APPLICATION OF GEOPHYSICAL METHODS TO GEOTHERMAL ENERGY EXPLORATION IN KENYA

For earth scientists, a wide range of geophysical, geo-chemical and geological surveying methods exist for geothermal energy investigations. For each of these methodologies, there is a typical physical/chemical property to which the technique is sensitive to. For geophysics, location of a geothermal reservoir may be determined by use of seismic velocity, electrical conductivity, magnetic or/and gravity methods. Effects of exploitation of a geothermal reservoir can be monitored using micro-seismic, micro-gravity, geo-chemical and temperature/pressure techniques. Though these may require complex methodology and relatively advanced mathematical treatment in interpretation, much information may be derived from simple qualitative assessment of the survey or monitoring data. Often many of these methods are used in combination to obtain a plausible inference. At the interpretation stage, ambiguity arising from the results of one survey may often be removed by consideration of results from a second survey method. This article provides a general introduction to the most important methods of geophysical exploration that have been employed at Olkaria Geothermal field, Kenya. The occurrence of surface manifestations in the country’s rift valley regions encouraged various people to carry out various geophysical investigations to establish the subsurface structure with a view of establishing its geothermal potential. Various levels of success have been achieved with each of the techniques. The activities resulted in the construction and commissioning of Africa’s first geothermal power plant at Olkaria with 45 MW capacity between 1981-1985. Changes in technology saw the deployment of modern geophysical techniques that included transient electromagnetics (TEM) and magnetotellurics (MT) which made it possible for shallow and deep conductors to be accurately imaged and thus more accurate geothermal models developed.