In well terminology, what does the term "casing" commonly refer to?

The term "casing" in well terminology refers specifically to the tubing or pipe that is installed in a well to support the hole and prevent the collapse of the surrounding soil or rock. This casing plays a crucial role in ensuring that the groundwater extracted from the well remains free from contamination and that the structure of the well itself is stable and protected from external elements. Casing can also help maintain water pressure and facilitate the flow of water to the surface.

In the context of the other possibilities, while sections of the aquifer are important to understand for groundwater flow and extraction, they do not define casing. A method of sealing wells is typically referred to as sealing or grouting, which is a separate process that ensures that contaminants do not enter the groundwater. Similarly, tools used for drilling are distinct from casing; they are involved in the construction process but do not represent the casing itself.