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Understanding The Underlying Mechanism of Mineral Scaling In The Salihli Geothermal Area, Western Turkey
High temperature fluids (>180 C) are being extracted, directed to binary ORC power plants and reinjected back into the reservoir in the Salihli (Manisa) Geothermal Field, located in the western part of Turkey. Mineral scaling and corrosion behavior of the geothermal fluids treated with scale inhibitor chemicals are constantly being monitored, based on several methods: (1) major ion and total silica analysis, (2) measurements of physicochemical parameters in the field, (3) regularly checking of deposition/corrosion coupons installed on the flowlines. Mineral scaling is observed on the capillary tubing used for injecting scale inhibitors below the flash point, starting from a certain depth below the surface (0-200m), in the production wells. If hard scales are formed and the scale thickness reaches up to 2-3mm, pulling the tubing from the well and wrapping it on a drum becomes problematic. Several types of minerals precipitate in production wells and clog the filters mounted on the brine pipelines. Therefore, filters are periodically cleaned. In addition to precipitated materials, clastic materials which are transported from reservoir to the surface are also observed inside the tubes and on the walls of the heat exchangers. The main purpose of the study is to understand the characteristics of the scale formation formed under the operating conditions of the power plant. In this context, the mineralogical and geochemical investigations were carried on the scale deposits and classified as: (1) directly precipitated minerals from the fluids, (2) transported minerals that previously precipitated in the deeper parts of the wellbore, (3) detrital/clastic particles belong to the geological units located in vicinity of the production wells. Almost all of the samples collected from filters and tubings mainly consist of Mg-smectite (80-100%). The sampled materials from the heat exchangers contain small particles (< 2mm) of elemental iron and iron oxide (magnetite), marbles as well as smectite clays. The obtained data indicate that the most significant triggers for scale deposition are: (1) oversaturation of certain mineral phases (SI>5 for Mg-smectite) due to flashing and adiabatic cooling in the well, (2) removal of the steam phase from the geothermal fluid and the consequent drastic change in physico-chemical parameters of the fluid after it passes through separator, (3) alteration of the flow regime due to filter structure and the change in diameter along flowline. By this, the performances of various scale inhibitors are tested for optimum antiscalant treatment of the geothermal fluid. As a conclusion, the routine chemical analysis of geothermal fluid and mineralogical analysis of the scales could be used for evaluating inhibitor efficiency.