Permeability Evolution of Naturally Fractured Coal Injected with High-Temperature Nitrogen: Experimental Observations

Permeability Evolution of Naturally Fractured Coal Injected with High-Temperature Nitrogen: Experimental Observations

The permeability of more than 70% of coal seams in China is less than 1 mD, creating difficulties in recovering underground coal methane. Therefore, a new technology of high-temperature nitrogen (HTN<sub>2</sub>) injection into the coal seam was proposed to improve the coal permeability...

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Main Authors: Shengcheng Wang, Haijian Li, Lanying Huang
Format: Article
Language:English
Published: MDPI AG 2021-02-01
Series:Processes
Subjects:
coal permeability
N<sub>2</sub> temperature
N<sub>2</sub> injection pressure
cycle number
triaxial test
Online Access:https://www.mdpi.com/2227-9717/9/2/296
id doaj-9fdeb389f80045af9172e058c9eaf585
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spelling doaj-9fdeb389f80045af9172e058c9eaf5852021-02-04T00:05:39ZengMDPI AGProcesses2227-97172021-02-01929629610.3390/pr9020296Permeability Evolution of Naturally Fractured Coal Injected with High-Temperature Nitrogen: Experimental ObservationsShengcheng Wang0Haijian Li1Lanying Huang2School of Civil Engineering, Xuzhou University of Technology, Xuzhou 221018, ChinaCollege of Geology and Mines Engineering, Xinjiang University, Urumqi 830047, ChinaSchool of Civil Engineering, Xuzhou University of Technology, Xuzhou 221018, ChinaThe permeability of more than 70% of coal seams in China is less than 1 mD, creating difficulties in recovering underground coal methane. Therefore, a new technology of high-temperature nitrogen (HTN<sub>2</sub>) injection into the coal seam was proposed to improve the coal permeability and gas extraction rate. In this paper, the effects of the N<sub>2 </sub>temperature, injection pressure and cycle number on the permeability of naturally fractured coking coal has been investigated. When HTN<sub>2</sub> was injected into coal samples, the results indicated that the permeability decreased over time in the beginning, suddenly increased to a large value, and was subsequently maintained in a relatively stable range. The maximum permeability ratio increased with the rise of the N<sub>2</sub> temperature and injection pressure. An analysis indicated that the increase of coal permeability was the result of the increase of the global coal strain caused by thermal expansion and the adsorption-induced expansion. The maximum permeability ratios in various cycles of multicycle N<sub>2</sub> injection into the coal sample were all greater than 1.0 while progressively declining. Obviously, the alternating stress was conducive to the further expansion of the coal fractures to increase the coal permeability. However, on the basis of the first period of expansion, re-expansion was difficult and required more energy. The effects of multicycle N<sub>2</sub> injection on coal permeability have been considerably improved when compared with N<sub>2</sub> injection with only one cycle. The research results are helpful for rapidly extracting methane and guaranteeing mine safety.https://www.mdpi.com/2227-9717/9/2/296coal permeabilityN<sub>2</sub> temperatureN<sub>2</sub> injection pressurecycle numbertriaxial test
collection DOAJ
language English
format Article
sources DOAJ
author Shengcheng Wang
Haijian Li
Lanying Huang
spellingShingle Shengcheng Wang
Haijian Li
Lanying Huang
Permeability Evolution of Naturally Fractured Coal Injected with High-Temperature Nitrogen: Experimental Observations
Processes
coal permeability
N<sub>2</sub> temperature
N<sub>2</sub> injection pressure
cycle number
triaxial test
author_facet Shengcheng Wang
Haijian Li
Lanying Huang
author_sort Shengcheng Wang
title Permeability Evolution of Naturally Fractured Coal Injected with High-Temperature Nitrogen: Experimental Observations
title_short Permeability Evolution of Naturally Fractured Coal Injected with High-Temperature Nitrogen: Experimental Observations
title_full Permeability Evolution of Naturally Fractured Coal Injected with High-Temperature Nitrogen: Experimental Observations
title_fullStr Permeability Evolution of Naturally Fractured Coal Injected with High-Temperature Nitrogen: Experimental Observations
title_full_unstemmed Permeability Evolution of Naturally Fractured Coal Injected with High-Temperature Nitrogen: Experimental Observations
title_sort permeability evolution of naturally fractured coal injected with high-temperature nitrogen: experimental observations
publisher MDPI AG
series Processes
issn 2227-9717
publishDate 2021-02-01
description The permeability of more than 70% of coal seams in China is less than 1 mD, creating difficulties in recovering underground coal methane. Therefore, a new technology of high-temperature nitrogen (HTN<sub>2</sub>) injection into the coal seam was proposed to improve the coal permeability and gas extraction rate. In this paper, the effects of the N<sub>2 </sub>temperature, injection pressure and cycle number on the permeability of naturally fractured coking coal has been investigated. When HTN<sub>2</sub> was injected into coal samples, the results indicated that the permeability decreased over time in the beginning, suddenly increased to a large value, and was subsequently maintained in a relatively stable range. The maximum permeability ratio increased with the rise of the N<sub>2</sub> temperature and injection pressure. An analysis indicated that the increase of coal permeability was the result of the increase of the global coal strain caused by thermal expansion and the adsorption-induced expansion. The maximum permeability ratios in various cycles of multicycle N<sub>2</sub> injection into the coal sample were all greater than 1.0 while progressively declining. Obviously, the alternating stress was conducive to the further expansion of the coal fractures to increase the coal permeability. However, on the basis of the first period of expansion, re-expansion was difficult and required more energy. The effects of multicycle N<sub>2</sub> injection on coal permeability have been considerably improved when compared with N<sub>2</sub> injection with only one cycle. The research results are helpful for rapidly extracting methane and guaranteeing mine safety.
topic coal permeability
N<sub>2</sub> temperature
N<sub>2</sub> injection pressure
cycle number
triaxial test
url https://www.mdpi.com/2227-9717/9/2/296
work_keys_str_mv AT shengchengwang permeabilityevolutionofnaturallyfracturedcoalinjectedwithhightemperaturenitrogenexperimentalobservations
AT haijianli permeabilityevolutionofnaturallyfracturedcoalinjectedwithhightemperaturenitrogenexperimentalobservations
AT lanyinghuang permeabilityevolutionofnaturallyfracturedcoalinjectedwithhightemperaturenitrogenexperimentalobservations
_version_ 1724285834090250240

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