What is the difference between float shoe and float collar?

Float collar and float shoe are important floating equipment in petroleum and natural gas fields. They are used to guide the casing to set in the hole and ensure the quality of cementing. They are widely used in the lower section of the well to help decrease strain on the derrick while directing packaging past edges and bog zones in the opening.

 

Float Shoe

The float shoe contains a backpressure valve that prevents fluids from entering the casing while the pipe is lowered into the hole and prevents cement from flowing back into the casing after placement while enabling circulation down through the casing. The float shoe includes a back pressure valve and serves basically the same function as the float shoe.

 

 

Float Collar

The float collar is run in a casing assembly, usually several joints above the float shoe. It provides a seat for the cement plugs to help top plugs shuts off the fluid flow and prevents over-displacement of the cement. The space between the float shoe and float collar provides a containment area to entrap the likely-contaminated fluids from the wiping action of the cementing plug, securing the contaminated fluid away from the shoe where a strong cement bond is of primary importance.

 

The float collar serves two important functions during cementing:

 

They act as a landing post for cement plugs. Typically two cement plugs, top, and bottom are fed through the casing string before and after the cement slurry. The bottom plug mates with the float collar, then a spike in pressure bursts a diaphragm in the bottom plug, and the cement slurry begins to fill in the annulus.

 

Once the cement slurry has been pumped through the wellbore, the top plug mates with the seat of the bottom plug. The surface operator has a positive indication that the slurry has been properly displaced when fluid pressure rises and pumping commences.The float collar then prevents the reverse flow of cement slurry through the casing bore.

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