Corrosion Mechanism Of HP-13Cr Stainless Steel Tubing In Western Oilfield Environment

With the rapid development of China's economy and the increasing emphasis on environmental protection,the demand for natural gas will continue to increase in the future.However,the extremely harsh mining environment in western China's oil fields also poses serious challenges to the service life and safe operation of the tubing.HP-13Cr stainless steel is the main material of oil and gas fields in western China,and its corrosion resistance has received more and more attention,but its research is still insufficient.In this paper,the effects of temperature,pressure and acidification process on the corrosion behavior of HP-13Cr stainless steel were studied by high temperature and high pressure electrochemical measurement,immersion experiment and microscopic characterization;Combined with the CFD numerical simulation results of the underground working conditions,the corrosion rate of HP-13Cr stainless steel under extremely harsh conditions that cannot be achieved by the laboratory is predicted.The main conclusions are as follows:(1)From the wellhead(90?2.9MPa)to 5000m downhole working condition(180?6MPa),the corrosion form of HP-13Cr stainless steel is pitting corrosion,and the pitting pits increase with the depth of the hole(temperature and pressure increase)The corrosion products increased from Fe CO₃ and Cr₂O₃ with better corrosion resistance to Fe O and Cr(OH)₃ with less corrosion resistance.With the increase of temperature and pressure,the thickness of the passivation film increases,the corrosion product film exhibits p-type semiconductor characteristics,the acceptor density increases,the stability of the passivation film decreases,and the corrosion resistance of HP-13Cr stainless steel decreases.(2)During the acidification process,HP-13Cr stainless steel suffered serious and comprehensive corrosion.As the temperature and pressure increase,the corrosion current density increases.Corrosion products under various conditions are mainly composed of Fe OOH and Ni(OH)₂,and are enriched with a large amount of Cr₂O₃ and Mo O₂;Ca(OH)₃ begins to form under the condition of 1,000 meters downhole(110?3.5MPa)and the content The increase in the depth of the underground continues to increase.The corrosion rate of HP-13Cr stainless steel increases linearly with the depth downhole.The corrosion current density of the acidified samples increased by 2.38 times on average compared with the samples without acidification.(3)Through CFD numerical simulation calculation,the temperature distribution and velocity distribution of natural gas wells with different gas content are obtained.Under the same gas content condition,the temperature decay is more severe closer to the wellhead;at the same depth position,the temperature decay is more severe as the gas content is higher;the medium in the pipe is continuously accelerated during the upward transportation,and the gas content The higher the speed,the more the speed increases.The existing corrosion rate prediction model was revised,and the corrosion rate of natural gas wells with different gas rates was predicted based on the numerical simulation calculation results.The results show that under the same gas content,the greater the depth of the downhole,the greater the annual corrosion depth of the gas well wall;the gas wells with different gas content are at the same depth.When the gas content is smaller,the well wall The more severe the corrosion.