Factors controlling the mechanical properties degradation and permeability of coal subjected to liquid nitrogen freeze-thaw

Lei Qin, Cheng Zhai, Shimin Liu, Jizhao Xu

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

Freeze-thaw induced fracturing coal by liquid nitrogen (LN2) injection exerts a significant positive effect on the fracture permeability enhancement of the coal reservoir. To evaluate the different freeze-thaw variables which modify the mechanical properties of treated coals, the effects of freezing time, number of freeze-thaw cycles, and the moisture content of coal were studied using combined uniaxial compression and acoustic emission testing systems. Freezing the samples with LN2 for increasing amounts of time degraded the strength of coal within a certain limit. Comparison to freezing time, freeze-thaw cycling caused much more damage to the coal strength. The third variable studied, freeze-thaw damage resulting from high moisture content, was restricted by the coal's moisture saturation limit. Based on the experimental results, equations describing the amount of damage caused by each of the different freeze-thaw variables were empirically regressed. Additionally, by using the ultrasonic wave detection method and fractal dimension analyses, how freeze-thaw induced fractures in the coal was quantitatively analyzed. The results also showed that the velocity of ultrasonic waves had a negative correlation with coal permeability, and the freeze-thaw cycles significantly augment the permeability of frozen-thawed coal masses.

Original languageEnglish (US)
Article number4019
JournalScientific reports
Volume7
Issue number1
DOIs
StatePublished - Dec 1 2017

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Coal
Permeability
Nitrogen
Freezing
Fractals
Acoustics
Injections

All Science Journal Classification (ASJC) codes

  • General

Cite this

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abstract = "Freeze-thaw induced fracturing coal by liquid nitrogen (LN2) injection exerts a significant positive effect on the fracture permeability enhancement of the coal reservoir. To evaluate the different freeze-thaw variables which modify the mechanical properties of treated coals, the effects of freezing time, number of freeze-thaw cycles, and the moisture content of coal were studied using combined uniaxial compression and acoustic emission testing systems. Freezing the samples with LN2 for increasing amounts of time degraded the strength of coal within a certain limit. Comparison to freezing time, freeze-thaw cycling caused much more damage to the coal strength. The third variable studied, freeze-thaw damage resulting from high moisture content, was restricted by the coal's moisture saturation limit. Based on the experimental results, equations describing the amount of damage caused by each of the different freeze-thaw variables were empirically regressed. Additionally, by using the ultrasonic wave detection method and fractal dimension analyses, how freeze-thaw induced fractures in the coal was quantitatively analyzed. The results also showed that the velocity of ultrasonic waves had a negative correlation with coal permeability, and the freeze-thaw cycles significantly augment the permeability of frozen-thawed coal masses.",
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Factors controlling the mechanical properties degradation and permeability of coal subjected to liquid nitrogen freeze-thaw. / Qin, Lei; Zhai, Cheng; Liu, Shimin; Xu, Jizhao.

In: Scientific reports, Vol. 7, No. 1, 4019, 01.12.2017.

Research output: Contribution to journalArticle

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