51312-01517-Qualification of scale and corrosion inhibitor for a subsea HPHT field with a MEG-loop

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Product Number: 51312-01517-SG

ISBN: 01517 2012 CP

Author: Jan Ivar Skar

Publication Date: 2012

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Vega is a gas condensate field located in the Norwegian continental shelf with tie-back to Gjøa. Vega consists of three subsea fields connected via a 55 km carbon steel multiphase pipeline that transports the fluids to the Gjøa platform. Mono-ethylene-Glycol (MEG) is used to prevent hydrates in the pipeline. The gas/condensate and MEG/water are separated at Gjøa and the MEG is regenerated by a vacuum reclaimer and lean MEG is injected subsea. CO2 corrosion of the carbon steel pipeline will be controlled by a combination of partly pH stabilization and corrosion inhibitor. Some formation water may be produced during the lifetime of the field. To be able to continue to use partly pH stabilization if formation water is produced a scale inhibitor will be injected to control calcium carbonate scaling downstream MEG injection point on the subsea templates. Continuous scale inhibitor injection will also be used in the wells to avoid calcium carbonate scaling when formation water is produced. Qualification of corrosion and scale inhibitor to control corrosion and scaling in the pipeline and downhole scaling has been performed. Several tests have been used during the qualification e.g. corrosion tests scale tests and compatibility tests which includes effect of corrosion inhibitor on scale efficiency effect of scale inhibitor on corrosion efficiency solubility tests thermal stability tests emulsion foaming gunking and formation water compatibility test at well conditions. The results show that it is very important to do compatibility testing e.g. corrosion testing where the scale inhibitor is present and vice versa. The testing proved that it is challenging to find a combination of corrosion and scale inhibitor that gives satisfactory corrosion and scale control.