Corbetti Geothermal Reservoir, Ethiopia: Pre-Drilling Structural and Heat Source Models for Resource Estimates

The Corbetti geothermal system is in an early exploration stage. The production of a conceptual model will aid this progression, consolidating further understanding and probing new avenues in investigation. This study has integrated a range of datasets, obtained from Corbetti Geothermal and available literature, to produce conceptual models and power capacity estimates of the reservoir, accounting for uncertainty in the data. The Corbetti caldera is located within the central Main Ethiopian Rift, which is part of the much larger East African Rift System. Localised surface fault expressions are combined with regional surface fault data to identify regional, buried faults passing through caldera. Geomechanical modelling is undertaken to infer the dilation tendency of such faults and assess which may have the potential to compartmentalise the reservoir. Remote sensing geochemical data are used in conjunction with surface fault data to demonstrate the surface expression of the reservoir. Microseismicity and resistivity data are then combined to constrain fault geometries at depth and to infer magma/mush zones. The results show an EW elongated reservoir zone present beneath Urji and Chabi, an EW elongated magma body and a series of orthogonal faults. The certainty of a reservoir present beneath Chabi is reduced without ground-truthed geochemical data. A final reservoir model displaying the two planned wells is produced. Three further well trajectories are suggested to achieve maximum fault interaction. Temperatures ranging from 259-359°C, alongside surface area estimations between 23-88km2, are combined with previously estimated parameters to assess the resource capacity. A thermal power range of 564-3070 MW is estimated for the total reservoir, while 236-988 MW is calculated for Urji, both of which sit comfortably above the early 150 MW development plans, ensuring a low risk of no heat reserve.