Research On The Evolution Of Fracture Around Borehole And Time-varying Rule Of Extraction Radius Under CO₂ Gas Fracturing Condition

Gas extraction is the main measure to control gas disaster and improve mine safety in China.In view of the difficulty and low efficiency of gas extraction in low permeability and thick coal seam,CO₂ gas phase fracturing technology is used to enhance the permeability of coal seam to improve the extraction effect.In this paper,through experimental research,numerical simulation and field measurement,the gas extraction radius before and after anti-reflection of CO₂ gas fracturing technology is compared and analyzed to verify the anti-reflection effect of CO₂ gas fracturing technology.In this paper,the gas content,a and b values of adsorption constants and CT scanning are measured in the target coal seam.The comprehensive analysis shows that the connected pores of the target coal seam are not developed,the permeability is low,the micropores are developed,the gas content is large,and the gas extraction is difficult.COMSOL numerical simulation software was used to simulate the evolution characteristics of peripore fractures and gas extraction radius before and after anti-reflection.The simulation results show that when the pumping time is 30 days,the pumping radius before anti-reflection is 2.7m,and after anti-reflection is 5.8m,and the pumping radius changes by 2.15 times.At the same time,the extraction boreholes before and after anti-reflection are peered.The results show that after fracturing,the fracture area around the pore increases,the fracture is obvious,and the anti-reflection effect of CO₂ gas fracturing is remarkable.The radius of gas extraction before and after measured reflection enhancement in the target coal seam.The measured results show that the extraction radius is 2.5m before anti-reflection and 5.5m after anti-reflection,and the change of extraction radius is 2.2 times of the original.The results are similar to the numerical simulation results,the error is less than 10%,the research results can provide a reference for the layout of gas extraction boreholes.