Application of Calcite Precipitation Rate in Predicting the Utilization Period of Calciting Wells in the Mindanao Geothermal Field, Philippines

Abstract

The empirically determined precipitation rate law (Shiraki and Brantley, 1995) was applied to calculate the utilization period of calciting wells where pipe geometry and varying boiling temperatures were considered. The results using the empirical precipitation rate law method showed extended utilization periods for saturation ratio (Q/K) less than or equal to 1.72, while shorter periods were calculated for saturation ratio above 1.72 as compared to direct deposition of excess calcite method. The applicability of the calcite precipitation rate law method in predicting the utilization period of calciting wells depends on the determination of the actual flash point temperature and calibration of the empirical equation to the field observations. The empirical equation was derived at laboratory conditions using reactor tanks with stirring at 100oC and modified (extrapolated) to include higher temperatures (Andre et al., 2006). The laboratory test set-up is perceived to be an approximation but does not mimic the complex flow regime observed in geothermal wells. Information on the utilization period of a calciting well derived from the modified rate law method will help in refining steam availability evaluation of the geothermal field as well as devise appropriate work over schedule.