Acoustic Response Law Of Coal With Different Metamorphic And Deformed Degrees

With the increasing depth of coal seam mining,various disasters and accidents occur frequently,which has seriously affected the safe mining of coal.Seismic exploration can be used to divide gas-rich areas and tectonically deformed coal distribution,so as to achieve efficient utilization of coalbed methane and effective identification of hidden hazard-causing bodies of coal and gas outbursts.Therefore,the research on the mechanism of coal geophysical response is of great significance for guiding the safe and efficient production of coal mines.This thesis selects two sets of coal samples with different degrees of metamorphism and deformation,and uses the experimental test method to characterize the evolution of coal macromolecular structure,the characteristics of pore and fracture structure,and the characteristics of elastic parameters,and reveals the acoustic response law of coal with different degrees of metamorphism and deformation.In addition,the study also established a threedimensional molecular structure model of coal to calculate its elastic parameters,and explain the mechanism of coal and rock geophysical response from the molecular level.The thesis has obtained the following main understandings and achievements:Coal structure evolution was revealed by high-resolution transmission electron microscopy(HRTEM)and Fourier transform infrared spectroscopy(FT-IR).The experimental results of infrared spectroscopy show that the alkyl side chains and oxygen-containing functional groups are rapidly reduced under the action of coalification in low-middle rank coals.Quantitative analysis of HRTEM data showed that most of the aromatic streaks were short and curved with disordered streak orientations in low-middle rank coals.With an increasing coalification degree,the order of the aromatic ring structure continued to increase,the average interlayer spacing of the aromatic rings decreased,and the average layer size increased.Based on X-ray computed tomography technology,the structural characteristics of coal rock pores and fractures with different coal body structures were studied.The 3D reconstruction of pores,fractures,coal matrix and inorganic mineral components was carried out using the optimal segmentation method.The real fracture shape is approximated to the maximum effect by dividing the fracture space unit by point connectivity.The study found that the pore and fracture structure characteristics of undeformed coal and cataclastic coal are not much different;under the action of tectonically deformed stress,wrinkle coal develops a large number of pores and fracture of different sizes;under the action of tectonic stress,granulitic coal has good pore connectivity.In addition,in the undeformed coal and cataclastic coal,there are many pores and fracture developed along the bedding direction as the degree of deformation continues to intensify.The existence form of pores and fracture in granulitic coal and wrinkle coal gradually evolves to be dominated by vertical cleats.The elastic parameters of coal with different degrees of metamorphism were measured by ultrasonic testing technology.The correlation between the ultrasonic wave velocity and the molecular structure differs in different coalification stages.In the first stage(Ro = 0.6%-～1.6%),the ultrasonic wave velocity of coal keeps decreasing during the maturation process due to the aromatization of the coal molecular structure and the cleavage of alkyl side chains.In the second stage(Ro = 1.6%-～3.0%),the average layer size of the coal molecular structure increases and the average interlayer spacing decreases,which makes the wave velocity of coal increase continuously.The evolution of the molecular structure of coal is an important influencing factor for its elastic properties.The irregular parts(alkyl side chains and functional groups)play a major role in elastic ultrasonic velocity,followed by the average layer size and the average interlayer spacing of aromatic layers.The elastic properties of anthracite are studied by molecular dynamics simulation method,and the experimental and calculated values of P-wave velocity and elastic modulus are relatively close to the experimentally measured values and the simulated calculated values.Based on the ultrasonic testing technology,undeformed coal,cataclastic coal,granulitic coal,wrinkle coal and reshaped mylonitic coal were measured.Combined with the development characteristics of pores and fracture,the elastic distribution characteristics and changing laws of different coal structure samples were studied.The study found that there is a good negative correlation between the porosity of coal samples and the elastic wave velocity value,and the number of pores and fracture is not the main factor determining the elastic parameters.Under the action of tectonic stress,the pores and fracture of the undeformed coal continue to develop,and the elastic parameter values continue to decrease.The degree of orientation of pores and fractures has an important influence on the anisotropy of elastic parameters of the coal body.In addition,the value of elastic parameters can be qualitatively determined by the development of bedding and cleats in tectonically deformed coal.