Analysis of Sealing Mechanical Properties of Fracturing Packer Under Complex Conditions

As the core component of the fracturing tool, the packer cartridge plays a vital role in a horizontal well stimulation and transformation process (Sun and Bai in Pet Explor Dev 44:1022–1029, 2017). Influenced by many factors such as formation workflow, borehole structure and construction conditions, the mechanical response of the packer rubber cylinder in sealing is complex and changeable (Jun et al. in J Pet Sci Eng 171:495–506, 2018; Tong et al. J Pet Sci Eng 172:964–975, 2019; Zhu et al. J Pet Sci Eng 151:311–317, 2017b). In order to study the mechanical response mechanism of the packer tool under complex working conditions, tensile tests of rubber under the corrosion environment of carbon dioxide formation fluid were carried out and the constitutive material parameters of Yeoh model after corrosion were obtained. The results showed that the tensile strength of hydrogenated nitrile butadiene rubber (HNBR) decreased by 7.86–17.01% after corrosion in simulated formation fluid, and the elongation at break increased by 2.09–19.74%. Compared with AFLAS (tetrapropyl fluoro elastomer), HNBR rubber had better stability and can be used as the preferred material for the service environment of permanent packers. Based on the mechanical properties of numerical calculation results before and after corrosion, it was found that the contact pressure and compression distance of the whole HNBR packer changed slightly, which met the requirements of field construction. On the basis of optimum selection of rubber material, the sealing performance of packer in borehole casing with enlargement/reduction caused by formation is analyzed. The results show that the casing with expansion deformation will lead to setting lag or lax, and the shrinkage casing will lead to setting advance or even stress failure. The analysis results provide theoretical support for the improvement in permanent packer string and its adaptation to complex formation.