| Abstract |
The Mindanao Geothermal Production Field (MGPF) has been producing since the last quarter of 1996. Steam is supplied from ten wells in the Marbel sector. An average of 1390 TPH is extracted from production wells and an average 1040 of TPH of separated brine is injected into four re-injection wells at the Matingao-Kullay sector. Cold condensate, cooling tower blowdown and brine overflow from M2GP sumps varying from 70 to 145 TPH are also injected into another reinjection well in the same area. lncreased mineralization in the discharge fluids was detected in selected production wells in th8 first quarter of 1998 roughly one year affer continuous operation. Wthin this period injection returns faom Matingao became more apparent and have affected production wells in Marbel namely, AP03D, APO 1 D and SK2D. Reinjection fluids further intruded into the production sector affecting SP4D and SK4B. However, no significant thermal degradation has been observed implying sufficient heating and slow rate of reinjection return. The second power plant at Mt. Apo began commercial operation in June 1999, and is supplied by steam from production wells at the Sandawa-Tambaan sector. These wells produce an average of 650 TPH of two-phase fluids, and separated brine averaging 225 TPH is accommodated into an in-field reinjection well. Additional steam for M2GP is tapped from the Mandarangan sector producing an average of 122 TPH coupled with an average 900 TPH from reworking of M1 GP separated brine. Localized boiling and steam condensation are evident in Tambaan-Sanda wa sector. Vapor recharge is the effect of degassing higher temperature fluids. The process is contemporaneous with the present stable geochemical trends of the injection-affected wells in Marbel indicating recovery from injection returns. Exploitation of the Sandawa-Tambaan sector induces vapor and liquid recharge and inflow of the advancing injection front from Marbel. |