Precautions for the use of oil casing ‌pipe

Importance of oil casing pipe:

Oil casing pipe plays a vital role in the oil industry ‌. First of all, oil casing provides stable structural support for oil and gas wells. During the drilling process, the well wall may collapse due to geological pressure and other reasons. The existence of oil casing can effectively prevent this from happening, ensure the stability of the wellbore, and provide a safe channel for subsequent oil and gas production ‌.

Secondly, oil casing can isolate different strata. In oil and gas wells, there may be multiple strata with different pressures and different properties. Oil casing can separate these strata to prevent fluids between strata from interfering with each other and ensure the smooth progress of oil and gas production.

In addition, oil casing helps control the flow of oil and gas. Through special devices and valves on the casing, the flow and pressure of oil and gas can be adjusted and controlled to ensure that oil and gas are transported from the bottom of the well to the ground in a safe and stable manner ‌.

Finally, oil casing can also protect wellhead equipment and ground facilities. During the oil and gas production process, wellhead equipment and ground facilities may be affected by high pressure, high temperature and corrosive fluids from the well. Oil casing can provide effective protection for these equipment and extend their service life.

The following aspects should be paid attention to when using oil casing pipe:

‌1. Water quality management‌
When using oil casing, it is necessary to ensure that the water quality meets the standards and strictly conduct water quality testing and management. Implement separate injection of cleaning and pollution, strengthen the cleaning of the main water pipeline, ensure that the water quality in the station and at the bottom of the well meets the standards, so as to reduce the introduction of corrosion sources into the annular space.

‌2. Casing operation procedures‌
When lowering the casing, it is necessary to perform large-volume well washing to ensure that the performance indicators of the drilling fluid meet the requirements of the cementing design, and the wellbore is clean and free of sand before drilling. During the drilling process, the drilling fluid should be filled in time to prevent the well wall from collapsing. The preparation of casing and tools includes checking each cover, measuring the length, cleaning and checking the threads, and arranging them on the pipe rack in order.

‌3. Stacking precautions‌
The stacking of oil casing should be flat and firm, and should not be tilted or collapsed to prevent accidents. The stacking location should be selected on a flat site, away from flammable and explosive items and fire sources. Before stacking, check whether the casing is intact, and regularly inspect, maintain and treat it with anti-corrosion to ensure the safety and service life of the casing‌.

‌4. Purchase precautions‌
When purchasing oil casing, you should try to buy it from a regular oil casing manufacturer to ensure the quality of raw materials. Check the product quality certificate and the certificate number of the production license, and pay attention to the trademark logo, factory name (or trademark) and diameter on the surface of the oil casing.

In addition, the inner and outer surfaces of the oil casing shall not have defects such as folding, hairline, delamination, cracks, rolling, and scarring. These defects should be completely removed, and the removal depth shall not exceed 12.5% of the nominal wall thickness. The casing length is not fixed, and its range is 8-13m. However, casing not shorter than 6m can be provided, and its quantity shall not exceed 20%.

Casings should be supplied with threads and couplings, or in any of the following pipe end forms: flat end, round thread without coupling or with coupling, trapezoidal thread with coupling or without coupling, direct thread, special end processing, sealing ring structure. The surface of casing and coupling threads should be smooth, and burrs, tears and other defects that are sufficient to interrupt the threads and affect the strength and tight connection are not allowed.

Anti-corrosion measures for oil casing pipe:

1. First of all, ensure that the water quality meets the standards and strictly test and manage the water quality. Implement separate injection of cleaning and pollution, strengthen the cleaning of the main water pipeline, ensure that the water quality in the station and at the bottom of the well meets the standard, and reduce the introduction of corrosion sources into the annular space;
2. For newly commissioned water injection wells, adopt annular protection fluid mainly for sterilization, and form a system to add it regularly;
3. In view of the accelerated effect of mechanical abrasion on oil casing corrosion, it is recommended to add a rubber ring to the tubing coupling or a centralizer to the part with serious well deviation to avoid the tubing scratching the casing and one side contacting the casing during the operation and water injection process;
4. In view of the serious bacterial corrosion under the scale and the slow growth and killing of SRB at high temperature, 100 degrees Celsius high-temperature water or water vapor can be regularly injected into the annulus to kill the SRB under the scale;
5. Before the corrosion in the casing of the water injection well is effectively controlled, it is not recommended to promote the use of cathodic protection and coated casing.

Classification and application of oil casing pipe:

Oil casing is finely divided into multiple steel grade categories according to different engineering requirements and bearing performance, such as J55, K55, N80, L80, C90, T95, P110, Q125, V150, etc. These steel grades represent different strength levels of casing materials. In the case of complex and changeable downhole conditions, it is particularly important to choose the right steel grade casing. For example, J55 and K55 are suitable for shallow wells, while N80 and L80 are suitable for deeper wells. In places with complex geological conditions, casing is also required to have anti-collapse and anti-corrosion properties.

Different types of casing pipe used in the oil production process:
Surface oil casing: protects the drilling well from pollution by shallow water and shallow gas layers, supports wellhead equipment and maintains the weight of other layers of casing.
Technical oil casing: separates the pressure of different layers so that the drilling fluid can circulate normally and protect the production casing, and installs anti-burst devices, anti-leakage devices and tail pipes in the drilling well.

Oil layer casing: It is used to guide oil and gas from the reservoir layer under the surface. It is used to protect drilling and stratify drilling mud. When oil casing is produced, the outer diameter is usually 114.3 mm to 508 mm.

Read more: API 5CT Steel Casing and Tubing Chart or Casing Pipe and Drill Pipe