Pre and post-expansion mechanical behavior of petroleum tubulars

Some of the challenges being faced by the petroleum development industry worldwide are low-cost and more efficient well completion, water-shutoff and other types of zonal isolation, production from mature or abandoned reservoirs, etc. Successfully addressing these issues, solid expandable tubulars (SETs) are being frequently used for enhanced oil recovery from difficult or damaged wells. All SET applications revolve around cold expansion of the tubular against a casing or in an open hole, by hydraulically pushing a cone through the tubular, or by mechanically pulling it. Issues such as maximum expansion ratio and post-expansion pipe integrity are directly linked with material properties of the tubular before and after expansion. An SET expansion test rig has been designed, fabricated, and commissioned at the Engineering Research Lab, Sultan Qaboos University in collaboration with Petroleum Development Oman. Various types of material testing and characterization equipment augment this facility. The current paper presents some results from an ongoing study about comparison of pre and post-expansion mechanical properties of the tubular material subjected to different expansion ratios. Material properties specifically addressed here are elastic modulus, yield strength, tensile strength, fracture stress, fracture strain, and ductility. Some of the important findings are that this steel has a much lower elastic modulus as compared to normal steels, and shows small variations as a result of the amount of tubular expansion. Yield strength is higher for larger expansion ratios, and for a fix-fix connection (as compared to a fix-free one). Ultimate strength increases a little for larger amounts of tubular expansion. As expected, ductility goes down with increasing amount of cold work, but is not affected much by whether the expansion is hydraulic or mechanical. Patterns observed in microstructures and fractographs support the experimental results.