What is the definition of "casing" in drilling?

Casing refers to a series of steel pipes that are inserted into the wellbore to provide structural support and stability. This is essential for protecting the well from collapse and aiding in the control of fluids throughout the drilling and production processes. Casing serves multiple purposes, such as isolating water-bearing formations, preventing contamination of groundwater, and allowing for the safe extraction of hydrocarbons. Properly installed casing is critical for maintaining the integrity of the well and ensuring safe operations.

The other choices pertain to different concepts in drilling. Measuring well depth relates to techniques used in assessing how deep a well has been drilled, while drilling fluids serve specific functions during the drilling process, such as cooling the drill bit and removing cuttings from the wellbore. The geometric term related to well design focuses on the spatial and structural aspects of the well rather than the physical support systems employed during drilling.