Interpretation of Radon Concentration in the Serrazzano Zone of the Larderello Geothermal Field

Abstract

Wellhead concentrations of radon were made at 22 wells in the southwest region of the Larderello geothermal fields by two analytical methods, a field measurement as reported by D'Amore and laboratory measurement as reported by Semprini and Kruger. Agreement between the two methods was satisfactory. The radon concentrations were correlated with average specific volume of superheated steam for each well estimated from available thermodynamic parameters of the reservoir. The correlation was improved by adjusting the specific volume of steam by a mass steam saturation value calculated at the boiling front from chemical fluid composition for each well by a method developed by D'Amore and Celati. A compressible flow model for radon transport developed by Sakakura et al. was also tested. .I The results confirm that radon behavior in geothermal systems is characterized by thermodynamic conditions in the reservoir. In the Serrazzano zone, abnormally high values of radon concentration with respect to estimated specific volume in four of the 22 wells were observed an area of proposed low permeability. The high values may also result from higher emanating power or lower porosity in this zone. A cross-section normal to the zone of low permeability between the two basins shows a similar radon profile as noted in a Geysers production zone. I