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Fractal Characterization of Complex Hydraulic Fractures in Oil Shale via Topology

1
College of Architecture and Environment, Sichuan University, Chengdu 610065, China
2
Institute of New Energy and Low-Carbon Technology, Sichuan University, Chengdu 610207, China
3
State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Research Institute of Petroleum Exploration and Development of SINOPEC, Beijing 100038, China
*
Author to whom correspondence should be addressed.
Academic Editor: Reza Rezaee
Energies 2021, 14(4), 1123; https://doi.org/10.3390/en14041123
Received: 30 January 2021 / Revised: 13 February 2021 / Accepted: 18 February 2021 / Published: 20 February 2021
(This article belongs to the Special Issue Oil and Gas Markets: Current Challenges and Future Perspectives)
The formation of complex fracture networks through the fracturing technology is a crucial operation used to improve the production capacity of tight gas/oil. In this study, physical simulation experiments of hydraulic fracturing were conducted with a true triaxial test system on cubic shale oil samples from the Yanchang Formation, China. The fractures were scanned by CT both before and after the experiments and then reconstructed in 3D. The complexity of fracture networks was investigated quantitatively by the fractal theory with topology. Finally, the effect of the horizontal stress ratio, fluid viscosity, and natural fractures on the complexity of the fracture networks was discussed. The results indicate that the method based on fractal theory and topology can effectively characterize the complexity of the fracture network. The change rates of the fractal dimension (K) are 0.45–3.64%, and the fractal dimensions (DNH) of the 3D fracture network after fracturing are 1.9522–2.1837, the number of connections per branch after fracturing (CB) are 1.57–2.0. The change rate of the fractal dimension and the horizontal stress ratio are negatively correlated. However, the change rate of the fractal dimension first increases and then decreases under increasing fluid viscosities, and a transition occurs at a fluid viscosity of 5.0 mPa·s. Whether under different horizontal stress ratios or fluid viscosities, the complexity of the fracture networks after fracturing can be divided into four levels according to DNH and CB. Complex fracture networks are more easily formed under a lower horizontal stress ratio and a relatively low fluid viscosity. A fracturing fluid viscosity that is too low or too high limits the formation of a fracture network. View Full-Text
Keywords: shale oil; hydraulic fracturing; fractal theory; topology; 3D fracture networks shale oil; hydraulic fracturing; fractal theory; topology; 3D fracture networks
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MDPI and ACS Style

He, Q.; He, B.; Li, F.; Shi, A.; Chen, J.; Xie, L.; Ning, W. Fractal Characterization of Complex Hydraulic Fractures in Oil Shale via Topology. Energies 2021, 14, 1123. https://doi.org/10.3390/en14041123

AMA Style

He Q, He B, Li F, Shi A, Chen J, Xie L, Ning W. Fractal Characterization of Complex Hydraulic Fractures in Oil Shale via Topology. Energies. 2021; 14(4):1123. https://doi.org/10.3390/en14041123

Chicago/Turabian Style

He, Qiang, Bo He, Fengxia Li, Aiping Shi, Jiang Chen, Lingzhi Xie, and Wenxiang Ning. 2021. "Fractal Characterization of Complex Hydraulic Fractures in Oil Shale via Topology" Energies 14, no. 4: 1123. https://doi.org/10.3390/en14041123

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