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Cathodic Protection against corrosion of Oil Well Casings

With the rapid development of the petroleum industry, serious corrosion of oil well casings, buried pipelines, and storage tank bottom plates in oil fields, especially oil well casings, has severely affected the production, development, management and environment of the oil field. Corrosion exists on the inner and outer walls of oil and gas well casings, of which the internal corrosion is more serious.

In addition, in the well section with large deviations, the mechanical damage of the tubing to the casing during operation accelerates the corrosion and perforation of the casing; the welding defects in the weld, the gap of the thread and other parts may easily cause differences in the electrochemical properties of the steel pipe surface. It also leads to more serious corrosion damage. Usually, the severely corroded well section is above 1000m.

To solve the corrosion problem of the inner wall of oil well casing, generally add fungicides, corrosion inhibitors, adjust PH value, airtight oxygen isolation technology in the annular space of oil wells, and select low-strength tubing and casing in sulfur-bearing oil and gas fields.

To solve the corrosion problem of the outer wall of oil well casing, cathodic protection technology should be adopted. At present, this has been recognized by people in the anti-corrosion community at home and abroad. To prevent soil corrosion of underground steel structures, cathodic protection is the most economical, reasonable and effective technical measure. Cathodic protection is a safe and mature anti-corrosion technology. It has the characteristics of strong protection ability, simple construction and low investment. This technology is more and more widely used in oil and gas, petrochemical, municipal construction and other sectors.

Cathodic protection technology can not only prevent the corrosion of newly-built oil well casings, but is also very effective for old oil well casings that have been built. It can extend the service life and reduce the number of replacements. The economic benefits are very obvious.

Anti-corrosion countermeasures of oil casing pipe:

1. First, make sure that the water quality meets the standards, and strictly monitor and manage the water quality. Implement cleaning and separate injection, strengthen the cleaning of main water pipelines, ensure that the water quality in the station and the bottom of the well meets the standard, and reduce the introduction of corrosion sources into the annular space;
2. For water injection wells that have been newly put into production, adopt annulus protection liquid mainly for sterilization, and form a system to do it regularly;
3. In view of the accelerated effect of mechanical abrasion on the corrosion of oil casing, it is recommended to add a rubber ring to the tubing coupling or add a centralizer to the serious part of the well deviation to avoid the tubing scratching the casing and the casing during the operation and water injection One side touches the casing;
4. In view of the severe bacterial corrosion under the scale and the slow growth and killing of SRB at high temperature, high temperature water or steam of 100 degrees Celsius can be injected into the annulus regularly to kill the SRB under scale;
5. It is not recommended to promote the use of cathodic protection and coated casing before the corrosion in the casing of the water injection well is effectively controlled.

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