CO₂ Gas Fracturing in High Dip Angled Coal Seams for Improved Gas Drainage Efficiency at Hashatu Coal Mine

Abstract

Effective gas drainage for the gassy coal seam is a technological measure to prevent excessive gas outing and gas related mine hazards. CO2 gas fracturing (CO2-Frac) is a new technology for coal mine gas control, and its effectiveness has been proven from many coal fields across China. CO2-Frac has been successfully implemented for gas drainage in single gently inclined coal seam, but it has not been experimented in steeply inclined multicoal seam. In this study, a pilot CO2-Frac project was carried out in Hashatu coal mine, a steeply inclined multicoal seam formation. To attain an effective gas drainage, three different types of CO2- Frac boreholes were drilled and experimented for a long-period gas drainage. One borehole type is the penetrating borehole through two seams, and other two types of in-seam boreholes include strike borehole and up-dipping borehole. With continuous field gas drainage and observation results, the gas drainage efficiency was found to be significantly improved in in-seam borehole and penetration borehole with CO2 fracturing, and the maximum methane flow rate increased 2.4 times for a given borehole length and the efficient drainage radius increased 3–4 times. In addition, the drainage effect of original drainage boreholes within the CO2-Frac circle influenced region was also significantly improved due to the borehole interference. The fractures radius of CO2-Frac in the penetrating borehole was larger than the two types of in-seam boreholes in the steeply inclined seam formation. This may be closely related to the developing property of bedding and cleat system in coal seam. This study provides both theoretical and practical evidence for effectiveness CO2-Frac in the area with steeply inclined angle and multicoal seam formations.

Mechanism and Practice of Multifracturing Using Dynamic Loads in a Low-Permeability Coal Reservoir

“…In the CO 2 blasting experiment, a type φ89 mm fracturing pipe made by Henan Polytechnic University, , China, was used. The fracturing pipe consisted of an inflation valve, heater, fracturing tube, controlled-pressure shears, and jet valve.…”

“…CO 2 blasting is a green fracturing technology, has less impact on the formation and environment, and has the potential of mitigating global warming . CO 2 blasting is a dynamic load fracturing technique, which involves the conversion of liquid CO 2 into the gas phase to release a large amount of energy into the coal rock, thus producing a fracturing effect. − Compared with high-energy gas fracturing, the dynamic load formed by CO 2 blasting has a lower frequency and longer wavelength, which can form a large fracture system in coal reservoir. CO 2 blasting has been shown to have great technical advantages in underground gas drainage in coal mines. , The influence radius of a single hole reaches 7–12 m, the permeability of the reservoir increases by 50–100 times on average, and the flow rate of the single-hole gas extraction increases by 2–8 times .…”

“… 32 CO 2 blasting is a dynamic load fracturing technique, which involves the conversion of liquid CO 2 into the gas phase to release a large amount of energy into the coal rock, thus producing a fracturing effect. 33 − 36 Compared with high-energy gas fracturing, the dynamic load formed by CO 2 blasting has a lower frequency and longer wavelength, which can form a large fracture system in coal reservoir. CO 2 blasting has been shown to have great technical advantages in underground gas drainage in coal mines.…”

Application and Research of Microseismic Monitoring System and Hydraulic Fracturing Technology in Coal Mines

“…If the gas is not fully discharged and operators enter the mine, the problem of gas poisoning will occur. Moreover, the gas is flammable and explosive, and reaching the ignition point under aerobic conditions will cause an explosion [12]. Therefore, it is critical to effectively discharge mine gas and reduce its concentration.…”

Research on Pore-Fracture Structure Alteration and Gas Emission Homogenization in an Outburst Coal Seam Induced by CO2 Gas Fracturing

“…Like gas fracturing technology, it can effectively improve the permeability of coal and rock. , The introduction of this technology to China showed that CO 2 -Frac led to an increase in gas concentration in the coal mine roadway, demonstrating its potential feasibility for gas control. Over the past decade, Cao’s team − conducted large-scale industrial experiments for gas control in Luan Group, Huayang Group, and other coal mining areas. These experiments involved the completion of hundreds of thousands of meters of experimental roadways, and the results revealed that the permeability of coal seams increased by 1–2 orders of magnitude, while gas extraction concentration and flow rate increased by 1 order of magnitude.…”