What could cause bridging when cleaning the finishing mud rotary rock hole prior to development?

• A. Too much fluid flow removing solids too quickly.
• B. Drill string rotation out of phase.
• C. Formation pressure too low.
• D. Excessive accumulation of cuttings or debris, insufficient circulation, or the use of inappropriate drilling fluids that do not adequately suspend or transport the solids, leading to blockages in the borehole.

Answer: (D)

Bridging happens when solids from the cuttings aren’t kept in suspension and transported out of the borehole, so they accumulate until they form a plug or bridge across the borehole. In finishing mud cleaning before development, the fluid must carry solids upward; if circulation is insufficient or the fluids don’t suspend the solids well, the solids settle and stack, creating blockages.

The described cause points to this exact scenario: an excessive buildup of cuttings or debris combined with inadequate circulation or using drilling fluids that don’t properly suspend or transport the solids. That combination leads to blockages in the borehole, i.e., bridging.

The other possibilities don’t fit as well because they don’t directly describe the solids handling failure that creates a bridge. Too much fluid flow would tend to flush solids away rather than form a bridge; rotation of the drill string out of phase is a mechanical issue not specifically about solids suspension; formation pressure being too low affects pressures, not the suspension/transport of solids to prevent bridging.