Coalbed Methane Research Articles

Production characteristics and adsorption control mechanism of CO2-rich CBG wells

To investigate the productivity laws of coalbed gas (CBG) wells in carbon dioxide (CO2)-rich coalfield, the Haishiwan coal mine in Yaojie coalfield, Gansu Province, China, which is rich in CO2 of different concentrations in CBG, was selected as the study area. Using numerical simulation technology, the production capacity of CBG wells was simulated, and the thermodynamic factors influencing gas adsorption differences on production capacity were discussed. Numerical simulation indicates that with the increase of CO2 concentration, the gas breakthrough time is prolonged, and the gas production first increases and then decreases. Research considers that changes in CBG production capacity result from the combined effects of temperature and pressure on gas adsorption. At shallow coal seams, pressure is the dominant factor that promotes gas adsorption, resulting in increased gas content and production. However, due to the competitive adsorption of CO2 and methane (CH4), CO2 preferentially adsorbs on coal, hindering desorption. Therefore, gas breakthrough in CBG wells with high CO2 concentration is slower, but the production period is longer. On the contrary, high temperatures inhibit gas adsorption in deeper coal seams, reducing gas content and promoting CH4 desorption. Therefore, CBG wells with low CO2 concentration have faster gas breakthroughs, but overall production is lower. The findings of this study help to better understand the drainage characteristics of CO2-rich CBG wells and provide guidance for developing such resources.

Proppant embedding-based optimal design method for fracturing coalbed methane wells in Qingshui basin

Fracturing design needs to consider the effect of proppant embedding as the production decreases rapidly due to proppant embedding after fracturing of coalbed methane wells. Coal fracture conductivity experiments were carried out to analyze the changes in coal fracture conductivity due to proppant embedding. A model of coal fracture conductivity was established considering proppant embedding. A proppant index method, which considers the dynamic change of conductivity over time, was adopted to establish a proppant embedding-based optimal design method for fracturing coal bed methane wells. The optimal design of coalbed methane wells in the southern block of Qinshui Basin was carried out. The results show that the fracture conductivity decreased with the increase of formation closure pressure. It increased with the rise of proppant grain size, number of placement layers, and Young’s modulus of the formation. The simulation results were in good agreement with the indoor fracture conductivity experiments. The proppant embedding reduced the fracture width and fracture conductivity. The optimized fracture length considering proppant embedding decreased with an average decrease of 10.6%, and the fracture width increased with an average increase of 11.5%. Consideration of proppant embedment during fracture optimization of coalbed methane wells compared to no consideration resulted in a decrease in design fracture length, an increase in design fracture width, and a relative increase in average production. The validity and practicability of the method were verified, and it was of great guiding significance for the optimal design of fracturing in coalbed methane wells.

Prediction of Coalbed Methane Production Using a Modified Machine Learning Methodology

Compared to natural and shale gas, studies on predicting production specific to coalbed methane (CBM) are still relatively limited, and mainly use decline curve methods such as Arps, Stretched Exponential Decline Model, and Duong’s model. In recent years, machine learning (ML) methods applied to CBM production prediction have focused on the significant data characteristics of production, achieving more accurate predictions. However, throughout the application process, these models require a large amount of data for training and can only achieve accurate forecasts over a short period, such as 30 days. This study constructs a hybrid ML model by integrating a long short-term memory (LSTM) network and Transformer architecture. The model is trained using the mean absolute error (MAE) loss function, optimized using the Adam optimizer, and finally evaluated using metrics such as MAE, root mean square error (RMSE), and R squared (R2) scores. The results show that the LSTM-Attention (LSTM-A) hybrid model based on small training datasets can accurately capture the CBM production trend and is superior to traditional methods and the LSTM model regarding prediction accuracy and effective prediction time interval. The methodologies established and the results obtained in this study are of great significance to accurately predict CBM production. It is also helpful to better understand the mechanisms of CBM production.

Does Topic Matter? Investigating Students’ Interest, Emotions and Learning when Writing Stories About Socioscientific Issues

Does Topic Matter? Investigating Students’ Interest, Emotions and Learning when Writing Stories About Socioscientific Issues

Summary of Development and Utilization Status and Prospect Enlightenment of Coalbed Methane

Coalbed methane is an important hazard source in the process of coal mine production, and it is also an important clean energy source with multiple ways of power generation and civil use. This paper summarizes the present situation of the development and utilization of coalbed methane, and discusses its prospect. Through the systematic review of the distribution of domestic coalbed methane resources, mining technology, policy environment and market demand, it is revealed that the importance of coalbed methane as a clean energy in the transformation of China 's energy structure is increasingly prominent. This paper analyzes the main technical paths in the current coalbed methane development and the application effect in improving the recovery rate. At the same time, the challenges faced in the development and utilization of coalbed methane are pointed out, such as complex geological conditions, water resource consumption, environmental pollution risk and economic benefit fluctuation. Furthermore, based on the existing research and practice, the paper looks forward to the innovation trend of coalbed methane development technology. In addition, the potential contribution to achieving the goal of carbon neutrality is also discussed. In summary, the development and utilization of coalbed methane is entering a new stage of rapid development. Technological innovation and policy guidance will be the key factors to promote its sustainable development, and provide strong support for the optimization of energy structure and environmental protection.

Improved estimation methods for surface coal mine methane emissions for reporting, beneficial use, and emission reduction purposes and relative to Australia's safeguard mechanisms.

Methane is responsible for 30% of global warming, with coal mining contributing 31% of 2023 methane emissions in the energy sector. Australia's Bowen Basin is the largest metallurgical coal (MC) producing region with a need to reduce fugitive coal mine methane (CMM) emissions, most notably from surface coal mining operations, as underground mines have increased pre-drainage with flaring or beneficial use. Australia's regulatory framework is moving to mine-specific models, based on measured data and reservoir modelling, to evaluate CMM emissions more effectively and quantify the benefit of projects that reduce emissions. This paper highlights the definitions, classifications, and determinations in the Australian Safeguard Mechanisms to define surface mining and underground CMM emissions. While underground mining has a broad range of potential mitigation strategies, open-cut MC mine mitigation strategies are more limited and will be the focus of this paper. Australian-specific open-cut MC mine examples will illustrate the potential reductions in emissions and positive cash-flow benefits possible by implementing pre-drainage and new technologies (e.g., subterranean barriers). Six CMM scenarios, based on representative data from Australia's Bowen Basin coal mines and typical beneficial use strategies, show that a typical pre-drainage strategy at a surface mine can reduce CMM emissions by 38% without any further beneficial use of produced gas. Further, implementing a pre-drainage strategy with subterranean barriers can reduce emissions by 46%, a 10% improvement over pre-drainage alone. The emissions estimation methodology proposed can be applied to other carbon pricing frameworks and regions to define the impacts and benefits of implementing emissions reduction strategies.

Impact of controllable parameters in hydraulic slotting on stress relief effects around coal seam

Hydraulic slotting technology has broad application prospects in coal seam gas management. Using the FLAC3D finite difference software and an evolution model considering plastic damage, the unloading damage characteristics under unequal pressure conditions during the hydraulic slotting process are simulated. The results show that factors such as borehole diameter, drilling depth, slot radius, and borehole spacing significantly impact the unloading damage effect. Specifically, increasing the borehole diameter, drilling depth, and slot radius expands the unloading damage area, forming “butterfly-shaped” or “elliptical” plastic zones. Reducing the spacing between parallel slots causes overlapping unloading damage in the coal body between adjacent slots, further enhancing the stress reduction effect. The “high–low–high” pattern of parallel slots effectively supplements and strengthens the weak stress unloading zones, better fracturing the coal seam. Field testing confirms that hydraulic slotting significantly increases borehole radius and gas extraction. These results validate simulations and enhance coalbed methane extraction's safety and efficiency, providing robust guidance for optimizing parameters.

Boosting partial oxidative reforming via Ni-Fe modified La0.5Sr0.5Fe0.8Ni0.1Mo0.1O3-δ catalyst for direct low concentration coal mine methane solid oxide fuel cell

Boosting partial oxidative reforming via Ni-Fe modified La0.5Sr0.5Fe0.8Ni0.1Mo0.1O3-δ catalyst for direct low concentration coal mine methane solid oxide fuel cell

Surface Deformation Monitoring and Inversion Techniques for the Pressure Analysis of CO2-Enhanced Coalbed Methane Reservoir

Surface Deformation Monitoring and Inversion Techniques for the Pressure Analysis of CO2-Enhanced Coalbed Methane Reservoir

Study of Key Factors for Efficient Coalbed Methane Extraction: Pore Structure, Desorption Rate and Seepage Characteristics.

Effective coalbed methane extraction is a key strategy for boosting natural gas production and storage in addition to raising the safety of the production standard of coal mines. In order to examine the effects of important variables such as pore parameters, desorption rate under temperature and pressure conditions, and seepage capacity on coalbed methane production during the coalbed methane extraction process. The low-temperature nitrogen adsorption tests (LTN2A), methane adsorption/desorption experiments at various temperatures, and the changes in the desorption rate constants, the initial desorption rate, and the desorption rate decay index with temperature and pressure were quantitatively analyzed. And COMSOL software was used to simulate the seepage characteristics of coalbed methane under various reservoir pressures. The results demonstrated that the large interior pore volumes of the samples are beneficial for gas adsorption. Because of its better pore connectivity, the QL sample had a desorption amount that was 55.65% and 48.01% higher at 313.15 and 333.15 K than the WJB sample. The three parameters of k, V1 and kt are at a high level with increasing temperature; hence, the desorption rate peaks at 333.15 K and pressures between 1 and 4 MPa. Furthermore, the WJB sample is more sensitive to the temperature than the QL sample. The COMSOL simulation shows that the methane pressure inside the reservoir can be released better when the reservoir pressure is below 10 MPa. The Darcy seepage rate is fast and stable, which is favorable for the seepage of coalbed methane. The findings show a relationship between the desorption and seepage properties of CBM and its pore structure, which may offer empirical and theoretical support for the successful development of the CBM.

Enhanced Coal Bed Methane (ECBM) Recovery by Injecting Different Gas Components

Enhanced Coal Bed Methane (ECBM) Recovery by Injecting Different Gas Components

Genetic Types and Gas Source Analysis of Jurassic Deep Coalbed Methane in Baijiahai Uplift, Junggar Basin.

Multiple sets of source rocks are developed in the Baijiahai Uplift of the Junggar Basin. The gas genetic types and sources of deep coalbed methane (CBM) in the Jurassic period of the Baijiahai Uplift are inconclusive. Based on the analysis of geochemical characteristics, maturity, natural gas composition, and carbon isotope of source rocks, combined with plate verification and seismic interpretation, the genetic types of deep CBM in Jurassic were identified, and the gas source and migration path of deep CBM in Jurassic were revealed. The results show that the three sets of source rocks of Carboniferous, Permian, and Jurassic in Baijiahai Uplift have good hydrocarbon potential. The organic matter types of Jurassic source rocks are mainly II2 and III, and the evolution of organic matter is in the low-maturity stage. The deep CBM in Jurassic atoms is a mixed gas containing exogenous input gas. The coal-type gas is derived from the Carboniferous, Permian, and Jurassic humic kerogens, with an average proportion of 54.47%. The oil-type gas is derived from the Permian sapropelic kerogens, with an average proportion of 45.43%. In the plane, the closer to the fault, the greater the proportion of oil-type gas. The genetic types and gas sources of Jurassic deep CBM in the Baijiahai Uplift are clarified in this study area. The research results are helpful to deepen the understanding of the enrichment law of deep CBM and provide references for the optimization of favorable exploration areas.

CO2 storage capacity of coal seams: a screening and geological review of carboniferous coal formations of Kazakhstan

The increasing atmospheric CO2 concentration linked to human activity results in global warming by the greenhouse effect. This anthropogenic CO2 may be sequestrated into geological formations, e.g., porous basalts, saline aquifers, depleted oil or gas reservoirs, and unmineable coal seams. Furthermore, carbon capture, utilization, and storage (CCUS) methods are an acceptable and sustainable technology to meet the goals of the Paris Agreement, in which Kazakhstan is expected to reduce greenhouse gas emissions by 25% compared with the 1990 level. Unmineable coal seams are an attractive option among all geostorage solutions, as CO2 sequestration in coal comes with an income stream via enhanced coalbed methane (ECBM) recovery. This paper identifies four carboniferous coal formations, namely Karagandy, Teniz-Korzhinkol, Ekibustuz, and Chu coal basins of Kazakhstan, as CO2 geostorage solutions for their unmineable coal seams. The ideal depth of CO2 storage is identified as 800 m to ensure the supercritical state of CO2. However, the Ekibustuz coal basin fails to meet the required depth of 800 m in its unmineable coal seams. The conventional formula for calculating CO2 storage in coal basins has been modified, and a new formula has been proposed for assessing the CO2 storage potential in a coal seam. The CO2 storage capacities of unmineable coal seam of these coal basins are 24.60 Bt, 0.61 Bt, 14.02 Bt, and 5.42 Bt, respectively. The Langmuir volume of the coal fields was calculated using the proximate analysis of coalfields and found to vary between 36.42 and 98.90 m3/ton. This paper is the first to outline CO2 storage potential in Kazakhstani coal basins, albeit with limited data, along with a detailed geological and paleographic review of the carboniferous coalfields of Kazakhstan. A short overview of the CO2-ECBM process was also included in the paper. Instead of any experimental work for CO2 storage, this paper attempts to present the CO2 storage capacity of carboniferous coal formation using the modified version of previously determined formulas for CO2 storage.

Exploration of 3D Coal Seam Geological Modeling Visualization and Gas Content Prediction Technology Based on Borehole Data

Exploration of 3D Coal Seam Geological Modeling Visualization and Gas Content Prediction Technology Based on Borehole Data

Gas Desorption Characteristics of Different Coal Ranks

It is crucial to understand the desorption and diffusion characteristics of coal seam gas to prevent gas disasters in coal mines. This study conducted constant-temperature gas dispersion tests on lignite, fiery coal, and anthracite to uncover the complexities of gas diffusion in coal samples under the influence of coal metamorphism. The main focus was on determining their gas desorption and diffusion characteristics and analyzing the mathematical models of gas dispersion for coal samples with varying degrees of metamorphism over different durations. The results indicated that highly metamorphosed coal samples reached the desorption limit quickly, while low-rank lignite required more time to reach the limit. The gas desorption diffusion rate was notably sensitive to the level of coal metamorphism. In the first 10 min, the gas desorption rate remained stable for lignite and fiery coal, whereas anthracite exhibited a rapid desorption rate in the initial 4 min followed by stability in the subsequent 6 min. Additionally, the effective gas diffusion coefficient showed a strong negative linear correlation with the degree of metamorphism, indicating reduced gas diffusion ability with increased metamorphism. The empirical formulas applied to anthracite showed stable correlation indices, with Formula 3 considered more suitable for describing the gas desorption processes of lignite and fiery coal.

Numerical Study of Optimal Injected Gas Mixture Proportions for Enhancing Coalbed Methane Recovery.

A comprehensive thermo-hydro-mechanical numerical model for gas mixture-enhanced coalbed methane recovery was developed, in combination with coal deformation, competitive adsorption, ternary gas seepage, gas-water migration, and heat transfer. The model, implemented using COMSOL Multiphysics, investigates optimal gas injection proportions under varying conditions of injection temperature, initial water saturation, and initial permeability. The results demonstrate that higher injection temperatures and initial permeability, with lower initial water saturation, significantly enhance methane production. Specifically, at an injection temperature of 340 K and a permeability of 1.028 mD, optimal CO2 concentrations are 50 and 70%, resulting in cumulative methane productions of 6.3 × 106 and 7.2 × 106 m3, respectively. In contrast, at an initial water saturation of 0.8, a CO2 concentration of 30% proves to be the most effective, yielding a cumulative methane production of 5.8 × 106 m3. These findings offer critical insights into optimizing the balance between CO2 and N2 proportions, thereby maximizing methane recovery while minimizing the risks of premature breakthrough and permeability reduction caused by coal matrix swelling.

CH4 and CO2 Desorption Characteristics of Low-Gas Mine Coals

ABSTRACT Mastering coal gas desorption characteristic is the key to improve coalbed gas recovery and prevent coal mine gas outburst. However, relevant research targets frequently tend to the high-gas coal mines rather than low-gas mines, even though huge potential coalbed gas resource deposit and not a few gas outburst accidents exist in the low-gas mines. To further address the research gap on low-gas coal mines and clarify the gas desorption patterns of CH4 and CO2 within these mines, we selected four low-gas coal samples and investigated the effects of temperature, adsorption equilibrium pressure, and particle size on the desorption of CH4 and CO2. Pore structure characteristics were also analyzed to explain the gas desorption patterns. The findings indicated that the effects of these three factors on the desorption amount of low-gas coal were similar to those of high-gas coal. Nonetheless, the desorption curves more closely aligned with the Qin Yueping model, based on Darcy’s law. Additionally, the initial process of desorption could be described by the Fick’s law-based exponent model, and the effective diffusion coefficients of the low-gas coals were larger than those of high-gas coals. These findings shed light on figuring out gas release characteristics of low-gas coal mines.

In Situ N-Doped Low-Corrosion Porous Carbon Derived from Biomass for Efficient CH4/N2 Separation

The separation of CH4 and N2 is essential for the effective use of low-concentration coalbed methane (CBM). In this study, a series of nitrogen-doped porous carbons were synthesized using an in situ nitrogen doping method combined with K2CO3 activation. The study systematically examined how changes in the physical structure and surface properties of the porous carbons affected their CH4/N2 separation performance. The results revealed that in situ nitrogen doping not only effectively adjusts the pore structure and alters the reaction of K2CO3 on the carbon matrix, but also introduces nitrogen and oxygen functional groups that significantly enhance the adsorption capabilities of the materials. In particular, sample S3Y6−800 demonstrated the highest methane adsorption capacity of 2.23 mmol/g at 273 K and 1 bar, outperforming most other porous carbons. This exceptional performance is attributed to the introduction of N-5, N-6, C-O, and COOH functional groups, as well as a narrower pore-size distribution (0.5–0.7 nm) and the formation of carbon nanotube structures. The introduction of heteroatoms also provides additional adsorption sites for the porous carbon, thus improving its methane adsorption capacity. Furthermore, dynamic breakthrough experiments confirmed that all samples effectively separated methane and nitrogen. The Toth model accurately described the CH4 adsorption behavior on S3Y6−800 at 298 K, suggesting that the adsorption process follows a sub-monolayer coverage mechanism within the microporous regions. This study provides a mild and environmentally friendly preparation method of porous carbons for CH4/N2 separation.

Investigation of an Adsorption Model of Wet Coal That Considers Coal Seam Gas Pressure and Temperature Effects.

To investigate the effects of gas pressure and temperature in different coal seams on the adsorption behavior of water-bearing coal, an equilibrium constant was introduced to combine the L-F model and dual-L model to construct an excess adsorption model that accounts for changes in the volume and density of the adsorption phase. The results showed that the newly developed model effectively described the gas adsorption behavior of coal under varying temperature and moisture conditions. In the initial stage of gas pressure increase, the methane molecules rapidly occupied the micropore adsorption sites, leading to a rapid increase in adsorption phase density. As the pressure increased, the adsorption sites gradually approached saturation, causing the increase in the adsorption phase density to slow. As the temperature increased, the kinetic energy of the gas molecules increased, leading to desorption and a further reduction in adsorption phase density. Moreover, a positive correlation was observed between excess adsorption and adsorption phase density, with significant temperature sensitivity. At higher adsorption phase densities, an increase in temperature led to a decrease in excess adsorption. Compared with the L-F model and dual-L model, the newly developed adsorption model demonstrated significant advantages in terms of fitting accuracy and physical significance, thus providing more accurate predictions of coal adsorption capacity under the combined effects of gas pressure, temperature, and moisture in coal seams.

Piezoelectric characteristics of coal rock leakage under uniaxial compression

In coal mining, coal rock fracturing damage and leakage pose significant challenges. To study the relationship between piezoelectric signals and seepage characteristics during uniaxial compression, and to achieve leakage monitoring based on piezoelectric signals, a coal rock fracturing damage and leakage monitoring experiment was carried out using coal from the Zhaogu Mine in Henan Province. The wavelet packet energy was introduced to investigate the piezoelectric characteristics. The results indicate the relative variation in wavelet packet energy server as a damage index during the uniaxial compression of coal, correlating closely with permeability changes. The wavelet packet energy at the end of the elastic deformation stage was 0.26 V2, similar to the pre-compression value of 0.29 V2. Therefore, the overall damage in the compression and elastic deformation stages was approximately 0. Permeability values remained stable, fluctuating from 0.26 × 10−16 m2 to 0.11 × 10−16 m2. In the plastic deformation stage, wavelet packet energy decreased while the damage index and permeability rose. Prior to peak stress, wavelet packet energy and damage index plateaued, signaling a precursor to a sudden increase in permeability. Post-peak stress, a marked decline in wavelet packet energy and an increase in the damage index and permeability were observed. This study offers a method for monitoring coal rock leakage, contributing valuable insights for efficient coalbed methane extraction and timely safety alerts.