The Propagation Behavior of Hydraulic Fracture in Rock Mass with Cemented Joints

Abstract

The formation of the fracture network in shale hydraulic fracturing is the key to the successful development of shale gas. In order to analyze the mechanism of hydraulic fracturing fracture propagation in cemented fractured formations, a numerical simulation about fracture behavior in cemented joints was conducted based firstly on the block discrete element. And the critical pressure of three fracture propagation modes under the intersection of hydraulic fracturing fracture and closed natural fracture is derived, and the parameter analysis is carried out by univariate analysis and the response surface method (RSM). The results show that at a low intersecting angle, hydraulic fractures will turn and move forward at the same time, forming intersecting fractures. At medium angles, the cracks only turn. At high angles, the crack will expand directly forward without turning. In conclusion, low-angle intersecting fractures are more likely to form complex fracture networks, followed by medium-angle intersecting fractures, and high-angle intersecting fractures have more difficulty in forming fracture networks. The research results have important theoretical guiding significance for the hydraulic fracturing design.

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

“…2k sin(π/2) = cos θ 2k ; thus, Equations (29) and (31) degenerate to (24) and (25), indicating that the results of this inference are consistent; fτ and fn at δ = π/2 are plotted in Figure 11a, which is consistent with Figure 5. See Appendix B for the specific derivation process…”

“…The Goodman element is adopted in this calculation, i.e., K sn and K ns are set as 0, and K n and K s are used to describe the normal deformation and tangential deformation of the structural surface, respectively. The Goodman element is one of the most commonly used interface elements to describe the interface characteristics of discontinuous medium such as faults or joints [23], and the Goodman elements method is employed in some numerical software such as RFPA [24] or 3DEC [25]. The details about the Goodman element method can be found in [26].…”

“…In the hydro-mechanical coupling of fractures, the influence of mechanical deformation on fracture permeability is mainly manifested as a change in fracture aperture. In the elastic stage, the fracture aperture is expressed as an equation related to the effective stress [25]:…”

“…In the plastic stage, considering the expansion caused by joint slip, the fracture opening can be expressed as [25]:…”

“…Then, z = a + r 0 e iθ = a + ζ See Appendix A for the specific derivation process. Equations (24) and (25) are functions independent of a, but related to the relation coefficient k between d and a. Once the k value is determined, the distribution of fij function in the joint (y-direction) can be obtained; fij represents the coefficient of induced stress and is related to θ, but the distance along the y direction and angle θ are nonlinear.…”