Temperature model and tracer test analysis for the Ribeira Grande geothermal system, São Miguel Island, Azores

Abstract

On São Miguel Island (Azores - Portugal) EDA Renováveis, S.A., exploits the resources of the Ribeira Grande geothermal field, a 240ºC liquid-dominated reservoir, and operates two binary ORC (organic Rankine cycle) geothermal power plants, Ribeira Grande and Pico Vermelho, with a combined capacity of 23 MWe. At present, the production from the geothermal resource represents 43% of the total power production of the island and 22% of the archipelago of the Azores. In 2008, a numerical model of the Ribeira Grande geothermal reservoir was recalibrated using up-to-date temperature, pressure, production and tracer test data. Forecasts of reservoir performance under several injection configurations were made, providing important information on how power production may be maximized, while minimizing the potential cooling impact caused by the return of injected water. Based on these forecasts, EDA Renováveis, S.A., decided to relocate the injection area in the Pico Vermelho sector, by drilling new injection wells farther from the production area.

The present work was developed under the scope of the final project for the Geothermal Training Programme of the United Nations University, in Iceland. An updated model of the temperature and pressure distribution in the Pico Vermelho sector of the Ribeira Grande geothermal field was developed based on warm-up temperature and pressure data from new wells PV9, PV10, PV11 and RG5, suggesting some continuity of the reservoir to the northeast, as previously indicated by AMT/MT surveys. A simulation and interpretation of the tracer test data conducted in the same sector of the field in 2007-2008, using the programs of the software package ICEBOX, is also part of this final project. The results show an overall strong hydraulic connection between the injection and production wells in this sector of the geothermal field.