| Abstract |
The contact zone between a magmatic intrusion and circulating meteoric fluids is of great interest both for understanding the thermal stucture and hydrological controls of high-enthalpy geothermal systems as well as for improving the future prospects of geothermal power production at near-magmatic temperature and pressure conditions. While there have been numerous complex conceptual and numerical models for this zone, they share in common a sharp drop in permeability at temperatures above the brittle-plastic transition temperature, which produces a boundary across which heat is transferred conductively from the intrusion to meteoric fluids. In addition, studies have recognized that non-linear changes in temperature- and pressure-dependent fluid properties play a critical role in optimizing energy transport. We report numerical simulations of the transient evolution of fluid flow and heat transport in high-enthalpy geothermal systems around cooling intrusions, including the deep, ‘supercritical’ roots. We employ the CSMP++ fluid flow and heat transport code, and analyze the temperature, pressure, enthalpy, phase state distribution, as well as the contribution of magmatic fluids. For a relatively shallow magma chamber (~2 km depth) and assuming that the onset of permeability reduction occurs above 550°C (reasonable for basalt), the simulations predict that large fluxes of a single-phase fluid of vapor-like density (superheated steam or supercritical fluid, depending on the external hydrostatic pressure) will be present around the intrusion. These results of fluid phase distribution, temperature and fluid enthalpy above the intrusion are generally consistent with observations from the Iceland Deep Drilling Project, Well 1 (IDDP-1), and indicate that such hydrological models may be useful for informing future geothermal exploration at near-magmatic conditions. |