Abstract
Stainless steel alloys with 13% chromium are often used in the oil and gas industry as a well tubular material. Typical alloys are 13Cr, 13Cr4Ni1Mo and 13Cr5Ni2Mo, in strengths ranging from 80 to 125 ksi (550 to 860 MPa).This work concerns identification of the operating window of a 13Cr4Ni1Mo material, 110 ksi SMYS (758 Mpa). There is a lack of clarity on the suitability and safe operating envelope of this alloy in mildly sour gas environments. The environment limits of 13Cr4Ni1Mo material were assessed in order to evaluate future use, and to assess suitable operating limits for current applications with increasing H2S due to well souring in High Pressure/High Temperature conditions. A comprehensive test program with artificial brine showed Sulfide Stress Cracking (SSC) susceptibility is limiting the application window of the material more than Stress Corrosion Cracking (SCC). SSC was found at as low as 2.5 mbar ppH2S with 20 bar CO2, 290 g/L NaCl at 40-25°C.
Petroleum Development Oman (PDO) has around 58 wells completed with 13Cr4Ni1Mo tubing material. A number of these wells have been continuously producing in environments with H2S, CO2, and Cl- > 150,000 mg/L. Detailed surveillance and analysis of the operating data of sample wells shows that 13Cr4Ni1Mo tubing material has been continuously exposed to H2S partial pressure above the threshold defined by the test without reported failure. This paper addresses the discrepancy between laboratory test results and field experience, and defines a practical interpretation approach to ensure cost effective decisions and safe operations for both existing wells and new well designs.
