Analysis of sealing performance of the rotary blowout preventer rubber ring in ultra deep wells

A finite element model for analysing the sealing performance of three types of wellhead rotary blowout preventer rubber ring structures in use on site was established. By using this model, the stress, deformation and contact pressure distribution of the passive rubber ring during pre-tightening conditions were calculated when the inner annulus of the passive rubber ring passed through the 5-inch drill pipe body and the 7-inch joint. The distribution position, length, and magnitude of contact pressure on the contact surface between the three types of rubber rings and the outer wall of the drill string under different pressure penetration loads under rated working conditions were calculated. Overall, the sealing performance of the active rubber ring is the best while the sealing performance of the passive rubber ring is the worst. However, the passive rubber ring has a simple structure and does not require a hydraulic system, which makes it impossible to adjust the sealing strength of the rubber ring in real time based on the actual fluid pressure on site. On the other hand, the I-type rubber ring uses part of the rotating blowout preventer structure as the hydraulic chamber wall, which can thicken the rubber layer in contact with drill pipe. Therefore, passive rubber rings are more suitable for low fluid pressure drilling operations. When the fluid pressure at the lower part of the rubber ring exceeds the rated maximum fluid pressure, it will lead to a sharp decrease in the sealing performance of the rubber ring. Therefore, stricter control of the use of the rubber ring is needed during on-site use, especially in drilling conditions with wellhead fluid pressure. The research methods and achievements in the article provide theoretical guidance for the safety evaluation of rotary blowout preventers used in ultra deep wells unbalanced drilling.