Anionic thermoviscosifying water-soluble polymers, preparation method and application thereof

1. A method for preparing an anionic thermoviscosifying water-soluble polymer, comprising the following steps:

(1) preparing an aqueous phase with an acrylamide monomer, an anionic monomer, a temperature-sensitive polyether, an inorganic salt, and deionized water, with pH values in between 6.5 and 7.5;

preparing an oil phase by adding an emulsifier to an oil; wherein a percentage of the aqueous phase ranges from 10% to 90% based on a total mass of both the aqueous phase and the oil phase;

obtaining an emulsion by uniformly mixing the aqueous phase and the oil phase under stirring or gradually adding the aqueous phase to the oil phase to be emulsified;

adding an initiator in the emulsion under an inert gas atmosphere to form an emulsion system;

increasing a temperature of the emulsion system to 40-60° C. to initiate a polymerization, or performing a photo-initiated polymerization on the emulsion by heating the emulsion to 40-60° C. without adding the initiator; and

after completing the polymerization or the photo-initiated polymerization, keeping the temperature for 2-6 hours to obtain an inverse emulsion of the anionic thermoviscosifying water-soluble polymer;

wherein, mass percentages of various components in the aqueous phase are as follows: 20%-50% of the acrylamide monomer, 5%-15% of the anionic monomer, 1%-20% of the temperature-sensitive polyether, and 1%-10% of the inorganic salt; in the oil phase, a mass percentage of the emulsifier is 1%-20%; and

the emulsifier is a triblock polymeric emulsifier of long-chain fatty acid-polyoxyethylene-long-chain fatty acid, the initiator is at least one selected from the group consisting of a hydrogen peroxide-based initiator, an azo-based initiator, and a benzoin-series initiator; the hydrogen peroxide-based initiator is ammonium peroxide or potassium peroxide, the azo-based initiator is 2,2′-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride or azobisisobutyronitrile, and the benzoin-series initiator is benzoin dimethyl ether; and an amount of the initiator is 0.006% to 0.3% based on a total mass of the acrylamide monomer, the anionic monomer, and the temperature-sensitive polyether, the anionic monomer is a salt obtained by a neutralization of acrylic acid, methacrylic acid, or 2-acrylamide-2-methylpropanesulfonic acid, and a base used for the neutralization is at least one selected from the group consisting of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate; and

(2) precipitating, washing, centrifuging, and drying the inverse emulsion to obtain a dry powder of the anionic thermoviscosifying water-soluble polymer; or adding a reverse demulsifier to the inverse emulsion to obtain an emulsion of the anionic thermoviscosifying water-soluble polymer, followed by dissolution in water and dilution to obtain desired diluted solutions,

wherein the temperature-sensitive polyether is a triblock polymer of polyoxyethylene-polyoxypropylene-polyoxyethylene with a structural formula of:

wherein a structure and a property of the temperature-sensitive polyether vary with values of m and n.

2. The method for preparing the anionic thermoviscosifying water-soluble polymer of claim 1 , wherein, the acrylamide monomer is acrylamide or a mixture of acrylamide and another monomer, wherein the other monomer is at least one selected from the group consisting of methacrylamide, N,N-dimethylacrylamide, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, and N-vinylpyrrolidone; and a mass percentage of the acrylamide in the mixture is greater than 50%.

3. The method for preparing the anionic thermoviscosifying water-soluble polymer of claim 1 , wherein, the inorganic salt is at least one selected from the group consisting of sodium chloride, sodium acetate, sodium nitrate, and potassium nitrate.

4. The method for preparing the anionic thermoviscosifying water-soluble polymer of claim 1 , wherein, the oil is at least one selected from the group consisting of a cycloalkane, an aromatic hydrocarbon, a linear saturated hydrocarbon and a linear unsaturated hydrocarbon.

5. An anionic thermoviscosifying water-soluble polymer prepared by the method of claim 1 , wherein a molecular weight of the anionic thermoviscosifying water-soluble polymer is from greater than 2.0×10 6 g·mol −1 to 8.6×10 6 g·mol −1 .

6. A method of a polymer flooding in an enhanced oil recovery, comprising the step of injecting the anionic thermoviscosifying water-soluble polymer of claim 5 into an underground formation.

7. The anionic thermoviscosifying water-soluble polymer of claim 5 , wherein, the acrylamide monomer is acrylamide or a mixture of acrylamide and another monomer, wherein the other monomer is at least one selected from the group consisting of methacrylamide, N,N-dimethylacrylamide, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, and N-vinylpyrrolidone; and a mass percentage of the acrylamide in the mixture is greater than 50%.

8. The anionic thermoviscosifying water-soluble polymer of claim 5 , wherein, the inorganic salt is at least one selected from the group consisting of sodium chloride, sodium acetate, sodium nitrate, and potassium nitrate.

9. The anionic thermoviscosifying water-soluble polymer of claim 5 , wherein, the oil is at least one selected from the group consisting of a cycloalkane, an aromatic hydrocarbon, a linear saturated hydrocarbon and a linear unsaturated hydrocarbon.