FLOW REGIME IN SELF-AFFINE FRACTURES INFERRED FROM FIELD OBSERVATIONS AND STATISTICAL ANALYSIS (Invited Presentation)

The impact of fracture surface pattern to flow regime is of major importance to the hydrotesting design in reservoir engineering. In this context, the dependency of roughness and Reynolds Number have been often investigated. Especially at the high rate flow injection in geothermal applications into fractured rock, there are often contradicting indications on laminar or Non-Darcian behavior. The presentation will focus on the quantification of fluid flow in rough fractures ranging from observations in field experiments over standard interpretation to new sophisticated analyses of stochastic rough self-affine fractures. Our analyses are trending towards probabilistic model runs of fractures defined from an incremental shear displacement of the fracture walls. In order to analyze their impact on fracture flow, such as anisotropy and channeling, Local Cubic Law (LCL) model based on 2D Darcy fluid flow and Navier Stokes Models on the real 3D fracture geometry including tortuosity were simulated. The particularity of this approach is the combination of a stochastic generation of self-affine fractures with a statistical analysis on the validity range of the LCL’s aperture constraint on fracture flow. The results show that aperture definition affects the quantitative interpretation of flow anisotropy and channeling as well as the aperture distribution of the fractures with shearing. In addition, flow anisotropy is significantly sensitive to the flow regime with a typical channeling development resulting at higher total flow rates. Channeling is initiated along the high-aperture sections but also prevails at their low-aperture intersections. Along these channels the 3D Navier Stokes models support the validity of LCL even at Re~100 when other areas fall into non-laminar range. These findings link the observation of the validity of laminar flow to channeling structures as function of the roughness profile of the void fracture space and on their specific flow velocity distribution.