Study of the influencing factors of the liquid CO2 phase change fracturing effect in coal seams

Abstract

To study the influence of different factors on the cracking effect of the liquid CO2 phase transition, the mechanics of coal rock crack extension based on liquid CO2 phase change blast loading were studied. Through the application of simulation software to analyze the influence of coal seam physical parameters (in situ stress, gas pressure, modulus of elasticity and strength of coal) and blasting parameters (fracturing pore size and peak pressure of detonation)on the effect of liquid CO2 phase change cracking, the simulation results showed that the cracking effect of liquid CO2 phase change was positively correlated with the changes in gas pressure, elastic modulus, fracture hole diameter and peak vent pressure, negatively correlated with the variation in situ stress and compressive strength, and nearly independent of the tensile strength. In addition, by using Gray correlation analysis to analyze the influence degree of six main factors on the cracking effect, the calculation results showed that the effect of blasting parameters was greater than that of physical parameters. The main controlling factor that affected the blasting effect was the peak pressure of blasting release. By conducting comparative engineering trials with different blasting parameters, the test results showed that the crack effect of the coal seam was positively correlated with the change in fracture hole diameter and peak venting pressure, which was consistent with the results obtained from the simulation. The experimental results and simulation results for the effective radius of coal seam fracturing were basically consistent, with the error between the two types of results falling below 10%. Therefore, the reliability of the blasting numerical model was verified. In summary, the research results provide theoretical guidance for applying and promoting liquid CO2 fracturing technology in coal mines.

Current Status of Research on the Coal and Gas Outburst Control Technology of Hydration and Anhydrous

“…In order to better apply the liquid CO 2 phase change fracturing technology to the field of low-permeability coal seam permeability enhancement and reinforced anti-outburst field, a field test of liquid CO 2 phase change fracturing for enhanced prepumping coal seam gas through the seam was conducted in the 13th mine of Pingjiang coal mine and through the gas extraction effect after fracturing the coal seam to determine the reasonable placement of liquid CO 2 blasting holes. Jia et al 88 used LS-DYNA software to simulate and analyze the effects of physical parameters of coal seams and borehole diameter on the effect of liquid CO 2 phase change fracturing on coal seams, and the results show that there are positive relationships between the fracturing effect of coal seams and the pressure, modulus of elasticity, and borehole diameter, there are negative relationships with the geopathic stress and compressive strength, and the process is nearly irrelevant to the tensile strength. Hu et al 89 tablished a multiphysical field coupling model and found that the longer the liquid CO 2 phase transition cracking time, the greater the fracturing radius.…”

Study on prediction of blasting cracking radius of liquid CO2 in coal

“…Then they conducted a numerical simulation of CO 2 phase change cracking. The results showed that the influence radius of cracking was 2.55-2.70 m. Jia et al [26], based on the gray correlation analysis method, the effects of different factors on the phase change cracking effect of liquid CO 2 were studied. The results showed that the phase change cracking effect of liquid CO 2 was positively correlated with the changes of gas pressure, elastic modulus, fracture hole diameter, and detonation peak pressure, and this effect was negatively correlated with the changes of in ground stress and compressive strength, and was almost independent of tensile strength.…”

Prediction of the penetration radius of cumulative blasting

“…Therefore, researchers in the industry have focused on determining the factors that affect blasting cracking and nding methods to improve prediction accuracy. Jia et al [19] studied the in uence of different factors on the phase change cracking effect of liquid CO 2 based on the gray correlation analysis method. The results showed that the gas pressure and ground stress directly affected the blasting cracking effect.…”