Exploration Status of the Kibiro Geothermal Prospect, Western Uganda
Peter MAWEJJE, Nicholas H. HINZ, William CUMMING, Edward ISABIRYE, Isa LUGAYIZI, and James F. NATUKUNDA
[Dept. of Geological Survey and Mines, Uganda, Uganda]
Kibiro geothermal field is located in western Uganda in the administrative district of Hoima along shores of Lake Albert. The regional structure along which the field is located is the North Toro – Bunyoro fault (NTBF) of the Western branch of the East African rift system which is an extensional terrain. The field has three main hot springs; Mukabiga, Muntere and Mwibanda with measured surface temperature of 37 – 86.7˚C, maximum observed flow rate estimated at 4 litres per second discharging brines mainly sodium chloride with an average total dissolved solids of 4500 mg per kilogram. The interplay of the NTBF together with other step (synthetic) faults and intersections, resulted into formation of the Kibiro sub-graben that is characterised by a highly fractured zone with a series of stepovers. From recent structural studies, it has been observed that the mid synthetic fault of the Kibiro sub-graben has an upper hand in terms of surface manifestations within the sub-graben. The interplay of different fault systems caused a down throw of the sub-graben in the NE –SW manner. It has been noticed that the Northeast part of the sub-graben is more down thrown that the Southwestern end. Recently, six (6) TGH were sited, Alexander et al (2016) based on transient electromagnetic surveys (TEM) from which a shallow secondary reservoir has been suggested at 300 metres depth within Kibiro delta. Recent structural analysis tried to map all possible fault systems within the survey area together with their angles of Dip. This will allow for TGH to be strategically positioned in order to, 1) try to hit the NBTF at optimum depth (from angle of dip), 2) try to ascertain the secondary predicted shallow reservoir from TEM surveys and 3) establish the most probable fault intersection zone of the NTBF based on dips and orientation of fault systems within Kibiro. This will give the first category of reservoir in highly damaged zones of the basement, (the second one being the predicted shallow 300m depth reservoir thought to be hosted within gravels, sands and conglomerates). Many of the measured faults are of the order N 40 - 48˚E strike and 45 - 46˚ dip but the NTBF has a measured dip of 650 Alexander et al (2016) and Hinz et al (2018). Detailed mapping and temperature measurement of the spring reveal that Muntere and Mwibanda springs are probably located on another linear structure buried within the sediments. Structural mapping data sets will avail strain data, fault slip history which will be integrated with temperature gradient data, heat flow data, spring temperature, fluid geothermometry and Geophysical data to refine the conceptual model of Kibiro. From recent mapping, soil temperatures above 45˚C have been measured 1Km away from the main hot spring and it has been noticed the damaged area coupled with surface manifestations that Kibiro is a wider reservoir than previously thought. Therefore the number of targeted temperature gradient holes have been changed from six to eight to cover all the low resistivity TEM anomaly and to include the now much wider fault step over area.
|        Topic: Exploration||Paper Number: 11052|