Study On Desorption Permeability Law And Numerical Simulation Of Microwave Heating Coalbed Methane

China's coalbed methane reserves are abundant,but generally coal reservoirs have the geological characteristics of"high storage and low permeability",which greatly leads to difficulties in the extraction and development of my country's coalbed methane industry.Microwave heating is considered to be a promising new method of coal seam promotion and penetration enhancement due to its high heating rate,selective heating,and environmental protection.The technology of microwave heating to promote desorption and anti-reflection is an emerging research field.It is of great significance to explore the desorption seepage model of coalbed methane in low-permeability reservoirs and the mechanism of coalbed methane migration and production under the action of microwave radiation.In this paper,with the help of experimental research,theoretical analysis and numerical simulation and other methods and means to carry out in-depth research on coal desorption seepage law,desorption seepage equation,engineering application and other contents under the action of microwave radiation,the following important results have been obtained:Firstly,a triaxial coalbed methane desorption permeation experiment was carried out under different microwave powers and different pore pressures.The results of microwave desorption experiments show that microwave has a good ability to promote desorption of coal samples after desorption at room temperature.The same pore pressure The amount of desorption in the range increases with the increase of microwave power,and the greater the pore pressure,the greater the increase in the amount of desorption.From the perspective of experimental data and the principle of microwave heating of coal and rock,it is confirmed that there is a desorption hysteresis in the early stage of microwave heating desorption.The results of microwave seepage experiments show that during the process of microwave heating of gas-bearing coal,the temperature and pore pressure of coal continue to increase,and the permeability of coal increases with the increase of pore pressure and temperature.Increasing microwave power can increase coal.When the permeability and pore pressure are low,the effect of increasing the microwave power to increase the permeability of coal is more obvious.Secondly,based on the existing desorption diffusion model,the desorption lag time t₀ is introduced,and the influence of microwave radiation heating coal and rock thermal difference is considered,and a double desorption-diffusion model of coalbed methane under the action of directional microwave radiation with time lag is constructed.From the experimental data and the calculation model,it is concluded that the desorption lag time is negatively related to the microwave power.The greater the microwave power,the smaller the desorption lag time.Increasing the microwave power can effectively alleviate the desorption lag.Thirdly,considering the influence of factors such as slippage effect,thermal expansion of the coal matrix caused by temperature changes,thermal cracking,and coal adsorption/desorption on permeability,the relationship between temperature increment and pore pressure change is obtained based on the Clapeyron equation,and the substitution method is used to replace the temperature correction.The Langmuir equation established a double-L adsorption model,and an improved gas-containing coal permeability dynamic evolution model under the coupling of temperature and pore pressure was proposed.Finally,based on the characteristics of microwave heating coal and rock,the improved permeability is further theoretically deduced,and a permeability model with microwave characteristics is deduced.Finally,in view of the overheating phenomenon caused by microwave heating and the efficient utilization of microwave energy,the pulsating microwave cycle method of heat injection is proposed to exploit low-permeability coalbed methane,and the electromagnetic-heat-fluid-solid multiphysics coupling mathematical model is established and applied Multi-physics coupling software carries out engineering application numerical simulation research,and the results show that:pulsating microwave cycle heating has an important influence on coal reservoir temperature,heating effective radius,permeability,gas content and cumulative production.Sensitivity analysis shows that high-power,2450MHz microwave pulsation cycle heating and extraction of coalbed methane is the first choice.Pulsating microwave is more suitable for the heat radiation of low-grade coal,and extending the heating time of microwave can effectively improve the efficiency of coalbed methane extraction.This paper has 53 pictures,10 tables,and 81 references.