Test on the corrosion behavior of X65 steel in the simulated CO₂/oil/water environment

In order to deeply understand the corrosion behavior of CO₂ in actual gathering pipelines, the corrosion environment of oilfield gathering pipeline was simulated using high temperature and high pressure dynamic corrosion reactor, and the corrosion behavior of X65 steel in CO₂/oil/water environment was investigated by means of mass loss method, scanning electron microscope, X-ray diffraction and energy spectroscopy analysis. It is shown that when the water cut of crude oil is lower (40%-50%), uniform corrosion occurs on the surface of X65 steel due to the sweating action of crude oil, but local pitting corrosion appears due to the inhomogeneous adsorption of crude oil. When the water cut is in the range of 70%-80%, the barrier effect of crude oil on the surface of X65 steel is weakened, the corrosion scales are thick and loose and partial loss of the corrosion products leads to mesa corrosion. When the water cut is up to 90%, the mesa corrosion is aggravated further, the damage area is enlarged and X65 steel is corroded seriously. The existence of crude oil can change crystal size, piling pattern, and structure and chemical composition of corrosion scale, so as to play a certain role in corrosion inhibition. With the decrease of crude oil in the corrosion environment, its corrosion inhibition effect gets weak gradually.