Corrosion in the Oil Industry- Disk 2

For help in preparation of this article, thanks to Dylan Davies, Schlumberger Cambridge Research, Ahmad Madjidi, Schlumberger GeoQuest, Abu Dhabi, UAE; Nabil Mazzawi, Schlumberger Wireline & Testing, Tripoli, Libya; Perry Nice, Statoil, Stavanger, Norway; Barry Nicholson, Schlumberger Wireline & Testing, Jakarta, Indonesia; Daniel Roche, Elf, Bergen, Norway; Philippe Rutman and Derek Stark, Schlumberger Wireline & Testing, Montrouge, France; Dave Thompson, Schlumberger Wireline & Testing, Bergen, Norway; and Piers Temple, Joe Vinet and Mohamed Watfa, Schlumberger Wireline & Testing, Abu Dhabi, UAE. CET (Cement Evaluation Tool), CORBAN, CPET (Corrosion and Protection Evaluation Tool), FACT (Flux Array Corrosion Tool), IDCIDE, IDFILM, IDSCAV, METT (Multifrequency Electromagnetic Thickness Tool), PAL (Pipe Analysis Log), UBI (Ultrasonic Borehole Imager) and USI (UltraSonic Imager) are marks of Schlumberger. Corrosion costs US industries alone an estimated $170 billion a year. The oil industry, with its complex and demanding production techniques, and the environmental threat should components fail, takes an above average share of these costs.1 Corrosion—the deterioration of a metal or its properties—attacks every component at every stage in the life of every oil and gas field. From casing strings to production platforms, from drilling through to abandonment, corrosion is an adversary worthy of all the high technology and research we can throw at it. Oxygen, which plays such an important role in corrosion, is not normally present in producing formations. It is only at the drilling stage that oxygen-contaminated fluids are first introduced. Drilling muds, left untreated, will corrode not only well casing, but also drilling equipment, pipelines and mud handling equipment. Water and carbon dioxide—produced or injected for secondary recovery—can cause severe corrosion of completion strings. Acid—used to reduce formation damage around the well or to remove scale—readily attacks metal. Completions and surface pipelines can be eroded away by high production velocities or blasted by formation sand. Hydrogen sulfide [H2S] poses other problems (next page). Handling all these corrosion situations, with the added complications of high temperatures, pressures and stresses involved in drilling or production, requires the expertise of a corrosion engineer, an increasingly key figure in the industry. Because it is almost impossible to prevent corrosion, it is becoming more apparent that controlling the corrosion rate may be the most economical solution. Corrosion engineers are therefore increasingly involved in estimating the cost of their solutions to corrosion prevention and estimating the useful life of equipment. For example, development wells in Mobil’s Arun gas field in Indonesia have been monitored for corrosion since they were drilled in 1977. Production wells were completed using 7-in. L-80 grade carbon steel tubing—an H2S-resistant steel—allowing flow rates in excess of 50 MMscf/D [1.4 MMscm/D] at over 300°F [150°C]. High flow rates, H2S and carbon dioxide [CO2] all contributed to the corrosion of the tubing. Laboratory experiments simulated the Arun well conditions, alongside continued field monitoring. These help find the most economical solution to the corrosion problem.2 The results showed that the carbon steel tubing would have to be changed to more expensive chromium steel or to corrosion-resistant alloy (CRA).