FIELD: physics.
SUBSTANCE: invention relates to compositions and methods using delayed liquefaction of fluids used in treating an underground formation. Composition containing aqueous fluid, viscoelastic surfactant - surfactant and at least one diluent compound - a hydrophobically modified alkali-swellable emulsion polymer formed from a polymerisation mixture containing approximately 10–75 wt. % of acid monomer or salt thereof, approximately 10–75 wt. % of non-ionic monomer or salt thereof and approximately 0.1–25 wt. % of components of the associative monomer or salts thereof, all based on the total weight of the monomer mixture. Method of treating an underground formation in which there is a wellbore, comprising providing said composition, introducing it into an underground formation through a wellbore, where the composition is present in the formation as a viscous fluid, and enabling the diluting reagent to act on the viscous fluid with reduced viscosity. Use in treating a subterranean formation of said copolymer as a diluent for a viscous fluid medium containing a viscoelastic surfactant to reduce viscous fluid viscosity. Invention is developed in claims of the formula.
EFFECT: technical result is the increase in the treatment efficiency.
14 cl, 7 ex, 1 tbl, 17 dwg
