Improvement of coalbed methane recovery rate by carbon dioxide phase transition blast fracturing

Carbon dioxide phase transition blast (CPTB) fracturing is an effective way to recover coalbed methane. The key to this technology lies in reasonable parameters; however, there is no practical way to determine and optimize parameters. An orthogonal experimental design was used to create this study; multi-factor analysis of range and variance was combined to study the significance of multi-factor influence and the optimization of fundamental carbon dioxide phase change blasting parameters. The main influencing factors of cracking and antireflection effect of phase change blasting are studied from coal properties and blasting parameters. The significance levels of different elements were determined. The cracking scheme was designed according to the significant factors. The blasting damage model of the coal body was established by numerical simulation to compare and analyze the cracking effect of critical parameters. The optimal scheme of crucial carbon dioxide phase change blasting parameters is determined as the simultaneous initiation of a single carbon dioxide blasting tube with a charging amount of 2.0 kg and a hole spacing of 7 m. The field practice shows that the cracking effect of the optimized blasting using carbon dioxide phase change is significantly improved, the coal cracking area increases, and the gas extraction concentration and extraction purity increase by 3–5 times.