Environmentally assisted cracking performance research on casing for sour gas wells

Flowage in rock salt may induce extrusion deformation on casing pipes; this hinders performance in the production process in injection wells and also challenges security in oilfields. The typical treatment for this problem is to grind or expand the deformed sections of the casing, which itself may cause additional damage (cold hardening) in the casing. Cold hardening may degrade the performance of casing materials, especially when the materials are exposed to a high-sulfur environment. Since it is common for casing pipes materials exposure in the H2S/CO2 environment like Puguang gas field, the cracking sensitivity of C110 after cold hardening is very important. To investigate the environmentally assisted cracking performance of C110, a series of tests were conducted, including the basic mechanical property test, the electrochemical corrosion test, the Double Cantilever Beam test (DCB), and the four-point bending test. The results indicate that cold hardening increases the yield strength, reduces the impact toughness, and degrades sulfur-resistance which greatly increases the potential risk to the integrity of the wellbore.