TY - JOUR
T1 - Propagation behavior of hydraulic fracture across the coal-rock interface under different interfacial friction coefficients and a new prediction model
AU - Jiang, Yulong
AU - Lian, Haojie
AU - Nguyen, Vinh Phu
AU - Liang, Weiguo
PY - 2019/8/1
Y1 - 2019/8/1
N2 - Indirect fracturing from rocks to coal is a promising technology of coalbed methane exploitation in soft and low-permeability coal seams. Central to this technology is the prediction of the propagation path of the fluid-driven fractures at the coal-rock interfaces, which requires a deep understanding of the role of the friction properties of coal-rock interfaces. In this paper, we performed hydraulic fracturing experiments using coal-rock blocks with interfaces that were not lubricated, lubricated by oil grease or Vaseline. The results show that the fracture behaviors at different interfaces depend mostly on the vertical stress and the interfacial friction coefficients. Only when the vertical stress reaches a certain threshold, can the fractures directly penetrate the interfaces, where the threshold value increases gradually as the interfacial friction coefficient decreases. Moreover, the abrupt change in the interfacial friction causes hydraulic fractures to deflect at the interface. The injection pressure evolution curves are significantly different due to different fractures behaviors at the interfaces. When hydraulic fractures penetrate the interface, the injection pressure evolution curve shows a significant secondary rise. A distinct prediction model of hydraulic fractures across the coal-rock interface that considers the interfacial friction, the stress state and the intersection angle between the hydraulic fracture and the coal-rock interface was established. This model shows high accuracy in predicting the propagation behavior of hydraulic fracture at different interfaces in hydraulic fracturing.
AB - Indirect fracturing from rocks to coal is a promising technology of coalbed methane exploitation in soft and low-permeability coal seams. Central to this technology is the prediction of the propagation path of the fluid-driven fractures at the coal-rock interfaces, which requires a deep understanding of the role of the friction properties of coal-rock interfaces. In this paper, we performed hydraulic fracturing experiments using coal-rock blocks with interfaces that were not lubricated, lubricated by oil grease or Vaseline. The results show that the fracture behaviors at different interfaces depend mostly on the vertical stress and the interfacial friction coefficients. Only when the vertical stress reaches a certain threshold, can the fractures directly penetrate the interfaces, where the threshold value increases gradually as the interfacial friction coefficient decreases. Moreover, the abrupt change in the interfacial friction causes hydraulic fractures to deflect at the interface. The injection pressure evolution curves are significantly different due to different fractures behaviors at the interfaces. When hydraulic fractures penetrate the interface, the injection pressure evolution curve shows a significant secondary rise. A distinct prediction model of hydraulic fractures across the coal-rock interface that considers the interfacial friction, the stress state and the intersection angle between the hydraulic fracture and the coal-rock interface was established. This model shows high accuracy in predicting the propagation behavior of hydraulic fracture at different interfaces in hydraulic fracturing.
KW - Coal-rock interfaces
KW - Fracture propagation behavior
KW - Hydraulic fracturing
KW - Interface friction
KW - Prediction model
UR - http://www.scopus.com/inward/record.url?scp=85066290651&partnerID=8YFLogxK
U2 - 10.1016/j.jngse.2019.05.007
DO - 10.1016/j.jngse.2019.05.007
M3 - Article
AN - SCOPUS:85066290651
SN - 1875-5100
VL - 68
JO - Journal of Natural Gas Science and Engineering
JF - Journal of Natural Gas Science and Engineering
M1 - 102894
ER -