Assessment of Exploitable Geothermal Resources Using Magmatic Heat Transfer Method, Maule Region, Southern Volcanic Zone, Chile

摘要

The Andean volcanic arc includes over 200 active strato-volcanoes and at least 12 giant caldera systems. Nevertheless, there is not a standard procedure for estimating geothermal resources associated with unexplored volcanic systems. The study area corresponds to the main cordillera in the Maule region, Chile, along the Southern Volcanic Zone (SVZ) between 34.8° and 36.5° S. The tectonic style and magma emplacement model of this zone favors the occurrence of volcanic associated geothermal systems, due to the presence of shallow magmatic chambers and Cenozoic thrust faults that generate secondary permeability and allows the development of geothermal systems in the upper crust.In order to identify areas with a high probability of geothermal system development, and using a GIS based superposition method, a geothermal favorability map was created. This favorability map involves using geological, geophysical and geochemical data, which is analyzed in the light of different volcanic related systems around the world.A GIS-based method is presented for estimating the volume of the volcanic edifice of the major volcanic complexes in the zone. This value is then approximated to the volume of magma emplaced under the volcanoes, and used as a certainty parameter in the magmatic transfer method.The method of magmatic heat transfer (Smith and Shaw, 1975; Sanyal et al., 2002) was applied in the main volcanic complexes of the area. This method involves using principles of conductive heat transfer and volcanology to calculate temperature distribution in time and space following magma emplacement, then calculates potentially recoverable geothermal energy resources. The analysis of resources obtained for volcanoes in the area includes a variety of factors, such as age, temperature and depth of magma emplacement, and establishes a semi-logarithmic correlation between the resources and the volume of magma emplaced in the upper crust. Other heat-in-place techniques have been developed for estimating geothermal resource size (e.g., Williams et al., 2008; Garg and Combs, 2010; 2011), but these methods are better suited for explored and identified geothermal systems.The mean calculated resources for the Maule region are ~1,400 MWe. These values are distributed between five main eruptive complexes with individual values that range from 177 to 392 MWe for 30 years.