Abstract: A method is provided for reducing lost circulation when aqueous, oil, or synthetic based drilling fluid is used. The method includes injecting two fluids into the well bore and lost circulation zone. The first fluid is an aqueous liquid containing at least one polymer capable of absorbing water in an alkaline environment. The aqueous liquid has a pH that inhibits at least one polymer from absorbing water. The second fluid contains a hardening composition in a base fluid having a pH sufficient to increase the pH in situ to allow at least one polymer to absorb water and expand with the absorbed water and substantially increase in size to close off the lost circulation zone and allow the hardening composition to create a plug in the well bore and set up.

Abstract: 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.