Permeability evolution in fractured coal - Combining triaxial confinement with X-ray computed tomography, acoustic emission and ultrasonic techniques

Yidong Cai, Dameng Liu, Jonathan P. Mathews, Zhejun Pan, Derek Elsworth, Yanbin Yao, Junqian Li, Xiaoqian Guo

Research output: Contribution to journalArticle

87 Citations (Scopus)

Abstract

Cyclic loading of coals impacts permeability due to reversible deformation and irreversible damage and extension to pre-existing fracture networks. These changes in permeability influence the effectiveness of degassing of coal prior to mining, the recovery of coalbed methane by both conventional and enhanced methods and potential for sequestration of CO2. We explore these interactions of stress and damage that contribute to changes in permeability through imaging with X-ray computed tomography (X-ray CT), acoustic emission (AE) profiling together with the concurrent measurement of P-wave velocities. We use these techniques to examine the evolution of the 3D fracture network during stressing through failure. A total of five semi-anthracite/anthracite coal cores (~40mm in diameter and 80mm in length) are sequentially loaded to failure (~37.53MPa) with concurrent measurements of permeability. Intermittent scanning by X-ray CT, AE profiling and measurement of the evolving P-wave velocity effectively determine changes in the 3D fracture network with applied stress. These results are correlated with the "V-shaped" variation of permeability with increasing axial stress under the imposed triaxial stress conditions. This is consistent with observations on hard rocks where increasing stresses initially close fractures before fractures ultimately dilate, propagate and coalesce as the peak strength is reached. The increase in fracture volume is non uniform within the sample and is largest at the end platens. The permeability evolution was similarly dynamic with coal permeability reduced by one to two orders of magnitude in some cores (0.18-0.004mD) until increasing dramatically as failure is approached (14.07-37.53MPa).

Original languageEnglish (US)
Pages (from-to)91-104
Number of pages14
JournalInternational Journal of Coal Geology
Volume122
DOIs
StatePublished - Feb 1 2014

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acoustic emission
Acoustic emissions
tomography
Tomography
Ultrasonics
Coal
permeability
coal
X rays
fracture network
Anthracite
anthracite
P-wave
wave velocity
Degassing
damage
coalbed methane
cyclic loading
hard rock
degassing

All Science Journal Classification (ASJC) codes

  • Fuel Technology
  • Geology
  • Economic Geology
  • Stratigraphy

Cite this

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title = "Permeability evolution in fractured coal - Combining triaxial confinement with X-ray computed tomography, acoustic emission and ultrasonic techniques",
abstract = "Cyclic loading of coals impacts permeability due to reversible deformation and irreversible damage and extension to pre-existing fracture networks. These changes in permeability influence the effectiveness of degassing of coal prior to mining, the recovery of coalbed methane by both conventional and enhanced methods and potential for sequestration of CO2. We explore these interactions of stress and damage that contribute to changes in permeability through imaging with X-ray computed tomography (X-ray CT), acoustic emission (AE) profiling together with the concurrent measurement of P-wave velocities. We use these techniques to examine the evolution of the 3D fracture network during stressing through failure. A total of five semi-anthracite/anthracite coal cores (~40mm in diameter and 80mm in length) are sequentially loaded to failure (~37.53MPa) with concurrent measurements of permeability. Intermittent scanning by X-ray CT, AE profiling and measurement of the evolving P-wave velocity effectively determine changes in the 3D fracture network with applied stress. These results are correlated with the {"}V-shaped{"} variation of permeability with increasing axial stress under the imposed triaxial stress conditions. This is consistent with observations on hard rocks where increasing stresses initially close fractures before fractures ultimately dilate, propagate and coalesce as the peak strength is reached. The increase in fracture volume is non uniform within the sample and is largest at the end platens. The permeability evolution was similarly dynamic with coal permeability reduced by one to two orders of magnitude in some cores (0.18-0.004mD) until increasing dramatically as failure is approached (14.07-37.53MPa).",
author = "Yidong Cai and Dameng Liu and Mathews, {Jonathan P.} and Zhejun Pan and Derek Elsworth and Yanbin Yao and Junqian Li and Xiaoqian Guo",
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Permeability evolution in fractured coal - Combining triaxial confinement with X-ray computed tomography, acoustic emission and ultrasonic techniques. / Cai, Yidong; Liu, Dameng; Mathews, Jonathan P.; Pan, Zhejun; Elsworth, Derek; Yao, Yanbin; Li, Junqian; Guo, Xiaoqian.

In: International Journal of Coal Geology, Vol. 122, 01.02.2014, p. 91-104.

Research output: Contribution to journalArticle

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T1 - Permeability evolution in fractured coal - Combining triaxial confinement with X-ray computed tomography, acoustic emission and ultrasonic techniques

AU - Cai, Yidong

AU - Liu, Dameng

AU - Mathews, Jonathan P.

AU - Pan, Zhejun

AU - Elsworth, Derek

AU - Yao, Yanbin

AU - Li, Junqian

AU - Guo, Xiaoqian

PY - 2014/2/1

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N2 - Cyclic loading of coals impacts permeability due to reversible deformation and irreversible damage and extension to pre-existing fracture networks. These changes in permeability influence the effectiveness of degassing of coal prior to mining, the recovery of coalbed methane by both conventional and enhanced methods and potential for sequestration of CO2. We explore these interactions of stress and damage that contribute to changes in permeability through imaging with X-ray computed tomography (X-ray CT), acoustic emission (AE) profiling together with the concurrent measurement of P-wave velocities. We use these techniques to examine the evolution of the 3D fracture network during stressing through failure. A total of five semi-anthracite/anthracite coal cores (~40mm in diameter and 80mm in length) are sequentially loaded to failure (~37.53MPa) with concurrent measurements of permeability. Intermittent scanning by X-ray CT, AE profiling and measurement of the evolving P-wave velocity effectively determine changes in the 3D fracture network with applied stress. These results are correlated with the "V-shaped" variation of permeability with increasing axial stress under the imposed triaxial stress conditions. This is consistent with observations on hard rocks where increasing stresses initially close fractures before fractures ultimately dilate, propagate and coalesce as the peak strength is reached. The increase in fracture volume is non uniform within the sample and is largest at the end platens. The permeability evolution was similarly dynamic with coal permeability reduced by one to two orders of magnitude in some cores (0.18-0.004mD) until increasing dramatically as failure is approached (14.07-37.53MPa).

AB - Cyclic loading of coals impacts permeability due to reversible deformation and irreversible damage and extension to pre-existing fracture networks. These changes in permeability influence the effectiveness of degassing of coal prior to mining, the recovery of coalbed methane by both conventional and enhanced methods and potential for sequestration of CO2. We explore these interactions of stress and damage that contribute to changes in permeability through imaging with X-ray computed tomography (X-ray CT), acoustic emission (AE) profiling together with the concurrent measurement of P-wave velocities. We use these techniques to examine the evolution of the 3D fracture network during stressing through failure. A total of five semi-anthracite/anthracite coal cores (~40mm in diameter and 80mm in length) are sequentially loaded to failure (~37.53MPa) with concurrent measurements of permeability. Intermittent scanning by X-ray CT, AE profiling and measurement of the evolving P-wave velocity effectively determine changes in the 3D fracture network with applied stress. These results are correlated with the "V-shaped" variation of permeability with increasing axial stress under the imposed triaxial stress conditions. This is consistent with observations on hard rocks where increasing stresses initially close fractures before fractures ultimately dilate, propagate and coalesce as the peak strength is reached. The increase in fracture volume is non uniform within the sample and is largest at the end platens. The permeability evolution was similarly dynamic with coal permeability reduced by one to two orders of magnitude in some cores (0.18-0.004mD) until increasing dramatically as failure is approached (14.07-37.53MPa).

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