• Casing pipes lines the borehole. It is subject to axial tension by its dead weight, internal pressure by fluid purging, and external pressure by surrounding rock formations.
• Casing are particularly exposed to axial tension and internal pressure by the pumped oil or gas emulsion.
• Casing that is cemented in place, aids the drilling process in several ways:
1. Prevent contamination of fresh water well zones.
2. Prevent unstable upper formations from caving in and sticking the drill string or forming large caverns.
3. Provides a strong upper foundation to use high-density drilling fluid to continue drilling deeper.
4. Isolates different zones that may have different pressures or fluids – known as zonal isolation, in the drilled formations from one another.
5. Seals off high pressure zones from the surface, avoiding potential for a blowout
6. Prevents fluid loss into or contamination of production zones.
7. Provides a smooth internal bore for installing production equipment.
• Casing pipes are usually between five and ten centimeters in diameter and around 27 to 32 feet in length (Range 2). Longer lengths, up to 45 feet, exist (Range 3).