1. n. [Drilling Fluids]
Formed by dissolving silica or silicate minerals in NaOH solutions. The silicate anion, SiO4-4, is found in solutions of sodium silicate. Silicate anions form polysilicates, or colloidal silica gel. A silicate mud is a type of shale-inhibitive water base drilling fluid that contains sodium silicate or potassium silicate polymeric ions. These ions adsorb on the shale surface and form a semipermeable osmotic membrane that prevents the transport of water and ions internal to the shale structure. This physicochemical barrier helps improve wellbore stability and provides in-gauge holes through troublesome shale sections that otherwise might require a nonaqueous drilling fluid. Silicate-gel drilling muds were first used in the 1930s to control problematic shales. In the 1990s, silicate nondispersed polymer drilling fluids were reintroduced to provide a high-performance shale-inhibitive water-base fluid, as an alternative to oil-base fluids. The highly inhibitive silicate fluid not only provides wellbore stability but also improves solids control performance with minimal environmental impact.