Study On Expansion Cracking Of Coal Seam Drilling And Increasing Permeability

Gas disasters seriously influence the safety of coal mine and production efficiency.Gas suction by drilling is one of the main measures to prevent and control gas disasters and accidents,but most of the coal seam in our country belongs to low permeability of coal seam,which the effect of gas drainage is poorer;and can't reach the purpose of the gas control.In order to gain gas drainage effectively,and increase coal seam permeability,expanding gas drainage radius are the key to improve the gas drainage rate.Through theoretical research and laboratory test method of crushing mechanism,expansion material was studied,and the effect of the factors such as time,temperature,water cement ratio,and the size of bore was analyzed.The setting time of sodium phosphate,sodium tripolyphosphate,sodium citrate,borax,and gypsum retarder was determined setting time by the experiment.By the ratio and expansion pressure of test the expansion pressure was determined to be 45~65 MPa,which can control the expansion pressure,maximum reaction temperature,reaction rate of the expansion material by adding admixture.Based on the mechanical properties of coal,the use of similar material text and numerical simulation for crack drilling and drainage gas was analyzed.Similar material test showed that when the expansion material mixture ratio was reduced response time is slow,and the 3~4 main crack width is also relatively small.Numerical simulation results showed that coal seam drilling expansion crack could enlarge the gas drainage range,and improved the effect of the gas drainage.The results show that reasonable decorate expansion borehole in the coal seam is filled materials,relied on its expansion pressure to breaking coal,increases the drainage range of gas and coal seam permeability,shortening the time of the gas drainage,thus improving the efficiency of gas drainage in low gas permeability coal seam.