Water-soluble or water-swellable polymers as water loss reducers in cement slurries

1. A method for cementing deep wells using a cement slurry, wherein the cement slurry comprises a water-soluble or water-swellable polymer having a k value of 100 to 300, measured in 0.5% by weight solution in distilled water, containing

a) 25-35 mol % of one or more recurrent structural units derived from monomers selected from the group consisting of acryloyldimethyltaurate, acryloyl-1,1-dimethyl-2-methyltaurate, acryloyltaurate, and acryloyl-N-methyltaurate,

b) 3 to 8 mol % of one or more recurrent structural units of the formula (2)

in which

R 1 is hydrogen, methyl or ethyl,

X + is H + , NH 4 + , Li + , Na + , K + , ½ Ca ++ , ½ Mg ++ , ½ Zn ++ , ⅓ Al +++ , organic ammonium ions of the formula [HNR 5 R 6 R 7 ] + where R 5 , R 6 and R 7 may each independently be hydrogen, a linear or branched alkyl group having 1 to 22 carbon atoms, a linear or branched, mono- or polyunsaturated alkenyl group having 2 to 22 carbon atoms, a C 6 -C 22 -alkylamidopropyl group, a linear monohydroxyalkyl group having 2 to 10 carbon atoms or a linear or branched dihydroxyalkyl group having 3 to 10 carbon atoms, and where at least one of the R 5 , R 6 and R 7 radicals is not hydrogen, or mixtures of these ions,

B is a chemical bond, or a linear or branched alkylene group having 1 to 6 carbon atoms, and

n is an integer from 0 to 5,

and

c) 57 to 72 mol % of one or more recurrent structural units of the formula (3)

in which

R 1 is hydrogen, methyl or ethyl, and

R 3 and R 4 are each independently hydrogen, methyl, ethyl, n-propyl, isopropyl or butyl.

2. The method as claimed in claim 1 , wherein the structural units of the formula (2) are derived from methacrylic acid, acrylic acid, carboxyethyl acrylate or higher oligomers of the formula (2) in which n is an integer of 2 or more.

3. The method as claimed in claim 1 , wherein the structural units of the formula (3) are derived from acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-diethylmethacrylamide, N, N-diethylacrylamide, N, N-dimethylmethacrylamide, N,N-dimethylacrylamide, N-isopropylacrylamide, N-tert-butylacrylamide and N-butylacrylamide.

4. The method as claimed in claim 1 , wherein X + in formula (2) is selected from the group consisting of H + , NH 4 + , Na + and combinations of these ions.

5. The method as claimed in claim 1 wherein the water-soluble or water-swellable polymer contains

a) 27.5 to 32.5 mol % of one or more recurrent structural units derived from acryloyldimethyltaurate,

b) 4.5 to 7.5 mol % of one or more structural units of the formula (2) selected from the group consisting of structural units derived from acrylic acid, and

c) 60 to 68 mol % of one or more structural units of the formula (3) selected from the group consisting of structural units derived from acrylamide.

6. The method as claimed in claim 1 , in which the neutralization level of the structural units a) is 95 to 100 mol %.

7. The method as claimed in claim 1 , in which n=0 in at least 70% of all the structural units of the formula (2).

8. The method as claimed in claim 1 , in which n is 0 or 1.

9. The method as claimed in claim 1 , in which formula (3) is derived from acrylamide.

10. The method as claimed in claim 1 , wherein the water-soluble or water-swellable polymer contains 27.5 to 32.5 mol % of the structural units a), 4.5 to 7.5 mol % of the structural units of the formula (2) and 60 to 68 mol % of the structural units of the formula (3).

11. The method as claimed in claim 1 , in which structural unit a) is derived from acryloyldimethyltaurate, formula (2) represents one or more structural unit derived from acrylic acid and formula (3) represents one or more structural unit derived from acrylamide.

12. The method as claimed in claim 1 , wherein the polymer is prepared by subjecting monomers from which the structural units of components a) to c) derive to free-radical precipitation polymerization in a polar solvent, and the monomers are optionally neutralized prior to the polymerization, or the polymer is optionally neutralized after the polymerization, with ammonia, ammonium carbonate or organic amines or an Li + − , Na + − , K + − , Ca ++ − , Mg ++ − , Zn ++ − or Al +++ -containing base.

13. The method as claimed in claim 12 , wherein the polar solvent has a boiling point of 60 to 110° C.

14. The method as claimed in claim 12 , wherein the polar solvent is a solvent mixture of

d) water

and

e) one or more further polar solvents.

15. The method as claimed in claim 12 , wherein the polar solvent comprises methanol, ethanol, 1-propanol, 2-propanol, 2-methyl-2-propanol, 1-butanol, 2-butanol, dimethyl ketone, diethyl ketone, pentan-2-one, butanone, tetrahydropyran, tetrahydrofuran, 2-m ethyltetrahydrofuran, 1,3-dioxane or 1,4-dioxane.

16. The method as claimed in claim 12 , in which the polar solvent comprises 2-methylpropan-2-ol.

17. The method as claimed in claim 12 , wherein the polar solvent comprises 1% to 5% by weight of water.

18. The method as claimed in claim 12 , wherein 27.5 to 32.5 mol % of acryloyldimethyltaurate, and 4.5 to 7.5 mol % of acrylic acid, 60 to 68 mol % of acrylamide is subjected to free-radical precipitation polymerization in a mixture of 1% to 8% by weight of water and 92% to 99% by weight of 2-methylpropan-2-ol, and the monomers prior to the polymerization or the polymer after the polymerization are/is optionally neutralized with ammonia, ammonium carbonate, sodium hydroxide, or sodium carbonate.