An Investigation into the Effects of Weak Interfaces on Fracture Height Containment in Hydraulic Fracturing

Abstract

Hydraulic fracturing is an effective method for developing unconventional reservoirs. The fracture height is a critical geometric parameter for fracturing design but will be limited by a weak interface. Fracture containment occurs when fracture propagation terminates at layer interfaces that are weaker than the surrounding rock. It always occurs in multilayer formation. Therefore, the mechanism of fracture height containment guides fracture height control in hydraulic fracturing. In order to study the fracture containment mechanism, this paper first calculates the propagation behaviour of the fracture in 3D under the influence of a weak interface through a block discrete element method and analyzes the geometric characteristics of the fracture after it meets the weak interface. Then, the induced stress of the hydraulic fracture on the weak interface is calculated by fracture mechanics theory, and the mechanism of blunting at the fracture tip is explained. Then, two kinds of interface slippage that can lead to blunting of the fracture tip are discussed. Based on the behavior of shear slippage at the interface, a control method for multilayer fracturing in thin sand-mud interbed and pay zone fracturing in shale is proposed. The results show that the fracture height is still limited by the weak interface in the formation without the difference of in-situ stress and rock properties. Interface slippage is the main factor impeding fracture propagation. Fracture height containment can be adjusted and controlled by changing the angle between the hydraulic fracture, the interface, and the stress state to strengthen and stiffen the interface. This study has a certain guiding significance for fracture height control in the design of hydraulic fracturing of shale or thin sand-mud interbed reservoirs.

Influence of the bedding plane on the propagation of multiple hydraulic fractures

“…One surface is regarded as the target surface, and the other is considered the contact surface. The details of BDEM were introduced and elaborated on in our previous work (Zheng et al, 2019a andZheng et al, 2019b).…”

“…Furthermore, the approach angle between the fracture and the bedding plane also affects the propagation behavior. The study of Zheng et al (2019b) indicated that a longer main fracture may form at a higher approach angle if the cementation of BPs is not weak. On the contrary, for fracture propagation in BPs, stress intervention, smaller injection rate, and smaller fluid viscosity are useful in general.…”

“…For capturing the heterogeneity of rock mass, we should ensure the regular accuracy of the simulated results. We have already discussed the mesh dependency of the simulation results in our previous work (Zheng et al, 2019b). The size of the mesh is determined by the edge.…”

“…Relevant studies have shown that BPs can affect the propagation of fractures. Zheng et al (2019a) Zheng et al (2019b) examined the effect of the bedding plane on a single fracture by using the 3DEC software. The results suggested that the fracture propagation behavior was relevant to the intersection angle between the fracture and bedding, and when the bedding was perpendicular to the fractures, the bedding possibly hindered the fracture propagation.…”

Multi-Fracture Synchronous Propagation Mechanism of Multi-Clustered Fracturing in Interlayered Tight Sandstone Reservoir

“…They discovered that even when the interface strength is low, hydraulic fractures can penetrate the lithologic interface if the vertical stress difference and interface angle are large enough. When the included angle between the hydraulic fracture and the interface is less than 45 • and the tensile strength ratio of the pay layer and the interlayer is less than 0.3, the hydraulic fracture cannot penetrate the interface no matter how large the vertical stress difference is [13,14]. Some studies experimentally discovered that the fracture can directly penetrate the interface only when the vertical stress reaches a certain threshold, but the threshold gradually increases with the decrease in the interface friction coefficient [15,16].…”