Abstract: The underwater oil production system is usually arranged on the seabed, and its protection measures are crucial for the working stability and safety of the production system. According to the actual marine environmental conditions and the requirements of water channels, there are currently projects that innovatively use large-diameter steel cylinders embedded below the seabed as protection structures for underwater production systems. For this type of protective structure and engineering application, the stability of the steel cylinder will be affected when the spudcan penetration and extraction operation is performed near the jack-up drilling ship, which will bring potential safety hazards. In this paper, the coupled Euler and Lagrangian finite element numerical method is used to simulate and analyze the disturbance of the steel cylinder caused by double spudcans penetration. The deformation and stress changes of the soil and the steel cylinder foundation during the spudcan penetration process are studied, so as to analyze the stability and safety of the steel cylinder protection structure. The results show that the additional stress and displacement of the wall of the steel cylinder increase with the penetration depth of the spudcan at the initial stage and tend to be stable after reaching the peak; when the spudcan penetrates to a certain depth, the soil on the upper part of the spudcan reflows. As a result, the influence on the steel cylinder is reduced; the influence of the double spudcans on the steel cylinder is weakened with the increase of the distance between the spudcans and steel cylinder, but its influence range is significantly expanded compared with the single spudcan. The numerical analysis results in this paper will provide an effective reference for the design and field application of protection measures for underwater oil production systems.

Key words: Jack-up Drilling Ship, Spudcan Penetration, Steel Cylinder, CEL Method, Large Deformation of Soil