Use of Oxygen Scavenger in Well Safety Valve Balancing Operations

Monoethylene glycol (MEG) is often used to reduce the differential pressure across well valves so that they can be opened without damage. This MEG ultimately commingles with production fluids and if not deoxygenated contributes to the overall content of dissolved oxygen that may be seen by a receiving production facility. Normally, the dissolved oxygen levels would be removed to insignificant levels during fluid transport. Since the corrosion reactions sequester the oxygen as the fluids are exposed to less noble materials of construction, such as carbon steel. However, in facilities that utilise corrosion resistant alloys (CRA) the residual dissolved oxygen level can be so significant that it warrants reduction using oxygen scavengers. This paper reports on corrosion studies that illustrate the consequence of dissolved oxygen levels being carried through to a MEG reclamation unit constructed of CRA, and laboratory and field validation studies on the use of a bisulfite-based scavenger for removal of oxygen in 90wt% MEG used for equalising pressure of Subsurface Safety Valves.