Numerical simulation and analysis of holebottom pressure fluctuations during tripping operations in deep and complex wells

Tripping is an essential process in drilling operations, but improper handling can lead to downhole complications, such as blowouts, lost circulation, or borehole instability. To address the issue of holebottom pressure fluctuations during tripping operations, this study establishes a full-scale wellbore bottom hole assembly (BHA) fluid–structure interaction model. Using Fluent's dynamic mesh technology, numerical simulations were conducted to analyze the axial motion of the BHA and the dynamic disturbances of drilling fluid in the annulus during tripping operations. The effects of tripping speed, drilling fluid viscosity, density, and annular radius on holebottom pressure fluctuations were investigated, and the dynamic variations in holebottom pressure fluctuations were quantitatively extracted. Analysis of simulation results under various conditions revealed that the surge pressure caused by tripping in is more sensitive to changes in influencing factors, while the swab pressure caused by tripping out is relatively smaller. The study shows that increasing tripping speed, drilling fluid viscosity, or density, as well as reducing annular radius, significantly increases the amplitude of holebottom pressure fluctuations, posing potential risks to downhole safety. The proposed numerical model and calculation method, validated with high accuracy, provide theoretical support and technical guidance for controlling wellbore pressure fluctuations and optimizing drilling engineering.