Reservoir Models of the Olkaria Geothermal Project (1975 ñ 1985)

Abstract

Over most of the surface of the earth conductive heat flow from deep in the crust is normal, and on the average this heat flux is 60mW/msq and this maintains an average temperature gradient of 300 C/km. Both this heat flux and the temperature attained at reasonable depths are too low to have any economic value at present. However, in anomalous regions the local heat flux and geothermal gradient may be much higher than these values and there may be surface discharges of hot water and steam. These zones thus provide a source of energy (hot rock) and the transport medium (fluid) through which we may exploit this energy. Surface studies are thus usually made in the "steam seep" zones and exploratory wells are drilled. The potential of any "hot" anomaly, however, has to be evaluated before any development can be initiated and recently there have been efforts to apply the most modern geological and reservoir engineering principles in order to quantify the reservoir parameters, particularly those related to estimates of reserves and future productivity. This paper discusses the relation between geological, geochemical, geophysical prospecting and reservoir assessment during the exploration and development phase of a geothermal prospect. The Olkaria Geothermal Project in Kenya (45MWe) is cited as a case study.