Reservoir evaluation and modelling of the Eburru geothermal system, Kenya

Abstract

Production capacity of the Eburru geothermal system is assessed in this study using both volumetric method and numerical modelling. A conceptual reservoir model is first proposed based on previous geoscientific research and downhole logging data. The Eburru geothermal system covers an area ranging from 1-6 km2 and appears to be confined within the caldera region only. One upflow is exhibited with recharge into the geothermal system occurring from all directions. Volumetric method applied together with Monte Carlo calculations indicates that the reservoir can sustain 7-11 MWe by 90% probability for a period of between 30-50 years. Results of a numerical model simulation are also presented with forward modeling applied in parameter estimation. The results are achieved through a single run calibration process where the system is driven to a steady-state then automatically proceeded to production phase. The model is calibrated using 15 kg/s of fluid with 1260 kJ/kg injected into a layer above the inactive bedrock, simulating hot inflow into the system. The natural state model matches observed physical conditions reasonably well but production history match is overestimated. Predictions from the model show that Eburru geothermal field can support 5 MWe for a period of 10 years even without reinjection. However, to double the current production, the model predicts that at least two more production wells have to be added.