Carbon Dioxide Corrosion Rule, Filtration Of Corrosion Inhibitors, And Their Corrosion Inhibition Mechanism In Certain Gas Well Of Chuanxi Gas Field

Corrosion is an important destruction factor for modern industry and life. Our country's corrosion losses account for 6 % of gross national product every year. At present, among all kinds of the methods preventing metal from corrosion, adding corrosion inhibitor is a convenient cheap applicable method, and capabilities in protecting resources and reducing material losses. Therefore, this method is widely used in many kinds of fields, such as producing and processing petrochemicals, chemical rinse, atmosphere environment, water usage in industry, instrument and meter manufacturing, etc. With the development of oil and gas field with CO₂, the accident of oil and gas field corrosion becomes more and more, so it is very important to find the suited corrosion inhibitors to control the CO₂ corrosion.The content of CO₂ in a certain gas well in Chuanxi gas field is up to 0.34% 0.60% (v/v), as a result of which, it has a severe problem of CO₂ corrosion. In order to control and resolve the CO₂ corrosion of this gas well, the ethisis mainly includes two aspects. Firstly, the CO₂ corrosion rule of this corrosion meidium is investigated. On the other hand, through several methods to test the anti-corrosion efficiency of the ten corrosion inhibitors widely used in many oil and gas field, the efficient corrosion inhibitors that can be used in the certain corrosion medium are screend out and the anti-corrosion mechanism of the effective corrosion inhibitors are investigated. The methods and conclusions of this thesis respectively as follows:1. Weightlessness experiments under normal temperature and normal pressure are used to investigate the influence of temperature and different ion with different concentration on the corrosion behavior of given corrosion medium. It is found that: (1) Temperature will increase the cathodic and anodic reaction rate. At the same time, the formation of corrosion scale become easier, which can protect the matrix metal. But when the temperature reaches 85℃, the corrosion rate increases evidently because of local corrosion. (2) Depend on the selective scope, Ca²⁺ and CO₃^2- in the liquid medium saturated with CO₂ have great effect on the corrosion rate, the next ion is Fe²⁺, other ion have little influence. It is also found that, with the increase of the concentration of Cl^-, the corrosion rate firstly increases and then decreases but the change is not obvious; and with the increase of the concentration of Fe²⁺, the corrosion rate of the medium reduce; and with the concentration of SO₄^2- and Mg²⁺, the corrosion rate increase, but Mg²⁺ has little influence; with the increase of the concentration of Ca²⁺ and CO₃^2-, the corrosion rate decreases and then increases.2. Electrochemistry experimentation equipments are used to test corrosion behavior of N80 steel in the condition of normal temperature & pressure and high temperature & pressure. It is found that, under the condition of normal temperature & pressure, with the prolong of the time N80 dipps in the corrosion medium, the corrosion potential of N80 surface removes to negative direction and the corrosion electrical current density reduces; and that under the condition of high temperature & pressure, the corrosion rate of N80 steel is evidently higher than that of normal temperature & pressure, and the electrical current is more negative.3. Classical weightlessness method, electrochemistry instruments and reluctance probe technology respectively are used to evaluate several corrosion inhibitor widely used in oil and gas well in the condition of normal temperature & pressure, in order to screen out appropriate corrosion inhibitor for practice application. It is found that, the corrosion inhibition of HGY-9, HGY-10 and BUCT-C are more perfect than the other laboratorial corrosion inhibitors under the same condition, and the increase of temperature has little influence on their corrosion inhibition, and that, the experiment results of reluctance probe technology are consistent with the results of weightlessness experiments and electrochemistry experiments, but because of its rapid corresponding time, this technology can realize on-line inspection and can be popularized in fieldwork.4. Electrochemistry instruments are used to test the inhibition of the corrosion inhibitor HGY-9 and IMC-80-N in the condition of high temperature & pressure. It is found that HGY-9 has a good perfect corrosion inhibition and its inhibition performance is much steady, and that, the corrosion inhibition mechanism of HGY-9 is"negative catalysis effect". But IMC-80-N has not a perfect anti-corrosion effect, although the ant-corrosion efficiency of the high temperature & pressure is much higher than that of the normal temperature and normal pressure.5. Weightlessness experiments under the condition of high temperature & pressure are used to test the anti-corrosion efficiency of the five corrosion inhibitors (HGY-9, BUCT-C, IMC-80-ZS, IMC-80-N and HGY-10) in high temperature & pressure. The result indicates that the anti-corrosion effects of the five corrosion inhibitors have little difference. However, comparing with the anti-corrosion efficiency of normal temperature & pressure, that of high temperature & pressure are lower and they can not control the corrosion rate of the medium to below 0.076mm/a. Therefore, the corrosion inhibitors can not be used under condition of high temperature / pressure.