ABSTRACT:
Flow and transport through fractures has been well characterized by their orientation and equivalent hydraulic aperture sizes. A recent study on colloid transport by Boutt et al. (2006), however, showed that the micro-roughness geometry of the fracture surface has a major impact on the macroscopic fluid flow and transport behavior in rock discontinuities. Modeling of flow and transport through fracture systems can be ultimately improved not only by accurate prediction of fracture networks but also by incorporating information regarding the surface topography. This study proposed a geostatistical methodology that takes roughness characteristics into account to estimate the fracture surface topography. The fracture surface roughness was summarized by how it behaves locally using so-called ¡°local roughness pattern¡± that indicates whether or not the heights of adjacent locations are greater than that of a given location. By incorporating two additional components, the minimization of the local error variance and the reproduction of the local roughness characteristics, into the objective function of simulate annealing, the fracture surface topography downscaling was improved compared to standard geostatistical methodologies
1 INTRODUCTION
Fluid flow through rock fractures cannot be characterized by flow based on the parallel plate model except when the aperture (or separation distance between the two fracture walls) is large relative to roughness (Thompson & Brown 1991). When the surface roughness is taken into account, fluid flow is deviated from the well-known cubic law and channel flow can be observed (Brown 1987). A recent study on colloid transport by Boutt et al. (2006) also has revealed that a significant tailing in the breakthrough curves and a sensitivity of the breakthrough to flow direction in the fracture can be related to the micro-roughness geometry. Colloids, simulated as microspheres, were observed to be trapped in low velocity zones inside the fracture.