Complexity and tortuosity hydraulic fracture morphology due to near-wellbore nonplanar propagation from perforated horizontal wells

Abstract

Perforated fracturing enhances single well production in the tight sandstones formations with low porosity and permeability effectively, however, some issues are caused after such achievements, such as high breakdown pressure, short fracture length, and limited proppant migration. All are tightly related to hydraulic fracture complex propagation behavior near wellbore. To understand its mechanism, a 3D near-wellbore fracture propagation model is established based on the combination of finite element method and post-failure damage mechanism. The model is applied on a cased and perforated horizontal well to investigate fracture initiation characteristics, near-wellbore fracture non-planar propagation behavior, and torturous hydraulic fracture morphology. Moreover, the effects of stress shadow and perforation parameters are discussed. Based on induced hydraulic fracture initiation position and propagation speed, three main fracture propagation behaviors are observed under the stress shadow effect in simulation results: limited propagation, nonuniform circular propagation, and opposite direction propagation. These nonplanar propagation behaviors cause complexity and tortuosity hydraulic fracture morphologies near the wellbore, which could be mainly divided into four types: spiral-shaped fracture, multi-spiral shaped fracture, horizontal-vertical crossing shaped fracture, and multi-layered shaped fracture. In addition, the reasonable perforation parameter design could reduce torturous fracture surface, resulting in a near flat fracture. The increase in perforation density or perforation diameter could shorten perforation spacing to provide a small diversion angle for induced fractures to interact with each other and form a small spiral degree fracture geometry. However, increased perforation phase causes many perforations in the same direction to create a longitudinal fracture that has a short fracture length for the horizontal well. Therefore, based on above analyses, high perforation density, small perforation phase, and large perforation diameter are suggested to be an effective perforation parameter combination to conduct the perforated fracturing in tight sandstone formation, in order to create a near flat fracture surface with a minimum tortuosity as well as to increase hydraulic fracture propagation area.