Important Casing Accessories Fitted to the Casing String to Improve Cement Quality

casing_hardware

A number of components are fitted to the casing string to enable it to be cemented in place. In order to successfully cement each casing string, casing accessories should be installed and the necessary components are listed below;

Float Shoe

A float shoe is a short and rounded shape component with non-return value inside which is installed at the end of the casing. The advantages of a float shoe are as follows;

  • Prevent mud flowing back while running casing and prevent cement from outside U-tubing back into casing due to unbalanced conditions while performing cementing operation.
  • Help running casing to the well. The round shape of a float shoe prevents a casing string from hanging up and guiding a string into a wellbore. Some float shoes are made of high strength drillable material and can be used to reciprocate and rotate to pass any obstructions in a wellbore.
Float Shoe

Float Shoe

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Tubing Length Change due to Buckling

tubing-lenght-change-due-to-buckling

When tubing is freely suspended, it can be buckled by an upward force applied at the bottom of tubing. A section of tubing exposed to compression force will have a chance of being buckled. However, a part which is under tension will not face a buckle issue.

The neutral point is the boundary below which buckling can possibly be occurred and above which buckling will not happen.

 

Figure 1 - Wellbore Diagram with Tubing Buckling Due to Compression Force

Figure 1 – Wellbore Diagram with Tubing Buckling Due to Compression Force

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Tubing Length Change due to Thermal Load

tubing-lenght-change-due-to-thermal-load-cover

Difference in temperature causes steel to contract or expand. If tubing is free to move, length of the tubing will be either longer or shorter due to thermal expansion. On the other hand, if the tubing is not free to move, there will be a change in axial force due to the temperature effect.

Figure 1 illustrates an increase in length due to heat and Figure 2 demonstrates a decrease in length because of cooling.

Figure 1 – Tubing Lengthen by Temperature Increase

Figure 1 – Tubing Lengthen by Temperature Increase

Figure 2 - Tubing Shorten by Temperature Decrease

Figure 2 – Tubing Shorten by Temperature Decrease

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Piston Force on Closed-Ended Tubular (Plugged Tubular)

Piston-Force-on-Closed-Ended-Tubular

According to the previous post (piston force on open-ended tubular), applied surface pressure will reduce tensile force on surface. In this article, this is an analysis on the piston force on a plugged tubular string and the details are shown below;

Tubing Detail

  • 5” Tubing
  • ID of tubing = 3.696”
  • Packer seal bore OD = 5.25”
  • Weight per length = 17.7 lb/ft
  • Total Length = 10,000 ft
  • Plugged tubing depth = 10,000 ft
  • Fluid density = 10 ppg
  • Tubing is free to move in the packer
  • Applied surface pressure = 5,000 psi

Figure 1 shows the wellbore schematic. Applied pressure (5,000 psi) will cause a piston effect to push the tubing. Therefore, at the bottom of tubing buoyancy and piston force will act in an upwards direction (compression).

Figure 1 - Wellbore Schematic

Figure 1 – Wellbore Schematic

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Piston Force on Open-Ended Tubular

Piston-Force-on-Open-Ended-Tubular

Piston force is a load caused directly by changes in pressure acting on the exposed cross sectional area of pipe. This results in changing in length of tubular and force acting against tubular. In this article, it generally demonstrates force distribution based on a simple tubular diagram.

Piston-Force-on-Open-Ended-Tubular

Tubing Detail

  • 5” Tubing
  • ID of tubing = 3.696”
  • Weight per length = 17.7 lb/ft
  • Total Length = 10,000 ft
  • Fluid density = 10 ppg
  • Tubing is free to move in the packer
  • Applied surface pressure = 5,000 psi

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