| Abstract |
Production well BLlD is one of the wells supplying steam to the 20 MWe Balas-balas modular power plant of the Southern Negros Geothermal Production Field Central Philippines. BLlD 's discharge pH sharply declined to 3.5 in 1997 to 1998,from its former StabiIizedpHrange of 4 to 5, resulting to the rapid corrosion of its sursace and sub-swface equ@ment. Sulfuric acid (H2SOJ is mainly responsible for the changes in the discharge pH of well BLlD in the perioh 1991 to 1993, and 1997 to 1998. The acid enters the well fiom the shallower, two-phase feed zones (1075-1200 mMD and 1397-1 600 mMD), and mixes with the neutral liquid feed coming from the deeper feed zones (2200 mMD and below). lke chemistry of this acid-S04jluid is inferred to be akin to the Kaipohan waters. The reduction of the liquidfeedfiom the deeper zones, especially dzning 1997 to 1998, because of well blockage, resulted to the shifi of chemistry to the two-phase feed where the acid-SO4 dominates, causing the pH to decline. The mechanical workover conducted in July 1998 succeeded only in opening up partly the permeable zone at 1397 to 1600 mMD, where the feed is still two-phase. The chemistry did not change significantly, because the blockage at 1557 mMD was not cleared to allow the neutral liquid feedporn the bottom to re-contribute. |