Axial Stress Prediction and Collapse Resistance Calculation of Tubing in CCUS Injection Wells

Abstract

This study investigates tubing collapse resistance during low-temperature dense-phase CO2 injection in carbon capture, utilization, and storage (CCUS) wells. A coupled temperature–pressure–tubing mechanics–collapse model was developed. CO2 density, specific enthalpy, isobaric heat capacity, and the Joule–Thomson coefficient were calculated using the Span–Wagner equation of state, while wellbore temperature and pressure profiles were obtained from mass, momentum, and energy conservation equations. Tubing axial stress and triaxial collapse resistance were evaluated considering self-weight, thermal effects, ballooning, and fluid friction. Comparison with multi-depth measurements from one injection well produced bottomhole temperature and pressure errors of 0.99% and 0.71%, respectively. Sensitivity analysis showed that each 5 °C decrease in injection temperature reduced collapse resistance by approximately 2% on average. Each 5 MPa increase in injection pressure reduced it by only approximately 0.3% because the resulting combined-stress change was small relative to the tubing yield strength and the thermal contribution remained nearly unchanged. Increasing injection rate shortened heat-exchange time, lowered fluid temperature, and increased tubing loads, but had a weaker influence than injection temperature. The model provides a basis for optimizing injection parameters and verifying tubing strength.