Abstract: The invention relates to a temperature-stable hydrogel comprising electrolytic water and a copolymer cross-linked to multivalent metal ions. The invention is characterized in that the copolymer contains at least structural units which are derived at up to 0.005-20% by weight from an ethylenically unsaturated phosphonic acid and alkali metal salts thereof and/or ammonia salts, up to 5-40% by weight from an ethylenically unsaturated sulfuric acid and alkali metal salts thereof and/or ammonia salts and up to 5-94.995% by weight from an amide of an ethylenically unsaturated carboxylic acid selected from the group of acrylamide, methacrylamide and/or C1-C4 alkyl derivatives, wherein the percentages are based on the total mass of the monomers used during copolymerization, and that the multivalent metal ions for cross-linking of the copolymers belong to the groups IIIA, IVB, VB, VIIIB and/or VIIIB of the periodic system of elements.

Abstract: A method for synthesize hydrogels, that may be used in fracturing operations, with increased viscosity from a solution containing water, a copolymer and a dissolved salt of an alkaline metal, an earth alkaline metal and/or an organic amine by addition of a zirconium compound as a crosslinker which comprises: i) providing a copolymer containing structural units of formula I, structural units of formula II, and structural units of formula Ill ii) preparing an aqueous solution by adding the copolymer prepared in step i) to a solution comprising water and the dissolved salt, iii) forming a network of a hydrogel by addition of at least one zirconium-compound to the aqueous solution prepared in step ii), and iv) selecting the amount of the dissolved salt in the hydrogel to range from 0.15 and 10 weight %.

Abstract: The invention relates to a temperature-stable hydrogel comprising electrolytic water and a copolymer cross-linked to multivalent metal ions. The invention is characterized in that the copolymer contains at least structural units which are derived at up to 0.005-20% by weight from an ethylenically unsaturated phosphonic acid and alkali metal salts thereof and/or ammonia salts, up to 5-40% by weight from an ethylenically unsaturated sulfuric acid and alkali metal salts thereof and/or ammonia salts and up to 5-94.995% by weight from an amide of an ethylenically unsaturated carboxylic acid selected from the group of acrylamide, methacrylamide and/or C1-C4 alkyl derivatives, wherein the percentages are based on the total mass of the monomers used during copolymerization, and that the multivalent metal ions for cross-linking of the copolymers belong to the groups IIIA, IVB, VB, VIIIB and/or VIIIB of the periodic system of elements.

Abstract: An electrolyte-containing aqueous polymer solution is described with a salt content of 5% to 35% by weight with respect to the total weight of the polymer solution, containing at least one dissolved synthetic copolymer which contains structural units which are derived from (i) at least one amide of an ethylenically unsaturated carbonic acid and from (ii) at least one ethylenically unsaturated sulphonic acid or their alkali metal salts and/or ammonium salts, and containing at least one non-ionic surfactant selected from the group formed by alkoxylated fatty alcohols, alkoxylated alkylphenols and/or alkoxylated fatty acids, with the proviso that the mean degree of alkoxylation of said surfactants is 8-10. The aqueous polymer solution is used for the tertiary recovery of crude petroleum and is characterized by very good filtration behaviour, in particular in the presence of saline water.