Characteristics and formation mechanism of the Olkaria geothermal system, Kenya revealed by well temperature data

Abstract

The Olkaria geothermal system located on the Red Sea - Gulf of Aden - East African Rift high-temperature geothermal belt is a typical rift-volcanic geothermal system. The formation of this system is closely related with lithospheric extension, magmatic intrusion, and hydrothermal activities within the rift. In order to achieve a better understanding of the characteristics and mechanisms within the system, this study analyzes and categorizes the temperature logs from different areas in Olkaria. The impact of the heat sources and heat transfer processes, the permeable structures and flow patterns, as well as the upflow and recharge zones are identified and discussed based on temperature logs. The heat flow state of the Olkaria system is similar to the neighboring Menengai volcano, which could be a compound result of mantle thermal anomaly, magmatic activity, and hydrothermal circulation. The impacts of heat sources are more pronounced in the Olkaria Domes and Olkaria West; while in the Olkaria East and Northeast the hydrothermal redistribution of heat plays a dominant role. The recharge flows are identified along the Suswa fault, the Gorge Farm fault, the Olkaria Fracture, and possibly the southeast periphery of the Domes. Major upflows are found near the center of each producing area. The nature of feed zones within the boreholes and the flow patterns within the geothermal system are discussed. Based on the analysis and comprehensive studies, the characteristics and formation mechanism of the geothermal system are summarized, and an updated conceptual model is proposed. This study can be used as an analog for the exploration and development of high temperature geothermal system in equivalent settings.