Status of Geothermal Energy Exploration at Buranga Prospect, Uganda

Abstract

The recent studies in Buranga incorporated geological, geochemical, hydrogeological and geophysical methods to elucidate subsurface temperatures and the spatial extent of the geothermal system. The results indicate that the geothermal activity at Buranga appears to be a fault-controlled deep circulation system rather than a magmatically heated system associated with volcanoes. The geothermal surface manifestations include hot bubbling springs, water pools, gas vents (H2S and CO2 gas), travertine tufas, hydrothermally altered rocks and geothermal grass. Buranga has the most impressive hot springs in the Western Branch of the East African Rift System with the highest surface temperature of 98.7˚C. The main geological structure is the Bwamba escarpment that forms the western part of the Rwenzori horst mountain massif. This main rift fault is cut by numerous perpendicular and oblique striking faults which together with other faults/fractures contribute to the re-charge and up-flow permeability for the geothermal fluids at Buranga. Subsurface temperatures of 120 - 150˚C have been predicted by geothermometry. The hot springs show isotopic composition compatible with the local meteoric water line, confirming the meteoric origin of the water circulating in the geothermal system. Results from isotopes of hydrogen and oxygen (δDH2O, δ18OH2O) suggest that the recharge is from high ground in the Rwenzori Mountains. Micro-seismic surveys located a subsurface anomaly within the vicinity of the thermal activity at Buranga. the results and conceptual models from the recent TEM and MT surveys indicate a low resistivity anomaly underlain by a high resistivity at a shallow depth. This suggests a shallow sediment hosted outflow in addition to the fault-controlled outflow. The clayey sedimentary formations provide the cap rock of the geothermal system. Eight temperature gradient wells have been sited in the prospect to test the conceptual models and discover a geothermal reservoir. The results will be used to update the conceptual models that will be a basis for locating deep exploration wells.