Post-expansion characterization of expandabletubular: Progress and challenges

Although more than a decade of work is behind the successful use of Solid Expandable Tubular (SET) in oil and gas industry for a wide range of applications, a thorough review of literature indicates that most of the research and development work is based on finding a fit-for-purpose solution for specific field problems. A significant aspect, which in certain circumstances is not well understood, is the pre and post expansion material and mechanical characterization of SET. Simple analytical and numerical models are developed to estimate the operational parameters like expansion force, length shortening, wall thinning etc., without having an appropriate understanding of material transformation and contact effects, which the tubular experiences during expansion. Although the calculated parameters are not optimum, these have significant effect on SET performance during its operational life in the well. In order to understand the critical mechanical properties and design accordingly, a predictive control of the material characteristics in the deformation process is essential. The current study is based on the comparison of experimental and simulation results of the expansion process for SET. Experimental work done using expandable tubular test-rig and simulation using finite element analysis has been done on 174.625 mm, 177.8 mm and 182.88 mm inner diameter tubular for expansion ratios varying from 12% to 28%. However, only the results of selected tubular are presented. The results clearly indicate that the maximum expansion ratio is severely limited by the post expansion collapse pressure of the tubular. Simple calculations as well as numerical simulation show that the thickness reduction beyond 13% results in considerable reduction in collapse rating. The microscopic study of the tubular material after burst and fracture zone showed regions of overload, shallow dimples and fine microscopic cracks. The elongated dimples intermingled with fine microscopic voids are reminiscent of localized ductile failure. These informations will lead to a better understanding of possible SET failure mechanism during its operational life and comprehensive data to manufacturers and scientists to seek improved material with higher ductility while maintaining strength after expansion. A good progress will result in extending the operational envelope of the tubular and its applications.