Fluid-Structure Interaction Analysis of Carbon Dioxide Injection Strings

Abstract

Pressure fluctuations induced by fluid flow within CO₂ injection strings can lead to vibrations, which may severely compromise the operational stability of the string. To ensure stable operation, a detailed investigation into the dynamic characteristics of CO₂ injection strings was conducted. The finite element simulation software ANSYS was employed to simulate and compare the effects of different CO₂ coupling conditions, as well as the influence of wall thickness and pipe length on the natural frequency of the string. Additionally, the mechanical response of the string under axial tensile and compressive loads resulting from internal pressure generated during CO₂ fluid injection was calculated. The results indicate that compared with an empty string, both liquid-solid coupling and supercritical CO₂ coupling reduce the natural frequency—by 9.8% and 7.1%, respectively. The natural frequency of the string decreases with increasing wall thickness, and the natural frequency of the tubing decreases with increasing pipe length. Under the action of CO₂ fluid pressure, as tensile and compressive loads increase, the stress on both the pipe body and the threaded connections increases accordingly. Once the stress reaches a certain threshold, the operational stability of the string can be compromised, potentially leading to failure of the CO₂ injection string. These findings provide a valuable reference for subsequent research.