Numerical modeling of the thermo-physical hydrology of volcanic geothermal systems

Numerical modeling of fluid flow and heat transfer plays an important role in elucidating the structure and dynamics of hydrothermal systems. Although past studies have provided important insights into the physical factors governing fluid convection, most numerical models have been limited by temperature restrictions or other simplifications that have limited the applicability of model results to natural geothermal systems. This study applies the fluid flow and heat transport code CSMP++ to simulate the cooling of intrusions and the sub-surface structure and evolution of hydrothermal systems. Early simulations are focused on characterizing the influence of ';primary' factors such as magma chamber depth and geometry as well as system-scale permeability. Later simulations will test the influence of fluid salinity, topography, as well as heterogeneous/anisotropic permeability. Preliminary results show that the depth of the magma chamber plays an important role in system evolution, strongly influencing whether two upflow zones develop on the margins of the chamber or a single upflow zone develops directly over the center. If the roof of the magma chamber is near 2-2.5 km depth, extensive two-phase zones can develop above the magma chambers and are able to transport heat much more rapidly than for single-phase upflow zones. As shown by previous studies, higher host rock permeability results in lower upflow temperatures and thus two-phase zones are more short-lived and confined to shallower depths. However, since the total fluid flux around the magma chamber is much greater, higher permeability causes magma chambers to cool more rapidly and develop more numerous, narrower upflow zones than develop at lower permeability. Although relatively little is known about the geometry of magma bodies acting as heat sources for geothermal systems, results from these simulations show that information obtainable from drilling, such as the locations and temperatures of upflow zones, may be able to constrain the depth and geometry of possible heat sources. Similarly, while permeability is difficult to directly measure in natural reservoirs, simulation results show that upflow zone temperatures are very sensitive to the system-scale permeability. Future simulation efforts will build on these early results in a systematic way in order to quantitatively examine the main governing factors and their physical effects.