Exploitation of Olkaria geothermal field started in 1981 when Olkaria I (East) reservoir began producing steam for the 45 MWe Olkaria I power plant. During the twenty eight years of production, the reservoir has performed quite well with minimal drawdown in the range of 20 bars in the deep water dominated reservoir. Some decline in production occurred in the first ten years of exploitation due to depletion of the steam zone but after connection of make-up wells in 1996, there has been no more decline experienced. Only eight make-up wells have been drilled and total steam available has been in excess since connection of the make-up wells. Deepening of well OW-5 from 901 m to 2200 m showed an untapped deeper reservoir. There has been no significant change in overall chemistry but wells located at the center of the field have experienced more boiling. Olkaria I reservoir seems to have reached steady state under the current production rate and no cooler incursion has occurred. In summary, after the twenty eight years of production, no significant negative change has occurred. Due to this good performance, numerical simulation was done to establish how much more additional power could be generated from Olkaria I and based on the results of the study, additional 140 MWe project is now underway.

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