Rsearch On The Theory And Application Of The Heat-Fluid-soild In Coalbed Methane Heat Injection Production

Coal seams in my country generally have the characteristics of micro-porosity,low permeability,and high adsorption,which severely restrict the exploitation of coalbed methane.As a new coalbed methane production increase technology,hot steam is injected into the coalbed as the heating medium.Coal seams increase the desorption rate of coalbed methane and strengthen the migration and extraction of desorbed gas.This paper takes the technology of thermal steam injection to increase the production of coalbed methane as the engineering background.The main idea is to study the heat-fluid-solid coupling mechanism of hot steam on the coal in the process of coalbed methane mining by thermal injection of coal seams,using experimental testing and numerical simulation.Method to expand the research content.Analyzed and studied the evolution of coal pores and cracks after the action of hot steam;explored the evolution of permeability of coal samples with different water content under the action of hot steam;based on basic theories such as seepage mechanics,elastic mechanics,and heat transfer,Comsol Mltiphysics was used The multi-physical coupling model of coalbed methane production by steam injection in coal seams is simulated and calculated.The following main conclusions:(1)Using low-temperature carbon dioxide adsorption,low-temperature nitrogen adsorption,and high-pressure mercury intrusion methods to test coal samples and raw coal samples after thermal steam treatment,and extract the pore size data corresponding to the advantages of the three experiments for combined analysis.After the action of hot steam,the total pore volume,porosity,and average pore diameter of the coal body are increased.The hot steam has an erosion effect on the pore structure of the coal body and produces a certain pore expansion effect;the hot steam effectively promotes the pores of the coal body matrix.Development,expansion and penetration,the closed pores and semi-closed pores inside the coal body transform to development holes,and the small pores to large pores;the fractal dimension of coal samples after thermal steam treatment is significantly higher than that of raw coal samples.(2)Research on the permeability behavior of coal samples under the coupling of confining pressure,pore pressure and temperature.The permeability of coal samples increases exponentially with the increase of pore pressure,and the permeability has a high pore pressure sensitivity;under low confining pressure,the increase in permeability shows an exponential trend;under high confining pressure,the increase in permeability shows a linear trend.Under the conditions of constant temperature and pore pressure,the permeability of coal samples shows a downward trend as the confining pressure increases.Without considering temperature changes,as the confining pressure increases,the fitted a and b values decrease.trend.The permeability of coal samples showed a downward trend as the temperature increased.Without considering the changes in confining pressure,as the temperature increased,the fitted values of a and b also showed a downward trend;the fit of the experimental results was both Above0.9,the fitting effect is better.The effect of hot steam on the permeability of coal samples with different moisture content was carried out.With the increase of water content,the permeability of coal samples shows a downward trend as a whole,and the relationship between permeability and water content is negative exponential,and the fit between the two is above 0.9.For the same coal sample with the same moisture content,the permeability increased significantly after the hot steam treatment,and the higher the coal sample's moisture content,the greater the increase in permeability after the hot steam treatment.After the action of hot steam,the permeability of the water-bearing coal sample was effectively increased.Permeability.(3)In the process of simulating the heat injection mining of CBM,it is found that the heat transfer in the coal seam is mainly heat conduction and heat convection.The temperature between the heat injection well and the extraction well has a large range of temperature changes,which is mainly affected by heat convection.With the increase of time,the production of coalbed methane shows a trend of first increasing and then decreasing,and the daily production of water gradually decreases with the increase of time.The lower the initial coal seam temperature,the initial water saturation of the coal seam,and the initial coal seam permeability,the higher the daily production of coalbed methane,the shorter the time for the peak of daily production,and the higher the cumulative gas production.