Auto-invertible inverse polymer emulsion

1. An auto-invertible inverse emulsion comprising:

oil;

water;

at least one water-in-oil surfactant; and

at least one polymer having a molecular weight of between 5 and 30 million g/mol and containing:

monomer units of at least one water-soluble monomer selected from acrylamide, 2-acrylamido 2-methylpropane sulfonic acid (ATBS), acrylic acid (AA), and quaternized or salified dimethylaminoethyl acrylate (ADAME), and

10 −5 to 5 mol % of a lower critical solution temperature (LCST) macromonomer, said LCST macromonomer having a molecular weight of between 500 and 200,000 g/mol and having units from:

at least one monomer selected from AA, ATBS, and quaternized or salified dimethylaminoethyl methacrylate (MADAME); and

at least one LCST monomer selected from diethylacrylamide, N-isopropylacrylamide, dimethylacrylamide, and ter-butylacrylamide,

provided that where the monomer units of the at least one water-soluble monomer are units of ATBS, the LCST macromonomer does not have units from AA or ATBS.

2. The inverse emulsion according to claim 1 , wherein the polymer having a molecular weight of between 5 and 30 million g/mol contains monomer units of 2-acrylamido 2-methylpropane sulfonic acid (ATBS),

and wherein the LCST macromonomer has units from quaternized or salified dimethylaminoethyl methacrylate (MADAME).

3. The inverse emulsion according to claim 1 , wherein the polymer having a molecular weight of between 5 and 30 million g/mol contains monomer units of acrylic acid.

4. The inverse emulsion according to claim 1 , wherein the polymer having a molecular weight of between 5 and 30 million g/mol contains monomer units of quaternized or salified dimethylaminoethyl acrylate (ADAME).

5. The inverse emulsion according to claim 1 , wherein the inverse emulsion is free of oil-in-water surfactant.

6. The inverse emulsion according to claim 1 , wherein the LCST macromonomer has a weight average molecular weight between 1,000 and 100,000 g/mol.

7. A method for preparing an inverse emulsion according to claim 1 , said method comprising the following steps:

a) preparing an aqueous phase comprising at least one water-soluble monomer and at least one LCST macromonomer,

b) preparing an oily phase comprising at least one oil and at least one water-in-oil surfactant,

c) mixing the aqueous phase and the oily phase in order to form an inverse emulsion, and

d) once the inverse emulsion is formed, polymerizing the monomers in the aqueous phase using a radical polymerization initiator.

8. A polymeric aqueous solution obtained by inversion of the inverse emulsion according to claim 1 in an aqueous medium in the absence of an oil-in-water surfactant.

9. A method for thickening an aqueous medium, comprising adding the inverse emulsion according to claim 1 to the aqueous medium.

10. A method for flocculating suspended particles in an aqueous medium, comprising adding the inverse emulsion according to claim 1 to the aqueous medium.

11. A method for reducing the level of frictional resistance during transport of an aqueous medium, comprising adding the inverse emulsion according to claim 1 to the aqueous medium.

12. A method for fracturing an underground formation, which comprises:

aa) providing an inverse emulsion according to claim 1 ;

bb) inverting the inverse emulsion by adding it to an aqueous fluid in order to form an injection fluid;

cc) optionally, adding at least one propping agent in the injection fluid;

dd) introducing the injection fluid into part of the subterranean formation; and

ee) fracturing the underground formation with the injection fluid.

13. A method for the improved recovery of hydrocarbons by sweeping in an underground formation, which comprises:

aaa) providing an inverse emulsion according to claim 1 ;

bbb) inverting the inverse emulsion by adding it to an aqueous fluid in order to form an injection fluid;

ccc) introducing the injection fluid into part of the subterranean formation;

ddd) sweeping part of the subterranean formation with the injection fluid; and

eee) recovering a mixture of hydrocarbons, gas and aqueous fluid.

14. A method for:

thickening an aqueous medium;

flocculating suspended particles in an aqueous medium; or

reducing the level of frictional resistance during transport of an aqueous medium;

said method comprising adding an inverse emulsion to the aqueous medium, wherein said inverse emulsion is an auto-invertible inverse emulsion comprising:

oil;

water;

at least one water-in-oil surfactant; and

at least one polymer having a molecular weight of between 5 and 30 million g/mol and containing monomer units of at least acrylamide, 2-acrylamido 2-methylpropane sulfonic acid (ATBS), and 10 −5 to 5 mol % of a lower critical solution temperature (LCST) macromonomer, said LCST macromonomer having a molecular weight of between 500 and 200,000 g/mol and having units from:

at least one anionic monomer selected from acrylic acid and ATBS; and

at least one LCST monomer selected from diethylacrylamide, N-isopropylacrylamide, dimethylacrylamide, and ter-butylacrylamide.

15. The method according to claim 14 , for thickening an aqueous medium, comprising adding the inverse emulsion to the aqueous medium.

16. The method according to claim 14 , for flocculating suspended particles in an aqueous medium, comprising adding the inverse emulsion to the aqueous medium.

17. The method according to claim 14 , for reducing the level of frictional resistance during transport of an aqueous medium, comprising adding the inverse emulsion to the aqueous medium.