Objective The aim is to study the impact on wellbore column pressure fluctuation by gas lift technology parameters and the dynamic process of wellbore dropsy.

Method The transient multiphase flow simulation software was used to establish a full-size ultra-deep wells casing structure model to simulate the motion state of gas-liquid two-phase flow in the wellbore during the gas lift process of ultra-deep wells. The model was verified by field data, and then the influence of gas lift parameters on the pressure of dangerous points of the string was analyzed.

Result In the analysis of the gas lift process, the distribution characteristics of the dangerous points of annulus pressure, tubing pressure, and external extrusion pressure had been identified. The maximum pressure in the annulus occurred during the gas injection start-up stage, located at the annulus packer; the maximum pressure in the tubing appears after stopping injection when the accumulated fluid was not completely discharged, located at the tubing shoe; the maximum external extrusion pressure in the annulus emerged after the start of gas injection, with the dangerous point situated in the wellhead area.

Conclusion The annular gas injection volume, wellhead oil pressure and liquid accumulation volume all have a great influence on the pressure of the dangerous point of the string during the gas lift process, while the wellhead temperature has no obvious influence on the pressure of the dangerous point of the string during the gas lift process. The research results can provide a reference for the wellbore integrity assessment during the gas lift operation of ultra-deep wells.