Influence of reservoir properties on the methane adsorption capacity and fractal features of coal and shale in the upper Permian coal measures of the South Sichuan coalfield, China

Pore structure plays an essential role in the reservoir heterogeneity and methane adsorption capacity. Significant progress has been made in the pore structure classification of porous materials (such as coal and shale). Considering the pore structure characterization of the coal measures and the measuring range of high-pressure mercury intrusion porosimetry and low-pressure N2/CO2 gas adsorption, an integrated classification for coal and shale is provided. They are micropore (<2 nm), mesopore (2–100 nm), macropore A (100 nm–1 µm), macropore B (1–10 µm), and micro-fracture (>10 µm). For coal and shale samples from Guxu mining area, the micropores and mesopores largely control the gas adsorption while micro-fractures and macropore B are significant for the storage and flow of free gas. The fractal dimensions calculated from limited N2 adsorption data are not suitable for the coal samples which are not developed in mesopore and macropore A; these samples are precisely corresponding to the N2 adsorption/desorption isotherms of group B (reversible isotherm). Furthermore, the main factors influencing the methane adsorption capacity of coal and shale in the coal measures are micropore frequency, micro-fracture width, clay mineral composition, and total organic carbon content.

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Changes in Pore Structure of Coal Caused by CS2 Treatment and Its Methane Adsorption Response

Geofluids ◽

10.1155/2018/7578967 ◽

2018 ◽

Vol 2018 ◽

pp. 1-11 ◽

Cited By ~ 4

Author(s):

Run Chen ◽

Yong Qin ◽

Pengfei Zhang ◽

Youyang Wang

Keyword(s):

Pore Structure ◽

Adsorption Capacity ◽

Gas Adsorption ◽

Recovery Process ◽

Micropore Volume ◽

Methane Adsorption ◽

Coal Bed ◽

Methane Recovery ◽

Before And After ◽

Key Issues

The pore structure and gas adsorption are two key issues that affect the coal bed methane recovery process significantly. To change pore structure and gas adsorption, 5 coals with different ranks were treated by CS2 for 3 h using a Soxhlet extractor under ultrasonic oscillation conditions; the evolutions of pore structure and methane adsorption were examined using a high-pressure mercury intrusion porosimeter (MIP) with an AutoPore IV 9310 series mercury instrument. The results show that the cumulative pore volume and specific surface area (SSA) were increased after CS2 treatment, and the incremental micropore volume and SSA were increased and decreased before and after Ro,max=1.3%, respectively; the incremental big pore (greater than 10 nm in diameter) volumes were increased and SSA was decreased for all coals, and pore connectivity was improved. Methane adsorption capacity on coal before and after Ro,max=1.3% also was increased and decreased, respectively. There is a positive correlation between the changes in the micropore SSA and the Langmuir volume. It confirms that the changes in pore structure and methane adsorption capacity due to CS2 treatment are controlled by the rank, and the change in methane adsorption is impacted by the change of micropore SSA and suggests that the changes in pore structure are better for gas migration; the alteration in methane adsorption capacity is worse and better for methane recovery before and after Ro,max=1.3%. A conceptual mechanism of pore structure is proposed to explain methane adsorption capacity on CS2 treated coal around the Ro,max=1.3%.

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Full-size pore structure characterization of deep-buried coals and its impact on methane adsorption capacity: A case study of the Shihezi Formation coals from the Panji Deep Area in Huainan Coalfield, Southern North China

Journal of Petroleum Science and Engineering ◽

10.1016/j.petrol.2018.10.100 ◽

2019 ◽

Vol 173 ◽

pp. 975-989 ◽

Cited By ~ 10

Author(s):

Qiang Wei ◽

Xianqing Li ◽

Jizhen Zhang ◽

Baolin Hu ◽

Wenwei Zhu ◽

...

Keyword(s):

Pore Structure ◽

Adsorption Capacity ◽

North China ◽

Methane Adsorption ◽

Structure Characterization ◽

Full Size ◽

Huainan Coalfield ◽

Deep Area

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Pore structure characterization and its effect on methane adsorption in shale kerogen

Petroleum Science ◽

10.1007/s12182-020-00528-9 ◽

2020 ◽

Cited By ~ 1

Author(s):

Tian-Yu Wang ◽

Shou-Ceng Tian ◽

Qing-Ling Liu ◽

Gen-Sheng Li ◽

Mao Sheng ◽

...

Keyword(s):

Pore Structure ◽

Adsorption Capacity ◽

Gas Storage ◽

Methane Adsorption ◽

Structure Characterization ◽

Sem Image ◽

Scanning Confocal Microscopy ◽

Pore Structures ◽

Slit Pore ◽

The Right

Abstract Pore structure characterization and its effect on methane adsorption on shale kerogen are crucial to understanding the fundamental mechanisms of gas storage, transport, and reserves evaluation. In this study, we use 3D scanning confocal microscopy, scanning electron microscopy (SEM), X-ray nano-computed tomography (nano-CT), and low-pressure N2 adsorption analysis to analyze the pore structures of the shale. Additionally, the adsorption behavior of methane on shales with different pore structures is investigated by molecular simulations. The results show that the SEM image of the shale sample obviously displays four different pore shapes, including slit pore, square pore, triangle pore, and circle pore. The average coordination number is 4.21 and the distribution of coordination numbers demonstrates that pores in the shale have high connectivity. Compared with the adsorption capacity of methane on triangle pores, the adsorption capacity on slit pore, square pore, and circle pore are reduced by 9.86%, 8.55%, and 6.12%, respectively. With increasing pressure, these acute wedges fill in a manner different from the right or obtuse angles in the other pores. This study offers a quantitative understanding of the effect of pore structure on methane adsorption in the shale and provides better insight into the evaluation of gas storage in geologic shale reservoirs.

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Experimental Analysis of Pore Structure and Fractal Characteristics of Soft and Hard Coals With Same Coalification

10.21203/rs.3.rs-824436/v1 ◽

2021 ◽

Author(s):

Barkat Ullah ◽

Yuanping Cheng ◽

Liang Wang ◽

Weihua Yang ◽

Izhar Mithal Jiskani ◽

...

Keyword(s):

Pore Structure ◽

Adsorption Capacity ◽

Gas Adsorption ◽

Hysteresis Loops ◽

Control Measures ◽

Practical Significance ◽

Coal Bed ◽

Hard Coal ◽

Pore Surface ◽

Soft Coal

Abstract Accurate and quantitative investigation of the physical structure and fractal geometry of coal has important theoretical and practical significance for coal bed methane and the prevention of dynamic disasters such as coal and gas outbursts. This study investigates the pore structure and fractural characteristics of soft and hard coals using nitrogen and carbon dioxide (N2/CO2) adsorption. Coal samples from Pingdingshan Mine in Henan province of China were collected and pulverized to the required size (0.2-0.25mm). N2/CO2 adsorption tests were performed to evaluate the pore size distribution (PSD), specific surface area (SSA), and pore volume (PV). The pore structure was characterized based on fractural theory. The results unveiled that the strength of coal has a significant influence on pore structure and fracture dimensions. The obvious N2-adsorption isotherms of the coals were verified as Type IV (A) and Type II. The shape of the hysteresis loops indicates the presence of slit-shaped pores. There are significant differences in SSA and PV between both coals. The soft coal showed larger SSA and PV than hard coal that shows consistency with adsorption capacity. The fractal dimensions of soft coal are respectively larger than that of hard coal. The greater the value of D1 (complexity of pore surface) of soft coal is, the larger the pore surface roughness and gas adsorption capacity is. The results enable us to conclude that the characterization of pores and fractures of soft and hard coals is different, tending to different adsorption/desorption characteristics and outburst sensitivity. In this regard, results provide a reference for formulating corresponding coal and gas outburst prevention and control measures.

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Influence of solvents on pore structure and methane adsorption capacity of lacustrine shales: An example from a Chang 7 shale sample in the Ordos Basin, China

Journal of Petroleum Science and Engineering ◽

10.1016/j.petrol.2019.03.052 ◽

2019 ◽

Vol 178 ◽

pp. 419-428 ◽

Cited By ~ 4

Author(s):

Yan Cao ◽

Hui Han ◽

Hou-wu Liu ◽

Jian-chao Jia ◽

Wei Zhang ◽

...

Keyword(s):

Pore Structure ◽

Adsorption Capacity ◽

Ordos Basin ◽

Methane Adsorption ◽

Shale Sample ◽

The Ordos Basin ◽

Influence Of Solvents

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Gas Adsorption/Desorption Isotherm for Pore Structure Characterization

Materials Science and Engineering of Carbon ◽

10.1016/b978-0-12-805256-3.00011-8 ◽

2016 ◽

pp. 227-247 ◽

Cited By ~ 2

Author(s):

Yoko Nishi ◽

Michio Inagaki

Keyword(s):

Pore Structure ◽

Gas Adsorption ◽

Structure Characterization ◽

Desorption Isotherm ◽

Adsorption Desorption

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Effect of Kerogen Thermal Maturity on Methane Adsorption Capacity: A Molecular Modeling Approach

Molecules ◽

10.3390/molecules25163764 ◽

2020 ◽

Vol 25 (16) ◽

pp. 3764 ◽

Cited By ~ 1

Author(s):

Saad Alafnan ◽

Theis Solling ◽

Mohamed Mahmoud

Keyword(s):

Molecular Modeling ◽

Adsorption Capacity ◽

Gas Adsorption ◽

Material Balance ◽

Methane Adsorption ◽

Source Rocks ◽

Thermal Maturity ◽

Reserve Estimation ◽

Adsorbed Gas ◽

Key Factor

The presence of kerogen in source rocks gives rise to a plethora of potential gas storage mechanisms. Proper estimation of the gas reserve requires knowledge of the quantities of free and adsorbed gas in rock pores and kerogen. Traditional methods of reserve estimation such as the volumetric and material balance approaches are insufficient because they do not consider both the free and adsorbed gas compartments present in kerogens. Modified versions of these equations are based on adding terms to account for hydrocarbons stored in kerogen. None of the existing models considered the effect of kerogen maturing on methane gas adsorption. In this work, a molecular modeling was employed to explore how thermal maturity impacts gas adsorption in kerogen. Four different macromolecules of kerogen were included to mimic kerogens of different maturity levels; these were folded to more closely resemble the nanoporous kerogen structures of source rocks. These structures form the basis of the modeling necessary to assess the adsorption capacity as a function of the structure. The number of double bonds plus the number and type of heteroatoms (O, S, and N) were found to influence the final configuration of the kerogen structures, and hence their capacity to host methane molecules. The degree of aromaticity increased with the maturity level within the same kerogen type. The fraction of aromaticity gives rise to the polarity. We present an empirical mathematical relationship that makes possible the estimation of the adsorption capacity of kerogen based on the degree of polarity. Variations in kerogen adsorption capacity have significant implications on the reservoir scale. The general trend obtained from the molecular modeling was found to be consistent with experimental measurements done on actual kerogen samples. Shale samples with different kerogen content and with different maturity showed that shales with immature kerogen have small methane adsorption capacity compared to shales with mature kerogen. In this study, it is shown for the first time that the key factor to control natural gas adsorption is the kerogen maturity not the kerogen content.

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

Advances in Civil Engineering ◽

10.1155/2021/1425227 ◽

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.

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