Roughness Decomposition and Effects on Fluid Flow in Single Rock Fractures

The rock fractures usually consist of surfaces with different orders or scales of roughness, which have critical effects on the fluid flow behavior inside the fractures. In this paper, a two dimensional representative single rock fracture model was built, based on a laser scanned data of rock surface of granite. The surfaces roughness of the fracture was then quantitively decomposed into several levels of surface roughness by applying the wavelet analysis. A self-developed Finite Volume Method solver was then applied to solve the Navier-Stokes equations for numerical modelling of fluid flow in the fracture models formatted with four levels of decomposed roughness, respectively, with different Reynolds numbers varying from 0.001 to 1000.0. Then, the features of velocity profiles and the effective hydraulic apertures at each level of rough fractures decomposition and Reynolds numbers were calculated and analyzed. The results show that when the Reynolds number is small (less than 10.0), the effective hydraulic aperture slightly increase nearly linearly with the decomposed roughness levels. When the Reynolds number is large, the effective hydraulic apertures decrease dramatically, and the non-linear flow behaviors represented by expansion of the eddy flow regions caused by roughness: the larger extent of high-frequency roughness, the more obvious and complicate eddy flow regions yielded.