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

Abstract

This invention relates to water-soluble or water-swellable polymers, containing a) 25-35 mol. % of one or more recurrent structural units of formula (1), where R.sup.1 and R.sup.2 represent hydrogen, methyl or ethyl, A represents a linear or branched C.sub.1-C.sub.12-alkylene, and Q.sup.+ stands for NH.sub.4.sup.+, Li.sup.+, Na.sup.+, K.sup.+, ½ Ca.sup.++, ½ Mg.sup.++, ½ Zn.sup.++, ⅓ Al.sup.+++, or organic ammonium ions of the formula [HNR.sup.5R.sup.6R.sup.7].sup.+, b) 3 to 8 mol. % of one or more recurrent structural units of formula (2), where R.sup.1 represents hydrogen, methyl, or ethyl, X.sup.+ stands for H.sup.+, NH.sub.4.sup.+, Li.sup.+, Na.sup.+, K.sup.+, ½ Ca.sup.++, ½ Mg.sup.++, ½ Zn.sup.++, ⅓ Al.sup.+++, or organic ammonium ions of the formula [HNR.sup.5R.sup.6R.sup.7].sup.+, B is a linear or branched alkylene group with 1 to 6 carbon atoms, and n is a whole number between 0 and 5, and c) 57 to 72 mol. % of a (meth)acrylamide.

Claims

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) ##STR00005## in which R.sup.1 is hydrogen, methyl or ethyl, X.sup.+ is H.sup.+, NH.sub.4.sup.+, Li.sup.+, Na.sup.+, K.sup.+, ½ Ca.sup.++, ½ Mg.sup.++, ½ Zn.sup.++, ⅓ Al.sup.+++, organic ammonium ions of the formula [HNR.sup.5R.sup.6R.sup.7].sup.+ where R.sup.5, R.sup.6 and R.sup.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.sub.6-C.sub.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.sup.5, R.sup.6 and R.sup.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) ##STR00006## in which R.sup.1 is hydrogen, methyl or ethyl, and R.sup.3 and R.sup.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.sup.+ in formula (2) is selected from the group consisting of H.sup.+, NH.sub.4.sup.+, Na.sup.+ 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.sup.+.sub.−, Na.sup.+.sub.−, K.sup.+.sub.−, Ca.sup.++.sub.−, Mg.sup.++.sub.−, Zn.sup.++.sub.− or Al.sup.+++-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.

Description

EXAMPLES

(1) In polymerization processes A to B described below, typical preparation processes for the polymers of the invention are described.

(2) In the examples, there was variation of the polar solvent used, with the aid of which the polymers of the invention can be prepared. With the aid of polymerization methods A1 to A5 and B1 to B3, further polymers of the invention were prepared by the variation of the monomers. These polymers and polymerization processes used for the synthesis thereof are summarized in table 1a) to table 1i).

(3) Polymerization process A1: Polymerization in 2-methylpropan-2-ol/water (3.5%) as polar solvent

(4) In a 2 liter Quickfit flask with anchor stirrer, reflux condenser with offgas scrubber, combined thermometer/pH meter and a gas inlet tube, 772 g of anhydrous 2-methyl-propan-2-ol are admixed with 28 g of distilled water. The reaction vessel is within a thermostatted heating bath.

(5) This reaction vessel is blanketed with nitrogen gas and, in a gentle nitrogen countercurrent, 113.2 g of acryloyldimethyltaurate are introduced. The acryloyldimethyltaurate does not dissolve completely in the 2-methylpropan-2-ol/water mixture and is partly in the form of a dispersion of solids. The pH of this mixture is below pH 1. Through the gas inlet tube, gaseous ammonia is introduced above the liquid phase until the pH of the dispersion is between 7 and 8. On attainment of the desired pH range, the mixture is stirred for another 1 hour and the pH is recorded continuously. The reaction vessel is blanketed with nitrogen and 79.2 g of acrylamide and 7.6 g of acrylic acid are introduced. After the acrylamide has been introduced, the pH is checked again and optionally corrected into the pH range of 7 to 8. A constant nitrogen stream is passed through the solution for at least 1 hour. After this inertization time, the residual oxygen is checked by means of an oxygen electrode. Should the measured value of residual oxygen in the liquid phase exceed the value of 1 ppm, another inertization is necessary until this value is attained. Thereafter, in a gentle nitrogen stream, 2 g of 2,2′-azobis(2,4-dimethylvaleronitrile) are added and the reaction tank is heated to 40° C. Shortly after attainment of an internal temperature of 40° C., the introduction of nitrogen gas is ended and commencement of the polymerization reaction is observed, which can be identified by a temperature increase of 10-35° C. About 5-15 minutes after onset of the polymerization reaction, the temperature maximum has been exceeded and the temperature in the reaction vessel is increased by means of the heating bath up to the boiling point of the 2-methylpropan-2-ol/water mixture. Under gentle reflux, the now viscous mixture is stirred for a further two hours. The reaction product, present in the form of a viscous suspension of polymer in the 2-methylpropan-2-ol/water mixture, is removed by filtration and subsequent drying in a vacuum drying cabinet.

(6) Yield: 215.4 g of polymer 1

(7) Dry content (IR drier, 15 minutes at 120° C.): 94%

(8) K value (0.5% solution in distilled water): 212

(9) pH (0.5% solution in distilled water): 4.76

(10) Polymerization process A2: Polymerization in 2-methylpropan-2-ol/water (2%) In a 2 liter Quickfit flask with anchor stirrer, reflux condenser with offgas scrubber, combined thermometer/pH meter and a gas inlet tube, 784 g of anhydrous 2-methylpropan-2-ol are admixed with 16 g of distilled water. The reaction vessel is within a thermostatted heating bath. The further steps of polymerization process A2 are conducted analogously to polymerization process A1.

(11) With the aid of polymerization method A2, further polymers of the invention were prepared by varying the monomers. These polymers are summarized in table 1.

(12) Polymerization process A3: Polymerization in 2-methylpropan-2-ol/water (4.5%)

(13) In a 2 liter Quickfit flask with anchor stirrer, reflux condenser with offgas scrubber, combined thermometer/pH meter and a gas inlet tube, 764 g of anhydrous 2-methylpropan-2-ol are admixed with 36 g of distilled water. The reaction vessel is within a thermostatted heating bath. The further steps of polymerization process A3 are conducted analogously to polymerization process A1.

(14) Polymerization process A4: Polymerization in 2-methylpropan-2-ol/water (1.5%)

(15) In a 2 liter Quickfit flask with anchor stirrer, reflux condenser with offgas scrubber, combined thermometer/pH meter and a gas inlet tube, 788 g of anhydrous 2-methylpropan-2-ol are admixed with 12 g of distilled water. The reaction vessel is within a thermostatted heating bath. The further steps of polymerization process A4 are conducted analogously to polymerization process A1.

(16) Polymerization process A5: Polymerization in 2-methylpropan-2-ol/water (7.5%)

(17) In a 2 liter Quickfit flask with anchor stirrer, reflux condenser with offgas scrubber, combined thermometer/pH meter and a gas inlet tube, 748 g of anhydrous 2-methylpropan-2-ol are admixed with 52 g of distilled water. The reaction vessel is within a thermostatted heating bath. The further steps of polymerization process A5 are conducted analogously to polymerization process A1.

(18) Polymerization process B1: Polymerization in 2-methylpropan-2-ol, dimethyl ketone and water as polar solvent (50:50, 3.4% water)

(19) In a 2 liter Quickfit flask with anchor stirrer, reflux condenser with offgas scrubber, combined thermometer/pH meter and a gas inlet tube, 384 g of anhydrous 2-methylpropan-2-ol and 384 g of dimethyl ketone are admixed with 26.4 g of distilled water. The reaction vessel is within a thermostatted heating bath.

(20) This reaction vessel is blanketed with nitrogen gas and, in a gentle nitrogen countercurrent, 130 g of acryloyldimethyltaurate are introduced. The acryloyldimethyltaurate does not dissolve completely in the 2-methylpropan-2-ol/dimethyl ketone/water mixture and is partly in the form of a dispersion of solids. The pH of this mixture is below pH 1. Through the gas inlet tube, gaseous ammonia is introduced above the liquid phase until the pH of the dispersion is between 7 and 8. On attainment of the desired pH range, the mixture is stirred for another 1 hour and the pH is recorded continuously. The reaction vessel is blanketed with nitrogen and 60 g of acrylamide and 10 g of acrylic acid are introduced. After the acrylamide has been introduced, the pH is checked again and optionally corrected into the pH range of 7 to 8. A constant nitrogen stream is passed through the solution for at least 1 hour. After this inertization time, the residual oxygen is checked by means of an oxygen electrode. Should the measured value of residual oxygen in the liquid phase exceed the value of 1 ppm, another inertization is necessary until this value is attained. Thereafter, in a gentle nitrogen stream, 2.05 g of 2,2′-azobis(2,4-dimethylvaleronitrile) are added and the reaction tank is heated to 40° C. Shortly after attainment of an internal temperature of 40° C., the introduction of nitrogen gas is ended and commencement of the polymerization reaction is observed, which can be identified by a temperature increase of 10 to 35° C. About 5-15 minutes after onset of the polymerization reaction, the temperature maximum has been exceeded and the temperature in the reaction vessel is increased by means of the heating bath up to the boiling point of the 2-methylpropan-2-ol/water mixture. Under gentle reflux, the now viscous mixture is stirred for a further two hours. The reaction product, present in the form of a viscous suspension of polymer in the 2-methylpropan-2-ol/water mixture, is removed by filtration and subsequent drying in a vacuum drying cabinet.

(21) Polymerization process B2: Polymerization in 2-methylpropan-2-ol, dimethyl ketone and water as polar solvent (75:25, 3.0% water)

(22) In a 2 liter Quickfit flask with anchor stirrer, reflux condenser with offgas scrubber, combined thermometer/pH meter and a gas inlet tube, 582 g of anhydrous 2-methylpropan-2-ol and 194 g of dimethyl ketone are admixed with 24 g of distilled water. The reaction vessel is within a thermostatted heating bath. The further steps of polymerization process B2 are conducted analogously to polymerization process B1.

(23) Polymerization process B3: Polymerization in 2-methylpropan-2-ol, dimethyl ketone and water as polar solvent (25:75, 5.0% water)

(24) In a 2 liter Quickfit flask with anchor stirrer, reflux condenser with offgas scrubber, combined thermometer/pH meter and a gas inlet tube, 194 g of anhydrous 2-methylpropan-2-ol and 582 g of dimethyl ketone are admixed with 24 g of distilled water. The reaction vessel is within a thermostatted heating bath. The further steps of the polymerization process are conducted analogously to polymerization process B1.

(25) TABLE-US-00001 TABLE 1a Examples of polymers of the invention prepared by polymerization processes A1 to A5 and B1 to B3 ACDMT Acrylic acid Acrylamide V-65 ® mol mol mol % by k Polymer Process g % g % g % g wt. value  2 A1 110.0 29.6 10.00 7.7 80.0 62.7 2.00 1.0 215  4 A1 113.2 30.9 7.60 6.0 79.2 63.1 2.00 1.0 210  6 A1 98.0 32.0 6.40 6.0 65.0 61.9 1.90 1.1 208  7 A1 119.0 32.5 5.70 4.5 79.2 63.0 2.25 1.1 200  8 A1 104.5 28.5 9.60 7.5 80.4 64.0 2.25 1.2 204 12 A2 110.0 29.6 10.00 7.7 80.0 62.7 2.25 1.1 192 13 A2 113.2 30.9 7.60 6.0 79.2 63.1 2.20 1.1 188 14 A2 119.0 32.5 5.70 4.5 79.2 63.0 2.20 1.1 179 16 A3 113.2 30.9 7.60 6.0 79.2 63.1 2.20 1.1 216 18 A3 110.0 29.6 10.00 7.7 80.0 62.7 2.25 1.1 222 20 A4 90.0 25.1 6.20 5.0 86.0 69.9 2.18 1.2 176

(26) TABLE-US-00002 TABLE 1b Examples of polymers of the invention prepared by polymerization processes A1 to A5 and B1 to B3 ACDMT Acrylic acid Acrylamide V-65 ® mol mol mol % by k Polymer Process g % g % g % g wt. value 25 B1 109.5 29.5 9.70 7.5 80.3 63.0 2.30 1.2 203 26 B1 100.0 28.5 6.10 5.0 80.0 66.5 2.10 1.1 211 28 B1 113.2 31.0 7.60 6.0 79.0 63.0 2.20 1.1 213 31 B2 99.5 34.5 8.00 8.0 56.8 57.5 1.80 1.1 219 33 B2 110.0 34.3 3.40 3.0 69.0 62.7 2.00 1.1 227 34 B2 119.0 32.5 5.70 4.5 79.2 63.0 2.25 1.1 228 35 B2 110.0 29.6 10.00 7.7 80.0 62.7 2.25 1.1 221 36 B2 113.2 30.9 7.60 6.0 79.2 63.1 2.25 1.1 227 38 B3 113.2 30.9 7.60 6.0 79.2 63.1 2.20 1.1 216 40 B3 110.0 29.6 10.00 7.7 80.0 62.7 2.25 1.1 218

(27) TABLE-US-00003 TABLE 1c Polymers of the invention by polymerization process A1 Methacrylic ACDMT acid Acrylamide V-65 ® k Polymer Process mol % mol % mol % g value 42 A1 30 7 63 2.00 208 44 A1 31 6 63 2.00 219

(28) TABLE-US-00004 TABLE 1d Polymers of the invention by polymerization process A1 Methacrylic Dimethyl- ACDMT acid acrylamide V-65 ® k Polymer Process mol % mol % mol % g value 47 A1 30 7 63 2.0 201 49 A1 31 6 63 2.0 198

(29) TABLE-US-00005 TABLE 1e Polymers of the invention by polymerization process A1 ACDMT CEA Acrylamide V-65 ® k Polymer Process mol % mol % mol % g value 52 A1 30 7 63 2.0 217 54 A1 31 6 63 2.0 209

(30) TABLE-US-00006 TABLE 1f Polymers of the invention by polymerization process A1 Dimethyl- ACDMT CEA acrylamide V-65 ® k Polymer Process mol % mol % mol % g value 57 A1 30 7 63 2.0 218 59 A1 31 6 63 2.0 207

(31) TABLE-US-00007 TABLE 1g Polymers of the invention by polymerization process A1 CEA oligomer Acrylamide Polymer Process ACDMT mol % mol % mol % V-65 ® g k value 62 A1 30 7 63 2.0 214 64 A1 31 6 63 2.0 205

(32) TABLE-US-00008 TABLE 1h Polymers of the invention by polymerization process A1 CEA Dimethyl- ACDMT oligomer acrylamide V-65 ® k Polymer Process mol % mol % mol % g value 67 A1 30 7 63 2.0 208 69 A1 31 6 63 2.0 218

(33) ACDMT=acryloyldimethyltaurate

(34) AA=acrylic acid

(35) AM=acrylamide

(36) CEA=carboxyethyl acrylate

(37) CEA oligomer=carboxyethyl acrylate oligomer mixture with n=0 to 5

(38) V-65=2,2′-azobis(2,4-dimethylvaleronitrile)/V-65 is a registered trademark of Wako Pure Chemicals Industries, Ltd Comparative Example 1 (not in accordance with the invention, prepared according to EP-1045869, copolymer prepared in precipitation polymerization, 44.5 mol % of acryloyldimethyltaurate and 55.5 mol % of acrylamide).

(39) In a 3 liter Quickfit flask with anchor stirrer, reflux condenser with offgas scrubber, combined thermometer/pH meter and a gas inlet tube, 1700 g of anhydrous 2-methylpropan-2-ol are admixed with 50 mL of distilled water. The reaction vessel is within a thermostatted heating bath.

(40) This reaction vessel is blanketed with nitrogen gas and, in a gentle nitrogen countercurrent, 245 g of acryloyldimethyltaurate are introduced. The acryloyldimethyltaurate does not dissolve completely in the 2-methylpropan-2-ol/water mixture and is partly in the form of a dispersion of solids. The pH of this mixture is below pH 1. Through the gas inlet tube, gaseous ammonia is introduced above the liquid phase until the pH of the dispersion is between 7 and 8. On attainment of the desired pH range, the mixture is stirred for another 1 hour and the pH is recorded continuously. The reaction vessel is blanketed with nitrogen and 105 g of acrylamide are introduced. After the acrylamide has been introduced, the pH is checked again and optionally corrected into the pH range of 7 to 8. A constant nitrogen stream is passed through the solution for at least 1 hour. After this inertization time, the residual oxygen is checked by means of an oxygen electrode. Should the measured value of residual oxygen in the liquid phase exceed the value of 1 ppm, another inertization is necessary until this value is attained. Thereafter, in a gentle nitrogen stream, 2 g of AIBN are added and the reaction tank is heated to 60° C. Shortly after attainment of an internal temperature of 60° C., the introduction of nitrogen gas is ended and commencement of the polymerization reaction is observed, which can be identified by a temperature increase of 10-15° C. About 5-15 minutes after onset of the polymerization reaction, the temperature maximum has been exceeded and the temperature in the reaction vessel is increased by means of the heating bath up to the boiling point of the 2-methylpropan-2-ol/water mixture. Under gentle reflux, the now viscous mixture is stirred for a further two hours. The reaction product, present in the form of a viscous suspension of polymer in the 2-methylpropan-2-ol/water mixture, is removed by filtration and subsequent drying in a vacuum drying cabinet.

(41) Yield: 365 g

(42) Dry content (IR drier, 15 minutes at 120° C.): 96%

(43) K value (0.5% solution in distilled water): 212 Comparative Example 2 (not in accordance with the invention, prepared according to EP-0244981, copolymer prepared in an aqueous gel polymerization, 18.6 mol % of acryloyldimethyltaurate, 10 mol % of acrylic acid and 71.3 mol % of acrylamide)

(44) In EP-0244981, reference is made in the examples to a gel polymerization in a conventional manner. No detailed preparation process for the polymers in EP-0244981 is described.

(45) For comparative example 2, a 1 liter Quickfit flask with anchor stirrer, reflux condenser with offgas scrubber, combined thermometer/pH meter and a gas inlet tube was initially charged with 390 g of distilled water, 40 g of acryloyldimethyltaurate, 7.5 g of acrylic acid and 52.5 g of acrylamide. Nitrogen gas is passed through the reaction solution for 1 hour. Thereafter, 2 g of ammonium peroxodisulfate dissolved in 10 g of distilled water are added as initiator. This mixture is heated to 40° C. until a polymerization reaction occurs after 10-15 minutes. After passing through the temperature maximum, the internal temperature is adjusted to 60° C. by means of the thermostat. A clear gel of high viscosity forms. The gel is comminuted mechanically and dried in a vacuum drying cabinet. Comparative Example 3 (not in accordance with the invention, prepared according to EP-0244981, copolymer prepared in an aqueous gel polymerization, 34 mol % of acryloyldimethyltaurate, 11.4 mol % of acrylic acid and 54.6 mol % of acrylamide)

(46) For comparative example 3, a 1 liter Quickfit flask with anchor stirrer, reflux condenser with offgas scrubber, combined thermometer/pH meter and a gas inlet tube was initially charged with 390 g of distilled water, 60 g of acryloyldimethyltaurate, 7 g of acrylic acid and 11.4 g of acrylamide. Nitrogen gas is passed through the reaction solution for 1 hour. Thereafter, 2 g of ammonium peroxodisulfate dissolved in 10 g of distilled water are added as initiator. This mixture is heated to 40° C. until a polymerization reaction occurs after 10-15 minutes. After passing through the temperature maximum, the internal temperature is adjusted to 60° C. by means of the thermostat. A clear gel of high viscosity forms. The gel is comminuted mechanically and dried in a vacuum drying cabinet. Comparative Example 4 (not in accordance with the invention, prepared according to EP-0244981, copolymer prepared in an aqueous gel polymerization, 10.3 mol % of acryloyldimethyltaurate, 5.9 mol % of acrylic acid and 84.9 mol % of acrylamide). Comparative example 4 was prepared analogously to comparative example 2.

(47) For comparative example 4, a 1 liter Quickfit flask with anchor stirrer, reflux condenser with offgas scrubber, combined thermometer/pH meter and a gas inlet tube was initially charged with 390 g of distilled water, 25 g of acryloyldimethyltaurate, 5 g of acrylic acid and 70 g of acrylamide. Nitrogen gas is passed through the reaction solution for 1 hour. Thereafter, 2 g of ammonium peroxodisulfate dissolved in 10 g of distilled water are added as initiator. This mixture is heated to 40° C. until a polymerization reaction occurs after 10-15 minutes. After passing through the temperature maximum, the internal temperature is adjusted to 60° C. by means of the thermostat. A clear gel of high viscosity forms. The gel is comminuted mechanically and dried in a vacuum drying cabinet. Comparative Example 5 (not in accordance with the invention, prepared according to U.S. Pat. No. 4,015,991, copolymer prepared in an aqueous gel polymerization, 10.3 mol % of acryloyldimethyltaurate, 5.9 mol % of acrylic acid and 84.9 mol % of acrylamide).

(48) A 3 liter Quickfit flask with anchor stirrer, reflux condenser with offgas scrubber, combined thermometer/pH meter and a gas inlet tube is initially charged with 328 g of distilled water and 116.4 g of acryloyldimethyltaurate. The acryloyldimethyltaurate is neutralized by adding 45 g of a 50% sodium hydroxide (NaOH) solution. After the neutralization reaction, a clear solution having a pH between 7 and 8 is obtained. 14.7 g of acrylamide are dissolved gradually in the solution thus neutralized. Nitrogen gas is passed through the reaction solution for 1 hour. Thereafter, 0.69 g of tert-butyl peroxypivalate and 1.0 mL of an iron ammonium sulfate solution as redox initiator pair are added. The iron ammonium sulfate solution is prepared by dissolving 0.098 g of Fe(NH.sub.4).sub.2(SO.sub.4).sub.2 in 500 g of water. This mixture is additionally stirred at room temperature until, after 1-2 hours, a polymerization reaction occurs. The exothermic polymerization reaction, in the case of adiabatic polymerization, increases the temperature to 50-60° C. After passing through the temperature maximum, the internal temperature is adjusted to 60° C. by means of the thermostat. A clear gel of high viscosity is formed. The gel is comminuted mechanically and dried on a roller drier.

(49) Yield: 152 g of comparative polymer 5

(50) According to the testing in U.S. Pat. No. 4,015,991, this base polymer should have only poor water-loss reducing action. In contrast, at low temperatures, 28° C., the partly hydrolyzed products should have good performance properties. These products were prepared and tested as in comparative example 6. Comparative Example 6 (not in accordance with the invention, prepared according to U.S. Pat. No. 4,015,991) Controlled hydrolysis of comparative polymer 5

(51) 45.3 g of comparative polymer 5 are dissolved in 1500 mL of distilled water while stirring. On completion of dissolution of the polymer, 1.68 g of potassium hydroxide which have been dissolved in 20 mL of water beforehand are added thereto. This mixture is heated to 60° C. then stirred at this temperature for one hour. The reaction product is dried again with the aid of a roller drier. In this way, 50% hydrolysis is achieved.

Examples: Synergistic Mixtures Comprising Starch and the Polymers of the Invention

(52) For the synergistic mixtures comprising starch and the polymers of the invention, the following starch types were used:

(53) Starch A: corn starch

(54) Starch B: manioc starch

(55) Starch C: “cook up modified starch”

(56) Starch D: hydroxypropyl starch

(57) Table 2 describes the mixtures made with the starches A to E and the polymers of the invention.

(58) TABLE-US-00009 TABLE 2a Synergistic mixtures comprising starch and the polymers of the invention Mixture Starch % by wt. Polymer % by wt. 1 A 30  (4) 70 2 A 50  (4) 50 3 A 70  (4) 30 4 B 50  (4) 50 5 D 60  (4) 40 6 A 25 (42) 75 7 A 40 (42) 60 8 A 65 (42) 35 9 B 25 (42) 75 10 B 40 (42) 60 11 B 65 (42) 35 12 B 50 (52) 50 13 C 50 (52) 50 14 D 50 (52) 50

(59) TABLE-US-00010 TABLE 2b Synergistic mixtures comprising starch and the polymers of the invention Mixture Starch % by wt. Polymer % by wt. 15 D 40 (52) 60 16 D 60 (52) 40 17 A 75  (7) 25 18 D 50  (7) 50 25 A 45 (26) 55 26 E 65 (26) 35 27 A 50 (49) 50 28 A 45 (49) 50 29 A 65 (49) 35 30 B 50 (49) 50 31 C 45 (49) 50 32 D 65 (49) 35 33 A 50 (54) 50 34 B 50 (54) 50 35 D 50 (54) 50

Examples: Test Results

(60) The testing is effected according to API spec. 10. In an atmospheric consistometer, the cement slurry is stirred/conditioned at analysis temperature and then, at the same temperature, the rheology with the FANN model 35SA viscometer is measured (at high temperature, conditioning is effected at 93° C. and the viscosity is measured). At temperatures of >93° C., the water loss is measured with a stirring fluid loss apparatus (SFLA).

(61) Table 3 shows the water loss-reducing properties of selected abovementioned examples according to API spec. 10 at 35° C. (95° F.) in a static filtration test in the Baroid HTHP filter press. It becomes clear that the water loss reduction with the polymers of the invention can be improved considerably at low temperatures compared to the comparative examples. Of course, at these low temperatures, the polymers based on acryloyldimethyltaurate and acrylamide as claimed in EP-1045869, reworked in comparative example 1, also reduce water loss. However, it becomes clear from table 1 that the water loss of comparative example 1 is nearly twice as high compared to the inventive polymer 4. The gel polymers described in EP-0244981, reworked in comparative examples 2 to 3, show a high water loss even at very low temperatures and are unsuitable for use. For this reason, comparative examples 2 to 3 were not considered in the measurements which follow. The two comparative examples from U.S. Pat. No. 4,015,991, based on partly hydrolyzed poly(acrylamide-co-acryloyldimethyltaurate), reworked in comparative examples 5 and 6, in direct comparison with polymer 4, likewise have nearly twice to three times the water loss. These polymers too appear unsuitable for use.

(62) Formulation of the cement slurries:

(63) 100 g of Dyckerhoff Class G

(64) 44 g of distilled water

(65) 0.3-0.5 g of polymer

(66) TABLE-US-00011 TABLE 3 (Use test at 95° F. (35° C.)) Rheology after mixing at 75° F. (24° C.), scale divisions at X revolutions per minute Polymer Concentration Revolutions per minute (rpm) API fluid No. % by wt. 600 300 200 100 6 3 loss mL  2 (P) 0.5 95 74 46 33 6 3  60  4 (P) 0.3 108 77 44 30 5 3.5  58  8 (P) 0.3 103 73 39 28 4 3  72 13 (P) 0.3 90 72 38 25 4 3  75 16 (P) 0.3 110 87 53 36 5 3.5  95 18 (P) 0.3 95 73 45 26 4 3  85 20 (P) 0.5 88 67 47 28 4.5 3.5  66 28 (P) 0.3 87 69 39 26 5 3  65 33 (P) 0.3 98 82 59 30 6 3.5  70 36 (P) 0.3 86 63 42 30 5 3.5  68  1 (C) 0.3 94 68 39 26 5 3 115  2 (C) 0.3 290 167 118 67 7.5 4.5 470*  3 (C) 0.3 120 105 77 56 11 5 660*  4 (C) 0.3 275 151 116 59 9 6.5 270*  5 (C) 0.3 168 88 68 38 11 11.5 143*  6 (C) 0.3 225 117 84 43 7 4.5 178* (P) = inventive polymer (ex.: 30 (P) = inventive polymer 30 from Table 1a)) (C) = non-inventive comparative example (ex. 5 (C) = comparative example 5) *values are calculated, since all the water had been expressed before the test had ended.

(67) Table 4 shows the water loss-reducing properties of selected abovementioned examples according to API spec. 10 at 121.1° C. (250° F.) in a stirred filtration test in the Fann HTHP filter press (stirring fluid loss apparatus, SFLA). In order to better show the improved properties of the polymers of the invention compared to the state of the art of the polymers claimed in EP1045869 (comparative example 1), the concentration of the polymers used was varied between 0.25% and 0.5% by weight. It becomes clear that, with the polymers of the invention at lower concentrations (0.25% by weight), water loss is reduced by 40% compared to by weight (80 mL) than with the claimed polymers in EP 1045869 (130 mL).

(68) Formulation of the cement slurries:

(69) 100 g of Dyckerhoff Class G Cement

(70) 35 g of silica flour

(71) 54.8 g of distilled water

(72) Polymer in the concentration specified in table 3 or 4

(73) 0.3 g of dispersant (polynaphthalenesulfonate, PNS)

(74) 0.5 g of retarder (lignosulfonate)

(75) TABLE-US-00012 TABLE 4 (Use test at 250° F. (121.1° C.)) Rheology after mixing at 75° F. (24° C.), scale divisions at X revolutions per minute Polymer Concentration Revolutions per minute (rpm) API fluid No. % by wt. 600 300 200 100 6 3 loss mL  1 (C) 0.25 167 91 63 34 5 3.5 130  1 (C) 0.5 >300 168 117 64 7.5 5.0 52  4 (P) 0.25 170 91 63 34 5 3.5 80  4 (P) 0.5 >300 174 119 65 7 4.5 42  2 (P) 0.5 295 164 113 62 7 4.5 44  4 (P) 0.5 >300 174 119 65 7 4.5 42 13 (P) 0.5 >300 179 126 70 8 5 40  7 (P) 0.5 >300 174 123 68 7 4 43 31 (P) 0.5 >300 167 121 58 7.5 3.5 54 26 (P) 0.5 295 173 119 64 7 4.5 60 (P) = inventive polymer (ex.: 30 (P) = inventive polymer 30 from Table 1a))

(76) Table 5 shows the water loss-reducing properties of selected abovementioned mixture of starch and the polymers of the invention according to API spec. 10 under various temperature conditions (250° F., 300° F. and 350° F.) in a stirred filtration test in the Fann HTHP filter press (stirring fluid loss apparatus, SFLA).

(77) Formulation of the cement slurries:

(78) 100 g of Dyckerhoff Class G Cement

(79) 35 g of silica flour

(80) 54.8 g of distilled water

(81) Polymer in the concentration specified in table 3 or 4

(82) 0.3 g of dispersant (polynaphthalenesulfonate, PNS) 0.5-1.5 g of retarder (lignosulfonate)

(83) TABLE-US-00013 TABLE 5 (Use tests of the mixtures at different temperatures) Rheology after mixing at 75° F. (24° C.), scale divisions at X revolutions per minute Polymer Revolutions per minute (rpm) API fluid No. Temp. ° F. 600 300 200 100 6 3 loss mL 2 250 188 104 71 38 5 4 102 4 250 173 93 63 34 6 5 106 3 250 208 115 79 43 6 4.5 60 2 300 191 108 74 42 8.5 9 52 4 300 203 113 78 43 7.5 6.5 46 3 300 242 133 94 52 9 7.5 43 3 300 228 127 88 49 9 7.5 41 2 350 206 119 91 50 15 14 96 3 350 217 123 89 54 13.5 12.5 92 (P) = inventive polymer (ex.: 30 (P) = inventive polymer 30 from table 1a))

(84) It was therefore an object of the present invention to provide polymers which can help to achieve improved control of liquid loss in the cement slurries for cementing wellbores at temperatures between 80° F. and 300° F. WO-99/26991 describes copolymers of AMPS and acrylamide. Table 4 on page 23 discloses that there is a distinct decline in the water loss-reducing properties of the polymers described within a temperature range between 100° F. and 200° F., and doubling of the water loss in some cases in the use test. The addition of acrylic acid in the polymers of the invention distinctly improves the water loss compared to the polymers of WO-99/26991. The comparative examples which follow are intended to demonstrate this.

(85) Comparative examples according to WO-99/26991: Comparative Polymer 7: (not in accordance with the invention, prepared according to WO-99/26991—copolymer of acryloyldimethyltaurate 70% by weight and acrylamide 30% by weight)

(86) In a 3 liter Quickfit flask with anchor stirrer, reflux condenser with offgas scrubber, combined thermometer/pH meter and a gas inlet tube, 50 ml of distilled water are added to 1700 g of anhydrous 2-methylpropan-2-ol. The reaction vessel is in a thermostated heating bath.

(87) This reaction vessel is blanketed with nitrogen gas and, in a gentle nitrogen countercurrent, 245 g of acryloyldimethyltaurate are introduced. The acryloyldimethyltaurate does not dissolve completely in the 2-methylpropan-2-ol/water mixture and is partly in the form of a dispersion of solids. The pH of this mixture is below pH 1. Gaseous ammonia is introduced through the gas inlet tube above the liquid phase until the pH of the dispersion is between 7 and 8. On attainment of the desired pH, the mixture is stirred for a further 1 hour and the pH is recorded continuously. The reaction vessel is blanketed with nitrogen, and 105 g of acrylamide are introduced. After the acrylamide has been introduced, the pH is checked again and, if necessary, corrected to the range of pH 7 to 8. A constant nitrogen stream is passed through the solution for at least 1 hour. After this inertization period, the residual oxygen level is checked by means of an oxygen electrode. Should the residual oxygen value in the liquid phase exceed the value of 1 ppm, another inertization is necessary until this value is attained. Thereafter, in a gentle nitrogen stream, 1.5 g of AIBN are added and the reaction vessel is heated to 60° C. Shortly after the attainment of an internal temperature of 60° C., the introduction of nitrogen gas is ended and commencement of the polymerization reaction is observed, which can be identified by an increase in temperature of 10 to 15° C. About 5-15 minutes after onset of the polymerization reaction, the temperature maximum has been exceeded and the temperature in the reaction vessel is increased by the heating bath up to the boiling point of the 2-methylpropan-2-ol/water mixture. Under gentle reflux, the now viscous mass is stirred for a further two hours. The reaction product, in the form of a viscous suspension of polymer in the 2-methylpropan-2-ol/water mixture, is separated off by filtration and subsequent drying in a vacuum drying cabinet.

(88) Yield: 362 g

(89) Dry content (IR drier, 15 minutes at 120° C.): 97.5%

(90) K value (0.5% solution in distilled water): 208 Comparative Polymer 8 (not in accordance with the invention, prepared according to WO-99/26991 copolymer of acryloyldimethyltaurate 60% by weight and acrylamide 40% by weight)

(91) The comparative example is prepared analogously to comparative polymer 7. Rather than the amounts specified in comparative polymer 7, 210 g of acryloyldimethyltaurate and 140 g of acrylamide are used.

(92) Yield: 371 g

(93) Dry content (IR drier, 15 minutes at 120° C.): 95.5%

(94) K value (0.5% solution in distilled water): 219 Comparative Polymer 9 (not in accordance with the invention, prepared according to WO-99/26991 copolymer of acryloyldimethyltaurate 60% by weight and acrylamide 40% by weight)

(95) The comparative example is prepared analogously to comparative polymer 7. Rather than the amounts specified in comparative polymer 7, 280 g of acryloyldimethyltaurate and 70 g of acrylamide are used.

(96) Yield: 363 g

(97) Dry content (IR drier, 15 minutes at 120° C.): 96%

(98) K value (0.5% solution in distilled water): 201

Examples of Test Results

(99) Testing is effected according to API spec. 10. In an atmospheric consistometer, the cement slurry is stirred/conditioned at analysis temperature and then, at the same temperature, the rheology is measured with the FANN model 35SA viscometer (at high temperature, conditioning is effected at 93° C. and the viscosity is measured) and the water loss is measured at below 120° C. with a Baroid HTHP filter press and at above 120° C. with the stirring fluid loss test apparatus. The setting times were determined with an Autoclave Engineers HTHP consistometer. Formulation of the cement slurries: ad 100% Dyckerhoff Class G Cement, 43.7% distilled water, 0.3% polymer.

(100) Table 6 shows the water loss-reducing properties of selected abovementioned examples according to API spec. 10 at 35° C. (95° F.) in a static filtration test in the Baroid HTHP filter press. This makes it clear that it was possible with the polymers of the invention to considerably improve the reduction in water loss at low temperatures compared to the comparative examples. Comparative example 7 differs from comparative example 1 merely by a somewhat smaller amount of initiator (1.5 g rather than 2.0); the measured K value for both polymers mentioned is identical to the value reported in WO-99/26991 and is 212. Both polymers were synthesized by the same method as a precipitation polymer in tert-BuOH.

(101) TABLE-US-00014 TABLE 6 API spec. 10 at 35° C. (95° F.) of the polymers of the invention compared to comparative examples 1 and 6 to 8 Rheology after mixing at 75° F. (24° C.), scale divisions at X revolutions per minute Polymer Concentration Revolutions per minute/rpm API fluid No. % by wt. 600 300 200 100 6 3 loss mL  2 (P) 0.5 95 74 46 33 6 3 60  4 (P) 0.3 108 77 44 30 5 3.5 58  8 (P) 0.3 103 73 39 28 4 3 72 13 (P) 0.3 90 72 38 25 4 3 75 20 (P) 0.5 88 67 47 28 4.5 3.5 66 28 (P) 0.3 87 69 39 26 5 3 65 33 (P) 0.3 98 82 59 30 6 3.5 70 36 (P) 0.3 86 63 42 30 5 3.5 68  1 (C) 0.3 94 68 39 26 5 3 115  7 (C) 0.3 96 72 41 26 4.5 3.5 109  8 (C) 0.3 113 81 47 29 6 3 121  9 (C) 0.3 87 75 54 33 6 4 116 (P) = polymer (C) = comparative example

(102) TABLE-US-00015 TABLE 7 API spec. 10 at 250° F. (121.1° C.) of the polymers of the invention compared to comparative examples 1 and 6 to 8 Rheology after mixing at 75° F. (24° C.), scale divisions at X revolutions per minute Polymer Concentration Revolutions per minute/rpm API fluid No. % by wt. 600 300 200 100 6 3 loss mL  4 (P) 0.5 >300 174 119 65 7 4.5 42  2 (P) 0.5 295 164 113 62 7 4.5 44 13 (P) 0.5 >300 179 126 70 8 5 40  7 (P) 0.5 >300 174 123 68 7 4 43 31 (P) 0.5 >300 167 121 58 7.5 3.5 54  1 (C) 0.5 >300 168 117 64 7.5 5.0 52  7 (C) 0.5 >300 175 113 67 7 5 54  8 (C) 0.5 >300 187 129 72 8 6 60  9 (C) 0.5 >300 159 110 63 7 4.5 58 (P) = polymer (C) = comparative example

(103) In table 6, it was possible to detect an improvement in the water loss-reducing properties at 95° F. The water loss-reducing properties of comparative example 7 by direct comparison with comparative example 1 show nearly identical values and demonstrate the reproducibility of the process used. Nevertheless, the water loss of comparative polymers 1 and 6 to 9 at an average of 115 mL+/−5 mL is distinctly higher than that of the polymers of the invention. The difference in the water loss of the polymers of the invention relative to the comparative polymers was between 30 and 55 mL. This demonstrates clearly that the addition of acrylic acid leads to a technical improvement at low temperatures.

(104) Table 7 shows the water loss-reducing properties of selected abovementioned examples according to API spec. 10 at 250° F. (121.1° C.) in a static filtration test in the Baroid HTHP filter press. In this test too, it was possible to show that the polymers of the invention have a demonstrably lower water loss at temperatures between 80° F. and 300° F. and under identical experimental conditions than the polymers of WO-99/26991. Running the comparison between comparative example 7 of WO-99/26991 and comparative example 1 (according to EP 1045869) again, the good reproducibility of the process used is shown in this test as well. The use tests conducted according to API spec. 10 at 95° F. and 250° F. demonstrate clearly that addition of acrylic acid to the polymers of the invention leads to an improvement in the water loss-reducing properties.