Geothermal Geology of the Outflow Zone of the Ribeira Grande Geothermal System, Sao Miguel Island, Azores

摘要

The Ribeira Grande geothermal system has a 245°C two-phase liquid dominated reservoir whose limits have been only partially defined by deep drilling. The positions of its southern and western boundaries were inferred with reasonable confidence from older wells, but its eastern and northern limits had not been defined previously. In this study, we have investigated geological and geothermal data from recent exploratory wells drilled in the northern part of the field, interpreting these along with surface geological data and geothermal data from nearby wells to improve the local conceptual model of the geothermal system. The results allowed us to delineate the extent of the outflow zone of the high-temperature reservoir, which is restricted laterally to the western side of the scoria cone of Pico das Freiras. This suggests that the Pico das Freiras eruptive fissure may be a volcano-tectonic flow barrier that limits northeastward outflow.