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: DD

See related terms: aggregation,  flowline,  greasing out,  HLB number,  soap,  surfactant