Lattice boltzmann simulation of fluid flow in mismatched rough fractures based on Gaussian distribution

Key words:  Gaussian distribution  rough fractures  mismatch length  Lattice Boltzmann simulation  grey correlation analysis

Abstract:

It is of great significance to understand the flow behavior in rough fractures for unconventional resource development, such as shale gas and oil. In this study, a Gaussian function was introduced to describe the fracture surface property based on the fracture surface height distribution in shale rocks. A 3D rough fracture model was built in the consideration of different parameters, including roughness, fractal dimension, mismatch length and anisotropy. A Lattice Boltzmann method combined with the orthogonal experimental results and grey correlation analysis was adopted to study the flow behavior in 3D mismatch rough fractures. The results show that the permeability in rough fractures is approximately 20%-50% of that in parallel plate fractures, and the permeability in mismatched fractures is slightly lower than that in matched fractures and a backflow may occur in the mismatched area. In order to ensure the fracture aperture, it should avoid to engender a mismatch in fractures, and decrease the fracture surface roughness and fractal dimension. The aperture and roughness of fracture are the two most important influencing factors to the fracture permeability, and the fractal dimension, anisotropy and mismatch length are also important factors. The roughness distribution along the fracture surface also has a great influence on the fracture permeability. In the case study of shale rocks, with the anisotropic coefficient increases, the fracture permeability firstly increases and then decreases, with a maximum value appears when the anisotropic coefficient is 0.7.