Sealing performance and failure mechanism of rubber core for conical blowout preventer during the well shut-in process

Abstract

Blowout preventer reliability is important for safe drilling operation. In order to study the sealing mechanism and failure mechanism of conical blowout preventer, this paper establishes a numerical model of conical blowout preventer based on the theory of large deformation of rubber, and studies the deformation law, stress distribution and sealing performance of rubber core in well shut-in operation. The results show that there are stress concentrations in the contact area between the rubber core and the piston, the grooves in the middle of the adjacent support ribs, and the chamfered corner of the inner wall of the rubber core, the main form of failure at these locations is rubber cracking. Higher stress is present in the neck region of the upper plate and the back region of the lower plate of the support ribs. The inner wall surface of the rubber core gradually produces stripes of wrinkles, and the smaller the size of the sealed drill pipe, the more obvious the wrinkles are. When the drill pipe joint is sealed by the rubber core, there is a sealing buffer zone at the shoulder, and the contact pressure change abruptly. The lower portion of the rubber core’s inner wall serves as the primary sealing area. Increasing the piston displacement appropriately can enhance the sealing performance of the rubber core. The results of the study can provide a theoretical basis for the optimization design of the conical blowout preventer.