Coal Matrix Deformation and Pore Structure Change in High-Pressure Nitrogen Replacement of Methane

Ji, Xiaofeng; Song, Dangyu; Ni, Xiaoming; Li, Yunbo; Zhao, Haotian

doi:10.3390/en11010175

Cited by 11 publications

(8 citation statements)

References 47 publications

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“…In addition, the amorphous surface of coal enriches functional groups, possessing strong adsorption capacity for polar molecule adsorbates [5][6][7], such as water vapor. In coal preparation and utilization processes, including coalbed methane (CBM) recovery and CO 2 geosequestration, both surface properties and pore structure are important aspects to be investigated [8,9].…”

Section: Introductionmentioning

confidence: 99%

Surface Properties and Pore Structure of Anthracite, Bituminous Coal and Lignite

et al. 2018

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Properties of coal surface and pore structure are important aspects to be investigated in coal preparation and utilization. In order to investigate the limits of different probe methods, a comprehensive approach was comparatively used to probe surface properties and pore structure of anthracite, bituminous coal and lignite. Surface morphology of the three coal samples was analyzed by scanning electron microscopy (SEM). Combining mercury intrusion porosimetry (MIP), physisorption method with carbon dioxide (CO 2) at 273 K and nitrogen (N 2) at 77 K was used to quantify a broad pore size distribution of coals, while FT-IR and water vapor sorption methods were used to study the coal surface properties. The results show that wedge-shaped pores develop with the increase of coal rank due to compression effect. The determined specific surface area (SSA) and pore volume of N 2 decrease with the increase of coal rank, while CO 2 SSA and pore volume are of a kind of U-shaped function of coal rank. MIP results indicate that that the pore size of 10-100 nm accounted for 70.7-97.5% of the total volume in the macropore range. Comparison of different methods indicates that micropores cannot be fully covered by the standard probes. CO 2 adsorption technique can only probe micropores in the range of 0.5 nm to 0.9 nm. Water vapor is not an effective probe to detect the micropores in coals, due to that the water clusters is mainly filled in mesopores and macropores. The results also show that both water vapor adsorption and FT-IR analysis can provide qualitative information of coal surface, rather than qualification of functional groups.

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Section: Introductionmentioning

confidence: 99%

Surface Properties and Pore Structure of Anthracite, Bituminous Coal and Lignite

et al. 2018

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“…These results indicated that some of the gas remained in the coal after gas desorption. Previous research found that the coal matrix will swell or shrink after gas adsorption–desorption, and the pore structure and distribution characteristics of coal will change . In this part, the pore structure of low-pressure gas adsorption was tested.…”

Section: Resultsmentioning

confidence: 99%

“…Previous research found that the coal matrix will swell or shrink after gas adsorption− desorption, and the pore structure and distribution characteristics of coal will change. 36 In this part, the pore structure of low-pressure gas adsorption was tested. Meanwhile, the deformation characteristics of different types of nanopores were analyzed.…”

Section: Resultsmentioning

confidence: 99%

Influence of Nanopore Structure Deformation on Gas Migration in Coal

Song

Shi

et al. 2021

ACS Omega

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To better understand the influence and control of nanopore characteristics on gas migration, three kinds of coal samples with different metamorphic degrees were selected for the experiments including high-pressure isothermal gas adsorption, low-pressure CO2 adsorption, and low-pressure Ar adsorption. The changes of the pore volume (PV) and specific surface area (SSA) of coal samples before and after adsorption–desorption were compared and analyzed. The adsorption data of all coal samples at a low pressure stage (<8 MPa) conformed to the Langmuir equation, and the adsorption capacity of powdered coal samples was higher than that of columnar coal samples. Some adsorption data deviated from the original fitting curve at a high pressure stage (>8 MPa), and this was the most remarkable in columnar coal samples. There was a positive correlation between the cumulative SSA of pores and adsorption capacity of coal samples. When the adsorption time was more than 10 min, the adsorption efficiency of 200 mesh coal samples from YJL was lower than those of 200 mesh coal samples from CZ and WY, which was due to the good development and connectivity of micro-fissures and nanopores in YJL coal samples. The pore size distribution of coal samples had changed after adsorption–desorption, and the cumulative deformation of the nanopore structure was anisotropic. As a result of the swelling or shrinkage deformation of the coal matrix, the PV and SSA with the same pore size presented many forms, such as almost unchanged, increased, or decreased. There are two types of deformation mechanisms: the whole collaborative deformation and partial deformation. Both gas adsorption and desorption can lead to the shrinkage or swell deformation of nanopores and fissures. In brief, the research provides theoretical and technical support for reservoir evaluation, fine drainage, and efficient development of coalbed methane.

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“…Methane productivity of some CBM wells is quite low and even did not produce gas in part wells, which like Z-7H, Z-159, and Z-163 wells in the experiment. Gas foam fracturing has been used in these wells to expand crack and improve coal permeability (Ji et al 2018). However, the effect was not satisfying.…”

Section: Introductionmentioning

confidence: 99%

Primary studies on the effect of coal bio-gasification in situ in the Qinshui basin

Xiao

Zhang

et al. 2021

J Petrol Explor Prod Technol

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Coal bio-gasification is one in situ coal gasification technology that utilizes the digestion of organic components in coal by methanogenic bacteria. It is not only an effective technology to enhance the recoverable reserves of coalbed methane, but also an important technical method to promote clean coal utilization. Relevant laboratory researches have confirmed the technical feasibility of anthracite bio-gasification. However, in the complex environment of coal bed, whether in situ gas can be yield with methanogenic bacteria needs to be verified by in situ experiments. In this study, a vertical well and a horizontal well were used in Qinshui basin to perform field experiments to confirm the technical industrial feasibility. The concentration of Cl− ion and number changes of Methanogen spp. were used to trace nutrition diffusion. Gas production changes and coalbed biome evolution were used to analyze technical implementation results. The trace data and biome evolution identified that: (1) The development of Methanoculleus spp. has a significant positive correlation with culture medium diffusion; (2) the structure of coalbed microbial community was significantly changed with the injection of nutrition, and the newly constructed methanogenic community was more suitable for fermentation of coal; and (3) the evolution of dominant microflora has further enhanced bio-gasification of coal. Gas production data showed that the gasification of coal lasted 635 and 799 days and yielded 74,817 m3 and 251,754 m3 coalbed methane in Z-159 and Z-7H wells, respectively. One nutrition injection in coalbed achieved an average of 717 days of continuous gas production in experimental wells. Results confirmed that coalbed methane enhancement with bio-gasification of coal is a potential technology to achieve the productivity improvement of coalbed methane wells. And the findings of this study can help to further understand the mechanism of in situ coal bio-gasification and provide theoretical support for the development of biomining of coal.

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Coal Matrix Deformation and Pore Structure Change in High-Pressure Nitrogen Replacement of Methane

Cited by 11 publications

References 47 publications

Surface Properties and Pore Structure of Anthracite, Bituminous Coal and Lignite

Surface Properties and Pore Structure of Anthracite, Bituminous Coal and Lignite

Influence of Nanopore Structure Deformation on Gas Migration in Coal

Primary studies on the effect of coal bio-gasification in situ in the Qinshui basin

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