Influence of internal and external pressure on equivalent axis force and stability of pipe string in oil wells

Key words:  casing  tubing  external pressure  internal pressure  stability  buckling  fictitious force  equivalent axis force

Abstract:

Pipes are under actions of internal and external pressure of fluid in oil well drilling and production, so the stability of the pipes is affected by the pressures. The traditional mechanical model and fictitious force were discussed. A mechanical model representing true tubular conditions was established. Equations of calculating equivalent axis force used for stability analysis of pipes were established based on constant axis strain. The results show that the internal and external pressure of fluid and their change have no effect on stability of hanging pipes, and have effect on equivalent axis force and stability of pipes fixed at two ends. For pipes fixed at two ends, equivalent axis force decreases with internal pressure increasing and increases with external pressure increasing. The increase of internal pressure or decrease of external pressure may make equivalent axis force negative, even less than critical buckling force.