A Study on the Factors Influencing Coal Fracturing Range Caused by Liquid Carbon Dioxide Phase Transition

Abstract

Liquid carbon dioxide phase transition fracturing technology (LCPTF) is an effective method to increase coal seam permeability, but there are many factors that affect the fracturing effect. Blasting pressure, vent diameter, and blasting time are important factors that affect the fracturing effect. However, very limited studies were performed in this regard. Therefore, in this paper, a multifield coupled model for fracturing coal bodies by LCPTF is established; the effect of blasting pressure, vent diameter, and blasting time on blasting effectiveness was studied; a numerical simulation study based on the seepage field and stress field is performed and verified in the field based on the specific geological conditions of Hujiahe mine. Experimental results show that the fracturing radius and the maximum displacement of coal increase with the increase of blasting pressure, and the fracturing radius is 4.875 m when the blasting pressure is 280 MPa, which is 9.6% higher than that of 200 MPa, and the effect is obvious. The fracturing effect improves with the increase of vent diameter but the effect is modest. In general, the fracturing effect increases with the increase of CO2 impact duration, and when there is no gas impact, the fracturing radius basically remains the same. The maximum displacement gradually decreases with time, and its maximum displacement of the coal body decreases by 33.69% at 200 s. After field blasting, the gas flow attenuation coefficient was reduced by up to 85.7% and the effective radius of influence was between 4 and 5 m.

Comparative Experimental Study of Fracture Mechanisms and Characteristics of Coal-like Materials under Quasi-Static and High-Pressure Air Blasting Fracturing

“…An escalation in blasting pressure has multiple implications, which ultimately result in a surge in crack propagation speed. First, the high-pressure dynamic impact produces longer initial dynamic cracks, which in turn curtails the propagation length of quasi-static gas wedge cracks . Second, the high-pressure dynamic impact reduces the mechanical strength of the sample, thereby facilitating crack propagation.…”

“…First, the high-pressure dynamic impact produces longer initial dynamic cracks, which in turn curtails the propagation length of quasi-static gas wedge cracks. 39 Second, the high-pressure dynamic impact reduces the mechanical strength of the sample, thereby facilitating crack propagation. Lastly, the quasi-static pressure increases after high-pressure dynamic impact, leading to faster crack propagation.…”

Laboratory Study of Supercritical CO2 Shock Fracturing in Hot Dry Rock: The Utilization of CO2 in Geothermal Stimulation

“…Compared to hydraulic fracturing that characterized by quasi-static loading and typical two-wing straight fracture planes, SCS fracturing has the following advantages in the stimulation of HDR reservoirs: ① Instantaneous dynamic shock loading can crush the near-wellbore zone dramatically (zone A as shown in Fig. 15) to create a complex interconnected fracture network with high conductivity in a certain distance (a few meters to tens of meters as reported by Hu et al [39] ) around the wellbore. This zone significantly reduces the skin factor and corresponding flow resistance near the wellbore, enhancing the injection capacity and production rate of heat extraction fluid.…”

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

“…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. After the fracturing, the fracturing radius remained almost unchanged, and the greater the gas pressure, the more significant the increase in the coal seam permeability.…”