Proceedings World Geothermal Congress 2010 Bali, Indonesia, 25-29 April 2010 1 Geochemical Studies about the Well 4175 from Tăşnad - Romania Radu Sebeşan*, Mioara Sebeşan**, Oana Stănăşel** * University of Oradea, Faculty of Electrical Engineering and Information Technology, 1,University Street, 411087, Oradea, Romania ** University of Oradea, Faculty of Sciences, Department of Chemistry, Oradea, Universitatii 1, Romania E-mail address <rsebesan@uoradea.ro> Keywords: well 4175, chemical geothermometers, ternary diagram. ABSTRACT Due to its economical importance, well 4175 from Tăşnad was studied. The chemical composition of geothermal waters from this well was established using standard methods of analysis. Classification of these waters was carried out, taking into account the major anions and cations, using ternary diagrams. The temperature of the geothermal reservoir was assessed and scaling problems were predicted during the well utilization, based on the chemical composition and the use of computer simulation programs. Solid depositions were collected and analyzed and the results were compared to those estimated by the simulation program. 1. INTRODUCTION Well 4175 in Tăşnad is situated in the county Satu –Mare. The geothermal energy from Tăşnad is utilized for heating military units, to heating of greenhouses and to heating of houses. People have been using the geothermal resources from the beginning of civilization for cleaning purposes or as place for agreement. Since the XXth century geothermal energy has been used for heating, for industrial uses and for electricity generation. This paper studies the production well 4175 from Tasnad. This well has artesian production, the wellhead temperature being in the range of 80-85 C. During the utilization of well 4175 solid depositions were noticed, which formed especially from the wellhead to the degasing system. 2. EXPERIMENTAL In order to get the chemical composition, geothermal water was sampled. The measured temperature at collection was 85 C. The methods of analysis are presented as follows: - sodium and potassium were flame photometrically determined at λ=589 nm and 767 nm, respectively; - calcium and magnesium – complexonometric titration; - ferrum – spectrophotometric determination at λ=510 nm, using o-phenantroline; - boron – spectrophotometric determination at λ=420 nm; the method is based on the reaction with azomethine in a buffer solution; - silica – spectrophotometric determination at λ=410 nm; this method is based on the reaction with molibdates at pH=1,2-1,5 when is formed a yellow silica-molibdate complex; - chloride was determined by using the Mohr method; - sulphate concentration was determined by titration with barium perchlorate; thorin was used as indicator; - total carbonate was analysed by titration with HCl solution with metilorange as indicator; - total dissolved solids – gravimetric analysis. Severe scaling was recorded at well 4175, which made necessary to remove the pipe until the degasing system after each winter. Solid deposits were sampled and analyzed. The deposition sample was then structurally analyzed by the use of X-Ray diffraction with KαCu radiation. The thermic and thermo-differential analysis was made by using a derivatograph Q-1500D. The termic conditions were 20 C/ minute until 1000 C. 2.1. Chemical characterization of geothermal waters The chemical composition of the analyzed geothermal water is shown in table 1. These waters present a slight basic pH and a high mineralisation. For an initial classification, in terms of the major anions Cl, SO 4 and HCO 3, a triangular diagram was used. On this diagram (Figure 1) geothermal waters form Tasnad plot near to the chlorine corner in the field of peripheral waters. Table1. Chemical composition of geothermal water, in mg/l Depth [m] 1500- 2000 Anions [mg/l] Cations [mg/l] PH 7,6 Cl - 4875 Na + 4210 Mineraliz. 11280 SO 4 2- 6 K + 38,5 HCO 3 - 1521 Ca 2+ 52,4 Total dissolved solids 13100 PO 4 3- 0,22 Mg 2+ 30,2 O 2 2,90 SiO 2 40 Dissolved gases [mg/1] CO 2 1460 Phe- nols 0,03