Casing is an important part of a drilling operation, stabilizing the hole, isolating the formation, and preventing well collapse. Different types of casing are suitable for different drilling stages. Understanding the functions and correct installation of each type of casing helps to ensure the safety and stability of the well.

1. Type of casing

Pipe: In the outermost layer of the well, the main function is to strengthen the well wall, avoid the surface gravel layer and unbonded rock falling into the well, and protect the surface formation.

Structural pipe: Between the conduit and the surface pipe, the purpose of this casing is to address recurrent leakage or collapse problems and to minimize kicks of shallow gas.

Surface casing: Used to isolate the fresh water layer to prevent collapse and contamination of the groundwater supply during drilling, to isolate weak zones that cannot withstand the backpressure required to control the wellhead, to provide conditions for installing a blowout preventer, and to support the weight of all layers of casing that are smaller than the surface casing.

Intermediate casing: Used to isolate unstable formations, such as high-pressure, collapse-prone or saltwater zones, to prevent the formation from affecting the drilling. In some special cases, intermediate casing is also used to isolate salt or expansive and collapsible shale rocks.

Liner: The liner has the same function as the intermediate casing. As a part of the production casing, it is usually suspended in the intermediate casing or production casing to play a supporting role and save costs.

Production casing: Also known as reservoir casing. Used to protect the production zone and ensure safe recovery from the oil and gas zone.

2. Casing installation

Hole cleaning
Importance: Before installing casing, ensure that the hole is clean and unblocked to avoid hole collapse or debris blockage, which may affect the smooth running of casing.
Action: Clean the hole with drilling fluid to ensure there are no large cuttings or formation debris.

Correct casing size selection
Importance: Ensure that the casing size and design is appropriate for the specific conditions of the hole, including formation pressure, well depth, and hole diameter.
Measures: Calculate the appropriate casing size and wall thickness according to the design to avoid blowout or collapse due to insufficient casing pressure.
Speed control when running casing
Importance: Running the casing too quickly can lead to downhole accidents, such as wall breakage or sudden pressure changes. Too slow will affect the efficiency of work.
Measures: To maintain a uniform running speed, especially when passing through complex formations, it is necessary to control the pipe rhythm to avoid excessive wall pressure changes.

Connection and sealing of casing
Importance: Casing connections must be strong and leak-free, or they may result in a loss or blowout.
Measures: Use high quality threaded connections and apply leak-proof sealant. Check the integrity of the joint regularly to ensure that there is no loosening or wear.

cementing
Importance: Once the casing is in the hole, it needs to be secured in the hole through cementing operations to prevent formation fluid leakage or casing displacement.
Action: Use suitable cement slurry to fill the annular space between casing and wellbore wall to ensure cementing quality and avoid cementing defects.

Pressure test
Importance: After installation, the casing should be pressure tested to ensure that it can withstand the designed working pressure and avoid the situation of insufficient pressure during mining.
Measures: Gradually increase the pressure in the well, check the casing for leakage or deformation, and confirm that the casing strength meets the operation requirements.

In summary:

Casing selection and installation is the key link in drilling operation, and different types of casing have their own application scenarios. During installation, attention should be paid to the steps such as hole cleaning, casing sizing, connection sealing and cementing to ensure safe and efficient drilling.