SUSTAINABILITY OF A VOLCANIC GEOTHERMAL SYSTEM: THE NEVADOS DE CHILLAN VOLCANIC COMPLEX CASE STUDY

Geothermal energy is a base-load, sustainable, and environmentally friendly energy source. However, excessive geothermal exploitation can result in reservoir depletion mainly for economic reasons or a misunderstanding behavior of the geothermal system. Therefore, it is essential to know the behavior of the geothermal reservoir before starting its exploitation. Numerical models, based on robust conceptual models, serve as a tool to approximate a geothermal reservoir’s behavior in each period. Several attempts are to develop conceptual models of hydrothermal systems, which show the key elements that control a geothermal system and how these components interact. However, an individual characterization is needed because each geothermal case has a different geological context. The Nevados de Chillan Geothermal System (NChGS), hosted in the active Nevados de Chillan Volcanic Complex (NChVC), is used as a case study, an example of a fractured volcanic geothermal system. The performance of NChGS is controlled by the geology of the NChVC, mainly due to the presence of regional lineaments of NE and NW orientation from which fractured zones are inferred at depth so that a high secondary permeability favors the circulation of hydrothermal fluids. Specifically, the theoretical proposal presents how the geothermal potential of the reservoir of the NChGS, which would be at approximately 220-250°C at 1.1 km depth, could be exploited today by quantifying the potential production level. We propose to generate a first attempt 3D model with COMSOL Multiphysics® software using the Subsurface Flow Module, which includes heat transfer and fluid dynamics considerations. The Darcy and heat transfer equations govern the model, generating a hydrothermal (HT) model. NW regional sub-vertical lineaments define the limit of the structural permeability difference in each unit. In addition, the preliminary results show a deviation of the isotherms, which are controlled by the structural geology of the area, specifically by the defined lineaments and the mapped reverse fault.

The Chilean ANID-FONDECYT project #1220729 and CEGA support this work. We also thank Enel Green Power for access to the Nieblas-1 borehole data.