THE IMPACT OF STRUCTURAL CONTROL ON THE POTENTIAL OF OL-KARIA GEOTHERMAL FIELD
Printer-friendly version

ABSTRACT

The study was conducted in Olkaria area which is a high-temperature geothermal system located within the central sector of the Kenya Rift Valley. The presence of the graben structure in the Olkaria region influences steam production in the geothermal area. The major hydrogeological structures of the Olkaria system include Olkaria fracture, Olkaria fault, Suswa fault, Gorge farm fault and Ololbutot fault. Most of the faults are located in the Olkaria east zones.

Although geothermal energy has been successively exploited for electric energy in this area it still remains a major challenge when it comes to setting up new wells which is usually hampered by unsuccessful drilling. This is usually encountered due to poor selection of drill sites. Also there is need for higher production due to the high demand of power in the country. These can be achieved by considering structures in siting of wells. This is so since the intersection zone of faults generates an area of highly fractured rock forming a weak field through which magmatic material find their way to shallow sub-surface which in turn heats water to generate steam. The geothermal fluid up-flow zones occur at the intersection of these regional zones in the vicinity of heat source. Faults being the major structures in this area allow for deep circulation hydrothermal water where it‟s heated and return to shallow crustal levels. Faults provide the pathways for geothermal fluids and steam within the crust and therefore control efficient transfer of heat from deep to shallow crustal levels where the steam can be exploited. Re-injection and enlarging the area of a fracture can lead in high production. However structures may have a negative effect as they act as conduits for cold water flow from the Rift-valley scarps. Despite the significance of faults in controlling geothermal system, very little is done to ensure the most favorable structural setting is used for setting a geothermal well.

In this study Landsat ETM+ image, TEM resistivity method, Gravity method and comparison of data in upflow and downflow zones have been used. Landsat image is used to verify major faults that can be seen on the surface using satellite image. These structural zones are seen inform of lineament or drainage in the area following a certain order. TEM method was used to locate high temperature areas and how they are generally affected by structural control. Temperature data in different wells can be used to show how structural control affects geothermal production in terms of upflow and downflow zones.

From the analysis it‟s clear that structures can affect geothermal production in a negative or positive way thus influencing the potential in the Olkaria area. In downflow zone the temperature are lower than upflow zones. This is due to cooling of the geothermal well by meteoric water hence low production. It‟s also clear that the geothermal resource is majorly controlled by NW to SE structures which can be seen from both Landsat ETM+ image and the resistivity-structural image. Other structures controlling the resource in the area are the NE- SW faults seen from resistivity-structural map. Therefore structures affect the potential in geothermal field with high production area being located in upflow zones caused by structures and can also cause low production due to in flow of meteoric water through faults. More studies need to be done to determine which faults; segments of faults or structural settings are most conducive for geothermal activity. Knowledge of such structures would facilitate siting of productive wells in known, but as yet undeveloped fields, expansion in producing fields, identification of possible blind geothermal resources and sustainability of a well by using the downflow zones as reinjection wells.