Assessment of scaling formation in steam pipeline of production well KMJ-67 in Kamojang geothermal field, West Java, Indonesia

Abstract

Kamojang, the first Indonesian operating geothermal field, has been producing electricity since 1983. The total installed capacity is 140 MWe and 1100 tons/h steam are produced from 33 production wells. Condensate is injected into five injection wells. Although only apparently dry steam is produced from the wells, scaling has been observed in the pipeline from one of the production wells. The scale builds up on the pipe walls, especially near the tee connection of steam transmission line, about 18-22 m from the wellhead. The scales were discovered during an annual maintenance shut down. X-ray diffraction and Scanning Electron Microscopy, including backscatter imaging and energy dispersive spectroscopy, demonstrate that the scale consists of well crystallized quartz with minor impurities. Scale morphology indicates that they formed by precipitation from aqueous solution. Observed temperature-pressure conditions in the surface pipeline were used to evaluate the water fraction in the steam. The resulting water fraction was equal to 0.43%. Observed static pressure as a function of depth in the well are inconsistent with the presence of dry steam only but are in good agreement with a water fraction of about 0.5% in the steam. Mass balance calculations based on observed amounts of scales, estimated silica concentration in the water fraction and steam flow-rate indicate that the water fraction is equal to only 0.05%. The apparent discrepancy between these methods indicates that either the concentration of silica in the water fraction is much lower than assumed in mass balance calculations or that only 10% of the available silica is deposited in the pipeline. If the latter is true, 90% of the dissolved silica in the water fraction is carried through the steam pipeline, as dust....