Temperature-stable, electrolytic hydrogel and method for stimulating crude oil and natural gas deposits

Abstract

The invention relates to a temperature-stable hydrogel comprising electrolytic water and a copolymer cross-linked to multivalent metal ions. The invention is characterized in that the copolymer contains at least structural units which are derived at up to 0.005-20% by weight from an ethylenically unsaturated phosphonic acid and alkali metal salts thereof and/or ammonia salts, up to 5-40% by weight from an ethylenically unsaturated sulfuric acid and alkali metal salts thereof and/or ammonia salts and up to 5-94.995% by weight from an amide of an ethylenically unsaturated carboxylic acid selected from the group of acrylamide, methacrylamide and/or C.sub.1-C.sub.4 alkyl derivatives, wherein the percentages are based on the total mass of the monomers used during copolymerization, and that the multivalent metal ions for cross-linking of the copolymers belong to the groups IIIA, IVB, VB, VIIIB and/or VIIIB of the periodic system of elements.

Claims

1. Temperature-stable hydrogel containing water, comprising: at least one electrolyte and a copolymer cross-linked with polyvalent metal ions, wherein said copolymer contains structural units of which 0.005-20% by weight of the total mass of monomers of said copolymer are of an ethylenically unsaturated phosphonic acid and at least one alkali metal salt or ammonium salt of said ethylenically unsaturated phosphonic acid; 5-40% by weight of the total mass of monomers of said copolymer are of an ethylenically unsaturated sulfonic acid and at least one alkali metal salt or ammonium salt of said ethylenically unsaturated sulfonic acid; and 5-94.995% by weight of the total mass of monomers of said copolymer are an amide of an ethylenically unsaturated carboxylic acid selected from the group consisting of acrylamide, methacrylamide and C.sub.1-C.sub.4-alkyl derivatives thereof, wherein said polyvalent metal ions are selected from the group consisting of groups IIIA, IVB, VB, VIB, VIIB and/or VIIIB of the periodic table; and wherein the electrolyte content in said hydrogel is between 0.075 and 25% by weight relative to the total mass of the hydrogel.

2. The hydrogel of claim 1, wherein said hydrogel has a gel character up to 250 C.

3. The hydrogel of claim 1, wherein the electrolyte content of said hydrogel is between 0.1 and 10% by weight relative to the total quantity of said hydrogel.

4. The hydrogel of claim 1, wherein said electrolyte comprises at least one of alkali-metal halides and alkaline earth metal halides.

5. The hydrogel of claim 1, wherein said electrolyte comprises salts of organic amines.

6. The hydrogel of claim 1 wherein said ethylenically unsaturated phosphonic acid is selected from the group consisting of vinylphosphonic acid, allylphosponic acid, their alkali metal salts and ammonium salts.

7. The hydrogel of claim 1, wherein said amide of the ethylenically unsaturated carboxylic acid is selected from the group consisting of acrylamide and methacrylamide.

8. The hydrogel of claim 1, wherein said ethylenically unsaturated sulfonic acid is selected from the group consisting of vinylsulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 2-methacrylamido-2-methylpropane sulfonic acid, styrene sulfonic acid, their alkali metal salts and ammonium salts thereof.

9. The hydrogel of claim 1, wherein said copolymer additionally contains structural units comprising: at least one of an ethylenically unsaturated carboxylic acid, its alkali metal salts and ammonium salts; and an additional copolymerisable monomer, selected from the group consisting of alkyl esters of ethylenically unsaturated carboxylic acids, oxyalkyl esters of ethylenically unsaturated carboxylic acids, esters of ethylenically unsaturated carboxylic acids with N, N-dialkylalkanol amines and N-vinylamides.

10. The hydrogel of claim 9, wherein said ethylenically unsaturated carboxylic acid is a derivative of acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid, crotonic acid, their alkali metal salts and ammonium salts.

11. The hydrogel of claim 9, wherein said alkyl ester is of acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid or crotonic acid; wherein said oxyalkylester is a 2-hydroxyethyl ester of acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid or crotonic acid; wherein said ester of ethylenically unsaturated carboxylic acids is N,N-dimethylethanolamine methacrylate, its salts or quaternary products; and wherein said N-vinylamides are at least one of N-vinylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide and cyclic N-vinylamide compounds.

12. The hydrogel of claim 1, wherein said copolymer has been produced by inverse emulsion polymerisation.

13. The hydrogel of claim 1, wherein said copolymer has a weight-average molecular weight of at least 1 million Daltons when measured in a non-cross-linked state.

14. The hydrogel of claim 1, wherein said polyvalent metal ions are selected from the group consisting of cations of zirconium, aluminium, boron, titanium, chromium and iron.

15. The hydrogel of claim 1, wherein said copolymer is present in a concentration of 0.1 to 10% by weight, relative to the total quantity of said hydrogel.

16. A method for hydraulic fracturing of crude oil or natural gas deposits or reservoir stimulation of underground waters, comprising: pressing a hydrogel containing water into a crude oil or natural gas deposit wherein said hydrogel comprises: at least one electrolyte and a copolymer cross-linked with polyvalent metal ions, wherein said copolymer contains structural units of which 0.005-20% by weight of the total mass of monomers of said copolymer are of an ethylenically unsaturated phosphonic acid and at least one alkali metal salt or ammonium salt of said ethylenically unsaturated phosphonic acid; 5-40% by weight of the total mass of monomers of said copolymer are of an ethylenically unsaturated sulfonic acid and at least one alkali metal salt or ammonium salt of said ethylenically unsaturated sulfonic acid; and 5-94.995% by weight of the total mass of monomers of said copolymer are an amide of an ethylenically unsaturated carboxylic acid selected from the group consisting of acrylamide, methacrylamide and C1-C4-alkyl derivatives thereof, wherein said polyvalent metal ions are selected from the group consisting of groups IIIA, IVB, VB, VIB, VIIB and/or VIIIB of the periodic table; and wherein the electrolyte content in said hydrogel is between 0.075 and 25% by weight relative to the total mass of the hydrogel.

17. The method of claim 16, wherein said hydrogel is made by: adding said copolymer to an electrolyte solution to make an electrolyte-containing copolymer solution; adding a buffer to said electrolyte-containing copolymer solution, wherein said copolymer forms a three dimensional network; adding additives and supporting bodies to said electrolyte-containing copolymer solution; and introducing into said crude oil or natural gas deposit a solution of a salt containing a polyvalent cation of at least one of groups IIIA, IVB, VB, VIB, VIIB and/or VIIIB of the periodic table.

18. The method of claim 16, wherein saline is used to make said copolymer solution.

Description

EXAMPLES 1-4

POLYMERISATION IN INVERSE EMULSION

Example 1

Preparation of Polymer 1

(1) 37 g of sorbitan monooleate was dissolved in 160 g of C.sub.11-C.sub.16-isoparaffin. 100 g of water was placed in a glass beaker, cooled to 5 C. and 50 g of 2-acrylamido-2-methylpropane sulfonic acid and 10 g of vinylphosphonic acid were added. The pH was adjusted to 7.1 by means of an aqueous ammonia solution (25%). 223 g of acrylamide solution (60% solution in water) was then added.

(2) The aqueous monomer solution was added to the solution of C.sub.11-C.sub.16 isoparaffin and sorbitan monooleate whilst agitating vigorously. It was rendered inert for 45 min with nitrogen.

(3) For starting, 0.5 g of azoisobutyronitrile was dissolved in 12 g of C.sub.11-C.sub.16 isoparaffin and added to the reaction mixture. The solution was then heated to 50 C.

(4) As soon as the maximum temperature was reached, the solution was heated by means of an oil bath for 2 h to 80 C. The suspension was cooled to room temperature and could be used without further processing.

Example 2

Preparation of Polymer 2

(5) Preparation took place similarly to polymer 1 but with the following monomer composition:

(6) 50 g of 2-acrylamido-2-methylpropane sulfonic acid, 223 g of acrylamide solution (60% solution in water), 18 g of vinylphosphonic acid.

Example 3

Preparation of Polymer 3 (Comparison)

(7) Preparation took place similarly to polymer 1 but with the following monomer composition:

(8) 50 g of 2-acrylamido-2-methylpropane sulfonic acid, 223 g of acrylamide solution (60% solution in water), 10 g acrylic acid.

Example 4

Preparation of Polymer 4 (Comparison)

(9) Preparation took place similarly to polymer 1 but with the following monomer composition:

(10) 50 g of 2-acrylamido-2-methylpropane sulfonic acid, 223 g of acrylamide solution (60% solution in water).

(11) The comparative polymers 3 and 4 were prepared in order to show that the preparation of the hydrogel is predominantly based on the interaction of the phosphonic acid function with the cross-linking agent ion. Only when vinylphosphonic acid is present, is it possible to produce reversibly cross-linkable hydrogels in the presence of salt ions. This should be confirmed by Examples 5 to 10.

Example 5

(Comparison): Cross Linking of the Polymer from Example 4 in Deionized Water

(12) In a commercially available Waring Blender 1 g of isotridecanolethoxylate (6EO) was dissolved in 199 g of de-ionized water by rapid mixing. Then 0.24 g of sodium thiosulfate was added whilst agitating. 3.23 g of the polymer emulsion from Example 4 (solid content: 27%) was injected into the funnel of the agitating container and agitated for another four minutes. Then 1 g of acetic acid solution (6% solution in water) and 1.04 g of zirconium (IV)-triethanolamine solution (25% solution in water) were added slowly whilst stirring and agitated for another one minute.

(13) The gel was poured into a cylindrical measuring cell of a rheometer flushed with N.sub.2 and the cell was sealed in a pressure-tight manner. In order to prevent boiling of the sample, the closed measuring cell was exposed to a differential pressure of 50 bar. N.sub.2 gas was used for the pressurization.

(14) Initially the reversibility of the cross-linking of the comparative polymer containing acrylic acid was investigated in de-ionized water at 65 C. and 200 C. The following shear rate ramp was predefined for these viscosity measurements: 6 cycles with the shear rate ramp 511 (3.5 min), 360 (15 s), 170 (15 s), 100 (15 s), 75 (15 s), 100 (13.5 min). The total measurement took 90 minutes.

(15) FIG. 1a shows the reversibility of the cross-linking of the comparative polymer from Example 4 at 65 C. The upper curve in FIG. 1a shows the behaviour of the viscosity and the lower curve shows the behaviour of the shear rate.

(16) FIG. 1b shows the reversibility of the cross-linking of the comparative polymer from Example 4 at 200 C. The upper curve in FIG. 1b shows the behaviour of the viscosity and the lower curve shows the behaviour of the shear rate.

(17) The viscosity measurement at 65 C. with the comparative polymer 4 shows that the cross-linking with the zirconium cross-linking agent in distilled water is only weakly defined (FIG. 1a). At 200 C. the viscosity is so low that no hydrogel capable of carrying supporting media is present (FIG. 1b).

Example 6

(Comparison): Cross-Linking of the Polymer from Example 4 in 2% KCl Solution

(18) In a commercially available Waring Blender, 1 g of isotridecanolethoxylate (6EO) was dissolved in 199 g of de-ionized water by rapid mixing. Then 0.24 g of sodium thiosulfate and 4 g of KCl were added whilst agitating. 4.39 g of the polymer emulsion from Example 4 (solid content: 27%) was injected into the funnel of the agitating container and agitated for a further four minutes. Then 0.5 g of 6% acetic acid solution and 0.8 g of a zirconium (IV)-triethanolamine solution (32.5% solution in ethanol) was added slowly whilst agitating and agitated for another one minute.

(19) The gel was poured into a cylindrical measuring cell of a rheometer flushed with N.sub.2 and the viscosity was measured at a shear rate of 100 s.sup.1, at 50 bar and 65 C.

(20) FIG. 2 shows the viscosity of the hydrogel in the presence of 2% KCl (comparative polymer from Example 4, 100 s.sup.1 and 65 C.).

(21) The hydrogel from Polymer 4 has a low viscosity at constant shear in the presence of 2% KCl and is not suitable for fracturing formulations with HCl (FIG. 2).

Example 7

(Comparison): Cross-Linking of the Polymer from Example 3 in De-Ionized Water

(22) The gel was prepared and characterized using the polymer emulsion from Example 3 similarly to the procedure described in Example 5.

(23) FIG. 3a shows the reversibility of the cross-linking of the comparative polymer from Example 3 at 65 C. The upper curve in FIG. 3a shows the behaviour of the viscosity and the lower curve shows the behaviour of the shear rate.

(24) FIG. 3b shows the reversibility of the cross-linking of the comparative polymer from Example 3 at 200 C. The upper curve in FIG. 3b shows the behaviour of the viscosity and the lower curve shows the behaviour of the shear rate.

(25) The hydrogel from comparative polymer 3, a copolymer of AMPS, acrylamide and acrylic acid has a higher viscosity in distilled water compared to the comparative polymer from Example 4 both at 65 C. and at 200 C. (FIGS. 3a and 3b).

Example 8

(Comparison): Cross-Linking of the Polymer from Example 3 in a 2% KCl-Solution

(26) The gel was prepared and characterized using the polymer emulsion from Example 3 similarly to the procedure described in Example 6.

(27) FIG. 4 shows the viscosity of the hydrogel in the presence of 2% KCl (comparative polymer from Example 3, 100 s.sup.1 and 65 C.).

(28) The hydrogel from the comparative polymer 3, a copolymer of AMPS, acryl-amide and acrylic acid, like the hydrogel from Example 4 in the presence of KCl shows no stability (FIG. 4).

Example 9

Cross-Linking of the Polymer from Example 1 in De-Ionized Water

(29) The gel was prepared and characterized using the polymer emulsion from Example 1 similarly to the procedure described in Example 5.

(30) FIG. 5a shows the reversibility of the cross-linking of polymer 1 at 65 C. The upper curve in FIG. 5a shows the behaviour of the viscosity and the lower curve shows the behaviour of the shear rate.

(31) FIG. 5b shows the reversibility of the cross-linking of polymer 1 at 200 C. The upper curve in FIG. 5b shows the behaviour of the viscosity and the lower curve shows the behaviour of the shear rate.

(32) Hydrogels from polymer 1 show structurally viscous behaviour in distilled water both at 65 C. and at 200 C. They are reversibly cross-linkable and suitable for transporting supporting agents in fracturing applications.

Example 10

Cross-Linking of the Polymer from Example 1 in a 2% KCl Solution

(33) The gel was prepared and characterized using the polymer emulsion from Example 1 similarly to the procedure described in Example 6.

(34) FIG. 6 shows the viscosity of the hydrogel in the presence of 2% KCl (Polymer 1, 100 s.sup.1 and 65 C.).

(35) The hydrogel from polymer 1 also has a high viscosity in the presence of 2% KCl and is suitable for use as thickening agent in frac fluids.

Example 11

Cross Linking of the Polymer from Example 2 in a 2% KCl-Solution at 200 C., 160 C. and 82 C.

(36) The gel was prepared using the polymer emulsion from Example 2 similarly to the procedure described in Example 6. The gel viscosity was measured on the rheometer at 50 bar, 160 C. and a shear of 100 s.sup.1.

(37) FIG. 7 shows the viscosity of the hydrogel in the presence of 2% KCl at 200 C., 160 C, 82 C. (Polymer 2, 100 s.sup.1).

(38) Stable hydrogels are formed with polymer 2 which also have sufficiently high viscosity in the presence of 2% KCl at temperatures of 200 C.

Example 12

Polymer from Example 2 in Artificial Seawater at 160 C. and 82 C.

(39) In a commercially available Waring Blender, 5.97 g of NaCl and 0.60 g of CaCl.sub.2 were dissolved in 192.43 g of de-ionized water by rapid mixing. In the following examples this water was called artificial seawater or electrolyte water. Then 0.24 g of sodium thiosulfate was added whilst agitating. 4.39 g of the polymer emulsion from Example 1 (solid content: 27%) was poured into the funnel of the agitating container and agitated for another four minutes. 1 g of 6% acetic acid solution and 0.26 g of a zirconium (IV)-triethanol-amine solution (32.5% solution in ethanol) were added slowly whilst agitating and agitated for another minute.

(40) The gel was poured into the cylindrical measuring cell of a rheometer flushed with N.sub.2 and the viscosity was measured at the shear rate of 100 s.sup.1, 50 bar and 82 C. or 160 C.

(41) FIG. 8 shows the viscosity of the hydrogel in artificial seawater at 82 C. and 160 C. (Polymer 2, 100 s.sup.1).

Example 13

(Comparison): Rehealing of Hydrogels with Polymer from Example 3 in Artificial Seawater

(42) The gel was prepared using the polymer from Example 3 similarly to the procedure described in Example 12. The investigation of the reversibility of the cross-linking of the acrylic-acid-containing comparative polymer from Example 3 in artificial seawater was carried out on a rheometer at 50 bar and the respective temperature. The following shear rate ramp was predefined for these viscosity measurements: 6 cycles with the shear rate ramp 511 (3.5 min), 360 (15 s), 170 (15 s), 100 (15 s), 75 (15 s), 100 (13.5 min). The total measurement took 90 minutes.

(43) FIG. 9a shows the reversibility of the cross-linking in electrolyte water containing 3% NaCl and 0.3% CaCl.sub.2 (comparative polymer from Example 3 at 82 C.). The upper curve in FIG. 9a shows the behaviour of the viscosity and the lower curve shows the behaviour of the shear rate.

(44) FIG. 9b shows the reversibility of the cross-linking in electrolyte water containing 3% NaCl and 0.3% CaCl.sub.2 (comparative polymer from Example 3 at 130 C.). The upper curve in FIG. 9a shows the behaviour of the viscosity and the lower curve shows the behaviour of the shear rate.

(45) In electrolyte water comprising 3% NaCl and 0.3% CaCl.sub.2 the hydrogel from the acrylic-acid containing polymer exhibits no stability.

Example 14

Rehealing of Hydrogels with Polymer from Example 2 in Artificial Seawater

(46) The gel was prepared similarly to the procedure described in Example 12 and was characterised on the rheometer according to Example 13.

(47) FIG. 10a shows the reversibility of the cross-linking in electrolyte water containing 3% NaCl and 0.3% CaCl.sub.2 (polymer 2, at 82 C.). The upper curve in FIG. 10a shows the behaviour of the viscosity and the lower curve shows the behaviour of the shear rate.

(48) FIG. 10b shows the reversibility of the cross-linking in electrolyte water containing 3% NaCl and 0.3% CaCl.sub.2 (polymer 2, at 130 C.). The upper curve in FIG. 10b shows the behaviour of the viscosity and the lower curve shows the behaviour of the shear rate.

(49) Unlike the hydrogel from the acrylic-acid-containing polymer, the hydrogel from the vinylphosphonic acid-containing polymer 2 exhibits structurally viscous behaviour and can be used for the transport of supporting agents during the hydraulic fracturing of deposit rock.