US Patent 7226895 Drilling fluid systems for reducing circulation losses

A circulation loss combination for water-based drilling fluid system(s) comprising: a first amount of alkali metal silicate; a second amount of water insoluble particulate; and, a quantity of water soluble activating agent effective to reduce the pH of the water-based drilling fluid system to a value sufficiently low to form an effective circulation loss structure at a desired period of time after addition to the water-based drilling fluid system.