Corrosion Assessment of Different Production Casings and Material Selection in Sour Gas Wells

AbstractIn order to assess the applicability of three steel specimens (T95, 110SS-2Cr and 825 steel) in sour gas well, corrosion tests were conducted in a simulated gas field solution containing both 0.55MPa H2S and 0.75MPa CO2 at 55 °C-100 °C for 72h in an autoclave. Then the corresponding corrosion products were analyzed and compared through EDS and SEM technologies. The stress corrosion cracking (SCC) behavior of three steel specimens had been tested using four point bending (FPB) technique and constant-load test. The results showed that the 825 steel had lowest corrosion rate among all those steels. The corrosion rate of T95 steel was higher than 110SS-2Cr steel for its looser corrosion products. With the increase of temperature, T95 steel and 110SS-2Cr steel corrosion product film thickened, and the trends of crystallization and agglomeration were clear. The main components of the film were FexSy, FeCO3 and compounds containing a small amount of Cr. It could also be found that the Cr content of 110SS-2Cr steel corrosion products was higher than that of T95 steel, which may contribute to its lower corrosion rate. According to the FPB results, all of those three steels did not get broken under 85% stress state in the simulated field condition. The constant load tests also showed that under 72% stress state, the T95 steel and 110SS-2Cr steel were not broken, indicating a good resistance to environmental cracking with low stress corrosion sensitivity. As a result, the 825 steel could be used below the packer of production casing; the 110SS-2Cr steel is appropriate to be used in the middle of production casing; the T95 steel is suitable for the wellhead of production casing.