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

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.

Failure Patterns and Mechanisms of Hydraulic Fracture Propagation Behavior in the Presence of Naturally Cemented Fractures

“…Accordingly, as shown in Fig. 3, displacement u(x) in the domain can be approximated as [8,20,25,29,30].…”

“…The extended criterion accounted for the effect of the approach angle on crossing, and the artificial fracture was more likely to divert along the interface than to cross it when the approach angle was less than 90 degrees. In terms of the numerical simulation of the interaction between HFs and NFs, different factors such as the approach angle and the cohesive and frictional properties of NFs have been analyzed to capture their mechanical behaviors in the geometry of HFs [1,14,[23][24][25]. The interaction between HFs and NFs may lead to arrest, crossing, or offset [7,22].…”

Using Cohesive Zone Model to Simulate the Hydraulic Fracture Interaction with Natural Fracture in Poro-Viscoelastic Formation

“…When the shale tensile Energies 2019, 12, 1254 9 of 12 strength is moderately larger than the crack tensile strength, it is easy to generate the single-wing fracture. When the shale tensile strength is almost equal to the crack tensile strength, HF crosses NF [23].…”

Recent Advances in Flow and Transport Properties of Unconventional Reservoirs

“…The third category focuses on hydraulic fracturing. By means of the extended finite element method, Wang et al [15] investigated the diversion mechanisms of a fracture network in tight formations with frictional natural fractures. The effects of some key factors, for example, the location of natural fracture, the intersection angle between natural fracture and hydro-fracture, the horizontal stress difference, and the fluid viscosity on the mechanical diversion behavior of the hydro-fracture, were analyzed in detail.…”