Numerical Modeling for Resource Management at Ribeira Grande, Sao Miguel, Azores, Portugal

Abstract

numerical simulation model of the Ribeira Grande geothermal reservoir, São Miguel Island, Azores, has been developed to support the ongoing development and management of the resource for generating electric power. This model has been calibrated using data obtained since startup, including the results of new deep wells drilled during 2005, operations of the Ribeira Grande and Pico Vermelho power plants, logging, testing and sampling of the various wells, and the results of a tracer test conducted during 2007-2008. The numerical model of the reservoir has been calibrated first by matching the initial subsurface temperature distribution interpreted from temperature-profile measurements in the deep wells. With iterations back to the initial state, the model was then calibrated to the historical production/injection data and to the new tracer data. Following calibration, the model was used to forecast field performance under various operating conditions. The results of forecasts indicate that significant cooling of the Pico Vermelho production sector could occur if the present injection configuration is maintained, with or without a planned increase in the level of power generation. Fluid injected into the existing injection wells returns quickly to the production wells, causing a relatively high rate of cooling. This high rate of cooling can be reduced significantly if injection is relocated to the northeastern part of the field, and based on the results of the model forecasts, a plan for drilling alternative injection sites during 2009 was put into place, in zones that are more distant from the production area than the existing injection wells.