Which of the following is NOT listed as a factor affecting hole cleaning and penetration rates in air rotary drilling?

• A. Drilling Fluid/Injection
• B. Drill Pipe Size and Depth
• C. Cutting Size and Volume
• D. Measurement of Borehole Temperature

Answer: (D)

Hole cleaning and penetration rates in air rotary drilling hinge on how effectively cuttings are transported out of the borehole. The way you flush the hole with drilling fluid or air directly controls this transport: better flushing carries cuttings upward more efficiently, allowing the bit to cut more rock without re-entrainment of debris, which speeds penetration.

Drilling fluid or injection plays a central role because the fluid or air stream provides the lifting force for the cuttings. If the flow isn’t adequate or is poorly controlled, cuttings accumulate near the bit and walls, choking the hole and slowing progress.

Drill pipe size and depth matter because the size of the drill string affects the available annular space for the flush to move through and the friction losses along the depth. A larger pipe diameter reduces the annular area for the same borehole size, which can reduce flushing efficiency and raise the effort needed to push cuttings to surface, especially deeper in the hole where friction and pressure losses accumulate. Depth also introduces more resistance to flushing and can influence the overall rate at which cuttings are carried away.

Cutting size and volume influence how easily debris can be transported. Larger or more numerous chips are harder to move in the same flushing stream, which can slow hole cleaning and reduce penetration rate if the flushing system isn’t capable of handling the increased load.

Measurement of borehole temperature is not a factor listed for hole cleaning and penetration rates. While temperature can affect fluid properties and equipment performance in other contexts, it isn’t typically cited as a direct driver of how quickly a hole is cleaned or penetrated in this setting.