The Research And Application On Displacement Coalbed Methane On Coal Rock

This paper takes the No.4 coal seam of binchang mining area as the research object.Mainly through the laboratory simulation experiment on displacement CBM（coal bed methane）and field test to get the optimal injection solution.It would be providing a reference for the CBM development in the furture.Via CT scanner to study the physical deformation characteristics of coal samples after injection of CO₂.It is found that with the increase of injection pressure,the mean value of grayvalues increase while the porosity decreases continuously.In the process of increasing pressure,the whole coal sample expanded.This is because the adsorption of CO₂ on the surface of coal and rock cracks will cause the expansion and deformation of coal samples,and the fracture is squeezed to narrow leads the porosity decreased.Via gas permeability experiment to see the permeability change after the injection of N₂and CO₂,respectively,shows that the permeability increases significantly when N₂ is injected,5.57mD is the highest it reached,then decreases with the increase of injection pressure,but it is still higher than the original permeability which is 2.1mD.While the permeability is obviously lower when CO₂ is injected and it is even lower than the original permeability,0.446 is the lowest it reached.The analysis of the displacement mechanism of the two gases is carried out,and CO₂ will have competitive adsorption and lead to the coal rock expaned.While N₂ purge the CH₄ via changing the pore pressure turn the adsorbed CH₄ into free state,which can obviously increase the permeability.Innovative using the nuclear magnetic resonance（NMR）to simulate the displacement CBM experiment with N₂,CO₂ and mixed gas（N₂:CO₂=1:1）with compare these three gas displacement effiency and displacement ratio.It is found that in the range of 1.5MPa to5.5MPa injection pressure,the displacement efficiency of both continuous injection and interimission injection are CO₂>mixed gas>N₂.The displacement efficiency of N₂ reached80.52%,which is very much close to the displacement efficiency of CO₂ in continuous injection under the injection gas pressure is 3.5MPa,furthermore,it is only 5.01%different with the CO₂ in the same condition.The efficiency of N₂ is not good in interimission injection way.From displacement ratio analysis,it was found that N₂ consumed 64%less than CO2when displacing the same volume of CH₄ in 3.5MPa injection pressure.Therefore,it is feasible for N₂ gas injection to replace CBM,and the best injection pressure should be3.5MPa.Via the mature filling tube device to simulate the displacement CBM experiment to prove the former experiment’s feasibility.The two experiments with defferent devices get the same results.At the same time,by comparing the adsorption capacity of CH₄ after displacing the different gas in the sand filling tube,it was found that the adsorption amount of N₂ was slowly changed with the increase of injection pressure,while the residual adsorption amount of CO₂increased rapidly with the increase of injection pressure.The latter has 2.2 times that the former.It is explained that N₂ injection would be useful to the development of CBM.According to the data obtained from the laboratory experiments,the experiment of displacement CBM by injection N₂ on the single well on the DFS-135 site has been carried out,and the good results have been achieved in the field.