GB2161492A - The manufacture of inverse microlattices - Google Patents

Abstract

Inverse microlattices of water-soluble polymers are prepared by polymerization within an inverse microemulsion obtained by admixing an aqueous phase containing the water-soluble monomer to be polymerized and at least one alkali metal salt of a saturated aliphatic monocarboxylic acid, e.g. from C2 to C4, of an organic phase and a non-ionic surfactant or a mixture of non-ionic surfactants, said alkali metal salt being in a proportion of 0.1/1 to 0.3/1 by weight of the monomer to be polymerized. The resultant microlattices can be used to improve the production of hydrocarbons (in enhanced recovery techniques or methods for preventing water inflows in producing oil wells).

Description

SPECIFICATION The manufacture of inverse microlatices This invention relates to a process for the manufacture of inverse microlatices as well as to inverse microlatices obtained by this process.

Background of the Invention The preparation of inverse latices by polymerisation of water-soluble polymers in an inverse emulsion obtained by mixing an aqueous phase containing one or more water-soluble monomers to be (co-) polymerized, with an organic phase and one or more surfactants is known.

In such preparations, the surface-active agent is generally selected from non-ionic surfactants having a low H L B (Hydrophilic Lipophilic Balance) whereby an emulsion of the water-in-oil type is obtained. The surfactant usually comprises a sorbitan monooleate or monostearate. On the other hand, it has been stated that certain surfactants of higher H L B ( > 7) are also capable of giving water-in-oil emulsions.

The major disadvantages of inverse lactices is their lack of stability which, over time, results in a substantial settling.

The preparation of inverse microlatices using anionic or cationic surfactants has also been described (French Patent Application 2 524 895).

Summary of the Invention We have now discovered a process for manufacturing inverse microlatices using non-ionic surfactants and having the advantage, that the water-soluble polymer content of the inverse microlatex may be increased.

Thus, in accordance with the invention there is provided a process for the manufacture of inverse microlatices which comprises: (a) preparing a stable and transparent microemulsion of the water-in-oil type, by admixing: (i) an aqueous solution comprising a vinyl monomer to be polymerized and an alkali metal salt of a saturated aliphatic monocarboxylic acid, with (ii) an oily phase, comprising at least one hydrocarbon liquid, (iii) in the presence of at least one non-ionic surfactant whose H L B value ranges from 8 to 11 (when using a mixture of surfactants, the H L B of the mixture is considered); and (b) subjecting the obtained inverse microemulsion of step (a) to conditions so as to effect polymerization and production of a stable, transparent, inverse microlatex of high molecular weight.

In the inverse microemulsions for use in the preparation of the microlatices according to the invention, the water-soluble vinyl monomer may comprise, for example, acrylamide, methacrylamide or N-vinyl pyrrolidone. The alkali metal salt of the saturated aliphatic monocarboxylic acid may be, for example, an alkali metal salt of a C24 acid i.e. acetic, propionic or butyric acid. In general, sodium acetate is preferred.

The preferred conditions for preparing an inverse microemulsion are generally dependent on the following parameters: surfactant concentration, H L B of the surfactant or of the surfactant mixture, temperature, nature of the organic phase and composition of the aqueous phase.

The monomer content of the aqueous phase is generally 20-80% and conveniently 30-70% by weight. The weight ratio of alkali metal carboxylate to monomer is generally from 0.1/1 to 0.3/1.

If desired, the aqueous phase may also contain sodium hydroxide or potassium hydroxide.

There may be thus obtained, by judiciously adjusting the amount of said product, a hydrolyzed polyacrylamide which is particularly advantageous for certain applications, particularly in enhanced oil recovery. Alternatively, hydrolysis may be effected after polymerization.

The selection of the organic phase has a substantially effect on the minimum surfactant concentration necessary to obtain the inverse microemulsion. This organic phase may comprise a hydrocarbon or a hydrocarbons mixture. Paraffinic and/or isoparaffinic hydrocarbons or mixtures thereof are the most suitable since inexpensive formulations may be obtained (with a low surfactant content).

The weight ratio of the amount of aqueous phase to the amount of hydrocarbon phase is chosen to be as high as possible, so as to obtain, after polymerization, a microlatex of high polymer content. This ratio may range, for example, from 0.5 to 3/1.

The surfactants are selected to obtain a H L B value in the range 8 to 11.

We have found that outside this range, inverse microlatices either cannot be obtained, or require a considerable amount of surfactants, incompatible with an economical process. In addition, within this H L B range, the surfactant content must be sufficient to obtain an inverse microlatex. Too low a concentration of surfactant leads to inverse latices similar to those of the prior art.

In the above H L B range, the minimum concentration of surfactant, related to all the constitutents of the microemulsion, generally varies according to the H L B value. A lower limit of about 9% by weight is particularly convenient for a H L B range from about 8.5 to 9.5. For H L B ranges from 8 to 8.5 and from 9.5 to 11, the lower limit is generally higher.

Thus, for a H L B value of about 10, for example, the minimum surfactant content is generally about 20% by weight.

The upper limit of the surfactant concentration, is desirably limited to about 25% by weight of all the constituents of the inverse microemulsion for economical reasons.

When preparing the inverse microemulsion, the temperature of the mixture should generally be carefully controlled, in view of the sensitivity to temperature of the inverse microemulsions in the presence of non-ionic surfactants. This temperature dependence is higher as the surfactant concentration is closer to the minimum content required for obtaining an inverse microemulsion.

In order to reduce the required surfactant content and to limit to a minimum the temperature influence on the stability of the inverse microemulsions, the latter will be, as much as possible, prepared at a temperature as close as possible to that selected for the polymerization.

The water-soluble vinyl monomer present in the above-described inverse microemulsion may be polymerized photochemically or thermally. Photochemical initiation may be effected with, for example, ultraviolet radiation. Thermal initiation may be effected with a free radical generator, either a hydrophobic compound such as, for example, azobisisobutyronitrile, or a hydrophilic compound such as, for example, potassium persulfate.

Polymerization generally takes place very quickly, for example in a few minutes, in a photochemical way, quantitatively, and leads to the formation of stable and transparent microlatices with a particle size of the order of 20-50 nanometers and with a narrow distribution range.

The size of the particles dispersed in the inverse microlatices according to the invention may be determined by quasi-elastic diffusion of light. The light source of a light diffusion apparatus for determining the particle size may consist of an argon-ion Spectra Physics laser operating at 488 nm. The time correlation function of the diffused intensity is obtained by using a digital correlator with 72 channels. The intensity correlation data have been treated by using the method of cumulating values, giving the average decreasing time < P - > of the correlation function and the variance V.The latter measures the amplitude of the distribution of the decreasing times and its value is given by the formula: v=( < P > 2 - r2,)/ < r,2 wherein < r2 > is the second moment of distribution.

For polymer solutions of low polydispersity, the variance V, as a first approximation, is related to the polydispersity index Mw/Mn (weight molecular weight/number molecular weight) by the relationship: Mw/Mn = 1 + 4V The molecular weight of the polymer obtained depends on the mode of activation selected for polymerization; photochemical activation favoring very high molecular weights, provided that the polymerization temperature is kept below 30"C. This activation mode will be always preferred when very high molecular weights are desired, such as for inverse microlatices intended for use in enhanced hydrocarbon recovery.

The process of the invention provides stable and transparent inverse microlatices of high water-soluble polymer content, e.g. 10 to 35% by weight and usually 10 to 25% by weight.

The inverse microlatices obtained by the process of the invention may be used in many applications, particularly in oil production: Enhanced Hydrocarbon Recovery, ground consolidation, manufacture of drilling muds, prevention of water inflows during the commissioning of oil wells, and as completion or fracturation fluids.

Generally, Enhanced Oil Recovery methods using polymer aqueous solutions comprise injecting said solutions in the oil field, through at least one injection well, to circulate it through the rock formation and recover the displaced hydrocarbons from at least one producing well.

Methods using inverse microlatices of the invention for Enhanced Recovery are generally similar to prior art methods using water-in-oil emulsions. The inverse microlatices considered in this invention are auto-inversable and it is not necessary, generally, to add an additional surfactant to favor inversion, as in certain of the methods described previously. The microlatices of the invention may be used, for example after dilution in water, in a proportion of 50 to 5000 ppm, preferably 100 to 2000 ppm by weight of copolymer with respect to the resultant aqueous phase. Tests conducted in laboratory have shown the efficiency of these inverse m icrolatices.

A method for preventing water inflows in producing wells comprises injecting at the producing well, in the part of the oil field to be treated, an aqueous solution of polymer, prepared according to the invention by inverse microlatex dissolution in water. The polymer is adsorbed to a large extent on the walls of the formation surrounding the well wherefrom it is injected. When said well is then brought again into production, the oil and/or the gas selectively traverse the treated zone whereas water passage is reduced.

In addition to these applications, the water soluble polymers, prepared as a microemulsion, may be used as: coagulants for separating solids suspended in liquids -floatation and draining adjuvants in the manufacture of paper pulp; or as -flocculants in water treatment.

The inverse microlatices obtained by the process of the invention may also be used in assembling glass fibers, in the leather industry or in the paint industry.

EXAMPLES The following non-limiting examples serve to illustrate the invention. Examples 1, 4, 10, 14 and 1 5 are given by way of comparison.

EXAMPLE 1 (comparative) To 250 g of an aqueous solution containing 106 g of acrylamide are added 300 g of an insoparaffinic cut having an initial distillation point of 207"C and a final point of 254"C and 1 57 g of a mixture of non-ionic surfactants consisting of sorbitan sesquioleate (22g) and polyoxyethylene sorbitol hexaoleate (135 g). The surfactant mixture has a resultant H L B of 9.3.

0.32 g of azobisisobutyronitrile are added to the so-obtained monophasic mixture which is degased for 30 minutes and polymerized under UV radiation at 19"C for 15 minutes, thereby giving a turbid and unstable latex.

EXAMPLE 2 Example 1 is repeated, except that 1 5.9 g of sodium acetate are added to the aqueous phase.

After polymerization, a stable and transparent inverse microlatex is obtained, the particle size of which determined by quasi-elastic diffusion of light, is 37 nm, the variance being 3%.

By precipitation in acetone and successive washing with acetone and methanol, a polyacrylamide is obtained (with total conversion) whose intrinsic viscosity, determined at 25"C in water of 5.85 g/l NaCI content, has been found equal to 920 cc/g.

EXAMPLE 3 Example 2 is repeated, except that the aqueous phase contains 25.3 g of sodium acetate. A stable and transparent microlatex is obtained with characteristics very close to those mentioned in Example 2: RH = 38 nm, variance = 3% The intrinsic viscosity of the polyacrylamide, determined under the conditions of Example 2, is equal to 847 cc/g.

EXAMPLE 4 (comparative) When repeating Example 2 with a sodium acetate amount of 4.5 g, an unstable latex is obtained after polymerization.

EXAMPLE 5 470 g of the isoparaffinic cut of Example 1 and 1 50 g of the surfactant mixture of Example 1 are added to 378 g of an aqueous solution containing 142 g of acrylamide and 34.5 g of sodium acetate. The so-obtained monophasic mixture is polymerized at 20"C under UV radiation for 15 minutes. The size of the so-obtained inverse microlatex particles is 42.3 nm with a variance of 5%. The intrinisic viscosity of the obtained polymer is 772 cc/g at 25to.

EXAMPLE 6 300 g of the isoparaffinic cut of Example 1 and 1 50 g of the surfactant mixture of Example 1 are added to 550 9 of an aqueous solution containing 218 g of acrylamide and 60.5 9 of sodium acetate. The so-obtained monophasic mixture is polymerized at 20"C under UV radiation for 1 5 minutes, thus giving a stable and transparent microlatex. The polyacrylamide, isolated as described in Example 2, has an intrinsic viscosity of 878 cc/g at 25"C.

EXAMPLE 7 419 g of dodecane and 216 g of the surfactant mixture of Example 1 are added to 365 g of an aqueous solution containing 143 g of acrylamide and 21.4 g of sodium acetate. The soobtained monophasic mixture is heated to 45"C for 3 hours, thus giving a stable and transparent inverse microlatex containing a polyacrylamide whose intrinsic viscosity at 25"C is equal to 635 cc/g.

EXAMPLE 8 Example 7 is repeated except that dodecane is replaced with decane. After polymerization, an inverse microlatex containing a polyacrylamide having an intrinsic viscosity of 533 cc/g is obtained.

EXAMPLE 9 Example 7 is repeated, except that dodecane is replaced with heptane. After polymerization, a stable and transparent inverse microlatex containing a polyacrylamide having an intrinsic viscosity of 453 cc/g at 25"C is obtained.

EXAMPLE 10 (comparative) When Example 2 is repeated, except that sodium acetate is replaced by the same weight of sodium chloride, a turbid and unstable latex is obtained after polymerization.

EXAMPLES 11 to 13 Under the conditions of Example 5, the proportions of each of the surfactants are varied and the minimum content of surfactant necessary to obtain a stable and transparent inverse microlatex after polymerization is determined for different values of the H L B.

The results are reported in the following table: Minimum surfactants content required to obtain a stable and transparent EX H L B microlatex 11 9 9 12 9.3 9 13 10 20 In % by weight with respect to all the initial constitutents of the microemulsion.

EXAMPLE 14 (comparative) When Example 5 is repeated, except that the proportions of the two surfactants is so modified as to obtain a resultant H L B of 7.5, it is not possible to obtain an inverse microemulsion, even when adding substantial amounts of surfactant (more than 45% by weight).

EXAMPLE 15 (comparative) When, under the conditions of Example 5, everything else being unchanged, the proportion of the two surfactants is so modified as to obtain a resultant H L B of 11.5, it is not possible to obtain an inverse microemulsion, even when adding substantial amounts of surfactant (more than 25% by weight).

EXAMPLE 16 530 9 of the isoparaffinic cut of Example 1 and 101 g of the surfactant mixture formed of 20.3 g of sorbitan sesquioleate and 80.7 g of polyoxyethylene sorbitol hexaoleate are added to 369 9 of an aqueous solution containing 145 g of acrylamide and 1 8.6 g of sodium acetate.

The surfactant mixture has a resultant H L B of 8.9. 0.48 g of azobisisobutyronitrile is added to the so-obtained monophasic mixture, which is degased for 30 minutes and polymerized under UV radiation at 19"C for 30 minutes, thus giving a transparent inverse microlatex of low viscosity.

EXAMPLE 17 497 g of the isoparaffinic hydrocarbon cut used in Example 1 and 99 g of the same surfactant mixture as in Example 16 (H L B = 8.9) are added to 404 g of an aqueous solution containing 1 68 9 of the acrylamide and 20.2 9 of sodium acetate.

Polymerization is performed under the same conditions as in Example 1 6. A transparent inverse microlatex is obtained which contains about 16.8% by weight of polymer of high molecular weight.

Claims (11)

1. A process for the manufacture of an inverse microlatex, which comprises: (a) preparing an inverse microemulsion of the water-in-oil type by admixing: -an aqueous solution comprising a water-soluble vinyl monomer to be polymerized and at least one alkali metal salt of an aliphatic monocarboxylic acid, in a weight ratio of said alkali metal salt to said vinyl monomer of from 0.1/1 to 0.3/1; -an oily phase comprising at least one hydrocarbon liquid; and -a non-ionic surfactant or mixture of non-ionic surfactants having an H L B from 8 to 11, in an amount sufficient to give an inverse microemulsion; and (b) subjecting the inverse microemulsion from step (a) to polymerization conditions.

2. A process according to claim 1 wherein the vinyl monomer of step (a) is acrylamide, methacrylamide or N-vinylpyrrolidone.

3. A process according to either of claims 1 and 2 wherein the alkali metal salt is sodium acetate.

4. A process according to any one of the preceding claims wherein the oily phase of step (a) comprises at least one isoparaffinic or paraffinic hydrocarbon.

5. A process according to any one of the preceding claims wherein the weight ratio of the monomer aqueous solution to the oily phase in step (a) is from 0.5 to 3/1.

6. A process according to any one of the preceding claims wherein the proportion of surfactant or surfactant mixture in step (a) is higher than about 9% by weight related to all the constituents of said inverse microemulsion.

7. A process according to any one of the preceding claims wherein the proportion of surfactant or surfactant mixture in step (a) is at most 25% by weight related to all the constituents of said inverse microemulsion.

8. A process according to any one of the preceding claims substantially as herein described.

9. A process for the preparation of an inverse microlatex substantially as herein described in any one of Examples 2, 3, 5-9, 11-13, 16 and 17.

10. An inverse microlatex obtained by a process according to any one of claims 1 to 9.

11. An inverse microlatex according to claim 10, wherein its polymer content is about 10-35% by weight.

1 2. A process for improving the hydrocarbon production of an oil field, comprising the injection in an injection well or in a producing well of a polymer solution obtained by diluting with water a microlatex according to either of claims 10 and 11.

1 3. Each and every novel process, product, method, feature and combination of features substantially as herein described.