Two Case Studies of Corrosion from an Injection Water Pipeline in the North Sea

394Oil rigs and installations have a high risk of corrosion due to temperature and pressure conditions, a natural saline environment, and high CO₂ concentration. In addition, high concentrations of sulfate and organic carbon stimulate anaerobic microorganisms that may cause microbially induced corrosion. However, the type of corrosion and severity of corrosion development vary at different oilfields.

Here we present two case studies from a corroding injection water pipeline on an oil rig in the North Sea, and also the adjustments made in operational conditions that provided lower corrosion rates, lower production maintenance costs, and higher security. At the study site, Utsira formation water from the subsea aquifer was used for oil reservoir injection, due to its anaerobic qualities and low sulfate content. However, corrosion-monitoring studies revealed high corrosion rates and aggressive pitting corrosion. The problem was addressed with optimization of the mixing ratio between production water and aquifer water and changing of the carbon source in added chemicals, thereby forming a stable noncorrosive microbial community in the pipeline. Hence, the pitting corrosion in the injection pipeline decreased to low rates.

Furthermore, the effect of https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315157818/b88feab0-0f22-4134-ae27-3d98760b4b5f/content/inline-math20_1.tif"/> NO 3 − mitigation was studied by using advanced in situ flow rig systems in combination with extensive monitoring of chemical and microbial parameters in the pipeline. Experiments showed that https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315157818/b88feab0-0f22-4134-ae27-3d98760b4b5f/content/inline-math20_2.tif"/> NO 3 − mitigation caused aggressive pitting corrosion, and qPCR data confirmed changes in the microbial community such as increased abundance of nitrate reducers and sulfur reducers. We hypothesize that microbially produced nitrite and sulfur-related processes play a main role in this corrosion situation. Hence, https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315157818/b88feab0-0f22-4134-ae27-3d98760b4b5f/content/inline-math20_3.tif"/> NO 3 − can have a severe effect on corrosion development and should not be universally used for mitigation in similar systems without a thorough assessment.