1. n. [Drilling Fluids]

An asphaltic mud additive that has been reacted with sulfite to add anionic sulfonate groups to the complex molecular structure. Sulfonate groups make an additive water dispersible, depending on the extent of sulfonation. Such an additive is used to stabilize wellbores and as a filter-cake additive for water- and oil-base muds.

See: asphaltic mud additive,  filtercake,  oil-base mud,  polar,  water-based drilling fluid