| Title | Direct uses as environmental mitigation measure in Ribeira Grande Geothermal Field (S. Miguel, Azores Islands, Portugal) |
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| Authors | Martins Carvalho, J; Nunes, J C; do Rosário Carvalho, M |
| Year | 2016 |
| Conference | European Geothermal Congress |
| Keywords | Ribeira Grande, geothermal field, direct uses, Azores islands |
| Abstract | Within the 2009/2010 drilling campaign on the NE part of the Ribeira Grande Geothermal Field, in São Miguel island, a geothermal well (RG4) intercepted a shallow thermal aquifer at about 230-250 meters depth, causing high levels of superficial steaming activity and geologic and environmental problems in the nearby areas, including houses located at Caldeiras da Ribeira Grande, at a distance of about 250 m away, were a traditional fumarolic field and an old thermal bath building exists since 1811. The well was sealed and abandoned. Afterwards, a new fumarolic field and strong CO2 diffuse discharge developed in an NW-SE trending area, initially about 200,000 m2 around well RG4. Aiming the mitigation of its effects, a monitoring and intervention program was established, that included wells for temperature monitoring, spatial distribution of the diffuse CO2 emissions and soil temperature, isothermal imaging with a thermal camera, monitoring of water composition and gas of fumaroles and soil emissions and reflection seismic studies, among others. Overall interpretation of the investigations revealed that hot water and steam originating from a depth of about 240 m was entering a shallow trachyte lava flow through fracturing channels mostly controlled by local tectonics. Thermal groundwater and steam are inferred to circulate mainly through the upper part of the trachyte lava flow, which develops about 10-30 m below surface covered by tuffs and pyroclastic pumice fall deposits. Chemical and isotopic signature of the new degassing area indicates close similarity with the fumaroles ever known in Caldeiras da Ribeira Grande site. Among the several mitigation and remediation measures accomplished in the area, it was decided to implement non invasive mitigation measures and to develop approaches to promote the new fumarolic field as a thermal resource, does trying to convert a problem into an opportunity. Among those measures was the creation of leisure and recreational structures for direct uses of geothermal fluids, including traditional “geothermal cooking” spots, most appreciated by the local population. |