Study on the Evolution Law and Mechanism of Fracture Imbibition in Loaded Coal Based on Micro-CT

The important factor affecting coal imbibition is the complex fracture formed under the influence of mining stress. In order to reveal the evolution law and mechanism of fracture imbibition in loaded coal, the NanoVoxel-3502E X-ray three-dimensional scanning imaging system and Deben in situ loading test device were used to carry out the Micro-CT in situ scanning test of coal under uniaxial compression, and real-time CT data under different stress conditions were obtained. The real penetrating fracture structure model was obtained by 3D reconstruction, and the numerical simulation of coal imbibition was carried out. The results show that the single fracture gradually propagates and connects with each other to form complex fractures during the loading process. The single fracture structure can be equivalent to the imbibition in the multibeam capillary. The wetting phase of complex fractures first appears at the intersection of fractures. When the bottom of the fracture is wetted, its imbibition characteristics are similar to those of the single fracture structure. The water molecules in the imbibition have a tendency to diffuse preferentially in the longitudinal direction. In the initial stage of imbibition, the water molecules first rise along the inner wall of the fracture. As the imbibition progresses, the imbibition fluid preferentially saturates the concave liquid surface. In the early stage of imbibition, capillary force and inertial force play a leading role in the occurrence of imbibition. When the imbibition continues, the viscous force and liquid gravity effect begin to appear. The evolution of the wetting front is significantly affected by fracture aperture. The fracture imbibition characteristics are related to the fracture opening, length, and height. The expansion direction of the wetting phase in the fracture is dominated by the dynamic mechanism of imbibition.