With the development of high-pressure, high-temperature wells, the sealability of premium connections is being threatened by heavy loads. For the sake of researching the sealability of premium connections at the microlevel on the sealing surface, a rough profile was characterized according to a fractal function, and the influence of the fractal parameters of contact behavior on the rough surface was analyzed. A full-size premium connection model with a fractal surface FEM was established using ABAQUS software to analyze the Von Mises stress and contact pressure, and the sealability was then analyzed using contact strength theory. It was found that utilizing fractal functions to describe the rough morphology on the sealing surface of premium connections could reveal the contact behavior of the sealing surface more realistically. The premium connection’s fractal FEM was closer to the actual situation, considering the effect of the asperities’ elastic–plastic deformation on the sealability. The fractal dimension D had a greater influence on the contact area and contact pressure than the scale coefficient G. When the fractal dimension D was less than 2.5, the maximum Von Mises stress and maximum contact pressure on the sealing surface were 8.81 × 10⁸ Pa and 1.20 × 10⁹ Pa, respectively, making the surface prone to gluing. The sealability of the premium connection was primarily affected by the axial tension. When the axial tension was 1.2 × 10⁶ N, the sealing surface experienced significant displacement along the axial direction, the effective contact length reduced from 2.72 × 10⁻³ m to 2.24 × 10⁻³ m, and the maximum contact pressure reduced from 8.10 × 10⁸ Pa to 6.39 × 10⁸ Pa, which led to a 30% decrease in sealing strength, which may pose a high risk of sealing failure. When the internal pressure reached 1 × 10⁸ Pa, the effective contact length increased from 9.08 × 10⁻³ m to 1.06 × 10⁻² m, the maximum contact pressure increased from 8.67 × 10⁸ Pa to 1.37 × 10⁹ Pa, and the sealing strength increased by 23%.

Due to the uncertainty of the formation and the complexity of downhole tubular string loads and deformations, the existing tubular string static theory is difficult to explain and lacks support from measured data of tubular string dynamic loads. Therefore, a dynamic loads monitor for oil and gas tubular string is developed, which can synchronously measure the internal pressure, external pressure, axial force, and vibration acceleration for the string during the whole operation process. The monitor realizes simultaneous monitoring of tubular string load and vibration response parameters while meeting the requirements of various sensor placement spaces and structural strength safety, simplifying the on-site test process. By adding a power control circuit to the circuit system, the working time of the monitor is extended. The high temperature calibration test of the monitor is carried out, and the maximum calibration error is 0.10%, which meets the requirements of measurement accuracy.

The premium connection is an important section of the tubing column. Under intricate downhole conditions, axial vibration generates alternating loads that cause energy dissipation between the sealing surfaces of the premium connection, reducing sealing performance. To investigate this issue, the mutual conversion process of sticking, slipping, and macroscopic slipping stages between the sealing surfaces of the premium connection under axial loads must be assessed. In this study, a finite element analysis model of a taper–taper Φ88.9 mm × 6.45 mm P110 premium connection is developed based on the discrete Iwan model’s ontological relationship, and the sealing surface’s force–displacement hysteresis curve is obtained. The equivalent Iwan model for this particular premium connection is constructed by discretizing the hysteresis curve and identifying the model’s four sets of parameters. The correctness of the parameter identification method of the equivalent Iwan model is verified by comparing and analyzing the similarity of the two models. The energy dissipation in the sealing surfaces of the premium connection for different working conditions under dynamic loading is analyzed. This study reveals that the area similarity of the hysteresis curves of the two models is more than 92%, while the positional error is less than 2%. The sealing surface displacement amplitude of the premium connection is between 0.04 mm and 0.07 mm, while the sealing surface energy dissipation increases linearly, which may lead to a decline in sealing performance.

Traditional static analysis cannot effectively explain the issue of the sealing performance of the premium connection being decreased due to the vibration of the tubing, leading to the failure of the connection sealing. In this paper, based on the energy dissipation theory and considering the influence of the micro contact slip of the sealing surface under the vibration of the tubing, a finite element model of the premium connection is established. The natural frequency and vibration mode are obtained through modal analysis experiments, and the accuracy of the finite element model is verified. The results show that the first five natural frequencies are mainly concentrated in the axial direction of the tubing, with the amplitude of the radial vibration mode being small. The vibration mode results are applied to the model as boundary conditions. It is found that an increase in the axial displacement amplitude leads to an increase in the energy dissipation of the sealing surface of the premium connection, which reduces the normal contact pressure and the effective length of the sealing surface, ultimately leading to a decrease in the sealing performance.

To investigate corrosion and resulting changes in the sealing performance of premium connections in corrosive CO₂ environments, we carried out a simulation analysis of their secondary current distribution and structural mechanics based on multi-physics field coupling. A finite element calculation model of Ф88.9 mm × 6.45 mm taper–taper premium connections (steel grade P110) was established using COMSOL6.0 general software. By analyzing corrosion laws under different environmental parameters, five internal pressures and tensile displacements were set. We simulated premium connections under different operating conditions using a secondary current distribution module. To investigate the distribution of the corrosion current density in premium connections under different operating conditions, the sealing performance before and after corrosion was quantitatively evaluated using a seal strength index. The results show that the current density is higher at the torque shoulder of the premium connections, which is more susceptible to damage. As the internal pressure increases, the current density in the inner wall of the column increases, and on the threads, the current density is highest at the rounded corners of the root of the thread, which is also more likely to be damaged. Under different internal pressures, although the sealing strength of the premium connections meets the sealing criterion, the corroded ones show a significant reduction in sealing performance. The results of this study provide a reliable theoretical basis for research on sealing premium connections in corrosive environments.