Research On Hydraulic Jetting Technology For Increasing The Permeability Prevention In Low-gas-permeability And High-gas-permeability Coalsearn

Coal is the basic energy in our country. While the production process of coal,the outburst of the coal and gas is a dominant factor restricting the safety of coalmining, thus ensuring the safe production of coal is a prerequisite to protect the rapidand sustainable development of the national economy and socio-economic. The coalseam without the conditions of exploitation protective layer in our country show lowgas permeability, soft coal seam, big coal and gas outburst risk, so hydraulicfracturing, hydraulic extrusion, coal seam affusion are used as regional outburstprevention measures. As a new regional outburst prevention method, hydraulicpunching enhancing gas extraction technologies has some advantages of high security,short cyclical and easy operation, and have made a better removing outburst effect inthe mining area all over the country. However, due to geological conditions, theparameters design, equipment selection, coal output controlling did not form awidely applied technology, hydraulic punching technology needs further systematicstudy.This work focuses on the coal seam of low permeability, soft and non-protectivelayer mining conditions, Pan Er coal mine11223second west working face as testsites, combined theoretical analysis, numerical simulation and field tests, research onthe following three aspects:(1) Hydraulic punching mechanism researchBased on the water jet dynamics, study the destruction process of water jet to thecoal, analysis the broken coal mechanism of hydraulic punching and the main impactfactors of jet cutting the coal, and leads to the outburst elimination effect ofhydraulic punching by elaborating the mechanism of coal and gas outburst.(2) Numerical simulation of enhancing gas permeability by hydraulic punchingBased on the conditions of experimental field, establish the mathematical model ofstress and gas flow around the coal after hydraulic punching. Theoreticalcalculations show that the effectively range of coal stress can be up to5times ofthe diameter after hydraulic punching (initial stress variation less than5%); analysisthe coal gas pressure, the effect of eliminating outburst of different hole afterhydraulic punching based on the simulation, the results show radius of influenceis up to4.5m for0.7m aperture. Using different aperture simulation to determine theeffective radius of extraction, then optimize the method of hydraulic punching toguide the practice.(3) Hydraulic punching technology field test and effect According to the results of the simulation, analyzed the field test ofhydraulic punching gas outburst eliminating technology; during the experimentof excavation along the groove in Pan Er coal mine11223second west workingface Bottom Road after pre-pumping gas, mainly analyzes the pre-pumping gaseffect and permeability changes after hydraulic punching, the permeability raisedfrom (0.19to0.473) m~2/(mpa~2/d), gas attenuation coefficient is only1/3of theoriginal, increase the amount of gas drainage. Coal was excavated in coal roadwayafter outburst elimination examination. During the excavation, analyze theprominent risk indicators and gas emission parameters to verify the effectiveness ofpre-pumping gas outburst eliminating technology. The results show thathydraulic punching can promote the coal fracture and scope, had bettereffectiveness of gas outburst eliminating and application prospects.