| Abstract |
Production of fluids from high-temperature (>200 °C) geothermal reservoirs by deep drilling has provided extensive information on the origin and chemistry of these fluids, the associated hydrothermal alteration and various hydrological characteristics of such systems. Geothermal geochemistry is used to identify the origin of geothermal fluids and to quantify the processes that govern their compositions and the associated chemical and mineralogical transformations of the rocks with which the fluids interact. Six (6) geothermal wells from the Menengai Geothermal Field in Kenya have been used in this study to infer the reservoir fluids with respect to species composition. Steam fraction, is estimated to range from 0.1 ? 0.5 of the total well discharge, with the fluids feeding the aquifer having a near neutral pH. Correlation of aqueous silica species with increasing temperature gives a linear pattern indicative of silica as a temperature indicator. Fluid gas concentrations show an increase with increasing aquifer temperature with the one phase wells having the highest aquifer concentration of CO2, H2S and H2. The CO2 concentrations show a systematic correlation with respect to selected aquifer temperature, indicating that activity of dissolved CO2 in the deep fluid is controlled by local equilibrium between geothermal solution and secondary minerals but this correlation can be disturbed by excessive CO2 input due to magmatic intrusions in the roots of the geothermal system. |