Anionic thermoviscosifying water-soluble polymers, preparation method and application thereof

Abstract

A method for preparing an anionic thermoviscosifying water-soluble polymer includes the following steps: performing an inverse emulsion polymerization by using acrylamide, acrylic acid and Pluronic triblock polymer. The high reactivity of acrylamide and the inverse emulsion polymerization can increase the molecular weight of the thermoviscosifying polymer, and exhibit an obvious thermoviscosifying effect even at a low polymer concentration, which can reduce the application cost. The dissolution rate of the obtained polymer emulsion is significantly higher than the dissolution rate of the dry powder of the polymer. The obtained emulsion-diluted solution has a relatively strong thermoviscosifying behavior after further adding a small amount of reverse demulsifier, and the emulsion-diluted solution exhibits different thermoviscosifying behaviors as the amount of the reverse demulsifier is increased.

Claims

1. A method for preparing an anionic thermoviscosifying water-soluble polymer, comprising the following steps: (1) preparing an aqueous phase with an acrylamide monomer, an anionic monomer, a temperature-sensitive polyether, an inorganic salt, and deionized water, with pH values in between 6.5 and 7.5; preparing an oil phase by adding an emulsifier to an oil; wherein a percentage of the aqueous phase ranges from 10% to 90% based on a total mass of both the aqueous phase and the oil phase; obtaining an emulsion by uniformly mixing the aqueous phase and the oil phase under stirring or gradually adding the aqueous phase to the oil phase to be emulsified; adding an initiator in the emulsion under an inert gas atmosphere to form an emulsion system; increasing a temperature of the emulsion system to 40-60 C. to initiate a polymerization, or performing a photo-initiated polymerization on the emulsion by heating the emulsion to 40-60 C. without adding the initiator; and after completing the polymerization or the photo-initiated polymerization, keeping the temperature for 2-6 hours to obtain an inverse emulsion of the anionic thermoviscosifying water-soluble polymer; wherein, mass percentages of various components in the aqueous phase are as follows: 20%-50% of the acrylamide monomer, 5%-15% of the anionic monomer, 1%-20% of the temperature-sensitive polyether, and 1%-10% of the inorganic salt; in the oil phase, a mass percentage of the emulsifier is 1%-20%; and the emulsifier is a triblock polymeric emulsifier of long-chain fatty acid-polyoxyethylene-long-chain fatty acid, the initiator is at least one selected from the group consisting of a hydrogen peroxide-based initiator, an azo-based initiator, and a benzoin-series initiator; the hydrogen peroxide-based initiator is ammonium peroxide or potassium peroxide, the azo-based initiator is 2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride or azobisisobutyronitrile, and the benzoin-series initiator is benzoin dimethyl ether; and an amount of the initiator is 0.006% to 0.3% based on a total mass of the acrylamide monomer, the anionic monomer, and the temperature-sensitive polyether, the anionic monomer is a salt obtained by a neutralization of acrylic acid, methacrylic acid, or 2-acrylamide-2-methylpropanesulfonic acid, and a base used for the neutralization is at least one selected from the group consisting of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate; and (2) precipitating, washing, centrifuging, and drying the inverse emulsion to obtain a dry powder of the anionic thermoviscosifying water-soluble polymer; or adding a reverse demulsifier to the inverse emulsion to obtain an emulsion of the anionic thermoviscosifying water-soluble polymer, followed by dissolution in water and dilution to obtain desired diluted solutions, wherein the temperature-sensitive polyether is a triblock polymer of polyoxyethylene-polyoxypropylene-polyoxyethylene with a structural formula of: ##STR00003## wherein a structure and a property of the temperature-sensitive polyether vary with values of m and n.

2. The method for preparing the anionic thermoviscosifying water-soluble polymer of claim 1, wherein, the acrylamide monomer is acrylamide or a mixture of acrylamide and another monomer, wherein the other monomer is at least one selected from the group consisting of methacrylamide, N,N-dimethylacrylamide, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, and N-vinylpyrrolidone; and a mass percentage of the acrylamide in the mixture is greater than 50%.

3. The method for preparing the anionic thermoviscosifying water-soluble polymer of claim 1, wherein, the inorganic salt is at least one selected from the group consisting of sodium chloride, sodium acetate, sodium nitrate, and potassium nitrate.

4. The method for preparing the anionic thermoviscosifying water-soluble polymer of claim 1, wherein, the oil is at least one selected from the group consisting of a cycloalkane, an aromatic hydrocarbon, a linear saturated hydrocarbon and a linear unsaturated hydrocarbon.

5. An anionic thermoviscosifying water-soluble polymer prepared by the method of claim 1, wherein a molecular weight of the anionic thermoviscosifying water-soluble polymer is from greater than 2.010.sup.6 g.Math.mol.sup.1 to 8.610.sup.6 g.Math.mol.sup.1.

6. A method of a polymer flooding in an enhanced oil recovery, comprising the step of injecting the anionic thermoviscosifying water-soluble polymer of claim 5 into an underground formation.

7. The anionic thermoviscosifying water-soluble polymer of claim 5, wherein, the acrylamide monomer is acrylamide or a mixture of acrylamide and another monomer, wherein the other monomer is at least one selected from the group consisting of methacrylamide, N,N-dimethylacrylamide, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, and N-vinylpyrrolidone; and a mass percentage of the acrylamide in the mixture is greater than 50%.

8. The anionic thermoviscosifying water-soluble polymer of claim 5, wherein, the inorganic salt is at least one selected from the group consisting of sodium chloride, sodium acetate, sodium nitrate, and potassium nitrate.

9. The anionic thermoviscosifying water-soluble polymer of claim 5, wherein, the oil is at least one selected from the group consisting of a cycloalkane, an aromatic hydrocarbon, a linear saturated hydrocarbon and a linear unsaturated hydrocarbon.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is showing viscosity-temperature curves (shear rate {dot over ()}=10 s.sup.1) of aqueous solutions of TVP-P1 powder and TVP-P2 powder obtained in example 19 and example 20 at a concentration of 0.20%;

(2) FIG. 2 is showing viscosity-temperature curves ({dot over ()}=10 s.sup.1) of aqueous solutions of TVP-P1 powder and TVP-P4 powder respectively obtained in example 19 and example 22 at a concentration of 0.20%;

(3) FIG. 3A is showing viscosity-shear rate curves (T=45 C.) of aqueous solutions of TVP-P1 powder obtained in example 19 at different concentrations;

(4) FIG. 3B is showing viscosity-shear rate curves (T=45 C.) of aqueous solutions of TVP-P2 powder obtained in example 20 at different concentrations;

(5) FIG. 3C is showing viscosity-shear rate curves (T=45 C.) of aqueous solutions of TVP-P3 powder obtained in example 21 at different concentrations;

(6) FIG. 3D is showing viscosity-shear rate curves (T=45 C.) of aqueous solutions of PAMA powder obtained in example 24 at different concentrations;

(7) FIG. 4A is showing viscosity-temperature curves ({dot over ()}=10 s.sup.1) of aqueous solutions of TVP-P1 powder obtained in example 19 at different concentrations;

(8) FIG. 4B is showing viscosity-temperature curves ({dot over ()}=10 s.sup.1) of aqueous solutions of PAMA powder obtained in example 24 at different concentrations;

(9) FIG. 5A is showing viscosity-temperature curves ({dot over ()}=10 s.sup.1) of aqueous solutions (0.20%) of TVP-P1 powder obtained in example 19 at different concentrations of saline water;

(10) FIG. 5B is showing viscosity-temperature curves ({dot over ()}=10 s.sup.1) of aqueous solutions (0.20%) of PAMA powder obtained in example 24 at different concentrations of saline water;

(11) FIG. 6A is showing viscosity-temperature curves (0.45% NaCl solution, {dot over ()}=10 s.sup.1) of aqueous solutions of TVP-P1 powder obtained in example 19 in saline water at different concentrations;

(12) FIG. 6B is showing viscosity-temperature curves (0.45% NaCl solution, {dot over ()}=10 s.sup.1) of aqueous solutions of PAMA powder obtained in example 24 in saline water at different concentrations;

(13) FIG. 7 is showing viscosity-temperature curves (pure water, {dot over ()}=10 s.sup.1) of an emulsion-diluted solution of ETVP-P1, an aqueous solution of TVP-P1 powder, and an unpolymerized emulsion-diluted solution (0.20%) according to example 19.

(14) FIG. 8 is showing viscosity-temperature curves (pure water, {dot over ()}=10 s.sup.1) of an emulsion-diluted solution (0.20%) of ETVP-P1 obtained in example 19 at different adding amount of a reverse demulsifier.

(15) FIG. 9 is showing viscosity-temperature curves (pure water, {dot over ()}=10 s.sup.1) of an emulsion-diluted solution of EPAMA and an aqueous solution (0.20%) of PAMA powder according to example 24;

(16) FIG. 10 is showing dissolution rate curves (pure water, 25 C., {dot over ()}=10 s.sup.1) of an aqueous solution of TVP-P1 powder, and an emulsion-diluted solution (0.20%) of ETVP-P1 according to example 29 and example 30;

(17) FIG. 11 is showing aging curves (0.45% NaCl solution, T=45 C., {dot over ()}=10 s.sup.1) of an aqueous solution (0.15%) of TVP-P1 powder obtained in example 31 and an aqueous solution (0.20%) of PAMA powder obtained in example 32;

(18) FIG. 12 is showing aging curves (0.45% NaCl solution, T=45 C., =10 s.sup.1) of an aqueous solution (0.15%) of TVP-P1 powder obtained in example 31 and an emulsion-diluted solution (0.10%) of ETVP-P1 obtained in example 33;

(19) FIG. 13 is showing flowing curves (0.45% NaCl solution, T=45 C.) of an aqueous solution (0.15%) of TVP-P1 powder obtained in example 34 and an aqueous solution (0.20%) of PAMA powder obtained in example 35;

(20) FIG. 14 is showing flowing curves (0.45% NaCl solution, T=45 C.) of an aqueous solution (0.15%) of TVP-P1 powder obtained in example 34 and an emulsion-diluted solution (0.10%) of ETVP-P1 obtained in example 36;

(21) FIG. 15 is showing core flooding curves (0.45% NaCl solution, T=45 C.) of an aqueous solution (0.15%) of TVP-P1 powder obtained in example 37 and an aqueous solution (0.20%) of PAMA powder obtained in example 38 (R, Recovery factor; F, Pore pressure, i.e., pressure difference between inlet and outlet in porous media during a polymer flooding process); and

(22) FIG. 16 is showing core flooding curves (0.45% NaCl solution, T=45 C.) of an aqueous solution (0.15%) of TVP-P1 powder obtained in example 37 and a diluted emulsion solution (0.10%) of ETVP-P1 obtained in example 39 (R, Recovery factor; F, Pore pressure, i.e., pressure difference between inlet and outlet in porous media during a polymer flooding process).

DETAILED DESCRIPTION OF THE EMBODIMENTS

(23) The following examples further describe the present invention in detail. The examples are intended to help those skilled in the art to understand the present invention completely, but are not intended to limit the present invention in any way.

(24) In the following examples, mass percentages of various components in the aqueous phase are recited based on 100% of the total mass of the aqueous phase, and mass percentages of various components in the oil phase are recited based on 100% of the total mass of the oil phase.

(25) The molecular weight of the polymers in the following examples is determined by static light scattering.

(26) The initial viscosity of the polymer solutions used in the subsequent aging, flow and core flooding experiments in the following examples are consistent. The concentration of the emulsion-diluted solution is measured by the concentration of the anionic thermoviscosifying water-soluble polymers, and the active content of the emulsion should be calculated upon dilution: active content of emulsion=mass of anionic thermoviscosifying watersoluble polymer/mass of emulsion100%.

Examples 1-18

(27) In the following tables, the optimal inverse emulsion ratio was examined from four aspects, i.e., emulsifier type, oil-water ratio, monomer loading, and presence or absence of NaAA, to obtain the optimal anionic thermoviscosifying polymer.

(28) TABLE-US-00001 TABLE 1 Effect of nature of emulsifier on emulsion state Oil phase Oil-water Emulsion No. Oil Emulsifier ratio state Note.sup.a 1 Mineral oil Span 85 5:5 O/W x 2 Mineral oil Span 85:HB246 = 21:1 5:5 O/W x 3 Mineral oil Span 85:HB246 = 7:1 5:5 O/W x 4 Mineral oil Span 85:HB246 = 4:1 5:5 O/W x 5 Mineral oil Span 85:HB246 = 2:1 5:5 O/W x 6 Mineral oil MOA-3 5:5 O/W x 7 Mineral oil HB246 5:5 W/O .sup.ax denotes that no inverse emulsion is successfully prepared, and denotes that an inverse emulsion is successfully prepared.

(29) TABLE-US-00002 TABLE 2 Effect of oil-water ratio on emulsion state Oil phase Oil-water Emulsion No. Oil Emulsifier ratio state Note.sup.a 1 Mineral oil Span 85 5:5 O/W x 8 Mineral oil Span 85 4.5:5.5 O/W x 9 Mineral oil Span 85 4:6 O/W x 10 Mineral oil Span 85 3.5:6.5 O/W x 11 Mineral oil Span 85 3:7 O/W x 2 Mineral oil Span 85:HB246 = 2:1 5:5 O/W x 12 Mineral oil Span 85:HB246 = 2:1 4.5:5.5 O/W x 13 Mineral oil Span 85:HB246 = 2:1 4:6 O/W x 14 Mineral oil Span 85:HB246 = 2:1 3:7 O/W x 7 Mineral oil HB246 5:5 W/O 15 Mineral oil HB246 4.5:5.5 W/O 16 Mineral oil HB246 4:6 O/W x .sup.ax denotes that no inverse emulsion is successfully prepared, and denotes that an inverse emulsion is successfully prepared.

(30) TABLE-US-00003 TABLE 3 Effect of monomer loading on the thickening power of produced polymer Oil phase m.sub.AM/m.sub.F127 Oil-water Polymer No. Oil Emulsifier (wt/wt) ratio property Note.sup.a 15 Mineral HB246 7:1.5 4.5:5.5 Vscosifying oil 17 Mineral HB246 7:0.1 4.5:5.5 Less oil viscosifying .sup.a denotes that the obtained dry powder of the polymer has no thermoviscosifying capacity, and denotes that the obtained dry powder of the polymer has the thermoviscosifying capacity.

(31) TABLE-US-00004 TABLE 4 Effect of presence or absence of NaAA monomer on polymer property NaAA Oil phase m.sub.AM/m.sub.F127 (in aqueous Oil-water No. Oil Emulsifier (wt/wt) phase) ratio Polymer Note.sup.a 15 Mineral oil HB246 7:1.5 0 4.5:5.5 Poor solubility 18 Mineral oil HB246 7:1.5 4.9% 4.5:5.5 Rapid dissolution .sup.a denotes that the obtained dry powder of the polymer requires a long time to be dissolved dissolution, and denotes that the obtained dry powder of the polymer can be rapidly dissolved in water.

(32) Taking example 18 as an example. For preparing an aqueous phase, 31.6% (w/w, the same hereinafter) of acrylamide, 9.5% of sodium acrylate, 8.6% of F127, and 5.0% of sodium chloride were dissolved in deionized water, and the pH value was adjusted to 7.0. 14% of emulsifier HB246 was dissolved in mineral oil, followed by heating to 50 C.; after dissolution of comonomers, the oil phase and the aqueous phase (mass ratio of 4.5:5.5) were successively added to an agitator with homogeneous stirring and emulsification at a high speed. The obtained emulsion was a stable water in oil (W/O) emulsion.

Example 19

(33) For preparing an aqueous phase, 31.7% (w/w, the same hereinafter) of acrylamide, 9.5% of sodium acrylate, 8.6% of F127, and 5.0% of sodium chloride were dissolved in deionized water, and the pH value was adjusted to 7.0. 14% of emulsifier HB246 was dissolved in mineral oil, followed by heating to 50 C.; after dissolution of the comonomers, the oil phase and the aqueous phase (mass ratio, 4.5:5.5) were successively added to an agitator to be emulsified homogeneously under stirring. After the emulsification was completed, the mixture was transferred to a 250 mL four-necked bottom flask equipped with a stirrer, a nitrogen inlet, and a digital thermometer, and the temperature was increased to 45 C. in a water bath. After purging with the nitrogen gas for a certain duration, the initiator AIBN was added, and the polymerization was started. When the temperature reached 45 C., the mixture was continuously stirred at 45 C. for 2 hours. The inverse emulsion ETVP-P1 of the anionic thermoviscosifying water-soluble polymers was obtained, and the obtained inverse emulsion was precipitated, washed, centrifuged, and freeze-dried to obtain dry powders, i.e., TVP-P1. The molecular weight of the polymer was determined to be 7.810.sup.6 g.Math.mol.sup.1.

Example 20

(34) For preparing an aqueous phase, 31.7% (w/w, the same hereinafter) of acrylamide, 9.5% of sodium acrylate, 8.6% of F108, and 5.0% of sodium chloride were dissolved in deionized water, and the pH value was adjusted to 7.0. 14% of emulsifier HB246 was dissolved in mineral oil, followed by heating to 45 C.; after dissolution of the comonomers, the oil phase and the aqueous phase (mass ratio, 4.5:5.5) were successively added to an agitator to be emulsified homogeneously under stirring. After the emulsification was completed, the mixture was transferred to a 250 mL four-necked bottom flask equipped with a stirrer, a nitrogen inlet, and a digital thermometer, and the temperature was increased to 45 C. in a water bath. After purging with nitrogen gas for a certain duration, the initiator AIBN was added, and the polymerization was started. When the thermometer reached 45 C., the mixture was continuously stirred at 45 C. for 2 hours. The inverse emulsion ETVP-P2 of the anionic thermoviscosifying water-soluble polymers was obtained, and the obtained inverse emulsion was precipitated, washed, centrifuged, and freeze-dried to obtain dry powders, i.e., TVP-P2. The molecular weight of the polymer was determined to be 7.410.sup.6 g.Math.mol.sup.1.

Example 21

(35) For preparing an aqueous phase, 31.7% (w/w, the same hereinafter) of acrylamide, 9.5% of sodium acrylate, 8.6% of F68, and 5.0% of sodium chloride were dissolved in deionized water, and the pH value was adjusted to 7.0. 14% of emulsifier HB246 was dissolved in mineral oil, followed by heating to 45 C.; after dissolution of the comonomers, the oil phase and the aqueous phase (mass ratio, 4.5:5.5) were successively added to an agitator to be emulsified homogeneously under stirring. After the emulsification was completed, the mixture was transferred to a 250 mL four-necked bottom flask equipped with a stirrer, a nitrogen inlet, and a digital thermometer, and the temperature was increased to 45 C. in a water bath. After purging with nitrogen gas for a certain duration, the initiator AIBN was added, and the polymerization was started. When the temperature reached 45 C., the mixture was continuously stirred at 45 C. for 2 hours. The inverse emulsion ETVP-P3 of the anionic thermoviscosifying water-soluble polymers was obtained, and the obtained inverse emulsion was precipitated, washed, centrifuged, and freeze-dried to obtain dry powders, i.e., TVP-P3. The molecular weight of the polymer was determined to be 7.510.sup.6 g.Math.mol.sup.1.

Example 22

(36) For preparing an aqueous phase, 36.8% (w/w, the same hereinafter) of acrylamide, 9.5% of sodium acrylate, 3.3% of F127, and 5.0% of sodium chloride were dissolved in deionized water, and the pH value was adjusted to 7.0. 14% of emulsifier HB246 was dissolved in mineral oil, followed by heating to 50 C.; after dissolution of the comonomers, the oil phase and the aqueous phase (mass ratio, 4.5:5.5) were successively added to an agitator to be emulsified homogeneously under stirring. After the emulsification was completed, the mixture was transferred to a 250 mL four-necked bottom flask equipped with a stirrer, a nitrogen inlet, and a digital thermometer, and the temperature was increased to 45 C. in a water bath. After purging with nitrogen gas for a certain duration, the initiator AIBN was added, and the polymerization was started. When the temperature reached 45 C., the mixture was continuously stirred at 45 C. for 2 hours. The inverse emulsion ETVP-P4 of the anionic thermoviscosifying water-soluble polymers was obtained, and the obtained inverse emulsion was precipitated, washed, centrifuged, and freeze-dried to obtain dry powders, i.e., TVP-P4. The molecular weight of the polymer was determined to be 8.310.sup.6 g.Math.mol.sup.1.

Example 23

(37) For preparing an aqueous phase, 23.7% (w/w, the same hereinafter) of acrylamide, 9.5% of sodium acrylate, 16.6% of F127, and 5.0% of sodium chloride were dissolved in deionized water, and the pH value was adjusted to 7.0. 14% of emulsifier HB246 was dissolved in mineral oil, followed by heating to 50 C.; after dissolution of the comonomers, the oil phase and the aqueous phase (mass ratio, 4.5:5.5) were successively added to an agitator to be emulsified homogeneously under stirring. After the emulsification was completed, the mixture was transferred to a 250 mL four-necked bottom flask equipped with a stirrer, a nitrogen inlet, and a digital thermometer, and the temperature was increased to 45 C. in a water bath. After purging with nitrogen gas for a certain duration, the initiator AIBN was added, and the polymerization was started. When the temperature reached 45 C., the mixture was continuously stirred at 45 C. for 2 hours. The inverse emulsion ETVP-P5 of the anionic thermoviscosifying water-soluble polymers was obtained, and the obtained inverse emulsion was precipitated, washed, centrifuged, and freeze-dried to obtain dry powders, i.e., TVP-P5. The molecular weight of the polymer was determined to be 5.210.sup.6 g.Math.mol.sup.1.

Example 24

(38) For preparing an aqueous phase, 40.3% (w/w, the same hereinafter) of acrylamide, 9.5% of sodium acrylate, and 5.0% of sodium chloride were dissolved in deionized water, and the pH value was adjusted to 7.0. 14% of emulsifier HB246 was dissolved in mineral oil, followed by heating to 50 C.; after dissolution of the comonomers, the oil phase and the aqueous phase (mass ratio, 4.5:5.5) were successively added to an agitator to be emulsified homogeneously under stirring. After the emulsification was completed, the mixture was transferred to a 250 mL four-necked bottom flask equipped with a stirrer, a nitrogen inlet, and a digital thermometer, and the temperature was increased to 45 C. in a water bath. After purging with nitrogen gas for a certain duration, the initiator AIBN was added, and the polymerization was started. When the temperature reached 45 C., the mixture was continuously stirred at 45 C. for 2 hours. The inverse emulsion EPAMA of the anionic thermoviscosifying water-soluble polymers was obtained, and the obtained inverse emulsion was precipitated, washed, centrifuged, and freeze-dried to obtain dry powders, i.e., PAMA. The molecular weight of the polymer was determined to be 8.610.sup.6 g.Math.mol.sup.1.

(39) For the inverse emulsions and the aqueous solutions of the polymer dry powder prepared in examples 19-24, the viscosity of the solutions was measured as a function of temperature or shear rate. Further, viscosity of different polymer concentrations in different salt concentrations were measured. Moreover, viscosity of emulsion-diluted solutions with different amounts of reverse demulsifier added were measured at different temperatures. The results were shown in FIG. 1, FIG. 2, FIGS. 3A-3D, FIGS. 4A-4B, FIGS. 5A-5B, FIGS. 6A-6B, FIG. 7 and FIG. 9. The obtained dry powders of the thermoviscosifying polymers have significant thermoviscosifying power in both pure water and saline water, and the obtained emulsion-diluted solutions of the polymers also have significant thermoviscosifying power, and with increasing the amount of the reverse demulsifier, the thermoviscosifying power becomes more obvious.

Example 25

(40) For preparing an aqueous phase, 26.6% (w/w, the same hereinafter) of acrylamide, 5.1% of N-vinylpyrrolidone, 13.5% of sodium acrylate, 8.6% of F127, and 2.0% of sodium chloride were dissolved in deionized water, and the pH value was adjusted to 7.0. 14.0% of emulsifier HB246 was dissolved in mineral oil, followed by heating to 50 C.; after dissolution of the comonomers, the oil phase and the aqueous phase (mass ratio, 4.5:5.5) were successively added to an agitator to be emulsified homogeneously under stirring. After the emulsification was completed, the mixture was transferred to a 250 mL four-necked bottom flask equipped with a stirrer, a nitrogen inlet, and a digital thermometer, and the temperature was increased to 45 C. in a water bath. After purging with nitrogen gas for a certain duration, the initiator AIBN was added, and the polymerization was started. When the temperature reached 45 C., the mixture was continuously stirred at 45 C. for 2 hours. The inverse emulsion ETVP-P6 of the anionic thermoviscosifying water-soluble polymers was obtained, and the obtained dry powder of the polymer was TVP-P6.

Example 26

(41) For preparing an aqueous phase, 31.7% (w/w, the same hereinafter) of acrylamide, 9.5% of sodium acrylate, 8.6% of F127, and 5.0% of sodium chloride were dissolved in deionized water, and the pH value was adjusted to 7.0. 14.0% of emulsifier HB206 was dissolved in mineral oil, followed by heating to 50 C.; after dissolution of the comonomers, the oil phase and the aqueous phase (mass ratio, 4.5:5.5) were successively added to an agitator to be emulsified homogeneously under stirring. After the emulsification was completed, the mixture was transferred to a 250 mL four-necked bottom flask equipped with a stirrer, a nitrogen inlet, and a digital thermometer, and the temperature was increased to 45 C. in a water bath. After purging with nitrogen gas for a certain duration, the initiator AIBN was added, and the polymerization was started. When the temperature reached 45 C., the mixture was continuously stirred for 2 hours. The inverse emulsion ETVP-P7 of the anionic thermoviscosifying water-soluble polymers was obtained, and the obtained dry powder of the polymer was TVP-P7.

Example 27

(42) For preparing an aqueous phase, 31.7% (w/w, the same hereinafter) of acrylamide, 7.5% of 2-acrylamide-2-methylpropanesulfonic acid sodium, 8.6% of F127, and 7.0% of sodium chloride were dissolved in deionized water, and the pH value was adjusted to 7.0. 14.0% of emulsifier HB246 was dissolved in mineral oil, followed by heating to 50 C.; after dissolution of the comonomers, the oil phase and the aqueous phase (mass ratio, 4.5:5.5) were successively added to an agitator to be emulsified homogeneously under stirring. After the emulsification was completed, the mixture was transferred to a 250 mL four-necked bottom flask equipped with a stirrer, a nitrogen inlet, and a digital thermometer, and the temperature was increased to 45 C. in a water bath. After purging with nitrogen gas for a certain duration, the initiator AIBN was added, and the polymerization was started. When the temperature reached 45 C., the mixture was continuously stirred at 45 C. for 2 hours. The inverse emulsion ETVP-P8 of the anionic thermoviscosifying water-soluble polymers was obtained, and the obtained dry powder of the polymer was TVP-P8.

Example 28

(43) For preparing an aqueous phase, 31.7% (w/w, the same hereinafter) of acrylamide, 9.5% of sodium acrylate, 8.6% of F127, and 5.0% of sodium acetate were dissolved in deionized water, and the pH value was adjusted to 7.0. 14.0% of emulsifier HB246 was dissolved in mineral oil, followed by heating to 50 C.; after dissolution of the comonomers, the oil phase and the aqueous phase (mass ratio, 4.5:5.5) were successively added to an agitator to be emulsified homogeneously under stirring. After the emulsification was completed, the mixture was transferred to a 250 mL four-necked bottom flask equipped with a stirrer, a nitrogen inlet, and a digital thermometer, and the temperature was increased to 45 C. in a water bath. After purging with nitrogen gas for a certain duration, the initiator AIBN was added, and the polymerization was started. When the temperature reached 45 C., the mixture was continuously stirred at 45 C. for 2 hours. The inverse emulsion ETVP-P9 of the anionic thermoviscosifying water-soluble polymers was obtained, and the obtained dry powder of the polymer was TVP-P9.

Example 29

(44) 0.20 g of dry powder of polymer TVP-P1 obtained in example 19 was added into 99.80 g of deionized water under mechanical agitation at 600 rpm. The mixture was sampled during a designed interval, and the corresponding viscosity was measured using an Anton Paar rheometer MCR 302 until the viscosity of the emulsion-diluted solution reached constant.

Example 30

(45) 50 g of the inverse emulsion ETVP-P1 obtained in example 19 was demulsified with 1.5 g Hypinvert 3110, and the mixture was homogeneously mixed by continuous shaking for 1 hour in a shaker. 106.0 g of water was added to a beaker under mechanical agitation at 600 rpm. 2.0 g of the emulsion after homogenous mixing was directly injected into stirred water along the vortex shoulder. The mixture was sampled during a designed interval, and the corresponding viscosity was measured using an Anton Paar rheometer MCR 302 until the viscosity of the emulsion-diluted solution reached constant.

(46) The variation in viscosity with increasing temperature corresponding to example 29 and example 30 is depicted in FIG. 10. The emulsion polymer can be rapidly dispersed and dissolved in water within 10 minutes, while the polymer powder requires 120 minutes to be dissolved in water. Therefore, the emulsion polymer obtained by the inverse emulsion polymerization can be directly dispersed in water, which is more convenient for practical use.

Example 31

(47) 0.75 g of dry powder of polymer TVP-P1 obtained in example 19 was dissolved in 499.25 g of 0.45% NaCl (w/w) aqueous solution under agitation at 100 rpm, it took 24 hours for complete dissolution. Under nitrogen gas atmosphere, such a prepared solution from the dry powder of TVP-P1 was placed in a glove box for further degassing to ensure oxygen content of the solution was less than 2 mg.Math.L.sup.1. The solution was then transferred to a sealed stainless-steel cylinder, and aged in an oven at 45 C. In order to ensure that no oxygen was penetrated into the solution, polymer solution was sampled from the cylinder in the glove box, and the corresponding viscosity was measured using the Anton Paar rheometer MCR 302 to obtain the corresponding aging curve of the polymer solution of TVP-P1 powders.

Example 32

(48) As a reference, 1.00 g of dry powder of polymer PAMA obtained in example 24 was dissolved in 499.00 g of 0.45% NaCl (w/w) aqueous solution under agitation speed of 100 rpm, and a dissolution time was 24 hours. Under nitrogen gas atmosphere, such a prepared solution from the dry powder PAMA was placed in a glove box for further degassing to ensure the oxygen content of the solution less than 2 mg.Math.L.sup.1. The solution was then transferred to a sealed stainless-steel cylinder for a long-term aging stability monitoring in an oven at 45 C. In order to ensure that no oxygen was penetrated into the solution, polymer solution was sampled from the cylinder in the glove box, and the corresponding viscosity was measured using the Anton Paar rheometer MCR 302 to obtain the corresponding aging curve of the polymer solution of PAMA powders.

(49) The comparison of the aging results corresponding to example 31 and example 32 is shown in FIG. 11. The viscosity of both polymer solutions is the same at an initial stage of aging, but the long-term thermal stability TVP-P1 solution is higher than that of the PAMA solution over continuous aging.

Example 33

(50) 2.50 g of the inverse emulsion ETVP-P1 containing reverse demulsifier, obtained in example 30, was dispersed in 497.50 g of 0.45% NaCl (w/w) aqueous solution under stirring at 600 rpm, and it took 10 minutes to be completely dissolved. Under nitrogen gas atmosphere, such a prepared emulsion-diluted solution ETVP-P1 was placed in a glove box for further degassing to ensure oxygen content less than 2 mg.Math.L.sup.1. The solution was then transferred to a sealed stainless-steel cylinder, and aged in an oven at 45 C. In order to ensure that no oxygen has penetrated into the solution, the polymer solution was sampled in a certain interval from the cylinder in the glove box, and the corresponding viscosity was measured using the Anton Paar rheometer MCR 302 to obtain a corresponding aging curve of emulsion-diluted solution of ETVP-P1.

(51) The comparison of the aging results corresponding to example 31 and example 33 is shown in FIG. 12. The viscosity of both polymer solutions is the same at an initial stage of aging, but the long-term thermal stability of TVP-P1 solution is higher than that of the emulsion-diluted solution from ETVP-P1 over continuous aging.

Example 34

(52) 0.75 g of TVP-P1 dry powder obtained in example 19 was dissolved in 499.25 g of 0.45% NaCl (w/w) aqueous solution under stirring at 100 rpm, and it took 24 hours to get complete dissolution. The prepared solution was then filtered through a G3-level sand funnel to remove any undissolved residues. After the core was saturated with the 0.45% NaCl aqueous solution, the temperature in the core flooding chamber was set at 45 C. Next, the 0.45% NaCl aqueous solution was injected into the core at a rate of 1 mL.Math.min.sup.1 until the pressure difference remained constant. Then the TVP-P1 solution was injected to displace saline water in the core at a rate of 1 mL.Math.min.sup.1 until the pressure difference reached to a constant value. Finally, the 0.45% NaCl aqueous solution was injected to displace polymer solution slug at a rate of 1 mL.Math.min.sup.1 until the pressure difference was unchanged. A curve of pressure difference was plotted against corresponding injected pore volume amount was plotted to reflect the propagation of TVP-P1 solution through the core.

Example 35

(53) As a reference, 1.00 g of PAMA dry powder of the polymer obtained in example 24 was dissolved in 499.00 g of 0.45% (w/w) NaCl aqueous solution under stirring at the rate of 100 rpm, and it took 24 hours to get a complete dissolution. The prepared PAMA was then filtered through a G3-level sand funnel to remove any undissolved residues. After the core was saturated with 0.45% NaCl aqueous solution, the temperature in the core flooding chamber was set at 45 C. Next, the 0.45% NaCl aqueous solution was injected into the core at a rate of 1 mL.Math.min.sup.1 until the pressure difference remained constant. Then the PAMA solution was injected to displace the saline water slug at a rate of 1 mL.Math.min.sup.1 until the pressure difference was unchanged. Finally, the 0.45% NaCl aqueous solution was injected to displace polymer solution slug at a rate of 1 mL.Math.min.sup.1 until the pressure difference was unchanged. A curve of pressure difference was plotted against corresponding injection pore volume is plotted to reflect the propagation of PAMA solution through the core.

(54) The comparison of the transportation of both polymer solutions corresponding to example 34 and example 35 in the cores is shown in FIG. 13. The resistance factor and residual resistance factor of TVP-P1 solution are higher than those of PAMA solution, suggesting the sweep efficiency of TVP-P1 solution is higher than that of PAMA solution, and the oil recovery factor from TVP-P1 solution may be higher than that of PAMA solution.

Example 36

(55) 2.50 g of ETVP-P1 inverse emulsion containing reverse demulsifier, obtained in example 30, was dispersed in 497.50 g of 0.45% (w/w) NaCl aqueous solution under stirring at 600 rpm, and it took 10 minutes to get complete dissolution. The prepared emulsion-diluted solution was then filtered through a G3-level sand funnel to remove any undissolved residues. After the core was saturated with 0.45% NaCl aqueous solution, the temperature in the core flooding chamber was set at 45 C. Next, the 0.45% NaCl aqueous solution was injected into the core at a rate of 1 mL.Math.min.sup.1 until the pressure difference reached constant. Then the ETVP-P1 emulsion-diluted solution was injected to displace the saline water slug at a rate of 1 mL.Math.min.sup.1 until the pressure difference was unchanged. Finally, the 0.45% NaCl aqueous solution was injected to displace the polymer solution slug at 1 mL.Math.min.sup.1 until the pressure difference was unchanged. A curve of pressure difference was plotted against corresponding injection pore volume was plotted to reflect the propagation of ETVP-P1 emulsion-diluted solution through the core.

(56) The comparison of the transportation of both polymer solutions corresponding to example 34 and example 36 is shown in FIG. 14. The resistance factor and residual resistance factor of the TVP-P1 solution are higher than those of the ETVP-P1 emulsion-diluted solution, suggesting the sweep efficiency of the solution prepared from dry powder of TVP-P1 is higher than that of the emulsion-diluted solution from ETVP-P1, and the oil recovery factor of the solution prepared from the dry powder of TVP-P1 may be higher than that of the emulsion-diluted solution of ETVP-P1.

Example 37

(57) 0.75 g of dry powder of TVP-P1 obtained in example 19 was dissolved in 499.25 g of 0.45% (w/w) NaCl aqueous solution under stirring at 100 rpm, and it took 24 hours to get complete dissolution. The prepared solution from TVP-P1 dry powder was then filtered through a G3-level sand funnel to remove any undissolved residues. After the core was saturated with 0.45% NaCl aqueous solution, the temperature in the core flooding chamber was set at 45 C. for core flooding experiments.

(58) First, the core was saturated with crude oil. Then, 0.45% NaCl aqueous solution was injected to displace crude oil at 1 mL.Math.min.sup.1 until the water cut was higher than 98%. Next, 0.5 pore volume (PV) TVP-P1 solution was injected to displace oil at 1 mL.Math.min.sup..Math.1. Finally, the 0.45% NaCl aqueous solution was injected to displace the polymer solution slug at 1 mL.Math.min.sup.1 as a subsequent water displacement until the water cut higher than 98%. The curves of pressure difference, the oil recovery factor was plotted against corresponding pore volume of saline water pre-flooding, polymer solution and saline water post-flooding to reflect both injectivity and oil recovery efficiency by TVP-P1.

Example 38

(59) As a reference, 1.00 g of PAMA dry powder obtained in example 24 was dissolved in 499.00 g of 0.45% (w/w) NaCl aqueous solution under stirring at 100 rpm, and it took 24 hours to get complete dissolution. The prepared PAMA solution was then filtered through a G3-level sand funnel to remove any undissolved residues. After the core was saturated with 0.45% NaCl aqueous solution, the temperature in core flooding chamber system was set at 45 C. for core flooding experiments.

(60) First, the core was saturated with crude oil. Then, 0.45% NaCl aqueous solution was injected to displace crude oil at 1 mL.Math.min.sup.1 until the water cut was higher than 98%. Next, 0.5 PV of PAMA solution was injected to displace cure oil at a rate of 1 mL.Math.min.sup.1. Finally, 0.45% NaCl aqueous solution was injected to displace polymer solution at a rate of 1 mL.Math.min.sup.1 as a post water flooding until the water cut is higher than 98%. The curves of pressure difference, the oil recovery factor was plotted against corresponding pore volume of saline water pre-flooding, polymer solution and saline water post-flooding to reflect both injectivity and oil recovery efficiency by PAMA.

(61) The comparison of the core flooding experiments from TVP-P1 and PAMA obtained from example 37 and example 38 is shown in FIG. 15. The oil recovery efficiency by the polymer solution prepared from TVP-P1 was 10.0%, while that of polymer solution prepared from dry powder of PAMA was 7.9%, indicating that the smart thermoviscosifying polymer, TVP-P1, showed stronger capacity to increase oil recovery than normal polymer, PAMA.

Example 39

(62) 2.50 g of the inverse emulsion ETVP-P1 containing reverse demulsifier obtained in example 30 was dispersed in 497.50 g of 0.45% (w/w) NaCl aqueous solution under stirring at 600 rpm, and it took only 10 minutes to get complete dissolution. The prepared emulsion-diluted solution was filtered through a G3-level sand funnel to remove any undissolved residues. After the core was saturated with 0.45% NaCl aqueous solution, the temperature in the core flooding chamber was set at 45 C. for further core flooding experiments.

(63) First, the core was saturated with crude oil. Then, the 0.45% NaCl aqueous solution was injected to displace crude oil at 1 mL.Math.min.sup.1 until the water cut is higher than 98%. Next, 0.5 PV of ETVP-P1 emulsion-diluted solution was injected to displace crude oil at 1 mL.Math.min.sup.1. Finally, 0.45% NaCl aqueous solution was injected as post water flooding to displace polymer solution slug at 1 mL.Math.min.sup.1 until the water cut was higher than 98%. The curves of pressure difference, the oil recovery factor was plotted against corresponding pore volume saline water pre-flooding, polymer solution and saline water post-flooding to reflect both injectivity and oil recovery efficiency by ETVP-P1.

(64) The comparison of the core flooding experiments corresponding to TVP-P1 and ETVP-P1 obtained from example 37 and example 39 is shown in FIG. 16. The oil recovery factor by TVP-P1 was 10.0%, while that from emulsion ETVP-P1 was 7.9%, indicating that the solution of the dry powder of TVP-P1 has a higher oil recovery efficiency compared to emulsion polymer.