What is the space between the well casing and drill stem called?

• A. The bore gap
• B. The annulus
• C. The drill string clearance
• D. The casing space

Answer: (B)

An annulus is the space between two concentric cylindrical surfaces. In oilfield terminology, it describes the gap between the outside of the drill stem (drill pipe) and the surrounding borehole wall or casing. This annular space is where drilling mud flows for circulation and where cementing operations occur around the casing. So the space between the well casing and the drill stem is an annulus. Other terms like bore gap, drill string clearance, or casing space aren’t the standard terminology for this gap.