The article presents the results of corrosion activity determination for low-pressure associated gas and gas-lift system gas in Vietsovpetro’s oilfields, as well as practical recommendations for mitigation of corrosion by using inhibitors. The data on concentrations of carbon dioxide, hydrogen sulfide and water in gas is provided for the last five years. It is demonstrated that the 1.5-fold increase of the rate of internal corrosion of gas pipelines was caused by the increase of carbon dioxide, hydrogen sulfide and water concentration in the associated gas. The results of corrosion rates determination by three different methods: weight-loss, electrical resistance probes method, and the rates obtained by pipe wall thickness measurements are discussed and analyzed together. The gas-lift pipelines, operated at high pressure (10 MPa or more), deserve a special attention because of high partial pressures of carbon dioxide and hydrogen sulfide that facilitate the development of the corrosion processes. The results of wall thickness measuring of the cut out pipeline segment confirm the high aggressiveness of the gas-lift system gas. This aggressiveness is also expressed in localized corrosion defects such as pitting.
Inhibitor protection is one of the well-established and efficient methods for mitigating corrosion of gas-lift pipeline systems. We discuss the essential requirements for corrosion inhibitors for use in gas-lift pipeline systems. Several corrosion inhibitors for gas-lift pipelines protection are suggested following the field trials performed. The dozing regimes and inhibitor consumptions rates were determined, depending on total length of the respective pipelines. Preliminary analysis of corrosion rates data, obtained from the oil field corrosion monitoring system, demonstrates that the selected inhibitors are highly efficient and lower corrosion rates to almost 10 times.
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