The subsea flow lines of a UK North Sea oilfield were at risk of corrosion and scale. The main corrosion risk was due to the presence of carbon dioxide and localized areas of high velocity flow. In certain locations, the predicted wall shear stress could be as high as 150 Pa. In addition, the flow lines were suffering from calcium carbonate scale deposition. Due to the limitations with respect to availability of subsea chemical injection umbilicals and equipment, a combined scale / corrosion inhibitor was required to maintain the pipeline integrity and prevent scale deposition. In addition, the recommended product was required to be environmentally acceptable. This paper describes in detail the research performed to develop a new environmentally friendly, multi-functional scale / corrosion inhibitor. The efficacy of the product in preventing scale and corrosion under the system conditions was confirmed in the laboratory using several standard tests (dynamic scale loop, corrosion kettle test and rotating cylinder electrode). Furthermore, corrosion inhibition performance in preventing weldment corrosion under high shear conditions was evaluated using a corrosion flow loop.
The operators of a UK North Sea oil field required a new combined scale / corrosion inhibitor to replace the incumbent product. A new product was required as the incumbent inhibitor was not classified as being environmentally acceptable under the UK regulations. The oilfield consists of 22 oil producing wells and 9 water injection wells that are tied back to a nearby Floating Storage Production and Offloading (FPSO) vessel. The oil wells produce approximately 60,000 bbl oil/day and are connected to the FPSO via 8 flow lines and risers. The field is located in an average water depth of 1,480 ft (450 m). There was a particular concern that the weldments could be subject to preferential corrosion at these flow velocities.
