Methane Adsorption Characteristics Research Articles

Methane Adsorption Characteristics of Marine-Continental Transitional Shales Based on the Experimental Study of Shanxi Formation of the Lower Permian in the Ordos Basin

Methane Adsorption Characteristics of Marine-Continental Transitional Shales Based on the Experimental Study of Shanxi Formation of the Lower Permian in the Ordos Basin

On the Use of the Multi-Site Langmuir Model for Predicting Methane Adsorption on Shale

Shale gas, mainly consisting of adsorbed gas and free gas, has served a critical role of supplying the growing global natural gas demand in the past decades. Considering that the adsorbed methane has contributed up to 80% of the total gas in place (GIP), understanding the methane adsorption behaviors is imperative to an accurate estimation of total GIP. Historically, the single-site Langmuir model, with the assumption of a homogeneous surface, is commonly applied to estimate the adsorbed gas amount. However, this assumption cannot depict the methane adsorption characteristics due to various compositions and pore sizes of shales. In this work, a multi-site model integrating the energetic heterogeneity in adsorption is derived to predict methane adsorption on shale. Our results show that the multi-site model is capable of addressing the heterogeneity of shales by a wide range of adsorption energy distributions (owing to the complex compositions and different pore sizes), which is different from the single-site model only characterized by single adsorption energy. Consequently, the multi-site model results have better accuracy against the experimental data. Therefore, applying the multi-site Langmuir model for estimating GIP in shales can achieve more accurate results compared with using the traditionally single-site model.

Supercritical Methane Adsorption Characteristics and Pore Structure Characteristics of Deep Middle Rank Coal

Abstract In order to accurately analyze the adsorption characteristics, pore structure, and fractal law of deep middle rank coal, high-pressure isothermal adsorption tests based on magnetic levitation high-pressure thermobalance and pore structure tests based on mercury intrusion method were carried out on coal samples collected from typical kilometer level deep wells. The fractal law of sponge model was studied. The results showed that: a. The weight method adsorption test showed “excess adsorption” phenomenon with the increase of equilibrium pressure, and the modified Gibbs surface excess adsorption theory was in line with the Langmuir adsorption model; b. The distribution of macropore volume in deep middle rank coal accounts for a dominant proportion of 57.44% to 62.47%, and the proportion of microporous specific surface area reaches 72.96% to 74.27%, indicating that microporous adsorption capacity is the strongest; c. The pore structure parameters and adsorption constants exhibit strong nonlinear characteristics.

Influence of Supercritical Conditions on Isothermal Adsorption Capacity Calculation of Methane and Model Optimization.

The study of isothermal adsorption models for coal and methane under supercritical conditions helps us to understand the gas content distribution in coal seams and improve gas management in coal mines. Coal samples from the Hebi mine and Longshan coal mine were selected for this research. Using the weight method, isothermal adsorption curves of supercritical methane at temperatures of 308, 313, and 318 K were measured. The adsorption phase density of supercritical methane was obtained by using the intercept method and model fitting, and the absolute adsorption capacity of methane was calculated. Simultaneously, the pore volume and specific surface area of the coal samples were tested, and the isothermal adsorption model for supercritical methane was studied and optimized. The results indicate that using mercury intrusion, low-temperature N2, and low-temperature CO2 adsorption methods for testing coal sample pore structures allows for multiscale characterization of the coal pore structure. Based on the Gibbs excess adsorption theory, the phase density of methane obtained from the intercept method and model fitting effectively represent the isothermal adsorption curve of supercritical methane. By combination of the specific surface area and pore volume distribution of the coal with the absolute adsorption capacity of methane, the number of methane adsorption layers on the coal surface was calculated to be between 1.11 and 1.3 layers. This suggests that the isothermal adsorption model for supercritical methane on coal is not solely micropore filling or single molecular layer adsorption but primarily single molecular layer adsorption with concurrent micropore filling adsorption. Based on this adsorption mechanism, an L-DA isothermal adsorption model for supercritical methane on coal was established. The L-DA isothermal model shows good fitting results and effectively explains the adsorption characteristics of supercritical methane on coal.

Monte Carlo Calculation of the Thermodynamic Characteristics of Methane and Ethane Adsorption on Graphite

Monte Carlo Calculation of the Thermodynamic Characteristics of Methane and Ethane Adsorption on Graphite

Molecular Dynamics Simulation of Methane Adsorption and Diffusion

To study the adsorption and diffusion mechanism of low-rank coal at the microscopic level, samples of Fukang low-rank coal were collected, and the elemental composition, carbon type distribution and functional group type of the Fukang low-rank coal structure were determined by elemental analysis (Ea), Fourier-transform interferometric radiometer (FTIR), X-ray photoelectron spectroscopy (XPS) and 13C nuclear magnetic resonance (13C NMR) experiments to construct a 2D molecular structure of the coal and a 3D macromolecular structure model. The adsorption and diffusion characteristics of methane were researched by giant regular Monte Carlo (GCMC) and molecular dynamics (MD) simulation methods. The results showed that the excess adsorption amount of methane increased and then decreased with the increase in pressure. The diffusion of methane showed two stages with increasing pressure: a sharp decrease in the diffusion coefficient from 0.5 to 5.0 MPa and a slow decrease in the diffusion coefficient from 5.0 to 15.0 MPa. The lower the pressure, the larger the effective radius of the CH4 and C atoms, and the higher the temperature, the more pronounced the diffusion and the larger the effective radius.

A Comprehensive Study on Methane Adsorption Capacities and Pore Characteristics of Coal Seams: Implications for Efficient Coalbed Methane Development in the Soma Basin, Türkiye

This study represents a comprehensive assessment of methane adsorption capacity and pore characteristics for the coal seams of the Soma Basin in Western Türkiye, with a focus on their implications for coalbed methane potential. Twenty-one exploration wells were utilized to obtain coal samples from the kP1 and kM2 coal seams in the Kınık coalfield of the Soma Basin. High-pressure methane adsorption experiments using the indirect gravimetric method were conducted to quantify the storage capacities of these coal seams. Results revealed a wide range of methane adsorption capacities, ranging from 10.5 to 28.3 m3/t (air-dry basis), indicating significant methane storage potential for the kP1 and kM2 coal seams. The gas contents, ranging from 1.1 to 4.3 m3/t (as-received basis), suggested that the coal seams were undersaturated. Low-pressure N2/CO2 adsorption tests, along with standard proximate and gross calorific value analyses, were performed to investigate the influence of coal quality and pore characteristics on methane adsorption capacities. The findings demonstrated correlations between coal quality parameters and adsorption capacity, with ash yield showing a moderately negative correlation and fixed carbon content and gross calorific values exhibiting moderately positive correlations. Microporosity was identified as the critical factor governing methane adsorption, with a strong positive correlation observed between micropore surface areas and volumes and adsorption capacity. These results highlight the significant methane storage capacities of the coal seams in the Soma Basin and underscore the importance of micropores in determining methane adsorption capacity. The findings provide valuable insights for optimizing methane extraction and utilization in the region and offer important considerations for reservoir characterization and development strategies in similar low-rank coal deposits.HighlightsExtensive evaluation of methane adsorption and pore characteristics in Soma Basin coals, uncovering substantial potential for coalbed methane.The study reveals a diverse range of methane adsorption capacities, indicating highly promising methane storage capabilities.Correlation between coal quality parameters and methane adsorption, offering valuable insights into gas storage influenced by coal composition.Emphasis on the crucial role of micropores in methane storage, underscoring their significance as primary adsorption sites.Practical implications for optimizing methane extraction and utilization, guiding reservoir development in low-rank coal deposits like Soma Basin.

Study of the Methane Adsorption Characteristics in a Deep Coal Reservoir Using Adsorption Potential Theory

The gas adsorption characteristics in deep coal reservoirs are the focus of deep coalbed methane geology research. In order to reveal the adsorption characteristics in deep coal reservoirs and quantitatively characterize the amount of adsorbed methane in the deep coal seams, four coals were collected from the Permian Longtan Formation in southern Sichuan Province. Methane isothermal adsorption tests were carried out on the collected coal samples at 30 °C. The adsorption characteristic curve was established based on the data of the isothermal adsorption. The adsorption potential theory was used to predict the isothermal adsorption curves under different temperatures and the evolutionary relationship between the methane adsorption capacity and the coal seam burial depth in the C17 and C25 coal seams of the Permian in southern Sichuan Province, China. The results showed that the methane isothermal adsorption curve at 30 °C belonged to the Type I isotherm adsorption curve. The methane isothermal adsorption curves for various samples at 45 °C, 60 °C, and 75 °C were predicted based on the uniqueness of the methane adsorption characteristic curve. The amount of adsorbed gas in deep coal reservoirs was comprehensively controlled by pressure and temperature. The pressure showed a positive effect on the amount of methane adsorbed, while the temperature showed a negative effect on the adsorption of methane. The negative effect of temperature became more significant with the increase in pressure. The results of the study are beneficial for further promoting the exploration and development of deep coalbed methane in the southern Sichuan Province of China.

Investigations of methane adsorption characteristics on marine-continental transitional shales and gas storage capacity models considering pore evolution

Methane adsorption is a critical assessment of the gas storage capacity (GSC) of shales with geological conditions. Although the related research of marine shales has been well-illustrated, the methane adsorption of marine-continental transitional (MCT) shales is still ambiguous. In this study, a method of combining experimental data with analytical models was used to investigate the methane adsorption characteristics and GSC of MCT shales collected from the Qinshui Basin, China. The Ono-Kondo model was used to fit the adsorption data to obtain the adsorption parameters. Subsequently, the geological model of GSC based on pore evolution was constructed using a representative shale sample with a total organic carbon (TOC) content of 1.71%, and the effects of reservoir pressure coefficient and water saturation on GSC were explored. In experimental results, compared to the composition of the MCT shale, the pore structure dominates the methane adsorption, and meanwhile, the maturity mainly governs the pore structure. Besides, maturity in the middle-eastern region of the Qinshui Basin shows a strong positive correlation with burial depth. The two parameters, micropore pore volume and non-micropore surface area, induce a good fit for the adsorption capacity data of the shale. In simulation results, the depth, pressure coefficient, and water saturation of the shale all affect the GSC. It demonstrates a promising shale gas potential of the MCT shale in a deeper block, especially with low water saturation. Specifically, the economic feasibility of shale gas could be a major consideration for the shale with a depth of <800 m and/or water saturation >60% in the Yushe-Wuxiang area. This study provides a valuable reference for the reservoir evaluation and favorable block search of MCT shale gas.

Microwave irradiation-induced alterations in physicochemical properties and methane adsorption capability of coals: An experimental study using carbon molecular sieve

In order to comprehend the applicability of microwave irradiation for recovering coalbed methane, it is necessary to evaluate the microwave irradiation-induced alterations in coals with varying levels of metamorphism. In this work, the carbon molecular sieve combined with KMnO4 oxidation was selected to fabricate carbon molecular sieve with diverse oxidation degrees, which can serve as model substances toward coals. Afterwards, the microwave irradiation dependences of pores, functional groups, and high-pressure methane adsorption characteristics of model substances were studied. The results indicated that microwave irradiation causes rearrangement of oxygen-containing functional groups, which could block the micropores with a size of 0.40–0.60 nm in carbon molecular sieve; meanwhile, naphthalene and phenanthrene generated by macro-molecular structure pyrolysis due to microwave irradiation could block the micropores with a size of 0.70–0.90 nm. These alterations in micropore structure weaken the saturated methane adsorption capacity of oxidized carbon molecular sieve by 2.91%–23.28%, suggesting that microwave irradiation could promote methane desorption. Moreover, the increased mesopores found for oxidized carbon molecular sieve after microwave irradiation could benefit CH4 diffusion. In summary, the oxidized carbon molecular sieve can act as model substances toward coals with different ranks. Additionally, microwave irradiation is a promising technology to enhance coalbed methane recovery.

Rigidity with Flexibility: Porous Triptycene Networks for Enhancing Methane Storage.

In the pursuit of advancing materials for methane storage, a critical consideration arises given the prominence of natural gas (NG) as a clean transportation fuel, which holds substantial potential for alleviating the strain on both energy resources and the environment in the forthcoming decade. In this context, a novel approach is undertaken, employing the rigid triptycene as a foundational building block. This strategy is coupled with the incorporation of dichloromethane and 1,3-dichloropropane, serving as rigid and flexible linkers, respectively. This combination not only enables cost-effective fabrication but also expedites the creation of two distinct triptycene-based hypercrosslinked polymers (HCPs), identified as PTN-70 and PTN-71. Surprisingly, despite PTN-71 manifesting an inferior Brunauer-Emmett-Teller (BET) surface area when compared to the rigidly linked PTN-70, it showcases remarkably enhanced methane adsorption capabilities, particularly under high-pressure conditions. At a temperature of 275 K and a pressure of 95 bars, PTN-71 demonstrates an impressive methane adsorption capacity of 329 cm3 g-1. This exceptional performance is attributed to the unique flexible network structure of PTN-71, which exhibits a pronounced swelling response when subjected to elevated pressure conditions, thus elucidating its superior methane adsorption characteristics. The development of these advanced materials not only signifies a significant stride in the realm of methane storage but also underscores the importance of tailoring the structural attributes of hypercrosslinked polymers for optimized gas adsorption performance.

Pore Structure and Methane Adsorption Characteristics of Primary Structural and Tectonic Coals

Pore Structure and Methane Adsorption Characteristics of Primary Structural and Tectonic Coals

Thermodynamic Characteristics of Methane Adsorption and Desorption on Varied Rank Coals: A Systematic Study

Thermodynamic Characteristics of Methane Adsorption and Desorption on Varied Rank Coals: A Systematic Study

Analysis of the influence of different pore ratios on methane adsorption characteristics of coal

The diverse pore structures in coal are pivotal in coalbed methane storage and transportation, making it highly significant to explore methane adsorption characteristics across varying pore sizes for effective prevention and control of coal mine gas disasters. Using the proposed graphene nanotube filling method, eight coal molecule models with varying pore size ratios were constructed, including four different pore radii: 0.35 nm, 0.55 nm, 0.75 nm, and 2 nm. Methane adsorption amount, methane density, and methane concentration distribution were obtained through Monte Carlo (GCMC) and molecular dynamics (MD) simulation methods. The research results show that coal consisting of multiple pore sizes had a better methane adsorption capacity than a single pore size. Combining pore sizes of 0.35 nm, 0.55 nm, and 0.75 nm in a 1:2:1 ratio resulted in the highest excess methane adsorption capacity in coal, reaching 5.623 mmol/g. The single pore size of 0.55 nm in coal had the lowest excess adsorption amount of methane, which was 2.236 mmol/g. The presence of mesopores weakened the methane adsorption capacity of coal, and this weakening effect increased with the increase of mesopore proportion. In the model composed of single pore size micropores, the methane concentration inside the pores was uniformly distributed. The coexistence of multiple micropores may lead to methane filling in the micropores in a monolayer adsorption form. The coexistence of micropores and mesopores does not alter methane filling in the micropores and monolayer adsorption in the mesopores. The research results provide new insights into our understanding of the impact of pores on methane adsorption in coal.

Theory and Engineering Practice of Intermittent Heat Injection-Enhanced Coalbed Methane Extraction.

Because of the strong adsorption characteristics of methane and the low permeability of coal seams, the extraction efficiency of coalbed methane (CBM) is very low. Here, based on the energy conservation equation, we propose the theory of heat injection-enhanced CBM extraction. We developed a device for heat injection-enhanced CBM extraction and performed an on-site heat injection test in the Chengzhuang coal mine. The results showed that when the water injection rate was 0.5 m3/h, the heat injection temperature was 145 °C, with two heat injections, yielding the best CBM extraction effect. This could fully utilize the heat injection equipment and achieve a fast, safe, and efficient extraction. The gas production law of the intermittent heat injection-enhanced CBM extraction method had obvious stages; the CBM concentration and daily gas production were very low during the heat injection stage but were greatly improved during the extraction stage after heat injection. The highest CBM concentration reached 100%, and the maximum daily gas production of CBM increased by 1269 times. The variation law of the cumulative gas production with time was fitted using Wang's empirical formula. Comparative analysis showed that, compared to traditional extraction, intermittent heat injection shortened the extraction time by 6.6 years. Compared with other enhanced CBM extraction methods, the intermittent heat injection method had obvious technical advantages and greater improvements in concentration and CBM extraction speed. Therefore, the results are of great significance for improving the recovery rate of CBM and for reducing greenhouse gas emissions.

Kinetic and Thermodynamic Characteristics of Supercritical Methane Adsorption on Organic-Rich Shale: A Case Study of Ordovician Wufeng and Silurian Longmaxi Gas Shale

Kinetic and Thermodynamic Characteristics of Supercritical Methane Adsorption on Organic-Rich Shale: A Case Study of Ordovician Wufeng and Silurian Longmaxi Gas Shale

Methane Adsorption in Anthracite Coal under Different Pressures and Temperatures—A Study Combining Isothermal Adsorption and Molecular Simulation

In situ gas content is an important parameter associating coalbed methane, while the influence of pressure and temperature on methane adsorption and desorption still needs to be revealed. In this study, the molecular structure and methane adsorption capacity of anthracite coal collected from Diandong Coalfield (China) were studied based on 13C nuclear magnetic resonance (13C NMR), Fourier transform infrared spectroscopy (FT-IR), and methane isothermal adsorption experiment. The results show that the carbon skeleton of coal sample is mainly composed by aromatic carbon (72%), followed by aliphatic carbon structure (14.2%). Carbons connected to the oxygen atoms contribute 13.7% of the total carbons in coal molecule, and the oxygen atoms are mainly in the form of carbonyl. The 2-dimension structure and 3-dimension molecular structure of coal sample was also reconstructed. The average chemical formula of the coal molecule is C200H133O21N3. The experimental methane adsorption isothermal data of the coal sample under different temperatures shows that with increasing the temperature, the methane adsorption amount at each pressure decreases obviously. At 7 MPa and 20°C, the methane adsorption amount of the coal sample is 28.5 cm3/g. Comparably, at 100°C and 7 MPa, the methane adsorption amount is only 15.9 cm3/g, decreasing by 44%. In mesopores, temperature has stronger influence on methane adsorption under higher pressure than that of lower pressure. On the contrary, in micropores, temperature has weaker effects on methane adsorption at higher pressure than that at lower pressure. The results can be beneficial for understanding methane adsorption characteristics of deep coal.

Methane Adsorption Characteristics Under In Situ Reservoir Conditions of the Wufeng–Longmaxi Shale in Southern Sichuan Basin, China: Implications for Gas Content Evaluation

Methane Adsorption Characteristics Under In Situ Reservoir Conditions of the Wufeng–Longmaxi Shale in Southern Sichuan Basin, China: Implications for Gas Content Evaluation

Thermodynamic characteristics of methane adsorption on coals from China with selected metamorphism degrees: Considering the influence of temperature, moisture content, and in situ modification

A better understanding of the thermodynamic characteristics of methane (CH4) adsorption on coal surfaces is needed for the high-efficiency coalbed methane (CBM) preextraction or prevention of coal and gas outbursts. In this study, atomistic representations of selected coal samples with different degrees of metamorphism, such as long flame coal, coking coal, and anthracite coal obtained from China were created; CH4 adsorption isotherms considering the temperature, moisture content, and microwave in situ modification for CBM preextraction were simulated and analysed. The coal molecular structural results showed that as the degree of coal metamorphism increased from long flame coal to coking coal and anthracite coal, the functional groups in the molecular structure of the coal reduced, while the degree of graphite increased. In situ modification of coal facilitated this process. The saturation adsorption capacity of CH4 decreased and then increased with increasing coal metamorphism degree and decreased linearly with increasing temperature. When water molecules were present, the adsorbed CH4 showed different degrees of decreasing trends with increasing moisture content. The isosteric heat of CH4 adsorption followed the order of coking coal > anthracite coal > long flame coal. The isosteric heat gradually decreased with increasing methane adsorption, and the presence of water molecules had a limited effect on the isosteric heat. In situ modification disrupted the self-conjugated hydrogen bonds, reduced the oxygen-containing functional groups, and decomposed some associated minerals in the coal samples. After in situ modification, the amount of methane adsorption decreased due to a greater contribution from the functional group change than that from the pore volume change, and the modification effect was more evident for the low-rank coal samples than for the middle and high metamorphism degree coal samples. In situ modification applied in the coal seams could contributed to designs for CBM exploration, and the results of this experiment and simulation could provide a novel theoretical basis for in situ modification technology.

Molecular Dynamics Simulation of Methane Adsorption and Diffusion: A Case Study of Low-Rank Coal in Fukang Area, Southern Junggar Basin

Adsorption and diffusion are the key factors affecting coalbed methane (CBM) accumulation, resource assessment and production prediction. To study the adsorption and diffusion mechanism of Fukang low-rank coal at the microscopic level, samples of Fukang low-rank coal were collected, and the elemental composition, carbon type distribution and functional group type of the Fukang low-rank coal structure were determined by elemental analysis (Ea), Fourier-transform interferometric radiometer (FTIR), X-ray photoelectron spectroscopy (XPS) and 13C nuclear magnetic resonance (13C NMR) experiments to construct a 2D molecular structure of the coal and a 3D macromolecular structure model. The adsorption and diffusion characteristics of methane were researched by giant regular Monte Carlo (GCMC) and molecular dynamics (MD) simulation methods. The results showed that the excess adsorption amount of methane increased and then decreased with the increase in pressure. The diffusion of methane showed two stages with increasing pressure: a sharp decrease in the diffusion coefficient from 0.5 to 5.0 MPa and a slow decrease in the diffusion coefficient from 5.0 to 15.0 MPa. The lower the pressure, the larger the effective radius of the CH4 and C atoms, and the higher the temperature, the more pronounced the diffusion and the larger the effective radius.