Abstract:
The Olkaria Domes Geothermal field is situated in the south of Lake Naivasha, in southern sector of the Kenya
Rift system, approximately 127 km northwest of Nairobi in Kenya. Geothermal reservoir evaluation involves
various kinds of tests, data interpretation and modelling. In this paper, heat-up temperature profiles tests during
well recovery for fourteen wells and the first occurrence of high temperature alteration minerals such as Illites
and Quartz data from five wells were analysed for the purpose of obtaining temperature distribution,
permeability structures, feed zone locations as well as the up-flow and down-flow zones. From the temperature
distribution results, two main heat sources were inferred; one to the Northwest and the second to the Eastern
side of the field. The two heat sources are separated by a SW-NE oriented fault that is believed to control the
fluid flow. The natural recharge to the reservoir comes from the SW direction. The reservoir had two major feed
zones at depths of (900-1300) masl and (250-0) masl. The Illites and Quartz contour distribution indicate the
minerals first appear shallower on the Eastern region as compared to the Western region of the field hence
elevated temperatures to the eastern side. This indicates that the heat source on the Eastern side is closer to the
surface compared to the west side and therefore SW-NE oriented fault could be as a result of differential
upward movement of the two magma chambers with more upthrow to the east as compared to the west. It is
recommended that more production wells be drilled in the eastern region of the geothermal field.
