Cementing is the process of mixing of cement slurry. Primary cementing is the process of placing a cement slurry around a casing.
The main purpose of primary cementing is to form a continuous and competent cement sheath within the well bore annulus. So that it control and prevent fluid migration between permeable zones.
Float equipment is the equipment that is used generally in the bottom section of the well.
Float equipment check valve preventing backflow of cement into the casing.
Once the casing is in place the separation of two hydrostatic columns of fluid and maintenance of differential pressure is achieved using float equipment while sustaining the goal of preventing backflow.
Floating Equipment is used to help in ways:
It reduces strain on the derrick during guided casing, past ledges and slough zones in the hole.
It provides a landing point from the bottom to the top cementing plugs. A cementing plug is a rubber plug which separates cement slurry from fluid.
A bottom plug is placed to minimize contamination of fluids inside the casing.
A valve, called diaphragm, in the plug body opens to allow the cement slurry to move after the plug reach the landing point.
Due to the increase in pump pressure, solid body top plug, provides fair indication contacting both landing point and bottom plug.
When the top plug has been bumped, a back pressure valve is there for not allowing cement from flowing back into the inner diameter of the casing.
Some basic floating equipment are float collar, guide shoe or float shoe. Their details are drilled below.
On the first joint of casing, the guide shoe runs into the hole to prevent casing from annular irregularities.
The guide shoes consists of side ports and an open end which helps in fluid circulation for mud conditioning, hole cleaning, and cement placement.
Floating shoe has a back-pressure valve, used to prevent fluids from entering the casing. Meanwhile, the pipe is lowered into the hole to check cement flowing back into the casing.
This permit circulation down through the casing. Float collars provide a place for the cement plugs. It may be placed one to three joints above the float shoes.
The top plug pumped back while the bottom plug pumped front of the full volume of cement slurry. Top plug once seated, cut off the fluid flow to prevent from over-displacement of the cement. There is a little space between Float collar and float shoe.
This space provides a restricted area of the top cementing plug. It secure the contaminated fluid away from the shoe because its primary importance is of a strong cement bond.
Floating collars performs the same function as the float shoe here through it’s back-pressure valve.
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