scholarly journals Methane adsorption characteristics and its influencing factors of the medium-to-high rank coals in the Anyang-Hebi coalfield, northern China

2018 ◽  
Vol 37 (1) ◽  
pp. 60-82 ◽  
Author(s):  
Sheng Zhao ◽  
Longyi Shao ◽  
Haihai Hou ◽  
Yue Tang ◽  
Zhen Li ◽  
...  
Keyword(s):  
Adsorption Capacity ◽  
Influencing Factors ◽  
Coalbed Methane ◽  
Vitrinite Reflectance ◽  
Negative Relationship ◽  
Methane Adsorption ◽  
High Rank ◽  
Gas Content ◽  
Coal Rank ◽  
Adsorption Characteristics

The variation of coal rank in the Anyang-Hebi (Anhe) coalfield has the phenomenon of anti-Hilt law, which makes the coalfield distinctive for coalbed methane exploration research. The methane adsorption characteristics and influencing factors of the medium-to-high rank coal samples of the Shanxi Formation in this coalfield were analyzed. The results indicate that the Langmuir volume ( VL) of coals in the shallow western part of the Anhe coalfield is generally higher than that in the deep eastern part. The coal rank and the coal macerals are the dominant factors that influence the methane adsorption capacity of coals in this anti-Hilt law area. The methane adsorption capacity, represented by VL, first increases and then decreases with the coal rank, and the highest VL value corresponds to the maximum vitrinite reflectance of ∼2.1%. The adsorption capacity has a positive correlation with the vitrinite and the moisture content, a negative relationship with the inertinite content. In general, the adsorption capacity of coal samples shows a “V-shaped” change with the ash yield, and the lowest VL value corresponds to the ash yield of ∼9%. A prediction model of the gas content of the Anhe coalfield was proposed based on changes of the methane adsorption capacity and principal component analysis. Areas with a critical depth ranging from 400 m to 700 m are suggested to be methane enrichment regions for coalbed methane exploration in the Anhe coalfield.

scholarly journals Application of a Modified Low-Field NMR Method on Methane Adsorption of Medium-Rank Coals

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Xiaozhen Chen ◽  
Taotao Yan ◽  
Fangui Zeng ◽  
Yanjun Meng ◽  
Jinhua Liu
Keyword(s):  
Adsorption Capacity ◽  
Coalbed Methane ◽  
Gas Adsorption ◽  
Vitrinite Reflectance ◽  
Methane Adsorption ◽  
Coal Rank ◽  
Nmr Method ◽  
Low Field ◽  
Low Field Nmr ◽  
The Absolute

Methane adsorption capacity is an important parameter for coalbed methane (CBM) exploitation and development. Traditional examination methods are mostly time-consuming and could not detect the dynamic processes of adsorption. In this study, a modified low-field nuclear magnetic resonance (NMR) method that compensates for these shortcomings was used to quantitatively examine the methane adsorption capacity of seven medium-rank coals. Based on the typical T 2 amplitudes obtained from low-field NMR measurement, the volume of adsorbed methane was calculated. The results indicate that the Langmuir volume of seven samples is in a range of 18.9–31.85 m3/t which increases as the coal rank increases. The pore size in range 1-10 nm is the main contributor for gas adsorption in these medium-rank coal samples. Comparing the adsorption isotherms of these coal samples from the modified low-field NMR method and volumetric method, the absolute deviations between these two methods are less than 1.03 m3/t while the relative deviations fall within 4.76%. The absolute deviations and relative deviations decrease as vitrinite reflectance ( R o ) increases from 1.08% to 1.80%. These results show that the modified low-field NMR method is credible to measure the methane adsorption capacity and the precision of this method may be influenced by coal rank.

scholarly journals Univariate and Multivariate Analyses of Influencing Factors on Methane Adsorption Capacity of Semianthracite

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Shihui Hou ◽  
Xiaoming Wang ◽  
Yudong Yuan ◽  
Sidong Pan ◽  
Zheng Dang ◽  
...  
Keyword(s):  
Specific Surface ◽  
Adsorption Capacity ◽  
Surface Area ◽  
Influencing Factors ◽  
Specific Surface Area ◽  
Multivariate Analyses ◽  
Methane Adsorption ◽  
Coal Rank ◽  
Strong Positive Correlation ◽  
Quantification Theory

Methane adsorption isotherm experiments on semianthracite (2.00-2.33% R o , max ) collected from the Xin’an coal mine, Henan Province, China, were conducted to investigate the effects of pore structure, coal quality, coal maceral, and coal rank on methane adsorption capacity with applications of univariate and multivariate analyses. Methane adsorption capacity varies significantly from 12.03 to 28.40 cm3/g. In univariate analysis, methane adsorption capacity has a strong positive correlation with pore specific surface area, weak positive correlations with pore volume and ash content, and weak negative correlations with moisture content and inertinite content. No correlation is observed between methane adsorption capacity and coal rank. In multivariate analysis, the mathematical model of methane adsorption capacity affected by the combined individual variables is established based on quantification theory I. There are similarities and differences between the two analyses. The similarities are that pore specific surface area has the greatest contribution to methane adsorption capacity, while coal rank has the least contribution. The differences are reflected in two aspects. Firstly, the other influencing factors contribute differently to methane adsorption capacity. Secondly, the positive or negative correlations of some influencing factors present the opposite. The mathematic model synthetically covers the combined effects of the influencing factors, which is more representative in evaluating methane adsorption capacity.

Investigation on the Structure and Fractal Characteristics of Nanopores in High-Rank Coal: Implications for the Methane Adsorption Capacity

2021 ◽  
Vol 21 (1) ◽  
pp. 392-404
Author(s):  
Yanhui Yang ◽  
Kun Yu ◽  
Yiwen Ju ◽  
Qiuping Hu ◽  
Bowen Yu ◽  
...  
Keyword(s):  
Pore Structure ◽  
Carbon Content ◽  
Adsorption Capacity ◽  
Negative Relationship ◽  
Methane Adsorption ◽  
High Rank ◽  
Fixed Carbon ◽  
Adsorption Volume ◽  
Fractal Characteristics ◽  
Fixed Carbon Content

The structure and fractal characteristics of nanopores of high-rank coal were investigated using an approach that integrates N2 adsorption and field emission scanning electron microscopy (FE-SEM). The results indicated that the high-rank coal of the Shanxi Formation has a complex pore-fracture network composed of organic matter pores, mineral-related pores, and microfractures. The pore type of high-rank coal tends to be complicated, and the main pore types are inkbottle pores and open pores, which are more conducive to methane enrichment. The Ro,max has a negative relationship with the total pore volume. In addition, the ash and inertinite contents show a positive correlation with the average pore size (APS), while the fixed carbon content exhibits a negative relationship with the APS. The pore structure of high-rank coal is controlled not only by the degree of metamorphism but also by coal composition, which leads to the variation in pore structure becoming more complicated. With the increase in coal metamorphism, high-rank coal with high amounts of fixed carbon content generally possesses a higher irregularity in pore structure. No obvious relationship was observed between D2 and the coal components, which indicates that the pore structure, ash content, moisture content and other factors controlled by the metamorphism of coal have different effects on D2 that lead to this inapparent relationship. A negative relationship exists between adsorption volume and D1, which indicates that the high irregularity of the pore structure is not conducive to methane absorption and that no obvious correlation exists between the adsorption volume and D2. In the high-rank coal, the high D1 value represents the complexity and heterogeneity of the pore structure and represents a low adsorption affinity for methane molecules; in addition, D2 has no effect on the methane adsorption capacity.

scholarly journals Simulation of methane adsorption in diverse organic pores in shale reservoirs with multi-period geological evolution

2021 ◽  
Author(s):  
Shangbin Chen ◽  
Chu Zhang ◽  
Xueyuan Li ◽  
Yingkun Zhang ◽  
Xiaoqi Wang
Keyword(s):  
Organic Matter ◽  
Pore Size ◽  
Adsorption Capacity ◽  
Thermal Evolution ◽  
Methane Adsorption ◽  
Storage Site ◽  
Pressure Sensitivity ◽  
Adsorption Characteristics ◽  
Shale Reservoirs ◽  
Organic Pores

AbstractIn shale reservoirs, the organic pores with various structures formed during the thermal evolution of organic matter are the main storage site for adsorbed methane. However, in the process of thermal evolution, the adsorption characteristics of methane in multi type and multi-scale organic matter pores have not been sufficiently studied. In this study, the molecular simulation method was used to study the adsorption characteristics of methane based on the geological conditions of Longmaxi Formation shale reservoir in Sichuan Basin, China. The results show that the characteristics of pore structure will affect the methane adsorption characteristics. The adsorption capacity of slit-pores for methane is much higher than that of cylindrical pores. The groove space inside the pore will change the density distribution of methane molecules in the pore, greatly improve the adsorption capacity of the pore, and increase the pressure sensitivity of the adsorption process. Although the variation of methane adsorption characteristics of different shapes is not consistent with pore size, all pores have the strongest methane adsorption capacity when the pore size is about 2 nm. In addition, the changes of temperature and pressure during the thermal evolution are also important factors to control the methane adsorption characteristics. The pore adsorption capacity first increases and then decreases with the increase of pressure, and increases with the increase of temperature. In the early stage of thermal evolution, pore adsorption capacity is strong and pressure sensitivity is weak; while in the late stage, it is on the contrary.

scholarly journals The influence of temperature on methane adsorption in coal: A review and statistical analysis

2019 ◽  
Vol 37 (9-10) ◽  
pp. 745-763 ◽  
Author(s):  
Zhijun Wang ◽  
Xiaojuan Wang ◽  
Weiqin Zuo ◽  
Xiaotong Ma ◽  
Ning Li
Keyword(s):  
Coalbed Methane ◽  
Methane Adsorption ◽  
Gas Content ◽  
Future Research ◽  
Temperature Dependent ◽  
Current State ◽  
Influence Of Temperature On ◽  
State Of Research ◽  
Increasing Temperature ◽  
The Relationship

The capacity of coal to adsorb methane is greatly affected by temperature and, in recent years, temperature-dependent adsorption has been studied by many researchers. Even so, comprehensive conclusions have not been reached and conflicting experimental results are common. This paper reviews the current state of research regarding the temperature-dependent adsorption of methane in coal and catalogs the conclusions from experiments conducted on that subject by 28 researchers, as published between 1995 and 2017. Probability theory and statistics are used to show that the conclusion generally accepted by most researchers is that the amount of methane adsorbed by coal decreases with increasing temperature. It is highly likely that the Langmuir volume decreases as the temperature rises, and it is also probable that the Langmuir pressure increases at higher temperatures. Equations are presented that express the relationships between methane adsorption, Langmuir volume, Langmuir pressure, and temperature. Future research should be directed toward determining the relationship between Langmuir pressure and temperature. The results of the study presented herein provide a theoretical basis for predicting the gas content in coal seams and improving the efficiency of coalbed methane development.

scholarly journals Variation of Petrophysical Properties and Adsorption Capacity in Different Rank Coals: An Experimental Study of Coals from the Junggar, Ordos and Qinshui Basins in China

Energies ◽  
2019 ◽  
Vol 12 (6) ◽  
pp. 986 ◽  
Author(s):  
Yingjin Wang ◽  
Dameng Liu ◽  
Yidong Cai ◽  
Xiawei Li
Keyword(s):  
Adsorption Capacity ◽  
Vitrinite Reflectance ◽  
Inhibitory Effect ◽  
Proximate Analysis ◽  
Methane Adsorption ◽  
Low Rank ◽  
Petrophysical Properties ◽  
Isothermal Adsorption ◽  
Variation Rule ◽  
Moisture Absorbent

The petrophysical properties of coal will vary during coalification, and thus affect the methane adsorption capacity. In order to clarify the variation rule and its controlling effect on methane adsorption, various petrophysical tests including proximate analysis, moisture measurement, methane isothermal adsorption, mercury injection, etc. were carried out on 60 coal samples collected from the Junggar, Ordos and Qinshui basins in China. In this work, the boundary values of maximum vitrinite reflectance (Ro,m) for dividing low rank, medium rank and high rank coals are set as 0.65% and 2.0%. The results show that vitrinite is the most abundant maceral, but the maceral contents are controlled by sedimentation without any relation to coal rank. Both the moisture content and porosity results show higher values in the low ranks and stabilized with Ro,m beyond 1%. Ro,m and VL (daf) show quadratic correlation with the peak located in Ro,m = 4.5–5%, with the coefficient (R2) reaching 0.86. PL decrease rapidly before Ro,m = 1.5%, then increase slowly. DAP is established to quantify the inhibitory effect of moisture on methane adsorption capacity, which shows periodic relationship with Ro,m: the inhibitory effect in lignite is the weakest and increases during coalification, then remains constant at Ro,m = 1.8% to 3.5%, and finally increases again. In the high metamorphic stage, clay minerals are more moisture-absorbent than coal, and the inherent moisture negatively correlates with the ratio of vitrinite to inertinite (V/I). During coalification, micro gas pores gradually become dominant, fractures tends to be well oriented and extended, and clay filling becomes more common. These findings can help us better understand the variation of petrophysical properties and adsorption capacity in different rank coals.

scholarly journals Controls on Gas Domains and Production Behaviour in A High-Rank CSG Reservoir: Insights from Molecular and Isotopic Chemistry of Co-Produced Waters and Gases from the Bowen Basin, Australia

Geosciences ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 74 ◽  
Author(s):  
Stephanie K. Hamilton ◽  
Suzanne D. Golding ◽  
Joan S. Esterle ◽  
Kim A. Baublys ◽  
Brycson B. Ruyobya
Keyword(s):  
Carbon Isotope ◽  
Vitrinite Reflectance ◽  
Isotope Analysis ◽  
Co2 Reduction ◽  
Production Performance ◽  
High Rank ◽  
Gas Content ◽  
Coal Seams ◽  
Gas Generation ◽  
Geographic Variations

This paper uses hydrochemical and multi-isotope analysis to investigate geological controls on coal seam gas (CSG) saturation domains and gas well production performance in a high-rank (vitrinite reflectance (Rv) > 1.1) CSG field in the north-western Bowen Basin, Australia. New hydrochemical and stable isotope data were combined with existing geochemical datasets to refine hypotheses on the distribution and origins of CSG in two highly compartmentalized Permian coal seams. Stable isotopic results suggest that geographic variations in gas content, saturation and production reflect the extent of secondary microbial gas generation and retention as a function of hydrodynamics. δ13C and δ2H data support a gas mixing hypothesis with δ13C-CH4 increasing from secondary biogenic values to thermogenic values at depth (δ13C −62.2‰ to −46.3‰), whereas correlated methane and carbon dioxide carbon isotope compositions, Δ13C(CO2–CH4) values and δ13CDIC/alkalinity trends are largely consistent with microbial CO2 reduction. In addition, below 200 m, the majority of δ13C-CO2 values are positive (δ13C: −1.2‰ to 7.1‰) and δ13CDIC shows an erratic increase with depth for both seams that is characteristic of evolution via microbial activity. The progression of carbon isotope values along the CO2 reduction fractionation line suggests progressive depletion of the CO2 reservoir with increasing depth. Faults clearly segment coal seams into areas having significantly different production, with results of geochemical analysis suggesting that pooling of biogenic gas and waters and enhanced methanogenesis occur north of a faulted hinge zone.

Factors affecting the nanopore structure and methane adsorption capacity of organic-rich marine shales in Zhaotong area, Southern Sichuan Basin

2020 ◽  
Vol 8 (2) ◽  
pp. T403-T419
Author(s):  
Panke Sun ◽  
Hanqing Zhu ◽  
Huaimin Xu ◽  
Xiaoni Hu ◽  
Linfeng Tian
Keyword(s):  
Adsorption Capacity ◽  
Sichuan Basin ◽  
Clay Content ◽  
Mineralogical Composition ◽  
Methane Adsorption ◽  
Gas Content ◽  
Quartz Content ◽  
Structure Characteristics ◽  
Longmaxi Shale ◽  
Nanopore Structure

As a national shale-gas demonstration zone in China, the Zhaotong area has great gas resource potential. However, the nanopore structure characteristics, methane adsorption capacity, and their affecting factors of the Lower Silurian Longmaxi Shale in this area remain unclear. To address these puzzles, we conducted a series of experiments, such as X-ray diffraction, field emission scanning electron microscopy, low-pressure [Formula: see text] adsorption, and high-pressure methane adsorption, and we calculated the relevant characteristic parameters, such as pore volume (PV), specific surface area (SSA), fractal dimension, and Langmuir parameters by using the nonlocal density functional theory method, Frenkel-Halsey-Hill theory, and Langmuir model, respectively. The results indicate that the nanopores of the Lower Longmaxi Shale in the Zhaotong area are composed of micropores and mesopores, which mainly exist as organic matter (OM) pores. The pore surface exhibits a high degree of heterogeneity as indicated by the fractal dimensions ranging from 2.845 to 2.866. The nanopore structure characteristics (i.e., SSA and PV) and methane adsorption capacity are mainly controlled by the total organic carbon (TOC) content. In addition, the mineralogical composition (i.e., the quartz and clay content) also contributes significantly to the micropore PV and gas content. The external provenance has a significant effect on the mineralogical composition, TOC content, and methane adsorption capacity. With the increasing influence of the external provenance, the biogenic quartz content decreases and the relationship between the quartz content and TOC content becomes more discrete, which indicates the change of depositional environment, and the clay content increases, which can dilute the OM concentration during the deposition and enhance the compaction potential, and it can eventually result in less gas content. The results of this study reveal the nanopore system characteristics of the Longmaxi Shale in the Zhaotong area and provide further insight into the influence of external provenance on reservoir characteristics and gas content variability of the Lower Longmaxi Shale in the southern Sichuan Basin.

scholarly journals Study on the Effect of Soft and Hard Coal Pore Structure on Gas Adsorption Characteristics

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Xun Zhao ◽  
Tao Feng ◽  
Ping Wang ◽  
Ze Liao
Keyword(s):  
Pore Structure ◽  
Adsorption Capacity ◽  
Residence Time ◽  
Coalbed Methane ◽  
Gas Adsorption ◽  
Nitrogen Adsorption ◽  
Hard Coal ◽  
Research Results ◽  
Adsorption Characteristics ◽  
Soft Coal

In order to grasp the effect of soft and hard coal pore structure on gas adsorption characteristics, based on fractal geometry theory, low-temperature nitrogen adsorption and constant temperature adsorption test methods are used to test the pore structure characteristics of soft coal and its influence on gas adsorption characteristics. We used box dimension algorithm to measure the fractal dimension and distribution of coal sample microstructure. The research results show that the initial nitrogen adsorption capacity of soft coal is greater than that of hard coal, and the adsorption hysteresis loop of soft coal is more obvious than that of hard coal. And the adsorption curve rises faster in the high relative pressure section. The specific surface area and pore volume of soft coal are larger than those of hard coal. The number of pores is much larger than that of hard coal. In particular, the superposition of the adsorption force field in the micropores and the diffusion in the mesopores enhance the adsorption potential of soft coal. Introducing the concept of adsorption residence time, it is concluded that more adsorption sites on the surface of soft coal make the adsorption and residence time of gas on the surface of soft coal longer. Fractal characteristics of the soft coal surface are more obvious. The saturated adsorption capacity of soft coal and the rate of reaching saturation adsorption are both greater than those of hard coal. The research results of this manuscript will provide a theoretical basis for in-depth analysis of the adsorption/desorption mechanism of coalbed methane in soft coal seams and the formulation of practical coalbed methane control measures.

scholarly journals Contribution of Ash Content Related to Methane Adsorption Behaviors of Bituminous Coals

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
Yanyan Feng ◽  
Wen Yang ◽  
Wei Chu
Keyword(s):  
Adsorption Capacity ◽  
Coalbed Methane ◽  
Textural Properties ◽  
Isosteric Heat ◽  
Micropore Volume ◽  
Ash Content ◽  
Heat Of Adsorption ◽  
Methane Adsorption ◽  
Adsorbed Phase ◽  
Adsorption Processes

Methane adsorption isotherms on coals with varying ash contents were investigated. The textural properties were characterized by N2adsorption/desorption isotherm at 77 K, and methane adsorption characteristics were measured at pressures up to 4.0 MPa at 298 K, 313 K, and 328 K, respectively. The Dubinin-Astakhov model and the Polanyi potential theory were employed to fit the experimental data. As a result, ash content correlated strongly to methane adsorption capacity. Over the ash range studied, 9.35% to 21.24%, the average increase in methane adsorption capacity was 0.021 mmol/g for each 1.0% rise in ash content. With the increasing ash content range of 21.24%~43.47%, a reduction in the maximum adsorption capacities of coals was observed. In addition, there was a positive correlation between the saturated adsorption capacity and the specific surface area and micropore volume of samples. Further, this study presented the heat of adsorption, the isosteric heat of adsorption, and the adsorbed phase specific heat capacity for methane adsorption on various coals. Employing the proposed thermodynamic approaches, the thermodynamic maps of the adsorption processes of coalbed methane were conducive to the understanding of the coal and gas simultaneous extraction.

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