Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers


Annular Well Casings

Last updated: December 31, 2018

What Does Annular Well Casings Mean?

These are alternating horizontal or vertical tubes used when constructing oil and gas wells to form annular spaces for cementing during a drilling operation; they appear in strings.They are normally made of:

  • Steel and its alloys
  • Plastic

Annular well casings are used to form a rigid wall around a well so that it does not curve into the bore and also provides protection from the contamination of the oil and gases; they can also shield the groundwater from contamination.


Corrosionpedia Explains Annular Well Casings

When digging a well, one has to first drill a bigger hole. Annular well casings are later used to create an annular space, where it will be filled with a material that does not allow the oil and gas from returning to the bottom through the sides. Since these tubes are not to be removed, they offer support to the wall so that it does not collapse.

The alternating hole and casing makes up a gas or oil well. They are of different diameters depending on the number of phases required with the first tube being the largest. The length of these tubes depends on the well standards and regulation requirements.

The annular well casings consist of the following:

  • Conductor casing
  • Surface casing
  • Intermediate casing
  • Production casing

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