Buletinul Ştiinţific al Universităţii “Politehnica” din Timisoara, ROMÂNIA Seria CHIMIE ŞI INGINERIA MEDIULUI Chem. Bull. "POLITEHNICA" Univ. (Timişoara) Volume 53(67), 1-2, 2008 222 Characterization and Geochemical Constraints on Formation Conditions in a Low-Temperature Geothermal Field O. Stănăşel * , A. Cărăban * , G. Gavriş * , G. Badea ** , M. Sebeşan * * Department of Chemistry, University of Oradea, Faculty of Sciences, 410087 Oradea, Romania Phone: (0259) 408 737, Fax: (0259) 432 789, E-Mail: ostanasel@uoradea.ro ** Department of Engineering and Energetic Management, University of Oradea, Faculty of Energetics, 410087 Oradea, Romania E-Mail: gbadea@uoradea.ro Abstract: A low temperature geothermal field is located in the north western part of the country. Scaling encountered in exploitation equipments yield to a decrease in the production efficiency, being a major problem at geothermal water utilization. The objectives of this work are to chemically characterize scales formed as a result of mixing of waters from different aquifers, to define the geochemical constraints and the formation mechanisms of the scales and to model those with the aid of geochemical speciation and reaction path programs. Scales, formed in surface pipelines have been characterized by chemical analysis, X-ray diffraction and thermo-differential analysis. With the aid of computer program for geochemical aqueous speciation, the geochemical constraints of the formation of scales were modeled. The experimental results obtained by analysing on scales were compared to those obtained by the use of simulation program. In order to minimize scaling, tests in static conditions have been conducted. Keywords: geothermal field utilization, scales, simulation program 1. Introduction The aim of this study was to appreciate the need for chemical monitoring and predict possible scaling during production in a Romanian geothermal field. The field chosen for this study is the Bors reservoir. It is situated in the Western Plain of Romania, about 6 km northwest of the town of Oradea. Bors is a closed aquifer with a small surface area of 12 km 2 . It is located in fractured Triassic limestones and dolomites. The production wells from Bors were used to provide base load and for the heating of 6 hectares of greenhouses. 2. Materials and methods The analytical methods used for geothermal water analysis [1] are noted in Table 1. The analytical procedures for depositions analysis are briefly described in Table 2 TABLE 1. Analytical methods used for the constituents determined from water Constituent Method Brief description pH Electrometric A glass electrode in combination with a reference electrode is inserted into the sample and pH and temperature values recorded. CO 2 Electrometric titration After the pH sample was adjusted to 8.2 it was titrated with HCl to pH=3.8. Na, K Flamephotometry λ=589 nm, respectively 767 nm. Ca, Mg Titration By using EDTA at pH=12-13 for calcium in presence of murexid as indicator and at pH=10 for Ca 2+ +Mg 2+ in presence of eriochrom, magnesium resulting by difference. Fe Spectrophotometry It was used the method with o-phenantroline, the absorption was read at 510 nm. B Spectrophotometry Azomethine H/ ascorbic reagent added, absorption was read at 420 nm. SiO 2 Spectrophotometry At pH=1-1.5 a silico-molibdate complex is formed, absorption was read at 410 nm. Cl Titration Mohr method, by using K 2 CrO 4 as indicator. SO 4 Titration The sample was titrated with Ba(ClO 4 ) 2 by using thorin as indicator. TDS Gravimetric Sample was evaporated and dried at 105°C The solid samples were also structural analysed: - thermogravimetric by the use of a Derivatograph Q-1500D; the sample was grounded very fine and it was heated up to 1000°C with a heating rate of 10° / minute; - by X-Ray diffraction; the diffraction patterns have been registered with a PHILIPS PW 1400 X-ray spectrometer with K α Cu radiations.