Experimental Study On Influence Of Different Rank Coal On Gas Adsorption Characteristics And CO₂-ECBM Influence

Coal will still be the main energy in China in the next two or three decades,and coalbed methane,as a cleaner energy,as an associated resource of coal mining,has great development and utilization value.However,due to the large buried depth and poor permeability of coalbed methane resources in China,it is difficult to improve the production of coalbed methane by traditional methods.As a kind of environmental protection and high efficiency technology,gas injection displacement has attracted much attention in recent years.Since the successful experiment of improving coalbed methane recovery by gas injection,scholars have carried out a lot of research on methane displacement in single rank coal samples,but there is a lack of research on displacement of different rank coal samples,especially on the variation law of coal permeability in the process of displacement.In this paper,the representative low rank lignite in Datong coalfield of Shanxi Province,the representative medium rank bituminous coal in Xutuan coalfield of Anhui Province and the representative high rank anthracite raw coal in Yangquan coalfield of Shanxi Province are taken as the research objects,and the experimental research on gas adsorption and gas injection displacement is carried out.The key research is carried out from the following aspects,and the relevant research results are obtained.(1)Pure gas adsorption experiments were carried out on three kinds of coal rank samples.The adsorption capacity of CO₂and CH₄on different coal rank was measured and fitted with Langmuir equation.From the fitting parameters,it was found that the adsorption capacity of gas decreased from high to low in order of coal rank,and the ratio of CO₂/CH4 showed a"V"shape with the increase of coal rank.The adsorption capacity of lignite and anthracite was higher than that of bituminous coal.The ratio of CO₂/CH4 decreases with the increase of pressure.(2)The displacement adsorption experiments were carried out on three kinds of rank coal samples.From the displacement amount,the displacement amount of CH₄in the displacement adsorption increased with the increase of pressure,and the trend of different rank coal was Q_Z(bituminous coal)>Q_Z(anthracite)>Q_Z(lignite).Different from the replacement amount,it is shown as?(lignite)>?(anthracite)>?(bituminous coal).The injection ratio of bituminous coal and anthracite decreases with the increase of pressure,while lignite increases first and then decreases.With the decrease of coal rank,the separation factor showed a trend of first decreasing and then increasing,showing that the adsorption capacity of CO₂on the adsorption site of anthracite was stronger than that of CH₄,and the adsorption capacity of bituminous coal was the weakest,but the three coal ranks were greater than 1.The adsorption capacity of CO₂on the adsorption site of coal sample was stronger than that of CH₄.On the whole,the displacement factor and the separation factor of each coal rank have the same trend,the displacement factors of each coal rank are all greater than 1,and the displacement factor increases with the increase of pressure.(3)After CO₂ displacement experiment,the permeability of coal decreases obviously,and the permeability changes obviously during the experiment,showing three stages of rapid decrease,rapid increase and stable.The permeability change range of lignite and anthracite is obviously larger than that of bituminous coal.As a whole,CH4 gas production increases with the increase of coal rank.The change of CH₄gas production can be divided into two stages.The first stage is before CO₂breakthrough.At this time,the gas production is mainly affected by permeability,and the relationship is lignite>anthracite>bituminous coal,showing the same trend with coal permeability.In the second stage,after CO₂breakthrough,the output of CH₄is mainly affected by the displacement effect,and the output relationship is anthracite>bituminous>lignite.The dissertation contains 25 figures,13 tables,and 85 references.