Narrow Results

Transport characteristics in porous media play a significant role in fields, such as oil and gas reservoir engineering, hydraulic engineering, mineral engineering and geology. In this study, based on the fractal theory of porous media, a fractal model for the permeability through micro/nano dual-porosity media considering the coupling effect of the EDL and slip is derived. This study discusses the effects of the original slip length, molar concentration, dip angle, maximum aperture, fractal dimension and maximum size ratio on the dimensionless permeability. The results show that the dimensionless permeability increases with the increases of the original slip length, dip angle, fracture tortuosity fractal dimension, and maximum size ratio; on the contrary, the dimensionless permeability decreases when the molar concentration, maximum aperture, fracture aperture fractal dimension and capillary tortuosity fractal dimension increase. Moreover, the fractal model predictions are in good agreement with experimental data. The proposed model may be able to provide guidance for the analysis of transport properties in micro/nano dual-porosity media.

Analytical solutions for hydraulic properties of dual-porosity media subjected to fluid–rock reaction under triaxial stresses are derived and the effects of inherent parameters of dual-porosity media and surrounding environments on the relative equivalent permeability are systematically investigated. The results show that the applied triaxial stresses close both fracture aperture and pore diameter, and decrease the equivalent permeabilities of both fractures and rock matrix. The fluid–rock reaction over time decreases the equivalent permeability of fractures, and increases the relative permeability that is the ratio of matrix permeability to fracture permeability. When the time is long, the reaction may be negligible and the relative permeability holds constants. The relative equivalent permeability is more sensitive to the fractal dimension of fracture aperture distribution than that to pore diameter distribution. The relative permeability is significantly influenced by both the maximum fracture aperture and the maximum pore diameter. The rougher fracture surface and the more tortuous capillary correspond to a longer distance that a particle needs to move, thereby resulting in the smaller permeability of fractures and matrix, respectively. In engineering practice, the inherent properties of dual-porosity media can be obtained through geological survey on the outcrops of fractured rock masses and experiments on rock matrix. The triaxial stress can be estimated through ground stress tests. Therefore, it is available to analytically characterize the hydraulic properties of dual-porosity media.

It is very difficult to characterize the transport properties of porous media due to the disorder of pores distribution in porous media. In this paper, we study heat conduction through porous media with randomly fractures which are considered as tree-like networks. An expression for effective thermal conductivity (ETC) of saturated dual-porosity media is derived based on the fractal characteristics of pores diameter and fractures size. It is shown that the ETC is a function of structure parameters of the fractal dimension ($D_g$), the porosity (${\varphi }_g$), the tortuous fractal dimension ($D_t$) and the maximum diameter (${\lambda }_{\mathrm{\text{max}}}$) for the porous matrix; the fractal dimension ($D_f$), the porosity (${\varphi }_f$), the maximum diameter ($d_{0\mathrm{\text{max}}}$), the diameter ratio ($\beta$), the length ratio ($\alpha$) and the branching levels (n) for the fracture networks. The dependence of structure parameters on the ETC is studied in detail. The results of our model are compared with the available experiments, which show good agreement. The proposed model for the ETC does not contain empirical parameters. The model is useful for predicting the heat conduction of materials.