Reconstruction of the 3D Model and Numerical Simulations of Fluid Flow Tests in a Rock Fracture

The fluid flow in rock fractures has been an important issue in rock mechanics and is investigated in this paper using Finite Element Method (FEM), considering evolutions of aperture and transmissivity under normal loading conditions as measured during laboratory tests. The characteristic surface parameters of natural fracture rock samples were obtained by using a high-precision laser 3-D profile scanner, and the surface morphology of the fractures was reconstructed by numerical simulation. A 3-D model of the natural fractures was established based on the principle used for calculating asperities height. The distributions of fracture aperture and its evolution during normal loading were calculated from the initial aperture, based on the laser-scanned sample surface roughness results. A special algorithm for treating the contact areas as zero-aperture elements was used to produce more accurate flow field simulations by using FEM. The normal loading tests were used a high-precision visual system to analyse the dynamic changes of fracture closure seepage. The results indicate that by inversely obtaining the natural fracture surface morphologic parameters and using 3-D space reconstruction, it is possible to describe the fracture space of subsurface rocks; the calculations performed using the finite element modelling represented the pressure distribution over a fracture surface during normal loading, as well as the pressure field and velocity field of the fracture flow. Comparison of the simulation and experimental results shows that the fracture closure process has an exponential downward trend with flows, and the two curves have the same decreasing trend. These findings have an important impact on the interpretation of the results of coupled hydro-mechanical experiments of rock fractures, and on more realistic simulations of fluid flow in fractured rocks.