Investigation of the smashing characteristics induced by energy distribution of CO₂ BLEVE for coalbed methane recovery

Failure in the near field of coal by liquid CO₂ phase transition blasting (LCO₂-PB) is the major reason for fracturing performance and enhancing coalbed methane (ECBM) recovery. Features to clarify this failure are of significant importance for the field projects. Some studies have revealed that the energy of LCO₂ releasing can determine the damage feature to some extent. This study was therefore initiated to investigate the effect of BLEVE energy on the fracturing performance of LCO₂-PB in coal. A series of LCO₂-PB fracturing tests was carried out on hard and soft coal to examine the effect of CO₂ BLEVE energy on fracture morphology. It was obtained that, compared with fractal dimension of hard coal under lower import energy (623.48 kJ) is around 2.17, the higher import energy (831.36 kJ) provides a larger fractal dimension (2.32), especially for high rupture pressure (95 MPa), which make fragments smash into a smaller radial. Although higher input energy favours a large superfluous energy density for any coal types, soft coal represents a stronger tendency to fracture in the stress drop stage. Lower input energy in hard coal seam products a longer main fracture, and excellent fracturing in soft coal prefers the higher import energy.