| Title | Calcite Inhibition in Well SPQD Mindanao Geothermal Production Field (MGPF) Philippines |
|---|---|
| Authors | J. B. Nogara, M. N. Ramos-Candelaria, M. B. Esberto, B. C. Buiiing, R. G. Trazona and A. C. Cabel, Jn |
| Year | 2001 |
| Conference | PNOC-EDC Geothermal Conference |
| Keywords | |
| Abstract | A calcite inhibition system consisting of slprface feed pumps and capillary tubing for down-hole injection was installed and operated for more than eleven months in well SP4D. The chemical inhibitor is an acrylate polymer which was continuously injected to attain a minimum dosage concentration of 5 mg/kg in the total discharge. Injection flow rate was maintained at an average of 16 Mr. This give the inhibitor a residence time of about 45 minutes inside the tubing. The injection pressures are between 200 and -240 IbMn2. The presence of a wellbore obstruction at 825 meters limited injection setthg depth to 815 meters. Because of this constraint, SP4D was operated at high wellhead pressure to maintain flash point above the injection setting depth. Well bore simulators were employed to predict the flashpoint depth using available well data. Decline in well head pressure, water flow and calcite saturation index (CSI) from September 1999 to March 2000 is consistent with progressive calcite deposition in the well bore. Drilling logs from subsequent work-over of the well show that majority (-85%) of the obstrucfions occurred below the injection depth where the inhibitor was absent. The lowering of the flash point below the injection depth is shown by presence of obstructions at 816-848 meters. Later analyses show that the basis for wellbore simulations were unstable initial discharge data and actual flash point depth occurs at deeper levels compared with the results of well bore simulations. In addition, calcite scales also developed at much deeper levels (1275-1356, 1372-1384 and 7454-1460 meters) and cannot be related to variations in flashpoint depth. These deep scales were formed from cooler (2 79░C) calcite saturated fluids originating below 1460 meters and later heated by the hotter (230-240░C) fluids discharged from 1300- 1305 meters. |