Abstract
Subsea test tree (SSTT) is an essential safety device for the completion testing operations of deepwater extraction of oil, natural gas, and natural gas hydrate. During the implementation of the emergency release procedure of the SSTT, the coiled tubing or steel wire running in it must be quickly and effectively sheared by its ball valve mechanism. Therefore, clearly revealing the shearing mechanism and accurately evaluating the shearing performance of the ball valve mechanism is essential for maximizing the safety performance of SSTT operation. The finite element numerical simulation method established a dynamic shear model of the SSTT's ball valve under different working conditions and structural parameters to clarify the influencing factors and laws of the ball valve shearing performance. The results of numerical simulation model agree well with the laboratory tests, verifying the scientific validity and accuracy of the numerical simulation method and the generated model. Further, the SSTT's shearing process under different working conditions and geometry was calculated based on the method and model mentioned above. It shows that the tension of coiled tubing is greater, the required of shear moment is smaller. The internal pressure lead to more difficult shearing conditions. In the eccentric position, the ball valve was subjected to a reaction force moment perpendicular to the rotation direction of the ball valve. The larger the ball valve diameter, the shear force required to shear coiled tubing. The SSTT upper seat Angle also affects shear failure performance, and coiled tubing can be shear at 10°, 30°, and 40° with less shear moment. The minimum shear moment is required when the edge of the shearing ball valve has a 1.5 mm circular chamfering. This study proposes an optimization method to improve the shear fracture performance of ball valves. Moreover, this study provides essential guidelines for the optimal design and application operation on the SSTT's ball-valve mechanism.
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