| Abstract |
The calcite dissolution potential of waste waters at Ohaaki geothermal field was evaluated by calculating their saturation indices using a simple computer program. The study included separated waters, pipeline condensate, and power plant condensate. Laboratory experiments on calcite dissolution kinetics were also conducted. All separated production well waters studied were found to be slightly supersaturated with calcite and therefore not useful for calcite scale removal. Power plant condensate is most suitable for calcite removal having a dissolution potential of 1000 mg calcite/kg fluid. Over a temperature range of 21░C to 100░C, the dissolution of calcite in geothermal wastewater increased the fluid saturation from 50% to 75% in the first minute of reaction. However, it took 90-100 minutes for calcite to reach full equilibrium. Power plant condensate becomes saturated when heated to 175 oC. Thus, high injection flow is needed to effectively dissolve calcite in the well and address near-well scaling. A numerical model is necessary to determine the optimum flow rates and duration of injection for a particular well. |