A Review of Mechanical Work-Overs in Bacman and Mindanao Geothermal Fields, Philippines

Abstract

Mechanical work-over operations are an integral part of well rehabilitation to sustain steam supply to geothermal power plants. In the Bacman Geothermal Production Field (BGPF), mechanical work-overs have been conducted in ten out of fourteen production wells (70%), and four out of seven reinjection wells (60%). On the other hand, in the Mindanao Geothermal Production Field (MGPF), six production wells have been mechanically rehabilitated out of the total nineteen production wells (30%). In Bacman and Mindanao, the three major reasons for conducting mechanical work-overs include: casing or liner damage, mineral scale deposition, and cement-plugging of cold or acid feed zones. Preliminary assessment of the results of mechanical work-over jobs indicate that the success of the operation varies depending on the reason for well rehabilitation. Mechanical work-overs are effective in repairing wells with damaged casings, especially if the casings were relined. Simple milling operations are not so successful in restoring original well output. For wells that need to cement-plug cold or acid feed zones, mechanical work-over operations result to an expected decrease in well output because the plugged feed zones no longer contribute to total well discharge. Mechanical work-over operations yield variable results in wells with mineral scale blockages such as calcite and silica; though most were not able to restore original well capacity. Even in cases where an increase in well output occurred right after the work-over, recurrence of mineral scaling warranted additional mechanical work-overs or acidizing operations.