HR: 09:00h
AN: H51B-05    [PDF]
TI: Dissolution of Limestone Fractures from Cooling Thermal Waters
AU: * Andre, B J
EM: andreb@colorado.edu
AF: University of Colorado at Boulder Civil, Environmental and Architectural Engineering, Campus Box 428, ECOT 441, Boulder, CO 80309-0428 United States
AU: Rajaram, H
EM: hari@colorado.edu
AF: University of Colorado at Boulder Civil, Environmental and Architectural Engineering, Campus Box 428, ECOT 441, Boulder, CO 80309-0428 United States
AB: Most previous studies of dissolution growth in karst fractures have focused on meteoric systems. Calcite has a retrograde solubility with respect to temperature, therefore different behavior would be expected in hydrothermal systems. As deep geothermal waters rise through karst formations, they cool and maintain their dissolutional aggressiveness. We have developed several models to investigate the growth of calcite fractures in an effort to understand hypogene cave development. Our models include three-way coupling between flow, heat and mass transfer. We will present results of this work in one and two dimensional variable-aperture fractures and contrast meteoric and geothermal cases. Growth of meteoric systems is commonly measured in terms of the breakthrough time. As the overall fracture aperture and flow rate increase, calcite-unsaturated water occupies the entire fracture. The time when this first occurs is considered the breakthrough time. In meteoric systems breakthrough typically appears at the onset of turbulent flow. Results from our one dimensional simulations indicate breakthrough occurs earlier in hypogene systems than in meteoric systems. In hypogene systems a thermal gradient along the fracture length combined with retrograde solubility allows growth along the entire fracture. When the aperture increases over the length of the fracture, a rapid increase in flow rate occurs. As the flow rate increases there is a switch from conduction dominated heat transfer to convection dominated heat transfer which reduces calcite solubility in the fracture and slows growth.
DE: 1829 Groundwater hydrology
DE: 3210 Modeling
DE: 5104 Fracture and flow
DE: 5114 Permeability and porosity
SC: Hydrology [H]
MN: 2003 Fall Meeting