Carbonate calcium scaling is one of the obstacles in utilizing high-temperature geothermal resources in China's Himalaya tectonic zone and it forms due to the higher quotient (Q) of Ca2+ and CO32- than their equilibrium constant (K), which is typically caused by the increase of pH values. Usually, geochemical processes, including boiling, case corrosion, depressurization during upwelling, and gases intrusion, lead to the increase of pH value and boiling always plays a dominant role. In this paper, a systematic method for assessing the scaling tendency, depth and amounts was proposed. First, based on the geochemical processes happened from the reservoir to surface, the geothermal fluid compositions was reconstructed by analyzing the surface samples, and then the tendency of scaling was predicted by calculating the Ryznar index and saturation index. Secondly, the scaling depth was detected by caliper logging or quantitatively assessed by using wellbore simulation and geochemical simulation. There are three ways to assess the total scale amount: the difference of Ca2+ between wellhead and reservoir fluid, equilibrium simulation, and scale thickness in pipes. For a scaling well in the western area of Sichuan basin, the scale amount was up to 151 ~ 300 kg or 1 ~ 3 cm thick within 48 production hours. The carbonate calcium scale formation analysis and quantitative assessment could provide guidance for scale prevention and inhibition.
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