Quartz reactivity in the formation of supercritical hydrothermal systems

Abstract

Supercritical geothermal is garnering increasing interest as an emerging geothermal resource. Its formation is closely associated with shallow magmatic intrusions, which induce intense geochemical reactions under conditions of extremely high pressure and temperature. Quartz is the most abundant mineral in the crust, whose geochemical behavior influences the porosity–permeability evolution and the heat transfer mechanism. Understanding dissolution and precipitation patterns of quartz is critical for targeting favorable reservoirs for supercritical geothermal development. In this study, we improved a widely-used, general-purpose reactive transport modeling program to enable its applicability under supercritical conditions. In our treatment, we developed an equation of state (EoS) module to consider fluid and heat flow, and incorporated empirical laws derived from the literature to account for quartz reactivity in liquid, gaseous, and supercritical phases under both equilibrium and kinetically-controlled conditions. A 2-D model is built based on the IDDP-1 well in Iceland to investigate quartz evolutionary patterns during the formation of a supercritical geothermal reservoir following the emplacement of a magmatic body at upper-crustal depth. Due to the enhanced reactivity under high-temperature conditions, we observed negligible differences between equilibrium and kinetically-controlled scenarios. Our findings indicate that quartz reactivity under supercritical conditions over a long period can be satisfactorily modeled with a computational approach based on equilibrium thermodynamics.