OPERATIONAL DYNAMICS IN WELL SP-4D WITH A CALCITE INHIBITION, MINDANAO GEOTHERMAL PRODUCTION FIELD, PHILIPPINES

Abstract

SP-4D is a production well in the Mindanao Geothermal Production Field (MGPF), Philippines, which develops calcite deposition under flowing conditions. An inhibition system was installed in the well to prevent active deposition after a second mechanical work-over. Prior to running-in the downhole injection assembly, an obstruction was encountered at 830 meters measured depth (mMD) which limited setting depth to 815 mMD. Wellbore simulation studies indicated that if the well were operated at full-open conditions, the flash point depth (FPD) would below 940 mMD, below the calcite inhibitor injection point. With this expectation, the well's operation was maintained at throttled conditions with a wellhead pressure greater than 12.7 kg/cm2g in order to raise the FPD above 815 mMD. The flow dynamics with time were modeled using water flow data from tracer dilution measurements. The results indicated that the injection depth was initially at the boiling transition. The well's output was observed to have deteriorated after about more than eleven months of utilization despite the continuous anti-scalant injection. This decline necessitated the pullout of the downhole injection set-up and capillary tubing which, surprisingly, was free of any calcite deposits.