A conceptual reservoir model and production capacity estimate for the Tendaho geothermal field, Ethiopia

Abstract

In this report the 6 wells drilled in the Tendaho geothermal field are briefly described. Formation temperatures and initial pressures for each well are estimated and a conceptual reservoir model presented. The Tendaho reservoir is divided into a shallow sedimentary reservoir of 220-250°C temperature and a deep one in volcanic basalts, ranging from 220-270°C in temperature. Inflow comes from depth in the east and flows diagonally to the surface, causing reversed temperatures in the present wellfield. Production data analysis indicate permeability-thickness in the range of 3-10 Dm in the shallow reservoir. A wellbore simulator study shows that the present wells maintain high flowrates despite either a 5 bars reservoir drawdown or a 20°C reservoir cooling. Both volumetric reservoir assessment and TOUGH2 reservoir model indicate that the present wellfield can sustain 70 kg/s production rate for 20 years. Installing a small 1-2 MWe back pressure pilot plant seems therefore feasible as an intermediate goal in the research activities. This, however, requires up to 1 year flow testing in order to define the nature of the outer reservoir boundaries. As more production and subsurface data becomes available, this very pessimistic production capacity estimate should be reconsidered.