Study on sensitivity of annular BOP parameters to sealing performance in gas well snubbing service

Abstract

Annular Blowout Preventer (BOP) is the core device for snubbing service in gas wells. The wellhead can be sealed by operating the BOP. Rubber core of annular BOP is the main part of the sealing process, and its failure will cause blowout accidents and endanger the operators. Rubber core failure is mainly caused by the serious wear and fracturing damage, compared with oil well, during the snubbing service of the gas well, there is dry friction between rubber core and tubing, which is more prone to rubber core wear. Based on the Yeoh constitutive model, this paper fits the material parameters through the data measured by the rubber tensile experiment, and establishes the sealing performance evaluation model of the annular BOP based on the theory of rubber hyperelastic, large deformation theory and dynamic sealing theory. Meanwhile, compare it with the rubber core failure cases which used in field to verify the accuracy of the model. Based on these, this paper studies the influence of piston stroke, tubing size, friction coefficient between rubber core and tubing, rubber core attrition rate on sealing performance, and fitting the relationship between tubing size and piston stroke. The results show that: properly increasing the piston stroke by 2 to 3 mm will help to improve the sealing performance; when the tubing size is smaller, the rubber core is deformed too much while the seal process completed, which is easy to cause the rubber core to fracturing; friction coefficient between rubber core and tubing has no significant effect on static sealing performance; the friction coefficient less than 0.2 has little effect on the dynamic sealing performance; when the friction coefficient exceeds 0.4, the dynamic sealing performance is reduced significantly; when the wear of rubber core is within 10 mm, the sealing performance gradually decreases, but the sealing requirements can still be met. When it is more than 10 mm, it cannot meet the sealing requirements of 35 MPa. The research work in this paper has certain guiding significance for the design, selection and use of the rubber core of annular BOP.

Keywords

• annular blowout preventer
• spherical rubber core
• large deformation of rubber
• numerical simulation
• sealing performance