Analysis of Collapse Strength and Life Prediction of Casings in Formation Water Service Environments.

Abstract

In oil and gas field development, the highly mineralized formation water environment often leads to casing corrosion, significantly reducing its collapse strength and service life. To investigate the corrosion characteristics and mechanical degradation of casings in formation water, this study combines high-temperature high-pressure (HTHP) corrosion experiments with finite element analysis to examine the influence of corrosion pit geometry and volume loss on casing collapse strength. Based on experimental data and simulation results, the safe service life of casing under various conditions is also predicted. The results show that greater material loss due to corrosion leads to lower collapse strength. Under the same volume loss, cylindrical pits cause the most severe reduction in collapse strength, while semi-ellipsoidal pits result in the least degradation. Elevated temperature and pressure significantly accelerate corrosion and further reduce mechanical performance. Under service conditions of 20 MPa-80 °C, 11 MPa-50 °C, and 2 MPa-20 °C, the predicted safe service life of the casing is 4.84, 7.57, and 11.61 years, respectively. The approach proposed in this study provides a reference for the evaluation of collapse resistance and service life prediction of casings exposed to formation water environments.