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Hydrothermal alteration at the exploration and production well in
Ömerbeyli, Germencik, Aydın, Turkey
a
Kasımoğlu ,
a
Karamanderesi ,Nevzat
Onur M.
İsmail H.
b
b
Tuğba A. Çalışkan , Ibrahim Ibrahim Abubakar
b
Özgür ,
a JEM
Jeolojik Etüt Müşavirlik Bürosu, Bornova/İzmir, Turkey
b Süleyman Demirel University, Faculty of Engineering, Department of Geological Engineering, Isparta, Turkey
ABSTRACT
The study area is situated 3 km NE of Ömerbeyli, located 12 km W of the principal province of Aydın, in western Anatolia, Turkey. Here, an exploration, production and reinjection borehole with a depth of approximately 2.200
m has been drilled. In this borehole, we have collected 38 samples of rock fragments in order to investigate hydrothermal alteration by X-ray diffraction and microscopic methods. In this geothermal area, the hydrothermal
alteration mineralogy depends upon i) temperature of geothermal system, ii) pressure of the system, iii) type of the rocks in the reservoir, iv) permeability of the reservoir rocks, v) geochemical composition of the reservoir rocks
and vi) stability of the minerals of the reservoir rocks. Since, usually there is a close relationship between the type of geothermal system and the related hydrothermal alteration, the monitoring of a given geothermal systems
can be ensured by parameters such as reservoir temperatures and hydrothermal alteration zones, providing that the hydrothermal alteration mineralogy has been investigated in detail. Therefore, the hydrothermal alteration
mineralogy of the exploration, production and reinjection borehole with a depth of approximately 2.200 m in Ömerbeyli has been shown.
1. INTRODUCTION
3.2 HİDROTERMAL ALTERATION
In Turkey, the geothermal waters show a great distribution in close connection with tectonic and volcanic
activities. In this case, high-enthalpy or high-temperature geothermal waters are mostly located in the
continental rift zones of the Menderes Massif which was resulted through compressional and later
extensional tectonic activities. For this reason, these high-temperature geothermal waters and the installed
geothermal power plants which will have a capacity of 750 up to 860 MWe until the end of 2018 are located
in the continental rift zone of the Büyük Menderes1,2,3 (Figure 1). One of these areas is the geothermal
exploitation area of Germencik with six geothermal power plants, where geothermal power plants of about
300 MWe of capacity are operated by private companies Güriş and Maren. A great number of exploration,
production and reinjection boreholes in the area were drilled. The aims of this study are (i) to update
geological knowledge of the study area within the tectonic development of the Menderes Massif with respect
to the up-to-date investigations, (ii) to describe, from the petrographic point of view, several rock fragments
collected from drill cores, (iii) to interpret the mineralogy of hydrothermal alteration by the study of collected
rock fragments showing water-rock interaction features, (iv) to define hydrogeochemical and isotopic
signatures of the collected water samples and to assign the relationships of the geothermal waters, and
finally (v) to clarify the relationship between hydrothermal alteration features and geothermal waters.
At the surface, the geothermal field of Tekkehamam and surroundings is recognized by a distinct color
change in the rocks. Generally, the sedimentary rocks are intensively altered through water-rock
interaction, and marked by silicic, phyllic, argillic, cabonatized, and hematitized alteration zones, identified
through petrographic and X-ray diffraction studies2. In the zones of high geothermal water-rock interaction,
there are mainly advanced argillic alteration represented by dickite, kaolinite and montmorillonite, identified
by X-ray diffraction studies.
2. MATERIAL AND METHODS
Figure 1. The continental rift zone of the Büyük
Menderes and locations of the geothermal
waters2,3.
Figure 2. Bozköy 1 well and hot spring in the
study area.
In the fieldworks, two different sampling was realized.
The first one is sampling of rock fragments of
exploration and production drilling. The depths of
these rock fragments in drilling are assigned. Later,
these rock fragments are washed and sieved
particularly so that the rock fragments can be purified
from the muds. Subsequently, the rock fragments are
determined under the binocular microscope and
recorded the data in protocol documents. The sieved
and washed rock fragments are divided in two parts.
The first one is archived for archival storage. The last
one is washed for clay contents particularly. The clay
contents in rock fragments are removed by washing
process.
Subsequently, the thin sections from the roch
fragments are prepared for the definition of these
rock fragments under the rock microscope
mineralogically and petrographically. In the last phase,
the rock fragments can be analysed by various
methods such as electron microscope, XRD, XRF,
ICP-OES and ICP-MS. analiz edilerek kuyu jeolojisi,
havza modeli, jeotermal sistemin geçmişi ve geleceği
hakkında modelleme çalışmaları yapılır. Üretim ve
geri besleme planlamaları buna göre organize edilir.
Finally, a modelling study on the history and future of
the geothermal system is realized. Thus, the
projections on productions and reinjections can be
done subsequently.
The second one is the sampling of the geothermal
waters in the study area. In the study area and
environs, a sampling of various geothermal waters
and in-situ measurements were realized. Aftermost, 2
(two) samples for anions, cations, stabile isotopes
(18O ve 2H) and tritium (3H) analyses and in-situ
measurements were realized from Bozköy 1 well and
Bozköy Mud Thermal Springs on August 20142
(Figure 2).
In the field, the pH values of the water samples for
cation analyses were adjusted in an interval between
2 and 3 by dropping of pure HCl.
The samples were analysed for cations and anions in
the Laboratory of the
Mineral Research and
Exploaration Institute, Ankara, Turkey and for stabile
istopes (18O ve 2H) and tritium (3H) analyses in the
Isotech Laboratories, Inc. .Illionis, USA (Table 1).
3. RESULTS
3.1 GEOLOGIC SETTING
The geological, geochemical, hydrogeological, isotopic and geothermal features of the study area and
surroundings were previously studied by MTA1 (General Directorate of Mineral Research and Exploration,
Ankara). The study area comprises mainly Paleozoic metamorphic rocks of the Menderes Massif and
Miocene, Pliocene and Quaternary sedimentary rocks and Middle Miocene volcanic rocks.
Stratigraphically, the metamorphic rocks mainly consist of gneisses, schists, marbles and quartzites.
Miocene sedimentary rocks are composed by the sequence of red conglomerates, sandstones and clays
(the lower sections of this sequence contain coals). Lower Pliocene sequence of conglomerates and
sandstones and Plio-Quaternary sequence of conglomerates with coarse gravels blocks and sandstones
overlie the last sedimentary sequence. In the study area, Pliocene sediments were crossed by Middle
Miocene volcanic rocks located in the eastern part of Germencik and in the western part of Söke. The
volcanic rocks at Söke are composed of basalts and andesites while at Germencik, close to Ortaklar, they
consist of dacites and andesites. Volcanic outcrops in the western part of Söke might be observed in terms
of lava dome chains of NE-SW direction. The dacite outcrop in the area of Çataltepe and Kaynaktaş, both
localities are situated in the north of Ortaklar, comprises an area of about 3 km2. Fresh rocks are yellowish,
hard, sharp angled, fractured, and their joint systems are evident (it extends along Ömerbeyli fault along
the WNW-ESE direction). The volcanic outcrops, which can be observed as acidic volcanic rocks on the
geological map, were initially evaluated as a possible potential key for geothermal energy exploration in the
study area2, 3. At the same time, it has contributed to the explaining the high temperature gradients of the
study area. Furthermore, an olivine basalt dyke was cut at a depth of 760-770 m by the borehole. Two
different reservoir rocks were crossed by the Ömerbeyli borehole, namely Miocene to Pliocene limestones
and Paleozoic marbles, quartzites and schists. These reservoirs were formed as a result of increased
permeability and secondary porosity of hard and fractured lithologies by step faults under extensively rift
tectonics.
3.3 HYDROGEOLOGY, HYDROGEOCHEMISTRY AND ISOTOPE
GEOCHEMISTRY
3.1 Hydrogeology
In the study area, the behavior of the groundwaters can be recognized by comparison and morphological criteria. In
the horst between the Büyük Menderes rift zone and the Küçük Menderes rift zone, the groundwaters waters flow
from north to south, feeding the geothermal reservoir. The distance from the horst to the geothermal reservoir
feeding area is about 8-10 km. Also, the geothermal reservoir feeding area is approximately 100-150 km2.
Generally, the continental rift zone of the Büyük Menderes shows features of continental climatic conditions with an
annual average rainfall of 430,15 mm and annual average temperature of 17,6 C. The precipitation in the area
occurs mainly in the winter season, from December to March. In comparison, the remaining months of the year are
very dry. The persistent long dry season causes deficit in groundwater. Miocene to Pliocene limestones are the rocks
of the shallow reservoir and the Paleozoic sequence of marbles and quartzites form the depth reservoir. Additionally,
Precambrian to Paleozoic gneisses, with well-developed fracture systems in the study area, plays an important role
for the formation of the third deepest reservoir.
3.3.2 Hydrogeochemistry
The geothermal waters of Ömerbeyli and surroundings can be classified as Na-(Cl)-HCO3 type waters (Figure 3). In
the study area, the geothermal waters with boron concentrations up to 100 mg/L (2, 3) indicate a sea water intrusion
from the Aegean Sea into the geothermal waters.
Table 1. In-situ measurements and hydrogeochemical
analyses of the geothermal waters in Ömerbeyli and
environs.
HCO3(mg/l)
CO3-2
(mg/l)
2.9
EC
(µS/c
m)
5630
2202
30
3.0
6200
1897
144
Örnek
Lokasyon
T
(°C)
pH
Eh
(mV)
O2
(mg/l)
OMK1
Bozköy1
Kuyusu
Bozköy Çamur
Kaplıcası
66.7
8.6
0
8.6
4
7.4
73.7
OMK 2
Örne
k
OMK
1
OMK
2
62.2
Na+ K+ Ca2 Mg SiO Al3 Li+ B3+ SO4 NO Cl+
2+
mg/l
mg
/l
mg/l mg/l
143
2
118
7
84 24, 23,
,1 5
3
98 109 59,
,3
8
2
mg/l
+
2-
mg/l mg/ mg/
l
l
mg/l
3
-
mg/l
105 1,1 5,4 51, 26,8 0,5
8
83, <0, 5,0 39, 10,3 0,7
2
2
1
PO4 F3-
mg/l
mg/l
mg/l
122 <0,
9
1
973 <0,
1
4,3
Figure 3. Geothermal waters of Ömerbeyli and
environs in Piper diagram.
2,6
3.3. Isotope geochemistry
Two samples of geothermal waters were collected and
analyzed for δ18O, δ2H and 3H2. Generally, rain waters,
groundwaters and mixed groundwater-geothermal water
systems lie on or along the Global Meteoric Water Line
(GMWL) whereas the high temperature deep geothermal
systems deviate from the GMWL, showing a strongly waterrock interaction under high temperature conditions (Figure 4).
δ18O values show a shift to the right of the GMWL, which
indicates a geothermal-cold grounwater mixture. This trend
was identified using δ2H, δ18O, δ13C, 3H, and 14C values3. The
tritium values in geothermal waters from the high temperature
geothermal systems of Kızıldere, Salavatlı and Germencik are
below detection limits, whereas some mineralized
groundwaters and thermal waters with a temperature up to 60
C contain atmospheric and anthropogenic origin indicated by
relatively low 3H contents3.
Figure 4. Geothermal waters of Ömerbeyli and
environs in δ18O versus δ2H diyagram.
4. CONCLUSIONS
The study area comprises Paleozoic metamorphic rocks of the Menderes Massif, Miocene, Pliocene and Quaternary sedimentary
rocks and Middle Miocene volcanic rocks. Hydrothermal alteration in the research area is distinguished macroscopically by
distinct color changes of the rocks. By X-ray diffraction methods, argillic, silicic and carbonatization alteration zones in the study
area have been described. In the study area, Miocene to Pliocene limestones form the shallow reservoir, and a sequence of
marbles, quartzites and mica schists form the second, deeper, reservoir. Both reservoirs are the source of the geothermal waters
(Figure 5). Additionally, the Precambrian-Paleozoic gneisses, with a good developed fractures and fissures, play an important role
for the development of third (deepest) reservoir. The geothermal waters in Ömerbeyli and surroundings are considered as Na(Cl)-HCO3 type waters. In the study area, the geothermal waters have boron values up to 100 mg/L indicating a sea water
(possibly from the Agean sea) intrusion into the geothermal waters.
Figure 5. Hydrogeological modelling of the geothermal waters in Germencik and environs2.
5. ACKNOWLEDGEMENTS
This study was funded by the Scientific Research Coordination Office within the Suleyman Demirel University, under contract
number 3706-YL2-13.
6. REFERENCES
1. Şimşek Ş, Hydrogeological and isotopic survey of geothermal fields in the Büyük Menderes Graben, Turkey. Geothermics 2003; 32: 669-678.
2. Kasımoğlu, OM, Ömerbeyli Köyü (Germencik, Aydın) yöresi jeotermal su arama ve üretim kuyusunda hidrotermal alterasyon modellemesi. M.
Sc. thesis, Süleyman Demirel Üniversitesi (in prep.).
3. Özgür N, Aktive und fossile Geothermalsysteme in den kontinentalen Riftzonen des Menderes-Massives, W-Anatolien/Türkei.
Habilitationsschrift, Freie Berlin, 171 p.