Geochemical Assessment of Korosi-Chepchuk Geothermal Prospect, Kenya Rift Valley

Abstract

Geochemical investigation of the Korosi-Chepchuk geothermal prospect was carried out to evaluate its geothermal potential. The occurrence of a geothermal system in the Korosi-Chepchuk prospect is manifested in the form of fumaroles, altered grounds and relatively high temperature water boreholes. Fluid samples from seven fumaroles and nine water boreholes were taken for reservoir characterization and hydrological assessment of the geothermal system. Gas results gave estimated reservoir temperatures in excess of 240°C as deduced from chemical geothermometry. Near surface soil gas survey for determinations of CO2 and radon (222Rn) concentrations in the soil air was also carried out to infer areas with enhanced subsurface permeability within the prospect area. About 200 soil gas sampling points were measured. Elevated percentages of CO2 in the soil gas and high radon (222Rn) concentrations were measured in the central, north and north west of Korosi; and north-eastern part of Chepchuk suggesting a high geothermal potential in these areas resulting from enhanced subsurface permeability. It is further observed that transport of the soil gases is majorly convective and controlled by structures as evidenced by the CO2 and radon gas flux anomalies. The findings also indicate the existence of separate hydrothermal systems in Korosi and Chepchuk with somewhat higher subsurface temperatures estimated for the Chepchuk hydrothermal system based on gas chemistry.