Encapsulated oil absorbent polymers as lost circulation additives for oil based drilling fluids

摘要

The disclosed invention is a novel drilling fluid additive for use in reducing lost circulation in wellbores and a method for employing the invention additive for reducing such lost circulation. The invention additive is a highly oil absorbent polymer encapsulated by a reaction- preventive protective casing to prevent the polymer from expanding by absorbing oil until it is desired to breach the casing. The reaction- preventive protective casing may be a film which will dissolve after a desired time of residence in the borehole or a film or clay which can be ruptured in the formation, releasing the oil absorbent polymer to expand by absorbing oil. The substantially expanded polymer will seal off their zones and fissures, reducing lost circulation.