Geochemical Mapping of Sulfur Within Olkaria Geothermal Field, Kenya

Abstract

This research paper focuses on the geochemical mapping of Sulfur to characterize the Olkaria geothermal field, a field associated with geothermal power generation in the northeast of Nairobi. The current geochemical methods used are CO2 and N2 however, a discrepancy associated with the biogenic sources of CO2 renders it less reliable. Sulfur in geothermal systems is magmatic, hence its utilization can help solve these discrepancies. The study utilized sulfur present in the geothermal well waters to identify the main features of a magmatic hydrothermal system, their distribution within the Olkaria volcanic complex and how they relate with the Olkaria structures. Secondary data of the concentrations of H2S and SO4 2- was used for mapping using ArcMap tool within ArcGIS. The distribution of the magmatic H2S facilitated the mapping of the possible up-flow zones and the heat sources within the study area. SO4 2- was used to map possible recharge zones within the study area. The mappings, that is, the up-flow zones, the heat source and the recharge zones are important, because they increase knowledge on where exactly to drill production wells, make up wells and the reinjection wells. Geochemical mapping performed on other fluid chemical species such as CO2, Cl- , N2, as well as the temperature, facilitated the correlation with the sulfur concentration variations. The distribution of various concentrations of sulfur as well as the correlation parameters were shown by different color scales on the geochemical maps. From the maps, the field-scale distributions, enabled the visualization of which faults establish the fluid ascension areas and which are more closely related to recharge zones. The findings indicate that up-flow zones were affiliated to the NW-SE trending faults as well as the Olkaria Fault while the recharge zones were associated with the Gorge farm fault, the ring structure and the Ololbutot fault. Geochemical mapping of Sulfur proved to be an effective method in the characterization of a geothermal field. Its utilization to complement conventional methods, improves precision for well siting. It should therefore, not be ignored during exploration campaign.