Abstract
Thick and porous reservoirs induce significant compaction with production, resulting in screen and casing failures within the reservoir section and inducing casing tensile/shear failures within the cap rock section. Designing these wells based on the conventional API specification requires excessively heavy duty casings, resulting in low hydrocarbon productivity with a high cost. However, casing failure problems often have not been eliminated by using high duty casings. The problem is the higher grade casings show a tendency to be more brittle than lower grade casings.
In actual fields, casings are often used beyond the yield point. Casings can be used as long as they don't excessively distort even if the stress exceeds the yield point to some extent. Therefore, this research focuses on the possibility of using casings under extreme conditions.
This research provides a new design concept based on the ultimate tensile strength and the strain. These values are obtained from the tension tests conducted for casings ranging from high grades to low grades. Especially, this paper emphasizes the importance of the strain rather than stress for judging the ultimate casing failure.
