Coalbed Methane Recovery Research Articles

Corrigendum to “Fracture propagation characteristics driven by liquid CO2 BLEVE for coalbed methane recovery” [Fuel 381(Part A) (2025) 133162]

Corrigendum to “Fracture propagation characteristics driven by liquid CO2 BLEVE for coalbed methane recovery” [Fuel 381(Part A) (2025) 133162]

Mini-Review on Influence of CO2-Enhanced Coalbed Methane Recovery and CO2 Geological Storage on Physical Properties of Coal Reservoir

Mini-Review on Influence of CO₂-Enhanced Coalbed Methane Recovery and CO₂ Geological Storage on Physical Properties of Coal Reservoir

Improving coalbed methane recovery in fragmented soft coal seams with horizontal cased well cavitation

Effective coalbed methane extraction from soft coal seams is essential for mine safety and energy supply. To enhance the extraction efficiency of coal mine methane (CMM) and reduce the risk of gas outbursts in coal mining areas, we developed an original and innovate horizontal well hydraulic cavitation method. A mathematical model that can quantitatively optimize construction parameters and improve the effectiveness of engineering applications was also constructed to calculate the technological parameters of this construction method. This technology differs from traditional approaches by relying on hydraulic erosion rather than water jets, and it can be implemented in cased horizontal wells. Utilizing the mathematical model grounded in porous media theory and Darcy’s law, numerical simulations with COMSOL Multiphysics were conducted and construction parameters optimized. The proposed technology significantly advances safe and efficient coalbed methane recovery, benefiting coal mine safety and environmental sustainability.

Data‐driven framework for predicting the sorption capacity of carbon dioxide and methane in tight reservoirs

AbstractAs energy demand continues to rise and conventional fuel sources dwindle, there is growing emphasis on previously overlooked reservoirs, such as tight reservoirs. Shale and coal formations have emerged as highly attractive options due to their substantial contributions to global gas reserves. Enhanced shale gas recovery (ESGR) and enhanced coalbed methane recovery (ECBM) based on gas injection are advanced techniques used to increase the extraction of gas from shale and coal formations. One of the key challenges associated with these formations and their enhanced recovery methods is accurately predicting the sorption process and its profile. This is crucial because it affects how methane (CH4) and carbon dioxide (CO2) are stored and released from the rock, and it significantly impacts the evaluation of gas content and the potential productivity of these formations. Due to the high cost of experimental procedures and the moderate accuracy of existing predictive approaches, this study proposes various cheap and consistent data‐driven schemes for predicting the sorption of CH4 and CO2 in shale and coal formations. In this regard, three intelligent models, including generalized regression neural network (GRNN), radial basis function neural network (RBFNN), and categorical boosting (CatBoost), were taught and tested using more than 3800 real measurements of CH4 and CO2 sorption in shale and coal formations. To find automatically their appropriate control parameters and improve their prediction ability, RBFNN and CatBoost were evolved using grey wolf optimization (GWO). The obtained results exhibited the encouraging prediction capabilities of the suggested models. In addition, it was found that CatBoost‐GWO is the most accurate scheme with total root mean square (RMSE) and determination coefficient (R2) of 0.1229 and 0.9993 for CO2 sorption, and 0.0681 and 0.9970 for CH4 sorption, respectively. Additionally, this approach demonstrated its physical validity by respecting the real sorption tendencies with respect to operational parameters. Furthermore, the CatBoost‐GWO model outperforms recently published machine learning approaches. Lastly, the findings of this study offer a significant contribution by demonstrating that the suggested model can greatly improve the ease of estimating CO2 and CH4 sorption in tight formations, thereby facilitating the simulation of other parameters related to this process. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

Investigation into Enhancing Methane Recovery and Sequestration Mechanism in Deep Coal Seams by CO2 Injection

Injecting CO2 into coal seams to enhance coal bed methane (ECBM) recovery has been identified as a viable method for increasing methane extraction. This process also has significant potential for sequestering large volumes of CO2, thereby reducing the concentration of greenhouse gases in the atmosphere. However, for deep coal seams where formation pressure is relatively high, there is limited research on CO2 injection into systems with higher methane adsorption equilibrium pressure. Existing studies, mostly confined to the low-pressure stage, fail to effectively reveal the impact of factors such as temperature, high-pressure CO2 injection, and coal types on enhancing the recovery and sequestration of CO2-displaced methane. Thus, this study aims to investigate the influence of temperature, pressure, and coal types on ECBM recovery and CO2 sequestration in deep coal seams. A series of CO2 core flooding tests were conducted on various coal cores, with CO2 injection pressures ranging from 8 to 18 MPa. The CO2 and methane adsorption rates, as well as methane displacement efficiency, were calculated and recorded to facilitate result interpretation. Based on the results of these physical experiments, numerical simulation was conducted to study multi-component competitive adsorption, desorption, and seepage flow under high temperature and high pressure in a deep coal seam’s horizontal well. Finally, the optimization of the total injection amount (0.7 PV) and injection pressure (approximately 15.0 MPa) was carried out for the plan of CO2 displacement of methane in a single well in the later stage.

Study on the effect of morphology of anthracite coal containing through-fracture on CO2 enhanced coalbed methane recovery

When CO2 is injected into the coal seam, different forms of fractures within the coal have different effective diffusion areas and distribution characteristics for the gas, affecting methane's adsorption-desorption-diffusion and seepage behavior. In this study, based on the control experiments of the intact coal sample, CO2 injection experiments were carried out on three groups of coals containing through-fracture to investigate the influence of fracture morphology on CO2-enhanced coalbed methane recovery behaviors and to discuss and analyze the changes in the volume of the coal samples, the composition of the tailing gas, and the changes in the permeability during the gas injection process. The results show that: the existence of fractures has an inhibitory effect on the volume expansion after gas adsorption of the coal, and the larger the surface area of fractures, the more obvious inhibitory effect, and at the same time, the faster the strain rate; the breakthrough time of CO2 in the fractured coal samples is much shorter than that in the intact samples; the increase in the surface area of the fractures and uniformity of distribution can enhance the concentration of CH4 in the tail gas, and in the pre-injection stage, uniformity of the distribution of the fractures is more important than the surface area of the fractures in increasing the output CH4 concentration; the magnitude of permeability change and the change rate of the coal samples during CO2 injection increased with the increase in the fracture surface area of the coal samples.

Microscopic adsorption study from coal rank comparison on the feasibility of CO2-rich industrial waste gas injection enhanced coal bed methane recovery

A new method of injecting CO2-rich industrial waste gas (CO2-rich IWG) to displace coal bed methane (CBM) is proposed for energy conservation and green growth. In this study, theadsorption mechanisms of this method were studied by the Giant canonical Monte Carlo and molecular dynamics methods in macromolecular coal models with three ranks (brown, bituminous, and anthracite coal). It is found that the proportion of gas molecules in the adsorbed state is higher in the anthracite coal slit than in the brown and bituminous slits, indicating that anthracite coal seams are more appropriate for waste gas sequestration. The adsorption selectivity of NO and CO2 is consistent among the three coal ranks, with the order of brown > bituminous > anthracite > 1.0, and that of N2 orders as 1.0 > bituminous > anthracite > brown.This is due to the different dominant factors affecting the competitive adsorption between different waste gas components and CBM, namely competition for adsorption sites in the NO and CO2 systems and thefilling effect in the N2 system. There is a positive correlation between the number of major competitive adsorption sites and the adsorption selectivity of theCO2(NO) system. CO2 and CH4 compete for COC structures in brown and bituminous coal and OH structures in anthracite coal, and OH structures in the three coals are the major adsorption sites for NO systems. Our work advances the understanding of the microscopic adsorption mechanisms of CO2-rich IWG in the CBM reservoirs, which provides a theoretical basis for CO2-rich injection-enhanced CBM recovery technology.

Feasibility of carbon dioxide geological storage in abandoned coal mine: A fully coupled model with validated multi-physical interactions

It has gained wide attention that Carbon dioxide (CO2) is to be injected into abandoned coal mines for geological storage of CO2-enhanced coalbed methane recovery. Although abundantly evidences in literature indicate that the injection of CO2 will cause lots of interactions among the mechanical characteristics of coal and the properties of CO2 flow, further studies on these multi-physical interactions are still necessary. In this work, a series of laboratory experiments to elucidate the multi-physical interactions of CO2 adsorption, softening effect of coal and the non-Darcy gas flow were conducted. Based on the experimental results, theoretical and empirical models to describe these coal-CO2 interactions were meticulously proposed and validated, the results turned out to be satisfactory. Consequently, the compressive strength and elasticity modulus of coal decrease exponentially with the increased injection CO2 pressure. The gas flow in coal obeys the Izbash non-Darcy model, and coal permeability can be well modified by the volumetric stress. By taking these coal-CO2 interactions into account, this study established of a fully coupled model for coal deformation and CO2 conservation. The model was then implemented into the numerical simulations of CO2 storage in abandoned coal mine by using the finite element method. A series of scenario-based numerical simulations was conducted to investigate the feasibility and limitation of CO2 storage in abandoned coal mine. The conducted experiments, models and numerical simulation will offer implications on the multi-physical interactions between coal and gas especially in CO2 storage in abandoned coal mines.

Fracture propagation characteristics driven by liquid CO2 BLEVE for coalbed methane recovery

Fracture propagation induced by liquid CO2 phase transition blasting (LCO2-PB) is the major reason for the spotty fracturing performance of LCO2-PB for enhancing coalbed methane (ECBM). Measures to effectively control the fracture propagation are of significant importance for ECBM recovery. Many researches to date have conducted the responses of the fracture propagation upon the CO2 fracturing under various injection conditions, and some have found that the thermodynamic state of CO2 can dominate the cracks distribution to some extent. This study therefore investigates the effect of various operated parameters of LCO2-PB on the fracture propagation alteration of coal seam subjected to the thermodynamic state of CO2 with different reservoir conditions. A series of fracture process simulations were performed based on the pressure–temperature-phase coupling model, and results indicate that high temperature of CO2 flow in the fracture process greater fracture expansion; the fracture width decreased around by 66.8 % from smaller smash district to larger one, especially for low CO2 flow rate; high elastic modulus and the temperature of coal seam favors greater length reduction and extensive crack connection, and as temperature of CO2 induces the interlaced fractures earlier formation in the higher reservoir temperature.

Enhanced coalbed methane recovery by microwave-induced thermal fracture

Abstract The investigation on microwave-induced permeabilization and response of coal under microwave heating is of great significance for the industrial application of microwave heating technology instead of traditional heating in coalbed methane mining. Santanghu coal is used as a sample to measure the permeability and porosity of coal samples before and after microwave heating. The fracture changes of coal samples before and after heating are compared to observe the penetration effect of microwaves on coal samples. Based on the technology of directional drilling and continuous tubing technology in petroleum engineering, a technology of increasing the production of coalbed methane by microwave heating in a wide range of coal seams is proposed. The feasibility of this enhanced production method is validated through COMSOL Multiphysics simulations, which model the temperature field distribution within coal seams under various microwave parameters. This approach highlights the potential of microwave technology in coalbed methane recovery. The results show that: (1) the thermal field of coal samples under microwave heating is inhomogeneous. The average length and area of the cracks of the coal samples increased under microwave radiation, and the cracking of the coal samples confirmed the cracking effect of microwaves on the coal samples. (2) With prolonged microwave heating, coal samples exhibit an initial decrease followed by an increase in porosity and permeability, a trend attributed to the expansion of solid particles that occupy and reduce pore spaces. (3) The in-situ microwave heating technique for coalbed methane extraction overcomes the challenges of long-distance microwave transmission loss and methane backflow in transmission pipelines, utilizing continuous pipelines for extensive microwave heating of coal seams. (4) The microwave power and intermittent heating duration have a significant effect on the temperature field distribution of the coal seam, and when the heating duration is 60 days, 1600 W is used to have an effective temperature field distribution while avoiding the waste of heat. When the power is constant at 1600 W, the effective temperature range is wider when the intermittent heating duration is 60 days.

Adsorption of CO2/CH4 on the aromatic rings and oxygen groups of coal based on in-situ diffuse reflectance FTIR

The adsorption mechanisms of CH4 and CO2 on the coal surface is the theoretical basis for CO2 sequestration with enhanced coalbed methane recovery (CO2-ECBM). Molecular simulation is the main method to study the adsorption mechanism at present, but the model used in the process of molecular simulation could not accurately characterize the coal macromolecular structure. Therefore, we used in-situ diffuse reflectance Fourier-transform infrared spectroscopy (FTIR) to study the adsorption of CO2/CH4 on the aromatic rings and oxygen groups of coal. The results showed that CO2 and CH4 were physisorbed on the aromatic rings, and the aromatic rings represented the primary competitive adsorption sites for CO2 and CH4, CO2 was preferentially adsorbed at the top of the aromatic ring compared to CH4. Both carboxyl and carbonyl groups were beneficial for CO2 adsorption but not for CH4 adsorption. Compared to aromatic rings, the adsorption affinity of carboxyl groups for CO2 were stronger. The results of this study revealed the adsorption mechanisms of CO2 and CH4 on the aromatic rings and oxygen groups, as well as the impact of oxygen groups on the gas adsorption capacity, providing a theoretical basis for applying CO2-ECBM in the medium-volatile bituminous coal reservoirs.

Competitive sorption of CH₄ and CO₂ on coals: Implications for carbon geo-storage

Geological carbon storage, particularly within coal seams, is recognized as a viable strategy for achieving net-zero emissions. However, following CO₂ injection into the coal seam, limited studies have addressed the competitive sorption dynamics of CH₄ and CO₂ on coal, despite the natural presence of CH₄ in these formations. In this work, sorption experiments were conducted using two types of coal: sub-bituminous coal and anthracite. Initially, pure CH4 and CO2 gases were employed to conduct individual sorption tests. Subsequently, the competitive sorption of CH4 and CO2 was evaluated using pre-mixed binary gas mixtures with varying CH4/CO2 ratios. Further, the displacement effect of CO2 on CH4 was investigated by injecting CO2 into coal samples that had been pre-adsorbed with CH4. The data reveal that, for both coals, the ideal selectivity calculated from pure gas measurements underestimates the corresponding values from real multicomponent systems. Anthracite demonstrates a higher selectivity for CO₂ over CH₄ during both adsorption and desorption processes when compared to the ideal selectivity calculated from pure gas sorption data. Conversely, the sub-bituminous coal initially shows lower selectivity for CO₂ than for CH₄ during adsorption, but this trend reverses and intensifies during desorption. If competitive sorption effects are neglected, coal selectivity for CO₂ over CH₄ under the examined conditions would be underestimated by a factor of 1.5 to 2.5. Due to the competitive sorption effects between CH₄ and CO₂, the Langmuir equilibrium constants for gas mixtures are influenced by compositional changes, leading to dynamic deviations from those observed under pure gas conditions. This finding contrasts with the traditional extended Langmuir model, which presumes that the equilibrium constants remain unchanged regardless of gas composition. In addition, the displacement study underscores the efficacy of CO2 in displacing CH4, with higher CO2 ratios intensifying displacement effects. The study highlights the substantial impact of real multicomponent scenarios on coal selectivity for CO₂ and CH₄, offering deeper insights into predicting competitive sorption behavior between CO₂ and CH₄ during CO₂-enhanced coalbed methane recovery and carbon storage processes.

Experimental study on the desorption behavior of high-volatile bituminous coals following CO2 and CH4 injection at various compositional ratios

CO2-ECBM (Enhanced Coalbed Methane recovery) offers the dual benefits of increasing methane production and reducing carbon emissions through sequestration. Previous studies have primarily focused on the competitive adsorption effects of different gas compositions during the CO2-ECBM. However, the dynamic changes in desorption volume, desorption strain, and gas composition for different compositional ratios of CO2/CH4 after injecting CO2 remain unclear. Therefore, high-volatile bituminous coals from the southern margin of the Junggar Basin are chosen for desorption experiments with five different compositional ratios of CO2/CH4. Desorption volume, desorption strain, and gas composition of the coal samples are monitored during the desorption process. Finally, the mechanism influencing the dynamic changes in gas composition during desorption is analyzed. The results indicate that as CO2 concentration increases, both desorption volume and desorption strain correspondingly increase. At the same desorption volume, a higher CO2 concentration results in greater desorption strain. For different compositional ratios of CO2/CH4, CH4 concentration gradually decreases while CO2 concentration gradually increases over desorption time. The concentration of the desorption gas is influenced by the initial CO2 concentration and the pore structure. Specifically, higher initial CO2 concentrations, better pore opening, and more developed mesopores and macropores lead to greater changes in composition concentrations during desorption. Different concentrations of CO2 all promote CH4 production, with higher CO2 concentrations enhancing CH4 production efficiency more significantly, especially for samples that are more difficult to produce. The research findings can provide guidance for the efficient production of CBM after CO2 injection.

The experimental study on multiple mechanisms of enhanced CBM recovery by autogenous nitrogen fracturing fluid

Hydraulic fracturing is a widely adopted technique for enhancing the permeability of coalbed methane (CBM) reservoirs, thus improving the recovery of CBM. Although previous studies have extensively explored the role of fracturing fluids in creating fractures and improving permeability, there remains a notable deficiency in the literature regarding the impact of these fluids on enhancing gas desorption and diffusion. This research employs an experimental investigation into a novel autogenous nitrogen (N2) fracturing fluid, demonstrating its significant potential for increasing CBM reservoir permeability and enhancing the desorption and diffusion of CBM. Through optimization experiments, the study initially determines the optimal proportions of sodium nitrite (NaNO2), ammonium chloride (NH4Cl), and an acidic activator to maximize the generation of N2. Kinetic experiments and subsequent analyses reveal that the autogenous N2 fracturing fluid releases a substantial amount of N2 and heat, with the reaction rate highly influenced by initial pressure and temperature conditions. Fracturing experiments on coal samples demonstrate that the release of N2 increases the fluid pressure within the pore spaces, initiating micro-fractures and enhancing permeability. Additionally, the increased pore pressure mitigates the water block effect and improves the gas diffusion. The heat and gas released during the reaction significantly facilitate the desorption of CBM within coals. This fracturing fluid offers a comprehensive approach for enhancing CBM recovery.

A Semianalytical Model for Advanced Description of Pressure Drop Funnel during Coalbed Methane Production.

Advanced description of pressure drop funnel is crucial in coalbed methane (CBM) production because of dewatering and depressurization methods. Improving the precision of the pressure drop funnel description facilitates obtaining the actual production status and productivity potential, both pivotal for responsible development plans. The study presents a semianalytical model that integrates pressure profiles and material balance equations, incorporating inner and outer boundary conditions, and dynamic reservoir characteristics. The pressure propagation characteristics in undersaturated coal reservoirs are described during the production life of CBM wells, and the model is validated using two wells with different production characteristics. The results indicate that the effect of water saturation on the expansion of the drainage radius surpasses that of the desorption radius, demonstrating a more precise prediction of the production boundary when dynamic water saturation is considered. Additionally, a rapid drop rate of bottomhole flowing pressure triggers simultaneous propagation of the drainage and desorption radii, resulting in a smaller production boundary and fewer well-controlled resources. Conversely, an appropriate production strategy results in a larger drainage radius and lower boundary pressure before massive gas desorption, thereby facilitating efficient propagation of the pressure drop funnel. Moreover, the pressure drop funnel characterized by the model can compute the dynamic CBM resources and recovery efficiency of a single well, providing a valuable basis for assessing productivity potential. In summary, this model offers a time-saving and practical tool for describing the dynamic pressure drop funnel in various CBM production stages and promoting efficient development for undersaturated CBM reservoirs.

A novel interdisciplinary model for optimizing coalbed methane recovery and carbon dioxide sequestration: Fracture dynamics, gas mechanics, and its application

The Carbon Dioxide Enhanced Coalbed Methane (CO2-ECBM) technique significantly enhances clean energy extraction and mitigates climate change. Central to this process is the dynamic evolution of rough fracture networks within coal seams, influencing the migration of CO2 and natural gas. However, existing research lacks a comprehensive, quantitative approach to examining the micro-evolution of these fractures, including fracture roughness, fracture density, fracture touristy, and fracture size, particularly under thermo-hydro-mechanical effects. Addressing this gap, our study introduces an innovative, fractal model for quantitative analysis. This model intricately characterizes fracture networks in terms of number, tortuosity, length, and roughness, integrating them with fluid dynamics affected by external disturbances in CO2-ECBM projects. Upon rigorous validation, the finite element method analysis reveals significant impacts of micro-parameters on permeability and natural gas extraction. For instance, increasing CO2 injection pressure from 4 to 6 MPa changes fracture network density by up to 6.4%. A decrease in fracture density (Df) from 1.6 to 1.5 raises residual gas pressure by 2.7% and coal seam stress by 9.5%, indicating crucial considerations for project stability. Applying the proposed interdisciplinary model to assess CO2 emissions in Australia, it is can be obtained that when Df decreases from 1.6 to 1.5, the total amount of CO2 storage reduces by 17.71%–18.04%. Our results demonstrate the substantial influence of micro-fracture behaviors on CO2-ECBM projects, offering a ground-breaking solution for efficient greenhouse gas reduction and clean energy extraction, with practical implications for the energy sector's sustainability.

Effects of supercritical CO2 fluids on pore structure and fractal characteristics of bituminous coal

Enhanced coalbed methane recovery with CO2 coal seam storage (CO2-ECBM) technology is an important way to achieve China's strategic goals of carbon peak and carbon neutrality. Presently, to date there has been rarely research conducted on the effect of coal sample scale on pore structure under supercritical CO2 (ScCO2) fluids. In this study, a high-pressure geological environment simulation system was adopted to analyze coal samples of different scales for ScCO2 saturation. Subsequently, low-pressure nitrogen gas adsorption (LP-N2GA), mercury intrusion porosimetry (MIP), and low-field nuclear magnetic resonance (LF-NMR) were used to analyze the pore structure and fractal dimension changes in saturated coal samples at different scales. The experimental results show that the mesopore ratios of cylindrical and granular coal decrease by an average of 1.68% and 2.30%, respectively, after the saturation of ScCO2. The proportion of macropores in cylindrical coal increased by an average of 5.50% after ScCO2 saturation, while the proportion of macropores in granular coal changed by 176.86% compared to cylindrical coal. The fractal dimension of the ScCO2 saturated coal samples obtained with LP-N2GA, MIP, and LF-NMR all show a decreasing trend, again confirming the modification of the coal pore surface by ScCO2. Finally, a conceptual model is presented to analyze the mechanism of the effect of coal sample scale on the pore structure under ScCO2. The difference in the transport paths of ScCO2 molecules at different coal scales is the main reason for the difference in the evolution of the pore structure. In addition, the impact of the amount of adsorption obtained in the laboratory using coal samples of different scales on the assessment of the CO2 storage capacity was discussed. Therefore, the results of this study are expected to provide a reference for the CO2 storage capacity assessment of the CO2-ECBM project.

Evaluation of parameters impacting grey H2 storage in coalbed methane formations

Injecting grey hydrogen into coalbed methane formations has the potential to transform coal into a geologically temporary “H2-Battery” and a permanent “CO2-sink”. This study aims to thoroughly evaluate crucial parameters-sorption, diffusion, and matrix swelling/shrinkage-that impact grey hydrogen injection in CH4-enriched coalbed formations. In terms of sorption capacity, CO2 exhibits the highest, followed by CH4 and then H2. Sorption data affirmed that anthracite coal has a certain degree of adsorption capacity for H2, with H2 demonstrating superior diffusive gas deliverability as indicated by its diffusion coefficient, which is approximately six times higher than that of CO2. These characteristic position coal as a promising candidate for temporary H2 storage and cleaning, optimizing injectivity and depletion efficiency. Interestingly, H2 adsorption induced matrix shrinkage in coal, in contrast to other strong sorption gases such as CH4 and CO2, which resulted in matrix swellings. Matrix deformations induced by H2–CO2 mixture (grey hydrogen) injection were conducted and quantified to evaluate grey hydrogen injection in future field trials. The results reveal that the majority of directional strains indicated that when the partial pressure of CO2 in the H2–CO2 mixture is equivalent to pure CO2 pressure, the latter case induces elevated swelling strains. This finding implicitly supports the hypothesis that H2–CO2 mixture injection causes less matrix swelling than pure CO2 injection at equivalent CO2 pressure. This work provides essential parameters to illustrate an enhanced synergism among hydrogen storage, carbon sequestration, and enhance coalbed methane recovery through grey hydrogen injection in coal formations.

Analysis of reservoir permeability evolution and influencing factors during CO2-Enhanced coalbed methane recovery

CO2-ECBM is an effective energy saving and emission reduction technology. Among them, the permeability of coal seam will affect the CO2 injection efficiency, which is the key factor affecting the CH4 production. In order to reveal the evolution of reservoir permeability, effective stress, adsorption/desorption effect, and binary gas seepage and diffusion are considered. The research results indicate that the evolution of permeability can be summarized into two stages. The permeability during the CO2 undisturbed period is mainly controlled by the effective stress, which exhibits a parabolic relationship with permeability. The CO2 disturbed period is mainly controlled by the strain, which exhibits a negative correlation with permeability. Increasing the injection pressure, during the CO2 undisturbed period, the effective stress increases, the strain decreases, and the higher the permeability. During the CO2 disturbed period, the lower the effective stress, the higher the strain, and the lower the permeability. Increasing the injection temperature, the greater the effective stress and permeability in the undisturbed period. In the CO2 disturbed period, the competitive adsorption intensifies, the larger the strain, and the faster the permeability decreases. Increasing the initial water saturation, the slower the gas transportation rate. The slower the effective stress rises in the CO2 undisturbed period, the lower the permeability. In the CO2 disturbed period, the smaller the strain, and the higher the permeability. In summary, injection pressure, temperature, initial water saturation will have an impact on the permeability, in engineering practice, it is not the case that the higher the injection pressure, the higher the injection temperature, the smaller the initial water saturation is the better.

Solid-liquid particle flow sealing mucus (PFSM) in enhancing coalbed methane (CBM) recovery: Multiple-perspectives analysis and mechanism insights

The paper presents an in-depth investigation of solid-liquid two-phase particle flow sealing mucus (PFSM) for enhanced coalbed methane (CBM) recovery. PFSM is composed of solid waste particles such as fly ash and rubber particles. The PFSM is assessed using multiple-perspectives analysis, which includes measurements of water retention, pressure expansion, rheological characteristics, adhesion, wettability, microscopy and field case studies. Single-factor and multi-factor studies are used to optimize slurry material ratios. The results show that PFSM has outstanding water retention characteristics, with over 80 % retention for 30 days at 30 °C, and impressive expansion performance, with 9.52 % at 0.6 MPa. The shear thinning curve conforms to the Cross model. After 30 s, the final contact angle is 75.17 °, which is about 6 ° smaller than that of cement based materials. Field experiments show that, after applying PFSM, the drainage gas concentration can be improved at least 60 % comparing to other sealing materials. This research findings could offer novel insights into enhancing CBM extraction, indicating potential for safer and more efficient coal mine production.