Tiwi Geothermal Field, Philippines: 30 years of Commercial Operation
Anthony J. Menzies, Larry B. Villaseńor and Eugene G. Sunio
Chevron Geothermal
Philippines Holdings, Inc, 14th Floor 6750 Building, Ayala Avenue, Makati City, Philippines
Abstract
The Service
Contract for the exploration and development of the Tiwi geothermal resource
was executed in 1971 between Chevron Geothermal Philippines Holdings, Inc
(CGPHI) and the National Power Corporation of the Philippines. The deep
discovery well, Naglagbong-1, was completed in June 1972 and demonstrated the
commercial viability of the resource. By May 1979, 45 wells had been drilled
and the first 55MWe turbine-generator unit had started commercial operation.
This was followed by a second 55MWe unit in August 1979 and by April 1982 the
installed capacity had reached 330MWe, with six 55MWe turbines located in three
power plants. This was a very aggressive development schedule but was
considered necessary due to the Philippines’ heavy dependence on imported oil
and the oil price shocks of the 1970’s. In 2004-05, four of the units were
rehabilitated and the base installed capacity was re-rated to 234MWe, with the
retirement of Unit 4 in 2000 and the designation of Unit 3 as a stand-by unit
in 2005.
Since the start of
commercial operation, gross generation at Tiwi has averaged 157MWe and
40.6TWe-hrs of electricity has been provided to the Luzon grid, saving the Philippines from importing 80.6 million barrels of oil (or equivalent fuel). This level of
generation is in line with early assessments of Tiwi’s long-term production
capacity. Generation in recent years has been affected by steam supply
limitations, power plant availability and the introduction of a competitive
wholesale electricity market (WESM) which initially resulted in the units being
used more as “load following” rather than “base load” plants, although this
situation did improve in 2008.
Management of the
Tiwi resource over the past 30 years has been a challenge, with specific
sectors of the field being affected at various times by: massive meteoric water
influx; injection breakthrough; steep reservoir pressure declines; high
non-condensible gas concentrations; significant enthalpy changes; and
production of corrosive fluids (both sulfuric and hydrochloric acids). These
difficulties have been overcome or managed by instituting a number of technical
and operational changes. In 2008 the decline in steam supply was minimal,
suggesting that the present capacity of ≈190MWe equivalent (based on
design consumption of 2.25 kg/s steam per MWe) is reasonably sustainable, based
on the existing reservoir production/injection strategy. Two new production
wells were drilled in late 2008 and early indications are that these wells will
assist in maintaining production at the present overall capacity and may also
suggest the existence of additional reserves that could increase or extend the
capacity in future years, if considered economically viable. CGPHI looks
forward to many more years of continued operation of this high-quality but
challenging geothermal resource.
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