Oil casing is a steel pipe used to support the walls of oil and gas wells to ensure the normal operation of the entire oil well after the drilling process is carried out and the well is completed. Each well requires several layers of casing according to different drilling depths and geological conditions. Cement is used for cementing after the casing is run down. Unlike tubing and drill pipe, it cannot be reused and is a disposable material. Therefore, casing consumption accounts for more than 70% of all oil well pipes.
With the rapid development of the petroleum industry, the severe corrosion of buried pipelines, oil well casings, and storage tank bottom plates in oil fields, especially oil well casings, has brought severe effects on the production, development, and environment of the oil field. Corrosion exists on the inner and outer walls of oil and gas well casings, and the internal corrosion is relatively severe. So how to protect the cathode and anode of tubing and casing? Let's briefly understand:
1. To deal with the corrosion problem of the inner wall of the oil well casing, generally add fungicides, corrosion inhibitors, adjust the pH value, airtight oxygen barrier skills in the annular space of the oil well, and select low-strength tubing and casing in sulfur-containing oil and gas fields.
2. To deal with the corrosion problem of the outer wall of oil well casing, the cathode maintenance skill is generally adopted. Now, this has been recognized by the anti-corrosion community at home and abroad. To avoid soil corrosion of underground steel structures, cathode maintenance is the most economical, reasonable and useful maintenance measure. Cathode maintenance is a safe and experienced anti-corrosion skill. It has the characteristics of strong maintenance ability, simple construction and low investment. This skill is used more and more widely in the petrochemical and oil and gas sectors.
Cathode maintenance skills can not only avoid corrosion of newly-built oil well casings, but are also very useful for old oil well casings that have been built. It can extend the service life and reduce the number of replacements, and the economic benefits are very significant.
Precautions for anti-corrosion countermeasures of oil casing:
1. First of all, ensure 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 reaches 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 scratches 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.