1. n. [Drilling Fluids]

A surfactant-type mud additive intended to prevent formation shales and clays from sticking to the drilling assembly and also to prevent gumbo shale from agglomerating and plugging the annulus and flowlines. Some DDs are claimed to be mud lubricants that lessen the torque and drag of the drillstring as it is rotated and moved up and down in the hole.

Alternate Form: drilling detergent

2. n. [Drilling]

An individual trained in the science and art of intentionally drilling a well along a predetermined path in three-dimensional space, usually involving deviating the well from vertical and directing it in a specific compass direction or heading. The directional driller considers such parameters as rotary speed, weight on bit, control drilling and when to stop drilling and take surveys of the wellpath, and works closely with the toolpusher.

Alternate Form: directional driller