Assessment of Post-Expanded Mechanical Performance of Materials and Evaluation of Material Expandability Limit

摘要

The expandable tubular technology has seen an increased diffusion in the well construction process. However, while it is accepted in well remediation activities, the consideration given to expandable technology as a primary option for well design is limited. The confidence of the casing material performance after expansion remains one of the main factors in preventing a larger adoption rate. Extreme expandable applications require very high expansion ratios, thus exceeding the elongation to failure of conventional casing materials; even specially selected casing materials are close to the limit of their deformation capability. Consequently, Statoil decided to extend the scope of a previous research program on materials for expandable applications to include an initial investigation into defining a material's expandability limit. A selected carbon steel grade was analyzed using specific experimental test methods and Finite Element Analysis (FEA), and employing previous results of other carbon steel grades and alloys. The experimental activities involved tensile tests on post-expanded material using optical systems for the strain measurement, a technique previously adopted for as received material. This method allowed the determination of the true stress-strain curve far beyond the range of standard methods. The uniformity of mechanical properties after expansion was also investigated. The test results showed the carbon steel grade investigated maintained a significant deformation capability even after large expansions. The FEA campaign analyzed the same materials using a 3D model, which incorporated the pipe eccentricity, to explore other cases and to verify the initial outcomes of expandability limits. The results allowed for the determination of a maximum deformation limit for the materials allowing a successful expansion.