Research On Coal And Rock Deformation Characteristics And Seepage Mechanism Under The Condition Of Coupling Of Force And Heat

Coalbed methane?CBM?,known as a clean and economical energy source,can not only alleviate the world energy problem,but also effectively prevent the occurrence of accidents in coal mines.The permeability of coal is a key parameter that affects the efficiency of CBM production.The permeability during CBM production is mainly affected by the effective stress,adsorption characteristics and slippage effect.With the increase of mining depth,the ground temperature and pore pressure rise gradually,and both are important factors affecting the adsorption and seepage characteristics of coal.Therefore,it is of great significance to study the deformation and seepage characteristics of coal under the coupling condition of stress and temperature for CBM production and CO₂ sequestration.In this paper,the coal of K2 coal seam in Songzao Coal Mine of Chongqing is taken as the research object,and an isothermal adsorption experiment at different temperatures and a seepage test in the gas loading process were carried out respectively.The modified Langmuir model considering temperature and excess adsorption capacity and the deformation-permeability model of coal considering the influence of temperature and slippage effect were established.Meanwhile,parallel experiments on helium were also carried out to investigate the influence of slipping effect and adsorption swelling.Some progresses were made in the following aspects:1)The isothermal adsorption test at different temperatures and the seepage test of constant effective stress with pore pressure increase were carried out,and the relationship among adsorption,deformation and permeability characteristics of coal under different temperature conditions were discussed respectively.The influence of temperature on the adsorption-deformation-seepage characteristics of coal is revealed.2)Based on the theory of isometric adsorption heat,the heterogeneity of coal surface is discussed,and an adsorption model considering temperature and excess adsorption capacity is established.Through the experimental results,the calculation results and prediction accuracy of each adsorption model are compared and analyzed,and the rationality of the improved model is verified.The L-F model considering temperature and excess adsorption capacity can truly reflect the behavior of gas adsorption by coal.3)The slippage effect and adsorption swelling model considering the coupling of pore pressure and temperature are established.The influence of slippage effect and adsorption swelling on the permeability of coal at different temperatures is discussed.The synergistic relationship between adsorption swelling of coal and slippage effect on the deformation and permeability of coal at different temperatures is further clarified.It is determined that coal adsorption swelling under the coupling of pore pressure and temperature is the main control factor that causes the permeability of coal to decrease.Temperature and pore pressure have important effects on the adsorption swelling and Slippage effect,and the evolution law of permeability under adsorption swelling and Slippage effect is revealed.4)The S&D model is systematically discussed,and a deformation-permeability model of coal considering the influence of temperature and slippage effect is established.Through the test results and comparative analysis with the S&D model and the permeability model without considering slippage effect,it is proved that the established permeability model can better reflect the relationship between pore pressure and permeability under different temperatures.Based on the research results,the variation of coal reservoir permeability with pore pressure during CBM extraction is systematically studied,it provides a basis for explaining whether the permeability of coal is promoted or inhibited under different temperatures and pore pressure.