Experimental study on CH4 permeability and its dependence on interior fracture networks of fractured coal under different excavation stress paths

- CH4 permeability of fractured coal under various excavation loads was measured.
- Variations in excavation stress paths caused complicated coal fracture networks.
- Fractal method was proposed to characterize spatial fracture network.
- Relationship between CH4 permeability and fracture characterization was derived.
- Fracture evolution modified the CH4 permeability of fractured coal.

CH4 permeation properties of fractured coal are of critical significance to coalbed gas recovery in coal seams. These properties are affected by the fracture network and by the dynamic evolution of fractured coal under excavation loads. Little information is presently available on the characteristics of fracture networks associated with different excavation methods and their influence on the CH4 permeability of fractured coal. This paper presents the results of an experimental investigation into CH4 permeation properties of fractured coal subject to three typical excavation stress paths and their dependence on the evolution of the interior coal fracture network. A triaxial testing machine and microfocus computed tomography (μCT) were used to measure the permeability of fractured coal and to identify dynamic changes in the interior fracture network under typical excavation loads. Three-dimensional (3D) spatial morphologies and changes in coal fracture networks were characterized using fractal methods. A relationship between CH4 permeability and fractal characterization of the fracture network of coal was formulated. Results show that variations in excavation stress loads associated with different excavation paths induce complicated evolution of the coal fracture network, significantly modifying the CH4 permeability of fractured coal.