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In Situ Deformation Analysis of a Fracture in Coal under Cyclic Loading and Unloading

Author

Listed:
  • Zhihui Liu

    (State Key Laboratory of Heavy Oil Processing, China University of Petroleum-Beijing at Karamay, Karamay 834000, China)

  • Yongfei Yang

    (Research Centre of Multiphase Flow in Porous Media, School of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, China)

  • Yingwen Li

    (Research Centre of Multiphase Flow in Porous Media, School of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, China)

  • Jiaxue Li

    (State Key Laboratory of Heavy Oil Processing, China University of Petroleum-Beijing at Karamay, Karamay 834000, China)

Abstract

The deformation analysis of fractures is vital for advantageous development of oil and gas fields, especially the coalbed methane (CBM) reservoir, since the change of fracture parameters can be directly evaluated through fracture deformation analysis. Then the flow capacity of CBM and the effect of various stimulation methods can be analyzed. In this study, X-ray CT image analysis is used to quantitatively characterize the deformation of a coal fracture in situ, and the evolution of fracture aperture under cyclic loading is presented. Furthermore, dimensionless permeability at different confining pressures by the Lattice Boltzmann method is simulated. The current results indicate that the fracture deformation changes significantly under cyclic loading. A dramatic change is observed in the initial loading stage, in which the coal is strongly compacted, and the fracture aperture and permeability are reduced to 13.9% and 0.1%, respectively, when the confining pressure is loaded to 10 MPa. When unloading to 0 MPa, the fracture aperture and dimensionless permeability are far less than that of the initial 0 MPa. It is worth noting that the deformation of the second cycle fracture is weaker, and the change range of permeability and aperture of coal fracture becomes smaller, but when unloading to 0 MPa in the second cycle, the fracture permeability can be restored to 50.8% compared with 0 MPa of the loading stage. Additionally, a special phenomenon has been observed that under cyclic loading, even when the confining pressure reaches 10 MPa, some areas of the fracture are still not closed. We infer that there are some large pore structures in fracture space, and high confining pressure leads to fracture closure, but the deformation of the pore structure is not prominent compared with the fracture space. These characteristics of fracture deformation are of great significance for the production of CBM and are worthy of further study.

Suggested Citation

  • Zhihui Liu & Yongfei Yang & Yingwen Li & Jiaxue Li, 2021. "In Situ Deformation Analysis of a Fracture in Coal under Cyclic Loading and Unloading," Energies, MDPI, vol. 14(20), pages 1-16, October.
    • Handle: RePEc:gam:jeners:v:14:y:2021:i:20:p:6474-:d:652941
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    References listed on IDEAS

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    1. Katarzyna Godyń & Barbara Dutka & Monika Chuchro & Mariusz Młynarczuk, 2020. "Synergy of Parameters Determining the Optimal Properties of Coal as a Natural Sorbent," Energies, MDPI, vol. 13(8), pages 1-17, April.
    2. Yongfei Yang & Zhihui Liu & Jun Yao & Lei Zhang & Jingsheng Ma & S. Hossein Hejazi & Linda Luquot & Toussaint Dono Ngarta, 2018. "Flow Simulation of Artificially Induced Microfractures Using Digital Rock and Lattice Boltzmann Methods," Energies, MDPI, vol. 11(8), pages 1-17, August.
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    Cited by:

    1. Jianchao Cai & Reza Rezaee & Victor Calo, 2022. "Recent Advances in Multiscale Petrophysics Characterization and Multiphase Flow in Unconventional Reservoirs," Energies, MDPI, vol. 15(8), pages 1-2, April.

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