Diffuse surface emanations as indicator of structural permeability in fault-controlled geothermal systems

Diffuse degassing processes provide valuable information on geothermal reservoir characteristics not only in the context of monitoring, but also for exploration purposes. Areas with increased gas emissions can be indicative of major upflow zones from the reservoir through deep-reaching, permeable fault zones. These fault zones may act as preferential target areas for geothermal production drillings. In this study it is successfully demonstrated that diffuse degassing measurements can be used for the detection and characterization of permeable structural elements. The combination of following techniques has been applied at the Brady's geothermal system in the Basin-and-Range Province (Nevada, USA): accumulation chamber method for carbon dioxide and hydrogen sulfide measurements, alpha-spectroscopic measurements of radon and thoron activity concentrations, and gamma-spectroscopic measurements of selected nuclides.