The Tiwi geothermal resource development was initiated by the completion of the discovery well Naglagbong-1 in 1972. Power generation began at Tiwi in 1979 with an initial 55-megawatt (MW) power plant expanding to an installed capacity of approximately 330 MW in 1982. Initially the largest liquid-dominated geothermal resource in the world, production-induced pressure drawdown produced resulted in a large steam zone. The Tiwi geothermal reservoir has multiple upflows, outflows, and compartments (e.g., Naglagbong, Matalibong, Kapipihan, and Bariis sectors). Resource supply declined as a result of exploitation due to reservoir pressure decline, meteoric and injection water breakthrough, and changes in enthalpy, non-condensable gas, and fluid corrosivity. The decline was differential across sectors. As part of the Unocal team, Dr. Dan Hoyer led the effort to rehabilitate the power plants in 2004 and 2005, and the capacity was derated to 234 MW. Aboitiz has owned and operated the Tiwi Geothermal Power plants since 2009 as APRI. Philippine Geothermal Production Company operates the steam fields and provides geothermal resources to the Tiwi power plants. Data from the Tiwi production and injection wellfields may provide critical insight into the potential resource of the project, depending on whether a subsurface connection exists or if the geologic setting is similar enough that the Tiwi geothermal reservoir can be an analogy for the project.
5. Startup and Operations