Numerical modeling of the Nevados de Chillán fractured geothermal reservoir

• Published in: Geothermics 2025-01, Vol.125, p.103181, Article 103181
• Main Authors: Oyarzo-Céspedes, Isa, Arancibia, Gloria, Browning, John, Crempien, Jorge G.F., Morata, Diego, Mura, Valentina, López-Contreras, Camila, Maza, Santiago
• Format: Article
• Language: English
• Subjects: COMSOL multiphysics; Fractured reservoir; Secondary permeability; Thermo-hydraulic coupling
• ISSN: 0375-6505
• DOI: 10.1016/j.geothermics.2024.103181

•The Nevados de Chillan geothermal system is composed of a highly fractured granodioritic reservoir, a clay cap formed by altered volcanic rocks and a system of low-angle surface faults.•Permeability is the parameter that mainly controls the behavior of the isotherms in the model, which is directly related to the heat transport mechanism. For permeabilities lower than 10–16 m2 heat tends to be transferred conductively, whereas at permeabilities higher than 10–14 m2 heat tends to be transferred in a convective regime.•The model suggests the presence of a geothermal reservoir in the zone of convective behavior of the isotherms, where granodioritic rocks are highly fractured.•Surface heat flux peaks value of 0.74 W/m2 are found in the case study. The highly fractured areas associated with damage zones around faults within the clay cap which act as pathways for the ascent of geothermal fluids.•The basal heat flux (without faults presence) of the regional área is capable of detecting geothermal anomalies indicative of a reservoir at depth. Numerical models can be utilized to understand and anticipate the future behavior of a geothermal reservoir, and hence aid in the development of efficient reservoir engineering strategies. However, as each system has a unique geological context, individual characterization is required. In this research, the Nevados de Chillán Geothermal System (NChGS) in the Southern Volcanic Zone of the Andes is considered. The NChGS is controlled by the geology of the active Nevados de Chillán Volcanic Complex (NChVC) including their basement units (Miocene lavas and volcaniclastic layers from Cura-Mallín Formation and the Miocene, Santa Gertrudis granitoids) as well as the key structural control from crustal scale faults, all of which combine to influence the reservoir characteristics. The presence of faults acts to generate a high secondary permeability which favors the circulation of hydrothermal fluids. Based on previous studies in the NChGS, we designed a thermo-hydraulic model in COMSOL Multiphysics® combining equations of heat transfer and Darcy's law in order to determine the distribution of isotherms and surface heat flux. The boundary conditions of the model were informed by a conceptual model of depth 3 km and width of 6.6 km which considers a highly fractured granitic reservoir, a clay cap behavior of Miocene lavas and volcaniclastic units, and transitional zones between a regional zone and the reservoir. A low-angle reverse fau