CO₂ Injection And Displacing Coalbed Methane Mechanism And Numerical Simulation In Deep Coal Seam

In this paper,through data collection and sample collection to study the reservoir characteristics of Changzhi Mine,Zhaozhuang Mine and Shizhuang Mine,analyze the coal,porosity,permeability and isothermal adsorption.According to the collected data and analysis results,use Comet3 and SimedWin software for sensitive analysis and numerical simulation of coalbed methane recovery by gas injection,provide reference for CO₂injection coal reservoir to enhance coal methane recovery.The coal samples are the native structure,develop strips and joint,have stepped fracture,calcite filling is visible in joint surface.They are low ash coal,fixed carbon content is over 75%.The sample product vitrinite/inertinite?V/I?values are between 0.25and 5.85,organic matter type is?kerogen,with a strong ability to produce gas.Coal crack develops,fracture density is at 21¹28/9cm²,is mainly D-type fracture,followed by C and B,A-type rare.The porosity is 2.7-6.2%,permeability is 0.13-0.76mD.The reservoir is low porosity and permeability.The mercury saturation in mercury-injection experiments is at 30.09%-43.65%,indicating poor communication pores.Efficiency of mercury withdrawal is up to 64%-75%,indicating high reservoir recovery,favorable to CBM exploitation.BET specific surface area of the sample is between 2.1226-10.647m²/g,BJH total pore volume is between 0.0052-0.0255ml/g.NMR experiment shows that samples of the three coal mines are mainly the small hole,the communication between the small and large bore hole is rather poor,but large holes and cracks are relatively good connected.Have CH₄,CO₂ and N₂ pure gases adsorption isotherm experiments on coal samples.The results show that the same coal sample for CH₄,N₂,CO₂ adsorption capacity is CO₂>CH₄>N₂.In Changping Mine,Zhaozhuang Mine and Shizhuang Mine,Langmuir volume of pure CH₄ gas is 37.05m³/t,27.66m³/t,40.64m³/t.Langmuir pressure is 2.84MPa,2.15MPa,2.70MPa.Langmuir volume of pure N₂ gas is 23.36m³/t,21.40m³/t,23.94m³/t.Langmuir pressure is 3.27MPa,3.24MPa,3.05MPa.Langmuir volume of pure CO₂ gas is65.74m³/t,51.95m³/t,54.91m³/t.Langmuir pressure is 1.67MPa,1.30MPa,1.23MPa.In sensitive analysis,with the increase of seam thickness,gas content,permeability,langmuir pressure,fracture length,the daily gas production peak gradually increased,also will increase the cumulative gas production.With langmuir volume,cleat porosity increases,gas production peak decreases gradually,the cumulative gas declines.In gas injection to enhance coalbed methane recovery simulation,from the accumulated methane production curve of"prod"Well,accumulation of gas production is the largest under the N₂-ECBM condition,followed by N₂+CO₂-ECBM,CO₂-ECBM and CBM.From the cumulative water production curve,cumulative water production is maximum under CO₂-ECBM condition,cumulative water production of N₂+CO₂-ECBM and N₂-ECBM is similar,the minimum is under CBM condition.