Limited Height Growth and Reduced Opening of Hydraulic Fractures due to Fracture Offsets: An XFEM Application

Abstract

Abstract Hydraulic fracture propagation through a layered medium often exhibits a complex fracture path due to lateral shifting of the fracture path after passing through an interface. The existence of these offsets in the fracture path has been confirmed by mapping of mined fractures and by laboratory experiments. In addition to the stress contrast and material contrast, these offsets act as another mechanism for fracture-height containment. In order to investigate fracture height growth problem, we have considered a case of plane-strain fractures propagating from an injection point and propagating in a predetermined path. Fracture offsets of a given length and angle are prescribed within the predetermined path. In this way, we parametrize the problem of fracture offsets in order to quantify their effects on the fracture height growth and fracture opening reduction at the fracture offset (pinching effect). This is done while keeping a hydrostatic state of confining stresses in order to observe only the geometric effect of the fracture offset. We use a recently developed hydraulic fracturing code based on the eXtended Finite Element Method (XFEM). This code solves the fluid flow in the fracture and the elastic response of the fracture in a fully coupled manner solving for the fracture velocity using the complete hydraulic fracture tip asymptotics. For different combinations of independent parameters (i.e., formation moduli, far-field stresses, fluid injection rate, ratio of offset length to the length of the straight fracture and the offset angles) we investigate the effect on the fracture height growth and the reduction in fracture opening at the fracture offset. A detailed parametric study shows that while each parameter affects the fracture height containment, the fracture opening reduction is dominated by the fracture offset angle which is a geometric effect of the fracture offsets. This has a profound effect on the proppant bridging at the fracture offset.