| Title | Use of Hydrothermal Mineralogy and Geological Structures in Identifying Drill Sites in Olkaria Domes Geothermal Field, Naivasha, Kenya |
|---|---|
| Authors | David WANJOHI |
| Year | 2016 |
| Conference | Stanford Geothermal Workshop |
| Keywords | Olkaria, structures, faults, hydrothermal alteration, secondary permeability |
| Abstract | Although most of the conventional geothermal systems in many parts of the world have been successfully exploited for electrical production and district heating, exploration and development of new systems is commonly limited or restricted by the risk of unsuccessful drilling. A major problem in selecting drill sites is that existing geothermal systems are generally poorly characterized in terms of favorable settings and structural-stratigraphic controls. Olkaria Domes field is one of the geo-sectors of Olkaria Volcanic Complex where geothermal activity is intense. Tectonically, four major fault systems namely; NW-SE, N-S, NE-SW and NNE-SSW are recognized from the study area. N-S and NNE-SSW are the youngest faults associated with later tectonic activities. NE-SW faults are related to the caldera formation whereas NW-SE faults are known to be the oldest faults of the system. Surface manifestations from geothermal resources are scarce due to a thick pyroclastic cover in this field. Hydrothermal alteration minerals are closely related to the interpreted intersection of faults with these areas having high temperatures, secondary permeability and the most extensive hydrothermal mineral development. Secondary permeability and the degree of hydrothermal alteration decreases towards the ring structure of the Olkaria domes field. The main geothermal reservoir appears to be located where there are fault intersections, with the highly fractured and hydrothermally altered trachytic rocks serving as the main conduits for vertical fluid flow and advective heat transport from deeper magmatic sources. Thus, correlation of hydrothermal alteration and faults signify that fluid flow in this geothermal system is structurally controlled and these two parameters are used in identifying drill sites in this geothermal field. |