Experimental Study On Gas Migration Law In Uniform Pore Of Different Scales

With the increase of mining depth,there are more and more nanoscale pores in the coal body,which seriously affects the migration and production of coalbed methane.The law of gas migration in nanometer pores is different from that of conventional Darcy flow.The flow mode is a nonlinear gas flow which varies with the pore size and coexists with various flow states.However,the mechanism and equation of gas flow under nanoscale pore and low pressure are still controversial.Therefore,the study of nonlinear gas flow in the nanopores is an important content and theoretical support in the aspect of coal seam gas migration,and is of great significance to the development and utilization of coal bed methane and the prevention and control of coal mine gas disasters.In order to study the flow law of gas in nano-scale pores,the following work was carried out: firstly,advanced and reliable experimental system and uniform porous alumina film with typical nanoscale pore size and micro-plate height were selected as samples.According to the SEM imaging of alumina film,the pore parameters of the film were calculated by MATLAB programming.The binary method and the maximum stable extremum region detection method were compared and analyzed.The advantages and disadvantages of the two methods were compared.The physical simulation experiments were carried out for the pore size,gas properties,cross section area and the variation law of gas flow with average pressure at different nanoscale.Based on the experimental results of gas flow,the governing equation of gas flow described by predecessors is compared and analyzed,and the governing equation of gas flow conforming to the wide-area Knussen number is introduced.Research results show that the characterization of the alumina membrane pore method,the largest stable extremal regions samples to detect the intrinsic permeability range is 0.0033 m D～0.7618 m D.Testing results of binarization is 0.0084 m D～1.1730 m D slants big.Verified by rendering and theory,nearly round hole shape membrane stable extremal regions largest method is more accurate,the hole shape and the deflection of thin film,circular binarization test results more accurate;The permeability of the gas in the nanoscale pore decreases with the increase of pressure,and the decreasing range increases with the increase of pore size.In the same sample of different gases,the measured permeability of helium gas is larger than that of nitrogen gas,but the permeability measured by different gases varies with Knudsen number.Different gases have different transport capacities.Different flow cross-sectional areas have almost no effect on permeability.When gas flows through pores of different scales,smaller pores occupy a dominant position.The flow model considering the addition of sliding flow and Knudsen diffusion weight shows better consistency with the experimental data.Based on the experimental study of gas in uniform nano-pore,the qualitative analysis of the law of gas flow in the pore,and verify the slip flow and the flow of Knudsen diffusion weighted additive model to describe the gas flow state is more appropriate,to establish a multi-scale pore model considering pore structure parameters of the foundation.