The produced multi-phase fluid of the Spy Island wells in the Alaskan North Slope field of Nikaitchuq is conveyed via a 5.7 km pipe-in-pipe 14x18" pipeline to the onshore plant "Oliktok Production Pad" for treatment and ship out of crude oil to the national pipeline network.
After carrying out intelligent pig runs, corrosion features had been identified along the bottom third of the pipeline and indicated pitting depths up to ~80% of the nominal design wall thickness. Immediate mitigation actions, including enhanced cleaning pigs & biocide treatments, were implemented. A further follow-up intelligent pig run had been conducted indicating that pitting depths had progressed to a maximum depth of 92% of the nominal design wall thickness. The root cause of the corrosion was determined to be Microbiologically Induced Corrosion (MIC).
In order to preserve the secondary containment of the pipeline and with the target to carry out a fast track repair activity, different options were evaluated. Between the options it had been selected to proceed with the insertion of a new 10.75" line-pipe into the existing pipe-in-pipe 14x18" pipeline; the first experience in Oil and Gas sector, considering the length of the pipeline, the complex operating conditions and the execution in harsh environment caused by the Alaskan winter season.
The paper will cover the assessment of the corrosion problem and the evaluation of the different repair options, the selection of the repair option and the relevant detailed engineering to conclude with the execution phase with a focus on the construction and installation activities.
The Nikaitchuq field consists of a drill site Spy Island Drillsite (SID), located approximately 5.7 km (4 miles) offshore from Oliktok Point, and an onshore facility Oliktok Production Pad (OPP) located on the north slope of Alaska. In addition to processing the production from Oliktok Point, OPP also processes the 3-phase production from SID which is transported via the existing buried pipeline bundle.
