Experimental and Numerical Modelling of Nonlinear Flow Behavior in Single Fractured Granite

Abstract

In this study, the hydromechanical behavior was experimentally investigated by conducting fracture geometry evolution-based gas flow tests on single fractured granite. The traditional fracture roughness value (Rp) of a single surface cannot adequately explain the intrinsic permeability in multiple samples. Instead, the permeability is better explained by aperture distribution, and it is positively correlated with the mean aperture size. The permeability is also affected by a combination of contact area and void space under changing confining stress. The average embedded depth increases rapidly under low-loading stress (less than 8 MPa) and slowly under high-loading stress (higher than 8 MPa). A simplified Hertz contact model was used to fit the experimental data. The model uses the reciprocal of the standard deviation of the aperture as the average curvature radius of the fracture. Good agreement was found between the experimental and theoretical results. A modified smooth parallel-plate model to describe flow friction in fractures was developed, which takes fracture contact and void space into account. A new friction model was also developed that takes both the nonlinear effect and the influence of fracture relative roughness into account by multiplying the ideal model by two power-law functions. This new model is effective in predicting the friction factor. Finally, taking into consideration the built permeability, mechanical, and friction models, a nonlinear flow model was proposed. The flow rate can be estimated based on the 3D fracture topography data, the applied loading stress, and the pressure gradient. The influence of four types of aperture distribution on the friction factor was investigated. The results showed that a high mean aperture size would result in a low friction factor. In addition, the influence of the mean aperture size on the friction factor is obvious, even under a very high-loading stress while the effect of the standard deviation is negligible when the loading stress is very high.

An Experimental Study on the Seepage Characteristics of Rough Fractures in Coal under Stress Loading

“…Singh KK et al [14] studied nonlinear fluid flow in granite under high confining pressure and high inlet pressure. Su et al [15] carried out a flow test on marble fractures under different effective stresses and found nonlinear fluid flow under high confining pressure. Li et al [16] analyzed the nonlinear flow characteristics of methane gas in shale fractures by conducting shale fracture seepage tests under stress loading and unloading paths.…”

Experimental and Numerical Study on the Anisotropic and Nonlinear Gas Flow Behavior of a Single Coal Fracture under Loading

“…In the last century, numerous studies were carried out to understand flow behavior in a rock fracture generated by different rock types including sandstone, − limestone, granite, , shale, , and coal − using different kind of fluids such as water, gas, and supercritical CO 2 . According to these studies, it was found that the fracture conductivity was controlled by the geometry of the fracture, the flow rate, and the fluid properties.…”