CARBON DIOXIDE CORROSION OF OILFIELD CASING AND TUBULAR GOODS IN MEDIA SATURATED WITH H₂S AND Cl

Carbon dioxide corrosion is one of the most common reasons for the failure of oil-production equipment. This issue is very urgent for the Russian Federation where the carbon dioxide content is high in the oilfield medium of the most production fields. The paper deals with the obtaining of information on the basic issues of development of tube steels resistant to the carbon dioxide corrosion: the type and the level of alloying of steels reducing carbon dioxide corrosion lower than 0.2 mm per year; the influence of high content of corrosive H₂S and Cl^- components in the carbon dioxide medium on the mechanism and kinetics of corrosion failure. To get this information, the authors carried out pilot tests maximally proximal to operating conditions. Oil-well tubing was tested on seven working wells with intermittent monitoring of pipe condition. The authors carried out field tests of oil-and-gas tubing on testing field of Priobskoye production field consisting of operating oil-pipeline, parallel with which a bypass line made of pipes of experimental steels was mounted. The production fields and wells where the oilfield media have high CO₂ content and the intensive carbon dioxide corrosion is manifested were used for the tests. In most cases, they are the production fields where the carbon dioxide medium is additionally saturated with the corrosive H₂S and Сl^- components. The authors divided steels under the study in two groups: steels with high chromium content (≈4.6 %) forming the passivating film when in operation and low-alloyed tube steels (Cr≤0.6 %). The tests show that: - high-chromium 15H5MFBCh steel is resistant to carbon dioxide corrosion even in carbon dioxide media with high H₂S and Cl^- content; - the high chlorine content in oilfield media intensifies corrosion failure and promotes the transition to more aggressive forms of local corrosion in low-alloyed tube steels; - according to the increase of resistance to carbon dioxide corrosion, the steels under the study can be arranged in the following sequence: 09G2Sà13HFAà08HMFAà15H5MFBCh.