GB2055106A - Aqueous solutions containing crosslinked hydroxyethyl carboxyethyl cellulose and their use - Google Patents

Abstract

Aqueous compositions including crosslinkable hydroxyethyl carboxyethyl cellulose provide aqueous solutions particularly suitable for use in oil or gas drilling, fracturing, flow diversion, completion and workover. The aqueous compositions provided include a crosslinked hydroxyethyl carboxyethyl cellulose, crosslinking being effected by a polyvalent metal in the form of an inorganic or organic acid salt, hydroxide or oxide.

Description

SPECIFICATION Aqueous solutions containing crosslinked hydroxyethyl carboxyethyl cellulose and their use This invention relates to aqueous solutions containing crosslinked hydroxyethyl carboxyethyl cellulose in which the crosslinkages are achieved through polyvalent metals as derived from polyvalent metals in the form of inorganic or organic acid salts, hydroxides or oxides.

Hydroxyethyl carboxyethyl cellulose polymers are known materials, see U.S. Patent3,829,415, example No. 22, and suitably employable as hydrophilic colloids which possess suspending, thickening, stabilizing, and film-possess suspending, thickening, stabilizing, and film-forming properties. As a general class they are cited as useful as thickening agents in textile printing pastes, latex dispersions, and in oil well drilling muds, see col. 7, lines 4248 of U.S.

Patent 2,618,635.

Fracturing is defined as a method of stimulating production from an underground formation of low permeability by inducing fractures and fissures in the formation and forcing the strata apart. In a typical "oil patch" fracture, sand is mixed into a thickened brine solution and pumped downhole under high pressures. When the fluid pressure exceeds the formation strength, i.e., the cohesive resistance of the formation to withstand the pressure applied, fractures occur which become filled with the sandcontaining fluid. When the applied pressure is relieved, the sand acts as a prop to support the structural integrity of the fracture.

Water soluble polymers such as hydroxyethyl cellulose have been employed in hydraulic or fluid fracturing of subterranean formations. However, their employment as the sole viscosifier for this purpose is quite limited owing to the large temperature coefficient of viscosity of aqueous hydroxyethyl cellulose thickened solutions. As such solutions are injected into a well to a subterranean formation, the increased temperature of the formation can cause the fluid to lose viscosity and drop out the sand before it can be deployed in propping open the formation fractures. To overcome this effect, it is necessary to alterthe chemical ingredients utilized for viscosification. Such alteration includes the substitution of crosslinkable thickeners such as modified guar gum (e.g. hydroxypropyguar gum, or hydroxyethyl carboxymethyl cellulose.The thickener is dissolved in, e.g., brine, crosslinker is added, and with the sand included, the solution is pumped down the hole into the formation. This technique is characterized in a number of patents. U.S. Patent No.

3,898,165 describes the use of hydroxyethyl carboxymethyl cellulose in fracturing fluids. U.S. Patent No.

3,845,822 describes plugging and sealing of fractures using primarily carboxymethyl cellulose, a CrF6 crosslinker and a reducing compound suitable for reducing the chromium compound to a lower valence state such as Cr+3. U.S. Patent No. 3,760,881 enhances the higher temperature viscosity retention of a fluid by crosslinking a hydroxyethyl carboxymethyl cellulose thickener with quaternary ammonium compounds. U.S. Patent No.3,926,258 modifies the thickening system of U.S. Patent No.

3,845,822 by adding a complexing agent such as citric acid to the formulation. U.S. Patent No.

3,978,928 uses the gel system of U.S. Patents Nos.

3,845,822 and 3,926,258 for controlling sand formation restriction at the bore hole.

Increasing the viscosity of a thickening agent (particularly carboxymethyl cellulose) utilized in aqueous solution for recovery of oil is described in U.S.

Patent No.3,800,872. U.S. Patent No.4,035,195 describes crosslinking of carboxymethyl hydroxyethyl cellulose with polyvalent metal ions. In some respects, the disclosure of this patent is similar to that of U.S. Patent No. 3,926,258, supra.

U.S. Patent No. 3,727,687 utilizes the thickening system of U.S. Patent No. 3,845,822 in secondary oil recovery and in drilling fluids used in drilling of oil wells, gas wells, etc. U.S. Patent No. 3,208,524 describes crosslinking polysaccharide thickening agents with polyvalent crosslinking agents. Such a system is utilized in plugging lost circulation zones and other highly porous strata.

U.S. Patent No. 3,804,174 describes oil well cementing using a thixotropic cellulosic solution achieved by crosslinking hydroxyethyl cellulose with zirconium chloride and the patent mentions a number of other cellulosic thickeners.

The process of this invention, indeed the compositions employed in the process of this invention, provides a number of unexpected but real advantages. It has been determined that crosslinked hydroxyethyl carboxyethyl cellulose requires significantly less crosslinking polyvalent metal ion in order to give the same viscosity increase that can be obtained with hydroxyethyl carboxymethyl cellulose. Not only is this an economic advantage with respect to the manufacture of a thickened system which has good high temperature viscosity retention even at high temperatures of a deeply situated subterranean strata, but it also provides for less metal contamination in the aqueous media thereby decreasing environmental concerns associated with the presence of such polyvalent metal ions.In addition, the aqueous solutions of hydroxyethyl carboxyethyl cellulose in fresh water or brine are clearer than solutions of hydroxyethyl carboxymethyl cellulose in similar solvents. It has been noted that aqueous solutions containing commercial hydroxyethyl carboxymethyl cellulose possess haze and such haze has been found to plug a coarsely porous material indicating the capability of the insoluble components which form the haze to plug the subterranean formation walls thereby reducing the passage of oil to the borehole.

The aqueous compositions of this invention find enhanced utility as water flow diversion agents, and as thickeners in the manufacture of drilling muds, and completion and workover fluids. In addition, compositions of this invention are easily obtained without the necessity of complex oxidizing and reducing agents in order to effect the appropriate crosslinking.

The compositions ofthis invention comprise an aqueous media which contains from about .01 to about 5 weight percent thereof of a hydroxyethyl carboxyethyl cellulose which has a M.S. (i.e., molar substitution) of hydroxyethyl from about 1.4 to about 2.6 and a D.S. (i.e., degree of substitution) of carboxyethyl groups ranging from about 0.25 to about 0.6. The aqueous solution can be fresh water or a salt containing aqueous solution ranging from a dilute aqueous salt solution to a saturated aqueous salt solution such as a saturated brine.

The polyvalent metal crosslinker is derived from polyvalent metals in the form of inorganic or organic acid salts, hydroxides and oxides, and mixtures thereof, and include polyvalent metals from Group IIA, lliB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA and metals of Group IVA and VA (excluding non-metals such as carbon, silicon, nitrogen, phosphorous and arsenic).

Particularly preferred are the following polyvalent metals: Be, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Ba, Ta, Hf, Ir, Re, Pt, Au, and the like.

The periodic table referred to above is taken from Lange's Handbook of Chemistry, ? ooth edition, published by McGraw-Hill, 1967.

In characterizing the terms M.S. and D.S., reference is made to the definition of those terms as recited in U.S. Patent No. 3,284,353, see col. 1, lines 69-72, to col. 2, lines 1 and 2 and the description at col. 3, lines 28-36 of U.S. Patent No. 4,035,195. Such characterizations are incorporated herein by reference.

In characterizing the above mentioned hydroxyethyl carboxyethyl cellulose it is to be understood that such materials are provided in their alkali metal salt form, particularly as the sodium carboxylate form, see U.S. Patent No. 3,845,822, at col. 4, lines 49-54.

The amount of the polyvalent metal which is employed in making the aqueous solution of this invention ranges from about .01 to about 1.5 moles of the metal for each mole of carboxy present in the hydroxyethyl carboxyethyl cellulose, preferably from about .01 moles to about 1.05 for each mole of carboxy in the hydroxyethyl carboxyethyl cellulose.

As stated previously, the polyvalent metal is utilized for the purposes of crosslinking the hydroxyethyl carboxyethyl cellulose in the inorganic or organic acid salt form, or the hydroxide form, or the oxide form, or mixtures thereof. For example, the metal can be in the form of its chloride salt, sulfate salt, perchlorate salt, iodide salt, bromide salt, per manganate salt, hydrogen peroxide salt, nitrate salt, acetate salt, citrate salt, propionate sait, butanoate salt, octanoate salt, benzoate salt, monochloroacetate salt, and the like.

In the preferred embodiment of this invention, the polyvalent metal is provided in combination with the hydroxyethyl carboxyethyl cellulose in an already stabilized form, preferably from an aqueous solution. In those cases where a metal is in a typically insoluble oxide form, it is desirable that it be treated with, for example, caustic sufficiently to provide enough solubility for use herein but not too much so as to alter the total oxide structure. After the polyval ent metal is rendered soluble, a solution of it is com bined with the hydroxyethyl carboxyethyl cellulose in the prescribed proportions in order to produce compositions suitable for the purposes of the present invention.

The hydroxyethyl carboxyethyl cellulose suitable for the practice of the present invention and having the prescribed M.S. and D.S., is produced by methods conventional in the art. For example, cellulose flock can be slurried in an alcohol water diluent such as an isopropyl alcohol/water diluent and the redaction system is purged to low oxygen levels with nitrogen. An aqueous caustic solution is added to prepare a homogeneous alkali cellulose.

Ethylene oxide is added and the temperature is increased to a cookout temperature which is held until all the ethylene oxide is consumed. The alkali content is adjusted as necessary and acrylamide is added in a convenient manner. The temperature is held until no acrylamide remains. The slurry is cooled and acidified with about 10 to 15% excess acid. The product is isolated by filtration and purified by multiple washings with isopropyl alcohol/water mixture.

The following is a more specific illustration of the manufacture of hydroxyethyl carboxyethyl cellulose suitable for use in this invention: EXAMPLE 1 Ten grams of cotton linters were slurried into 150 g of 12.5 weight percent aqueous isopropyl alcohol and the reactor was nitrogen-purged for one-half hour. A 22% weight percent aqueous sodium hydroxide solution (15.9 g) was added followed by onehalf hour stirring. Ethylene oxide (9.4 g) was added, the temperature was increased to 75"C over one hour and then held for 45 minutes. A 14.5 g portion of a 28.6 weight percent solution of acrylamide in isopropyl alcohol-waterwasadded and the mixture was stirred for two hours at75 C. The mixture was acidified with 6 g of acetic acid and cooled to room temperature.The solid was filtered, washed four times with hot 12.5 weight percent aqueous isopropyl alcohol, and dried. The product analyzed as having a M.S. of 1.47 and a D.S. of 0.31 and dissolved readily in water to give a clear, viscous solution.

Another illustration for making hydroxyethyl carboxyethyl cellulose useful in the practice of this invention is the following: EXAMPLE2 Following the procedure of Example 1, 16 g dry cotton linters and 240 g 12.5 weight percent aqueous isopropyl alcohol were charged to the reactor. The reactor was nitrogen-purged for one-half hour and 25.45 g of 22 weight percent sodium hydroxide was added. After one-half hour stirring, the ethylene oxide (25.20 g)was added, the mixture was heated to 75"C over one hour and the temperature was held one additional hour. A second 22 weight percent caustic charge of 1.75 g was made, 18.8 g of 5Q weight percent aqueous acrylamide was added, and the slurry was reacted for two hours. The mixture was cooled and acidified with 10.4 g glacial acetic acid. The product was washed four times with 12.5 weight percent aqueous isopropyl alcohol and dried.

The product analyzed at 2.21 M.S. and 0.30 D.S. and gave a clear, viscous solution in water.

In Table I below, are designated a series of cel lulosic compositions Athrough K with the analysis of their M.S. and D.S. Examples A through J inclusive are each hydroxyethyl carboxyethyl cellulose.

The product designated K is HECMC, which is a commercial hydroxyethyl carboxymethyl cellulose: TABLEI Product Analysis Designation M.S. D.S.

A 1.47 0.31 B 1.43 0.39 C 1.36 0.48 D 1.96 0.29 E 2.01 0.39 F 1.60 0.36 G 2.10 0.48 H 2.43 0.26 2.30 0.33 J 2.24 0.42 K (HECMC) 2.48 0.37 EXAMPLE3 Four one-quart wide-mouth bottles were charged with 700 ml of tap water and 3.70 g of the hydroxyethyl carboxyethyl cellulose designated A in Table I above was added slowly to each with agitation. After the polymer had completely dissolved the solutions had an apparent viscosity, AV, of 37.5 to 39.5 cps as measured on the Fann Model 35A viscometer at room temperature (about 23 C). To the individual solutions was added varying amounts of 2.5 weight percent CrC13 6H2O in water. The viscosity of the solutions vs. time was determined.The data are: Solution 1 2 3 4 g 2.5% CrCI3 6H2O solution added 1.65 2.2 3.3 6.6 Initial Viscosity 39.5 39 37.5 38.5 15 min. 46.5 52.5 66 - > 150 45 min. 58 73 150 150 75 min. 64 95.5 150 -150 Overnight 150 150 u 150 150 Thus, it was shown that hydroxyethyl carboxyethyl cellulose can be crosslinked and the degree and rate of crosslink can be varied by the concentration of trivalent crosslinking ion. This is indicated by the increase in viscosity occurring with increasing concentrations of the Cr crosslinker.

EXAMPLE 4 By an analogous procedure to Example 3, the 10 hydroxyethyl carboxyethyl cellulose samples and the hydroxyethyl ca rboxymethyl cellulose depicted in Table I above were evaluated. Each cellulosic polymer dissolved in tap water at a concentration (based on contained resin) equivalent to 2.0 lib./42 gal. barrel hydroxyethyl ca rboxymethyl cellulose (as received).

The samples were also evaluated in saturated NaCI brine with CrCI3 6H20 and in 2 percent KCI brine with Al2(S04)3.18H20.

During these studies, it was observed that the hydroxyethyl carboxyethyl cellulose solutions generally had better clarity than those of hydroxyethyl carboxymethyl cellulose and the observations about clarity which is an indication of lower formation damage and the crosslinkability of hydroxyethyl carboxyethyl cellulose with less trivalent ions (mole ratio bases) were noted.

EXAMPLE 5 In this example, the following hydroxyethyl carboxyethyl cellulose (designated L, M, N) was compared to the same hydroxyethyl carboxymethyl cellulose (designated K, see Table I also): TABLE lI Percent Percent Designation M.S D. S. Volatiles Salt, From Ash L 2.21 0.30 7.01 2.52 M 2.47 0.42 1.82 2.42 N 2.27 0.50 2.83 3.54 K 2.48 0.37 6.53 3.90 The aqueous solutions were made-up at 2.00 ib/bbl (4.0 grams/700 ml) hydroxyethyl carboxymethyl cellulose, i.e.,[4.0x (1.0-(.0653 - .0390))j = 3.58 grams polymer as control. The same concentration of contained polymer was maintained for the HECEO samples/700 ml.

Li3.58 (1.0-(.0701 .0252))J = 3.96 gms M13.58 (1.0-(.0182 .0242))J = 3.74 gms N[3.58 (1.0-(.0283 .0354))J = 3.82 gms K[4.0 x (1.0-(.0653 .0390))J = 3.58 gms By a procedure analogous to Example 1, the crosslinkability of the three samples was compared to HECMO* in 2 percent KCi solution using Al2SO4 as crosslinker. The results are: * HECEC as used herein means hydroxyethyl carbox yethyl cellulose.

HECMC as used herein means hydroxyethyl car boxymethyl cellulose, i.e., product designated K in Tables I and II.

Product Designation L Sample 1 2 3 4 gms. 10 wt. %AI2SO4.18H2O sol.

added(1) 0.76 1.20 1.54 3.08 initial viscosity, AV. cps. 29 29 29 29 afterl5min. 35 64 115 150 after45 min. 39.5 102.5 150 150 after75min. 42 102.5 -150 -150 Overnight 50 150 -150 150 ") solution = 700 ml aqueous solution containing on a weight basis, 2% KCI with 3.96 gm polymer.

Product Designation M Sample 1 2 3 4 gms.10 wt.%Al2(SO4)3.18H2O solution added (2) 1.06 1.62 2.96 4.22 initial viscosity, AV, cps. 22.5 22.5 22.5 22.5 after 15 min. 40 87.5 150 17.5 after45 min. 50 150 150 10 after 75 min. 57.5 -150 95 7 Overnight 150 150 55 6 t2) Same as (1) above except with 3.74 gm polymer.

Product Designation N Sample 1 2 3 4 gms. 10 wt. %Al2(SO4)3.18H2O solution added3 1.26 1.96 2.54 5.08 initial viscosity, AV, cps. 31 31 31 31 after 15 min. 40 37.5 150 75 after45min. 57.5 150 150 12.5 after75 min. 58.5 150 -150 9 Overnight 150 150 150 10 3' Same as (1) above except with 3.82 gm polymer.

Product Designation K HECMC Sample 1 2 3 4 5 6 gms. 10 wt. %Al2(SO4)3.18H2O sol.

added (4) 1.0 1.12 1.68 2.0 2.2 4.4 initial viscosity, AV, cps. 30 28 28 30 28 28 after15min. 42.5 46 72.5 105 110 131 after45 min. 45 48 91.5 117.5 123 87.5 after75min. 47 49 102.5 117.5 127 71 Overnight 67.5 67.5 '150 -150 150 11 (4) Same as (1) above except with 4.0 gm HECMC.

The viscosity in solutions containing the higher concentrations of Al2(SO4)3 broke due to syneresis.

The unexpected crosslinkability of the HECEC samples with less trivalent AP-;+ compared to HECMC was verified. HECEC crosslinks to the same viscosity increase with less-trivalent Al ion than HECMC. The lower initial viscosity of solutions of Product M was apparently due to air in the reactor during the reaction (preparation) which lead to a slight reduction in molecular weight. Product M is near the M.S. -D.S. composition of the HECMC tested.

EXAMPLE 6 To confirm the observation of haze in the HECMC solutions compared to the HECEC's and the tendency towards formation damage, the following was run: Each of the polymers (1500 ppm as received) L, M and N of Example 5 and two lots of commercial HECMC, one being Product K above, were dissolved in a 3% NaCI 0.3% CaCI2, by weight, brine.After standing overnight they were filtered through a coarse sintered glass filter to remove any large insoluble matter and 1,000 ml filtered under pressure (40 psig)through 0.8 micron cellulose acetate/cellulose nitrate millipore filter paper (Millipore (TM) AAWP04700). The initial solution viscosities were: Product Solution Designation Viscosity {1) L 6.8 cps M 4.9 cps N 9.6 cps HECMC K 6.2 cps HECMC 0 6.2 cps (1) Viscosity measured on LVT Brookfield viscome ter with UL attachment at 6 RPM at ambient temperature (about 23"C).

The three HECEC solutions passed through the sintered glass prefilter with ease. HECMC Product K passed the prefilter satisfactorily but the HECMC Product 0 was difficult to pass through the prefilter.

The prefiltered samples (1,000 ml) were then pressure filtered through the 0.8 micron filter and the volume passing vs. time were noted. The data are: Volume Time of Filtration, Seconds Through Filter, HECEC HECMC ml L M N K O 100 30 12 90 30 ml/400 sec 55 ml/400 sec 200 92 23 195 ml/400 sec 300 225 35 400 385 ml/400 sec 50 500 68 600 88 700 112 800 138 900 170 1000 212 These data show the improved filterability of HECEC over HECMC which is indicative of lower formation damage.

EXAMPLE 7 Two grams of Hyd roxyethylca rboxyethyi Cellulose (MS=2.4 DS=0.31 ) were dissolved in 350 ml of 2% KCI brine by being mixed in a Waring blender for 15 seconds followed by a gentle stirring in a widemouth bottle equipped with a paddle stirrer for 10 minutes. The viscosity of the resultant solution as measured on a Fann Model 35A viscometer was 41.25 cps (indicated by a dial deflection of 82.5 at 600 ppm).

One-half (175 ml) of the solution was then removed from the bottle and 0.8974 grams of 10% Al2(SO4)3 18H20 crosslinking solution were added to the HECEC solution in the bottle. After one minute, the gelled mixture was transferred to the Waring blender and stirred at low speed for about two minutes to make it uniform. The gelled solution was then transferred to a calibrated Model 50C Fann viscometer and the sample heated at 300 psig pressure.

The viscosity as indicated by dial deflection was measured at 100 and 200"F. The data are summarized in Table I below.

EXAMPLE 8 By a procedure similar to that described in Example 7,2.0 grams of the HECEC polymer described above were dissolved in 350 ml of 2% KCI. The viscosity of the solution as measured on a Fann Model 35A viscometer was 39.75 cps (indicated by a dial deflection of 79.5 at 600 rpm). 175 ml of the solution were crosslinked with 0.7614 grams of 10% A12(S04)2 1 8H20 and the viscosity-temperature relationship then measured on the model 50C Fann viscometer. The data are summarized in Table I below.

EXAMPLE 9 By a procedure similar to that described in Example 7, 2.0 grams of commercial hydroxyethylcarboxymethyl cellulose (MS =2.48, DS =0.37) were dissolved in 350 ml of 2.0% KCI brine. The viscosity of the resultant solution was 30 cps (indicated by a dial deflection of 60 at 600 rpm on a model 35A Fann viscometer).

One-half of the sample (175 ml) was then removed and 0.9005 grams of 10% Al2(SO4)3 '1 8H2O crosslinking solution added to the remaining HECMC solution. The viscosity of the resultant gelled solution was measured at 100" and 200"F. The data are summarized in Table I.

TABLET Viscosity of Crosslinked Initial Solution Solution at Elevated Example Polymer Viscosity, cps Temp.(') 10a F 200"F 7 HECEC 41.25 227 66 8 HECEC 39.75 120 54 9 HECMC 30 82 10 (' Data reported are dial deflection units -highernumbers indicate - higher viscosity.

From the data of Table lit is apparent that the solutions of HECEC had a slightly higher viscosity before crosslinking and that such viscosity was maintained after crosslinking and at elevated temperatures. This is significant in maintaining a constant fluid viscosity during fracturing operations.

EXAMPLE 10 This example demonstrates the ability to breakdown the viscosity of the aqueous crosslinked cellulosic composition of this invention to facilitate production of the well.

A300 cc. sample of a hydroxyethyl carboxyethyl cellulose, essentially the same as characterized in Example 3 above except it had been previouslycros- slinked with 0.523 g of an aqueous 2.5 weight percent chromium chloride solution, was employed in this example. The viscosity of the cross linked solid gelled structure was well over 300 on the Fann Model 35A viscometer dial at 600 rpm. A sample of the crosslinked structure was placed on a LightningTM mixer and the breaker of the composition was added with agitation. The breaker was a pre-mixed composition containing 24 drops (1.77 g) of 2 weight percent HCI, 0.88 g ammonium persulfate and 0.72 g ferrous sulfate. The viscosity dropped immediately and within a matter of minutes the Fann dial reading dropped to 20 (at 600 RPM's) and finally dropped to 3.5 (at 600 rpm) free of gels. The resulting solution was a wateryfluid afterstanding overnight.

The same effect can be achieved with a variety of acid, bases and other redox systems which are cap able of displacing the bond between the hydrox yethyl carboxyethyl cellulose and the polyvalent metal ion. Suitable viscosity breaker materials include a variety of acids and bases, a variety of alk ali and alkaline earth metal salts or materials which will serve to reduce the valence of the metal while at the same time effecting oxidation of the cellulose material. Metal salts combined with mineral acids constitute an effective breaker composition.

Claims (11)

1. A process for fracturing subterranean strata or recovering oil therefrom wherein an aqueous medium containing a viscosifier is employed, said viscosifier comprising a crosslinked hydroxyethyl carboxyethyl cellulose in which the crosslinking is effected by a polyvalent metal.

2. A process as claimed in claim 1, wherein said aqueous medium is a fracturing fluid.

3. A process as claimed in claim 1, wherein said aqueous medium is employed in the recovery of oil.

4. A process as claimed in any one of the preceding claims, wherein the metal is aluminium.

5. A process as claimed in any one of the preceding claims, wherein the metal is chromium.

6. A modification of the process as claimed in any one of claims 1 to 3, wherein said viscosifier is a crosslinkable hydroxyethyl carboxyethyl cellulose.

7. An aqueous composition comprising water and a crosslinked hydroxyethyl carboxyethyl cellulose in which crosslinking is effected by a polyvalent metal.

8. An aqueous composition comprising water and a crosslinkable hydroxyethyl carboxyethyl cellulose.

9. An aqueous composition as claimed in claim 7 or 8, wherein said cellulose is present in an amount of from about 0.01 to about 5 weight per cent.

10. A process as claimed in claim 1, substantially as hereinbefore described in any one of the foregoing Examples.

11. An aqueous composition as claimed in claim 7 or 8, substantially as hereinbefore described in any one of the foregoing Examples.