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Biot's Coefficient and Permeability Evolution of Damaged Anisotropic Coal Subjected to True Triaxial Stress
https://orcid.org/0000-0003-0409-3657
Abstract Studying the anisotropic seepage characteristics of coal is of great significance to the safe and efficient extraction of coalbed methane (CBM). The effective stress law (σe = σ – αp) is often used to solve the fluid–solid coupling problem of rocks. However, the Biot's coefficient α = 1 is often assumed in the current study, and the remaining researches on the α evolution of coal are mainly focused on the conventional triaxial stress state and the elastic range, which cannot reflect the anisotropic evolution of α of damaged coal under true triaxial stress state in actual formation. In the current study, an experimental study on the effect of induced damage on α and permeability of coal subjected to different true triaxial stress states was carried out, and the anisotropy of coal structure was also considered. The experimental results show that αij and permeability are closely related to the fracture evolution, and both increase with the increase in fracture density and opening. Influenced by the induced damage, αij exhibits a significant anisotropy. α1 achieves larger than α2 and α3, and α3 > α2 occurs in the horizontal direction, and the difference between α3 and α2 increases with the increase in the horizontal stress difference. Under different initial stress states, αij for high horizontal stress is lower than αij in the low due to the restraining effect of horizontal stress on fracture propagation. Under different flow directions, αij increases the most with the increase in axial strain under the gas flow perpendicular to bedding, indicating that the natural fractures distributed along the bedding face are more likely to propagate under the external stress drive compared with the face and butt cleats. At the initial plastic stage, αij exhibits αface cleat > αbutt cleat > αbedding, and the permeability also shows kface cleat > kbutt cleat > kbedding, indicating that the natural fractures distributed along the cleats are more than those near the bedding. In this study, a new coal permeability model considering the damage effect and anisotropy of Biot's coefficient is established, which shows good agreement with the experimental permeability of simulating mining stress disturbance, and considering anisotropic αij in the model is closer to the measured permeability than assuming αij = 1.
Highlights Biot's coefficient αij and permeability of damaged coal increase with fracture density and opening increase, and always show α1 > α3 > α2.Considering anisotropic coal structure, αface cleat > αbutt cleat > αbedding, and αij increases the most under gas flow perpendicular to bedding.New permeability model considering damage and αij is established, considering αij in the model is closer to the permeability than assuming αij = 1.
Biot's Coefficient and Permeability Evolution of Damaged Anisotropic Coal Subjected to True Triaxial Stress
https://orcid.org/0000-0003-0409-3657
Abstract Studying the anisotropic seepage characteristics of coal is of great significance to the safe and efficient extraction of coalbed methane (CBM). The effective stress law (σe = σ – αp) is often used to solve the fluid–solid coupling problem of rocks. However, the Biot's coefficient α = 1 is often assumed in the current study, and the remaining researches on the α evolution of coal are mainly focused on the conventional triaxial stress state and the elastic range, which cannot reflect the anisotropic evolution of α of damaged coal under true triaxial stress state in actual formation. In the current study, an experimental study on the effect of induced damage on α and permeability of coal subjected to different true triaxial stress states was carried out, and the anisotropy of coal structure was also considered. The experimental results show that αij and permeability are closely related to the fracture evolution, and both increase with the increase in fracture density and opening. Influenced by the induced damage, αij exhibits a significant anisotropy. α1 achieves larger than α2 and α3, and α3 > α2 occurs in the horizontal direction, and the difference between α3 and α2 increases with the increase in the horizontal stress difference. Under different initial stress states, αij for high horizontal stress is lower than αij in the low due to the restraining effect of horizontal stress on fracture propagation. Under different flow directions, αij increases the most with the increase in axial strain under the gas flow perpendicular to bedding, indicating that the natural fractures distributed along the bedding face are more likely to propagate under the external stress drive compared with the face and butt cleats. At the initial plastic stage, αij exhibits αface cleat > αbutt cleat > αbedding, and the permeability also shows kface cleat > kbutt cleat > kbedding, indicating that the natural fractures distributed along the cleats are more than those near the bedding. In this study, a new coal permeability model considering the damage effect and anisotropy of Biot's coefficient is established, which shows good agreement with the experimental permeability of simulating mining stress disturbance, and considering anisotropic αij in the model is closer to the measured permeability than assuming αij = 1.
Highlights Biot's coefficient αij and permeability of damaged coal increase with fracture density and opening increase, and always show α1 > α3 > α2.Considering anisotropic coal structure, αface cleat > αbutt cleat > αbedding, and αij increases the most under gas flow perpendicular to bedding.New permeability model considering damage and αij is established, considering αij in the model is closer to the permeability than assuming αij = 1.
Biot's Coefficient and Permeability Evolution of Damaged Anisotropic Coal Subjected to True Triaxial Stress
https://orcid.org/0000-0003-0409-3657
Abstract Studying the anisotropic seepage characteristics of coal is of great significance to the safe and efficient extraction of coalbed methane (CBM). The effective stress law (σe = σ – αp) is often used to solve the fluid–solid coupling problem of rocks. However, the Biot's coefficient α = 1 is often assumed in the current study, and the remaining researches on the α evolution of coal are mainly focused on the conventional triaxial stress state and the elastic range, which cannot reflect the anisotropic evolution of α of damaged coal under true triaxial stress state in actual formation. In the current study, an experimental study on the effect of induced damage on α and permeability of coal subjected to different true triaxial stress states was carried out, and the anisotropy of coal structure was also considered. The experimental results show that αij and permeability are closely related to the fracture evolution, and both increase with the increase in fracture density and opening. Influenced by the induced damage, αij exhibits a significant anisotropy. α1 achieves larger than α2 and α3, and α3 > α2 occurs in the horizontal direction, and the difference between α3 and α2 increases with the increase in the horizontal stress difference. Under different initial stress states, αij for high horizontal stress is lower than αij in the low due to the restraining effect of horizontal stress on fracture propagation. Under different flow directions, αij increases the most with the increase in axial strain under the gas flow perpendicular to bedding, indicating that the natural fractures distributed along the bedding face are more likely to propagate under the external stress drive compared with the face and butt cleats. At the initial plastic stage, αij exhibits αface cleat > αbutt cleat > αbedding, and the permeability also shows kface cleat > kbutt cleat > kbedding, indicating that the natural fractures distributed along the cleats are more than those near the bedding. In this study, a new coal permeability model considering the damage effect and anisotropy of Biot's coefficient is established, which shows good agreement with the experimental permeability of simulating mining stress disturbance, and considering anisotropic αij in the model is closer to the measured permeability than assuming αij = 1.
Highlights Biot's coefficient αij and permeability of damaged coal increase with fracture density and opening increase, and always show α1 > α3 > α2.Considering anisotropic coal structure, αface cleat > αbutt cleat > αbedding, and αij increases the most under gas flow perpendicular to bedding.New permeability model considering damage and αij is established, considering αij in the model is closer to the permeability than assuming αij = 1.
Biot's Coefficient and Permeability Evolution of Damaged Anisotropic Coal Subjected to True Triaxial Stress
Yu, Beichen (author) / Zhang, Dongming (author) / Li, Shujian (author) / Xu, Bin (author) / Liu, Chao (author) / Liu, Yubing (author)
2022
Article (Journal)
Electronic Resource
English
BKL:
38.58
Geomechanik
/
56.20
Ingenieurgeologie, Bodenmechanik
/
38.58$jGeomechanik
/
56.20$jIngenieurgeologie$jBodenmechanik
RVK:
ELIB41
Mechanical Properties of Layered Composite Coal–Rock Subjected to True Triaxial Stress
| Springer Verlag | 2020
Mechanical Properties of Layered Composite Coal–Rock Subjected to True Triaxial Stress
| Online Contents | 2020