Study On Cavitation Corrosion Behavior And Protective Technology Of Acid Gas Wells

With the increasing number of the "three high" gas field, the corrosion and safety problems caused by the annulus pressure gradually attracts people’s attention. In order to ensure the safety of production, it is necessary to carry out some researches on the corrosion behavior in annulus. Appropriate protective measures must be selected to make sure the corrosion rate under a reasonable range. For this purpose, some tests about the corrosion problem are carried out in the lab.Firstly, the CS350electrochemical workstation has been adopted to study the electrochemical corrosion behavior of VM110SS in the saturated H2S/CO2solution under the different temperature and room atmosphere. Then the influence law of the temperature has been obtained. The current density of the VM110SS steel increased with the temperature in the range of10℃-90℃。The result shows that the temperature is an important factor to affect the casing corrosion.Secondly, the HPHT kettle has been chosen to study the VM110SS and T95’s corrosion behavior under the simulated condition and the SEM and EDS have been used to analyzed the corrosion product film. The degree and law of the corrosion about the oil and casing steel was obtained. At the temperature of30℃-150℃, the corrosion rate of the annulus material increased first and then decreased. When the temperature is90℃, the rate reaches the maximum which means very serious and it exceeds the control index in the oil field standards. The corrosion rate has a close relationship with the corrosion product film. Under the condition of90℃, the corrosion product film is very bad,which has the loose structure and the poor adhesion.Finally, in order to inhibit the rate of the annulus corrosion, the HTHP kettle has been used to study the VM110SS’s corrosion behavior in the different injected medium and the inhibitory effects of each medium have been evaluated. In the simulated condition, the effect of the water-based and oil-based protection fluid is good, but the effect of the N2is poor. Under the condition of90℃, the water-based protection fluid can inhibit the corrosion degree which is higher than96%. The corrosion rate of the casing steel in this condition is lower than the simulated solution. In addition, the KlC of the VM110SS steel is about68MPa·m1/2in the water-based protection fluid, which is much higher than the ISO standard value.The result of this study can provide the necessary technical support for the optimization of the annulus protection measures and the integrity management in the acidic gas field.