Discussion on corrosion factors of the hottest oil

2022-08-09
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Discussion on oil well corrosion factors

Abstract: various main factors affecting oil well corrosion are systematically analyzed and discussed, which provides an effective theoretical basis for the control of oil well corrosion. Key words: oil well; Corrosion; Factor oil production is an important part of oilfield production, and the corrosion of oil well pipe string is one of the main reasons that seriously affect the normal production of oilfield. It is of great practical significance to systematically and carefully analyze and study the main factors causing oil well corrosion. 1 Influence of dissolved gas 1.1 influence of CO2 the most typical characteristics of CO2 corrosion are local pitting corrosion, ringworm like corrosion and mesa like pitting corrosion. Among them, the perforation rate of mesa pitting corrosion is very high, usually the corrosion rate can reach 3 ~ 7 mm · A-1, and when there is no oxygen, the corrosion rate can reach 20mm · A-1. The research shows that CO2 corrosion is related to the temperature, partial pressure and flow rate in its environment, in which the partial pressure plays a decisive role. When the temperature is constant, the greater the partial pressure of CO2 gas, the faster the corrosion of materials. The skin is made by winding dry carbon fiber tape; This is because when the partial pressure of CO2 is high, the ionization of carbonic acid and the increase of h+ concentration are promoted, and the corrosion is accelerated due to the depolarization of h+. Temperature is also an important parameter of CO2 corrosion. There are great changes in the kinetics of CO2 corrosion near 60 ℃. According to the influence of temperature on corrosion characteristics, the CO2 corrosion of iron is divided into three categories: (1) temperature <60 ℃, the corrosion product film FeCO3 is soft without adhesion, and the metal surface is smooth and uniform corrosion; (2) Near 100 ℃, with high corrosion rate and serious local corrosion (deep hole), the corrosion product layer is thick and loose, forming coarse crystalline FeCO3; (3) Above 150 ℃, fine, tight and strong adhesion FeCO3 and Fe3O4 films are formed, and the corrosion rate is reduced. 1.2 influence of H2S H2S dissolved in water is highly corrosive. Carbon steel pipelines or equipment will undergo hydrogen depolarization corrosion in the medium containing H2S. Iron ions, the anode product of carbon steel, combine with sulfur ions to form ferrous sulfide. Hydrogen sulfide in the medium has a more serious form of corrosion damage, which can rupture metal materials. Such cracking can occur in copper plastic plates for doors and windows, furniture, kitchen and bathroom and other purposes under low stress conditions, Intergranular stress corrosion cracking may occur even under very low tensile stress. When the acidic solution contains H2S, there is a synergistic effect between pH value and H2S concentration, that is, the stronger the acidity of the solution, the greater the H2S concentration, and the faster the corrosion rate. At the same time, due to the adsorption and electrocatalysis of H2S, the self corrosion potential of Tubing Steel shifts negatively and the passivation potential shifts positively, which makes it difficult for Tubing Steel to passivate and maintain the passivation state, and ultimately makes tubing steel more susceptible to corrosion. For systems where H2S and CO2 coexist, protective measures are often considered from the perspective of H2S corrosion damage. According to the solubility and ionization constant of corrosion products, dunlp et al. Pointed out that when the ratio of CO2 and H2S partial pressure is less than 500, FES will still be the main component of corrosion product film, and the corrosion process is still controlled by H2S. This inference was also confirmed by the experiments of Dougherty and French. 2. Influence of pH value of medium when pH value and dissolved oxygen are very low, the corrosion of water is mainly controlled by the depolarization of hydrogen. When the pH value is low and oxygen is contained, the hydrogen depolarization and oxygen depolarization reactions are carried out simultaneously on the surface of carbon steel. At this time, the process of acid action is actually carried out on the surface of carbon steel, and the corrosion characteristics are uniform corrosion. Viden et al. Confirmed that the increase of pH value will reduce the corrosion rate, and believed that when the HCO3 ion in the solution is sufficient and fe2+ is small, when the temperature is 70 ℃ and the iron ion concentration is very low (1 ~ 2mg · L-1), add NaHCO3 solution, and with the pH value rising from 4.1 to 6.2, the corrosion rate will almost reduce to the original L/2. Due to the continuous increase of pH value, carbon steel appears passivation, and FeCO3 protective film may be formed, but the appearance of this film is easy to cause corrosion under the scale and local corrosion. At this time, the influence of pH value will be more complex. 3. The influence of salts and various ions. The dissolved salts in oil field produced water have a significant impact on the corrosion of oil wells. The corrosion caused by acidic salts (salts that produce acidic solutions after hydrolysis) is mainly hydrogen depolarization. These salts include AICl3, NiSO4, MnCl2, FeCl2, etc. The presence of ca2+ and mg2+ ions will increase the mineralization and ionic strength of the solution. Generally speaking, when other conditions are the same, these two ions will increase the severity of local corrosion. HCO3 - ion can promote corrosion at low concentration, and its mechanism is that 98.07hco3 - can be used as cathode depolarizer; When HCO3 - is in high concentration and C1 - is present, it will cause local corrosion; HCO3 - can not only convert with CO2, but also produce h+ and CO32 after dissociation. The former accelerates corrosion, and the latter scales with ca2+. Hausler et al. Believe that when the concentration of fe2+ in the solution is high, the permeability of the membrane is high, and the growth rate of the membrane is higher than the dissolution rate of the membrane, making the membrane continue to grow. Therefore, when the concentration of fe2+ in the solution is high, the corrosion rate will be significantly increased. C1 - ion in the medium will promote the local corrosion of metals or alloys such as carbon steel and stainless steel. In chloride, iron and its alloys can produce pitting corrosion. The existence of chloride ion can accelerate the corrosion of metals. When the content of C1 - is high, it will lead to the spread of general pitting corrosion in the anode area. On the other hand, due to the small radius of C1 - it is easy to penetrate the protective film, which will aggravate the corrosion and produce local corrosion. With the increase of C1 - concentration, the pitting potential shifts negatively, which means that with the increase of corrosive ion concentration, the stability of passive film on the surface of steel decreases. Therefore, C1 - is the anion that has the greatest impact on the corrosion of carbon steel. Generally speaking, the main factors affecting chloride corrosion are alloy composition, medium temperature, or directly loosening the proximity switch to avoid triggering the metal restart, adjusting the medium flow rate of the moving beam, and the type of deposited salt. The chlorination corrosion rate of carbon steel and low alloy steel is often very high, and the nickel base alloy containing A1 has good corrosion resistance under chlorination conditions; In the petroleum production system, the structure

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