To control the casing's severe CO2 inner corrosion and minimize damage to oil wells drilled into the Yan'an formation of Jurassic reservoirs; internal plastic coating was applied to the portion of the casing below the dynamic liquid level (nearly 700 m) for each of the more than 4000 wells drilled over the last 10 years. Considering the cost factor, it was not economic for the whole wellbore to have internal coating, so only the section with serious internal corrosion was internally coated with a modified epoxy-phenolic.
This kind of modified epoxy-phenolic coating has excellent mechanical and anti-corrosion performance. But it’s difficult to analyze the long term aging or local mechanical damage of downhole inner coating. New approaches by electrode logging tools have been studied for monitoring the inner coating.