DOHA, Qatar -- Sam McFarland of Shell Global Solutions discussed dealing with corrosion on the Pearl GTL project at the Offshore Middle East 2008 Exhibition and Conference in Doha, Qatar.
Pearl GTL is a fully integrated project that will take 1.6 bcf/d of unprocessed gas from Qatar's North field into onshore gas processing plants, producing 140,000 b/d of GTL products and 120,000 b/d of natural gas liquids.
There will be no processing platforms on the two platforms, and all fluids produced will be transported to shore using the main pipelines for treatment onshore.
"There will be two 30-in. pipelines, carrying 800 MMscf/d each," said McFarland.
The gas has very high corrosion rates, so continuous injection of corrosion inhibitor (CI) into the pipelines is a must. And sea bottom temperatures can be below hydrate formation temperature so it is necessary in the winter months to inject kinetic hydrate inhibitor (KHI) into the pipeline. These highly corrosive conditions, plus minimal offshore intervention and high onshore plant uptime requirements caused some challenges for the project, McFarland said.
McFarland described how Shell dealt with the challenges, how they selected which chemicals to use and why, including issues with the compatibility of the chemicals used.
"Our primary goal was to reduce corrosion to a tolerable level," he said, which they determined was 0.1 mm/year, "and it had to be effective during a full range of operational conditions."
Through extensive research and testing, Shell developed an effective combination of CI and KHI for the Pearl project—a two-year process, McFarland said. A number of design and operating guidelines have been developed to support a high availability system, but to achieve 100% CI system availability requires dedicated, well-trained operations, maintenance, and material/corrosion/integrity staff, with clear roles and responsibilities and day to day attention to details and assessment of the CI/KHI system availability, he added.