Coal Seam Water Injection Research Articles

Mechanism of gas bubble migration in meso fissure of coal water injection based on CT images

Coal seam water injection is a key technology for achieving the co-mining of coal and coalbed methane. In response to the unclear mechanism of bubble migration in meso fissures that currently dominate the displacement of coalbed methane, this paper proposes a numerical simulation method based on CT images for exploring the migration mechanism of gas bubbles in the meso fissures of coal water injection. The meso fissure geometric modeling of coal water injection was reconstructed using CT scanning image analysis technology. Based on level-set theory, a bubble migration model under a two-phase fluid environment was constructed, and the influence characteristics of different fissure structures on bubble migration were explored. Furthermore, the mechanism of gas bubble migration within the meso fissures of coal water injection was revealed. Results show that the shape of the bubble with a radius of 0.03 mm oscillates obviously in the fissure structure with a length–width ratio of 1.3. The smaller the fissure structure diameter is, the larger the structure length–width ratio is, and the easier the bubble is to form gas resistance. Meanwhile, the larger the curvature of the fissure structure, the greater the contact angle between the bubble and the wall, and the easier it is for the bubble to detach from the wall. During the migration process, the size of the bubble constantly changes. With the increasing length–width ratio and width of the fissure structure, the equivalent radius of the bubble initially increases and then decreases. A negative correlation function is observed between bubble size and flow velocity. At low flow velocity, the volume of the bubble can increase by 18.17 %, and as the flow velocity increases, the volume of bubble can decrease by 54.53 %. In the bubbles aggregation process, an exponential function relationship can be observed between the bubble leading edge position and the bubbles spacing with a negative correlation. The influence of fissure structure on the bubbles is less than the interaction among bubbles. These results provide a theoretical basis for the efficient and increased extraction of coalbed methane.

Wetting characteristics and kinetic behavior of amphoteric ionic surfactant on the microscopic “solid-liquid” interface of coal - A case study

This study investigates the wetting characteristics and kinetic behavior of amphoteric ionic surfactant on the microscopic “solid-liquid” interface of coal based on low-field NMR experiment combined with molecular dynamics simulations, since the basic research on the wetting mechanism of coal seam water injection is not systematic and in-depth enough, which restricts the further development of dust control technology in mines. Firstly, the wetting characteristics of amphoteric surfactant (CAB-35) on coal with different degrees of metamorphism and the dynamic spreading of the wetting range were obtained by low-field NMR experiment, revealing the microscopic wetting law at the “solid-liquid” interface of coal; In order to establish the numerical simulation operation system of interfacial wetting of coal macromolecular structure characteristics based on coal surface chemical parameters and using molecular dynamics theory, the wetting dynamic behavior of amphoteric ionic surfactants on coal dust is studied from microscopic perspective, and the law of influence of surface chemical characteristics on coal wetting characteristics is obtained, so as to improve and enrich the theoretical system of coal wetting, in order to promote the development and enhancement of coal mine water injection and wetting and dust control technology and clean production, and realize the clean production of mines.

Optimization and Application of Water Injection Process in Gas-Bearing Coal Seam

Coal seam pre-drainage technology is widely used to prevent and control gas in China’s high-gas coal seams, and upward drilling is a safe and reliable technology. Using the Luling Coal Mine as the study location, according to the actual situation of the site, a layer-through drilling process was proposed. Relying on a cross-layer extraction borehole, coal seam water injection efficiency extraction and high-efficiency water injection dust prevention can be performed in the later stage of borehole extraction, enabling one-hole multi-purpose and “gas-powder” integrated prevention and control. In order to study the “stress-seepage” coupling characteristics of the coal around the borehole, a numerical simulation of the coal seam water injection process was conducted. Based on the simulation results, a field test of water injection in coal seam upward drilling was performed. The field monitoring data show that the water injection and water content of the coal seam were increased by about 3.07 m3 and 0.69%, respectively, compared with the traditional water injection process. The water injection effect is remarkable, which is of great significance to ensure the safe and efficient production of the mine.

Study on the Fractal Characteristics and Seepage Properties of Channels Filled by Coal Particles.

Studying the seepage process in fracture channels (where coal particles are deposited) is of great significance for improving the performance of both on-site coal seam water injection and dust reduction technology. Through a self-developed simulation experiment of water-borne coal particle migration and accumulation and computer graphics, we investigated the influencing factors of particle accumulation in water injection and their influence law on seepage, discussed the interaction relationship between the fractal structure of coal and the characteristics of accumulated coal particles, and established a new fractal model of fracture permeability based on different particle accumulation states. The results show that the seepage velocity and the particle size jointly affect the migration and accumulation process of water-borne coal particles. When the coal particle size is constant and the seepage velocity increases, then the output of the coal powder increases, the deposition decreases, and the structure fractal dimension D3 of fractures decreases. At the same seepage velocity, with the increase of the coal particle size, the output of coal powder decreases, the deposition increases, and the structure fractal dimension D3 of fractures increases. In addition, the amount of coal powder produced in the intermittent water injection process is smaller than that produced in the continuous water injection process, more easily leading to accumulation. The variation law of the theoretical permeability with porosity remains consistent for different particle accumulation states: with the increase of porosity, the structure fractal dimension D3 of fractures decreases, while the theoretical permeability increases. The above research results can provide a theoretical basis for reducing the seepage damage of coal under the particle blocking effect.

Characterization of the wetting properties of ionic liquids on lignite surfaces: Molecular dynamics simulations

In order to study the wetting mechanism of imidazole ionic liquids on lignite surfaces, molecular dynamics simulations combined with quantum chemistry were used to analyze the molecular level of 1-butyl-3-methylimidazolium chloride salt ([Bmim][Cl]), 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]), 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF4]) adsorption and wetting processes on the surface of lignite molecules. The electrostatic potentials and frontline orbital energy levels of [Bmim][Cl], [Bmim][BF4], and [Emim][BF4] and coal molecular models were analyzed to determine their nucleophilic and electrophilic regions based on the density flooding theory (DFT) in Gaussian 09 program. The water-coal system and ionic liquid–water-coal system were constructed from a microscopic perspective by dynamics simulations, and the relative concentration distribution of each system in the z-axis direction, the diffusion coefficients of water molecules in each system, and the non-bonding interactions of each system were analyzed. The results showed that [Emim][BF4] has the largest front-line orbital energy polarity and the best wettability for coal. [Emim][BF4] was more likely to interact with water molecules to form hydrogen bonds and had the highest number of hydrogen bonds with water molecules. The molecular dynamics simulations revealed that the adsorption of ionic liquids on the surface of lignite increased the adsorption thickness between water-coal systems, which led to a more extensive diffusion of water molecules, which increased the negative interaction energy between water-modified lignite and further improved the hydrophilicity of lignite, with [Emim][BF4] molecules having the strongest ability to improve the hydrophilicity of lignite. These results further demonstrated that [Bmim][Cl], [Bmim][BF4], and [Emim][BF4] can significantly improve the wettability of coal dust, which was important for improving the effect of coal seam water injection and reducing the dust concentration.

Characterization of water migration behavior during spontaneous imbibition in coal: From the perspective of fractal theory and NMR

The spontaneous imbibition (SI) of water plays a crucial role in determining the wetting effect of water injection in coal seams. It is significant to investigate the flow behavior of water in coal during the SI. Contact angle measurement, SI experiment, and low-field nuclear magnetic resonance (LF-NMR) tests have been conducted to measure the properties of coal from different regions of China. The mass change of the coal by SI is related to the square root of time divided into three-stage linear functions in which the slope represents the imbibition rate of coal. The imbibition rate decreases with the increased SI time. The contact angle of bituminous coal is smaller than that of anthracite and is negatively proportional to the SI rate and capacity index C. Water is primarily stored in the adsorption and seepage pores, and little in microfractures. It shows that the fractal dimensions of the partial free pore (Db) and total pores (D) decline in a form of power law, while the fractal dimension of the free pore (Dz) declines irregularly. D-10 and D10 are strongly linear with the T2 spectrum area of adsorption pores, seepage pores, and microfractures, respectively. It indicates that the low-probability measurement area can represent the adsorption pores, and high-the probability measurement area represents seepage pores and microfractures. Adsorption pores play an important role during SI (DSI). The difference between the amplitude increments of adsorption pore and that of seepage pores/microfractures is the key factor affecting multifractal parameters of T2 spectra. The linear relationship between H and Db reveals that water preferentially enters a pore with lower roughness and better connectivity DSI. The process of SI has been divided into three stages in terms of SI rate. The transport process of water within the coal at different stages has been discussed as well. The results of this work are of great significance for optimizing the coal seam water injection and reducing the risk of underground coal mine disasters.

Imbibition behavior of water on coal surface and the impact of surfactant

Coal seam water injection is vital in mitigating dust pollution in coal mining operations. To investigate water imbibition and adsorption behavior on the coal surface following injection into coal seams, as well as the impact of surfactants, coal particles with sizes of 6–8 mm, 3–5 mm, and 0.4–0.85 mm were selected from the Dongtan Coal Mine in Shandong Province, China. Coal particle imbibition experiments were designed for coal particles at varying surfactant concentrations and temperatures, and molecular simulation was employed to examine the micro adsorption behavior of water within coal rock pores. The findings indicate that smaller coal particles exhibit significantly higher water absorption capacity compared to larger particles when ample water supply is present. This suggests that coal pore water absorption is inherently limited. Moreover, elevated formation temperatures hinder the wetting process of water injection. Importantly, introducing surfactants leads to the blockage of coal fractures, constriction of fracture channels, and restriction of the effective wetting range of coal seam water. Furthermore, the influence of sodium dodecyl sulfate is greater than that of cetyltrimethylammonium bromide. In low-temperature environments, surfactants exert a more prominent inhibitory effect on water injection wetting. These research findings provide valuable theoretical guidance for coal seam dust prevention efforts and water injection technology.

Experimental study on the effects of ultrasonic excitation on pore structure of water-bearing coal

Coal seam water injection is one of the main coal mine dust control measures. To study the effects of ultrasonic excitation on the pore structure of water-bearing coal in depth, ultrasonic excitation experiments were conducted with varied variables including ultrasonic excitation time, ultrasonic power, and fluid pressure on coal. The effects of sodium dodecyl sulfate (SDS) treatment and ultrasonic excitation were also compared. The coal samples treated under different conditions are characterized by low-temperature nitrogen adsorption and scanning electron microscopy (SEM) respectively for the quantitative analysis of pore volume and specific surface area and qualitative analysis of surface pore and fracture structure. The results show that ultrasonic excitation can significantly increase the pore volume and specific surface area of coal and damages the inner wall surfaces of the pore to different extents, making the pore inner surfaces rougher. However, the effect of ultrasonic excitation becomes weaker after the pore volume increases to a certain extent, resulting in more uniform pore size and volume distributions. Ultrasonic excitation time affects the pores with smaller size more significantly, and there is a time threshold effect. The volume and specific surface area of large pores and fractures show limited responses (or increases) to as the excitation time increased. The energy is mainly used for the fracturing and expanding the pores with smaller size. The effect of ultrasonic excitation on pore expansion is more obvious under the fluid pressures lower than 4 MPa. High fluid pressures weaken the fracturing and expanding effect of ultrasonic excitation on the pore structure of water-bearing coal. The ultrasonic power threshold effect is also observed. Once exceeding a certain value, further increasing the ultrasonic power does not dramatically affect the pore structure of water-containing coal. Ultrasonic excitation can enlarge the primary pores and fracture and generate secondary pores and fracture in coal. In contrast, the 0.85% SDS treatment is only able to clean the primary small pores, and no new pore structures are formed.

Experimental Study on Migration and Intrusion Characteristics of Pulverized Coal in Propped Fractures

Aiming at the problem of pulverized migration and plugging propped fractures during coal seam fracturing, we experimentally studied the pressure changes and pulverized coal blocking characteristics with deionized water and solutions of three surfactants including 1227 (C21H38ClN), SDS (C12H25SO4Na) and TX-100 (C34H62O11). A device capable of visualizing propped fractures was established, and simulation experiments were conducted with solutions of different surfactants at different injection flow rates. The obtained images were binarized and analyzed to quantify the pulverized coal blockage degrees of facture under different conditions. The experimental results show that: (1) The higher the injection flow rate, the higher the inlet pressure. (2) All three surfactants can lower the injection pressure, as compared with water alone. SDS decreases the injection pressure more obviously at low injection flow rates, and the other two perform better at high injection flow rates. (3) Similar to their effects on inlet pressure, the ratio of pulverized coal in SDS solution is lower at low injection flow rates, while TX-100 and 1227 solutions show lower ratios of pulverized coal at high injection flow rates. Our work has provided a theoretical support for coal blockage removal and pressure reduction in propped fractures during coal seam fracturing to improve coal seam permeability and further improves the dust prevention effect of coal seam water injection.

Study on water seepage law of confined coal body and optimization of water injection parameters

To optimize water injection parameters, it is necessary to understand the water seepage characteristics of coal and establish an evaluation method for the coal seam water injection effect. Using low-field nuclear magnetic resonance (NMR) technology and a peripheral loading pressure experimental system, real-time Carr-Purcell-Meiboom-Gill sequence tests were conducted on coal samples under different water injection schemes. The dynamic migration characteristics of pressurized water in coal under a constant water injection pressure and injection flow were studied. The results showed that under a fixed water injection pressure, the change in water content with injection time was in concordance with first-order kinetics, indicating that the process is controlled by diffusion. Combined with the fitting results of the wetting rate constant and water injection pressure, the best water injection pressure was obtained. Moderate water injection flow, an increase in water injection volume, and an extension of the water injection time can improve the wetting effect. Under constant water pressure, water seepage in the coal includes two processes: the rapid migration of free water to the pore fractures of coal and the spontaneous water absorption process in the coal. Under constant water flow, the water seepage process in the coal is consistent with the Boltzmann equation. Based on the time constant and inflection point of the time growth obtained by the Boltzmann equation, the seepage process was divided into the water inflow, water transportation, and water adsorption stages. The peak area of the adsorbed water is proportional to the mass of coal moisture. This relationship can realize the mutual conversion between the NMR water signal quantity and moisture content in coal.

Effects of ultrasonic and surfactant coupling treatment on the wettability of coal

Coal wettability has an important influence on the permeability of water-injected coal seam. The coal seam water injection effectively improves the ultrasonic excitation effect, and the surfactant can mitigate the water lock effect produced during water injection. To study the effect of ultrasonic and surfactant coupling treatment on the wettability of coal, the ultrasonic excitation fracturing system was used to perform excitation experiments on different coal samples. The coal microscopic properties were determined, and the coal wettability was characterized based on the contact angles. The experimental results demonstrate that the general decrease in the content of hydrophilic groups after the coal was coupled with ultrasonic and surfactant compared to the alkyl polyglycoside (APG) treatment, and the decrease in the content of oxygen-containing functional groups was more obvious; the pore size, pore volume and specific surface area (SSA) of coal all increased to different degrees, especially for pore size and pore volume; under the treatment of ultrasonic or surfactant, the coal wettability was enhanced, while the wettability was further enhanced by the coupling treatment; when ultrasonic was coupled with the surfactant, an advantageous complementary effect could be formed, which improved the final effect of the coupling treatment.

Discussion on Dust Control Technology of Coal Mine Integrated Excavation Face

Coal is an important energy source in our country, and coal mine dust seriously endangers production safety and occupational health and safety, so it is necessary to take effective technical measures to prevent and control the coal mine. According to the main technical ways of dust prevention and control, the technical measures such as improving dust-proof water, strengthening coal seam water injection, carrying out high-pressure external spray, dust control and dust extraction purification, air flow purification and individual protection are discussed respectively. Finally, the technical measures of dust prevention and control in the future are prospected, and several technologies and equipment should be emphasized to break through.

Study on Coal Wettability under Different Gas Environments Based on the Adsorption Energy.

Coal seam water injection is a kind of comprehensive prevention and control measure to avoid gas outburst and coal dust disasters. However, the gas adsorbed in the coal seriously influence the coal-water wetting effect. With the deepening of coal seam mining, the gas pressure also gradually increases, but there is still a lack of in-depth understanding of the coal-water wetting characteristics under the high-pressure adsorbed gas environment. Therefore, the mechanism of coal-water contact angle under different gas environments was experimentally investigated. The coal-water adsorption mechanism in pre-absorbed gas environment was analyzed by molecular dynamics simulation combined with FTIR, XRD, and 13C NMR. The results showed that the contact angle in the CO2 environment increased most significantly, with the contact angle increasing by 17.62° from 63.29° to 80.91°, followed by the contact angle increasing by 10.21° in the N2 environment. The increase of coal-water contact angle in the He environment is the smallest, which is 8.89°. At the same time, the adsorption capacity of water molecules decreases gradually with increasing gas pressure, and the total system energy decreases after the coal adsorbs gas molecules, leading to a decrease in the coal surface free energy. Therefore, the coal surface structure tends to be stable with rising gas pressure. With the increase in environmental pressure, the interaction between coal and gas molecules enhances. In addition, the adsorptive gas will be adsorbed in the pores of coal in advance, occupying the primary adsorption sites and thus competing with the subsequent water molecules, resulting in a decline of coal wettability. Moreover, the stronger the adsorption capacity of gas, the more obvious the competitive adsorption of gas and liquid, which further weakens the wetting capacity of coal. The research results can provide a theoretical support for improving the wetting effect in coal seam water injection.

Analysis of the effects of coal facture shape factor on water seepage based on computerized tomography (CT) 3D reconstructed artificial fractures

Seepage during coal seam water injection occurs in coal fractures, and thus the properties of the fractures directly affect the water injection effect. Yet, the current research on the influence of fractures with different shapes on seepage is mostly based on the construction of idealized models, which is different from the actual coal structure. Therefore, a structural model containing five types of fractures, spherical fracture, tubular fracture, slot-shaped fracture, slit-shaped fracture, and flat facture, is conducted in CT images of real coal samples based on computerized tomography (CT) scan, 3D reconstruction and artificial fracture. The water injection seepage in the model was simulated using the Navier-Stokes equation, and the relationships between the fracture parameters (equivalent diameter, volume, coordination number, and maximum Feret diameter) and shape factor were calculated. The results show that the seepage velocity distributions in the fractures of different shapes are different. The seepage velocity increases with the increase of shape factor with the spherical fracture excluded. Compared with those of the model without the artificial fracture, the cross-sectional seepage velocity and permeability of the model with artificial fracture added increase by 2.9893–11.9923% and 0.8058–3.0267%, respectively. The number of fractures gradually decreases with the increase of shape factor, but other parameters including equivalent diameter, maximum Feret diameter, and coordination number tend to increase. The increases in the maximum Feret diameter and coordination number can improve the model connectivity, which is conducive to the continuous advance of seepage. The research results are helpful to evaluate the contribution of different shape fractures to coal seepage and provide theoretical guidance for coal seam water injection engineering.

Competitive adsorption effect during spontaneous external water imbibition in loaded gas-bearing coal and application of a normalized desorption rate model

The competitive adsorption effect of water and gas during the coal seam water injection process plays an important role in improving the coalbed methane (CBM) drainage rate of coal seams that do not meet the standards for gas drainage. However, competitive adsorption mainly occurs in the spontaneous imbibition process for coal seam water injection, which is not clear under the dual action of ground stress and gas pressure during spontaneous imbibition process. Here, some spontaneous imbibition experiments under isobaric water addition and isobaric desorption conditions are conducted using a spontaneous imbibition experimental system. The obtained results are as follows. (1) The accumulated replacement gas degree is negatively correlated with the gas pressure, which shows that the principle of spontaneous imbibition can be adopted to improve the gas drainage rate for coal seams whose gas drainage is not up to standard. (2) For spontaneous imbibition with loading stress does not change the adsorption pore structure, the average seepage pore diameter is negatively correlated with the wetting range, while the wetting range is positively correlated with the competitive adsorption effect. (3) The spontaneous imbibition process is a process of effectively wetting the pores of gas-bearing coal, which can effectively increase the pore water content and wetting uniformity. (4) A normalized desorption rate model of the relative replacement degree during spontaneous imbibition is established based on the dimensionless method. This study provides a technical method for improving the gas drainage rate for the drainage of substandard low-permeability coal seams.

Experimental study on the influence of acid fracturing fluid on coal wettability

With the continuous improvement of mechanized mining intensity, dust has seriously threatened the safety of mine production and the health of underground workers. Coal seam water injection is one of the effective means to moisten the primary coal dust in the coal body. Through testing by the surface tension tester, contact angle meter, FTIR, low-temperature liquid nitrogen adsorption, and SEM, the impact of acid fracturing fluid which can be used for coal seam water injection on the wettability and pore structure of coal was studyed. The results showed that HCl and CTAB had good synergistic acidification effect, which can effectively reduce the surface tension of CTAB by 10 ∼ 30 mN/m. Also the contact angle between the solution and the coal sample is significantly affected by the acidity of the solution. However, the impact of the acid fracturing fluid varies for coal with differing levels of metamorphism and mineral content. For low rank bituminous coal, the contact angle decreased by 39.55° after contact with the sample surface for 1 s, and the solution was completely immersed in the coal body after 5 s. The absorbance of hydrophilic functional groups of coal becomes stronger after treatment with acid fracturing fluid, which is conducive to upgrading the wettability of coal. Meanwhile, the acid fracturing fluid increases coal’s connectivity and average pore diameter, which in turn influences the wettability of coal. Exploring the influence of acid-based fracturing fluid on coal can provide guidance for improving the wettability of coal, reducing dust concentration and optimizing the underground working environment.

Study on time effect of acidified pulverized coal micro components and discussion on mathematical correlation of influencing factors

In this paper, 3 % HCl + 3 % CH3COOH + 3 % HF + 2 % KCl complex acid is used to dissolve pulverized coal, and the industrial analysis method, XRD and SEM experiments were used for testing. The results show that the relative contents of M, Fc, and V in coal samples increase with the dissolution time, the A decreases, the content of elements C and O increases, and the content of elements H, N, and S decreases. The effect of composite acid on the surface morphology of coal is significant. It can effectively remove the particles on the coal surface. According to the theory of factor analysis, the industrial component and element is reasonably analyzed, and the weight coefficient of industrial parts is greater than the element factor. This study provides theoretical support for the time effect of coal mine gas drainage and coal seam water injection.

Synthesis and properties of wettability-increasing agent with multi-layer composite network structure for coal seam water injection

To improve the efficiency of water injection and reduce the amount of dust from the source. In this paper, a wettability-increasing agent with a multilayer composite network structure was prepared. The modified sodium carboxymethyl cellulose (CMC) and linear micelles were rearranged and combined by using the optimal ratio experiment. Through proton nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction analysis, the functional-group structure and crystallinity of the modified CMC were investigated. The elemental compositions and surfaces of C1 and C2 were examined via energy dispersive spectrometer, optical microscopy, and transmission electron microscopy. A performance test revealed that C2 had excellent temperature shear resistance, and its wettability was good, which was conducive to reduce the spreading of pulverized coal. By observing the coal in dry and wet states, the reason why C2 was suitable for dust reduction was determined. The changes in the functional groups of the soaked coal were analyzed, and the soaking effect of the C2 on the coal was determined. Finally, molecular dynamics simulation was used to verify that C2 played an effective role in promoting moisture wetting of coal.

NMR experiments on the migration characteristics of water in bedding-bearing low rank coal

Coal seam water injection is an effective technique for dust reduction in coal mines. Imbibition is an important means of water transport in coal seams and is influenced by coal bedding. The spatial distribution of water in the seepage process was obtained, and the spontaneous seepage characteristics and water transport mechanisms of coals containing different layered angles were revealed by NMR. Results show that the bedding mainly serves as the water flow channels in the imbibition. When the angle increases, the imbibition rate of adsorption pores and seepage pores in the early stage decreases. The imbibition is firstly transported to the top quickly along the bedding flow channel, 1.5h for 0° bedding coal sample, 24h for 90°, when the water reached its apex, the curve no longer changed and imbibition proceeded slowly. With the increase of bedding angle, the imbibition equilibrium time increased from 3h to 30h, up to 9 times more, the maximum imbibition rate decreases significantly, reduced from 5.64 g/h to 1.13 g/h, the flow resistance increases, and the remaining capillary force after equilibrium increases from 0.007 Pa to 5.24 Pa. When the capillary force cannot overcome the flow resistance, the imbibition reaches equilibrium.

Cracking and improved wettability of coal through liquid CO2 cyclic cold soaking for dust prevention

To solve the problem of water injection in low–porosity and low–permeability coal seams, a new idea of liquid CO2 cyclic cold soaking to improve the water absorption and wetting efficiency of coal is proposed. The evolution of the pore structure and mechanical properties of coal were studied using low–field nuclear magnetic resonance and uniaxial compression tests. The wettability and water absorption of coal before and after the experiment were determined using contact angle and water absorption tests. The results show that as the number of cycles increases, the effective porosity of coal increases significantly, the mechanical strength is weakened, and the compressive strength and elastic modulus decrease. The wettability and water absorption of coal samples were significantly improved by liquid CO2 treatment, and the changes in porosity, mechanical strength, and water absorption wettability of coal samples in the saturated group were more obvious compared to dry coal. This paper lays a theoretical and experimental foundation for the development of a new technology for coal seam water injection dust prevention.