Fracture-matrix interaction in Topopah Spring Tuff: Experiment and numerical analysis

Fracture-matrix interaction is investigated through combined physical and numerical experimentation. Two slabs of Topopah Spring Tuff are mated to form a vertical saw cut fracture to which water is supplied. X-ray imaging is used to obtain the matrix porosity field and transient saturation fields as water moves from the fracture into the matrix. Porosity, hydraulic conductivity, and pressure/saturation relations of the matrix are measured on small cores taken from adjacent rock. Correlations between hydraulic properties and porosity are developed and modeled. Numerical simulations using TOUGH2 are accomplished with a series of property fields of increasing detail. Property fields are modeled using the measured porosity field divided into 1, 3, 5, 11, and 21 porosity groups with the hydraulic properties assigned from the developed correlations and the average porosity within each group. Comparison with experimental results allows us to begin to evaluate current matrix property measurement techniques, specific matrix property models, property estimation procedures, and effects of matrix property variability