1. n. [Drilling Fluids]

A group of compounds containing iron in +2 (ferrous) and +3 (ferric) valence states and sulfur in –2 (sulfide) valence states. Examples are ferric sulfide [Fe₂S₃], ferrous sulfide [FeS], and iron disulfide [FeS₂], which is found in the minerals marcasite and pyrite. Fe₂S₃ and FeS₂ are insoluble, but FeS dissolves in alkaline muds to form a gelatinous solid, Fe(OH)₂, and soluble S^–2 ions. FeS is the primary component in the mineral pyrrhotite, one of many possible sources of sulfides in water mud. Pyrrhotite might also coexist with BaSO₄ in some barite ores. Even in trace amounts, FeS in a barite supply could generate enough sulfides in a weighted mud system to cause stress-corrosion cracking of drillpipe.

References:

• Binder GG, Carlton LA and Garrett RL: "Evaluating Barite as a Source of Soluble Carbonate and Sulfide Contamination in Drilling Fluids," Journal of Petroleum Technology 33, no. 12 (December 1981): 2371-2376.
• Garrett RL: "Quality Requirements for Industrial Minerals Used in Drilling Fluids," Mining Engineering 39, no. 11 (November 1987): 1011-1016.

See: Garrett Gas Train,  hydrogen sulfide,  scale,  siderite,  sulfide,  sulfide scavenger