INTERNATIONAL SUMMER SCHOOL on Direct Application of Geothermal Energy

Under the auspice of the Division of Earth Sciences

HYDROGEOTHERMAL POTENTIAL OF THE VALLEY WITH A SPECIAL REVIEW OF THE BANSKO LOCALITY

Eftim Micevski GEOHYDROPROJECT Ð

S U M M A R Y 1. INTRODUCTION The Strumica valley with its skirt board The Strumica valley and its wide sur- with reference so tectonic sense belong to rounding were a subject of numerous geo- two structural-tectonica units. Serbo-Ma- logical, hydrogeological and geothermal cedonian massif and the Vardar zone. The explorations. They have been carried out valley itself presents a tectonic graben within the regional hydrogeological explo- which has been lowered in relation to the rations while making the Basic hydro- na d Smrdes horst, filled with geological map of , as well as Pliocene lake sediments while the skirt Ð the detailed explorations for solving vari- board is made of granite-gneisses. ous problems from the field of the water- The investigation-exploration drillhole supply, hydromeliorative systems, irrigati- B-1 with its 254 m. depth in the village on sites. Bansko dis-covered a deposit with In the period between 1982 Ð 91, a geothermal fluid at a depth of 150 Ð 103 special attention was paid to the Bansko m. in the granite-gneisses. Transmitters of locality, where detailed geothermal explo- the heart from the deeper depths are the rations were carried out. Here, active geo- waters from vadose origin which use large thermal springs and boreholes from the open fractures in the granite-gneisses and geothermal reservoir of Strumica are loca- the fresh granite which are found at great ted. From the several previous geother- depths of seismically-active Belasica fault, mal exploration boreholes (B-1 in the Ban- are likely to present a geating source. sko village, B-2 in the region of Staro Bal- The hydrogeothermal potential of the dovci, B-3 in the Saraj village and B-4 in Strumica valley is made upon the base of the vicinity of the Banica village), only the the results obtained from the investigation geothermal borehole B-1 yielded a capa- in the village Bansko, i.e. upon the base of city with positive characteristics for the the understanding of the dynamic reserves energetic exploitation. This bore-hole is where 51 l/sec. with temperature of 70oC actually a unit with the existing natural and 30 l/sec. with a temperature of 40oC spring above the hotel “Car Samoil” with have been taken. The effective usage is about ten smaller springs round it. It has 22,4oC, where a heating energy of 1,15x been drilled down to a depth of 254 m. 1011 KJ or 3,19x107 KWh is obtained. From the surface of the terrain down to a Concerning the hydrogeothermal in- depth of 143 m., the material in the bore- vestigations, the drilling should be conti- hole has been presented by various gra- nued, because of the determination of the nular Prolusion sediments, composed of spacious location of the collector to the fragments of granites and gneiss. From Strumica valley geothermal fluid. 142 m. to the final depth of the borehole, the lithological structure is composed of

- 241 - granitogneiss with interbeds of amphi- granular gravels, sands and clays. bolites and amphibole schists. The Quaternary formations cover al- most all the Strumica valley and are 2. SHORT PRESENTATION OF THE presented by sandy clay, gravel, sands GEOLOGICAL STRUCTURE AND and tufaceous sediments. The tufaceous STRUCTURAL GEOLOGICAL sediments occur in the Bansko village as a CHARACTERISTICS OF THE product of the deposition of the thermal STRUMICA VALLEY springs as contemporary paleohydro-geo- thermal occurrence and a process at the The Strumica valley which is situated village where it comes from the in the South-East part of Macedonia, ac- karst springs that occur in the marble. Du- cording to its spatial characteristics is a ring the drilling of the borehole B-1 (Ban- distinguished natural unit. There are seve- sko), at a depth of 30 m., a tufaceous plate ral geological units on this terrain, different was determined which points to the fact a in the lithological characteristics, geolo- long time ago thermomineral springs exis- gical age and tectonic features (fig. 1). ted at this area. The geological structure and its cha- Concerning the structural-tectonic as- racteristics of the geothermal reservoir pect, the Strumica valley and its peripheral Bansko are a part of the very charac- parts belongs to two tectonic units: The teristic geological struc-ture of the Strumi- Serbo-Macedonian mass and the Vardar ca valley where the Precambrian meta- zone. The area of interest can be sepa- morphites are the oldest, presented by rated into four structural geological units: various gneisses schists and magmatites. the Belasica horst, the Ograzden batho- The gneisses are the basic rocks of the liths, the Smrdes horst and the Strumica metamorphic complex while the remain- graben. Significant structure of hydrogeo- ing metamorphites are only facial transiti- thermal are the Ð Zleovo fault as ons. This complex has been represented well as the Belasica one, the Bansko Ð along the peripheral parts of the Strumica Gabrovo and the Ilovica fault as well as valley, which concerning the structural- hydrothermally altered zone Drvos Ð tectonic aspect belongs to the Serbo- Canakli. Macedonian mass, the schists have been The Strumica trench was formed by rep-resented in the Ograzden and Belasi- subsidence of the terrain along the Belasi- ca mountain and they are presented by ca and the Ograzden fault during the Plio- amphibolites, micaschists, leptinolites and cene. The depth in all the valley hasn’t amphibole schists. The magmatites has a been determined yet, but according to the local representation round the old Paleo- geophysical explorations it is from 700 Ð zoic granite intrusions in the gneisses 1200 m. which are feldspatized and silificated. The old Paleozoic rocks are presented 3. SHORT PRESENTATION OF THE by metamorphites and magmatites. The GEOLOGICAL STRUCTURE AND magmatates are presented by various gra- STRUCTURAL GEOLOGICAL nites, Rhyolites as well as gabbro repre- CHARACTERISTICS OF THE sented by several variants. They are STRUMICA VALLEY tectonically rather cracked and some- where hydrogeothermally altered. In order to determine the geothermal The Tertiary manifestations have been potential of the Strumica valley before per- pre-sented by Upper Eocene sediments, forming the exploration geothermal drilling, dacites, andezites and Pliocene tuff, many geological methods have been ap- conglomerate, sandstone and limestone plied whose final goal was to define the while the dacites and andezites occur as geothermal anomalies and to determine intrusions in the Paleozoic magmatites. the microlocations of the exploration bore- The Pliocene sediments are the most holes. The aerophoto-geological, structural repre-sentative phenomena in the explo- geological, geophysical, hydrochemical ration surfa-ces. They have been disco- and geothermic methods have been appli- vered along the peripheral parts of the ed. valley and identified in the exploration bo- By the analyses of the applied me- reholes and under the Quaternary sedi- thods for the Strumica valley, separation of ments in the valley, presented by different the tectonic elements, morphostructures

- 242 - and faults was made and their geothermal thermal manifestations by the correlation significance gas been determined accor- of the results obtained from all the applied ding to the existence of surface and hydro- methods.

- 243 - After the synthesis of the results of the Saraj village (the depth is 738 m., Q obtained from all the applied methods, a = 0,5 l/sec., T = 190oC), the locality Banica selection of the promising localities for (hot water was not identified, and the further detailed geothermal and the related temperature measured during the process hydrogeothermal explorations was done in of drilling is 28,4oC). order to discover the accumulation of the The microlocation of the exploration geothermal fluid, understanding of its geothermal boreholes B-1, B-2, GDB-1, spatial characteristics, calculation of the GDB-2 is in the Bansko village and its hot water reserves as well as under- surrounding (fig. 1). The borehole B-1 is standing of the economical justification for located in the centre of the Bansko village its exploitation. at a distance of about 50 m. and the hotel The most promising localities in the “Car Samoil”, while B-2 is situated at about Strumica valley, according to the previous 700 m. in the direction of the Mono-spitovo explorations, the following localities have village at a determined fault structure been established: according to the geophysical explorations ¥ The locality Bansko Ð Gabrovo Ð of that terrain, carried out in 1986. Svidovica (fig. 1); The other two boreholes GDB-1 and ¥ Canakli Ð Drvos; GDB-2 are located in the east side of the ¥ Banica Ð Vodoca Ð Veljusa; Bansko village, following the Belasica fault ¥ The area east of Ilovica Ð Stuka; towards the villages Gabrovo Ð Mokrievo Ð ¥ Monospitovo Smolari. The determination of the ¥ microlocation of all these boreholes has The exploration geothermal drilling been done according to the previously commenced in the Bansko locality, which performed geophysical explorations in is very understandable, because there are 1988 Ð 1989. geothermal springs and the water is used The exploration borehole B-1, was for balneological purposes. Here, on this drilled down to a depth of 254 m. (fig. 2), locality, four boreholes were drilled: B-1, from the surface of the terrain down to a B-2, GDB-1, GDB-2, whose obtained re- depth of 142 m., the material in the sults are rather significant. They will be borehole is presented by different granular presented and studied in details in this Proluvial sediments, compo-sed of frag- paper. ments of granites and gneiss. From the In the remaining localities, one bore- depth of 142 m. to the final depth of the hole was distinguished: the region of the borehole, the lithological profile is compo- Staro Bal-dovci, village (down to a depth sed of granite-gneiss with interbeds of of 420 m., over-flowing water of Q = 5 amphibolites and amphibole schists. l/sec., temperature T = 290oC, the region

Fig. 2: Lithological profile and results from the measurement of the temperature in the borehole B-1, Bansko 1. Proluvial sediments, 2. Gray-yellow clay with boulders of granite-gneisses, 3. Weathered blocks of granite-gneisses, 4. Fractured granite-gneisses.

- 244 - In order to examine the Bansko perature T = 22oC. The results of these locality until 1986, within the program for two exploration boreholes point to the fact further exploration, the borehole B-2 (fig. that in the fault rapture in the surface zo- 3) commenced to be drilled. This borehole ne, geothermal anomalies have been re- has been drilled down to a depth of 600 m. gistered. There is mixing with the cold sub- According to the previous explorations, the artesian waters, registered in this terrain. borehole intersected the Upper-Pliocene materials presented by different granular Hydrogeothermal characteristics of the sands, gravels, clays and muddy material terrain round the exploration boreholes down to a depth of 554 m., and down to 600 m. it entered the Upper zone of the According to the performed hydrogeo- granite-gneiss. The gra-nite-gneisses are logical explorations, during the drilling of rather mechanically cru-shed with many the borehole B-1, two horizons with fractures which are filled with calcite and subartesian water were registered at a quartz veins of 0,5 cm. depth of 30 Ð 35 m. and at 88 m., while at At the moment, the borehole is con- a depth of 108 m., a horizon with artesian served, i.e. filled with dense bentonite drill- water was registered. The largest flow of ling fluid. As hot water was not determined thermal water was registered at a depth of down to a depth of 600 m’, but having the 164 m. with a discharge of 60,3 l/sec. and previous under-standing from the explora- a temperature of 72oC. In the process of tions of this locality, we should continue drilling the discharge increases to 85 with the drilling, 100 m. more, so as to go l/sec., while the discharge in the main deeper in the granite-gneiss in order to get captage spring decreases to only 10 lit. hot water with a temperature higher than In the borehole B-2, thermal water 70oC and a yield at least approximately the was registered in the Proluvial sediments same as in the previous borehole B-1, at a depth of 34 m. as well as artesian whose capacity is 50 Ð 70 lit/sec. water occurred at the distance of 153 Ð In order to examine this locality in 185 m. in the sandy-gravel sediments details beside finishing the borehole B-2, presented in the profile of the borehole the people continued with further expected (fig. 4). exploration in the direction towards the The occurrence of geothermal water Gabrovo village by drilling the boreholes with a temperature of 72oC in the borehole GDB-1 and GDB-2, whose results achie- B-1 and at a depth of 156 Ð 163 m. is ved the expected goal by shallow sondage rather significant geothermal anomaly. boreholes, to do monitoring of the fault zo- After finishing the drilling, geothermal ne and record the geothermal anomalies logging was performed including the in that direction. The geothermal borehole thermologging. In accordance with the GTD-1 has been drilled down to a depth of measured temperatures in the borehole B- 220 m’, recorded temperature of 28,3oC, 1, the geo-thermal gradient was measured while the borehole GDB-2 has been drilled to be a basic parameter for characterizing down to a depth of 120 m’, and a quality of the geothermal re-servoir. The following overflowing water Q = 6 l/sec. and a tem- values were determined:

Fig. 3: Lithological profile, construction of the borehole and results of the measurements of the temperature to the borehole GD-2 in Bansko 1. Proluvial sediments (different granular sand, gravel and boulders with interbeds of clay) 2. Gray-yellow to dark brown clay with cobbles of granite-gneisses 3. Weathered blocks of the amplitoide granites and gneisses 4. Mechanically crushed and fractured granite-gneisses with fractures filled with calcite and quartz veins

- 245 - - in the distance between 179,2 and average heat conductivity of the granites 203,7 m., the greatest mean value of the and the gneisses, is has been considered geothermal degree was obtained, it was to be 100 to 110 mW/m2 (average value of 68,85 m/oC; the heat flow for the continental part of ¥ in the distance from 184 to 185 m., Europe is 60 mW/m2). the greatest anomaly with a geothermal gradient was considered Hydrochemical content of the water in the granite-gneiss was determined to be from 250oC/100 m., i.e. The chemical content of the water has geothermal degree of 6,4 m/oC; been determined by several analyses and ¥ average geothermal gradient down defined as potassium Ð sulphate type of to a depth of 254 m. is dT Ð the water with total mineralization of 1157, 19,71oC/100 m., i.e. the geothermal 2 mg/l. and with high content of boron and gradient is 5,07 m/oC. fluoride. It points to the fact that this water Such value of the geothermal degree originates from great depths. The relation is approximately 6 times greater than the of Na and K is greater than 1 and points to value of that parameter for the continental the fact that the water is vadose, i.e. the part of Europe (the average value for reservoir is feeding from the atmospheric Europe is 33 m/oC). The heat flow was not water. directly measured, but according to the

Table 1: Content of the major components of the chemical structure to the thermal water from the borehole B-1 (mg/l) Ð the Bansko village

Na K Cl Ca B F Na/K Na/Cl Cl/B Cl/F A mine

210 8,5 20,5 4,95 0,37 5,9 41,93 15,8 16,89 1,86 1157,2 mg/l

The chemical structure of the water flow within 75 Ð 80 l/sec. was measured., has been determined by several analyses with a temperature of 70oC. The drawing and has been defined as potassium Ð experiment, the hydraulic characteristics of sulphate type of water with total the borehole were determined, its hydra- mineralization of 1157,2 mg/l and with high ulic relation with the close thermal springs content of boron and fluoride. It points to was determined and according to the the fact that the water originates from results of these examinations, the sizes of great depths. The relation of potassium the possible capacities were determined and sodium is greater than 1 and indicates as well as the maximal capacity for a short to the fact that the water is vadose, i.e. the period of time, maximal permanent reservoir is feeding from the atmospheric discharge, the discharge of the resource water. during several years exploitation. The experimental explorations for the OPTIMAL USE OF THE PRESENT determination of the discharge of the CAPACITY OF THE HYDROGEO- geothermal fluid from the hydrogeothermal THERMAL SYSTEM BANSKO sys-tem Bansko, have been carried out the Geolo-gical Institute from Skopje and The determination of the discharge of Ljubljana in the period from 24.09.1983 to the geothermal resource in the region of 07.10.1983. First, when the drawing Bansko in the Strumica valley has been commenced in the borehole, the water based on several years measurements level was measured and it was 26.532 m. and monitoring of the geothermal water above the opening of the borehole. flow, of the previous natural spring Decreasing of the water flow during the (captage), as well as according to the flow time indicates that its size is decreasing through the present existing borehole B-1. from the starting 76,3 l/sec. to 64,6 l/sec., The exploration Ð exploitation borehole B- in a period of 8 days. 1 is 254 m. deep and the casing was done In the period from October Ð down to a depth of 157 m. The diameter of December 1991, the Geohydroproject the borehole is 156 mm. Immediately after carried out additional measurements of the finishing the technological works, as water discharges of all the springs, captage and

- 246 - boreholes. According to all these discharge of 50 l/sec and a temperature of explorations, whose results are presented 70oC, D-2 in the Drvos Ð Baldovci locality in graphic form (because of their legibility), with a temperature of 29oC and a we may draw the following necessary discharge of 5 l/sec. conclusions: The feeding of the reservoir is being - The direct hydraulic relation of the done through the granites which form the borehole B-1 with the remaining springs of Belasica mountain from the south and thermal water was determined. The main Ograzden from the north side of the valley. captage becomes dry immediately after This hydrogeothermal system belongs to several hours from the begining of drawing the group of open systems covered by from the borehole B-1; Tertiary sediments in one neotectonic - During the exploitation of the borehole depression (trench structure) situated B-1, we must consider the fact that almost among between the Belasica and the all surrounding springs will become dry Ograzden fault. (maybe only the spring at an elevation of The spreading of the reservoir in the 269,8 m. will remain the same, i.e. the old convective hydrogeothermal system Turkish health spa Salanci); Bansko has been estimated to about 100 - It was determined that the aquifer is km2, 1000 m. thick at a depth of 1 Ð 3 km. rather large. The minimal identified natural in the granite-gneisses from the Belasica feeding of the aquifer is more than 30 mountain, while the depth of the reservoir l/sec. under the Tertiary sediments in the valley - During large flows, hydraulic resistan- ranges from 1000 Ð 1500 m. ces occur. The installation of the pump for According to the chemical structure of drawing geothermal water we do not the thermal waters from Bansko, they expect significant increasing of the flow. belong to the group of sodium Ð sulphate - According to the diagrams of water type with a total mineralization of 1157 flow in the function of the time, by the mg/l, while the quartz and Na Ð K extrapolation of the results, it can be geotehrmometers yield prognosis tempe- prognosed for a longer period that: ratures from 90 Ð 120oC. ¥ the maximal permanent water quantity The geothermal system Bansko is still which can be continuously exploited is in a phase of formation and development. 50 l/sec.; Neither the characteristics of the geother- ¥ the maximal water quantity which can mal reservoir (necessary for defining the be temporary used from time to time optimal regime and its use), nor the joining (to 12 hours daily and seasonally) is sites are regularly technically completed 55 l/sec.; for using the heat energy from the ¥ water quantity which can be used for a geothermal distribution system, nor there longer period of time in an open is a team, technically capable and ready borehole is 52 l/sec. in the course of 2 go manage with the problems of manage- years and 45,5 l/sec. in the course of ment, maintenance and development of 19 years. such system. The existing proved great capacity of the geothermal reservoir Ban- CONCLUSIONS sko, allow organization of the usage and there are already joined consumers as According to the type of hydro- well as consumers that are willing to join geothermal system, the Strumica valley this system. belongs to the group of fracture systems In order to allow regular usage and whose reservoir has been composed of development of the system, it is necessary granites. The granites originate from the to define the carrier of the right of the Paleozoic and have been altered and are usage and its development as well as the mostly transited into granite gneiss. Ac- basic elements of the system which should ross the granites which form the valley be operated. tertiary sediments lie, 1200 to 1300 m. The characteristics of the geothermal thick. The reservoir of this system is being reservoir are not known enough yet. There drained through a group of several natural is a danger of its ruining and damage. springs with different temperatures from Enough quantum of necessary information 60 to 73oC and the exploration exploitation for technically regular completing the geo- boreholes B-1 in the Bansko village with a thermal system and regular usage of the

- 247 - geothermal system should be provided. based on the recent exploration, Seminar on new Developments in geothermal LITERATURE energy, Ankara (Turkey), 1995 1. Kotevski Geogri: Geothermal explorations 4. Micevski E. Popovski K : Heat potential of in the Strumica valley 1982-1983, phase. the geothermal field “BANSKO “, Geological Institute Ð Skopje, 1984 Macedonia, Int. Conference on Industrial 2. Micevski Eftim: A Report of the geothermal Uses of Geothermal Energy, Reykjavik , drilling of the boreholes D-2, D-3 and D-4, 1992 located in the regions of Baldovci, Saraj 5. Stolic Novica: A Report of the geophysical and Banica Ð Strumica. Geological Institu- logging of the borehole GTB-2 in Bansko Ð te Ð Skopje, 1984 Strumica. Geological Institute Ð 3. Micevski Eftim: Estimation of the hydro- Skopje, 1986 geo-thermal potential of Strumica valley

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