A New Fractal Permeability Model Considering Tortuosity of Rock Fractures

During methane extraction, the permeability of a coal seam is the vital factor affecting recovery. Although the permeability of a coal seam and its relationship with porosity have been studied in a few works, the calculation process of coal seam permeability is usually too simplistic or neglects the influence of microscopic fracture structures. Statistical research shows that the permeability of coal seams with the same porosity and different fracture structures is quite different. For the purpose of quantitatively investigating the contribution of fractures and pore structure in coal seams, a fractal permeability model considering the microstructure of coal seam fracture is established in this paper. The correctness of the model is verified by comparing with the previous research results. Then, the influence of the microscopic fracture structure on the equivalent permeability is analyzed. The simulation results show that the permeability of fractured coal is directly proportional to the fractal dimension of the fracture, the maximum fracture length and the azimuth. It is inversely proportional to the tortuous fractal dimension and the dip angle of the fracture surface. This conclusion provides the foundation for revealing the microstructure mechanisms of macroscopic seepage characteristics of coal seams, and implementing effective strategies to enhance gas recovery rates under different geological structures.

Automated summary

This paper establishes a fractal permeability model considering the microstructure of coal seam fractures, and analyzes the influence of microscopic fracture structures on equivalent permeability.