Thawing-Induced Crack Propagation in Variably Saturated Frozen Coal Analyzed by Acoustic Emission Energy Dissipation

Improving fracture structures is crucial for enhancing coalbed methane (CBM) production in low-permeability coal seams. To investigate energy evolution during the thawing of frozen coal, a self-developed acoustic emission (AE) monitoring system was employed. The results show that the AE energy exhibits two distinct phases: growth and quiescence. Peak energy increases linearly with water saturation, reaching approximately 1.74 times that of dry coal at 100% water saturation. Both the cumulative energy and AE events increase linearly with water saturation. AE count time series exhibits chaotic fractal behavior. Energy release efficiency during thawing increases exponentially with water saturation, reaching 34.00% at 100% water saturation, about 1.96 times that of dry coal (17.37%). Fractures are dominated by shear fractures, whereas tensile fractures, though less abundant, act as primary flow channels, and shear fractures enhance connectivity; together, they improve permeability and promote efficient CBM drainage.