Pore variation of three different metamorphic coals by multiple freezing-thawing cycles of liquid CO 2 injection for coalbed methane recovery

Jizhao Xu, Cheng Zhai, Shimin Liu, Lei Qin, Shangjian Wu

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

Liquid CO 2 (LCO 2 ) enhanced coalbed methane recovery had been studied in laboratory experiments and field applications, supporting many improvements and achievements. Previous studies primarily investigated the gas bursting, flooding effect and adsorption effect; however, the freezing-thawing phenomenon (drikold formation and gasification) that commonly occurs during the LCO 2 injection process was insufficiently studied. The freezing-thawing phenomenon might enhance the pore volume and change the permeability evolution of the coalbed; thus, cyclical LCO 2 injection was proposed to exploit the phenomenon, and the influence of multiple freezing-thawing cycles on the coal pores was investigated in this paper. Nuclear magnetic resonance (NMR) and infrared thermal imagery (ITI) were used to monitor the pore variation and surface temperature distribution, respectively. Low temperatures could make the saturated water in the pores freeze and undergo a 9% volume increase. The three coals used in this experiment displayed different crack intensities and forms with ITI. After cyclical LCO 2 injection, the NMR amplitude increased, and the T 2 range was widened under a saturation condition, while the cores under a centrifuge state had lower amplitudes and a narrower T 2 range; this difference indicated that the pore structure could be altered by multiple freezing-thawing cycles of LCO 2 . The more freezing-thawing cycles the cores experienced, the greater the change in pore structure was. The total porosity φ t and effective porosity φ e increased while the residual porosity φ r and T 2cutoff values decreased with more freezing-thawing cycles. However, the variations with coal rank were observed; with higher coal ranking, φ t and φ e increased less, and the φ r and T 2cutoff values decreased less, which suggests that lower ranking coals could be most easily affected by the LCO 2 enhanced recovery method and have the most improved pore connectivity. Moreover, the enhancement ratio of φ t and φ e increased for all three coals tested, which could be fit with quadratic functions with fit coefficients greater than 0.99. The increasing relative ratio D e / t of anthracite was fit with a linear function, while the lignite and bitumite were fit with quadratic functions. These functions all indicate that the multiple freezing-thawing cycles of LCO 2 injection had a positive impact on the enhancement efficiency of pore porosity. Finally, a potential field application of cyclical LCO 2 injection was also discussed to improve the fracturing effect.

Original languageEnglish (US)
Pages (from-to)41-51
Number of pages11
JournalFuel
Volume208
DOIs
StatePublished - Jan 1 2017

Fingerprint

Thawing
Coal
Carbon Monoxide
Freezing
Recovery
Liquids
Porosity
Pore structure
Nuclear magnetic resonance
Enhanced recovery
Infrared radiation
Anthracite
Coal bed methane
Centrifuges
Lignite
Gasification
Temperature distribution
Gases
Experiments
Cracks

All Science Journal Classification (ASJC) codes

  • Chemical Engineering(all)
  • Fuel Technology
  • Energy Engineering and Power Technology
  • Organic Chemistry

Cite this

@article{600f0c23769c4f2fad578e1c45b79f59,
title = "Pore variation of three different metamorphic coals by multiple freezing-thawing cycles of liquid CO 2 injection for coalbed methane recovery",
abstract = "Liquid CO 2 (LCO 2 ) enhanced coalbed methane recovery had been studied in laboratory experiments and field applications, supporting many improvements and achievements. Previous studies primarily investigated the gas bursting, flooding effect and adsorption effect; however, the freezing-thawing phenomenon (drikold formation and gasification) that commonly occurs during the LCO 2 injection process was insufficiently studied. The freezing-thawing phenomenon might enhance the pore volume and change the permeability evolution of the coalbed; thus, cyclical LCO 2 injection was proposed to exploit the phenomenon, and the influence of multiple freezing-thawing cycles on the coal pores was investigated in this paper. Nuclear magnetic resonance (NMR) and infrared thermal imagery (ITI) were used to monitor the pore variation and surface temperature distribution, respectively. Low temperatures could make the saturated water in the pores freeze and undergo a 9{\%} volume increase. The three coals used in this experiment displayed different crack intensities and forms with ITI. After cyclical LCO 2 injection, the NMR amplitude increased, and the T 2 range was widened under a saturation condition, while the cores under a centrifuge state had lower amplitudes and a narrower T 2 range; this difference indicated that the pore structure could be altered by multiple freezing-thawing cycles of LCO 2 . The more freezing-thawing cycles the cores experienced, the greater the change in pore structure was. The total porosity φ t and effective porosity φ e increased while the residual porosity φ r and T 2cutoff values decreased with more freezing-thawing cycles. However, the variations with coal rank were observed; with higher coal ranking, φ t and φ e increased less, and the φ r and T 2cutoff values decreased less, which suggests that lower ranking coals could be most easily affected by the LCO 2 enhanced recovery method and have the most improved pore connectivity. Moreover, the enhancement ratio of φ t and φ e increased for all three coals tested, which could be fit with quadratic functions with fit coefficients greater than 0.99. The increasing relative ratio D e / t of anthracite was fit with a linear function, while the lignite and bitumite were fit with quadratic functions. These functions all indicate that the multiple freezing-thawing cycles of LCO 2 injection had a positive impact on the enhancement efficiency of pore porosity. Finally, a potential field application of cyclical LCO 2 injection was also discussed to improve the fracturing effect.",
author = "Jizhao Xu and Cheng Zhai and Shimin Liu and Lei Qin and Shangjian Wu",
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Pore variation of three different metamorphic coals by multiple freezing-thawing cycles of liquid CO 2 injection for coalbed methane recovery . / Xu, Jizhao; Zhai, Cheng; Liu, Shimin; Qin, Lei; Wu, Shangjian.

In: Fuel, Vol. 208, 01.01.2017, p. 41-51.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Pore variation of three different metamorphic coals by multiple freezing-thawing cycles of liquid CO 2 injection for coalbed methane recovery

AU - Xu, Jizhao

AU - Zhai, Cheng

AU - Liu, Shimin

AU - Qin, Lei

AU - Wu, Shangjian

PY - 2017/1/1

Y1 - 2017/1/1

N2 - Liquid CO 2 (LCO 2 ) enhanced coalbed methane recovery had been studied in laboratory experiments and field applications, supporting many improvements and achievements. Previous studies primarily investigated the gas bursting, flooding effect and adsorption effect; however, the freezing-thawing phenomenon (drikold formation and gasification) that commonly occurs during the LCO 2 injection process was insufficiently studied. The freezing-thawing phenomenon might enhance the pore volume and change the permeability evolution of the coalbed; thus, cyclical LCO 2 injection was proposed to exploit the phenomenon, and the influence of multiple freezing-thawing cycles on the coal pores was investigated in this paper. Nuclear magnetic resonance (NMR) and infrared thermal imagery (ITI) were used to monitor the pore variation and surface temperature distribution, respectively. Low temperatures could make the saturated water in the pores freeze and undergo a 9% volume increase. The three coals used in this experiment displayed different crack intensities and forms with ITI. After cyclical LCO 2 injection, the NMR amplitude increased, and the T 2 range was widened under a saturation condition, while the cores under a centrifuge state had lower amplitudes and a narrower T 2 range; this difference indicated that the pore structure could be altered by multiple freezing-thawing cycles of LCO 2 . The more freezing-thawing cycles the cores experienced, the greater the change in pore structure was. The total porosity φ t and effective porosity φ e increased while the residual porosity φ r and T 2cutoff values decreased with more freezing-thawing cycles. However, the variations with coal rank were observed; with higher coal ranking, φ t and φ e increased less, and the φ r and T 2cutoff values decreased less, which suggests that lower ranking coals could be most easily affected by the LCO 2 enhanced recovery method and have the most improved pore connectivity. Moreover, the enhancement ratio of φ t and φ e increased for all three coals tested, which could be fit with quadratic functions with fit coefficients greater than 0.99. The increasing relative ratio D e / t of anthracite was fit with a linear function, while the lignite and bitumite were fit with quadratic functions. These functions all indicate that the multiple freezing-thawing cycles of LCO 2 injection had a positive impact on the enhancement efficiency of pore porosity. Finally, a potential field application of cyclical LCO 2 injection was also discussed to improve the fracturing effect.

AB - Liquid CO 2 (LCO 2 ) enhanced coalbed methane recovery had been studied in laboratory experiments and field applications, supporting many improvements and achievements. Previous studies primarily investigated the gas bursting, flooding effect and adsorption effect; however, the freezing-thawing phenomenon (drikold formation and gasification) that commonly occurs during the LCO 2 injection process was insufficiently studied. The freezing-thawing phenomenon might enhance the pore volume and change the permeability evolution of the coalbed; thus, cyclical LCO 2 injection was proposed to exploit the phenomenon, and the influence of multiple freezing-thawing cycles on the coal pores was investigated in this paper. Nuclear magnetic resonance (NMR) and infrared thermal imagery (ITI) were used to monitor the pore variation and surface temperature distribution, respectively. Low temperatures could make the saturated water in the pores freeze and undergo a 9% volume increase. The three coals used in this experiment displayed different crack intensities and forms with ITI. After cyclical LCO 2 injection, the NMR amplitude increased, and the T 2 range was widened under a saturation condition, while the cores under a centrifuge state had lower amplitudes and a narrower T 2 range; this difference indicated that the pore structure could be altered by multiple freezing-thawing cycles of LCO 2 . The more freezing-thawing cycles the cores experienced, the greater the change in pore structure was. The total porosity φ t and effective porosity φ e increased while the residual porosity φ r and T 2cutoff values decreased with more freezing-thawing cycles. However, the variations with coal rank were observed; with higher coal ranking, φ t and φ e increased less, and the φ r and T 2cutoff values decreased less, which suggests that lower ranking coals could be most easily affected by the LCO 2 enhanced recovery method and have the most improved pore connectivity. Moreover, the enhancement ratio of φ t and φ e increased for all three coals tested, which could be fit with quadratic functions with fit coefficients greater than 0.99. The increasing relative ratio D e / t of anthracite was fit with a linear function, while the lignite and bitumite were fit with quadratic functions. These functions all indicate that the multiple freezing-thawing cycles of LCO 2 injection had a positive impact on the enhancement efficiency of pore porosity. Finally, a potential field application of cyclical LCO 2 injection was also discussed to improve the fracturing effect.

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