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The development of pore structure in coal reservoirs determines the adsorption performance of coal gas. The pore structure of three coal samples with different degrees of metamorphism, namely long-flame coal, coking coal and anthracite, was tested by low-temperature liquid nitrogen adsorption experiments. The pore structure was quantitatively characterized based on fractal theory, and the effect of the pore structure on the methane adsorption properties of coals with different degrees of metamorphism was analyzed in depth in combination with the methane isothermal adsorption experiments. The results showed that the degree of metamorphism and the pore fractal dimension D1 showed a “bathtub” variation, and a linear negative correlation with D2; while the specific surface area and pore volume of the coal sample were positively correlated with the adsorption constant a. The larger specific surface area and pore volume, the stronger the adsorption capacity of coal. With the increase of pore fractal dimension D1, the adsorption constant a presents an approximate linear growth trend. It can be seen that the less smooth the pore structure of coal, the larger the specific surface area will be, so that the ultimate methane adsorption capacity of coal will also increase.

In order to study the influence mechanism of effective stress on permeability, the coal permeability test experiment under simultaneous loading of axial and confining pressure was carried out using the self-developed coal-rock gas adsorption-desorption-seepage platform. The mean effective stress parameter is introduced to characterize the loaded state of the coal body. At the same time, in order to eliminate the influence of the individual differences of the specimens, the effective stress sensitivity coefficient is defined, and the control mechanism and variation law of the effective stress on the permeability of the coal body are discussed in depth. The results show that when the gas pressure remains constant, the coal permeability decreases gradually with the increase of the effective stress, and its variation law conforms to the negative exponential relationship. With the increase of effective stress, the sensitivity coefficient gradually decreases, and it conforms to the power function relationship. At the same time, a mathematical model of coal sample permeability and effective stress is constructed based on the sensitivity coefficient.

The pore distribution characteristics of coal not only directly affect the gas storage and migration ability in coal seam, but also directly affect the development process of physical adsorption and chemical reaction between coal and oxygen. Therefore, in-depth study of the pore distribution characteristics of coal is conducive to the reasonable classification and evaluation of coal reservoirs, and then study and analyze the laws of gas storage and migration in coal seams and the low-temperature oxidation reaction mechanism of coal, improve the accuracy of gas content prediction and gas extraction efficiency, and describe the process of coal spontaneous combustion in detail. We have systematically summarized the current research theories and methods of pore distribution characteristics of coal through a large number of relevant literature investigations, and compared and analyzed various research theories and methods, pointed out their respective advantages and disadvantages. Finally, it is proposed that the next step can be carried out from three directions: accurate measurement of micro-pores and reasonable characterization at full scale, research on microscopic effects of coal pores, and establishment of accurate coal medium models.

Based on the systematic investigation, this paper summarizes the four important development stages of the prediction technology of mine gas emission in China from 1950s to now. It focuses on the basic principles, application scope, advantages and disadvantages of the source based prediction method, mine statistical method, gas geological mathematical model method, grey prediction method, neural network prediction method and combination prediction method. The main problems of each prediction method are analyzed in detail with the field application status. Finally, centering on the development goals of mine mechanization and intelligentization, three technological breakthroughs are proposed: improving the scientific selection of predictive parameters of source separation, promoting the modularization and integration of gas geological model prediction technology, and establishing information-based high-end fusion model, which points out the direction for future research on gas emission prediction technology.

Coal mine safety standard is the basis of ensuring coal mine safety production, mine ecological environment safety and employees’ safety and health, preventing coal mine accidents and occupational hazards, and is also an important support for the implementation of coal mine safety production supervision and the establishment of safety development concept. In order to deeply understand the current situation of China’s coal mine safety standards, 853 current effective coal mine safety standards were collected and analyzed from the perspectives of standard level and nature, standard release year, standard for risk category, etc. The problems such as weak binding force of standards in current standard work were pointed out, and suggestions such as paying attention to overall planning and top-level design were proposed for reference to improve the coal mine safety standard work in China.