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In the development of oil and gas fields, many wells have a phenomenon of wellhead growth originating in thermal stress of columns and cement sheaths poses severe challenges to shaft safety. Notably, the problem of wellhead growth is more serious in fully sealed oil and gas wells at sea. Therefore, this research on the wellbore cementation force, the wellbore lifting force, and wellhead growth for offshore oil and gas wells was critical. Based the effects on the comprehensive consideration of wellbore temperature change, annulus pressure, and performance parameters of cement sheath and casing, and then established the calculation method of cementing force, lifting force, and wellhead growth. Next, used the measured data and the data in the literature to validate the model. The results show that the calculation results of this model accord with the actual situation in the field. Finally, a gas well in the South China Sea was analyzed. Found that the increasing yield and annulus pressure will increase the height of wellhead growth, but the increasing thermal expansivity and the increasing elastic modulus of the cement sheath will decrease the height of wellhead growth. To avoid the wellhead growth, offshore oil and gas wells should adopt the submarine pipeline method (the height of the mud line relative to the deck was Zero). Thus, to improve the height of wellhead growth, the designed performance of the cement sheath, the management of annulus pressure, and the control of yield shall be introduced into the process of oil and gas field development. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • A dynamic simulation method of ball valve shearing is proposed and verified. • The dynamic simulation results are consistent with the experimental results. • The influence of ball valve on shear fracture performance is revealed. • An optimization method of ball valve is presented to improve shear fracture performance. [ABSTRACT FROM AUTHOR]