Collapse failure analysis of S13Cr-110 tubing in a high-pressure and high-temperature gas well

Abstract

Due to excellent CO2 corrosion resistance and low cost, martensitic stainless steels such as super 13Cr have been widely used as tubing strings in high-pressure and high-temperature wells. However, in recent years, with the further development of the oilfield, super 13Cr tubing failure accidents keep happening in high-pressure and high-temperature gas well, resulting in the loss of well integrity and huge economic losses. So a systematic research on the failure mechanism of the super 13Cr tubing in HPHT gas well under different service conditions is vital to the reduction of the failure accidents. In this paper, a collapse failure accident of S13Cr-110 tubing in a high-pressure and high-temperature gas well was investigated by metallographic microscope, scanning electron microscope, energy dispersive spectrometer, X-ray diffraction and finite element analysis, aiming to find out the root causes and put forward useful suggestion for the establishment of the preventive measures. The results showed that the chemical composition and mechanical properties of the tubing were all in accordance with the corresponding parameter requirements, and the collapse failure was attributed to the combined effect of formation sand production, high temperature and stress corrosion cracking on the outer surface. The tubing plugging induced by the formation sand production caused the increase of pressure difference between the annulus and tubing, which was the main reason for the collapse failure. In addition, high temperature in the downhole would result in a decreasing of the tubing’s anti-collapse ability. Meanwhile, the annular environment containing Cl-, PO43-, further induced the stress corrosion cracking under service stress. The presence of the cracks on the outer surface could cause a significant decrease of the pressure-bearing capacity of tubing strings, which would finally have an obvious influence on the acceleration of the failure process.