Study On Presplitting Mechanism Of Liquid CO₂ In Low Permeability Coal Seam

Coal deepness in China is generally characterized by low permeability,the research on coalbed antireflection technology has always been a research hotspot.As a newly emerging anti-reflection technology,presplitting of liquid carbon dioxide is not only simple in equipment,easy to transport,but also reliable in operation,controllable in burst pressure.There is no generation of fire and CO gas during the operation,which has high security and low overall costs,and play a greater role in improving coal seam permeability,This article will study the mechanism of liquid carbon dioxide presplitting,tomake the technology better applied in mine safety productionIn this paper,the thermodynamic properties of liquid carbon dioxide were discussed,and the initial parameters of detonation wave for liquid carbon dioxide presplitting were determined,including initial pressure p₀,initial particle velocity₀,and initial wave velocity₀.The propagation,reflection,transmission laws and characteristics of stress waves in coal were studied combined with blasting dynamics theory.What's more,the mechanism and scope of the crushing ring and crack ring caused by blasting stress wave in coal were also studied according to material mechanics and damage mechanics.Expansion model of high pressure carbon dioxide gas and methane gas to crack was determined and expansion criterion of complex crack was given.In this paper,the internationally recognized best non-destructive testing technology--CT imaging technology was used to get computerized tomography imaging of coal samples at different locations from pre-split holes.according to the Photoshop fixed-level threshold statistical analysis,it reflects the effect of liquid carbon dioxide pre-splitting technology on the pore fracture system of coal,statistics show that,the characteristic cracks at the 4m away from the blast point have doubled from the original.In this paper,a liquid carbon dioxide blasting numerical model and a presplit antireflection test model were established by ANSYS Explicit Dynamics transient analysis module.The stress disturbance process caused by pre-splitting blasting of liquid carbon dioxide in coal was studied by numerical simulation methods and the conclusion was that when the distance between the pre-split holes was 8 meters,the crack development was relatively complete,and there was a good pre-splitting effect.Finally,through the liquid carbon dioxide pre-cracking test in the mine working,it was found that the drilling volume was saved by 40%and the drainage effect is good after the liquid carbon dioxide re-enrichment technology was used.The average daily single-hole velocity of presplitting pipelines after pre-splitting was 0.008 m³/min,which was 1.67 times higher than the daily average single-hole volume of the non-pre-split unpresplitting pipelines of 0.0031 m³/min.The average volume fraction of gas extracted from a single hole of methane gas was 46.8%,which was 1.03 times higher than that of 23.1%without presplit holes.