Coal and gas outbursts are geological disasters occurring in the process of coal mining that can cause serious casualties and economic losses, among which CH₄ is the main component of coal mine gas. However, there are still many coal seams around the world that are dominated by CO₂. Although the frequency of CO₂ gas outburst accidents is relatively low, CO₂ outbursts are very violent, notably difficult to control and highly dangerous. The application of hydration curing technology to reduce the pressure and gradient of CO2 gas in the coal can effectively reduce the occurrence of coal and CO₂ outburst. Accordingly, in this paper, experimental studies on the growth kinetics of CO₂ hydrate with three driving forces (2, 2.5, 3 MPa) were carried out under four different coal particle sizes (C1: 0.425–0.850 mm, C2: 0.250–0.425 mm, C3: 0.180–0.250 mm, C4: 0–0.180 mm) to obtain kinetic parameters such as gas consumption, growth rate, and heat of decomposition during the synthesis of CO₂ hydrate. The results show that the hydrate nucleation time in the same particle size system does not follow the same decreasing trend with increasing driving force. Gas consumption of CO₂ hydrates in the same particle size system increased with increasing driving force, and there exists a critical value regarding the effect of the driving force on CO₂ hydrate generation in coal particles with the particle size. Under the same temperature conditions, increasing the driving force in the particle size system could increase the CO₂ hydrate growth rate. With decreasing coal particle size and increasing driving force, the promoting effect gradually exceed the inhibiting effect, which promote CO₂ hydrate formation. Through linear fitting, an equation of the average growth rate of CO₂ hydrates versus the driving force for the C1-C4 systems is fitted to provide a reference to predict the average CO₂ hydrate growth rate. In the same medium, with increasing driving force, more heat is required for complete decomposition, which remains relatively stable, and the heat of decomposition of CO₂ hydrates is the highest in the C1 medium, indicating that the presence of CO₂ hydrates in the C1 system represents the most stable state.

As a critical technical issue, gas extraction borehole sealing significantly restricts the effects of gas extraction. Polymer-modified cement-based composite (PMCC) sealing materials were developed to improve the sealing effect of gas extraction drilling. In this study, a self-built mechanical property and permeability test platform for grouting-based cemented coal bodies was used to test the viscosity, gelation time, and mechanical properties of PMCC sealing materials and the permeability of cemented coal bodies. Through the obtained relevant results, it was demonstrated that the material viscosity of PMCC sealing materials and the permeability and compressive strength of cemented bodies are under the influence of additive ratios. Moreover, the viscosity of sealing materials was found to be linearly related to the gelation time. In particular, the higher the viscosity, the shorter the gelation time. Additionally, on one hand, it was found that the viscosity of such sealing materials is positively correlated to the compressive strength of cemented coal bodies. On the other hand, it forms a negative correlation with their permeability. Based on relevant analysis outcomes, it was deemed that the sufficient hydration reaction and the interspace reticulate microstructure formed by the polymer of PMCC sealing materials allow the cemented coal body to achieve high compressive strength and low permeability.

Understanding mechanical behaviors of a methane hydrate–coal mixture are important for its associated application in coal and gas outburst prevention. A triaxial compression apparatus for a specimen of the methane hydrate–coal mixture was developed to measure its strength and deformation properties. Triaxial compression tests were performed on coal briquette samples under different confining pressures and methane hydrate saturation. Strain softening behavior of the methane hydrate–coal mixture can be identified for all the specimens under various conditions. The larger the methane hydrate saturation or confining pressure, the larger the peak strength, elastic modulus and peak strain. Mathematical relationships for correlating the peak strength with the methane hydrate saturation or confining pressure were also proposed.

Coal and gas outbursts are one of the main factors that restrict access to high-quality coal, and the adoption of gas hydration solidification technology is expected to reduce the chance of such accidents. In this study, experiments were conducted on the kinetics of CH₄ and CO₂ hydrate formation in four coal particle size systems (C1:0.425-0.850 mm, C2:0.250-0.425 mm, C3:0.180-0.250 mm, and C4:0.150-0.180 mm). An experimental apparatus for high-pressure visualization of gas hydrate generation was used to obtain kinetic parameters such as gas consumption and the average growth rate during hydrate formation. The results showed that gas consumption and average growth rate of CO₂ hydrate decreased with decreasing coal grain size, while gas consumption and average growth rate of CH₄ hydrate decreased and then increased slightly with decreasing coal grain size, indicating that larger coal grains were beneficial to hydrate formation within a certain particle size range. The results of this research study are expected to provide an experimental reference for the development and application of technology for the solidification of gas hydrates to limit surges.

The microfeatures of coal mine methane (CMM) hydrates, synthesized with three gas samples (CH₄/C₂H₆/N₂, G1 = 43 : 47 : 10, G2 = 60 : 30 : 10, and G3 = 74 : 16 : 10) in a self-made transparent high-pressure cell at 275.15 K and 5 MPa were investigated using Raman spectroscopy. As a discriminator, the vibrational band frequencies in the C–C regions of the recorded hydrate Raman spectra for C₂H₆ show that G1∼G3 hydrates are structure I. The three principal parameters used to study the microfeatures of the model CMM hydrates, including cavity occupancies, hydrate guest compositions, and hydration numbers, were calculated. The large cavity occupancies for C₂H₆ constantly decrease from 85.12 to 79.32%, while the small cavity occupancies for CH₄ have a continuous increase from 73.75 to 96.42%. However, CH₄ competes with C₂H₆ on entering the large cavities for their large cavity occupancies of 12.79–17.31%. The cavity occupancies of N₂ are less than 1.2%. The hydrate composition calculations show that the molar fractions of C₂H₆ are the maximum. The hydration numbers range from 6.221 to 6.00. Based on the hydrate guest compositions and hydration numbers, the molecular formulas of the three CMM hydrates are presented.