Benefits of Casing while Drilling

Casing while drilling provides immediate benefits, saving both time and money by altering the steps needed for the drilling process. On top of this, the CwD system also provides a whole host of additional benefits. The benefits of casing while drilling can be summarized below;

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Save Time and Cost

As mentioned in the introduction part, Basic Knowledge of Casing while Drilling (CwD), CwD is able to save operation time by cutting down flat time and reducing operational risk. When compared to conventional drilling, CwD can provide a time saving of between up to 37.5% of time spent on a well based on historical data from a field in Oman (136107-PA SPE Journal Paper – 2012). Continue reading

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Basic Knowledge of Casing while Drilling (CwD)

Casing while drilling (CwD) has been around for many years and it is one of proven technologies that can save both time and money. CwD is a process where a well is simultaneously drilled and cased; the casing is used for the drill string, and is rotated to the drill and cemented into the well at TD. One of the main benefits of this process is that it greatly cuts down on the tripping time needed to pull out the bottom hole assembly (BHA) and run the case- if not removing this need entirely. Therefore, the flat time is reduced, and the process is made more economically viable.

Figure 1- Casing while Drilling Operation (Courtesy of Weatherford)

Figure 1- Casing while Drilling Operation (Courtesy of Weatherford)

As shown in Figure 2 below, which is an example of Casing while Drilling utilized in one of oilfields in Oman for drilling surface section; this process can save up to 37.5% of time spent on a well based on historical data.

Figure 2 – A comparison between conventional drilling and casing while drilling of one field in Oman (136107-PA SPE Journal Paper - 2012).

Figure 2 – A comparison between conventional drilling and casing while drilling of one field in Oman (SPE 136107-PA ,SPE Journal Paper – 2012).

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

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

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

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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