Expected Silica Scaling from Reinjection Waters After Installation of a Binary Cycle Power Station at Berlin Geothermal Field, El Salvador, Central America

Abstract

A new binary cycle unit to generate electrical energy from the steam-separated waters of Berlin Geothermal Field is under construction. Silica scaling has been a common problem in the reinjection wells of this geothermal field. The waters will be reinjected at a new temperature of 140°C compared with a temperature of 175°C in the present operations. The pH will be lowered to 5.75 units from 6.5. In this way, the precipitation of silica within the plant and piping system will be avoided. However, precipitation should occur within the reservoir, probably increasing the clogging of the pores and decreasing even furthers the absorption capacity of the wells. In this paper, we present modeling results of the process of mixing between the reservoir waters and the new reinjection waters, under different scenarios of reinjected vs. reservoir water. The results of these simulations show that even when the change in temperature of the reinjection brine will be around 35 ºC, the amount of quartz precipitated during the future reinjection in Berlin Geothermal Field will not be too different from the mass of quartz that is precipitating with the present reinjection temperature. A maximum difference of 15% in the percent of clogged pores is expected. However, for a damaged zone of 10 m, the simulations show that after 10 years a great proportion of the well will be clogged in all the scenarios modeled and that probably the well will not be very useful (43 to 50% decrease in porosity). The same mass of silica per year as in the present operations will be reinjected. Then, the difference in precipitated quartz mass will come from the lower solubility of quartz at lower temperature in the reservoir water, which will be produced by colder reinjected water.