Analysis of downhole data and preliminary production capacity estimate for the Olakaria Domes geothermal field, Kenya

Abstract

As a geothermal resource exploration strategy, the Kenya Electricity Generating Company carried out drilling of three deep wells in the Olkaria Domes geothermal field in 1998 and 1999. The Domes are located just to the southeast of the Olkaria East production field, which has been generating 45 MWe since 1986. The two fields, though physically separated by Ol Njorowa gorge, are within the boundaries of the greater Olkaria caldera. Systematic analysis of down-hole temperature and pressure profiles, injection, fall-off and discharge tests resulted in a conceptual reservoir model for the Domes. A permeable horizontal layer at 210-230°C temperature is identified between 1000 and 1400 m a.s.l. Fluid flow appears to be generally from north to south. Well transmissivities range between 0.4 and 3 H 10-8 m3/Pa s, which equals 1-6 mD permeability, assuming 500 m reservoir thickness. Injectivities range from 1.2 to 6.2 lps/bar. The conceptual reservoir model of the Domes is added to the greater Olkaria conceptual model. A dominating trend observed is that fluid drains naturally southwards and that the Domes area is peripherical to the main geothermal system. An energy reserve of 2-5 MWe is estimated for the Domes. A feasibility study suggests that the field is optimal for re-injection of up to 100 kg/s without substantial cooling of the nearby East production field.