Shell Global Solutions
A new chemical has been developed by Shell Global Solutions that prevents hydrate blockages in subsea pipelines is expected to generate multimillion-dollar savings in the North Sea. The technology has been licensed to Baker-Petrolite, a leading supplier of oilfield chemicals, and AKZO Nobel, specialist chemical manufacturer.
The chemical will be applied in Shell UK Exploration & Production's (Shell Expro) 23-km Barque-to-Clipper pipeline in the Sole Pit area of the North Sea. This will enable the Bacton gas processing terminal in East Anglia, UK, to raise throughput without the need for extra, costly and space-consuming, onshore or offshore plants for the regeneration of the glycol that is used to prevent hydrate formation.
Hydrate crystals readily form when natural gas and water mixtures are transported under high pressure and at low temperature. Typically, they contain 90w% water and 10w% gas molecules. During formation, hydrate crystals behave like wet snow crystals in that they tend to form large slushy accumulations. In the worst conditions, these accumulations (called hydrate plugs) can halt pipeline flows completely.
Hydrate plug formation stops gas production somewhere in the world almost every day and it is not unknown for these shutdowns to last weeks. The traditional method for removing such plugs is to carefully reduce the pressure until the hydrates melt. Even at low pressure, melting of the hydrates can take a very long time and can cost millions of cubic metres of lost gas production.
In many fields, hydrate plug formation is prevented through the addition of anti-freezes (generally glycol or methanol) to depress the temperature of hydrate formation. But, in order to be effective, glycol must be added at rates of up to 100% of the weight of water. Once ashore, the expensive glycol has to be recovered from the production stream for reuse.
The Shell Global Solutions hydrate inhibitor takes a new approach. It does not prevent the formation of hydrate crystals but does stop them from combining to form plugs, according to Ulfert Klomp, Shell Global Solutions' hydrate support and research. "Essentially, the new anti-agglomerant inhibitor is a ‘one-use' chemical that (as has been demonstrated during field trials) can be effective at dosage rates of less than 1%," he explains. "This means far lower investment costs for equipment."
Use of the new anti-agglomerant in the Barque–Clipper line will enable Shell Expro to handle increased gas volumes without additional glycol injection equipment being installed offshore, or extra glycol recovery units onshore at the terminal. A complex and maintenance- intensive process is currently used to separate large quantities of salt from the regenerated glycol. Additional glycol desalination facilities would be required to handle the increased salt production. As a result of using the new inhibitor, additional desalination facilities will not be needed at Bacton. Although the inhibitor-treated flow will mix with existing glycol-treated flows from other fields en route to Bacton, the two can be handled together without any difficulty.
However, according to Klomp, the main benefit will be in application of the inhibitor in new fields. This will save investment in the millions of pounds worth of equipment that is currently used to store, handle and recover vast amounts of antifreeze.
Shell Global Solutions is a network of technology companies of the Royal Dutch/Shell Group with an extensive network of offices around the world all linked to its centers of excellence in Europe, the USA, and the Far East, and serving a wide range of industries, including: exploration & production, gas & LNG processing and storage, refining, and chemical production.