Study On The Evolution Law Of Permeability Of Adsorbed Gas Rock During The Deformation

China is a big country in the production and consumption of coal resources.Coal,as a vital basic energy source,occupies an important strategic position in the national economy.In the recent national energy strategies,although the policy of shutting down and de-capacity is implemented in coal mines for a long period,coal will still be the dominant energy source in China.During the mining of coal mines,coal and gas outburst accidents are one of the most serious and dangerous hazards,which seriously threatens the safe production of coal in China.However,the“harmful”gas in coal mine accidents can also be used as an alternative and clean energy.In the 1980s,after the successful extraction of coal bed methane(CBM)by the United States,people reconsidered gas as a clean resource.Gas will become one of the major energy sources in the 21st century,and gas drainage will also alleviate the shortage of new energy in China..Although China's CBM resources are abundant,the extraction of CBM is a major technical problem.Therefore,considering the resource reclamation and disaster prevention and control,research in the laws of gas flow in coal not only helps prevent gas accidents,also has positive guiding significance for CBM mining.In this paper,briquette is used instead of raw coal,and the independently developed three-axis mechanical permeability tester with gas-rock is used to test the permeability characteristics by orthogonal test.The seepage characteristics of briquette specimens under different stress conditions are compared and analyzed.The main experimental conclusions of this article are as follows:(1)The independently developed three-axis mechanical permeability tester for gas-bearing coal and rock includes four systems:gas filling system,coal and rock three-axis mechanical penetration test system,hydraulic loading system,and gas flow collection system.All the systems cooperate to complete the test of penetration characteristics.The hydraulic loading applied to the instrument has the advantages of simple operation and precise testing.The system employs a circumferential displacement testing device,which overcomes the difficulty of collecting the circumferential strain accurately in existing circumferential displacement testing devices.(2)Raw coal has certain defects in the permeability test.Raw coal similar materials were developed to replace the original coal for testing.The research into similar materials analyzed the influence of particle grading and cement concentration on the mechanical parameters of coal briquettes.The test results show that the uniaxial compressive strength,elastic modulus and cohesion of briquette increase with the increase of cement concentration,and the compressive strength can be adjusted within the range of 0.5MPa-2MPa.Briquetting coal has the similar adsorption properties with raw coal.The internal friction angle of briquette is mainly affected by the particle gradation.The repeated use of similar materials proves that the similar material can be reused to avoid resource waste.(3)The permeation characteristics of briquette under different strengths,gas pressures and confining pressures were measured.The test results show that:the independently-developed similar materials and the three-axis mechanical permeability tester with gas-containing coal rock have been successfully applied in the permeability research field.The initial permeability of briquette coal is between 78.6mD-182.8mD.Under the same conditions,the initial permeability of the specimen decreases with the increase in specimen strength and confining pressure.Within a certain pressure range,the permeability of gas-containing coal decreases with gas pressure increasing due to the Klinkenberg effect.The relationship between permeability and strain of gas-bearing coal in different triaxial stress states of the specimen shows the classic"V" trend and the final permeability is lower than the initial permeability.