| Title | Geothermal Exploration in the Kenya Rift: A Case Study of Silali Geothermal Prospect |
|---|---|
| Authors | Ngenoh, Daniel; Ochieng, Leakey |
| Year | 2011 |
| Conference | Geothermal Resources Council Transactions |
| Keywords | Hyrothermal; hydrogeological; magnetotellurics; intrusives; geothermometry; fumarole |
| Abstract | Silali geothermal prospect is characterized by a large caldera volcano, situated on the floor of the northern Kenya rift. Previous studies of the volcano and the surrounding area indicated occurrence of a hydrothermal system, signifying probable occurrence of a high temperature geothermal resource and recommended the prospect for further detailed investigations to determine its resource potential. The prospect covers an area of more than 900 km2.This paper discusses the methods employed during the field survey in pursuit of geothermal exploration which included geological mapping of the area to model the evolution of the volcano. Hydrogeological regimes and structural set up surveys were also undertaken to relate their association with the development of geothermal systems. Geophysical techniques employed during the exploration included, transient electromagnetic (TEM) and magnetotellurics (MT).. Gas and steam condensate samples were collected from fumaroles to determine the nature of the geothermal reservoir while ground radon and CO2 surveys were undertaken to indicate the presence of geothermal reservoirs and to map permeable zones. A high temperature geothermal system exists under Silali prospect. It is postulated that the geothermal reservoir is at temperatures of more than 280°C as inferred from gas geothermometry. Heat loss survey was carried out over the area to determine the nature and size of the heat source. Integrated results of the surveys indicate existence of a geothermal resource under Silali caldera which extends to the eastern flanks of the volcano. The heat source is associated with shallow magmatic intrusives beneath the caldera and to the eastern flanks. Estimated gas geothermometry temperatures range from 238- 287ºC. The high resource area covers an area of about 81km2; however, the resource area could be larger because the anomaly boundary to the east has not been defined. Using the average conversion rate of 15 MWe/km2, this translates to a potential of over 1200 MWe. It is therefore recommended that four (4) deep exploration wells be drilled; two (2) within the caldera floor and two (2) outside the caldera, to further confirm the nature and potential of the resource at Silali. |