High Strength Modified Martensitic Stainless Steel Production Tubing for Sour Wells

This paper describes the material selection and the relative testing for production tubing in two fields, one onshore and the other offshore. Both fields are characterized by sour conditions with relatively low concentrations of H₂S. The offshore field has moderate temperature (102ºC), high salinity (~23 g/l Cl^-), high concentration of bicarbonates and 23 mbar H₂S partial pressure. Conversely, the onshore field has a high temperature (193ºC), low salinity water phase (~2 g/l Cl^-) and 90 mbar H₂S partial pressure. The onshore field had a production tubing mechanical requirement of 110 ksi minimum yield strength while the offshore field needed 115 ksi or preferably 125 ksi minimum yield strength for the Vacuum Insulated Tubing. A preliminary study concluded that there was a possibility to use modified martensitic stainless steels but a program of testing needed to be performed to assess the applicability of these materials. Sulfide stress cracking, pitting and crevice corrosion tests were performed under simulated downhole conditions, taking into account the conditions of maximum susceptibility of these materials to these forms of corrosion. Results revealed that the onshore wells environment would be too aggressive while the high strength martensitic stainless steels could accommodate the conditions in the offshore wells.