What Is Double Casing in Borehole Casing and Why Is It Important?

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Double Casing Refers To The Special Construction Of A Borehole Where A Smaller Diameter Casing (140mm) Is Inserted Into A Larger Diameter Casing (180mm). 

This Strengthens The Borehole Structure and Reduces The Risk Of Siltation.
What Is Double Casing in Borehole Casing and Why Is It Important?
What Is Double Casing in Borehole Casing and Why Is It Important?
In some Boreholes, this Double Casing is used as Protection or Intermediate Casing that is run into the Borehole to separate challenging areas or problem zones, including areas of high pressure or lost circulation. 

 The 140mm Casing is the last type of Borehole Casing string that is run into the Borehole, and therefore the smallest in diameter.

Regardless of the construction method, Borehole Casings and screens have some common requirements. 

Strength must be adequate to withstand not only the stresses of installation but also other forces which may be applied during well completion, development and use. The forces of installation which tend to pull the Borehole Casing and Screen apart must be exceeded by the tensile strength of the material.

The resistance of the Borehole Casing to collapse must be greater than the external hydrostatic forces calculated. These stresses can rupture casings and screens. Another requirement related to strength is durability. 

What Is Borehole Casing?

Borehole Casing is a large-diameter pipe that is inserted into a recently drilled section of a borehole, to protect and support the borehole stream.
  
Once a Borehole has been drilled, if it is to become a production well, the well must undergo completion. While Drilling Borehole cuts through the rock formations and allows drilling engineers to reach the reservoir below, the raw sides of the Borehole cannot support themselves. 

Similar to the bones of your spine protecting the spinal cord, the casing is tubing that is set inside the drilled Borehole to protect and support the well stream.

In addition to providing stabilization and keeping the sides of the Borehole from caving in on themselves, casing protects the Borehole from outside contaminants, as well as any freshwater reservoirs from the oil or gas that is being produced.

Also known as setting pipe, casing a Borehole involves running the PVC pipes down the inside of a recently drilled Borehole. The small space between the casing and the untreated sides of the Borehole is filled with Gravel Pack to permanently set the casing in place.

Casing A Borehole:

The casing is fabricated in sections, or joints, that are usually about 40 feet long and joined together with Solvent Cement to form longer lengths of the casing, called casing strings.

The Purpose of Casing:
  • Prevents the pollution of water from the borehole.
  • Prevents unbalanced upper formations from caving in and sticking the drill string.
  • Provides a strong upper foundation to allow the use of high-density drilling fluid to continue drilling deeper.
  • Isolates various zones, which may have different pressures or fluids, in the drilled formations from one another.
  • Seals off high-pressure zones from the surface.
  • Prevents fluid loss into or contamination of production zones.
  • Provides a smooth internal bore for installing production equipment.

The Benefits Of Borehole Casing:

PVC is used for Borehole Casing. PVC is a wholly diverse material, used for a massive range of applications that span several industries. When it comes to plumbing and waterworks it is often the preferred material, which makes for little surprise that it is an ideal solution for borehole casing pipes. 

Any effective water pump design should account for protective measures, things that limit the ravages of weathering, corrosion, and age; things that keep the pump running efficiently for longer. PVC is able to provide this kind of protection at a fraction of the cost of other materials. 

Here are some of the top benefits offered by PVC, when used for borehole casing pipes.

1. Corrosion Resistant: Borehole pumps are particularly susceptible to both rust and corrosion since they are made up of metallic parts, and then throw a little water and electricity into the mixture, and in such cases, rust should be less of a concern than galvanic corrosion, which can reduce an appliance to a husk of its structure in no time at all. PVC piping is made from a versatile material, is completely corrosive resistant, making it ideal for borehole pumps which provide the exact kind of environment where galvanic corrosion thrives.

2. Durable and Long Lasting: PVC piping ages well, which is why it is commonly found in homes and buildings all over the world. Borehole pumps operate constantly and often under gruelling circumstances that may induce weathering and wear and tear over time. PVC is remarkably resistant to these types of damage, and as such is ideal for protective borehole casing pipes.

3. Simple to Install: PVC is a fairly simple material to work with, and requires few if any, specialized tools to manipulate and fit it. This makes PVC casing fairly simple to install and maintain when the need arises.


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