Resistência residual ao colapso de tubos danificados: uma abordagem baseada em dados de inspeção e modelagem numérica

Abstract

This work aims to contribute to the robust assessment of the structural integrity of tubulars in high-complexity and high-risk environments, such as the Brazilian pre-salt region. More specifically, a methodology is proposed for estimating the residual strength of tubes damaged by wear and/or corrosion in oil and gas wells, integrating geometric inspection of elements and numerical modelling. Additionally, a probabilistic approach to the problem is presented, where structural reliability is applied to estimate the failure probability of the damaged tube. Casing and production/injection columns are important safety barrier elements, providing structural stability and tightness, isolating the well and formation to prevent unwanted fluid flow. Wear and corrosion in these tubulars occur during different operations throughout their lifecycle and are conservatively considered in the design phase to avoid integrity loss events. However, there is considerable uncertainty in these predictions. Modern inspection technologies, such as ultrasonic and electromagnetic profiling tools, have enabled the assessment of the actual state of tubes in service. Tube radius, thickness, and mass loss are parameters measured along the well columns. Proper interpretation of this data allows for the identification and quantification of tube damage severity. In the applied methodology, an algorithm is developed to identify tube damage based on inspection data and the premise that the intact tube is appropriately modelled as a distorted ellipse. The residual collapse strength of the tubes is estimated using a two-dimensional nonlinear model with the Finite Element Method. In the final step, a probabilistic analysis is applied considering geometric and material parameters as random variables, including damage configuration parameters, such as maximum depth and position. The results obtained indicate that the initial geometric configuration of the damaged tube can result in significant variations in residual strengths for different damage parameters, such as depth, radius, position, and distribution. It is noteworthy that analytical models found in the literature consider these factors partially but not in their entirety. A case study is conducted using real ultrasonic inspection data to demonstrate the application of the proposed methodology, comparing the results with reference values. Finally, the probabilistic study evaluates the increase in failure probability due to damage, associating the parameters of greatest influence on the result. The proposed study supports a more realistic understanding of the condition of damaged tubular elements in oil wells.