Parameter optimization for controlling the complexity of near-wellbore fractures for perforated fracturing of horizontal wells

Perforated fracturing of horizontal wells is a key measure to exploit unconventional oil and gas reservoirs, but the competitive initiation of hydraulic fractures from perforation tunnels and the non-planar propagation near the wellbore are still unclear. Therefore, taking the well HX of shale oil reservoir as an example, a three-dimensional fully-coupled fracturing model with helical perforation is established by using the discrete lattice method. The interaction behavior and propagation evolution of multi-tunnel fractures for helical perforation are described in detail. The impacts of controlling factors such as horizontal stress difference, perforation density and phase angle on the propagation of near-wellbore fractures are systematically studied, and several engineering measures to control the complexity of near-wellbore fractures are put forward. The results show that there are longitudinal fractures and transverse fractures at the bottom of perforation tunnels in the initial stage of fracturing, then, transverse fractures propagate predominantly while longitudinal fractures are restrained due to the influence of in-situ stresses, and finally, a dominant transverse-fracture perpendicular to the direction of the minimum horizontal principal stress is formed at the far end after different communication between fractures initiated from adjacent tunnels. When the horizontal wellbore is oriented along the direction of the minimum horizontal stress, the low horizontal stress difference, high perforation density and low phase angle are beneficial to the creation of simple and continuous transverse-fractures near the wellbore. However, under the conditions of high horizontal stress difference, low perforation density and high phase angle, complex fractures with multiple branches are generated due to the difficulty in communication between fractures initiated from adjacent tunnels. The proposed three-dimensional fully-coupled model of perforated fracturing effectively describes the initiation and propagation of multiple-tunnel fractures, and the research results provide theoretical guidance for controlling the complexity of near-wellbore fractures by optimizing perforation completion. © 2022, Science Press. All right reserved.