corrosive species and scaling in wells at olkaria ... - Orkustofnun

2. GEOLOGICAL FEATURES OF THE STUDY AREAS
2.1 The Greater Olkaria Geothermal System
The Olkaria geothermal
system is located south of
Lake Naivasha on the floor of
the southern segment of the
Kenya rift which is part of the
East African Rift Valley. The
East African rift runs from
the Afar triple junction at the
Gulf of Eden in the north to
Beira in Mozambique in the
south. It is a segment of the
eastern arm of the rift that
extends from Lake Turkana
in the north to Lake Natron in
northern Tanzania to the
south. The rift system that
falls within Kenya and the
location of Olkaria is shown
in Figure 1.
The Olkaria geothermal
system is about 120 km
northwest of Nairobi, the
Kenyan capital. Initial
exploration work in Olkaria
began in the 1950’s and the
first exploration wells were
drilled around 1956. They did
not successfully discharge.
FIGURE 1: A map of the Kenya Rift showing the major
geothermal prospects and the Olkaria geothermal field
Systematic exploration was again began in 1970 under the initiative of the United Nations
Development Programme (UNDP) and the Government of Kenya and drilling recommenced in 1973
after extensive surface work, by the drilling of Olkaria well OW-01. The well proved to have low
temperatures. A second well, well OW-02 was drilled and this proved to be more successful. More
drilling was undertaken and in 1976 a prefeasibility study to utilize geothermal steam for electricity
generation was done by SWECO and VIRKIR consulting companies. The first unit of 15 MWe was
constructed in 1981, the second in 1982 and the third in 1985. After the intial five years of steam
production in Olkaria, steam decline was experienced in the steamfield. Make up wells were drilled
based on reservoir simulation studies by (Bodvarsson and Preuss, 1987) to increase steam production.
The resource is hosted within the Olkaria volcanic complex which consists of a series of lava domes
and ashes, the youngest of which has been dated at ~ 200 years (Clarke et al., 1990). This complex is
estimated to be 50-80 km 2 . Maximum temperatures in deep wells at Olkaria range between ~ 200°C
and ~340°C. The area has been divided into seven sectors for purposes of development (Figure 2).
The sectors are named Olkaria East, Olkaria North East, Olkaria North West, Olkaria South West,
Olkaria South East, Olkaria Central and Olkaria Domes. Four power plants are currently in operation
in the Greater Olkaria Geothermal Area with a total generating capacity of ~ 129 MWe. Two plants
are operated by KenGen, i.e. the Olkaria I and Olkaria II plants that generate ~ 115 MWe. The
Olkaria I plant has a capacity of 45 MWe and receives its steam supply from the Olkaria East
Production Field. The Olkaria II plant, which is about 3 years old, receives steam from the Olkaria
North East Field. Two independent power producers generate about 14 megawatts of electricity from
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