Initial conditions of wells OW 905A, OW 907A, OW 913A and OW 916A, and a simple natural state model of Olkaria Domes geothermal field

Abstract

Olkaria geothermal field has been in exploitation since 1982. The capacity has risen from the initial 15 MWe turbine installed by KenGen to the present combined total of 202 MWe. The rising fuel prices and rising demand of electricity has motivated KenGen to embark on rapid expansion of geothermal electricity generation. Olkaria Domes field received attention with extensive surface exploration ending in 1997 which resulted in the drilling of three deep exploration wells between 1998 and 1999. Production wells have since been drilled in the Domes field with excess steam to support a 140 MWe power plant. In this report, well test data are systematically analysed to obtain information characterizing the reservoir hosting the resource. Also, a brief description is given on surface exploration carried out in the area. Results are unified to a conceptual model of the geothermal system. An upflow zone of more than 300°C is assumed to be in the eastern and south eastern parts of the Domes field, bound within the caldera. The reservoir is two-phase and the upflow temperature and pressure profiles follow the boiling point curves in the wells. Effective permeability of the reservoir ranges from 2.3 to 3.4 mD. The conceptual reservoir model was simulated in a 3 dimensional grid using TOUGH2 simulator, and compared with measured physical data. The volumetric reservoir estimate shows that the field can support more than 210 MWe for a period of 50 years with 90% confidence.