Micro-CT characterization and fractal study on the fracture structure of coal under the liquid nitrogen cold soaking

• Liquid nitrogen cold soaking significantly enhances coal fracture networks, increasing fracture spectrum peak proportions by up to 79.939% in lignite. • The combination of micro-CT, VRA-UNet, and fractal analysis provides a robust method for quantifying fracture evolution in coal. • Fractal dimensions of coal fractures increase after liquid nitrogen treatment, indicating higher complexity and connectivity. • The findings support the application of liquid nitrogen fracturing for improving coalbed methane extraction efficiency.