Brittle transformation and energy evolution of coal under different liquid nitrogen treatment methods

Liquid nitrogen (LN2) fracturing is a promising technology for coalbed methane extraction, this article explores the mechanical degradation and ductile brittle transition characteristics of coal under different LN2 treatment methods using Brazilian splitting experiments. The freezing group increased brittleness by 6.3%, main crack length by 181.4%, and reduced unit crack energy by 78.5% with preserved skeleton integrity. The freeze-thaw group decreased brittleness by 40.5% but increased crack length by 351.2% and reduced energy by 84.0% with excessive damage. Freezing shows advantages over freeze-thaw in avoiding excessive damage, high energy utilization, and forming effective seepage channels, suitable for efficient permeability enhancement and gas extraction in deep soft coal seams.