METHOD OF TREATING BOTTOM ZONE OF FORMATION Russian patent published in 2007 - IPC E21B33/138 E21B43/32 

FIELD: oil and gas production.

SUBSTANCE: whole process comprises primarily exposing well on polymer-chalk mortar, perforating bottom zone of formation under polymer-chalk mortar layer, creating acid-degradable protective shield in bottom zone by forcing polymer-chalk mortar under pressure exceeding specified cementation pressure by 10-15%. Thereafter, casing string is descended, annular space is cemented, and bottom zone of formation is re-perforated through casing string and protective layer is destroyed with acid. Polymer-chalk mortar has following composition, wt %: soda ash 1-6, carboxymethylcellulose 1-6, polyacrylamide 2-3, clay 48-52, chalk 46-50, water - the balance.

EFFECT: increased productivity of formation due to prevented negative action of drilling fluids and appearance of softened bottom zone.