| Guizhou is known as the "southwest coal sea",with abundant coal reserves and coalbed methane resources.However,due to geological structure and coal seam occurrence conditions,most of the mining areas in Guizhou are high gas mines and coal and gas outburst mines,which have the characteristics of high gas content,difficult desorption and low permeability,and the gas disaster is serious.In view of the unsatisfactory field application of traditional coal seam physical permeability enhancement technology in Guizhou mining area,this paper is based on the theory of coal seam chemical permeability enhancement,and takes No.12 coal seam of Zhongzhichang Coal Mine in Guizhou Province as the research object.X-ray diffraction,infrared spectroscopy,acidification experiment,elemental analysis,X-ray photoelectron spectroscopy and nuclear magnetic resonance carbon spectrum experiment were carried out successively.With acid concentration and reaction time as the research focus,the best wetting modification conditions were optimized.The mechanism of acidification on the wetting modification of experimental coal samples was analyzed from the physical and chemical perspectives.The molecular structure information of coal samples was analyzed with the help of various experimental test results.On this basis,the macromolecular structure model of coal samples before and after modification was constructed.The method of combining molecular simulation and adsorption experiment was used to explore the response mechanism of acidification modification to gas in coal from macro and micro perspectives.Through the research of this paper,some progress has been madein the following aspects:1)The mineral composition of coal samples was determined by X-ray diffraction experiment.Combined with the principle of acid rock chemical reaction,hydrofluoric acid was determined as the main acid solution for acidification experiment.Taking hydrofluoric acid concentration and reaction time as the research focus,the infrared spectroscopy experiment was used to explore the variation law of wetting modification of experimental coal samples under different hydrofluoric acid concentration and reaction time conditions.The CRITIC-GRA method was used to optimize the best wetting modification conditions.The correctness of the method to optimize the best wetting modification conditions was verified by the experimental results of coal sample water absorption determination.2)Elemental analysis and infrared spectroscopy experiments were carried out to analyze the influence mechanism of acidification on the wetting modification of experimental coal samples from a chemical point of view.It was found that after acidification,the carbon and hydrogen elements negatively correlated with wettability decreased,while the oxygen elements positively correlated with wettability increased.The wettability of coal is the result of multi-factor coupling.After modification,the ratio of hydrophilic functional groups to hydrophobic functional groups in coal samples increases,indicating that the hydrophilicity of modified coal samples is enhanced.3)The surface pore and fracture structure characteristics of the test coal samples were observed by scanning electron microscopy.It was found that the surface pore and fracture development characteristics of the coal samples before modification were not obvious,and the interior was mostly filled with minerals,and the connectivity between pores was poor.After the modification treatment,a large amount of minerals on the surface are dissolved,and micro-cracks are developed at the structural defects of coal samples.The pores and micro-cracks communicate and expand with each other.The fractal dimension of coal samples before and after modification was calculated by island fractal method.It was found that the fractal dimension values of modified coal samples showed a decreasing trend under different magnifications,indicating that the surface roughness decreased and the hydrophilicity increased.4)The types and quantities of aromatic structure,aliphatic structure and heteroatom structure in the test coal samples were investigated by elemental analysis,nuclear magnetic resonance spectroscopy,X-ray photoelectron spectroscopy and infrared spectroscopy.The molecular structure model of the test coal samples before and after modification was constructed.The model optimization and density simulation of the constructed coal molecular structure were carried out,and the evolution law of potential energy with density under different periodic boundary conditions before and after modification was obtained.5)The isothermal adsorption characteristics of macromolecular structure and CH4,H2O molecules of coal samples before and after modification were calculated by Monte Carlo simulation.It was found that the adsorption isotherms of CH4 and H2O molecules on coal samples before and after acidification were in accordance with the langmuir model,but the wettability of coal samples after acidification was enhanced,and the adsorption capacity of CH4 was weakened.In the isothermal adsorption simulation of binary components,the adsorption capacity of coal macromolecular structure to H2O molecules is much higher than that of CH4 molecules,indicating that CH4 molecules xare at an absolute disadvantage in the competitive adsorption of CH4 and H2O.6)The results of isothermal adsorption test showed that the adsorption constants a and b values of acidified coal samples showed a decreasing trend,indicating that the adsorption capacity of coal samples to CH4 was weakened,which was consistent with the above molecular simulation results,and the correctness of the construction of coal macromolecular structure model before and after acidification modification was verified.Acidification can significantly improve the wettability of experimental coal samples and enhance the interaction between coal and water molecules.The wettability of experimental coal samples is negatively correlated with their gas adsorption capacity.The better the wettability of experimental coal samples,the weaker their gas adsorption capacity and the more significant the gas desorption effect. |
PDF Full Text Request