Forty Years of Power Generation at the Ribeira Grande Geothermal Field, Azores

Abstract

In the Azores, geothermal power generation has four decades of accumulated experience in the Ribeira Grande field, where the combined production from the Ribeira Grande and Pico Vermelho plants (23 MWnet) has been providing up to 44% of the electricity needs of São Miguel Island. This paper describes the field development, management practices and reservoir response to the production load. The main resource challenges have been related to mineral deposition inside production wells and to the risk of cooling the high-temperature production zones due to reinjection. Proper monitoring, along with geochemistry, tracer testing, and reservoir engineering studies were essential to successfully address these challenges, ensuring the sustainable exploitation of the resource. Likewise, experience and appropriate well intervention techniques allowed to optimize the performance of production and reinjection wells. With a history of 40 years, the geothermal exploitation has not caused any significant impact in the reservoir pressure or temperature. Recent numerical modeling forecasts indicate that the Ribeira Grande reservoir can support an expansion of 5 to 10 MW without the risk of over-exploiting the geothermal resource.