What is the purpose of casing in borehole drilling?

Casing in borehole drilling serves multiple essential functions, with one of the primary purposes being to keep the annular space open. When a borehole is drilled, the surrounding geological formations can be unstable and may collapse or deform, especially in softer or unconsolidated materials. Casing is inserted into the borehole to provide structural integrity, ensuring that the walls of the borehole remain stable and maintain their shape during and after the drilling process.

While preventing contamination of water, improving drilling speed, and enhancing structural stability are all important aspects in the context of borehole drilling, they are not the primary function of casing. Casing does help to isolate water-bearing zones from surrounding materials, which contributes to preventing contamination, and it can also indirectly support structural stability by maintaining the borehole shape. However, the fundamental role of casing specifically addresses the need to keep the annular space open, ensuring the drilling operation can proceed effectively and safely.