TY - JOUR
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
N1 - Funding Information:
This research was funded by the National Major Research Program for Science and Technology of China (grant nos. 2011ZX05034-001 and 2011ZX05062-006 ), the United Foundation from the National Natural Science Foundation of China and the Petrochemical Foundation of PetroChina (grant no. U1262104 ), the Program for New Century Excellent Talents in University (grant no. NCET-11-0721 ), the Foundation for the Author of National Excellent Doctoral Dissertation of PR China (grant no. 201253 ), the Fundamental Research Funds for Central Universities (grant no. 2652013006 ) and the Research Program for Excellent Doctoral Dissertation Supervisor of Beijing (grant no. YB20101141501 ).
PY - 2014/2/1
Y1 - 2014/2/1
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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U2 - 10.1016/j.coal.2013.12.012
DO - 10.1016/j.coal.2013.12.012
M3 - Article
AN - SCOPUS:84892177798
SN - 0166-5162
VL - 122
SP - 91
EP - 104
JO - International Journal of Coal Geology
JF - International Journal of Coal Geology
ER -