Basic Research on Float Collar and Float Shoe

Float collars and float shoes are critical tools in cementing operations, typically used as a matched set. The float collar and float shoe primarily serve to guide the casing string smoothly into the wellbore, adjust the buoyancy of the casing string during running, and utilize the back pressure valve to prevent cement slurry from flowing back into the casing. They also enable precise control of the cementing plug height within the casing during cementing, thereby ensuring cementing quality. The float collar additionally serves as a landing seat for the cementing plugs. The float collar and float shoe are installed on the casing string, with the float shoe positioned at the bottom of the casing string and the float collar located one to two joints above the float shoe, connected by threads.

Basic Structure

The float collar's structure is fundamentally identical to the float shoe, except its lower end features male threads for casing connection. The float shoe body is made of alloy structural steel, with the upper end connected to the casing and the lower end comprising a hemispherical cement or metal nose, which serves to guide the casing during running. A back pressure valve is installed internally to prevent cement slurry backflow and can be drilled out with a PDC bit. The upper and lower channels of the valve are open upon delivery from the factory. When the casing is initially run, there is no resistance from the well fluid to the float shoe. The pressure of the circulating mud pushes the valve head downward by a certain displacement, causing the three latches at the end of the valve stem to automatically disengage. After the pump stops, the valve is pressed tightly against the valve seat by the action of the spring, functioning as a check valve.

• Sealed internal chamber design. The internal design of the float collar and float shoe consists of a sealed cavity, which is typically installed at the bottom of the casing string. This cavity is sealed when run into the wellbore to prevent drilling fluid or other fluids from entering, thereby forming an 'air pocket' or low-density area that provides additional buoyancy to the entire casing string.
• The physical principle of buoyancy. According to Archimedes' principle, the magnitude of buoyancy depends on the weight of the displaced fluid. The sealed sections of the float collar and float shoe reduce the hydrostatic pressure that the casing string must withstand, significantly decreasing the total weight of the string in the well environment and thereby providing buoyancy assistance.
• Function of the check valve. Float collars and float shoes are typically equipped with check valves. These valves remain closed during the running-in process of the string, preventing drilling fluid from entering the cavities of the float collar and float shoe, thereby increasing the buoyancy of the casing string.

The materials for the float collar and float shoe are specified according to API 5L.

Common material types include: J55, K55, N80, L80, P110

• Butt Weld Float Shoe/Float Collar
• Stab-in Float Shoe/ Float Collar
• Non-Rotating Float Shoe / Float Collar
• Aluminum Alloy Float Shoe / Float Collar
• Float Ball Type Float Collar & Shoe
• Double Valve Float Shoe/Float Collar
• Down Jet / Up Jet Cement Float Shoe
• Differential Fill-Up Float Shoe

Butt Weld Float Shoe/Float Collar

• Features: The welded end utilizes a 30° butt weld interface and can be directly welded to the casing. The outer diameter of the butt-welded casing coupling matches that of the casing, and the upper end is beveled only, without any recess, allowing direct welding to the casing.
• Valve body and spring material: The one-way valve is made of drillable material, with the valve body constructed of phenolic resin and the spring made of tin bronze.
• Scope of application: Suitable for 12-3/4" – 30" large-diameter surface casing and shallow technical casing.

Butt Weld Float Shoe/Float Collar

• Features: In the context of float collars and float shoes, “stab-in” specifically refers to an installation method in which the connection is made via a stab-in joint to the internal casing seat, providing advantages such as cost savings, simplified operations, and enhanced sealing performance.
• Valve body and spring material: The one-way valve is made of drillable material, with the valve body constructed of phenolic resin and the spring made of tin bronze.
• Standard: Thread machining and inspection are performed in accordance with the API 5B Standard; overall performance complies with API RP 10F IIIC requirements.
• Scope of application: Applicable for single-stage cementing of large-diameter surface casing and technical casing, capable of supporting a drill string weight of 30 tons.

Non-Rotating Float Shoe / Float Collar

• Features: The internal design incorporates a non-rotating profile, which, when used with a non-rotating plug, prevents rotation during cementing plug drilling and facilitates easier removal. The non-rotating float collar and float shoe can secure both upper and lower plugs, reducing plug drilling time.
• Valve body and spring material: The one-way valve (with a non-rotating plate and rubber plug on the upper part) is made of drillable material. The main body is constructed from phenolic resin, and the spring is made of tin bronze.
• Standard: Thread machining and inspection are performed in accordance with the API 5B Standard; overall performance complies with API RP 10F IIIC requirements.
• Application scope: Primarily used to prevent casing rotation, ensure cementing quality, and maintain wellbore stability. It is especially suitable for directional wells, horizontal wells, and drilling operations in complex formations.

Aluminum Alloy Float Shoe / Float Collar

• Features: The one-way valve is made of drillable material, the main body is constructed from 6061 aluminum alloy, and the spring is made of tin bronze.
• Valve body and spring material: The one-way valve is made of drillable material, the main body is constructed from 6061 aluminum alloy, and the spring is made of tin bronze.
• Standard: Thread machining and inspection are performed in accordance with the API 5B Standard; overall performance complies with API RP 10F IIIC requirements.
• Scope of application: Suitable not only for general technical casing and production casing, but also for deep wells, ultra-deep wells, and special process wells. The one-way valve can withstand pressures up to 70 MPa.

Float Ball Type Float Collar & Shoe

• Features: It employs a float ball type check valve, which may include a back pressure valve, automatic fill valve, and drop ball. The float ball type float collar and float shoe are critical downhole tools used in oil and gas well cementing operations. Their primary function is to provide a check valve effect through an integrated float ball structure, ensuring the reliability of casing string running, cement injection, and subsequent operations.
• Scope of application: Suitable for vertical wells and low-deviation wells.

Double Valve Float Shoe/Float Collar

• Features: Both the float shoe and float collar utilize a double valve configuration.
• Scope of application: The double valve design enhances sealing and functionality, making it especially suitable for complex well conditions and demanding cementing operations.
• Valve body and spring material: The one-way valve is made of drillable material, with the valve body constructed of phenolic resin and the spring made of tin bronze.
• Standard: Thread machining and inspection are performed in accordance with the API 5B Standard; overall performance complies with API RP 10F IIIC requirements.
• Internal filling: Cement. The interior is filled with cement, utilizing high sulfide-resistant oil well cement, which provides good drillability and excellent erosion resistance.

Down Jet / Up Jet Cement Float Shoe

• Overview: Some float shoes also feature outlets other than the downward-facing central hole. They also have holes in the side that aid in removing mud from the hole near the shoe. Some of these holes direct the flow upwards, some to the side, and some downward.
• Features: In cement float shoes, 'down jet/up jet' essentially refers to the difference in cement slurry injection direction.
• Scope of application: Up jet fills from top to bottom and is suitable for conventional shallow well operations; down jet displaces from bottom to top and is suitable for complex deep well conditions.

Differential Fill-Up Float Shoe

• Features: The differential fill-up float shoe is equipped with a differential valve. Differential fill-up float collars and float shoes are oil and gas tools that enable measurement of casing fill while running downhole. They can reduce casing running time and decrease formation surge pressure.
• Working principle: The differential fill-up float collar allows the casing to be filled up to 90% during the running-in-hole process. The differential fill-up float collar and the differential fill-up float shoe can operate together; dropping a ball enables both devices to be converted into back pressure valves. A weighted ball can be dropped from the surface to convert the valve into a one-way cementing valve.