| Abstract |
The Makiling-Banahaw (Mak-Ban, also known as Bulalo) geothermal field was the second geothermal resource (after the Tiwi Field) developed by Chevron Geothermal Philippine Holdings, Inc. (CGPHI) under a service contract executed in 1971 with the National Power Corporation. The deep discovery well, Bul-1, was drilled in 1974. Commercial production began in 1979 with the operation of the first two 55MWe generating units. Capacity was increased to 220MWe in 1980 and then to 330MWe in 1984, with the six 55MWe units installed in three power plants. Six binary bottoming-cycle plants totaling 15.73MWe were installed in early 1994 followed by two 20MWe steam turbine units in 1995 and a further two 20MWe units in 1996, bringing installed capacity to 425.73MWe. In 2004-05, four units were rehabilitated bringing the current fieldwide installed capacity to 458.53MWe. However, the present plan is to base-load Mak-Ban at 402MWe with 40MWe on stand-by, plus the binary plants. To date, 113 wells have been drilled to measured depths ranging from 655m to 3,625m to support the production and injection capacity requirements. A total of 69 production wells presently provide steam to eight separation stations, while 23 injection wells provide the injection capacity for separated brine and power plant condensate re-injection. Generation in recent years has been affected by steam supply limitations, power plant availability and the introduction of a competitive wholesale electricity spot market (WESM) resulting in decreased generation and operational concerns when the units were used as load following rather than base load plants, but this situation has improved in 2008. Mak-Ban is a remarkable example of a stable, relatively problem-free geothermal reservoir, based on its performance during these 30 years. During the first few years, reservoir pressures drew down rapidly resulting in the expansion of the two-phase zone with increased discharge enthalpy and steam flash as the main effect on production. More recently, however, the reservoir has been affected by marginal recharge, injectate and meteoric water. The main effect of these fluids is seen in a decrease in average steam flash which was greater than 50% up to 2001 and is about 43% in 2008. Technical and operational measures have been taken to mitigate the effects of these various fluids on the resource and on generation. In the last 30 years, the Mak-Ban field operation has generated a total of 61,827 GWh of electricity saving the government from importing 114.67 million barrels of oil equivalent (MBOE). This high level of generation has been supported by an area of only ~7 km2, for a production density level of about ~57MWe/km2, with only modest declines. This is a very high density when compared to geothermal fields worldwide. The recent drilling program has accessed hotter, high pressure reserves deeper into the reservoir and the results are very encouraging. CGPHI therefore looks forward to many years of continued operation of this excellent geothermal resource. |