FRACTAL STUDY ON GAS PERMEABILITY IN UNSATURATED DUAL-POROSITY MEDIA BASED ON SOLID–LIQUID CONTACT ANGLE MECHANISM

Existing studies on the quantitative analysis of gas permeability in unsaturated dual-porosity media generally neglect the regulatory role of the solid–liquid contact angle of droplets on the interfacial geometric morphology, and have not established a quantitative correlation between contact angle parameters and permeability. Based on fractal theory, this paper constructs a theoretical model that cross-scale couples the dendritic branching network of matrix variable-section capillaries and fractured curved parallel plates. By introducing the influence mechanism of the contact angle on the equivalent height of droplets, the effective pore size distribution of the matrix-fracture systems in the unsaturated state is characterized. The study finds that gas permeability is positively correlated with the fractal dimension of fracture width and the fractal dimension of matrix pore size, and decreases with the increase of the tortuosity fractal dimension. In the wet state, the contact angle reduces the permeability by compressing the flow space compared with the dry state. The model is verified by numerical simulation results and experimental data, showing good consistency. It provides a new theoretical support considering interfacial geometric characteristics for gas transport in unsaturated porous media.