Study On Coal Damage And Gas Seepage Law In Gas Extraction Of Coal Seam

As the eastern mines in China gradually enter the deep mining stage,the problem of dynamic disaster management of coal seams with high gas content and low permeability is increasingly prominent.At present,there is no unified mathematical model to describe gas seepage law under deep conditions.Therefore,in this paper,by means of experimental research and theoretical analysis,the seepage law of gas,the mechanical properties of coal and the failure law of coal in the drilling process are studied.Based on the experimental results,the coupling mathematical model of doal porosity and dual permeability for coal seam gas drainage is established and solved numerically.Finally,the mathematical model is applied to the field project,and the gas extraction efficiency under the technical conditions of lateral mining pressure,softening of coal seam water injection and cumulative blasting is simulated and analyzed,and compared with the field data.The main research contents and results of this paper are as follows:The gas seepage experiment of coal sample was carried out,and the mechanical parameters and gas seepage characteristics of coal samples under different water content and different effective pressure conditions were studied.Finally,the permeability,uniaxial compressive strength and failure patterns of coal samples under different seepage conditions were obtained.In this section,the deformation,failure and ae law of large size coal and rock samples under drilling disturbance are studied.According to the different failure characteristics of samples,the damage of samples can be divided into three stages: initial drilling failure,small-scale drilling failure and large-scale structural failure.Based on the gas seepage experiment results,on the basis of analyzing the gas-solid coupling phenomenon of gas seepage in the coal seam,a dual permeability model of coal seam under anisotropic conditions was established.Furthermore,the mathematical model of gas drainage efficiency under the influence of mining,the mathematical model of gas-water two-phase seepage under the influence of coal seam water injection and the mathematical model of coal seam fracture and gas seepage under the action of shaped charge blasting are established,and the numerical solution and verification are carried out.The gas extraction efficiency under the influence of lateral mining pressure in No.4102 working face of Hebi No.3 Mine was studied by numerical simulation.The results of the study show that: under the influence of lateral mining pressure,the damage and destruction zone of the mining borehole helps to increase the permeability enhancement effect of the coal seam and promote the flow of gas into the borehole;while in the supporting pressure zone,the concentration of in-situ stress The original fracture opening and the permeability in the coal seam area are reduced,and the gas seepage is suppressed.The gas extraction efficiency is the result of the combined action of coal seam deformation and destruction and gas desorption flow.The established mathematical model was used to simulate the gas injection in the coal seam of 25010 working face of Pingmei No.10 Mine to eliminate gas emission.The results show that the injection of external water has two effects on softening and destroying the coal seam.For water-injected boreholes,the flow of free water has a significant effect on coal seam softening and destruction.The increase in coal permeability can help the gas dissipate toward the borehole and the surrounding area;but when it extends radially to the free water wetted area,the free water The plugging effect occupies a dominant position and promotes the transformation of gas from a single gas phase flow to a gas-water two-phase flow,which reduces the relative permeability of free gas and reduces the diffusion of pore gas into the fracture.The mathematical model is used to simulate the elimination of gas emission by water injection in 25010 working face of Pingdingshan No.10 coal mine.The results show that the injection of external water can soften and destroy the coal seam.For water injection drilling,the flow of free water has obvious effect on softening and destruction of coal seam,and the improvement of coal seam permeability is helpful for gas to dissipate to the borehole and surrounding area;however,when the radial direction extends to the free water wetting area,the free water blocking effect takes the dominant position,and promotes the gas flow from single gas phase to gas-water two-phase seepage,which reduces the relative permeability of free gas and reduces the permeability of free gas The pore gas diffuses into the fracture.There are 98 pictures in this paper,35 tables,and 134 references.