A series of experiments were conducted in autoclave to investigate corrosion properties of low Cr oil country tubular goods in CO 2 /H 2 S saturated brine solution (3 wt-%NaCl) at 90uC. Test material is 3Cr-80, which is gradually accepted in oil and gas industry, especially for downhole tubing and casing. The CO 2 partial pressure was fixed at 4?0 bar in all experiments, and the H 2 S partial pressure was varied from 0, 2, 4, 8, 20, 40 and 800 mbar to 4000 mbar (4 bar). The results show that when the pH 2 S varied at a lower range (2-40 mbar), 3Cr-80 materials' corrosion rates were restricted, and coupons' surface morphologies became glossy compared to the pure CO 2 corrosion. Under the condition of pH 2 S5800 mbar, H 2 S no longer have a retardation effect on CO 2 corrosion but acceleration. The average corrosion rate was higher than pure CO 2 corrosion. When the pH 2 S rise to 4000 mbar (equal to the CO 2 partial pressure), 3Cr corroded much more severe and serious mesa attack was observed.
This paper analyzed the corrosion environment of Missan oilfields and investigated the oilfield country tubular goods used in other similar oilfields. Summarized the effect of partial pressure ratio of H2S/CO2 and Cl-to the corrosion behavior of OCTG. This paper concluded the service condition, test results and anti-corrosion mechanism of carbon steel, low-chrome steel, modified martensitic stainless steel and nickel alloy. Finally arrived at conclusion that the nickel alloy can meet the requirement of Missan oilfields, some literature reported that the modified martensitic stainless steel can apply in H2S/CO2 environment. In the condition that be easy to replace the tubular, carbon steel and low-chrome steel tubular can meet the requirement with corrosion inhibitor.
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