Research On Seepage Evolution And Wetting Distribution Of Coal Under Fluid-Solid Coupling

Coal seam water injection,as a comprehensive prevention technology of rockburst,gas prevention and dust control,is faced with new challenges such as high ground stress,undeveloped fracture closure,low porosity permeability and high gas pressure when it is applied to the disaster prevention and control of deep coal mining.As a result,problems such as increased water injection pressure,reduced water injection flow and poor wetting effect occur when traditional water injection theory and technology guide deep coal seam water injection,which seriously restrict and affect the disaster prevention and mitigation effect of coal seam water injection.In this paper,aiming at the important parameters such as dust control,anti scour and pressure relief of coal seam water injection in the fully mechanized mining face,based on the theory of fluid solid coupling and wetting and dust suppression technology of coal seam water injection under the action of non-uniform load caused by water injection drilling and mining stress,the method of combining theoretical analysis,laboratory research,computer numerical simulation and field engineering practice is comprehensively applied to the evolution of coal rock seepage,failure range,and wetting distribution under the action of fluid-solid coupling.Based on both the important parameters such as dust control by flooding coal seams and pressure relief in fully mechanized coal mining face and theory of water injection fluid-solid coupling and wetting and dust suppression in coal under heterogeneous distributed load induced by water injection drilling and mining stress,the paper adopts the method of combining the theoretical analysis laboratory research with computer numerical simulation and field engineering practice to study the seepage evolution and wetting distribution of coal and rock under the action of convection-solid coupling.Based on darcy’s law,equation of state and continuity equation,the basic differential equation is derived and solved,and the theoretical solution of the seepage pressure distribution of borehole water injection surrounding rock is obtained.That is,under certain circumstances of coal seam physical and mechanical parameters,the relationship between water injection pressure,water injection time,damage range,and wetting radius is determined,which provides a theoretical basis for determining water injection dust and water injection parameters in coal seam mining.The analytical solution of the original in-situ stress and the redistributed stress caused by the borehole is carried out.Thus,the theoretical solution of the failure radius based on the Coulomb strength criterion under the effect of water-fluid-fluid-solid coupling of the borehole was obtained,which provides theoretical support for the problems such as anti-flooding,water injection and pressure relief,and gas drainage.The triaxial compression and seepage tests were carried out on the coal rock specimens by using the multi-field coupled seepage and permeability improvement experimental system,and the full stress-strain seepage characteristics of the raw coal and briquette specimens were revealed.At the same time,based on the analysis of the permeability characteristics and mechanical properties of briquette,based on the collection of the basic parameters of mechanics and seepage of the laid coal seam,based on the large-scale coal seam water injection seepage platform the coal seam water injection seepage simulation test is carried out.The influencing factors and distribution law of water flooding and wetting in coal seam were analyzed based on acoustic wave testing method.Based on the theory of the relationship between conductivity and moisture variation,the moisture detection system of pulverized coal was designed by combining single-chip microcomputer and humidity sensor.The numerical simulation of fluid pressure field velocity field and water increment effect in the process of borehole water injection was carried out by using Fluent.Based on the theoretical derivation function and experimental data,the seepage model is constructed and the factors such as the wetting range and seepage velocity of coal around the radial direction of borehole under different pore pressure and different stress are compared and analyzed.Combined with the actual and experimental data in the coal mine,the dynamic numerical simulation of stress-percolation coupling was realized through the mathematical model of volume deformation of the coal under stress field loaded by UDF and the mathematical model of porosity changing with pore water pressure.Based on the reality of fully mechanized mining face in fucun coal mine,the drilling spacing of important parameters of borehole water injection is determined by the analytical solution.In addition,the length of the water injection borehole,the borehole inclination and the water injection method were determined according to the site and analogy method.The test is done by performing water injection drilling on site,carrying out statistical analysis of injection volume of borehole and checking and verifying the wetting radius of coal seam water injection,and the test results show that the analytical solution is correct.It can be seen from the comparison that the water-injection process achieves better water-injection and dust-proof effects.This paper studies the regular of the evolution of coal seepage and the distribution of wetting under the coupling of fluid and solid.The relevant research results have important guiding significance for improving the permeability of coal,enhancing the wetting effect,and improving the effect of coal seam water injection on dust suppression.