Success of Geothermal Wells Drilled in Olkaria Domes Sector (Greater Olkaria Geothermal Area, Kenya)

Abstract

Geothermal energy is a low carbon, reliable, and renewable energy that has been in use for over 100 years. At Olkaria electric energy from geothermal resources has been harnessed for slightly over three decades. Despite its relatively low cost compared to other energy sources it is associated with high exploration risks and upfront costs. This prevents its wider adoption. In a typical geothermal development drilling costs comprise of between 35-40 % of the total capital costs. Developing and financing of geothermal projects need a clear understanding of the risks inherent in the project. In the Olkaria Domes Sector of the Greater Olkaria Geothermal Area we have more than 60 wells drilled to date. These wells provide a large data base from which the probability of drilling a successful well are assessed. The wells range in output from 1.5 MWe in well OW-901 (drilled as an exploration well) to ~ 30 MWe in well OW-921 A (a production well). Factors that may influence drilling success such as completion date, power capacity (MWe), depth to which the wells are drilled, feed zones, casing depth, deviated or vertical well, geological controls, permeability, enthalpy etc are assessed. Findings from this paper are aimed at determining the success in drilling at each stage from exploration, appraisal, to production drilling. Conclusions from this study would aid in increasing an understanding of selecting sites for drilling, reduce the risk of drilling a dry well, review the depth to which wells are drilled with regard to reservoir conditions, reduce the costs of drilling and negotiate better drilling contracts.