Study On Corrosion Mechanism And Protective Measures Of Wellbore And Ground System In Jiyuan Oilfield

In recent years,frequent corrosion and perforation of wellbore and pipeline in Jiyuan Oilfield have seriously threatened the safe production of the oilfield,increased maintenance costs,and restricted long-term stable production and efficient development of the oilfield.Therefore,this article first conducts on-site sampling of the tubing,sucker rods,and pipelines in the wellbore and surface systems of Jiyuan Oilfield.Through analysis and research on chemical composition,produced water quality,metallographic structure,microscopic morphology,corrosion products,or scale sample composition,the causes and rules of frequent corrosion perforation in the wellbore and pipelines of Jiyuan Oilfield have been preliminarily identified.Then,field hanging ring tests were conducted on frequently broken surface pipelines in Jiyuan Oilfield,and the corrosion failure mechanism of the wellbore and surface system in Jiyuan Oilfield was further clarified based on the test results of the macro morphology,micro morphology,and product layer composition of the corrosion hanging ring.Finally,in order to solve the frequent corrosion perforation problem faced by the wellbore and pipeline in Jiyuan Oilfield,based on the above research results and understanding,a feasibility study on corrosion prevention methods such as evaluation and optimization of corrosion inhibitors,and adaptability evaluation of high-performance pipe materials was conducted.Electrochemical analytical methods were used to systematically evaluate five corrosion inhibitors in use in oil fields,such as HHS08-1#,HHS08-3#,PD43-1,RX-201,and YD-03.High temperature and high pressure corrosion simulation tests and electrochemical methods were used to comprehensively analyze four commonly used oil wells or ground transportation pipes,such as 20#,N80,L80-13Cr,and TC4.Corrosion inhibitors and corrosion resistant pipes suitable for the operating conditions of Jiyuan Oilfield were selected,providing an effective means for safe and stable production in Jiyuan Oilfield.The main reseach work is as follows:（1）The corrosion mechanism and influence law of wellbore and ground transportation system in Jiyuan Oilfield were studied.The results show that the materials of wellbore and surface pipelines basically meet the requirements of national standards,and are not the main reason for frequent corrosion and perforation of wellbore and surface systems.The content of Cl^-in each station is generally high,far exceeding the normal level,and the risk of pitting corrosion is high.At the same time,the contents of Ca²⁺and Ba²⁺are relatively high,which can easily form barium sulfate scale or calcium carbonate scale attached to the inner wall of the pipeline,resulting in pipeline blockage and corrosion under the scale.The main types of corrosion are single CO₂ and single H₂S corrosion,but there are co corrosion cases of CO₂and H₂S in individual sites.（2）Systematic evaluation and optimization of 5 corrosion inhibitors in use were conducted.In order to ensure that the selected corrosion inhibitor is suitable for the wellbore and ground transportation system of Jiyuan Oilfield and can play a good role,the p H value,compatibility,and demulsibility of five corrosion inhibitors in use were measured.And the results showed that the five corrosion inhibitors met the standard requirements.The self corrosion potential and inhibition rate of five corrosion inhibitors were tested using electrochemical analysis methods.The results showed that all of the five inhibitors had certain inhibition effects,but the inhibition effects differed significantly.Among them,two corrosion inhibitors,PD43-1 and YD-03,have significant corrosion protection effects.After filling these two inhibitors,the self corrosion potential of the blank sample increases significantly,and the self corrosion current density decreases significantly.At the same time,the optimal injection concentration of the two corrosion inhibitors was further clarified.The research results show that the PD43-1 corrosion inhibitor has the best anti-corrosion effect at a concentration of 100 ppm,with a corrosion inhibition rate of 87.47%.The YD-03 corrosion inhibitor has the best anti-corrosion effect at a concentration of 50 ppm,with a corrosion inhibition rate of 78.62%.（3）Comprehensive evaluation and optimization of four commonly used oil well or groud pipeline materials were conducted.The results of electrochemical tests on four types of pipes,including 20#,N80,L80-13Cr,and TC4,show that TC4 exhibits excellent corrosion resistance at 25℃and 75℃,with self corrosion potential and self corrosion current density of-0.224V and 0.23×10^-6A·cm^-2 respectively at 25℃,self corrosion potential and self corrosion current density are-0.163V and 0.35×10^-6 A·cm^-2 respectively at 75℃,far superior to 20#steel and N80.The results of high temperature and high pressure corrosion simulation tests also show that the corrosion rate of TC4 is the lowest in the simulated oilfield environment,with a corrosion rate of 0.0119mm/a at 30℃and 0.0076mm/a at 60℃,which is far less than the 0.076mm/a required by national standards.