FIELD EXPERIENCE: IDENTIFICATION OF THE POTENTIAL MECHANISM OF FLOW ASSISTED CORROSION DUE TO A LARGE VISCOSITY CONTRAST IN BIPHASIC FLOW OF HEAVY CRUDE OIL.

摘要

Unexpected very fast line piercing was discovered in an onshore field producing heavy oil with lowGas Oil Ratio (GOR) in Africa. Corrosion started seven months after the first evidence of waterproduction(29 mm/y) with the piercings affecting the lines at the 6 o’clock position. The carbon dioxide contentof the associated gas (15%) was first suspected to be the major cause of corrosion despite of theexisting mitigation program. Similar leaks continued to develop in other lines although the corrosionrates measured in the inhibited produced water with Electrical Resistance (ER) probes were low.Cut sections of the lines revealed local piercings with smooth shapes or grooves at 6 o’clock.Through continuous trial and error, it was discovered that the corrosion rate was accelerated by theunexpected high velocity of the free water as a result of the large viscosity contrast between the oiland water.This paper describes the history of the field, the corrosion damage and the subsequent correctivemeasures adopted. This hypothesis of flow assisted corrosion due to high water flow rate occurringat the bottom of crude oil transportation pipes with the absence of a gas phase is proposed.