Theory And Application Study On Annular Kick-Control Technology Of Through-tubing Blowout Preventer In Downhole Operation

Annular kick-control technology of through-tubing blowout preventer is a key way to realize wellhead pressure control while tripping in and out of tubing, which is also a safe-guarding technology prevalent in worldwide oil fields. A blowout preventer is the key equipment used to control wellhead pressure, avoid blowout accidents and realize balanced-pressure drilling. In oil fields'practice, it is strictly required to safely seal the annular while tripping in and out tubing. However, the old technologies of annular seal and kick-prevention can no longer meet the requirement of the status quo of increased casing pressure. The study on the rubber core, a key elastic component, is the key to solve the difficult problem of sealing under pressure, prolong the seal's service life and improve the sealing effect.Through-tubing Blowout Preventer, a blowout prevention equipment of wellhead, depends on the elastic rubber core to realize the pressure control in tubing operation. In order to deeply study through-tubing blowout preventers, in this paper, a physical model, which is based on its practical structure has been established and finite element method is used to perform simulation calculation. Rules of the deformation and contact pressure of the rubber core are found while the tubings are going through.The rubber core of through-tubing blowout preventer is subject to varying control pressures in the course of the tripping in and out of tubing. The change of the values of control pressure and sealing pressure has a strong effect on the sealing quality and core's life. In order to study the fatigue failure mechanism of rubber core, and the interaction and relationship between system pressure and contact pressure need to be known.Based on fatigue life theory, calculation about the rubber core's fatigue life has been performed. On the basis of the calculation results, the rubber core's structure dimensions are optimized in order to increase the diameter scope of the sealed tubings and improve the integral sealing qualities. Using laboratory facilaties and based on the practical data of over ten oil wells, experiments of through-tubing-coupling blowout preventer are performed. The results show that the pressure control technology of the through-tubing blowout preventer is simple and flexible, and is an effective pressure control measure for polymer flooding. It can also improve the level of environment protection at the same time.In this paper, finite element method has been used to calculate and study the rubber core which is made of composite material. The calculation results can give a good theoretical instruction to prolonging its service life, reducing cost and improving the design. It is also of practical significance to the production in oil fields.Fuzzy reliability optimization method, a practical application of optimization design theory, can be used to establish an optimized model which can reflect the complexity and fuzziness of the system, correctly describe the reliability and practical condition of the system, and get rid of the shortcoming of conventional optimum design methods. In this paper, based on the specific characteristics of rubber core in operation, a mathematic model has been established by fuzzy reliability optimization method considering the randomness and fuzziness of its stress and strength; optimum solution has been obtained by using the optimizing level set approach.