Fracture is fluid pathway of oil, natural gas and highly relates to structural trap. Depending on reservoir conditions, fracture can work as seal layer and also leak pathway. Thus, the structural properties of fracture have a great influence on the permeability. Permeability of fracture is usually measured by laboratory experiments, however few studies focused on calculating permeability by using flow simulation on digital fracture models. Here we use Lattice Boltzmann Method (LBM) to calculate the fluid velocity and permeability. Using LBM fluid flow simulation, we can easily change the reservoir parameters, such as temperature and aperture length of fracture. Here we use two natural fracture data:
non-sheared, and
sheared fracture models obtained by Ishibashi et al. (2015).
After we digitalized these natural fractures, we numerically injected water into the two fracture models using LBM. To validate our simulation results, we compared the calculated permeability with the data of laboratory experiments. We then discussed the anisotropy of permeability on sheared model and the Representative Elementary Volume (REV) of the hydraulic properties of these fracture models as well. In this study, we extract several subdomains (i.e., small fracture models) from the whole model and estimate permeability of the subdomains. When the size of fracture model is smaller, the permeability estimated using LBM are scattered. However, the permeability is uniformly estimated when the model size is close to the whole model (0.1×0.15m). Therefore, the REV of the fracture model used in this study is ~0.1m. Because the hydraulic properties of fracture models smaller than REV are largely influenced by local heterogeneity, it is important to calculate hydraulic property by considering REV of sample.
