Oil field treatment fluids with viscosified brines

1. A method comprising:

introducing into a well bore a fluid comprising a zwitterionic polymer prepared by inverse emulsion polymerization of at least one monomer A b comprising a betaine group and optionally one or more nonionic monomers B a , the well bore being chosen from a natural gas well bore or an oil well bore, wherein the zwitterionic polymers exhibit an intrinsic viscosity of about 600 ml/g or greater in a 20% by weight aqueous NaCl solution.

2. The method of claim 1 , wherein the molar ratio of the monomers A b to the monomers B a ranges from about 4:96 to about 40:60.

3. The method of claim 1 , wherein the at least one monomer A b is chosen from sulphobetaines or phosphobetaines.

4. The method of claim 1 , wherein the at least one monomer A b is a substituted or unsubstituted compound chosen from alkylphosphonates of dialkylammonioalkyl acrylates, alkylphosphonates of dialkylammonioalkyl methacrylates, alkylphosphonates of dialkylammonioalkyl acrylamides, alkylphosphonates of dialkylammonioalkyl methacrylamides, alkylsulphonates of dialkylammonioalkyl acrylates, alkylsulphonates of dialkylammonioalkyl methacrylates, alkylsulphonates of dialkylammonioalkyl acrylamides, alkylsulphonates of dialkylammonioalkyl methacrylamides, alkylphosphonates of dialkylammonioalkoxyalkyl acrylates, alkylphosphonates of dialkylammonioalkoxyalkyl methacrylates, alkylphosphonates of dialkylammonioalkoxyalkyl acrylamides, alkylphosphonates of dialkylammonioalkoxyalkyl methacrylamides, alkylsulphonates of dialkylammonioalkoxyalkyl acrylates, alkylsulphonates of dialkylammonioalkoxyalkyl methacrylates, alkylsulphonates of dialkylammonioalkoxyalkyl acrylamides, alkylsulphonates of dialkylammonioalkoxyalkyl methacrylamides, heterocyclic betaine monomers, alkylphosphonates of dialkylammonioalkylallylics, alkylsulphonates of dialkylammonioalkylallylics, alkylphosphonates of dialkylammonioalkylstyrenes, alkylsulphonates of dialkylammonioalkylstyrenes, or betaines resulting from ethylenically unsaturated anhydrides and dienes.

5. The method of claim 4 , wherein at least one monomer A b is a heterocyclic betaine chosen from sulphobetaines derived from piperazine, sulphobetaines derived from vinyl substituted pyridines, or sulphobetaines derived from imidazoles.

6. The method of claim 1 , wherein the at least one monomer A b is chosen from compounds of formulae 10, 11, 12, 13, 18, 19, 20, 21, 22 or 23:

7. The method of claim 1 , wherein the at least one monomer A b is chosen from substituted or unsubstituted compounds of formula 24 or 25:

in which:

R 1 is hydrogen or methyl,

R 2 and R 3 , which are identical or different, are hydrogen or alkyls having from 1 to 6 carbon atoms,

Y 1 is —O— or NR 2 ,

Z − is SO 3 − ,

m is 2 or 3, and

n is 1-6.

8. The method of claim 1 , wherein the at least one monomer A b is chosen from: sulphopropyldimethylammonioethyl methacrylate, sulphoethyldimethylammonioethyl methacrylate, sulphobutyldimethylammonioethyl methacrylate, sulphohydroxypropyldimethylammonioethyl methacrylate, sulphopropyldimethylammoniopropylacrylamide, sulphopropyldimethylammoniopropylmethacrylamide, sulphohydroxypropyldimethylammoniopropylmethacrylamide, sulphopropyldiethylammonioethoxyethyl methacrylate, 2-vinyl-1-(3-sulphopropyl)pyridinium betaine, 4-vinyl-1-(3-sulphopropyl)pyridinium betaine, sulphopropyldimethylammonioethyl acrylate, 1-vinyl-3-(3-sulphopropyl)imidazolium betaine or sulphopropylmethyldiallylammonium betaine.

9. The method of claim 1 , wherein the at least one monomer A b is chosen from compounds of formula 1, 4, 6, 7 or 8:

10. The method of claim 1 , wherein during the polymerization, the monomer B a is a hydrophilic monomer.

11. The method of claim 1 , wherein the zwitterionic polymer is prepared by inverse emulsion polymerization of the at least one monomer A b and the one or more nonionic monomers B a , wherein the one or more nonionic monomer B a is chosen from hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, glycerol monomethacrylate, acrylamide, methacrylamide, N-methylolacrylamide, dimethylacrylamide, dimethylmethacrylamide, polyethylene oxide, polypropylene oxide, polyethylene/polypropylene oxide copolymers, α-methacrylates, vinyl alcohol or vinylpyrrolidone.

12. The method of claim 1 , wherein the polymer is in the form of an aqueous composition comprising the inverse emulsion with an aqueous phase comprising the polymer dispersed in the form of droplets in a hydrophobic external phase and other ingredients chosen from a surfactant, an organic salt, an inorganic salt, a detergent or a thickener.

13. The method of claim 1 , wherein the fluid is employed simultaneously with drilling of the well bore.

14. A method comprising:

introducing into a well bore a fluid comprising a zwitterionic polymer prepared by inverse emulsion polymerization of at least one monomer A b comprising a betaine group and one or more nonionic monomers B a , the well bore being chosen from a natural gas well bore an 4 or an oil well bore,

wherein the at least one monomer A b is chosen from sulphopropyldimethylammonioethyl methacrylate or sulphopropyldimethylammoniopropylmethacrylamide and the at least one nonionic monomer B a is acrylamide.

15. A method comprising:

introducing into a well bore a fluid comprising a zwitterionic polymer prepared by inverse emulsion polymerization of at least one monomer A b comprising a betaine group and optionally one or more nonionic monomers B a , the well bore being chosen from a natural gas well bore or an oil well bore, wherein the inverse emulsion polymerization comprises:

preparing an inverse emulsion comprising monomer A b and monomer B a in an aqueous phase dispersed in the form of droplets in a hydrophobic external phase of an inverse emulsion; and

after preparing the inverse emulsion, forming the zwitterionic polymer by polymerization of the at least one monomer A b and the one or more nonionic monomers B a .

16. The method of claim 15 , wherein preparing the inverse emulsion comprises mixing at least one emulsifying agent, monomer A b , monomer B a , the aqueous phase and the hydrophobic external phase.

17. The method of claim 15 , wherein the polymerization is carried out by bringing together monomers A b and monomers B a with an initiator compound that generates free radicals.

18. The method of claim 15 , wherein the polymerization is carried out at a temperature ranging from about ambient temperature to about 75° C.

19. A method comprising:

introducing into a well bore a fluid comprising a zwitterionic polymer prepared by inverse emulsion polymerization of at least one monomer A b comprising a betaine group and optionally one or more nonionic monomers B a , the well bore being chosen from a natural gas well bore or an oil well bore, wherein the aqueous composition is a saline composition comprising at least 25 g/l of a salt.

20. The method of claim 19 , wherein the saline composition is a brine.

21. The method of claim 20 , wherein the brine comprises divalent salts in an amount greater than about 25% by weight of the total salts in the brine.

22. The method of claim 20 , wherein the saline composition exhibits an ionic strength of at least about 0.7 mol/l.

23. A method comprising:

introducing into a well bore a fluid comprising a zwitterionic polymer prepared by inverse emulsion polymerization of at least one monomer A b comprising a betaine group and optionally one or more nonionic monomers B a , the well bore being chosen from a natural gas well bore or an oil well bore, wherein the fluid is employed to fracture the well bore.

24. A method comprising:

introducing into a well bore a fluid comprising a zwitterionic polymer prepared by inverse emulsion polymerization of at least one monomer A b comprising a betaine group and optionally one or more nonionic monomers B a , the well bore being chosen from a natural gas well bore or an oil well bore, wherein the fluid further comprises gravel, the fluid causing the gravel to be packed in the well bore.

25. A method comprising:

introducing into a well bore a fluid comprising a zwitterionic polymer prepared by inverse emulsion polymerization of at least one monomer A b comprising a betaine group and optionally one or more nonionic monomers B a , the well bore being chosen from a natural gas well bore or an oil well bore, wherein the zwitterionic polymers exhibit an intrinsic viscosity of about 320 ml/g or greater in a 20% by weight aqueous NaCl solution.