How does a float collar work?

A float collar is a cementing component installed near the bottom of the casing string. Their primary functions are to serve as a landing spot for the cement plug during primary well cementing and to prevent fluid flow-back during well cementing and case running operations.

 

1. Operation

Float collars are a short section of the casing with tool joints on both ends. They incorporate an integral backpressure valve which is most often a spring-loaded ball valve or flapper-type. The valve prevents the flow back of cement slurry during cementing and also helps "float" the casing string during case running operations. They mate with the casing string one to three sections above the guide shoe, a device that directs the casing string through the wellbore on the descent.

 

2. Case Running

During case running operations, the casing string is inserted into an open wellbore. The derrick supports the weight of the top portion of the casing string. As additional sections of casing are connected and fed into the wellbore, the backpressure valve in the float collar displaces reservoir fluids that would otherwise flow up through the bore of the casing centralizer. This helps control the rate of descent and supports a portion of the load.

 

3. Cementing

Cementing operations seal and secure the top portion of the casing string, referred to as the conductor casing, to an open wellbore. A cementing unit incorporating large slurry pumps displaces cement slurry down through the bore of the casing string and back up through the annulus (the void between the casing centralizer and the open wellbore).

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