Experimental Research On Gas Production Characteristics Of Coalbed Methane Well Associated With CO₂-ECBM

The paper takes the 3#coal reservoir of Sihe,Licun and Yuwu mines in the southern Qinshui Basin as the research object,and studies the geological conditions and coal reservoir characteristics of the Qinshui Basin as the research background and experimental conditions,and draws the theory of coalbed methane well extraction.Guided by technology,the experimental simulation system of CO₂ injection and CBM intensification development is used as an experimental platform.The experiment simulates the change of coal permeability under different temperature,confining pressure and injection pressure,and the gas production characteristics during CO₂-ECBM displacement.And use the COMET3 numerical simulation software to invert and demonstrate the experimental results.The experiment reveals the variation law of coal-rock gas permeability under different constraints,analyzes the key influencing factors and mechanism of CO₂-ECBM coalbed gas production in deep coal reservoirs,and establishes the mathematical model of coalbed methane extraction based on COMET3 software platform.The gas production process and its key influencing factors of CO₂-ECBM coalbed methane wells are summarized.The gas production law of CO₂-ECBM coalbed methane wells is summarized.The study has the following main insights:?1?The coal reservoir in the study area is the Shanxi 3#coal seam.Based on the low temperature liquid nitrogen,mercury intrusion and testing techniques,the pore structure of the coal reservoir is mainly microporous and mesoporous,and the macropores are less developed.The pore structure of Sihe and Yuwu coal samples was reconstructed by means of 3D visualization technology.The coal matrix pore density,pore network section and pore throat connectivity of Sihe coal samples were better than that of Yuwu coal.Under the same adsorption and desorption experiments,the adsorption and desorption of Sihe coal samples were larger than that of Yuwu coal samples,and the difference of pore structure had significant effects on the experimental simulation and numerical simulation results.?2?According to the geological characteristics of the study area and the characteristics of coal reservoirs,the coal permeability experiment and the CO₂displacement N₂ experiment with injection pressure,confining pressure and temperature as variables are designed.The experimental results show that the He gas permeability is greater than the N₂ and CO₂ test values.The injection pressure is positively correlated with the displacement efficiency.The confining pressure and the displacement efficiency are negatively correlated.The injection pressure and confining pressure change the permeability and CO₂ displacement.The efficiency impact is significant.The increase of injection pressure will lead to the increase of seepage pressure inside the coal matrix,and the increase of confining pressure will lead to the shrinkage of the pores inside the coal matrix.The above conditions change the effect on the pore structure of the coal matrix.The increase in temperature causes the gas activity to increase,the adsorption capacity decreases,the desorption capacity increases,and the temperature has a weak influence on the permeability and CO₂ displacement efficiency.?3?Based on the regularity of the experimental simulation,based on the COMET3simulation software,a numerical simulation experiment with a permeability of 0.1-1mD,a porosity of 1-5%,and a reservoir pressure of 10-12 MPa is designed.The simulation results show that:Under the influence of single-factor sensitive parameters,the coal reservoir achieved the best storage effect of CO₂ and the highest recovery effect of CH₄ under the conditions of permeability 1mD,porosity 1%and reservoir pressure10MPa.?4?The gas production process of CO₂-ECBM coalbed methane well is a multi-factor coupling process.In the field engineering practice of CO₂-ECBM coalbed methane well,comprehensive site selection,coal reservoir physical properties and coal reservoir occurrence should be considered comprehensively.Coupling effects of various factors such as conditions,gas production kinetics,and CO₂-ECBM coal seam injection and production processes.