Stainless steel alloys with 13 % Chromium are used in the oil and gas industry as wells tubular material. Typical alloys are 13Cr 13Cr4Ni1Mo and 13Cr5Ni2Mo in strength ranging from 80 to 125 ksi (550 to 860 Mpa). This work concerns identification of the operating window of a 13Cr4Ni1Mo alloy 110 ksi SMYS (758 Mpa). There is unclarity on the suitability and safe operating envelope of this alloy in mildly sour gas environments. The H2S limits of 13Cr4Ni1Mo are assessed in order to evaluate future use and to assess suitable operating limits for current applications with increasing H2S due to well souring. A comprehensive test program with artificial brine showed susceptibility of SSC is limiting the application window of the material more than SCC and pitting. SCC was found at as low as 2.5 mbar ppH2S with 20 bar CO2 290 g/L NaCL at 25°C. However Petroleum development of Oman has around 300 wells completed with SM13CrM110 (0.5% Mo) tubing material. A number of these wells are starting to produce in environments with H2S CO2 and CL > 150000 ppm. Detailed analysis of the operating data of a cluster with 20 wells shows SM13CrM110 (0.5% Mo) tubing exposed to H2S partial pressure above the threshold defined by the test. This paper addresses the discrepancy between laboratory test and field experience and define a practical approach to ensure safe operation of existing wells and for new wells design.Stainless steel alloys with 13 % Chromium are used in the oil and gas industry as wells tubular material. Typical alloys are 13Cr 13Cr4Ni1Mo and 13Cr5Ni2Mo in strength ranging from 80 to 125 ksi (550 to 860 Mpa). This work concerns identification of the operating window of a 13Cr4Ni1Mo alloy 110 ksi SMYS (758 Mpa). There is unclarity on the suitability and safe operating envelope of this alloy in mildly sour gas environments. The H2S limits of 13Cr4Ni1Mo are assessed in order to evaluate future use and to assess suitable operating limits for current applications with increasing H2S due to well souring. A comprehensive test program with artificial brine showed susceptibility of SSC is limiting the application window of the material more than SCC and pitting. SCC was found at as low as 2.5 mbar ppH2S with 20 bar CO2 290 g/L NaCL at 25°C. However Petroleum development of Oman has around 300 wells completed with SM13CrM110 (0.5% Mo) tubing material. A number of these wells are starting to produce in environments with H2S CO2 and CL > 150000 ppm. Detailed analysis of the operating data of a cluster with 20 wells shows SM13CrM110 (0.5% Mo) tubing exposed to H2S partial pressure above the threshold defined by the test. This paper addresses the discrepancy between laboratory test and field experience and define a practical approach to ensure safe operation of existing wells and for new wells design.

Key words: 13Cr4Ni1Mo steel, wells tubular. sour gas. production tubing