Sealability Analyses of Premium Connections Characterized by a Surface Fractal Function

Abstract

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%.