To analyze the relationship between macro and meso parameters of the gas hydrate bearing coal (GHBC) and to calibrate the meso-parameters, the numerical tests were conducted to simulate the laboratory triaxial compression tests by PFC3D, with the parallel bond model employed as the particle contact constitutive model. First, twenty simulation tests were conducted to quantify the relationship between the macro–meso parameters. Then, nine orthogonal simulation tests were performed using four meso-mechanical parameters in a three-level to evaluate the sensitivity of the meso-mechanical parameters. Furthermore, the calibration method of the meso-parameters were then proposed. Finally, the contact force chain, the contact force and the contact number were examined to investigate the saturation effect on the meso-mechanical behavior of GHBC. The results show that: (1) The elastic modulus linearly increases with the bonding stiffness ratio and the friction coefficient while exponentially increasing with the normal bonding strength and the bonding radius coefficient. The failure strength increases exponentially with the increase of the friction coefficient, the normal bonding strength and the bonding radius coefficient, and remains constant with the increase of bond stiffness ratio; (2) The friction coefficient and the bond radius coefficient are most sensitive to the elastic modulus and the failure strength; (3) The number of the force chains, the contact force, and the bond strength between particles will increase with the increase of the hydrate saturation, which leads to the larger failure strength.

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.

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.

Methane hydration is a safe, stable and environmentally friendly technology to bind and utilize excess coalbed methane gas. However, a limiting factor of the commercial application of coalbed methane hydration technology is the sluggish hydration reaction kinetics of methane hydrate formation, which needs to be improved. In this work, different micro-particle suspensions are prepared from an initial solution containing gellan gum and L-tryptophan, along with varying mass fractions of NiMnGa, Cu and carboxylated multi-walled carbon nanotubes, and their influence on the reaction kinetics in methane hydrate formation is examined. The results show that the formation of methane hydrate is enhanced by these micro-particles to varying degrees. Micro-particles show a synergistic solubilization effect with L-tryptophan and gellan gum at 6.2 MPa. The induction times of 1 wt.% NiMnGa system and 1 wt.% Cu system are the shortest. The 2 wt.% NiMnGa system has a pronounced impact on methane gas consumption, and the average gas consumption rates of the 0.1 wt.% Cu system and 1 wt.% NiMnGa system are faster. However, as the concentration of Cu micro-particles increases, both gas consumption and the average generation rate exhibits a linear decrease. This work offers valuable recommendations for choosing the experimental settings, micro-particle types and concentrations. We also lay the groundwork for the practical and sustainable application of coalbed methane storage and transportation technology employing the hydrate approach. Document Type: Original article Cited as: Wu, Q., Tang, T., Zhao, Z., Li, L., Elhefnawey, M., Zhang, B. Influence of micro-particles on gas hydrate formation kinetics: Potential application to methane storage and transportation. Advances in Geo-Energy Research, 2023, 10(3): 189-199. https://doi.org/10.46690/ager.2023.12.05