Characteristics and Important Factors That Influence the Development of Geothermal Systems in the Western Branch of East African Rift System

Abstract

The workshop was funded by ARGeo-UNEP and ICEIDA and organized at the request of countries of the western branch of East African Rift System (EARS) arising from poor results from previous geothermal projects. The main objectives of the workshop were to discuss the geologic setting and conditions that support the development of geothermal systems in the countries of the western branch of East African Rift System (EARS). Further, the workshop was geared to understanding the occurrence, nature and characteristics of the geothermal systems in the western branch and to discuss the appropriate exploration methods. Some of the key findings were that it is likely that medium to high temperature geothermal systems exist at several localities within the western EARS and that majority of the systems can be described by fault controlled model. It is believed that some localities that are associated with volcanoes may have magmatic geothermal systems. It was recommended that exploration of fracture controlled geothermal systems should incorporate drilling of TG wells in the programme. It is further suggested that the classification for the entire EARS geothermal systems (divergent plate boundary) should be modified from that used for convergent plate boundaries as chloride levels are naturally lower in the former due to low values in volcanic gases. It is also demonstrated that K-Mg and chalcedony/quartz geothermometers are the most reliable for most prospects in the western EARS. From B&R experience, it is clear that exploration for fracture controlled systems must be led by detailed geology and structural/fault analyses followed by drilling of temperature gradient wells and where necessary slim holes.