Study On The Effect Of CO₂ Injection Conditions On CBM Displacement In High Rank Coal Reservoir

China's high-rank coal,represented by the Qinshui Basin,is rich in resources.However,the low permeability characteristics of high-rank coal reservoirs make it extremely difficult to extract CBM in situ by traditional drainage and pressure reduction methods.Therefore,CO₂ is injected into the coal reservoirs.Improving the recovery rate of coalbed methane is the key to promoting the exploration and development of coalbed methane in the basin,and it can also realize the geological storage of CO₂coalbeds.This paper takes the Shizhuang South block and the surrounding area in the south of the Qinshui Basin as the research area,and takes the coalbed 3#coal,the main purpose of the exploration and development of coalbed methane in the area,as the research object.Based on coalbed methane geology,coalbed methane exploration and development,and CO₂ injection Coalbed methane recovery factor(CO₂-ECBM)and other theories,using relevant basic theoretical analysis,Datong and Qincheng coal mines downhole sampling and basic experimental testing,columnar sample CO₂ drive coalbed methane experimental simulation,reservoir geological modeling and CO₂-ECBM process numerical simulation and other methods have studied the effects of CO₂injection mode,injection pressure and its relationship with reservoir pressure,and injection rate on the process of CO₂ replacement and CH₄ displacement in high-rank coal reservoirs.The thesis research mainly achieved the following knowledge and results:(1)Datong Mine 3#coal sample has a R_o,max of 2.78%and a volatile content of10.72%,which is a bright-semi-bright lean coal.Qincheng Mine 3#coal sample has a R_o,max of 3.12%and a volatile content of 7.32%.It belongs to bright-semi-bright anthracite No.3.Datong and Qincheng mine 3#coal samples have low porosities,4.75%and 3.72%respectively,and are dominated by mesopores and macropores that are conducive to gas percolation,and micropores less than 2nm are not developed.The coal sample permeability of Datong Mine ranges from 0.0052m D to 0.2488m D,with an average of 0.0075m D,which is slightly higher than the average permeability of the Qincheng Mine of 0.0073m D.Both are low-permeability coal reservoirs.Affected by the degree of coal metamorphism,the Qincheng coal sample's CO₂ adsorption Lange volume and Lange pressure are 64.10m³/t and 1.75MPa,respectively,which are higher than the 52.63m³/t and 1.70MPa of the Datong coal sample.(2)When the CO₂ injection pressure increases with the sample N₂ adsorption equilibrium pressure,and the pressure difference between the two is constant at 1.5MPa to 1.6 MPa,the Datong DT-1,Qincheng QC-1 and QC-2 samples simulate the experimental process The total CO₂ injection volume,CO₂ storage volume,CO₂adsorption rate,N₂ output volume,and drive rate all show an upward trend,indicating that it is possible to inject CO₂ into deep coal reservoirs at a higher pressure to increase the recovery rate of coalbed methane.Theoretical basis.From the comparison of different coal samples,the total amount of CO₂ injected,CO₂ storage,CO₂ adsorption rate,N₂ output and drive rate during the experiment of Qincheng QC-1 and QC-2samples with low porosity and low permeability Both are lower than the Datong DT-1sample,indicating that the high-rank coal reservoirs with high metamorphism,low porosity,and low permeability are not conducive to the replacement and displacement of coalbed methane by CO₂.(3)When the equilibrium pressure of N₂ adsorption is stable at 3.5MPa,and the pressure of CO₂ injection is gradually increased from 4MPa to 7MPa,the total CO₂injection amount during the simulation experiment of Datong DT-1,Qincheng QC-1and QC-2 samples,The CO₂ storage capacity,CO₂ adsorption rate,N₂ output and displacement rate all show an increasing trend,indicating that the increase in injection pressure can significantly improve the effect of CO₂ displacement and replacement of coalbed methane.From the comparison of different coal samples,the low-porosity,low-permeability QC-1 and QC-2 samples of Qincheng QC-1 and QC-2 samples have a high total injection rate of CO₂,but the CO₂ storage capacity,CO₂ adsorption rate,and N₂ output are different from each other during the experiment.The displacement rates are lower than those of Datong DT-1,indicating that the characteristics of high-rank coal reservoirs also affect the replacement and displacement effects of CO₂ on coalbed methane.(4)COMET3 numerical simulation results show that the stimulation effect of CBM production wells under the condition of continuous CO₂ injection is better than that of intermittent injection,and the stimulation efficiencies of CBM production wells in 5 years under 4.5MPa and 6.5MPa injection pressures are 92%and 368,respectively%.Increasing CO₂ injection pressure and injection rate can significantly improve the gas production effect of CBM production wells.When the injection pressure increases from 4.5MPa to 6.5MPa,the stable daily gas production of CBM production wells will increase from 600m³/d to 1879m³/d.Compared with continuous high-pressure and high-speed CO₂ injection,intermittent low-pressure and low-speed injection is more conducive to the full replacement of CH₄ by CO₂ in coal reservoirs,and coal reservoirs have greater CO₂ storage capacity.Injecting CO₂ into coal reservoir to drive methane can not only promote the efficient development of coalbed methane resources,but also greatly reduce the content of CO₂ in the air,which has multiple meanings of resource utilization,economic development and environmental protection.This article selects persimmon Zhuang Na withdrawals Qinshui basin and its peripheral high rank coal reservoirs as the goal of the reservoir,based on"CO₂ injection and CBM strengthen development experiment platform",based on the data collection and literature research,combined with coal sample testing and simulation experiment,illustrate the influence on displacement control mechanism of reservoir property,physical simulation laboratory scale different injection pressure on displacement efficiency,establish proper geological model in the study area,to carry on the numerical simulation of different injection ways displacement,provides the experimental basis for the engineering construction and simulation prediction.This dissertation contains 57 figures,23 tables,157 references.