The transportation of coal-based solid waste filling slurry (CSWFS) through pipelines for underground goaf injection is essential for enhancing mine safety and promoting green, low-carbon coal mining. To address the issue of pipeline blockage caused by the suspension sensitivity of CSWFS during long-distance transportation, this study proposes the addition of the suspending agent hydroxypropyl methyl cellulose (HPMC) to transform the filling slurry into a stable suspending slurry. The mechanism by which the suspending agent modifies the rheological property of CSWFS was elucidated and verified. Firstly, an evaluation index system for the suspending state of CSWFS based on the “experimental test and theoretical calculation” was established. The values for layering degree, bleeding rate time-loss, and the corresponding average time-loss rate over 0 to 120 min of A1–A5 CSWFS were recorded as 24 mm–2 mm, 3.0–0.2%, 252.4–54.2%, and 149.6–14.6%, respectively. The concentration gradient evaluation result, C/C_A = 0.91 (≥0.8), confirmed that the suspending agent maintained a stable suspending state over time for CSWFS. Secondly, it was demonstrated that the suspending agent HPMC modified the rheological property of A1–A5 CSWFS by increasing its plastic viscosity, which strengthened the viscous resistance to particle settling, thereby transforming a semi-stable slurry into a stable one. Additionally, the formation of a spatial suspending network by the suspending agent ensures that no pipeline blockage accidents occured in practical engineering applications. Furthermore, the XRD and SEM tests were utilized to verify the microstructure of the top (T) and bottom (B) samples in A4 block. It was concluded that the type of hydration products, occurrence forms, lapping compactness, and microstructural development were consistent, ultimately forming a high-strength, dense, hardened filling block. Finally, numerical simulation confirmed that the addition of suspending agent in A4 slurry formed a comprehensive spatial suspending network and a well-structured, unified system. This is one effective approach which could contribute to addressing the technical issue of pipeline blockage during long-distance pipeline transportation.

The present research focuses on the mechanical properties and stress evolution of gas-bearing soft coal seams during drilling, which are affected by a multitude of complex factors such as high ground stress, gas pressure, and pre-existing fractures. In this study, a combination of PFC2D (Particle Flow Code in 2 Dimensions) numerical simulation and theoretical analysis is employed to investigate the borehole mechanics and fracture evolution characteristics under diverse complex conditions and to determine the factors influencing different forms of borehole failure in soft coal seams. The principal outcomes are as follows: (1) At a horizontal displacement of 0.1 m from the borehole orifice of the soft coal seam, a stress peak value of 13.9 MPa is attained; the peak value of the coal body contact force is 15.8 MPa; the peak value of the displacement is 0.008 m; and the porosity of the coal body around the borehole ranges from 0.14 to 0.35. (2) With an increase in the number of pre-existing fractures, the inclination progressively aligns with that of the pre-existing fractures. Maximum values of contact force (5.13–51.9 MPa), stress (3.19–37.2 MPa), shape dimension, and fracture angle (140–150°) are achieved under the highest lateral pressure coefficient and gas pressure (1.5 MPa). (3) The borehole energy is directly proportional to the number of pre-existing fractures, the lateral pressure coefficient, and gas pressure. The number of pre-existing fractures has the most significant impact on the damage degree, followed by the lateral pressure coefficient and then the gas pressure. (4) Two types of failure are identified: fracture-dominated failure, which is controlled by the geometric distribution of pre-existing fractures, and stress-dominated failure, wherein the failure zone gradually extends both upward and downward with an increasing lateral pressure coefficient.

Understanding stress redistribution within rock helps improve the safety and efficiency of mining projects. In order to better understand rock failure mechanism, a granite sample is prepared in a manner that facilitates shear failure along preconceived cracks. The testing process of this method employed several steps. First, the sample is loaded and then monitored in order to study the stress field associated with shear failure. Passive acoustic emissions systems are then used to monitor seismic events during the loading process. The data obtained from the test is processed by using the double-difference location algorithm. The velocity pattern of the sample is then calculated. The distribution of velocity is projected using double-difference tomography. It is shown that the sample failed along the plane where two parallel cracks were prepared. Most of the relocated events were located within or around the plane. The tomograms created from the recorded data accurately image the areas of interest within the rock samples. It is also shown that passive acoustic emissions monitoring systems coupled with double-difference tomography are capable of monitoring and forecasting the failure of rock.

Effectively controlling the adsorption and desorption of coal and mine gas is crucial to preventing harm to the environment. Therefore, this paper investigated the adsorption of coal and methane molecules from the perspective of microscopic energy through Gaussian simulation. Gaussian 09W and GaussView 5.0 software were used to construct and optimize the molecular model of four different metamorphic coals, namely lignite, sub-bituminous coal, bituminous coal, and anthracite, and their adsorption structure with methane as well as the energy, bond length, vibration frequency, infrared spectrum, and other data on the optimal structure were obtained. The binding energy of coal molecules and methane from large to small was as follows: sub-bituminous coal (7.3696 KJ/mol), lignite (6.6149 KJ/mol), bituminous coal (5.2170 KJ/mol), and anthracite (4.9510 KJ/mol). The equilibrium distance was negatively correlated with the binding energy, and the molecular structure and position of coal largely determined the binding energy. Additionally, adsorption was more likely to occur between methane molecules and hydroxyl groups. Many new vibration modes were observed during the adsorption of coal and methane molecules. This paper is of practical significance, as studying the adsorption of coal and mine gas can prevent and control mine gas outbursts and ensure safe production.

Hydraulic slotting is an effective technology that enhances gas extraction operations and prevents gas disasters in coal mines. Slotting parameters and spatial arrangements substantially affect permeability enhancements. The pressure-release range and effective extraction area under different slotting spatial parameters were obtained by constructing a hydraulic slotting pressure-release permeability and three-dimensional (3D) slotting numerical models. These models quantitatively characterized the influence rules of multiple slotting spatial arrangement parameters on the extraction efficiency at a 3D scale, clarified the interactions of multiple slottings and their combined effects on pressure relief and permeability enhancement, and verified the results using field engineering tests. The results showed that hydraulic slotting significantly alters local stress and strain distributions, creating high-strain and high-stress zones with clear spatial attenuation. The process enhances fracture development, reducing gas pressure from 1 MPa to 0.08 MPa, thereby improving extraction efficiency. Enlarging the slot dimensions from 1.5 to 2.5 m increases the gas pressure-relief efficiency by up to 41% and nearly triples the impact radius. Wider slot spacing (1.5 m to 3.5 m) and additional slots (from one to three) further reduce the borehole gas pressure by 23% to 25%, optimizing hydraulic slotting technology for practical applications.

CO₂ injection in shale reservoirs is more suitable than the conventional recovering methods due to its easier injectivity and higher sweep efficiency. In this work, Grand Canonical Monte Carlo (GCMC) simulation is employed to investigate the adsorption/desorption behavior of CH₄-C₄H₁₀ and CH₄-C₄H₁₀-CO₂ mixtures in organic and inorganic nanopores during pressure drawdown and CO₂ huff and puff processes. The huff and puff process involves injecting CO₂ into the micro- and mesopores, where the system pressure is increased during the huffing process and decreased during the puffing process. The fundamental mechanism of shale gas recovery using the CO₂ injection method is thereby revealed from the nanopore-scale perspective. During primary gas production, CH₄ is more likely to be produced as the reservoir pressure drops. On the contrary, C₄H₁₀ tends to be trapped in these organic nanopores and is hard to extract, especially from micropores and inorganic pores. During the CO₂ huffing period, the adsorbed CH₄ and C₄H₁₀ are recovered efficiently from the inorganic mesopores. On the contrary, the adsorbed C₄H₁₀ is slightly extracted from the inorganic micropores during the CO₂ puffing period. During the CO₂ puff process, the adsorbed CH₄ desorbs from the pore surface and is thus heavily recovered, while the adsorbed C₄H₁₀ cannot be readily produced. During CO₂ huff and puff, the recovery efficiency of CH₄ is higher in the organic pores than that in the inorganic pores. More importantly, the recovery efficiency of C₄H₁₀ reaches the highest levels in both the inorganic and organic pores during the CO₂ huff and puff process, suggesting that the CO₂ huff and puff method is more advanced for heavier hydrocarbon recovery compared to the pressure drawdown method. In addition to CO₂ storage, CO₂ sequestration in the adsorbed state is safer than that in the free state. In our work, it was found that the high content of organic matter, high pressure, and small pores are beneficial factors for CO₂ sequestration transforming into adsorbed state storage.