IN SEARCH OF GEOTHERMAL ENERGY IN KENYA: THE ROLE OF GEOPHYSICS

Various least-cost studies have identified geothermal as a least cost source of energy for Kenya. Initial regional exploration for geothermal resources in the country indicated that the Quaternary volcanic complexes of the Kenya rift valley provided the most promising prospects for geothermal exploration. Consequently, detailed exploration for geothermal power has been concentrated around volcanic centres within the rift valley. The geothermal potential of the area is associated with these magma chambers that constitute the heat sources. Gravity, MT, seismic and magnetic data show that the heat sources are shallow beneath the volcanic centres. In the 1950’s interest for geothermal energy was focused on Olkaria where two exploration wells, X-1 and X-2, were drilled in 1956. These wells were sited on the basis of surface steam discharges. Both wells could not sustain discharge due to low enthalpy fluids and low wellhead pressures. The United Nations Development Programme in collaboration with the Kenya Government conducted an exploration programme in 1970 that covered several prospects in the Rift Valley including Olkaria and Eburru. The geophysical methods employed in these studies were gravity, ground magnetics and resistivity. Scientific results from Olkaria were more encouraging and the infrastructure suitable for further exploration available. In 1981 a 45 MWe power plant was put up at Olkaria, the first of its kind in Africa. As the exploration techniques were further refined the success rate increased and, in time, drilling had discovered more steam than was required to run the plant. However by the late 1980’s, the supply of steam to the power plant had seriously declined. It was recommended that additional make-up wells be drilled to ensure sufficient steam for maximum power generation and allow some wells to be removed from the system for maintenance or monitoring. Geophysics, along with other disciplines, was called once again to recommend the location of the makeup wells. The station is now about 20 years old and has generally performed very well with the availability and load factor of about 97% and 92%, respectively. These geophysical techniques have enabled the discovery of further resources at Olkaria West, Olkaria Domes and Eburru as confirmed by exploration drilling.