A method and drilling fluid additive composition are provided for reducing
lost circulation and seepage loss when synthetic or oil based drilling
fluid is used. The method includes injecting drilling fluid and 1 to 50
pounds per barrel of a loss control additive having a composition
comprising 20 to 80 parts by weight fibrous particles, 10 to 40 parts by
weight lignite, and 10 to 40 parts by weight phenol-formaldehyde resin.