ROUGHNESS OF FRACTURE SKINS: IMPLICATIONS FOR FLUID FLOW AND TRANSPORT

The ability to accurately predict the behavior of flow through fractured media has implications for development of water resources, petroleum reservoir exploitation, contamination assessment and remediation alternatives, and site evaluation for repositories of nuclear material. Physical flow tests through discrete natural fractures in tuff show deviation from cubic law approximations at low Reynolds numbers due to the effects of fracture roughness. Three fracture skin types on granites show variable effects on resultant roughness and diffusion properties of the fracture wall. Current work at The University of Texas at Austin on characterizing rough fracture surfaces and the effects of roughness on fluid flow include using computed tomographic images sampled at 0.25mm spacing to ascribe profile and surface roughness for comparison across discrete fractures and consecutive fracture surfaces. The digital representations of discrete fractures are subjected to finite difference modeling calibrated to flow tests on the correlating physical specimens in an effort to develop a metric tied to physical fracture properties that can be incorporated into a Navier-Stokes type fluid flow equation to account for nonlinear behavior in fluid flow through fractured media. This presentation reports results of the effect on roughness of weathering rind, pyrolusite and iron oxide skin types on medium grained granites from Fredericksburg, TX, Elberton, GA and South Australia. Diffusion data for these skin types is also included. Comparison of the roughness characteristics and physical and modeled flow test results of two consecutive fractures in Santana Tuff from Big Bend National Park round out the data content.