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Abstract

A method and a treating mixture for controlling lost circulation of fluid from a wellbore to a formation wherein the treating mixture is flowed down the wellbore to block flow into the formation. The mixture is comprised of a non-aqueous carrier liquid (e.g. diesel) and particles of compressed sponge) which expands upon contact with an aqueous liquid in the formation. The mixture may also contain a second lost circulation material (e.g. unhydrolyzed polyacrylamide) which hydrates to bridge and plug any voids or spaces left between the expanded sponge particles. When used to control lost of an aqueous liquid, e.g. water-based mud, a non-aqueous liquid (e.g. diesel) is used ahead and behind the treating mixture to separate it from aqueous liquids. When used to control loss of an oil-based liquid, water is pumped behind the treating mixture to provide the aqueous liquid necessary for expanding the sponge particles once they are in place.

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First Claim