NUMERICAL SIMULATIONS OF HYDROTHERMAL FLOW AND CALDERA DEFORMATION – EFFECTS OF MULTIPHASE AND MULTI-COMPONENT DYNAMICS

There is increasing evidence that some of the measured ground-surface displacements in large calderas are associated with dynamics of gas and aqueous fluids in the shallow hydrothermal system. Numerical simulations coupling hydrothermal flow and mechanical deformation have demonstrated sensitivity to several hydrogeologic parameters, including permeability, injection rate of magmatic volatiles, and rock rigidity. Plausible values of these parameters allow measured ground-surface displacements in calderas to be simulated (Todesco et al., 2004; Hurwitz et al., 2007). Studies done to date have been limited to either single-phase or single-component fluid. Where H₂O-CO₂ fluid flow has been simulated, it has not been coupled with deformation. We are extending previous simulations to quantify the effects of multiphase (liquid-steam) and multi-component (H₂O-CO₂-NaCl) flow on mechanical deformation of large calderas. We carry out numerical simulations of fluid flow and rock deformation in an elastic porous medium with the coupled code TOUGH2-BIOT2 (Hurwitz et al., 2007). Phase distributions within the hydrothermal system are influenced by the water and gas injection rates, the temperature of the injected fluid, and the permeability distribution. Instantaneous permeability changes in the column adjacent to the axis of symmetry may lead to decompression and phase separation at depth. Ascent of buoyant, high-enthalpy steam formed at depth and migrating towards the surface may have a large effect on rock thermal expansion and ground-surface displacements.

Hurwitz, S., et al., J. Geophys. Res ., 112, 2007.

Todesco, M., et al., Geothermics, 33, 531-547, 2004.