Tiwi Geothermal Field: Reservoir Management After 40 Years of Commercial Operation

Abstract

The Tiwi Geothermal Field in Albay, Philippines is operated by Philippine Geothermal Production Company Inc. (PGPC). It began commercial operations in 1979 (Menzies et al, 2010a), initially with shallow production well drilling concentrated in the Naglagbong sector in the eastern part of the current production area. After a steep drop in productivity of the first wells due to the impact of entry of meteoric recharge into the reservoir, three other geographic sectors were developed for production starting in the late 1980s. These were the Kapipihan sector in the center and south, Matalibong sector in the northwest, and the Bariis sector in the southwest. Up until the mid-1990s, steam availability was maintained through drilling of new production wells across these new production sectors to support the 330 MW installed capacity of the power plants. Through the years, multiple challenges were managed through various technical and operational initiatives and from these experiences, improvements in the understanding of the reservoir contributed to the development of the current reservoir management strategy in order to increase and maintain steam supply. To recover steam production, drilling deep into the postulated upflow zones in the Bariis and South Kapipihan sectors aims to harness the deep liquid production zones, while casing deep isolates the well from the intrusion of acidic fluids found near the top of the liquid-dominated reservoir in some sectors. For existing wells, executing timely and appropriate well work options improves steam availability. On brine disposal, hot brine systems have proven much more reliable compared with cold brine systems and by utilizing idle wells, injection capacity shortfalls have been averted. At the same time, managing injection loads at different injection sectors should ensure adequate mass recharge with minimal thermal breakthrough, resulting to continued steam generation for years to come.