasement rocks and recharged by uprisingmagmatic fluids.

Development of the resource shouldfocus first on desalination processes tomeet an urging fresh water demand, tren-ding critical during the peak touristicmonths, although power generation via Or-ganic Rankine Cycles, a speculative out-come at this stage, cannot be readilydiscarded.

In these respects it is worth addingthat here, thanks to tactful communication,the population proves quite responsive togeothermal development prospects.

Nisyros (Dodecanese)

The island was selected in 1981 by

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PPC as a priority exploration target, furtherto the recommendations of an EU expertteam based on the following considera-tions (Vrouzi, 1985).(i) a relevant –active volcanic island arc-

geodynamic context supported by thepositive outcome achieved at Milos in asimilar setting,(ii) associated, late quaternary, volcano-

tectonic and structural features : calc-alkaline subduction zone magmatism, re-cent volcanic emissions of the Pliniantype, a typical caldera summital structure,post caldera events including historicalphreatomagmatic explosions (1872-1873),

fumaroles and hot springs on the outerflanks reservoir, at temperatures in excessof 200°C relatively shallow depth, and(iii) the possibility of exporting the locally

produced geothermal electricity sur-plus to the nearby islands of Kos,Kalymnos and, eventually, Rhodos viasub-marine cable transmission technologyin a shallow sea environment,as alreadypracticed in the area by the utility.

Two exploratory wells (see locations infig. 13) were drilled in the early 1980swhose main characteristics are summaris-ed in table 4 (Koutroupis, 1989).

Well Name N-1 N-2Year completed 1982 1983Total depth (m) 1,816 1,547

Productive interval (s) (m)360-695

1,420-1,8161,000-1,547

BHT (°C) 350 350WHT (°C) n.a. 178WHP (bars) n.a. 7.6Total flow (t/h) 13(*) 69Steam water ration 0.8(*) 0.5Specific enthalpy (kj/kg) 2,350(*) 1,520Non condensable gascontent (% wt) n.a. 5TDS (ppm) 150,000(*) 60,000

(*) superficial reservoirTable 4. Nisyros wells summary sheet

This drilling venture examplifiesincidentally the strong variability in bothreservoir occurrence and performance ,illustrated in fig. 14 temperature logs,typical of the Mediterranean island arcgeothermal reservoir environments noticedalready in the Aeolian arc. On well N-1only did the shallow seated reservoir ex-hibit productive, limited though, capacities.On the contrary well N-2, drilled on kilo-meter apart, evidenced a deeper seatedresource worth developing owing to a net3 MWe power output as compared to ahardly 1 MWe counterpart on well N-1.

In depth analysis of geochemical dataand phreatic explosion crater morphologyenabled Marini et al (1992) and Chiodini etal (1992) to produce a pertinent concept-ual model of the Nisyros geothermicsportrayed in fig. 14.

At present the N-1 and N-2 wells havebeen abandoned and cemented. No alter-native development schemes have shapedyet. The island community, whose popula-tion has decreased by one half in the past

decades, is still waiting the advent of inno-vative and challenging development op-portunities.

Kos (Dodecanese)

Kos is located at the extreme edge ofthe Aegean volcanic island arc. The wes-tern part of the island exhibits a dist-inctivecaldera structure, known as Volca-nia,which could favour the development of ahydrothermal convective system, a thesisadvocated by Bardinzeff et al (1989).

No geothermal investigations havebeen commissioned so far. However, theprosperous economics of the island, who-se population regularily increases, boostedby an explosive touristic income, mightdeserve reconsidering the geothermalcase in reclaming known/expected low tomedium enthalpy sources and subsequentdirect use applications.

Lesvos (North Aegean)

Eventhough Lesvos belonged once toa volcanic island arc, its tertiary origin no

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longer supplies active magmatic/volcanicprocesses manifest as in the Cycladesand Dodecanese. Neither do its grabentectonics shape as favourably as theireatsward Turkish replica. However, theisland is an active seismic area (1867earthquake) as a result of its distensivetectonics yielding higher than normal heatflows. It enjoys numerous hot springs andabundant water intakes which render theisland an attractive prospect addressinglow to medium enthalpy sources.

The thermal areas of Polichnitos,Petra/Argenos and Kalloni/Stipsi, locatednear the main, NE trending, grabenstructure have long been recognised aspriority exploration/development targets(Fytikas, 1980, Vrouzi, 1985).

Neotectonic investigations have asloidentified the Mythilene area as a reliablecandidate (Dotsika et al, 1995).

Recently, completion of a deep drillingwildcat well has confirmed these expec-tations by hitting a 98°C / 150 m3/h hotwater aquifer at 1,000 m depth.

The island which ambitions sharingtraditionally rooted, agriculture orientedeconomics, with well balanced touristic /residential trends deserves in deed perti-nent geothermal, direct use oriented,undertakings.

DEVELOPMENT PROBLEMATICS

The foregoing highlighted the techni-cal and non technical obstaclescontraining the development of islandgeothermal reservoirs.

Technical obstacles. They address thefollowing risks and hazards.

Exploration/exploitation risks

With the exception of the hundred percent drilling success ratio recorded in Mi-los most other island drilling ventures exhi-bited erratic reservoir and well performan-ces (vulcano, Pantelleria and, at a lesserextent though, Nisyros) as a result of thesharp changes noticed, both vertically andhorizontally, in reservoir properties.

It has been shown that fracturing andself sealing, typical of volcanic islland archydrothermal environments, are, alongsidemagmatism and tectonics, the key pro-cesses governing the formation of highenthalpy water dominated reservoirs. Self

sealing is regarded an asset as it securesthe confinement of the reservoir. It canalso be detrimental would it seal thereservoir to the point no permeabilitywould remain whatsoever. So fracturing isneeded to counter this adverse trendwhich requires active magmatic and regio-nal tectonic stresses which actually favourthe ascent of deep hot magmatic fluids.

In no way can fracture induced per-meability/porosity patterns be assumedcontinuous in such complex volcano-tectonic systems and caldera edifices.

However exploration in the Aeolianand Aegean is not starting from scratch.Previously reported investigations enabledto assess generic reservoir models provi-ding geothermal explorationists with rele-vant guidelines, thus reducing the geolog-ical risk inherent to any mining operation.

Scaling and injection are among themost critical exploitation problem areas.Heavy metal sulfide and silica scaledramatically impacted the operation of theMilos pilot geoelectric plant, causing itsshut down further to repeated unsuc-cessful trials and remedial failures.Although scaling affected here the surfacefacilities and brine transmission line, therisk of injection well impairment andreservoir damage should no be overlookedin future plant and brine handling designs.In this respect inspiration could be soughtfrom the brine processing concepts suc-cessfully implemented in the geothermalfields of Southern California (Cioppi et al,1982) whose fluids exhibit similar, if notmore hostile, thermochemical properties.These processes favour the precipitationof sensitives scale species under particu-late form which, after due filtering, achievethe injection of a crystal free brine.

Injection of the heat depleted brine inthe source reservoir, indeed an environ-mental (waste disposal) prerequesite, isanother matter of concern. The fracturednature of the reservoir may provoke wellshortcircuiting and subsequent, earlierthan anticipated, cooling of productionwells and shortening of reservoir life.Therefore, careful design of production vsinjection well spacings via reservoirsimulation codes, supported by long dura-tion well testing and fluid tracing studies, isrequired to thoroughly assess reservoirbehaviour and match fluid preferentialflow paths. This, bearing in mind thatlimited (inland) reservoir sizes (Vulcano,

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Nisyros), added to rapid lithological andstructural changes, are likely to reduce themining of the heat in place.

Environmental hazards

It goes without saying the islands ofthe Aelian, Sicilian channel and Aegeanface high, structural, volcanic and seismicrisks inherent to their active volcano-tectonic settings. As a matter of fact thelate major eruptive / seismic outburstsdate back to 1888/1891 – Vulcano – and1956 – Santorini. Both these islands arenow equipped with observatories monito-ring seismo-volcanic activity and signallingprecusory shows of paroxysmic eventswith a view to ultimately / tentatively secu-re eruption and eathquake prediction.

Whatever these risks neither havethey opposed to, long established, islandcommunity settlements nor dissuadedtouristic crowds. Given this context,obviously should any geothermal develop-ment prospect be designed and imple-mented in compliance with paraseismicvolcanic building/monitoring safety stan-dards widely applied worldwide, parti-cularily in geothermal power plant designin similar geodynamic environments inJapan, the Philippines and Indonesiaamong others. Hence these hazards canbe mastered in the framework of a topicalrisk management rationale.

Injection of cooled geothermal brineshas been reported to cause microseismicactivity and thermal stresses. These se-condary impacts could actually provebeneficial by (i) favouring the release oflong accumulated stresses wich otherwisemight have generated devastating earth-quakes, and (ii) upgrading, thanks to ther-mally induced fracturing, well injectivity.

Non technical obstacles

Most investigated islands share com-mon features, the so called insularity,characterised by (i) limited acreages, (ii)small communities, (iii) uneven topographyoften associated with oustanding sce-neries, (iv) tourism addicted economicssubstitued for traditionally oriented agricul-ture/sea activities, and (v) moderate (whennot hostile) social acceptance of geo-thermal development schemes.

As earlier discussed reduced islandacreages are limiting factors to reservoirdevelopment, an issue manageable regar-

ding native populations seldomly exceedi-ng a few hundred to several thousandinhabitants. This irrespective of peaksummer tourist crowds rising the popu-lation by one order of magnitude, if notmore, and energy, freshwater, food, man-power demands accordingly, wich poses acrucial base to peak load adjustmentproblem.

As regards island steep reliefs andrelated landscape esthetics, conventionalplant, hot water piping and power trans-mission line concepts should be readilydiscarded and alternative designs bepromoted instead. This arises critical envi-ronmental and social acceptance consi-derations. Geothermal energy, especiallypower generation, development is assimi-lated to industrial undertakings, indeed animage conflicting with Mediterranean sett-lements, whose origins are lost in themists of times and dedicated to agricul-ture, fishing, sailing and trade before theoverwhelming touristic boom took over.

This attitude, shared occasionally bytemporary residents, is often regarded byoutsiders as merely conservative if notarchaic. Both attitudes are in fact cari-catural.

It should be stressed here that themining industry in Milos is an importantpart of the island economics with orequarries producting yearly ca 1,000,000 tof Bentonite, 100,000 t of perlite and10,000 t of silica and kaolin. Obsidian wasalso extracted in ancient times in theAeolian.

Natural sites need to be protectedwhich implies that geothermal projectsmust fit into the landscape, hopefully bet-ter than recent residences and shops, builtaccording to somewhat anarchic urbanplanning criteria. Pollution control requiresthat sound and safe waste disposal andgas abatement procedures be implemen-ted to prevent from adding brines andgases to those of the existing hot springs,fumaroles and gas vents.

In these respects, reconciling geother-mal developments with nature and publicacceptance is examplified by Japan wheremost geoelectric power plants were built inNational parks and seismic areas, subjectto stringent environmental regulations.

Clearly the foregoing deserve inno-vative challenging development strategies.

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FUTURE PROSPECTS

Owing to insularity geothermal deve-lopment strategies are strongly sitespecific, to the stage each island can beregarded as a case study of its own.Nevertheless there are a number of com-mon features, as to identified geoelectricand geoheat sources, candidate conver-sion/recovery processes and eligibledomestic uses, allowing to draw generalguidelines, prior to reviewing, island wise,the resource to demand adequacy.

Development targets

Power generation

High and medium enthalpy, either drysteam or hot pressurised water, depositsare available almost everywhere. Powergeneration addresses the following con-version cycles (Ungemach, 1987) (i) directsteam expansion, (ii) back pressure, (iii)single/dual flash condensing, and (iv)binary, Organic Rankine Cycles (ORC) thelatter recommended within the 120 to 180°C temperature range.

Noteworthy is that electricity could beeffectively used for powering desalinationand freezing/cooling processes.

Desalination

It is deemed the most urgent need asa result of the endemic shortage of freshwater, critrical during the touristic season.The unit domestic and touristic demandsare estimated at 200 and 300 l/day res-

pectively. Fresh water could be recoveredfrom steam condensates whenever avai-lable and more generally, from sea wateror geothermal brines by means of thermalprocesses among which Multiple StageFlash (MSF) and Multiple Effect Distillation(MED) stand as the best candidates al-though Mechanical Vapour Compression(MVC) should not be excluded in caseexcess electric power be available on thesite.

Desalting sea or brackish water(World Wide Water, 1999) involves itsboiling/evaporation in a still, thus releasingsteam which condensed will form purewater. Stacking stills (i.e. staging) increa-ses process efficiency provided eachsucessive still is at lower pressure so thatboiling occurs at sucessively lowertemperatures. This is the basis for theMED process wich requires a constantinput of heat supply during boiling. TheMSF process consists of keeping theboiling water under pressure until releasedinto a vacuum vessel, causing the water toflash into steam. Summing up, connectingmultiple effects or stages at successivelylower pressures is the concept behind theMSF and MED processes whose diagramsare sketched in fig. 16 and 17 respectively.

In the MVC process the heat for eva-porating is supplied by vapour com-pression instead of direct heat exchangefrom the boiler steam. The process utilisesmost often electrically driven vapourcompressors. Process performances figu-res are displayed in table 5

Power RequirementsKwh/t

Steam Requirementskgs/kgd

Output Distillatekgd/kgsProcess

Min Max Min Max Min MaxMSF-OT 2.38 3.17 0.13 0.5 2 8MSF-BR 2.64 3.96 0.08 0.25 4 12MED 0.75 1.75 0.1 1 1 10MED-TC 0.75 1.5 0.07 0.33 3 15MVC 8.5 12 0.03 0.05 20 40

Symbols and subscriptsMSF : Multistage flash - OT : Once Through - BR : Brine RecirculationMED : Multiple Effect Distillate – TC : ThermocompressionMVC : Mechanical Vapour Compressions = steam, d=distillate

Table 5 : Performances of selected desalination processes

MSF plants are of large scale(capacity up to 50,000 m3/day) andoperate at high temperatures (90-110°C)downstream from the brine heater which

renders them sensitive to corrosion andscaling. They are also more energydemanding and are therefore often used incombination with power generation.

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MED units operate at lower tempera-tures, thus minimizing corrosion andscaling. They can be designed for capa-cities up to 20,000 m3/day and canachieve distillate/steam ratios as high as15 MED should appeal to geothermaldevelopers since it is less energy con-suming, requires lower process tempera-tures and uses the geothermal brine as asingle heating and feeding source.

The MED pilot plant serviced atKimolos, which supplies daily 77 m3 (i.e.ca 50 % of the domestic fresh waterdemand) from a 50 m 3/h – 61°Cgeothermal brine, should prove rewardingfor the whole area.

Direct uses

They include various applications suchas (i) cooling/freezing, best achieved viaheat pump and absorption systems (usingLithium bromide or Ammonia as refrige-rants), (ii) process heat for agricultural(vegetable, fruit) and industrial (oreprocessing) drying, and (iii) miscellaneous- space heating, balneology, aquaculture -uses.

Project review

This represents by all means a highlytentative, if not speculative, exerciseleading to the following expectations.

Vulcano

Insofar as they prove sustainable,deliverabilities of shallow dry steam wellsUV1 (100t/h) and UV2bis (7t/h) shouldachieve nominal geopower capacitiesamounting to ca 5,000 and 500 kWerespectively. The latter figure meets thepower requirements of the island popu-lation. The total capacity could supply thepeak summer demand. An alternativescenario could consist of connectingVulcano to the nearby Lipari island via asubmarine power transmission line.

Recovery of steam condensateswould allow to supply the local fresh waterdemand and, incidentally, to bypass wastereinjection.

In conclusion the domestic power andfresh water needs could be realisticallyfulfilled.

Lipari

Exploration should resume by drilling

two exploratory boreholes in order tocheck the conclusions of an integratedgeophysical survey, carried out over thethermal spring area, which inferred thepresence of a low enthalpy reservoir. Itshould also enable to reprocess the formergeophysical data.

The development objective is atpresent limited to low grade heataddressing space heating/cooling, thermaland medicinal uses with desalinationadded as an option.

Pantelleria

The island is a puzzling dilemma. Inspite of numerous surface naifestations,deep drilling exploration stood belowexpectations. Nonetheless a dry steamsource was evidenced that could easeaccessing to a dependable hight enthalpyreservoir, in which case power generationcould be contemplated to meet a localdemand estimated at ca 5 MWe.

There are elsewhere abundant low tomedium enthalpy sources, suggesting toselect desalination as a main developmentobjective, bearing in mind that a 90 °C –200 m3/h resource could sustain a ca 700m3/day fresh water output securing half ofdomestic requirements , presently suppli-ed by tankers.

Other direct use oriented applicationsare considered in the waiting of futuredrilling/testing assessments.

Milos

Milos has been shown to host thehighest geopower potentiel recorded todate in the whole Aelian/Aegean region,estimated at 15 MWe, based on existingwell deliverabilities. Whatever the pre-sently bleak outlook and low profile, powergeneration ought to be given, one day oranother, a chance to prove technicallyfeasible, economically viable, environ-mentally safe and be harnessed accor-dingly.

Priority is given to desalination pros-pects. A recently commissioned project,targeted at a 100 m3/h – 90° C brineproduction from shallow wells, shouldsupply a 240 m3/day fresh water output,covering 25 % of the island domesticdemand.

The locally active mining industryshould welcome the contribution ofgeothermal low enthalpy sources in driving

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the drying segment of the ore processingline.

Thira/Santorini

Desalination is given the highestpriority. It should be achieved by drillingwells of the type designed in the Milosscheme. They would allow to delineate thecandidate shallow reservoir, thuscomplementing the data collected fromearly slinehole drilling reconnaissance.

At this stage, a 150 m 3/h – 90° C welldeliverability, meeting ca 20 % of the freshwater needs of the island community,seems a realistic objective.

The existence of a, deeper seated,medium enthalpy reservoir remainshypothetical. Possibly could, in the future,exploratory wells be drilled and, ifsuccessful, lead ultimately to powergeneration using ORC technology.

Nisyros

Early development expectations,targeted at power generation capacities ashigh as 10 to 20 MWe, are nowabandoned in spite of an encouragingdeep drilling exploration outcome.

Prospects are at standby stage. Itwould be worth resuming geothermal"expro" by commissioning a small size,incentive, project to somehow counter theadverse island desertification trend.

In this perspective, the drilling of a wellaimed at a combined powergeneration/desalination plant rated at 500kWe/250 m3/day, capable of supplyingcommunity power/fresh water needs couldprovide the necessary stimulus.

KosLong considered a second ranked

geothermal objective, the island did notattract gethermal explorationists. However,the western located, Volcania calderasetting, assumed to host a hydrothermalreservoir, deserves further geophysical/gechemical investigations and exploratotrydrilling in order to thoroughly assess thelocal resource potentialities.

Lesvos

By far the most large and populatedisland, Lesvos hosts significant, provenand inferred, low to medium enthalpy re-sources as a result of graben active/

distensive tectonics and abundant waterrecharge.

Several exploration/development pro-jects, presently at commissioning stage,should lead to, presumably reliable, directuse oriented applications.

Although premature at this stage, inthe waiting of the actual temperaturestatus, power generation (ORC techno-logy) from medium enthalpy sources,could be foreseen to meet the demands ofisland communities either directly or viaconnection to te grid.

Implementation

Project evaluation and commissioningshould account for the followingconsiderations.(i) a significant geothermal energy poten-

tiel has been identified bu insignificantcommercial development has beennoticed yet,(ii) power generation from proven high

enthalpy sources, once thought themost promising development route, hasbeen abandoned,(iii) desalination instead raises a growing

interest from several island com-munities,(iv) toursim brought a massive income

which, conversely, added to alreadysensitive energy/fresh water supply prob-lems, not mentioning the consequencesof, season wise, unbalanced socio-economics,(v) the island communities, in most in-

stances, proved reluctant, when nothostile, to geothermal energy, particularilypower generation, development prospects.

Given this context geothermal energyhas to bridge a credibility gap addressingdecision makers, fund backers and islandcommunities. This clearly does not reduceto a simple image problem.

As a result, a unified approach tocommon problems, benefitting from theexpertise and knowhow availablethroughout the geothermal community isrecommended on both bureaucratic andpractical informal.

It could take the form of an informedtask force involving an expert core group,representatives of island communities andstakeholders among other parties in theframework of an ad-hoc Mediteraneanrewenable (geothermal) energy (sub)programme. Whatever bureaucratic this

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suggestion may be it coud ease accessingto decisions and funding and, last but notleast, formalise communication betweenconcerned actors and partners.

Practically, with a view to reduceentrepreneurial risks and gain credibility,the project evaluation and commissioningprocess should (i) focus on argumentedexploration targets, (ii) stick to small pilotexploitation units and convincingdemonstrative trials prior to full scalecommitments, (iii) favour modular designscompatible with local environmentalrequirements, (iv) secure project feasibilityand related technical/managerial skills,and (v) improve communication withwhoever is concerned.

CONCLUSIONS

Exploration, carried out since the early1950s (Aeolian) and 1970s (Aegean),confirmed the high geothermal potential ofthe Aeolian Sicilian channel and Aegeanregions expected from their distinctivegeodynamic settings (active volcanic is-land arcs, rift and tectonics) andhydrothermal environments.

So far no tangible developmentfollowed the discovery of high enthalpysources, eligible to power generation, inthe Vulcano, Pantelleria, Milos andNisyros islands, although the area at largefaces severe energy/fresh water supplyproblems particularily during peak touristicmonths.

This paradox has been analysed inthe light of the following limiting factorsand barriers.(i) exploration/mining risks, sensitive in

the Aeolian and Pantelleria,(ii) exploitation risks and environmental

hazards, examplified in Milos, and(iii) insularity, a generic label addressing

the island physical and socio-

economic features alongside the skeptic,when not hostile, attitude of the communitytowards geothermal, chiefly powergeneration, development opportunities.

Given the foregoing the followingdevelopment guidelines are suggested.(i) allocate to desalination, using

preferably the attractive MED process,the highest priority in meeting in the criticalfresh water demand of most islandcommunities,(ii) promote low to medium enthalpy

sources and related cooling/freezing,process heat, thermal/medicinal, spaceheating direct uses,(iii) give power generation, in spite of its

presently bleak outlook, a secondchance,(iv) focus on argumented exploration tar-

gets, small exploitation units prior tolarge scale commitments, modular, en-vironmentally compatible, designs, andreliable technical/managerial skills, and(v) last but not least, improve com-

munication with concerned islandcommunities.

These guidelines should bridge thecredibility gap geothermal energy is facingin the Mediterranean area and, ultimately,secure the development targets proposedin the, island wise, project review.

So, everything considered, geothermalenergy has a good chance.

ACKNOWLEDGEMENTS

Never could have this paper beenwritten without the contributions of MariaPapachristou, Adele Manzella and CeciliaGiussani who provided the author withinvaluable documentation and advice.Would also the organisers of the "IGD2002 Greece" meetings, particularily KirilPopovski, be thanked for their patience inwaiting for this paper.

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