Reservoir assessment and wellbore simulations for the Olkaria Domes geothermal field, Kenya

Abstract

The Greater Olkaria geothermal area is divided into seven sectors. Currently, three of the sectors are generating 90 MW of electricity and an additional 32 MWe will be commissioned by the end of 2003. Olkaria Domes field is the fourth sector to be considered for development. Three exploration wells were drilled in this field in 1998 and 1999 (OW-901, OW-902 and OW-903) and plans for drilling of 6 appraisal wells are at an advanced stage. Wells OW-902 and OW-903 discharge at wellhead pressures less than 5 bar-a for all lip pressure pipe sizes but well OW-901 can discharge at 5 bar through 4 and 5" lip pipes. A conceptual model shows that the Domes field has an upflow zone near Well OW-903 with a deep boiling resource. Wells in the Olkaria Domes field need to be cased deeper than the wells in the other sectors in order to seal off a cooler feedzone at 1000 m a.s.l. Higher output from each well can be obtained by drilling larger diameter wells and by cleaning up the wells after drilling to reduce the skin coefficient. Reserve estimates show that the areal extent of the Domes field is about 8 km2 and can support 40 MWe for about 25 years with 60% probability.