The Origin of Radon Anomalies Along Geological Structures and Degassing Pathways of the Geothermal System of Acoculco, Puebla (Mexico)
Edgar SANTOYO, Erika ALMIRUDIS, Daniel PEREZ-ZARATE, Mirna GUEVARA, Enrique PORTUGAL, Esther O. GARCIA, Gustavo SANTOS-RAGA
[Institute for Renewable Energy (UNAM), Mexico]
Abstract. The identification and development of blind or hidden geothermal systems (sometimes referred as hot-dry rock systems) are still recognized as geoscientific challenges to be achieved for the geothermal industry. The prospection of blind or hidden geothermal systems involves complex geochemical tasks because there are no available surface thermal manifestations (fluids) to be analysed which make difficult to identify and delineate the dry hot-rock reservoir and the primary heat source. Natural Earth degassing has been a matter of investigation in a large number of geothermal prospection studies. Among these studies, soil-gas radon surveys have been suggested as a suitable geochemical tool for the study of blind or hidden geothermal systems, specially, to detect permeable pathways above potential geothermal resources in areas with no surface thermal manifestations. The opportunity to explore blind or hidden geothermal systems in Mexico appeared with new geochemical studies carried out in the Geothermal System of Acoculco (GSA), Puebla. The GSA has been proposed as a potential hot-dry rock system based on a promissory high-temperature source of approx.300 °C, and an early exploration programme carried out by Comision Federal de Electricidad (CFE) of Mexico. Previous geological and geochemical studies have reported the presence of anomalous areas of active argillic alteration and cold-gas emissions with ambient surface temperatures. The lack of typical thermal manifestations (e.g., hot springs, fumaroles, geysers or boiling mud pots), the low permeability of rock, and the geochemical footprint of cold-gas emissions found in Acoculco have been referred in similarity with geothermal areas known as Kaipohans, which have been proposed to describe the type of anomalous manifestations discovered in this place. Based on the possible existence of a promissory blind or hidden system in Acoculco, measurements of radon in soil-gas and water-gas emissions for nearly three years of geochemical monitoring (2016-2018) were carried out. Spatial and temporal variability surveys of soil-gas radon concentrations were carried out to identify strong radon anomalies which were used to detect possible geological structures (buried faults or fractures) and degassing paths existing in the GSA. The characterization of soil-gas radon emissions, the production sources and the main transport mechanisms were also analysed. Details of a geochemical monitoring programme, including the measurement methodology, and the main results are outlined in this work.
|        Topic: Geochemistry||Paper Number: 14163|