Gas and oil production from an oil and gas well was delayed by a downhole tubing failure. Retrieved sections of the tubing were tested by a nearby laboratory. The testing results were inconclusive as to tubing type (N-80 vs. J-55). The retrieved tubing section from which tensile test, hardness and chemical analysis specimens were re-evaluated by Dr. Jerner are shown in Photograph A.
Photograph A Improperly prepared tensile test specimens.
It is a well known and long established metallurgical fact that cold work and plastic permanent deformation results in an increase in both the yield and tensile strengths of steel. Minimal amounts of deformation can result in the elevation of the yield and tensile strength by 10-50%. This fact substantiates that, without a doubt, the mechanical properties of the subject tubing, as measured by the other laboratory were elevated by downhole tubing deformation which occurred after the tubing was run into the subject well. The area from which improperly prepared test specimens were extracted is shown in Photograph B.
Photograph B Area from which improper tensile test specimens were extracted.
The tubing was determined to be consistent with J-55 and had been incorrectly supplied. Furthermore, the microstructure exhibited by the failed tubing was not consistent with quench and tempered microstructure expected for N-80 tubing.
Photograph C Overall view of twisted tubing from subject oil well.