Istituto di Geoscienze e Georisorse     
Duchi V., Minissale A., Ortino S., Romani L. Geothermal propecting by geochemical methods on natural gas and water discharges in the Vulsini Mts. volcanic district (central Italy). In: Geothermics, vol. 16 (2) pp. 147 - 157. Elsevier, 1987.
The Latera and Torre Alfina geothermal fields were discovered in the Vulsini Mts district (central Italy) in the 70s. The fluid produced by the two geothermal systems is a high pCO2 (around 7 MPa) sodium chloride solution (T.D.S. is 9200 ppm at Latera and 7800 at Torre Alfina), with high SiO2 and H3BO3 contents. The fluid temperature taken at well bottom is about 155C at Torre Alfina, whereas at Latera it ranges from 200 to over 350C. In spite of these temperatures, recorded in producing wells, previous geochemical prospectings using geothermometers in natural thermal manifestations had predicted temperatures no higher than 140C in all the Vulsini district. This contrasting feature between real temperatures and those evaluated during prospecting is caused by the fast circulation of large amounts of meteoric waters in the aquifer located in the shallow parts of the carbonate reservoir formations, and by the short interaction between the latter and the deep geothermal fluids. In the present study a new geochemical survey on thermal and cold springs, stream samples, as well as natural gas emissions has been carried out. A critical review of the main geothermometers, some considerations about the hydraulic behavior of the reservoir formations, and the cross comparison between NH4+/B ratio, pCO2 and SiO2 content in both cold and thermal waters, have led to the conclusion that in the Vulsini Mts there are no shallow anomalous areas apart from those already discovered at Latera and Torre Alfina. The present method could be successfully applied in other geothermal systems, where the potential reservoir is represented by carbonate formations.
URL: http://https://www.journals.elsevier.com/geothermics
Subject volcanic areas:northern Latium
gas:analytical data
waters:analytical data
geochemical thermometers
geochemical prospecting

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