| China's coal resources are rich but the geological conditions of coal seam are more complex,coal with high gas content,high gas pressure,high adsorption,low permeability characteristics,which make the coal mining is facing great difficulties,the coal and gas outburst,Gas emissions and other gas accidents occur frequently which is a serious threat to the safety of coal production,especially in recent years,the increase in the depth of coal mining has further increased the difficulty of coal seam gas control.Pre-pumping coal seam gas is the main regional measures for the prevention and control of gas disasters in coal seams without protective layer.However,due to the low permeability,the necessary pressure relief and reinforcement measures are needed.In this paper,the physical simulation of multi-field coupled coalbed methane mining physical simulation test system and rotary high pressure water punching physical simulation test device,with peephrometer and other instruments in the laboratory for hydraulic punching,hydraulic fracturing,the integration of hydraulic punching/fracturing The stress and strain parameters of the coal seam during the process of hydraulic pressure relief and reinforcement are studied,and the corresponding evaluation method of pressure relief effect is established.The main results are as follows:(1)According to the hydraulic punching equipment at the mine site,the physical simulation test device of rotary high pressure water punching is designed and developed.The device can adjust the parameters such as punching speed,water pressure and drilling speed.Size,according to different test methods to achieve different punching speed,different water pressure,different drilling speed and other conditions of the hydraulic punching physical simulation test.(2)The stress in each direction is weakened and the strain increases gradually.The strain in the direction of the hydraulic punching process of the displacement control is kept constant and the stress is gradually increased.During the process of hydraulic punching,the high pressure water jet is washed out of a large amount of pulverized coal,and a large hole is formed in the briquette specimen.The hole section is approximately circular.Punching speed and hole size is proportional to the greater the punching speed,the greater the hole out of the hole.The propulsion speed is inversely proportional to the size of the hole,the smaller the propulsion is,the greater the hole is.(3)The effect of hydraulic punching pressure relief is obvious.Compared with the gas extraction before punching,the gas pressure drop rate increases after the hydraulic punching,and the gas flow rate increases,and the time of eliminating the standard is shortened.Efficiency has improved significantly.In the case of hydraulic fracturing,the water injection pressure curve is affected by various factors such as stress,physical and mechanical properties of coal and other factors,but all it will undergo the following process: the water pressure increases slowly and then increases rapidly until it reaches the initiation Pressure,the coal is pressed,and then the pressure drops to the pressure required to extend the crack.(4)The effect of hydraulic fracturing pressure relief is obvious.After the hydraulic fracturing,the gas pressure drop rate increases and the gas flow rate increases,and the time of reaching the standard is shortened and the extraction efficiency is obviously improved.(5)Through the comparison of the descending rate of gas pressure during the extraction process,it is found that the integrated pressure relief effect of stamping is stronger than that of single hydraulic punching or hydraulic fracturing. |
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