Research on Stress Corrosion Sensitivity of C110 Casing in Wellbore Protection Fluid

Abstract

In the environment of HTHP and high H2S, the sour gas enters into the annulus as a result of various factors, leading to annulus pressure and inducing the risk of the stress corrosion cracking in the oil string or the upper casing. To solve the problem, the environmental fracture toughness of C110 high strength casing steel was tested in the NACE A solution and the wellbore protection fluid in simulated conditions in the CORTEST pressure testing system and homemade HTHP autoclave using NACE DCB method in this paper. Wellbore protection fluid is a corrosion inhibitor for steel in oil pipe and annulus. The results indicate that the environmental fracture toughness KISSC of C110 casing steel is 22.78 MPa•m1 / 2, showing strong environmental cracking sensitivity in the standard NACE A solution. In the wellbore protection fluid under the simulated down hole conditions, where the partial pressure of H2S is 1MPa, the partial pressure of CO2 is 0.6MPa, the total pressure is 48Mpa and the temperature is 110°C, it has good resistance to stress corrosion cracking. It can be concluded that excellent wellbore protection fluid greatly increases the resistance of the material properties to environmental cracking. Research results in the paper provide a reference to the safe operation and management to the annulus pressure well in high sour gas fields.