Study On Correlation Between Heat Transfer And Permeability Of Deep Sandstone

Taking surrounding rock(sandstone)of the coal mine tunnel as and adopting research methods combining with experimental research,theoretical analysis and numerical simulation,the paper studied the change rule of thermal conductivity and permeability coefficient of sandstone under the stress by utilizing WDW-300 universal testing machine,QTM-500 rapid conductometer and self-developed ZYS-1 multifunction triaxial coal permeameter.Based on the test result,the relation between thermal conductivity and porosity,relation between permeability coefficient and porosity under the continuous load are compared and analyzed between dry sandstone and unsaturated sandstone.Through heat transfer theory,fractal theory,modified mathematical model of Cheng-Vachon porosity-thermal conductivity and Menger sponge structure thought,the paper established the calculation model of thermal conductivity and porosity of sandstone and calculation model of thermal conductivity,porosity and permeability coefficient.Finally,taking Daqiang coal mine as the engineering background,the paper computes thermal conductivity with the buried depth of 800 m,1000m and 1200 m through the established thermal conductivity model for simulation of temperature filed.It has far-reaching significance on the calculation of thermal conductivity of deep engineering and providing basis for the simulation of temperature filed.Under the effect of continuous load,sandstone causes change of porosity.Through analyzing relationship of porosity,stress and thermal conductivity between dry sandstone and wet sandstone,the paper draws the conclusion that on the same conditions dry sandstone is solid-gas two-phase medium.With the increasing of stress,test piece behaves slight deformation,the overall volume becomes small and the heat conductivity is increased linearly.The unsaturated sandstone is solid-liquid-gas three-phase medium.The thermal conductivity of unsaturated sandstone is affected by solid particle,porosity and water saturation of pore jointly.When the porosity is the same,it is known the impact of water saturation of small pore on the thermal conductivity change rate of sandstone is greater than water saturation of big pore on the thermal conductivity of sandtone.By comparing the permeability coefficient change law of dry and wet sandstones when two of confining pressure,axial load and pore pressure are the same,we draw the conclusion that the changing curves of permeability coefficient of dry and wet sandstones are the same.With the increasing of confining pressure and axial load,the permeability coefficient decreases in terms of negative exponent.One part of unsaturated sandstone pores are filled with water,which resultsin reduction of permeation path of the tested gas and causes reduction of permeability coefficient of sandtone.We establish dynamic model of thermal conductivity and porosity of dry sandstone on different loading conditions and derived corresponding computation formula.Considering water content of the pore of sandstone on the actual working condition,we establish thermal conductivity model of unsaturated sandstone and thermal conductivity model of saturated sandstone.Moreover,we identify the parameter of test result of test piece with the established dynamic model of porosity and thermal conductivity by applying least square method.We adopt and combine the modified Liu Zhiyong calculation model of unsaturated rock permeability coefficient with the established unsaturated thermal conductivity-porosity model so as to establish dynamic model of thermal conductivity-porosity-permeability coefficient.Taking Daqiang Coal Mine as the engineering background,the paper computes thermal conductivity with the buried depth of 800 m,1000m and 1200 m through the established thermal conductivity and porosity,porosity and stress model for simulation of temperature filed.Moreover,the paper compares the simulated result with monitored data at site of coal mine and they are observed to be approximate,which provides basis for calculating thermal conductivity of deep engineering and simulation of temperature filed and thus has far-reaching significance.