GB2172008A - Powdered mobility control polymer for thickening aqueous solutions - Google Patents

Abstract

The powdered thickening agent comprises a water-soluble polymer composition having improved water dispersibility and solubility and is formed by combining a water-soluble polymer (for example a polysaccharide, a polyacrylamide, a polyethylene oxide or a polyvinyl pyrrolidine) and a non-acidic dissolving aid (for example a water-soluble surfactant such as sodium lignosulphonate, a petroleum sulphonate, a polyoxyethylene laurate or a polyethylene glycol). Such compositions may be made by admixture of the finely divided components or by adding the dissolving aid to a polymer broth, dehydrating the resultant mixture to produce a solid composition and pulverising the composition. Aqueous solutions of the polymer composition can be used in the recovery of crude oil from subterranean formations.

Description

SPECIFICATION Powdered mobility control polymer This invention relates to-polymer compositions for thickening aqueous solutions and methods for preparing and using such compositions. More particularly, this invention relates to dry water-soluble polymer compositions having improved water-contacting and dissolution properties.

Various water-soluble polymers have been developed which in aqueous solution exhibit superior thickening and flocculating properties at relatively low polymer concentrations. These polymers are being increasingly used in a number of commercial applications, such as in the clarification of aqueous solutions of uranium salts, in sizing paper and textiles, in the treatment of sewage and industrial wastes, as stabilizers for drilling muds, and in processes for recovering hydrocarbons from subterranean formations. Both natural polymers (also referred to as biopolymers) and synthetic polymers are useful in such applications. Two natural polymers particularly useful in oil recovery operations are the homopolysaccharide polymer Scleroglucan and the heteropolysaccharide polymer Xanthan.Examples of synthetic polymers are polyacrylamides (unhydrolyzed, partially hydrolyzed and hydrolyzed), polyethylene oxide, polyvinylpyrrolidine, poly(2-acrylamido-methyl-propyl sulfonate), and copolymers of acrylamide and 2-acrylamido-2methyl-propyl sulfonate.

Polymericviscosifiers are often available commercially as powders, or otherwise in finely divided solid form. However, they are most often utilized in aqueous solution. Accordingly, the solid polymer material must be dissolved in water. Although the various polymers are more or less soluble in water, difficulty is often experienced in preparing aqueous polymer solutions because of the slow and incomplete dissolution of many of these polymers.

Dissolution of dry polymer in water is hindered by the tendency of such polymer to cake on initial contact with water. Lumps of solid material are formed by the encapsulation of undissolved polymer in an outer coating of wet polymer. This wet polymer coating retards the penetration of additional water to the undissolved polymer. Although many of these lumps are eventually dissolved by continued agitation, it is frequently impractical to agitate the solution for a sufficiently long period to obtain complete dissolution. In many applications solids cannot be tolerated. Thus, the residual polymer solids must be removed by a separate filtration step resulting in increased preparation time and wasted polymer.

Most aqueous solutions of these polymers are non-Newtonian liquids exhibiting pseudoplastic flow under conditions of shear. Because of this characteristic, certain of these polymers have been adapted to thickening of aqueous liquids employed in various well stimulation and enhanced oil recovery processes.

The techniques of enhanced oil recovery (secondary and tertiary oil recovery) using polymeric viscosifiers as mobility control agents are well known. In typical secondary recovery operations, a water or brine pre-flush is followed by a waterflood. Flooding a reservoir with water alone (i.e., water which does not contain a mobility control agent) may give rise to "fingering". Fingering occurs when a less viscous fluid is used to displace a more viscous fluid. To minimize fingering effects, polymeric viscosifiers are added to the waterflood to provide mobility control by increasing the viscosity of the waterflood to a value greater than thatof displaced oil.

Tertiary chemical recovery processes conventionally employ microemulsions as displacement agents.

Microemulsions refer to a stable, transparent or translucent micellar solution or dispersion of oil, water or brine and at least one surfactant. A slug containing the displacing agent is injected into the formation through at least one injection means in an amount effective to displace oil. A driving fluid is then used to push the displaced oil to a production means. Water-soluble polymeric viscosifiers may be incorporated into the displacement fluid, the drive fluid or both as a means of providing mobility control.

Additionally, in some oil recovery processes, water-soluble polymer solutions are cross-linked to form gels-to plug high permeability or "thief" zones. These gels for plugging high permeability zones may be formed on the surface or in a subterranean formation by the addition of metal ions (such as chromium or aluminum ions) to an aqueous polymer solution.

When powdered polymeric viscosifiers are dissolved in water for enhanced oil recovery or other uses, the apparent viscosity of the solution is sharply increased, even in rather dilute solution. However, the preferred high molecular weight polymers are difficult to dissolve in water, particularly under field conditions encountered at the well site, due to the above-described tendency of the particulated solid polymer to cake and form lumps on contact with water. Time and energy are therefore needed to mix or agitate the partially dissolved polymer in an aqueous solution until the polymer is substantially dissolved. Also, the beneficial effect of the polymer is diminished by poor dispersion of the solid in the aqueous solution. Further, in enhanced oil recovery operations, injection of solid polymer into a producing formation can result in permanent plugging of the structure.

Currently, undissolved polymer is removed from aqueous polymer solutions by filtration. Two types of filters are commonly used. One such filter is a disposable cellulose acetate cartridge. After these filters are clogged they are discarded. The other type filter commonly used is composed of stainless steel mesh. These stainless steel filters are reusable but difficult and time consuming to clean. Thus, filtration by either method requires an extra step in polymer solution preparation and results in the waste of undissolved polymer. It is therefore desirable to develop a means for producing an aqueous polymer solution of the proper viscosity without producing undissolved solids which must be removed.

Heretofore various apparatus have been proposed to effedt dissolution of the solid polymer. Several of these devices function by creating a vortex into which the polymer solid is added in sufficiently small quantities that dissolution is substantially effected without caking or lumping. However, even with the best of such devices, dissolution of the polymer is time consuming and a certain amount of coagulation occurs.

As a result, additional filtration is necessary to ensure a solids-free aqueous polymer solution.

U.S. 3,402,137 (Fischer et al) discloses a method of producing a water-solublaacrylamide polymer with improved water dispersibility. A dry' water-soluble acrylamide polymer powder and a dry water-soluble acid salt are combined to form a dry mixture. This mixture can then be dissolved to produce thickened aqueous solutions. The acid salt is added to the polymer to improve the dispersibility of the polymer powder upon addition to aqueous solutions. However, a problem exists with polymer solutions prepared according to this patent in that there is an increase in the rate and degree of polymer degradation by hydrolysis. When dissolved polymers are degraded,their ability to thicken is reduced and the viscosity of the solution is decreased.

We have found that combining a non-acidic dissolving aid with a water-soluble high molecular weight polymer produces a polymer composition with improved water-contacting and water-solubilization characteristics. More particularly, we have found that an improved polymer composition comprised of awry, finely divided polymer and a dry, finely divided non-acidic dissolving aid produces a polymer which disperses and dissolves in an aqueous solution more readily and more completely than such water-soluble polymers alone. Additionally, we have found methods of producing such improved polymer compositions from either dry water-soluble polymer.or water-soluble polymer broth. Polymer solutions prepared according to this invention have significantly improved resistance to polymer degradation by hydrolysis.

The present invention discloses dry, non-acidic polymeric compositions which can be readily dissolved in an aqueous solution and methods for preparing and using such compositions. The polymer compositions of this invention are substantially dry mixtures of polymer and a non-acidic dissolving aid. Polymer solutions prepared with such compositions have significantly reduced susceptibility to polymer degradation by hydrolysis.

In general, non-acidic, water-soluble surfactants (also known as surface-active agents) which readily and substantially completely dissolve in aqueous solutions are suitable dissolving aids for the current invention.

Also, the dissolving aid should be a substantially dry solid, capable of being reduced to a finely-divided or powdered form. It may be additionally desirable to employ a dissolving aid which is tolerant of hard-water, that is, will not cause precipitation in the presence of polyvalent ions, such as calcium and magnesium.

Additionally, dissolving aids which are thermally stable are desirable if the polymer compositions containing the dissolving aids are used in high temperature environments.

Various non-acidic surfactants may be employed as a dissolving aid in the current invention. Examples of such surfactants are calcium lignosulfonate, ammonium lignosulfonate, petroleum sulfonates, polyoxyethylene oleate, polyoxyethylene laurate, polyethylene glycol, and block and graft copolymers of propylene oxide and ethylene oxide. A particularly useful, non-acidic dissolving aid is sodium lignosulfonate.

Lignosulfonates are anionic polyelectrolytes which are soluble in water and tolerant of hard water. They are also thermally stable in high temperature environments. Lignosulfonates are macromolecules built up by complex condensation of phenyl propane units. The sulfonate groups are attached to the aliphatic side chain, mainly to the alpha carbon. Lignosulfonates are water soluble and have molecular weights ranging from several thousand to about 50,000 or more. Lignosulfonates are readily available as by-products of the pulping industry. A more detailed discussion of lignosulfonates and a listing of commercially available lignosulfonates can be found in U.S. Patent 4,271,906 (Bousaid petal).

As discussed previously, both natural and synthetic polymers may be used to form the dry, non-acidic polymer compositions disclosed herein. Example natural polymers (also known as biopolymers) are guar gum, Scleroglucan and Xanthan. Scleroglucan and Xanthan have been found to be particularly useful in the compositions and methods of the current invention. Example synthetic polymers are polyacrylamides -(unhydrolyzed, partially hydrolyzed and hydrolyzed), polyethylene oxide, poiyvinylpyrrolidine, poly(2acrylamido-methyl-propyl sulfonate), and copolymers of acrylamide and 2-acrylamido-2-methyl-propyl sulfonate.

As demonstrated by the test results reported in Examples I-V below, the relative amounts of polymer and dissolving aid combined to form the polymeric compositions of the current invention may vary depending on the polymer and dissolving aid used, the aqueous solution and the desired final viscosity of the thickened aqueous solution. The ratios of polymer:dissolving aid in the tests performed employing a dissolving aid are summarized in Table 1. The dissolving aid used in all tests reported in Table 1-is sodium lignosulfonate (ERA-Petrolig 22S) manufactured by American Can Company).

Table 1 POLYMER TO DISSOLVING AID WEIGHT RATIOS Polymer: Dissolving Aid Aqueous Solution Polymer Solution No. 2 10:1 3.3%brine Scleroglucan Solution No. 4 10:1 3.3% brine Polyacrylamide Solution No. 6 1:1 3.3% brine Polyacrylamide Solution No.8 1:1 3.3% brine Scleroglucan Solution No. 10 1:1 Distilled Water Xanthan Solution No. 11 10:1 Distilled Water Xanthan Solution No. 13 1:1 3.3% brine Scleroglucan As indicated by the tests summarized in Table 1, improved dissolution of the dry polymer composition is positively demonstrated with polymer to dissolving aid weight ratios of 10:1 to 1:1. However, the dry non-acidic polymer compositions of the current invention are not limited to the specific weight ratios of Table 1 and Examples I-V.Such examples are provided to teach the utility and application of the compositions and methods of the current invention, not limit their scope.

Two methods for preparing the improved polymer compositions of the current invention are disclosed. In the first method, dry particulate polymer is mixed with a dry non-acidic dissolving aid. The resulting polymer composition is capable of improved dissolution in an aqueous medium. In the second method, a non-acidic dissolving aid is added to-a polymer broth. This polymer broth containing polymer and the dissolving aid is dehydrated to form a dry powder. When needed, a dry polymer composition prepared in accordance with either above-described process can be-dissolved in an aqueous medium more easily and more completely than the polymer alone.

The polymer compositions of the current invention may be employed in oil recovery processes such as viscous waterflooding and enhanced oil recovery processes using microemulsions.

In operation in viscous waterflooding, a polymer composition prepared in accordance with the current invention is dissolved in water or brine to give the desired viscosity for a particular flooding operation. The thickened water or brine may be injected into the reservoir throughout the waterflooding operation.

However, satisfactory results can generally be obtained by adding a polymer composition to only a portion of the water or brine injected into the reservoir. This leads to the establishment of a bank of viscous solution surrounding the injection well. Ordinary water or brine without the polymer composition or other thickener can then be injected in order to propel the bank of viscous solution through the reservoir toward one or more production wells from which the displaced crude is recovered.

In operation in enhanced oil recovery processes, a polymer composition of the current invention may be a component in a single-phase microemulsion which is introduced into subterranean formations to improve oil recovery. In addition to a polymer component, such microemulsions will also be comprised of an aqueous component, a surfactant and an oil component. Typically, a specific microemulsion is designed for a particular subterranean formation. One method for designing a suitable microemulsion is described in U.S.

Patent 4,271,907 (Gale). After designing a suitable microemulsion, a bank of thickened or unthickened water or brine may be injected into the formation before injecting the microemulsion. This bank may be thickened with a polymer composition of the current invention. Next, microemulsion slugs designed for the particular reservoir are injected into the formation. Generally, the microemulsion slugs injected into the subterranean formation are from about 0.02 to about 2 PV (pore volumes of the reservoir), preferably 0.05 to 0.5 PV.

Following injection of the thickened microemulsion, thickened water is preferably injected into the formation to displace injected microemulsion through the formation through one or more production wells. The thickened water may be ordinary water or brine containing a polymer composition of the current invention or another polymer Use of the polymer compositions of the current invention are described herein in waterflooding and enhanced oil recovery processes. However, such details descriptions are not intended to limit the polymer composition to such uses. Rather, the polymer composition of the current inventing presents distinct advantages in any process requiring dissolution of a polymer in an aqueous solution. Such processes include clarification of uranium salts, sizing paper and textiles, treatment of sewage and industrial waste and drilling operations.

The tests below were performed to demonstrate the improved dissolution and viscosifying properties of aqueous-solutions prepared with the modified dry polymer compositions of the current invention.

Example I This Example I qualitatively demonstrates the improved dissolution properties of compositions of the current invention. Two 50 ml test phials containing 40 ml 3.3% brine (3% NaCI and 0.3% CaCI2) were prepared. 0.5 gm dry Scleroglucan polymer (Actigum CS-1 I, manufactured by CECA, SA and available from Jetco, Corsicana, Texas) was added to the first phial to form Solution No. 1. 0.5 gm dry Scleroglucan polymer mixed with 0.05 gm dry sodium lignosulfonate (ERA-Petrolig 22e) manufactured by American Can Company) were added to the second phial to form Solution No. 2. Both phials were covered and agitated by hand. In the first phial, lumps of aggregated, undissolved Scleroglucan polymer were present in the brine solution. Continued vigorous agitation faiied to dissolve the aggregated Scleroglucan polymer.In the second phial, after only a few second of agitation, no lumps of aggregated, undissolved polymer were observed. This indicates substantially complete dissolution of the dry polymer mixture.

In addition to promoting ready dissolution of polymer, the use of the sodium lignosulfonate lessens or removes the need for extended agitation and filtering of the solution. Also, more complete dissolution of the polymer means more efficient use of the polymer since less polymer will be required to achieve an acceptable solution.

Additionally, it was observed that the solution was stable over time. The polymer mixture of Solution No. 2 did not precipitate out of the solution upon standing for over three years. During that same period, the polymer did not substantially degrade. To demonstrate the stability of aqueous solutions prepared with polymer compositions of the current invention, the viscosity of Solution No. 2 was measured at the beginning and the end of a 3-1/2 year period using a Contraves Low Shear 30 Viscometer at 25"C and 11 sec-1. At the beginning of the 3-1/2 year period the viscosity for Solution No. 2 of 37.3 cP was measured. At the end of the period, the viscosity of Solution No. 2 was 36.0 cP. This demonstrates essentially no polymer - degradation in aqueous solutions containing polymer compositions of the current invention.

Example lI Tests similar to those in Example I were conducted using the synthetic polymer polyacrylamide. Four solutions were prepared. Solution No.3 was prepared by adding 0.5 gm dry polyacrylamide (Dow Pusher 7009 manufactured by the Dow Chemical Company) to 40 ml 3.3% brine (3% NaCI and 0.3% CaCI2). Solution No.4 was prepared by adding a dry mixture of 0.5 gm dry polyacrylamide (Dow Pusher 7009) arid 0.05 gm dry sodium lignosulfonate (ERA-Petrolig 229) to 40 ml 3.3% brine. Both solutions were agitated by hand. No difference was noted in the dissolving capabilities of the two compositions; that is, aggregated, undissolved polymer remained visible in both Solution No.3 and Solution No.4.

Solution No. 5 was prepared by adding 0.1 gm polyacrylamide (Dow Pusher 700) to 100 ml 3.3% brine.

Solution No. 6 was prepared by adding a mixture of 0.1 gm polyacrylamide (Dow Pusher 7000') and 0.1 gm sodium lignosulfonate (ERA-Petrolig 22@) to 100 ml 3.3% brine. After several minutes of agitation by hand, undissolved polymer could be observed in both Solution No.5 and Solution No.6. Solution No.5 and Solution No. 6 were then separately placed in Cole-Palmer Model 4555-20 Solid State Speed Controller and agitated at 1,500 rpm for twenty minutes. After mechanical agitation, Solution No. 5 still contained visible, undissolved aggregates of polymer. No undissolved aggregates of polymer were visible in Solution No.6 which contained a dissolving aid.As further evidence ofthe improved dissolution of polyacrylamide in the presence of a dissolving aid, the viscosity of Solution No. 5 and Solution No. 6 was measured at various nominai shear rates using a Contraves Low Shear 30 Viscometer at 25"C. The results of this viscosity analysis are summerized in Table 2.

Table2 VISCOSITIES OF POLYACRYLAMIDE/SODIUM LIGNOSULFONATE SOLUTIONS AT VARIOUS SHEAR RATES Shear Rate Solution No. 5 Solution No. 6 (sex~1) Viscosity (cP) Viscosity (cP) 1.75 2.00 3.40 4.39 2.05 3.30 11.02 1.99 3.03 27.70 1.92 2.93 69.50 1.86 2.79 The increased viscosities for Solution No. 6 (containing a dissolving aid) indicates the more complete dissolution of the dry polymer in an aqueous solution in the presence of a dissolving aid.

Example 111 Tests were performed to quantitatively determine the effect of sodium lignosulfonate as a dissolving aid in the preparation of an aqueous polymer solution from dry Scleroglucan polymer powder.

An aqueous polymer solution (Solution No.7) was prepared by adding 0.15 gm dry Scleroglucan (Actigum CS-119) polymer to 100 ml 3.3% brine (3% NaCI and 0.3% CaCI2) in a graduated cylinder. The cylinder was vigorously agitated by hand to promote dissolution of the polymer. After several minutes of agitation, the solution still -contained a substantial quantity of lumps of undissolved polymer aggregate ranging in size from less than 1 mm to about 1 cm. The solution was allowed to stand for one hour at room temperature (approximately 25"C). At the end of the hour, the viscosity for Solution No.7 of 2.3 cP was determined using a Contraves Low Shear 30 Viscometer at a temperature of 25"C and a nominal shear rate of 11 sec-'.The test results are summarized in Table 3.

A modified dry polymer powder of the current invention was prepared by mixing 0.15 gm dry Scleroglucan (Actigum CS-il) polymer and 0.15 gm dry sodium lignosulfonate (ERA-Petrolig 228). This modified dry polymer mixture was added to 100-ml 3.3% brine (3% NaCI and 0.3% CaCI2) in a graduated cylinder to produce Solution No.8. The cylinder was shaken by hand for a few seconds. No lumps of aggregated, undissolved polymer were observed. The solution was allowed to stand at room temperature for 1 hour. At the end of the hour, a solution viscosity of 21.3 cP was measured using a Contraves Low Shear 30 Viscometer at a temperature of 25"C and a shear rate of 11 sec-1. These test results are contained in Table 3.Comparing the viscosity of the aqueous polymer solution without sodium lignosulfonate (2.3 cP for Solution No. 7) to the viscosity of the aqueous solution prepared with a modified polymer powder incorporating sodium lignosulfonate (21.3 cP for Solution No. 8) demonstrates some of the advantages of the current invention. The almost tenfold increase in the viscosity of the aqueous solution prepared using the modified polymer powder shows a more effective and efficient use of polymer. Also, the improved viscosity of Solution No. 8 viewed in combination with the lack of visible aggregates of undissolved polymer indicates a more complete dissolution is caused by the incorporation of sodium lignosulfonate into the dry polymer powder.

Example IV Tests were preformed to determine the effect of sodium lignosulfonate as a dissolving aid in the preparation of an aqueous polymer solution from dry Xanthan polymer powder. Three test solutions were prepared as follows. For Solution No. 9, 1 gm dry Xanthan polymer (Xanflood, manufactured by Kelco, San Diego, California, a division of Merck Co.) was blended with 500 ml water in a Gifford-Wood Homogenizer at 60 volts for 1 minute. For Solution No. 10, 1 gm dry Xanthan (Xanfloodo) polymer was hand-mixed with 1 gm dry sodium lignosulfonate (ERA-Petrolig 22) and this dry mixture was blended with 500 ml water in a Gifford-Wood Homogenizer at 60 volts for 1 minute.For Solution No. 11, 1 gm dry Xanthan (Xanflood) polymer was hand-mixed with 0.1 gm dry sodium lignosulfonate (ERA-Petrolig 229) and this dry mixture was blended with 500 ml water in a Gifford-Wood Homogenizer at 60 volts for 1 minute.

The viscosity of each of the three test solutions was measured using a Contraves Low Shear 30 Viscometer at 11 sec-l at 25"C. The viscosities are listed in Table 3. Also included in Table 3 are the viscosities of all polymer/sodium lignosulfonate solutions tested at a shear rate of 11 sec-l in Examples I-V.

Table3 VISCOSITIES OF POLYMER/SODIUM LIGNOSOLFONATE SOLUTIONS Sodium lignosul- Solution No. Polymer fonate (gm) Viscosity (cP) 2 0.5 gm Scleroglucan 0.05 37.3 5 0.1 gm polyacrylamide 0 1.99 6 0.1 gm polyacrylamide 0.1 3.03 7 0.l5gmScleroglucan 0 2.3 8 0.15 gm Scleroglucan 0.15 21.3 9 1 gm Xanthan 0 95.02 10 1 gmXanthan 1 216.08 11 1 gm Xanthan 0.1 93.54 Comparison of Solution No. to Solution No.9 indicates that sodium lignosulfonate in sufficient quantities will improve the dissolution of dry Xanthan polymer in water. This is shown by the significant increase in the viscosity of Solution No. 10 (which contains sodium lignosulfonate as a dissolving aid) over the viscosity of Solution No. 9 (which contains no sodium lignosulfonate).Thus, more complete, more rapid and more effective dissolution of Xanthan polymer in an aqueous solution results from the addition of a sufficient amount of sodium lignosulfonate.

Example V The following tests were performed to demonstrate aqueous polymer solutions prepared from dry polymers modified in accordance with the current invention are useful in oil recovery processes.

Prior to use in waterflooding and enhanced oil recovery processes, a two-step laboratory procedure may be performed on viscosified brines to determine the ability of such brines to propagate into the reservoir without plugging the formation pores. In the first step of the procedure, referred to as the prefiltration step, the aqueous polymer solution is passed through a filter medium having relatively iarge pore spaces (such as a 5 micron Nuclepore filter). This step simulates the field practice of filtration prior to injection, and is primarily for removal of particulate contaminants. In the second step, referred to as the injectivity test step, the aqueous polymer solution is passed through a filter medium having relatively small pore spaces (such as a 1.2 micron Gel man Versaporfilter). This step indicates the ability of the brine to flow through the reservoir.

Solution No. 12 (identical to Solution No.7) and Solution No. 13 (identical to Solution No.8) were prepared. Both Solution No. 12 and Solution No. 13 were diluted to 300 ppm polymer by the addition of 400 ml polymer solution. Filtration tests similar to those described above were performed on these diluted solutions to assess their usefulness in waterflooding for oil recovery. All filtration tests described below were carried out with a 40 psi pressure drop across the filter.

Four hundred milliiiters of diluted Solution No. 12, containing no sodium lignosulfonate, were placed in a pressurized vessel connected to a 5 micron Nuclepore filter medium having a diameter of 47 mm. The filter plugged quickly. Less than 10 ml of the 400 ml passed through the filter before plugging. This indicates substantial undissolved agglomerates or lumps of Scleroglucan polymer which, when injected into a hydrocarbon formation during oil recovery processes would tend to clog equipment and plug the pores of the formation.

Four hundred miliiliters of diluted Solution No. 13 were first filtered through a 5 micron Nuclepore filter in the prefiltration step described above. This prefiltered Solution No. was then passed through a 1.2 micron, 47 mm diameter, Gelman Versapor filter in the injectivity test described above. The test results are listed in Table 4.

Table 4 GELMAN VERSAPOR FILTER TEST RESULTS FOR SOLUTION No. 13 Elapsed Time - Accumulated Volume (sec) (ml) 7.08 100 17.39 200 24.05 250 32.11 300 48.31 400 A flow rate of 100 ml/min through the current test filter would indicate that the Scleroglucan polymer is well dissolved in the aqueous solution and will propagate well into the formation. 400 ml of Solution No. 13 passed through the test filter in less than one minute demonstrating that Solution No. 13 is an acceptable oil recovery injection fluid.

Claims (18)

CLAIMS 1. A finely divided solid water-soluble polymer composition comprising a mixture of water-soluble polymer and non-acidic water-soluble dissolving aid. 2. A composition according to claim 1 comprising finely divided particles of the water-soluble polymer and finely divided particles of the non-acidic water-soluble dissolving aid. 3. A composition according to either of claims 1 and 2 wherein the weight ratio of water-soluble polymer to non-acidic water-soluble dissolving aid is in the range of about 10 to 1 to about 1 to 1. 4. A composition according to any one of the preceding claims wherein said water-soluble polymer is Scleroglucan, Xanthan, polyacrylamide or a mixture thereof. 5. A composition according to any one of the preceding claims wherein said non-acidic water-soluble dissolving aid is sodium lignosulphonate. 6. A method of preparing a polymer mixture according to any one of the preceding claims comprising mixing the finely divided solid water-soluble polymer with the finely divided solid non-acidic dissolving aid to form a substantially homogeneous mixture. 7. A method of preparing a dehydrated polymer composition comprising (a) preparing a polymer broth, (b) adding non-acidic dissolving aid to said polymer broth to form a substantially homogeneous mixture, (c) dehydrating said homogeneous mixture to produce a solid composition and (d) forming said solid composition into finely divided particles. 8. A method according to claim 7 wherein said water-soluble polymer is Scleroglucan, Xanthan, polyacrylamide or a mixture thereof. 9. A method according to either of claims 7 and 8 wherein said non-acidic dissolving aid is sodium lignosulphonate. 10. An aqueous solution for injection into a subterranean formation for the recovery of hydrocarbons from such formation comprising a water-soluble polymer, a non-acidic dissolving aid and an aqueous solvent. 11. An aqueous solution according to claim 10 wherein the weight ratio of water-soluble polymerto non-acidic dissolving aid is in the range of about 10 to 1 to about 1 to 1. 12. An aqueous solution according to either of claims 10 and 11 wherein said water-soluble polymer is Scleroglucan 13. An aqueous solution-according to any one of claims 10 to 12 wherein said aqueous solvent is brine. 14. An aqueous solution according to any one of claims 10 to 14 wherein said non-acidic dissolving aid is sodium lignosulphonate. 15. A method for recovering crude oil from a subterranean formation penetrated by at least one injection means and at least one production means which comprises injecting an aqueous solution according to any one of claims 10 to 14 wherein the amount of water-soluble polymer is sufficient for mobility control, driving displaced oil through said formation and recovering said oil through said production means. 16. A composition according to claim 1 substantially as hereinbefore described with reference to the Examples. Amendments to the claims have been filed, and have the following effect: (a) Claims 1-16 above have been deleted or textually amended. (b) New or textually amended claims have been filed as follows:

1. A finely divided solid water-soluble polymer composition for use in enhanced oil recovery consisting of a mixture of water-soluble polymer and non-acidic water-soluble dissolving aid.

2. A composition according to claim 1 wherein the weight ratio of water-soluble polymer to non-acidic water-soiuble dissolving aid is in the range of about 10 to 1 to about 1 to 1.

3. A composition according to either of claims 1 and 2 wherein said water-soluble polymer is chosen from Scleroglucan, Xanthan, polyacrylamide and any mixture thereof.

4. A composition according to any one of claims 1 to 3 wherein said non-acidic water-soluble dissolving aid is selected from (1) sodium lignosulphonate, (2) calcium lignosulphonate, (3) ammonium lignosulphonate, (4) petroleum sulphonates, (5) polyoxyethylene oleate, (6) polyoxyethylene laurate, (7) polyethylene glycol, (8) block and graft copolymers of propylene oxide and ethylene oxide and (9) any mixture thereof.

5. A finely divided solid water-soluble polymer composition for use in enhanced oil recovery comprised of finely divided particles of water-soluble polymer and finely divided particles of lignosulphonate.

6. A method of preparing a polymer mixture consisting essentially of water-soluble polymer and non-acidic dissolving aid, said method comprising mixing finely divided solid water-soluble polymer with finely divided solid non-acidic dissolving aid to form a substantially homogeneous mixture wherein the water-soluble polymer to non-acidic dissolving aid weight ratio is in the range of about 10 to 1 to about 1 to 1.

7. A method according to claim 6 wherein said water-soluble polymer is selected from Scleroglucan, Xanthan, polyacrylamide and any mixture thereof.

8. A method according to either of claims 6 and 7 wherein said non-acidic dissolving aid is selected from (1) sodium lignosulphonate, (2) calcium lignosulphonate, (3) ammonium lignosulphonate, (4) petroleum sulphonates, (5) polyoxyethylene oleate, (6) polyoxyethylene laurate, (7) polyethylene glycol, (8) block and graft copolymers of propylene oxide and ethylene oxide and (9) any mixture thereof.

9. A method of preparing a dehydrated polymer composition consisting essentially of polymer and non-acidic dissolving aid, said method comprising (a) preparing a polymer broth, (b) adding non-acidic dissolving aid to said polymer broth to form a substantially homogeneous mixture, (c) dehydrating said homogeneous mixture to produce a solid composition and (d) forming said solid composition into finely divided particles.

10. A method according to claim 9 wherein said water soluble polymer is selected from Scleroglucan, Xanthan, polyacrylamide and any mixture thereof.

11. A method according to either of claims 9 and 10 wherein said non-acidic dissolving aid is selected from (1) sodium lignosulphonate, (2) calcium lignosulphonate, (3) ammonium lignosulphonate, (4) petroleum sulphonates, (5) polyoxyethylene oleate, (6) polyoxyethylene laurate, (7) polyethylene glycol, (8) block and graft copolymers of propylene oxide and ethylene oxide and (9) any mixture thereof.

12. A method for recovering crude ooil from subterranean formation penetrated by at least one injection means and at least one production means which comprises (1) injecting an aqueous solution comprising a water soluble polymer composition and an aqueous solvent said polymer composition consisting essentially of water-soluble polymer and a non-acidic dissolving aid, said polymer composition present in an effective amount for mobility control (2) driving displaced oil through said formation and (3) recovering said oil through said production means.

13. A method according to claim 12 wherein said aqueous solvent is brine.

14. A method according to either of claims 12 and 13 wherein said non-acidic dissolving aid is selected from (1) sodium lignosulphonate, (2) calcium lignosulphonate, (3) ammonium lignosulphonate, (4) petroleum sulphonates, (5) polyoxyethylene oleate, (6) polyoxyethylene laurate, (7) polyethylene glycol, (8) block and graft copolymers of propylene oxide and ethylene oxide and (9) any mixture thereof.

15. A method of preparing a polymer mixture comprising mixing finely divided solid water-soluble polymer with finely divided solid lignosulphonate to form a substantially homogeneous mixture wherein the water-soluble polymer to lignosulphonate weight ratio is in the range of about 10 to 1 to about 1 to 1.

16. A method according toclaim 15 wherein said water-soluble polymer is selected from Scleroglucan, Xanthan, polyacrylamide and any mixture thereof.

17. A method of preparing a dehydrated polymer composition comprising (a) preparing a polymer broth, (b) adding lignosulphonate to said polymer broth to form a substantially homogeneous mixture, (c) dehydrating said homogenous mixture to produce a solid composition and (d) forming said solid composition into finely divided particles.

18. - A method according to claim 17 wherein said water-soluble polymer is selected from Scleroglucan, Xanthan polyacrylamide and any mixture thereof.