What term describes the space around the drill string that allows drilling fluids to circulate back to the surface?

What term describes the space around the drill string that allows drilling fluids to circulate back to the surface?

• A. The borehole perimeter
• B. The annulus
• C. The casing gap
• D. The drill string clearance

Answer: (B)

The space through which drilling fluids return to surface is the annulus. This is the gap between the outside of the drill string and the borehole wall (and, when casing is set, can refer to the space between the drill string and the casing in that interval). Mud is pumped down the drill string and must flow back up this annular space to carry cuttings to surface and to help control well pressure. Other terms don’t describe this fluid pathway. The borehole perimeter is just the outer edge of the hole; a casing gap isn’t a standard term for the circulating path around the drill string; and drill string clearance isn’t used to denote the return-flow path.

The space through which drilling fluids return to surface is the annulus. This is the gap between the outside of the drill string and the borehole wall (and, when casing is set, can refer to the space between the drill string and the casing in that interval). Mud is pumped down the drill string and must flow back up this annular space to carry cuttings to surface and to help control well pressure.

Other terms don’t describe this fluid pathway. The borehole perimeter is just the outer edge of the hole; a casing gap isn’t a standard term for the circulating path around the drill string; and drill string clearance isn’t used to denote the return-flow path.