An offshore Mid-Norway oil field includes wells on sub-sea templates at a depth of 350m. The formation waters contain up to 300 mgl−1 of barium, giving a sulphate scaling potential on seawater breakthrough. Scale protection on the template and down-hole is provided by squeeze treatments. Deployment possibilities include bull-heading down the methanol injection line (a distance of 10km) and bull-heading directly to the sub-sea template from a boat. In the event of a produced gas leak into the system, the conditions dictate that a water-based squeeze inhibitor will be in the region for hydrate formation. In such an event hydrates would be formed in minutes, blocking the service line before it could be re-flooded with the thermodynamic hydrate inhibitor methanol.

Current scale inhibitors (SI) are hydrate-inhibited by formulation in MEG. This paper describes an innovative SI protected from hydrate formation by formulating with kinetic gas hydrate inhibitors (KHI).

The field scale squeeze inhibitor was modelled and shown to have the potential for hydrate formation under sub-sea conditions. The concentration of MEG required to avoid this region was also modelled as >50% based on water. This was followed by laboratory autoclave tests when gas hydrates formed as predicted by the model. Using the same SI formulated with a small addition of a KHI the hydrate induction time was extended beyond the SI residence time in the injection line. Further testing of SI efficiency demonstrated an improved efficiency over an equivalent scale inhibitor formulated in MEG.

Due to the spiralling costs of installing new oil production facilities the use of sub-sea templates is increasing. Any scale squeeze treatments must be protected against potential gas hydrate formation. This paper describes such a protection by adding a KHI to a water-based product rather than formulating in MEG thereby allowing formulation at higher SI actives, potential lower costs and a lower viscosity product at low temperature.

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