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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.