A New Conceptual Framework for the Deep Roots of Magma-Driven Geothermal Systems

Abstract

Recent developments in numerical simulation tools provide new insights into natural phenomena occurring in the deep roots of magma-driven geothermal systems, including the formation of supercritical geothermal resources, boiling and condensation processes, and the dynamics of heat transfer from intrusions. This contribution highlights several recent studies which employ the Complex Systems Modeling Platform (CSMP++) to investigate the thermo-hydraulic structure of high-enthalpy geothermal systems. CSMP++ is a C++ code library which uses unstructured meshes to represent complex, geologically realistic model geometries and features a highly modular structure that allows users to write modules for material properties (e.g., permeability as a function of temperature). The use of a control volume finite element method for solving the set of coupled equations governing heat and mass transport by fluid flow combined with a realistic description of fluid properties up to magmatic conditions (i.e., 1000 ºC, 500 MPa, and 0 to 100% NaCl) enables simulation of fluid flow near intrusions. The ability to include a transiently cooling magmatic heat source allows significantly improved methods of resource and sustainability assessment in high-enthalpy geothermal systems, and provides a virtual test bed to explore scenarios for supercritical resource exploitation. As an illustration of the robustness of model results, the simulations reproduce the measured characteristics of the IDDP-1 reservoir if basic geologic characteristics appropriate for the Krafla system are assumed for the model set-up. The dynamics of fluid flow and heat transfer near intrusions are significantly altered if the pore fluid consists of seawater rather than dilute meteoric water, due to the accumulation of dense, hypersaline brines upon boiling above the intrusion and the potential for the clogging of pore space by halite precipitation. However, heat transport by high-enthalpy vapor is maximized in saline systems if the intrusion is deeper than ~4 km, and condensation rather than boiling prevails near the intrusion.