Þeistareykir Geothermal Field: Control of Scaling in Steam Gathering System and Reinjection Line

Abstract

Some of the production wells in Þeistareykir geothermal field discharge high enthalpy fluid. The water-phase has low mineral content except for dissolved silica which is very high. During initial testing of the wells, scale formed in the test lines and clogged the flow measuring devices. This scale formed above the saturation temperature for amorphous silica. The scale was found to be amorphous aluminum-silicate. Extensive tests were performed in order to optimize the design and operation of the steam gathering system for the new plant. The tests showed that by operating the wells at high wellhead pressure and keeping the pressure high in the flow meter the scaling was controlled and the operation and flow measurement of the well secured. Precipitation still occurred though in the steam gathering lines which are operated at 9.5 bar (abs) pressure. During initial startup of the plant, dust particles from the dry wells entered the steam line. By mixing fluid from low-enthalpy and high-enthalpy wells before entering the separator plant the particles were successfully washed from the steam and clean steam obtained. Tests were also performed which proved that the separator water could be safely reinjected after diluting it by condensate from the powerplant. No scaling has been observed in the reinjection lines after two years of operation.