Auto-invertible inverse polymer emulsion

Abstract

The invention relates to an inverse polymer emulsion having the particular feature of auto-inverting without any need for the use of an inverting agent and containing a polymer of at least one water-soluble monomer and at least one LCST macromonomer. The invention also relates to the use of the inverse emulsion in the fields of the oil and gas industry, water treatment, slurry treatment, paper manufacturing, construction, mining, cosmetics, textiles, detergents or agriculture.

Claims

1. An auto-invertible inverse emulsion comprising: oil; water; at least one water-in-oil surfactant; and at least one polymer having a molecular weight of between 5 and 30 million g/mol and containing monomer units of at least acrylamide, 2-acrylamido 2-methylpropane sulfonic acid (ATBS), and 10.sup.−5 to 5 mol % of a lower critical solution temperature (LCST) macromonomer, said LCST macromonomer having a molecular weight of between 500 and 200,000 g/mol and having units from: at least one anionic monomer selected from acrylic acid and ATBS; and at least one LCST monomer selected from diethylacrylamide, N-isopropylacrylamide, dimethylacrylamide, and ter-butylacrylamide.

2. The inverse emulsion according to claim 1, wherein the inverse emulsion is free of oil-in-water surfactant.

3. A method for preparing an inverse emulsion according to claim 1, said method comprising the following steps: a) preparing an aqueous phase comprising at least one water-soluble monomer and at least one LCST macromonomer, b) preparing an oily phase comprising at least one oil and at least one water-in-oil surfactant, c) mixing the aqueous phase and the oily phase in order to form an inverse emulsion, and d) once the inverse emulsion is formed, polymerizing the monomers in the aqueous phase using a radical polymerization initiator.

4. A polymeric aqueous solution obtained by inversion of the inverse emulsion according to claim 1 in an aqueous medium in the absence of an oil-in-water surfactant.

5. Use of the inverse emulsion according to claim 1 for thickening an aqueous medium, for flocculating suspended particles or for reducing the level of frictional resistance during transport of an aqueous medium.

6. A method for fracturing an underground formation, which comprises: aa) providing an inverse emulsion according to claim 1; bb) inverting the inverse emulsion by adding it to an aqueous fluid in order to form an injection fluid; cc) optionally, adding at least one propping agent in the injection fluid; dd) introducing the injection fluid into part of the subterranean formation; and ee) fracturing the underground formation with the injection fluid.

7. A method for the improved recovery of hydrocarbons by sweeping in an underground formation, which comprises: aaa) providing an inverse emulsion according to claim 1; bbb) inverting the inverse emulsion by adding it to an aqueous fluid in order to form an injection fluid; ccc) introducing the injection fluid into part of the subterranean formation; ddd) sweeping part of the subterranean formation with the injection fluid; and eee) recovering a mixture of hydrocarbons, gas and aqueous fluid.

8. The inverse emulsion according to claim 1, wherein the LCST macromonomer has a weight average molecular weight between 1,000 and 100,000 g/mol.

Description

FIGURES

(1) FIG. 1 is a graph showing the change in the percentage of inversion of the EM1 inverse emulsion over time, in different fluids at a temperature of 25° C.

(2) FIG. 2 is a graph showing the change in the percentage of inversion of the EM1 inverse emulsion over time, in different fluids at a temperature of 80° C.

(3) FIG. 3 is a graph showing the change in the percentage of inversion of the EM2 inverse emulsion over time, in different fluids at a temperature of 25° C.

(4) FIG. 4 is a graph showing the change in the percentage of inversion of the EM2 inverse emulsion over time, in different fluids at a temperature of 80° C.

EXAMPLES OF EMBODIMENT OF THE INVENTION

(5) 1/ Synthesis of Telomers (or LCST Oligomers)

(6) To prepare a Telomere called T1, the following process is carried out.

(7) In a dual jacketed reactor:

(8) A hydroalcoholic solution (410 g) and the N-isopropylacrylamide (NIPAM, 113 g, or 1 mol), butyl methacrylate (7.9 g, or 0.055 mol) and acrylic acid (4.44 g, or 0.055 mol) monomers are loaded. The mixture is stirred. The pH of the mixture is adjusted to between 4.0 and 5.0 using a 40% by weight NaOH solution in water. The mixture obtained is heated to 50° C. The mixture is de-oxygenated with nitrogen bubbling for 40 minutes. Aminoethanethiol HCl (2.5 g) is added. 2,2′-azobis(2-methylpropionamidine)dihydrochloride (0.22 g) is added to initiate telomerization. After stabilization of the temperature, the mixture is stirred for 2 hours and then cooled to 25° C.

(9) A concentrated viscous solution containing 23% by weight of a telomer with a degree of polymerization of 50 monomer units (DPn 50) is obtained. The LCST of this T1 telomere was estimated at 38° C. according to the process described above.

(10) To prepare a Telomere called T2, the following process is carried out.

(11) In a dual jacketed reactor: The N-isopropylacrylamide (NIPAM, 113 g, or 1 mol), butyl methacrylate (4.44 g, or 0.031 mol) and chloromethyl dimethylamino-ethyl methacrylate (MADAME.MeCl, 2.16 g, or 0.01 mol) monomers are loaded in 445 g of a hydroalcoholic solution. The mixture is stirred. The pH of the mixture is adjusted to between 4.0 and 5.0 using a 40% by weight NaOH solution in water. The mixture obtained is heated to 50° C. The mixture is de-oxygenated with nitrogen bubbling for 40 minutes. Aminoethanethiol HCl (2.35 g) is added. 2,2′-azobis(2-methylpropionamidine)dihydrochloride (0.22 g) is added to initiate the polymerization. After stabilization of the temperature, the mixture is stirred for 2 hours and then cooled to 25° C.

(12) A concentrated viscous solution containing 21% by weight of a telomer with a degree of polymerization of 50 monomer units (DPn 50) is obtained. The LCST of this T2 telomere was estimated at 32° C. according to the process described above.

(13) TABLE-US-00001 TABLE 1 List and monomeric compositions of T1 and T2 telomeres. LCST Hydrophilic Hydrophobic LCST monomer monomer (B), monomer (C), telomere Telomere (A), mol % mol % mol % (° C.) T1 NIPAM, 90 Acrylic acid, Butyl 38 5 methacrylate, 5 T2 NIPAM 96 MADAME•MeCl, Butyl 32 1 methacrylate, 3
2/ Synthesis of Macromonomers

(14) The following process is carried out to prepare a macromonomer called M1.

(15) In a dual jacketed reactor: 400 g of Telomere T1 solution (5581 g/mol) at 23% by weight are loaded in water. The solution is stirred. The pH of the solution is adjusted to 7.5 using a 40% by weight NaOH solution in water. The solution is cooled to 5° C. Using a burette, 3.0 g of acryloyl chloride are added dropwise. The pH is continuously adjusted between 7 and 9 using a 40% by weight NaOH solution in water. The temperature is maintained at 5° C. throughout the reaction. After the end of the reaction, the solution is stirred for 2 hours while continuously checking the pH.

(16) A concentrated viscous solution containing 21.5% by weight of LCST macromonomer M1 (5711 g/mol) is obtained.

(17) The macromonomer M2 is prepared using the same process, with the telomer T2 (5740 g/mol). A concentrated viscous solution containing 21.5% by weight of LCST macromonomer M2 (5869 g/mol) is obtained.

(18) 3/ Synthesis of Polymers in Inverse Emulsion

(19) The following process is carried out to prepare an inverse emulsion called EM1.

(20) In order to prepare the aqueous solution of monomers, 146 g (74.997 mol %) of acrylamide, 157 g (25 mol %) of ATBS (2-acrylamido 2-methylpropane sulfonic acid), 0.5 g (0.003 mol %) of LCST macromonomer M1 and 370 g of water are loaded into a beaker. The pH of the monomer solution is adjusted between 5 and 6 using NaOH.

(21) The following additives are added: 0.37 g of Versenex 80 (complexing agent), 1.29 g of TBHP (terbutylhydroperoxide) (oxidant).

(22) 295 g of Exxsol D100 and 30 g of Span 80 are mixed before being transferred into a reactor together with the aqueous phase. Emulsification of the two-phase mixture is carried out using a mixer, this mixture is deoxygenated using an inert gas and then cooled to a temperature of 15° C.

(23) The synthesis starts with the addition of a solution of MBS (sodium metabisulphite, 1 g/l) at a flow rate of 1 ml/min. The temperature of the medium increases until it reaches a value of 40° C., which is maintained for 2 hours.

(24) The reaction medium is allowed to cool. An inverse emulsion with a polymer concentration of 30% by weight is thus obtained.

(25) An EM2 inverse emulsion is prepared according to the same process, with the LCST macromonomer M2. An EM2 inverse emulsion with a polymer concentration of 30% by weight is obtained.

(26) As a counterexample, the EM3 inverse emulsion is prepared according to the same process, but without using an LCST macromonomer. In other words, the 0.003 mol % of LCST macromonomer is replaced by 0.003 mol % of acrylamide.

(27) 4/ Test

(28) The test consists of studying the inversion of inverse emulsions over time, in different brines and at different temperatures. The inversion is characterized by a release of the polymer chains into the aqueous medium and thus by an increase in its viscosity.

(29) Materials and Method

(30) The speed of inversion is studied using Thermo instrument's iQ Rheometer. During the inversion test, the stress is recorded as a function of time. It increases in proportion to the viscosity released.

(31) The EM1, EM2 and EM3 inverse emulsions are tested, without any inverting agent being added to them.

(32) Four different fluids were used: tap water, and three brines of different concentrations: 15,000 TDS (Total Dissolved Solids) (1.5% by weight of NaCl), 33,000 TDS (3% by weight of NaCl and 0.3% by weight of CaCl.sub.2)), and 100,000 TDS (10% by weight of NaCl). The TDS corresponds to the quantity in ppm of organic and inorganic substances contained in a brine. In other words, 15,000 TDS equals 15,000 mg of salt per liter of fluid.

(33) The tests were carried out at 2 different temperatures: 25° C. and 80° C.

(34) To this end, 1.2 g of inverse emulsion are injected into 34 ml of brine under rotation of the elliptical module (U1) at 800 rpm. The emulsions are tested such that the polymer concentration is 10,000 ppm (by weight) in the four fluids. Another test is carried out with the same emulsions but at a concentration of 100 ppm (by weight), only in brine (33,000 TDS).

(35) 5/ Results

(36) The test results are recorded in the graphs of FIGS. 1 to 4. In these figures, the curves for the EM3 inverse emulsion are identical, regardless of the nature of the fluid and the temperature. Therefore, only one curve appears for the EM3 emulsion, that implemented in a brine of 33,000 TDS.

(37) As shown in FIGS. 1 and 2, the EM1 inverse emulsion according to the invention, in which the polymers comprise M1 macromonomer units, rapidly inverts in a very wide range of brine compositions ranging from tap water to a 10% salt brine (100,000 TDS), both at low temperature (25° C.) and at high temperature (80° C.). The EM1 emulsion also inverts very well at 100 ppm in brine at 33,000 TDS.

(38) Conversely, the EM3 inverse emulsion, which does not include an LCST macromonomeric unit, does not invert at all regardless of the fluid and the temperature.

(39) The same results are obtained with the EM2 inverse emulsion as shown in FIGS. 3 and 4. The EM2 emulsion inverts under all brine and temperature conditions, while the EM3 emulsion does not invert. The EM2 emulsion also inverts very well at 100 ppm in brine at 33,000 TDS.

(40) Consequently, the auto-inverting behavior of the EM1 and EM2 emulsions according to the invention is clearly observed, while these emulsions do not contain an inverting agent.

(41) These auto-inverting properties are highly sought after by users of inverse emulsions because they avoid all of the potential problems associated with the use of an inverting agent.