The corrosion problem of downhole oil casing pipe in China's offshore oil and gas fields is extremely serious, which seriously affects the service life of downhole oil casing and normal production of oil and gas fields. Through cement sealing, corrosion-resistant alloy pipes, injection of corrosion inhibitors, use of anti-corrosion coating pipes, and enhanced monitoring, the oil casing can be anticorrosive and the normal production of offshore oil and gas fields can be guaranteed.
1. Cement sealing and anticorrosion technology
In the earliest period, it was analyzed that the main cause of casing damage was due to insufficient cement return, which caused the external water layer to not be completely sealed, which caused corrosive gases in the water layer to erode the casing surface and cause corrosion. Therefore, in the 1980s, a strategy of increasing the cement return height was proposed to increase the corrosion resistance of the casing. Through this technology, the degree of casing corrosion is reduced, but it does not completely prevent casing corrosion, so it does not improve the corrosion resistance of the casing from the root cause.
2. Use corrosion resistant alloy pipe
Since 2000, the anticorrosion solution for offshore oil casing has begun to seek solutions from the material to improve the anticorrosion performance of the oil casing, thereby completely solving the corrosion problem of the oil casing. In recent years, through laboratory experiments, under certain temperature and pressure conditions and corrosive gas conditions, 1Cr, 3Cr, 9Cr, 13Cr and other Cr-containing pipes have been evaluated to develop a set of anticorrosive plates suitable for offshore oil and gas field oil casing.
3. Injection of corrosion inhibitor
From the completion process, if the formation contains oily corrosive gas, chemical antiseptics will be added to the well fluid to prevent scale, wax and corrosion. Therefore, it is also a common method at home and abroad to use chemical methods to protect the oil casing. Depending on the conditions of the oil and gas field itself, intermittent or continuous injection of corrosion inhibitors can be used for anticorrosion, and the injection amount also varies according to the corrosion environment of the oil and gas field. Because the addition of corrosion inhibitors has to be continued, on the one hand, the cost is higher, and it will also affect the on-site production.
4. Use anti-corrosion coating tubeFor oil casings, anticorrosive coatings are often used at home and abroad to prevent them from infiltrating in corrosive gases. It is also an effective anticorrosion method. Some oil fields use the nitriding process for the internal and external corrosion protection of tubing, which has good abrasion resistance. However, this method of both internal and external wall corrosion will accelerate the corrosion of the inner wall of the casing to a certain extent. At the same time, the nitrided tube is relatively rough and will cause the tubing Yuzaka is more severe than other types of pipes. In addition, some oil and gas fields use epoxy powder coating, titanium nano coatings, epoxy ester phenolic coatings and other methods to prevent corrosion.
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