The space around a pipe in a wellbore, the outer wall of which may be the wall of either the borehole or the casing, is the __________.

Correct Answer: Option B — annulus

The annulus is the space between the drill string and the borehole wall or casing. Maintaining proper annular pressure and fluid circulation is essential for well control, as it provides the path for drilling mud to return to the surface, carrying cuttings and balancing formation pressures during drilling operations.