Corrosion Inhibition of New 15 Chromium Tubulars in Acid Stimulation Fluids at High Temperatures

Abstract

Abstract Over the past several years, a substantial increase in deep water exploration and production has brought new challenges to corrosion and material technology. The production environments in deep wells normally involve high temperature, high pressure, and sweet/sour gas. These severe conditions require corrosion resistant alloy (CRA) for well completions and production. To meet industry demands, one manufacturer has recently developed a new 15 chromium (15Cr) steel tubular as a high strength tubular (125 ksi) to control CO2 corrosion. With its modified metal composition, the new 15Cr further improves the corrosion resistance of some of chemically enhanced 13Cr, and can be applicable at temperatures up to 392°F where the use of 22Cr duplex would otherwise be required. In other words, if not for this new 15Cr, they would have to use the 22Cr, which is more expensive. With the introduction of new 15Cr to oil and gas well operations, it becomes necessary to evaluate its corrosion behavior in acid stimulation fluids at high temperatures. Due to the corrosive nature of acids, understanding its corrosion behavior and optimizing effective acid corrosion inhibitors/inhibitor packages for 15Cr tubular are critical to maximize the life of tubulars and further improve overall well completion effectiveness. This paper presents results of acid corrosion tests performed on new 15Cr tubular samples at temperatures from 260 to 350°F. The acids tested included hydrochloric acid, hydrochloric-hydrofluoric acid (mud acid), acetic acid, formic acid and their combinations. Several acid corrosion inhibitors/inhibitor packages normally used for 13Cr were evaluated to determine their effectiveness on new 15Cr. Results indicated that corrosion behavior of 15Cr in acids can be completely different from that of conventional API 13Cr. It appears that the chemical compositions of 15Cr and heat treatments during the process of steel manufacturing play a significant role in corrosion behavior. Also, the data shows that some inhibitor packages typically used for 13Cr do not provide adequate corrosion protection on 15Cr materials. Furthermore, practical guidelines for the use of acid corrosion inhibitors/inhibitor packages with 15Cr CRA metallurgy are discussed.