Análise numérica da resistência ao colapso em tubulares de revestimento de poços dotados de imperfeições de manufatura e desgaste

Abstract

Casing systems for oil and gas wells consist of tubular elements installed along the depth, providing stability and tightness, and must meet the strict premises of structural integrity, especially in the case of offshore scenarios. Given this, some events may expose the casing to high differentials. pressure, leading the tubular to failure under external pressure, called collapse. Imperfections associated with casing tubular manufacturing processes, such as eccentricity, ovality of the cross section, and the residual stress of the steel, can have a significant influence on the failure mechanism by collapse. In addition to these, there is the presence of wear in wells performed, caused predominantly by the contact of the drilling column with the inner wall of the casing. In many cases, these imperfections can lead to a considerable reduction in the collapse strength, especially in thin-walled tubes, whose failure mechanism is associated with geometric instability caused by high transverse slenderness. Robust section tubes tend to fail under stress levels near to the yield limit or material tensile strength limit. This work presents a numerical analysis of the collapse strength of imperfect and internally worn tubulars, admitting the deformation plane state, in a physically and geometrically nonlinear regime. The finite element method is used in the analysis and verification of the collapse pressure of the tubes, as used by ABAQUS® software. The mechanical behavior of steel is described by the constitutive elastoplastic model with nonlinear hardening provided by the ASME BPVC (2015). Evaluation of finite element models is performed based on the responses obtained by the formulations and experimental results proposed by Clinedinst et al. (1939), Klever e Tamano (2006), and Moreira Junior (2012), for perfect tubes or with manufacturing and wear imperfections. The consideration of internal wear is made by removing material from the section in groove wear zones or by data obtained from profiling, based on real measurements of the internal wall of the casing. Parametric studies are presented to assess the influence of slenderness, wear, and imperfection parameters on the collapse strength. From the results obtained, it appears that the presence of manufacturing imperfections, depending on their levels, promotes considerable reduction of collapse strength, the most pronounced of which being ovality. Regarding the worn specimens, it is noted the influence of parameters such as wear depth, diameter of the tool joint that produces the groove, and their angular positions. In the case of profiled tubulars, it is verified that in addition to the depth of wear, its extension along the inner wall can imply a considerable decrease in collapse pressure.