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Journal of Volcanology and Geothermal Research 262 (2013) 68–79
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Journal of Volcanology and Geothermal Research
j ourna l homepage: www.e lsev ie r .com/ locate / jvo lgeores
Hydrogeochemical characterization and conceptual modeling of theEdremit geothermal field (NW Turkey)
Özgür Avşar a,⁎, Nilgün Güleç b, Mahmut Parlaktuna c
a Muğla Sıtkı Koçman University, Department of Geological Engineering, Muğla, Turkeyb Middle East Technical University, Department of Geological Engineering, Ankara, Turkeyc Middle East Technical University, Department of Petroleum and Natural Gas Engineering, Ankara, Turkey
⁎ Corresponding author at: Department of Geological EUniversity, TR48000 Kötekli-Muğla, Turkey. Tel.: +90 25(mobile); fax: +90 252 211 1912.
E-mail addresses: [email protected], [email protected] (N. Güleç), [email protected] (
0377-0273/$ – see front matter © 2013 Elsevier B.V. Allhttp://dx.doi.org/10.1016/j.jvolgeores.2013.05.015
a b s t r a c t
a r t i c l e i n f oArticle history:Received 25 January 2013Accepted 27 May 2013Available online 17 June 2013
Keywords:GeothermalHydrogeochemistryGeothermometryFluid-mineral equilibriaEdremit-Balıkesir
The Edremit geothermal field, with 42–62 °C discharge temperatures, is utilized for space heating. Alterna-tion of permeable and impermeable units created two superimposed aquifers in the area: an upperunconfined and a lower confined. Water samples from 21 (hot–cold) wells were taken in this study. 8 ofthese wells penetrate the deeper confined aquifer, while 13 penetrate the shallower unconfined aquifer. Geo-chemical analyses revealed that Na + K − SO4 (>40 °C), Ca − HCO3 (b30 °C) and Ca − SO4 (30–40 °C)waters occur. δ18O-δD compositions point to a meteoric origin for all waters, while 14C analyses suggest lon-ger subsurface residence times for the hot waters, compared to the cold/warm waters. Chemical and isotopiccompositions indicate that mixing and water–rock interaction are the possible subsurface processes. Whensilica and cation geothermometers are evaluated together with fluid-mineral equilibria calculations, a reser-voir temperature range of 92–150 °C is evaluated. Saturation indices do not indicate a serious potential ofscaling in the field. The hydrogeology of the study area is highly affected by faults. Infiltrated meteoricwater percolates (down to 4.5 km depth) via deep seated step faults, becomes heated and ascends to the sur-face at the low lands, especially through intersection of buried, mid-graben faults. During its ascent, geother-mal water invades the two superimposed aquifers where mixing between the hot and cold waters takesplace.
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
Owing to its setting in the tectonically active Alpine-MediterraneanBelt, Turkey has considerable geothermal potential. This potential hasbeen utilized in district heating (1494 MWt), balneology (552 MWt),heat pump applications (38 MWt) and electricity production (installedcapacity: 81.61 MWe) (Mertoğlu et al., 2010). Geothermal explorationand development activities are currently in progress to meet the in-creasing demand for energy to be utilized in electricity productionand heating.
The study area is located in the Edremit plain in NW Anatolia, tothe SW of Edremit (Balıkesir) (Fig. 1). By the discovery of geothermalenergy by the General Directorate of Turkish Mineral Research andExploration (MTA) in 2000, geothermal energy is used for heating5000 houses. Thermal water is pumped from 8 wells owned byEdremit municipality (Table 1). The district heating system contains
ngineering, Muğla Sıtkı Koçman2 2113156, +90 532 332 9008
@gmail.com (Ö. Avşar),M. Parlaktuna).
rights reserved.
a one way pipeline system, and building mounted heat exchangersbut no reinjection system.
The present study aims to evaluate the potential of the field forfuture utilization (electricity generation and/or developing districtheating) by means of hydrogeochemical characterization. In thiscontext, hydrogeochemical analyses were conducted on water sam-ples collected from the wells in the study area. The results wereinterpreted to assess hydrogeochemical facies, possible subsurfaceprocesses comprising water–rock interactions, subsurface residencetime, geothermometry applications (reservoir temperature estima-tion) and scaling potential.
2. Geologic and hydrogeologic outline
The Edremit geothermal field is situated in western Anatoliawhich is one of the neotectonic provinces of Turkey (Fig. 1a). Approx-imately E–W trending horsts and grabens formed by active extensionare the basic structural elements of this province (Fig. 1b) (Şengör etal., 1985). The widespread geothermal activity in western Anatolia isclosely associated with the tectonic evolution of the region. Almost allof the geothermal fields are located along the boundary faults ofthe major grabens (e.g. Büyük Menderes, Simav, Alaşehir grabens)which act as channelways for the thermal waters. The Edremit field
Fig. 1. (a)Major neotectonic elements of Turkey (Şengör et al., 1985), (b)major structural elements ofwesternAnatolia (Bozkurt, 2001), (c) geologicalmapof the Edremit region. (d) Locationsof the wells (red: >40 °C, orange: 30–40 °C, blue: b30 °C). Red dashed lines are the buried faults. Wells DOGANDERE and DSI-6 are coincident. The letters A–A′, B–B′,… refer to the crosssections provided in Supplementary Fig. 1.c, compiled from Bingöl et al., 1973; DSI, 1977; Sarp et al., 1998; Duru et al., 2004; MTA, 2007.
69Ö. Avşar et al. / Journal of Volcanology and Geothermal Research 262 (2013) 68–79
Table 1Coordinates, depths and well-head water temperatures of wells in the Edremit geothermal field. All the wells are vertical. U: upper unconfined aquifer, L: lower confined aquifer,IB: Iller Bank, DSI: State Hydraulic Works, M: Non-governmental miscellaneous firms. (ED-2 was not sampled as its discharge flow rate is not adequate but well log data was used;TOTAL and EMINKUYU were sampled only for stable isotope studies).
Aqui. Well no. Drilledby
Drillingdate
Coordınate (UTM/European 1950)
Elev.(m)
Depth(m)
Dynamic well-headtemperature(°C)
Static bottom-holetemperature
Measured max. dischargeof the wella
(l/s)
Discharge capacityof the pump installeda
(l/s)E N
L ED-3 MTA 2001 503639 4380394 22 495 62 50.1 18 20L ED-1 MTA 2000 503718 4380329 22 189 62 59 72 72L EDJ-3 IB 2005 503634 4380252 21 266 59 50 86 72L EDJ-2 IB 2008 503916 4380049 24 300 58 40 75 72L EDJ-5 IB 2005 504054 4380273 23 216 55 57.7 45 45U DERMAN M – 503731 4380197 22 100 53 – – –
U ENTUR M 2000 503743 4380178 22 90 51 – – –
L EDJ-7 IB 2005 503968 4380402 23 246 51 49 30 30L EDJ-4 IB 2005 503458 4380136 19 296 50 49 86 20L ED-2 MTA 2001 504014 4380293 23 496 47 51 – –
L EDJ-8 IB 2007 503815 4380491 23 250 43 60 39 30U YAGCI M – 503729 4380591 23 100 42 – – –
U DSI-6 DSI 1970 503753 4379919 24 95 39 – – –
U TOTAL M – 503729 4380591 24 – 36 – – –
U DOGANDERE M – 503753 4379919 24 30 32 – – –
U DSI-9 DSI 1974 502958 4380668 20 122 32 – – –
U HASTANE DSI 1975 504099 4381130 28 90 31 – – –
U DSI-5 DSI 1970 503949 4380066 24 91 30 – – –
U DSI-7 DSI 1970 504088 4379653 22 132 21 – – –
U DSI-8 DSI 1972 505195 4380605 26 83 18 – – –
U EMINKUYU DSI – 503129 4382054 28 – 18 – – –
U EMINDSI DSI 1975 502824 4382144 24 100 12 – – –
a There is no discharge measurement device installed at well-heads. These values are given to give an idea about the discharge capacities of the wells. Maximum discharge valuesare from the well completion tests that were conducted by using a weir by the drilling company directly after drilling. The source of the data about the discharge capacity of thepumps is the supplier company.
Fig. 2. Generalized cross section of the study area showing confined and unconfinedaquifers.
70 Ö. Avşar et al. / Journal of Volcanology and Geothermal Research 262 (2013) 68–79
lies within the Edremit graben in the NW part of the region, close tothe Gulf of Edremit (Fig. 1c), where the faults have both normal andstrike-slip components (Taymaz et al., 1991). The study area is tec-tonically located on the branches of the North Anatolian Fault (NAF)(Herece, 1990). The NE–SW oriented faults in the Biga Peninsulacomprise the westernmost extensions of the NAF. The region gainedits present geometry through the extensional tectonic activities thatbegan by at least the late Miocene and continued throughout theQuaternary.
The geologic map of the Edremit geothermal field is given inFig. 1c. The basement is made of metamorphic rocks (schists,gneisses, amphibolites, metadunites, migmatites, marbles) of theKazdag Massif (Bingöl, 1969, 1976). Spilitic basalts, radiolarites andclastics of Karakaya Formation (Bingöl et al., 1973) overly the base-ment and are themselves overlain by the sandy limestones of BilecikFormation (Altınlı, 1973). These rocks are intruded by the EybekGranodiorite which is genetically related to the overlying Hallaçlarvolcanics. The Ballıca Formation (Akyürek and ve Soysal, 1982) andthe Plio-Quaternary sediments form the youngest units in the field.
The major source of information about the hydrogeology comesfrom the wells drilled in the field either for irrigation purposes orfor geothermal exploration and utilization. The data relevant tothese wells are given in Table 1.
There are two superimposed aquifers in the field. One is a deeperconfined aquifer and the other is a shallower unconfined aquifer(Fig. 2). The shallower aquifer is comprised of Quaternary andPlio-Quaternary loosely cemented, unconsolidated sandstone, mud-stone and conglomerate units. This shallow aquifer overlies theBallıca Formation of siltstone–marl–conglomerate–sandstone–clayeylimestone which is impermeable and acts as an aquiclude for theupper unconfined aquifer. It acts also as an aquiclude for the lowerconfined aquifer. The lower confined aquifer is composed of agglom-erate and conglomerate units which are permeable and overlain andunderlain by the Ballıca Formation and basement rocks, respectively.
Detailed analyses of well logs were used to delineate the dipangles and orientations of previously proposed (Sarp et al., 1998;MTA, 2001; IB, 2005; Jeotermal Araştırma ve Tesisler A.Ş., 2007) bur-ied faults in the field. Cross-sections with different orientations(Fig. 1d; Supplementary Fig. 1), prepared through the utilization ofthese well logs, revealed that the buried faults intersect each otherat the center of the geothermal field where most of the wells are lo-cated (Fig. 1d).
3. Material and methods
Water samples were collected from 21 vertical wells in the studyarea. The locations of the wells are given in Fig. 1d; coordinates,depths, dynamic well head and static bottom-hole temperatures(as obtained from temperature logs) are in Table 1.
Table2
Major
anion–
cation
andtraceelem
entco
ncen
trations
.May
2009
sampling.
U:u
pper
unco
nfine
daq
uifer,L:
lower
confi
nedaq
uifer,T.:tempe
rature,E
.C.:electrical
cond
uctivity,T
.A.:totala
lkalinity,
T.H.:totalh
ardn
ess,CB
E:ch
arge
balanc
eerror.
Sampleno
.Dateof
sampling
Ta (°C)
pHE.C.
(μs/cm
)T.A.
(mg/l)
T.H.
(mg/l)
SiO2
(mg/l)
HCO
3
(mg/l)
Cl (mg/l)
SO4
(mg/l)
Na
(mg/l)
K (mg/l)
Ca (mg/l)
Mg
(mg/l)
Al
(mg/l)
Fe (mg/l)
B (mg/l)
NO3
(mg/l)
CBE
(%)
Facies
ED-3
12.05.09
627.76
1060
4463
3254
4836
019
33.4
250.2
0.06
60.05
81.6
0.18
0.06
Na+
K−
SO4
ED-1
12.05.09
627.65
1310
3590
5243
6247
023
55.5
360.1
b0.00
50.02
1.6
0.13
−0.29
Na+
K−
SO4
EDJ-3
12.05.09
597.65
1260
3283
4539
5846
022
85.1
330.1
0.06
2b0.00
11.4
0.18
−0.64
Na+
K−
SO4
EDJ-2
12.05.09
587.67
1200
3678
5044
5742
021
75.1
310.1
0.03
50.03
11.6
0.13
0.23
Na+
K−
SO4
EDJ-5
12.05.09
557.99
756
7633
4293
4619
014
03
130.1
0.07
90.02
31.2
0.66
0.34
Na+
K−
SO4
DER
M.
20.05.09
537.81
1300
5498
4766
6244
022
85.1
380.7
0.12
0.07
31.4
0.13
0.04
Na+
K−
SO4
ENT.
20.05.09
517.95
1200
7183
4487
5939
021
54.5
320.7
0.03
60.03
81.3
0.26
−0.40
Na+
K−
SO4
EDJ-7
12.05.09
517.61
1380
3098
4837
6350
024
65.7
390.1
0.08
80.07
91.5
0.22
0.03
Na+
K−
SO4
EDJ-4
12.05.09
507.81
1110
5593
2667
5138
019
23.7
360.7
0.13
0.07
61.1
0.35
−0.71
Na+
K−
SO4
EDJ-8
20.05.09
438.00
751
8212
910
050
180
147
4.6
4.9
b0.1
0.57
0.06
0.68
0.22
−0.24
Na+
K−
SO4
YAGCI
14.05.09
428.13
874
125
7732
153
4722
015
43.1
300.6
0.09
40.08
10.83
1.60
−0.53
Na+
K−
SO4
DSI-6
14.05.09
398.07
1080
154
328
3918
853
320
108
3.7
105
16b0.00
50.03
20.73
8.9
0.49
Ca−
SO4
DOG.
13.05.09
328.14
934
178
320
3721
747
230
803.2
102
160.11
0.00
70.5
8.9
1.51
Ca−
SO4
DSI-9
13.05.09
328.09
1060
158
380
3319
357
310
823.6
126
160.19
0.02
60.55
8.4
0.17
Ca−
SO4
HAST
.13
.05.09
318.06
817
123
307
3115
054
200
493.4
100
140.08
70.13
0.19
3.8
1.30
Ca−
SO4
DSI-5
14.05.09
308.06
962
139
264
3517
052
220
824.1
7817
b0.00
50.03
60.5
140.73
Ca−
SO4
DSI-7
20.05.09
218.14
466
150
144
3018
321
2423
1.8
429.5
0.01
30.01
70.07
34.0
−2.09
Ca−
HCO
3
DSI-8
14.05.09
188.12
975
175
324
3021
410
171
392
8726
0.11
0.03
10.03
144
2.45
Ca−
HCO
3
EMIN
DSI
13.05.09
128.14
438
171
198
1920
917
3714
1.5
649.3
0.03
60.02
10.03
4.4
−0.74
Ca−
HCO
3
aOn-
site
(well-he
ad)mea
suremen
ts.
71Ö. Avşar et al. / Journal of Volcanology and Geothermal Research 262 (2013) 68–79
The samplingwas performed from both deep and shallowwells atthe well-heads, in September 2008 and May 2009. Four water sam-ples per well were collected into polyethylene bottles for each sam-pling site. 100 ml water samples were taken to measure their anioncontents, 100 ml for cation and trace element contents (acidified),100 ml for δ18O and δD isotope analyses, and 1000 ml for 14C analy-sis. The samples were kept cold until they were sent to thelaboratories.
Major anion–cation and trace element analyses were carried out atSRC Analytical laboratory (Canada). Cation (Na, K, Ca, Mg) and trace el-ement (Al, Fe, Ba, B, Cr, Cu, Pb, Mn, Mo, Ni, Sr, Zn) analyses wereperformed by ICP-AES. The alkalinity was determined by sulphuricacid titration to fixed end points of pH 4.5 and 8.3. The carbonate andbicarbonate contentswere calculated from the alkalinity determination.Chloride was determined colorimetrically with the mercuric thiocya-nate method. Nitrate was determined colorimetrically. Hardness wascalculated from Ca and Mg concentrations. Stable isotope analyseswere performed by the TUBITAK-MAM laboratories using EA-IRMS(Element Analyzer-Isotope Ratio Mass Spectrometer). 14C analyseswere conducted at the BETA Analytics laboratory (USA) on the DIC(dissolved inorganic carbon) fraction of the waters.
4. Water chemistry
Major anion–cation and trace element concentrations are given inTable 2 along with temperature, electrical conductivity, total alkalin-ity, total hardness and charge balance error. Stable isotope composi-tions and 14C dates of water samples are presented in Tables 3 and4, respectively.
Major anion–cation contents are used to recognize (determine)the hydrogeochemical facies, interactions between wells, scaling po-tential and reservoir temperature (geothermometry applications).Trace element contents and stable isotope compositions (18O/16Oand D/H ratios) provide additional information about the source ofthe waters, water–rock interactions and probable subsurface process-es. Interpretations about the subsurface residence time of groundwa-ter are based on 14C analyses.
4.1. Hydrogeochemical facies and origin of waters
The hydrogeochemical facies of the waters are defined by thedominant cation–anion pair using the concentrations in meq/l units,and are depicted in terms of Schoeller diagram in Fig. 3. As can beseen from this figure, waters >40 °C are of “Na + K − SO4” type, wa-ters b30 °C are of “Ca − HCO3” type and those with temperatures be-tween 30 and 40 °C are “Ca − SO4” type.
All water samples plot in between Mediterranean Meteoric WaterLine (MMWL) and Global Meteoric Water Line (GMWL) (Fig. 4),pointing to a meteoric source for all waters. Given their higher δ18 Oand δD values than hot waters, the colder aquifers appear to berecharged by precipitation at lower altitudes, whereas hot wateraquifers are fed by precipitation at higher altitudes.
4.2. Subsurface residence time of waters
The 14C dating results obtained from the dissolved inorganic car-bon (DIC) within seven water samples are given in Table 4 withδ13C of TDIC, 14C fraction of modern (fmdn) and calculated radiocar-bon groundwater ages. Corrected ages of the relatively hot waters(>40 °C) range between 1215 ± 40 and 6610 ± 60 years, whilecolder waters are modern. The reported ages are used here as a rela-tional tool to interpret hydrologic differences between wells. In thisrespect, the fact that sample EDJ-8 has a rather young 14C age(1215 ± 40 years), compared to the other (relatively) hot waters(2338 ± 40 to 6610 ± 60 years), deserves particular attention asabout a 10 °C decrease in water temperature within the last 1 year
Table 3Stable isotope analysis results (‰ relative to VSMOW). August/September 2008 sam-pling. U: upper unconfined aquifer, L: lower confined aquifer.
Welltype
Sample no. Well-headtemp.(°C)
Date ofsampling
δD(‰)
Std dev. δ18O(‰)
Std dev.
L ED-3 62 10.09.08 −52.19 0.48 −9.19 0.13L ED-1 62 06.08.08 −52.22 0.31 −9.47 0.08L EDJ-5 55 06.08.08 −50.45 0.29 −7.60 0.08L EDJ-7 51 10.09.08 −47.15 0.43 −7.24 0.03L EDJ-4 50 06.08.08 −49.70 0.31 −8.26 0.19L EDJ-8 43 10.09.08 −45.94 0.58 −7.18 0.43U DSI-6 39 06.08.08 −47.55 0.24 −7.95 0.30U TOTAL 36 11.09.08 −48.69 0.62 −7.91 0.16U DOGANDERE 32 11.09.08 −43.28 0.05 −7.91 0.02U DSI-9 32 12.09.08 −47.07 0.30 −7.76 0.49U HASTANE 31 12.09.08 −43.26 0.72 −6.71 0.41U DSI-7 21 06.08.08 −43.06 0.21 −6.95 0.37U DSI-8 18 11.09.08 −38.72 0.23 −7.24 0.29U EMINKUYU 18 11.09.08 −38.77 0.06 −6.88 0.05U EMINDSI 12 12.09.08 −39.63 0.03 −8.11 0.31
Fig. 3. Schoeller diagram of waters from wells in the Edremit geothermal field (red:>40 °C, orange: 30–40 °C, blue: b30 °C).
72 Ö. Avşar et al. / Journal of Volcanology and Geothermal Research 262 (2013) 68–79
was recorded in this well by staff of Edremit Municipality. This de-crease, along with a shorter (younger) residence time, points to apossible mixing between cold and hot water in this well.
4.3. Spatial distribution of physical and chemical parameters
As mentioned previously there are two superimposed aquifers inthe study area and the wells penetrate either the upper aquifer (shal-low wells drilled by DSI and miscellaneous non-governmental firms)or the lower confined aquifer (about 250 and 500 m deep and drilledby MTA and IB; Table 1). No well penetrates both aquifers. It shouldalso be noted here that the waters derive from the hottest zones(according to the temperature logs), and these hottest zones are lo-cated at the bottom of the wells except EDJ-3 in which the hottestzone is 60 m above the bottom of the well (around 200 m).
Iso-contour maps of the well-head temperatures, SO4, HCO3 con-centrations and δ18O values of both aquifers (Supplementary Fig. 2),reveal that spatial distribution of the geothermal groundwater ishighly affected by the buried faults.
4.4. Possible subsurface processes
Mixing between deep-hot and shallow-cold waters and/or water–rock interaction are common subsurface processes in geothermal sys-tems. In this section, as a first approach, a possible subsurface mixingprocess is examined for the Edremit field. Since chloride (Cl) is ac-cepted to be a good tracer (non-reactive) in geothermal fluids, a Clvs. temperature plot (Fig. 5) is used here which presents a likelymixing between hot and cold water end members. Taking samplesED-1 as the hot and EMINDSI as the cold end members, a theoreticalmixing line is drawn in Fig. 5. The samples plotting around this mixingline are assumed to represent the products of mixing between these
Table 414C dating results (ages refer to radiocarbon years before present, “present” = AD 1950; U
Type of well Sample no. Date of sampling 13C/12Ca
(‰)Fraction(fmdn)
L EDJ-3 12.05.09 −10.1 0.4125 ±L EDJ-7 12.05.09 −12.0 0.4054 ±L EDJ-4 12.05.09 −10.9 0.6267 ±L EDJ-8 20.05.09 −14.4 0.9522 ±U DSI-9 12.09.08 −9.1 0.9451 ±U DSI-8 20.05.09 −13.4 1.0850 ±U EMINDSI 12.09.08 −9.5 0.9677 ±
a Relative to PDB-1 standard.b 14C half-life = 5568 years, A0 = 1.0 fmdn (100% modern).c A0 (corrected) = δ13CTDIC/(δ13Csoil − ε), δ13Csoil = −22‰, ε = 9‰ (Agarwal et al., 20
end members. The apparent mixing in Fig. 5 is modeled via computerprogram PHREEQC (Parkhurst, and Appelo, 1999) by generating mix-tures with the hot/cold water ratios obtained from orthogonal projec-tions. For a graphical comparison, measured vs. model-calculatedconcentrations for major ions, as well as boron (B), are plotted andgiven in Fig. 6. Examination of the figure indicates that some constitu-ents (Na, K, B) plot around y = x line supporting the validity of themixing process. On the other hand, plots of some other constituentssuch as Ca, Mg, SiO2 and SO4, deviate from the y = x line. Thedata points lying below the y = x line suggest dissolution of minerals(e.g. dolomite which accommodates Ca and Mg), while those abovethe y = x line points to precipitation of minerals (e.g. quartz). Anotherreason for the deviation of the data points from the y = x line can bethe inappropriate compositions assigned to endmembers. A further dis-cussion of these alternatives is given in Sections 5 and 6.
Another important underground process is contamination, whichcan be evaluated by means of B and NO3 contents. As seen on
: upper unconfined aquifer, L: lower confined aquifer).
of modern Apparent 14Cb ages Corrected 14Cc
agesWell-head temp.(°C)
0.0036 7110 ± 70 5086 ± 70 590.0030 7250 ± 60 6610 ± 60 510.0031 3750 ± 40 2338 ± 40 500.0047 390 ± 40 1215 ± 40 430.0047 450 ± 40 Modern 320.0050 Modern Modern 180.0048 260 ± 40 Modern 12
06).
Fig. 4. δ18O–δD diagram [MMWL:MediterraneanMeteoricWater Line (IAEA, 1981); GMWL: GlobalMeteoricWater Line (Craig, 1961); red: >40 °C, orange: 30–40 °C, blue: b30 °C].
73Ö. Avşar et al. / Journal of Volcanology and Geothermal Research 262 (2013) 68–79
Fig. 7a, the B contents are proportional to well head temperatures.Boron is probably dissolved from the Oligo-Miocene volcanics (HallaçlarFormation) in the region (Palmer and Helvacı, 1997). However, its con-tent does not exceed 1.6 mg/l even in the hottest waters. This amount issubstantially less than recorded for other western Anatolian geothermalfields (e.g. Kizildere, Germencik), which have up to 30 mg/l B (Vengoshet al., 2002; Tokçaer, 2007). When NO3 concentrations of waters arecompared with the depth of the wells (Fig. 7b), there seems to be a neg-ative correlation between the two. This implies that shallowwell watersare affected by surface activities such as agriculture.
5. Geothermometry applications and fluid mineral equilibria
An estimation of the reservoir temperature in Edremit geothermalfield is realized through the use of chemical geothermometers andfluid-mineral equilibria calculations.
5.1. Chemical geothermometers
Silica (quartz) and cation (Na/K) geothermometers were applied tothe hot waters. The results of geothermometric calculations are given inTable 5 and the estimated reservoir temperatures are in the 92–211 °C
Fig. 5. Well head temp
range. It is apparent in Table 5 that the sample EDJ-8 has the lowest esti-mate for reservoir temperature from silica, but the highest from thecation geothermometers. The low temperature estimated from silicageothermometers may be engaged to a degradation in silica concentra-tion in this sample due to the concepts (dilution due tomixing, precipita-tion) previously discussed in Sections 4.2 and 4.4. Regarding the cationgeothermometers, it is important to note that EDJ-8 is the only samplewhich seems to have precipitated Na (above x = y line in Fig. 6) anddissolvedK (belowx = y line in Fig. 6) (Section 4.4). Thismaybe respon-sible for a decrease in Na/K ratio, and hence an overestimated reservoirtemperature by cation geothermometers. Leaving aside sample EDJ-8,the highest estimate fromboth silica and cation geothermometers belongto sample ED-1 which is located at the center of the geothermal field.
5.2. Fluid mineral equilibria
The water–rock interaction in the Edremit geothermal field wasstudied by using the PHREEQC computer program. Chemical resultsgiven in Table 2 are the inputs for PHREEQC. During this study, thewater samples that were taken from the wells were assessed in termsof their saturation states of some common geothermal minerals. Results
erature vs. Cl plot.
Fig. 6. Measured vs. calculated ionic concentrations derived from theoretical mixingmodel.
Fig. 7. (a) B vs. well-head temperature plot, (b) NO3 vs. well depth plot. The sampleswere taken from separate wells from the well heads.
Table 5Chemical geothermometer results for Edremit geothermal field (values in °C).
Well Well-head temp. Quartza Quartzb Na-Kc Na-Kd Na-Ke
ED-3 62 167 190 103 92 124ED-1 62 189 211 118 107 138EDJ-3 59 182 205 115 104 136EDJ-2 58 187 209 118 107 138EDJ-5 55 179 202 113 102 133DERMAN 53 184 206 115 104 136ENTUR 51 181 204 112 101 132EDJ-7 51 185 207 117 106 138EDJ-4 50 159 182 107 97 128EDJ-8 43 117 137 134 123 154YAGCI 42 167 191 110 99 130
a Fournier and Potter (1982).b Arnorsson (1985).c Fournier (1979).d Nieva and Nieva (1987).e Giggenbach (1988).
74 Ö. Avşar et al. / Journal of Volcanology and Geothermal Research 262 (2013) 68–79
are evaluated as an approach to the i) reservoir temperatures and ii) de-termination of scaling potentials.
As a first approach, in order to predict the reservoir temperatures,the saturation states of different minerals were investigated at differ-ent temperatures for each water sample. These calculations wereperformed for a temperature range of 30–210 °C by considering thedischarge temperatures and reservoir temperatures estimated fromthe silica and cation geothermometers. The results of the saturationstates are presented by plots of saturation index (SI) versus tempera-ture diagrams in Fig. 8. Assuming a temperature-dependent chemicalequilibrium between mineral(s) and fluid in the deep reservoir, thetemperatures at which the mineral saturation indices intersect theSI = 0 value were recorded graphically and these temperatureswere assumed to represent the reservoir temperatures. The minerals
selected for SI calculations are the hydrothermal alteration minerals(a total of 14) determined, using XRD technique, by Koç et al.(1994) in their study on the epithermal mineralization potentialof Balıkesir area. As can be seen from the graphs, the curvesrepresenting the SI variation with temperature generally intersectwith the equilibrium line (SI = 0) in the range of 60 and 150 °C.This range partially overlaps with that obtained from chemicalgeothermometers (92–211 °C, Table 5). In this respect, a range of92–150 °C (zone of overlap between chemical geothermometersand fluid-mineral equilibria calculations) is considered to representthe most likely reservoir temperature for the Edremit geothermalfield.
As a second approach, the saturation indices were used toestimate the potential for scaling which is one of the majorproblems in geothermal fields especially at the operating stage.In Turkey (especially in western Anatolia), calcite and/or silica
75Ö. Avşar et al. / Journal of Volcanology and Geothermal Research 262 (2013) 68–79
precipitation causes serious scaling problems in most of the geo-thermal fields.
Investigation of Fig. 9a, which indicates changes of saturationindices of calcite in waters with changing temperature, revealsthat all waters are oversaturated with respect to calcite at temper-atures above 110 °C. In some wells, waters are oversaturated tocalcite at temperatures above 50–60 °C (EDJ-4 and ENTUR), or
Fig. 8. Temperature vs. SI diagram for well
even 30 °C (YAGCI). Most waters are oversaturated with respectto quartz at temperatures below 90 °C (Fig. 9b). Amorphous silicais undersaturated for the temperatures ranging between 30 and210 °C (Fig. 9c). At the discharge temperatures, waters are notoversaturated in calcite and slightly oversaturated in quartz, there-fore a serious scaling problem is not expected in Edremit geother-mal field.
s (waters with T > 50 °C are shown).
Fig. 9. Temperature versus saturation index graph of Edremit field waters for calcite (a), quartz (b) and amorphous silica (c).
76 Ö. Avşar et al. / Journal of Volcanology and Geothermal Research 262 (2013) 68–79
6. Hydrogeochemical modeling
In order to investigate the subsurface hydrologic properties of theEdremit geothermal field, some water level measurements weremade on the geothermal wells between 19.05.2009 and 21.05.2009(Supplementary Table 1). The measurements were performed to de-lineate the piezometric surface of the lower confined aquifer, there-fore the wells which penetrate the lower confined aquifer (well logs
Fig. 10. Generalized cross section showing the hydrogeological outline of the study area. Dasin °C. Not to scale.
provided by Iller Bank (IB, 2005, 2009, 2010)) were selected forwater level measurements. An evaluation of data via contour maps(Supplementary Fig. 2) reveal a potentiometric (piezometric) highat the intersection of the two buried faults named F1 and F2 coincid-ing with the low resistivity anomaly reported in previous studies(Kaynak et al., 1996; Jeotermal Araştırma ve Tesisler A.Ş., 2007). Ap-parently the faults are creating high and nearly vertical hydraulic con-ductivity zones regardless of stratigraphy, and deep seated, high
hed lines represent the proposed iso-temperature contours and numbers on these lines
77Ö. Avşar et al. / Journal of Volcanology and Geothermal Research 262 (2013) 68–79
pressure geothermal water is ascending especially through the inter-section of these zones.
The consideration of the physical and chemical parameters rele-vant to the wells, such as piezometric surface data, well-head tem-peratures, depths of wells, water chemistry, and the utilization ofwell logs provided by Iller Bank (IB, 2005, 2009, 2010) and theState Hydraulic Works (DSI, 1977), led to the categorization of thewells into 5 groups used in the construction of a 2D conceptualmodel (Fig. 10).
6.1. Type 1 wells (T1): ED-1, EDJ-3, EDJ-2
These wells cut one (or both) of the deep seated faults in the studyarea (Fig. 10). These wells produce the hottest water in the field(Table 1). Moreover, the smallest drawdowns were observed in type 1wells during measurements (Supplementary Fig. 3). These wells are
Fig. 11. Block diagrams illustrating the 3D conceptual model of the study area. (a and b) Edrthe geothermal field (not to scale).
isolated from the upper Quaternary aquifer and penetrate the lowerconfined aquifer. The waters from these wells are of Na + K − SO4
type.
6.2. Type 2 wells (T2): ED-3, EDJ-4, EDJ-5, EDJ-7, EDJ-8
These wells penetrate only the lower confined aquifer and do notcut any fault (Fig. 10). Although the waters of these wells are ofNa + K − SO4 type (same as Type 1), their discharge temperatures(Table 1) are lower than those of Type 1 wells.
6.3. Type 3 wells (T3): DERMAN, ENTUR, YAGCI
These wells are about 20–100 m deep and penetrate only the shal-low unconfined aquifer. Their well head temperatures range between42 and 53 °C (Table 1). They cut neither the deep confined aquifer nor
emit plain within the framework of the regional graben structure, (c) close-up view of
78 Ö. Avşar et al. / Journal of Volcanology and Geothermal Research 262 (2013) 68–79
any deep seated fault, but take their water from a shallow aquiferwhich is fed by hot and deeply circulating waters coming from deepseated faults (Fig. 10). They do not cut faults but they are so close tothem that their waters have a geothermal character although theyare relatively shallower than geothermal wells and penetrating onlythe upper unconfined aquifer. The hydrogeochemical facies of thewaters of Type 3 wells are again Na + K − SO4 type.
6.4. Type 4 wells (T4): DSI-6, TOTAL, DOGANDERE, DSI-9, HASTANE, DSI-5
These are shallow wells and drilled by DSI except DOGANDERE.They penetrate only the upper unconfined aquifer. The waters fromthese wells are warm and are categorized as of Ca − SO4 type. Theyare located in the mixing zone of the shallow aquifer (Fig. 10).
6.5. Type 5 wells (T5): DSI-7, DSI-8, EMINDSI, EMINKUYU
These wells were drilled by DSI and penetrate only the upperunconfined aquifer. They are sufficiently far away from geothermalactivity center to be categorized as producing cold waters with tem-peratures ranging between 12 and 21 (Table 1 and Fig. 10). Thehydrogeochemical facies of their water is Ca − HCO3.
The Na + K − SO4 type hot water appears to be rising from thedeeper in the crust via faults, while both confined and unconfinedaquifers contain Ca − HCO3 type cold water. The Na + K − SO4
type hot water is essentially meteoric in origin, like the Ca − HCO3
type cold water, and fed by precipitation at higher elevations of theKazdağ Mountain (Section 4, Figs. 1 and 6). It seems to have had alonger subsurface residence time (Section 4, Table 4), thereforeattaining a higher temperature and chemical maturity as a result ofprolonged water–rock interactions. This water has a higher hydro-static pressure than the present cold water since it is fed from higherelevations. Because its hydrostatic pressure is higher than that of coldwater in the confined and the unconfined aquifers, the hot water in-vades the cold water aquifers, rising along fault zones up to few hun-dred meters (Fig. 1). This invasion results in mixing between hot andcold waters inside the existing aquifers and the production of Ca − SO4
type warm water.
7. Conclusions
The Edremit geothermal field is located in the Edremit graben. Al-though it appears to be an integral part of the western Anatolian grabensystem, where the grabens are formed by normal faulting, the Edremitgraben — being located at the western extension of the NAF — is struc-turally controlled by E–W and NE–SW trending right lateral strike slipand/or oblique faults. There are two superimposed aquifers in thefield: the lower confined (conglomerates, agglomerates) and theupper unconfined (alluvium). Of a total of 21 wells sampled in thisstudy, 8 penetrate the lower confined, and 13 penetrate the upperunconfined aquifer.
Geochemical analyses revealed the Na + K − SO4 nature of the hot(>40 °C), Ca − HCO3 nature for the cold (b30 °C) and Ca − SO4 naturefor the warm (30–40 °C) waters. δ18O-δD compositions point to a mete-oric origin for the hot, warm and cold waters and 14C analyses suggestlonger subsurface residence times for hot waters compared to the cold/warmwaters. Chemical and isotopic compositions indicate that “mixing”and “water–rock interaction” are possible subsurface processes.
Geothermometry applications, together with fluidmineral equilibriacalculations, suggest a reservoir temperature range of 92–150 °C for thefield and saturation indices of the waters do not indicate a serious scal-ing problem.
The hydrogeology of the study area is highly affected by the faultsproviding hydraulically conductive zones for the groundwater. Thewater percolates via deep seated grabens forming step faults, is heatedat depth and ascends in the center of the graben especially at the
intersection of buried mid-graben faults. Based on the assumption of anaverage geothermal gradient of 3 °C/100 m, the difference between theambient temperature (16 °C) and the estimated/expected reservoir tem-perature range (92–150 °C) reveals a 2.5 to 4.5 km percolation depth forthe waters.
Fig. 11a–b are block diagrams of the Edremit region where E–Wtrending major fault systems dominate the regional structure forminga depressional basin (Edremit plain/graben) between two E–Wtrending upthrown blocks (horsts): the Kazdağ Mountain in the northandMadraMountain in the south. The stratigraphical units differentiat-ed by the previousworkers (Fig. 1) are also shown in the block diagramalong with structural features. A close-up view of the 3D geometry ofgeothermal system in Edremit region is presented in Fig. 11c. As canbe seen from the figure, the geothermal system is centered around theDerman spa which is located at the intersection of two buried faults.The more productive wells of the geothermal field are the ones cuttingthe faults (i.e.well no. ED-1, EDJ-2 and EDJ-3). During its ascent towardsthe surface, geothermal water invades the two superimposed aquifers.Mixing between hot and cold waters takes place in the aquifers.
Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.jvolgeores.2013.05.015.
Acknowledgments
This work was supported by the Middle East Technical UniversityResearch Project Fund (METU-BAP-2008-03-09-03). N. Karahanoğluand H. Mutlu are acknowledged for their constructive criticism at var-ious stages of the research. Appreciation is extended to two anony-mous referees for their critical comments that helped improve themanuscript.
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