Conceptual Model Based on Preliminary Observation of Ongoing Geothermal Resource Appraisal at the Domes Wellfield, Olkaria, Kenya

Abstract

At least 31 wells have now been drilled in the Domes Sector of the Olkaria geothermal system, Kenya. Their current total steam yield is approximately 1820 tons/hour which is sufficient to produce 260 MWe of electric power. Wellfield appraisal is ongoing and the data used in this paper are limited to preliminary observations. The collective use of geothermometers, measured well discharge enthalpy, subsurface pressure distribution, temperature build-up in wells after completion tests and circulation losses during drilling weighed against spatial distribution of outputs in the geothermal wellfield have led to the development of a conceptual model that tends to separate promising from non-promising areas. As the model demonstrates, well outputs are highest where reservoir pressures and enthalpy are highest and where the producing aquifers are deepest. A low temperature zone runs north-south through the middle of the wellfield. In this zone well discharges have liquid enthalpy but discharge enthalpy increases both to the west and east, while good wells are observed to lie preferentially to the east of the cold zone. The conceptual model suggests that new wells should be drilled within the southeastern part of Domes.