Research On Gas Extraction Technology By Borehole Through Soft Strata And Low Permeability Coal Seam

Based on the difficult gas extraction by borehole in soft floor and low permeability of coal, carried on the research and practice from improving permeability and outburst elimination, rock grouting, borehole sealing and extraction parameter optimization. Studied the stress distribution of coal around borehole, rule of permeability change and outburst elimination mechanism through drainage of gas. Measured gas parameters of second1coal in HeMei NO.10coal mine, set up the coupling model of gas extraction, combine with RFPA2D-Flow software, simulate the influence of physical and mechanical parameters of coal and gas flows by different extraction time, hole diameter and extraction pressure, determined the reasonable parameters of gas extraction. Studied the cylindrical diffusion theory of bingham slurry, it shows that grout diffusion radius is proportional to the grouting pressure, rock permeability, grouting time and pipe radius, and inversely proportional to the concentration of cement grout, Represents a3d graph of cylindrical diffusion when the water cement ratio is0.7or1.0combined with the floor of second1coal seam, provides the basis theory for pressure grouting of rock and borehole sealing. Analyzed the leak form and the reason of borehole, established borehole leakage model, aiming at the condition of soft and broken of the second1coal seam floor, the grouting should be taken to reduce the rock fracture, reduce the negative pressure for extraction, increase the length of borehole sealing and use the small diameter and high-strength pipe, the length of borehole sealing should be longer than11m. In field practice, plugging fracture with pressure grouting on the surrounding rock of gas extraction borehole, actual grouting amount is10.4%higher than theory; used the PDC bit to enlarge the diameter in the coal seam; used the pressure grouting to sealing the borehole, and also used the small diameter (1") and high-strength gas extraction pipe. Examines gas concentration and flow rate in the borehole and the influence radius of extraction, Achieve the purpose to improve the effect of gas drainage by the implementation of a number of technical measures.