Three-dimensional modeling and application of permeability characteristics ofheterogeneous porous media in goaf

The permeability of goaf has a significant impact on the accuracy of numerical fluid dynamic simulation in goaf.In this paper, the distribution of heterogeneous porous media is analyzed on the basis of Rock Beam Theory and “O”-Ring Theory. Then,a three dimensional mathematical model is established to compute the porosity and permeability of goaf. A numerical model is also built to simulate the CO2 injection fire prevention and extinguishing technology in No.7271 fully-mechanized caving face of Yaoqiao Coal Mine. The gas migration for different coal permeability are studied in the model with FLUENT and compared with field measurements.The results show that the porosity of coal is larger near the working face. The porosity changes dramatically along the inclined direction of the working face.The porosity changes are larger in the area near coal pillars than that in compacted area.It is also found that it is more difficult for CO2 to accumulate when the porosity is larger as the amount of air leakage increases.When permeability decreases, the concentration of CO2 increases gradually from return air roadway side to intake air roadway side.The average difference of permeability between the numerical simulation results using permeability obtained from the 3D permeability distribution model and the measured data is 8.0%, which is smaller than the difference when using constant permeability.The paper provides a basic reference for numerical simulation of air flow in goaf.