TY - JOUR
T1 - Nano-CT measurement of pore-fracture evolution and diffusion transport induced by fracturing in medium-high rank coal
AU - Jia, Qifeng
AU - Liu, Dameng
AU - Cai, Yidong
AU - Lu, Yuejian
AU - Li, Rui
AU - Wu, Hao
AU - Zhou, Yingfang
N1 - Acknowledgements
This research was funded by the National Natural Science Foundation of China (grant nos. 42130806, 41830427 and 41922016), 2021 Graduate Innovation Fund Project of China University of Geosciences, Beijing (grant no. ZD2021YC035) and the Fundamental Research Funds for Central Universities (grant no. 2-9-2021-067). We are very grateful to the reviewers and editors for their valuable comments and suggestions.
PY - 2022/10/1
Y1 - 2022/10/1
N2 - Fracturing, as a common fracture-making technique, can improve the permeability of coal seams to enhance fluid transport efficiency. To quantitatively evaluate the microscopic characteristics of medium-high rank coal, the loaded pore-fracture system was characterized by computerized tomography (CT) scanning under triaxial loading, followed by the analysis of stress-strain evolution, stress sensitivity and three dimensional (3D) fractal dimension. Combined with snow algorithm and incompressible steady laminar flow simulation, the heterogeneous distribution of fluid pressure is investigated, focusing on the diffusion effect of gas transport. The results show that the strain of the high-rank coal Chengzhuang (CZ) in the linear elastic stage increases from 0.25% to 1.25%, greater than that of the medium-rank coal Qiyi (QY) from 0.75% to 1.63%, demonstrating a slight lag of the high-rank coal from the linear elastic stage into the yielding stage. The porosity of CZ changes from 1.66% to 13.58% and that of QY varies from 1.74% to 22.28% after fracturing, reflecting that the primary and secondary pores of the medium- and high-rank coals form a complex network structure for fluid transport through continuous connection-expansion. When the strain is between 0.75% and 1.25%, the stress sensitivity coefficient of CZ decreases from 0.13 to 0.02. Moreover, there are many mutation points in the 3D fractal dimension of coal samples after fracturing, mainly due to the generation of new pore-fractures at different locations of the computational domain. For fluid transport, the pressure of QY after fracturing spreads in a wider range than CZ, accompanied by more distribution of high fluid pressure. The diffusion coefficient of the fractured CZ is 350 times higher than that of the original coal under the gas pressure condition of 0.5 MPa, which provides the possibility for more gas to be converted from Knudsen diffusion to transition diffusion or Fick diffusion in the channel.
AB - Fracturing, as a common fracture-making technique, can improve the permeability of coal seams to enhance fluid transport efficiency. To quantitatively evaluate the microscopic characteristics of medium-high rank coal, the loaded pore-fracture system was characterized by computerized tomography (CT) scanning under triaxial loading, followed by the analysis of stress-strain evolution, stress sensitivity and three dimensional (3D) fractal dimension. Combined with snow algorithm and incompressible steady laminar flow simulation, the heterogeneous distribution of fluid pressure is investigated, focusing on the diffusion effect of gas transport. The results show that the strain of the high-rank coal Chengzhuang (CZ) in the linear elastic stage increases from 0.25% to 1.25%, greater than that of the medium-rank coal Qiyi (QY) from 0.75% to 1.63%, demonstrating a slight lag of the high-rank coal from the linear elastic stage into the yielding stage. The porosity of CZ changes from 1.66% to 13.58% and that of QY varies from 1.74% to 22.28% after fracturing, reflecting that the primary and secondary pores of the medium- and high-rank coals form a complex network structure for fluid transport through continuous connection-expansion. When the strain is between 0.75% and 1.25%, the stress sensitivity coefficient of CZ decreases from 0.13 to 0.02. Moreover, there are many mutation points in the 3D fractal dimension of coal samples after fracturing, mainly due to the generation of new pore-fractures at different locations of the computational domain. For fluid transport, the pressure of QY after fracturing spreads in a wider range than CZ, accompanied by more distribution of high fluid pressure. The diffusion coefficient of the fractured CZ is 350 times higher than that of the original coal under the gas pressure condition of 0.5 MPa, which provides the possibility for more gas to be converted from Knudsen diffusion to transition diffusion or Fick diffusion in the channel.
KW - Nano-CT
KW - Fracturing
KW - Strain
KW - Pore
KW - Fluid Flow
KW - Diffusion transport
U2 - 10.1016/j.jngse.2022.104769
DO - 10.1016/j.jngse.2022.104769
M3 - Article
VL - 106
JO - Journal of Natural Gas Science & Engineering
JF - Journal of Natural Gas Science & Engineering
SN - 1875-5100
M1 - 104769
ER -