Stress and deformation distribution law of wellbore under pressure fluctuation load

Rapid drill-string tripping causes transient pressure fluctuations, triggering complex fluid-structure interac-tion (FSI) in the wellbore. This study uses FSI theory to model stress distribution and deformation under such loads. We develop and validate a three-dimensional numerical model—capable of simultaneous transient pressure and structural stress simulation—with laboratory and field data. Simulations across inclinations from 0o to 90o and varying tripping speeds show that pressure waves propagate with reflection and attenua-tion, with higher inclinations reducing attenuation. Pulsating pressures generate axial tensile stress, while drill-string inertia induces bending and lateral deformation. Bottom constraints critically affect stress: a rigid bottom raises peak stress by over 60%, whereas a free bottom has minimal impact. Above ~15o inclination, bottom-constraint effects weaken sharply. Sensitivity analyses recommend slower tripping, optimized fluid properties to damp surges, and reinforced casing in critical zones to enhance integrity. Applied to a high-pressure gas well in eastern Sichuan, the model accurately predicted transient pressures and stress patterns matching field monitoring. This work improves understanding of pressurestructure interactions in wellbores and informs safety measures in high-risk drilling.