Amphiphilic block polymers soluble in strongly saline medium

Abstract

The present invention relates to the preparation of polymers that are of use in particular as a rheology agent, and are suitable for use in very concentrated saline media, which comprises a step of micellar radical polymerization in which are brought into contact, in an aqueous medium: —hydrophilic monomers; —hydrophobic monomers in the form of a micellar solution, containing micelles comprising these hydrophobic monomers; —a radical polymerization initiator; and —preferably an agent for controlling radical polymerization, wherein said micelles comprise at least one surfactant of amphoteric nature. The polymers obtained according to the invention are in particular of use for enhanced oil recovery.

Claims

1. A method comprising regulating rheology of a liquid medium comprising more than 50 g/l of salt by dissolving in the liquid medium a polymer composition comprising a polymer, wherein the polymer is a block copolymer prepared by a process comprising a step (E) of micellar radical polymerization in which the following are placed in contact, in an aqueous medium (M): hydrophilic monomers, dissolved or dispersed in said aqueous medium (M); hydrophobic monomers in the form of a micellar solution containing, in dispersed form in the aqueous medium (M), micelles comprising these hydrophobic monomers; at least one radical polymerization initiator, and optionally, at least one radical polymerization control agent, wherein said micelles comprise at least one surfactant of amphoteric nature; and wherein the polymer composition comprises at least one surfactant of amphoteric nature from the micellar free radical polymerization.

2. The method as claimed in claim 1, wherein the liquid medium comprises more than 100 g/l of salt.

3. The method as claimed in claim 1, wherein the radical polymerization control agent is a compound that comprises a thiocarbonylthio —S(C═S)— group.

4. The method according to claim 3, wherein the compound that comprises the thiocarbonylthio —S(C═S)— group is a xanthate.

5. The method as claimed in claim 3, wherein the radical polymerization control agent is an oligomer which is of water-soluble or water-dispersible nature bearing a thiocarbonylthio —S(C═S)— group and which is soluble or dispersible in the aqueous medium (M) used in step (E); and/or is not suitable for penetrating into the micelles of the micellar solution.

6. The method as claimed in claim 3, wherein the radical polymerization control agent is a prepolymer bearing at least one thiocarbonylthio —S(C═S)— group obtained on conclusion of a step)(E.sup.0), prior to step (E), said step)(E.sup.0) comprising placing in contact hydrophilic monomers; a radical polymerization initiator; and a control agent bearing a thiocarbonylthio group —S(C═S)—.

7. The method as claimed in claim 1, wherein the amphoteric surfactant is selected from the group consisting of: betaines; sulfobetaines; alkylamphoacetates and alkylamphodiacetates; alkylamphopropionates or alkylamphodipropionates; alkyl amphohydroxypropyl sultaines; iminopropinates; alkyl amine oxides; and mixtures of surfactants comprising one or more of the abovementioned compounds.

8. The method as claimed in claim 7, wherein the at least one surfactant of amphoteric nature is selected from the group consisting of: cetyl betaine; sulfobetaines; alkylamphoacetates and alkylamphodiacetates; alkylamphopropionates or alkylamphodipropionates; alkyl amphohydroxypropyl sultaines; iminopropinates; alkyl amine oxides; and mixtures of surfactants comprising one or more of the abovementioned compounds.

9. The method as claimed in claim 1, wherein the hydrophobic monomers of step (E) comprise a C.sub.1-C.sub.30 alkyl.

10. The method as claimed in claim 9, wherein the hydrophobic monomers of step (E) comprise a C.sub.4-C.sub.22 alkyl α,β-unsaturated ester.

11. The method as claimed in claim 10, wherein the hydrophobic monomers of step (E) comprise lauryl methacrylate.

12. The method according to claim 1, wherein the liquid medium is an aqueous medium.

13. The method according to claim 12, wherein the aqueous medium is for oil or natural gas extraction.

14. The method according to claim 13, wherein the aqueous medium is for forming drilling fluids, for fracking, for stimulation or for enhanced oil recovery EOR.

Description

EXAMPLES

Example 1 (Comparative)

(1) Synthesis of a Polymer P1 in the Presence of SDS

(2) 144 g of sodium dodecyl sulphate (SDS), 565.67 g of distilled water and 10.33 g of 4-tert-butylstyrene (t-BS) were introduced, at 20° C., into a plastic flask (HDPE, 1000 ml). The mixture was stirred using a magnetic stirrer bar for 1 hour, until a clear micellar solution was obtained.

(3) 320.1 g of the micellar solution previously prepared, 376.9 g of water, 592.8 g of acrylamide (aqueous solution at 50% by weight), 478 g of AMPS (aqueous solution at 51% by weight), 5.56 g of Rhodixan A1 (ethanolic solution at 1.0% by weight) and 8.94 g of ammonium persulfate (aqueous solution at 5% by weight) were introduced, at 20° C., into a Dewar flask (3000 ml) fitted with a lid which allows it to be atmosphere-tight. The mixture was degassed by bubbling with nitrogen for 40 minutes. 17.7 g of sodium formaldehyde sulfoxylate, in the form of an aqueous solution at 1% by weight, were added to the medium, in a single portion. The mixture was degassed by bubbling with nitrogen for 15 minutes.

(4) The polymerization reaction was then allowed to take place, with stirring. When the viscosity of the medium increased, the stirring was stopped and the polymerisation reaction was allowed to take place overnight. At the end of the polymerization, a gel was obtained.

Example 2

(5) Synthesis of a Polymer P2 in the Presence of Mackam LAB

(6) 128.8 g of Mackam LAB at 30%, 145.18 g of distilled water and 2.28 g of 4-tert-butylstyrene (t-BS) were introduced, at 20° C., into a plastic flask (HDPE, 1000 ml). The mixture was stirred using a magnetic stirrer bar for 1 hour, until a clear micellar solution was obtained.

(7) 247.1 g of the micellar solution thus prepared, 447.8 g of water, 593.8 g of acrylamide (aqueous solution at 50% by weight), 478.7 g of AMPS (aqueous solution at 51% by weight), 5.57 g of Rhodixan A1 (ethanolic solution at 1.0% by weight) and 9 g of ammonium persulfate (aqueous solution at 5% by weight) were introduced, at 20° C., into a Dewar flask (3000 ml) fitted with a lid which allows it to be atmosphere-tight. The mixture was degassed by bubbling with nitrogen for 40 minutes. 18 g of sodium formaldehyde sulfoxylate, in the form of an aqueous solution at 1% by weight, were added to the medium, in a single portion. The mixture was degassed by bubbling with nitrogen for 15 minutes.

(8) The polymerization reaction was then allowed to take place, with stirring. When the viscosity of the medium increased, the stirring was stopped and the polymerisation reaction was allowed to take place overnight. At the end of the polymerization, a gel was obtained.

Example 3

(9) Synthesis of a Polymer P3 in the Presence of Mackam CET

(10) 122.87 g of Mackam CET, 45.77 g of distilled water and 11.36 g of 4-tert-butylstyrene were introduced, at ambient temperature (20° C.), into a 500 ml HDPE flask. The mixture was stirred using a magnetic stirrer bar for 30 minutes, until a clear solution was obtained.

(11) 72.8 g of the micellar solution thus prepared, 623.8 g of water, 592.8 g of acrylamide (aqueous solution at 50% by weight), 478.0 g of AMPS (aqueous solution at 50% by weight), 5.568 g of Rhodixan A1 (O-ethyl S-(1-methoxycarbonyl)ethyl xanthate-ethanol solution at 1.0% by weight) were introduced, at 20° C., into a Dewar flask (3000 ml) fitted with a lid which allows it to be atmosphere-tight.

(12) The pH (initial pH=7.9) of the monomer solution was measured and adjusted to 6 by adding a hydrochloric acid solution (aqueous solution at 10% by weight).

(13) The mixture was degassed by bubbling with nitrogen for 60 minutes. Following this degassing, 18.0 g of sodium formaldehyde sulfoxylate, in the form of an aqueous solution at 1% by weight, and 9.0 g of sodium persulfate (aqueous solution at 5% by weight), were added to the medium, in a single portion. The mixture was pre-degassed by bubbling with nitrogen for 15 minutes.

(14) The polymerization reaction was then allowed to take place with stirring for 16 hours, as a result of which the polymer P3 was obtained in the form of a gel.

Example 4

(15) Solubility Tests

(16) The solubility of the P1 and P2 polymer compositions were tested in a brine S consisting of an aqueous solution of the following salts:

(17) NaCl: 119.54 g/l

(18) CaCl.sub.2: 9.92 g/l

(19) MgCl.sub.2: 6.02 g/l

(20) Na.sub.2SO.sub.4: 2.85 g/l

(21) A piece of gel (respectively of P1 or P2) was placed in a 100 ml glass flask, and the brine was added so as to obtain a solution in which the concentration of polymer (P1 or P2, respectively) is 2 g/l. The mixture was stirred using a magnetic stirrer bar for 12 h.

(22) The appearance of the compositions in the flask was visually verified after 12 hours of stirring:

(23) Polymer P1 in the Brine S after 12 h of Stirring (Comparative): presence of pieces of the initial gel, slightly swollen and with a whitish appearance

(24) Polymer P2 in the Brine S after 12 h of Stirring: transparent homogeneous solution

Example 5

(25) Rheology

(26) 0.3973 g of P3 polymer gel as obtained at the end of example 3 was placed, with a magnetic stirring bar, in a 100 ml glass flask, to which were added 59.2041 g of a brine with the following composition:

(27) TABLE-US-00001 NaCl 119.54 g/l CaCl.sub.2  9.92 g/l MgCl.sub.2  6.02 g/l Na.sub.2SO.sub.4  2.85 g/l
The mixture was left to stir on a magnetic stirrer plate for 48 h.

(28) The viscosity was then measured as a function of the shear rate using an ARG2 rheometer from TA Instruments, equipped with a 14-15 mm aluminum Couette geometry.

(29) A viscosity of 7.3 mPa.Math.s is obtained at 25° C. for a shear rate of 10 s.sup.−1.