ADVANCES IN THE STODY OP SOLIDS DEPOSITION IN GEOTHERMAL SYSTEMS

' ' / Abstract - The International Workshop on Deposition of Solids in Geothermal systems was held in August 1988. Papers were presented on field and laboratory studies of scale deposition from geothermal fluids and in geothermal reservoirs. Scale types investigated included carbonate minerals, amorphous silicates, and mixed metal oxides and sulfides. Scale formation was reported to occur in geothermal systems under a wide range of enthalpy and chemical conditions. The predominant factors found to control the solubility of scale-forming minerals include changes in temperature and pH with lesser control being exerted by the concentrations of other ionic species and by kinetic effects. The range of conditions under which scale mineral formation occurs has resulted in the deposition of these minerals throughout the geothermal utilization system including production wells, surface equipment, and wastewater reinjection wells. Chemical and engineering methods applied to the treatment of scale-forming minerals during extraction of geothermal heat included the addition of chemical inhibitors, control of fluid pressures and temperatures, and mechanical and chemical removal of deposited scale minerals. The work reported at the conference indicated that the success of these methods was somewhat limited, and additional work was recommended on more effective methods of chemical inhibition of scale mineral deposition.