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Energies 2018, 11(11), 3035; https://doi.org/10.3390/en11113035

A Numerical Study on the Diversion Mechanisms of Fracture Networks in Tight Reservoirs with Frictional Natural Fractures

1,2,†,‡
,
3,‡
,
1,* , 1
,
4
,
1
and
4
1
School of Mechanical Engineering, Beijing Key Laboratory of Pipeline Critical Technology and Equipment for Deepwater Oil & Gas Development, Beijing Institute of Petrochemical Technology, Beijing 102617, China
2
School of Aeronautic Science and Engineering, Beihang University, Beijing 100083, China
3
Jiangsu Key Laboratory of Advanced Manufacturing Technology, Huaiyin Institute of Technology, Huai’an 223003, China
4
The Conventional Natural Gas Research Institute, China Univeristy of Petroleum, Beijing 102249, China
Current address: 19 Qing-yuan North Road, Huang-cun, Da-xing District, Beijing 102617, China.
These authors contributed equally to this work.
*
Author to whom correspondence should be addressed.
Received: 25 September 2018 / Revised: 21 October 2018 / Accepted: 31 October 2018 / Published: 5 November 2018
(This article belongs to the Special Issue Flow and Transport Properties of Unconventional Reservoirs 2018)
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Abstract

An opened natural fracture (NF) intercepted by a pressurized hydro-fracture (HF) will be diverted in a new direction at the tips of the original NF and subsequently form a complex fracture network. However, a clear understanding of the diversion behavior of fracture networks in tight reservoirs with frictional NFs is lacking. By means of the extended finite element method(XFEM), this study investigates the diversion mechanisms of an opened NF intersected by an HF in naturally fractured reservoirs. The factors affecting the diversion behavior are intensively analyzed, such as the location of the NF, the horizontal principal stress difference, the intersection angle between HF and NF, and the viscosity of the fracturing fluid. The results show that for a constant length of NF (7 m): (1) the upper length of the diverted fracture (DF) decreases by about 2 m with a 2 m increment of the upper length of NF ( L u p p e r ), while the length of DF increases 9.06 m with the fluid viscosity increased by 99 mPa · s; (2) the deflection angle in the upper parts increases by 30.8° with the stress difference increased by 5 MPa, while the deflection angle increases by 61.2° with the intersection angle decreased by 30°. It is easier for the opened NF in lower parts than that in upper parts to be diverted away from its original direction. It finally diverts back to the preferred fracture plane (PFP) direction. The diversion mechanisms of the fracture network are the results of the combined action of all factors. This will provide new insight into the mechanisms of fracture network generation in tight reservoirs with NFs. View Full-Text
Keywords: hydraulic fracturing; tight reservoirs; fracture diversion; extended finite element method; fracture network hydraulic fracturing; tight reservoirs; fracture diversion; extended finite element method; fracture network
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Wang, D.; Shi, F.; Yu, B.; Sun, D.; Li, X.; Han, D.; Tan, Y. A Numerical Study on the Diversion Mechanisms of Fracture Networks in Tight Reservoirs with Frictional Natural Fractures. Energies 2018, 11, 3035.

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