The analytical model of hydraulic fracture initiation for perforated borehole in fractured formation

Abstract

Hydraulic fracturing has been the common method of stimulation treatment. Effective fracture network needs to be formed for having efficient hydraulic fracturing. The forming process of fracture network can be divided into 2 parts, i.e., initiation and propagation. In particular, the initiation part is the foundation of forming fracture network, and also basic parameter for analyzing fracture propagation. However, in fractured formation, it is very tricky to obtain initial fracture pressure due to the influence of rich natural fractures. Therefore, based on the rock mechanics and spatial geometry theory, this paper presents a mechanical model for predicting fracture initiation in fractured formation. Unlike conventional model, this new model considers multiple fractures conditions and the intersection method between natural fractures and perforated borehole. The model has been used to investigate influence factors of initial fracture pressure. These computed results reveal that the initial fracture pressure has complex distribution, and changes with variable occurrence of natural fracture. There are different kinds of intersections between natural fracture and perforated borehole. When fracture plane intersects through perforated borehole, influence of fracture plane on fracture initiation is relatively larger. Furthermore, with increasing number of natural fractures, initial fracture pressure decreases and the initiation mode tends to be tensile failure along natural fracture plane. Additionally, engineering parameters, like well trajectory and perforation azimuth, are related to fracture initiation pressure. Their optimizations can contribute to perform optimization of reservoir stimulation. Results from this model used in this paper aim at offering reference for field fracturing practice in fractured formation.