Corrosion behavior and failure mechanism of V150 drill pipe in HPHT and ultra-deep drilling process

According to the simulation corrosion test of V150 drill pipe samples with different surface conditions in the field drilling fluid, different drilling fluid types and different temperature conditions had a great influence on the corrosion resistance of drill pipe. After immersion in one particular type of drilling fluid at 150 C, scaling on the surface of the drill pipe sample caused serious pitting corrosion, and the average corrosion rate reached 0.85 mm/a. When the temperature was lowered to 120 C, the scaling phenomenon disappeared and the average corrosion rate decreased to 0.2 mm/a. The corrosion behavior of V150 drill pipe was dominated by oxygen corrosion. When there was a scale layer on the surface of the drill pipe, a macroscopic oxygen concentration cell was formed inside and outside the scale layer, which promoted the acidification and autocatalysis process under the scale. Eventually, the under-deposits corrosion would be accelerated.