Fractal Characterization of Complex Hydraulic Fractures in Oil Shale via Topology

Qiang He, Bo He, Fengxia Li, Aiping Shi, Jiang Chen, Lingzhi Xie and Wenxiang Ning
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Qiang He: College of Architecture and Environment, Sichuan University, Chengdu 610065, China
Bo He: College of Architecture and Environment, Sichuan University, Chengdu 610065, China
Fengxia Li: 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
Aiping Shi: 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
Jiang Chen: College of Architecture and Environment, Sichuan University, Chengdu 610065, China
Lingzhi Xie: College of Architecture and Environment, Sichuan University, Chengdu 610065, China
Wenxiang Ning: College of Architecture and Environment, Sichuan University, Chengdu 610065, China

Energies, 2021, vol. 14, issue 4, 1-17

Abstract: 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 ( D NH ) of the 3D fracture network after fracturing are 1.9522–2.1837, the number of connections per branch after fracturing ( C B ) 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 D NH and C B . 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.

Keywords: shale oil; hydraulic fracturing; fractal theory; topology; 3D fracture networks (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (2)

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