Polysaccharides, methods for preparing such polysaccharides and fluids utilizing such polysaccharides

Claim 2

A water-soluble cellulose ether containing pendent vic dihydroxy structure having or capable of assuming a cis geometry and having a shear-thermal stability characteristic of at least about 30 at 250° F. for a 0.6 percent by weight aqueous solution of said cellulose ether crosslinked by a polyvalent metal ion.

Claim 3

The water-soluble cellulose ether of claim 1 wherein said cellulose ether has said shear-thermal stability characteristic of at least about 60.

Claim 4

The water-soluble cellulose ether of claim 2 wherein said cellulose ether has said shear-thermal stability characteristic of at least about 90.

Claim 5

The water-soluble cellulose ether of claim 1 wherein said pendent vic dihydroxy structure is present in an amount to provide a degree of substitution of from about 0.3 to about 1.3.

Claim 6

The water-soluble cellulose ether of claim 4 wherein the degree of substitution is in the range of from about 0.5 to about 1.2.

Claim 7

The water-soluble cellulose ether of claim 1 wherein said pendent vic dihydroxy structure comprises the residue of glycidol.

Claim 8

The water-soluble cellulose ether of claim 1 wherein said cellulose ether is a hydroxyethyl cellulose, a hydroxypropylhydroxyethyl cellulose, a carboxymethyl cellulose or a hydroxypropyl cellulose.

Claim 9

The water-soluble cellulose ether of claim 7 wherein said cellulose ether is hydroxyethyl cellulose.

Claim 10

The water-soluble hydroxyethyl cellulose of claim 8 wherein said cellulose ether has, as a 1 percent by weight solution in water, a Brookfield viscosity at 20° C. of at least about 1,200 centipoise.

Claim 11

The water-soluble hydroxyethyl cellulose of claim 9 wherein the Brookfield viscosity is at least about 1800.

Claim 12

The water-soluble hydroxyethyl cellulose of claim 9 wherein the Brookfield viscosity is at least about 2500.

Claim 13

A process for preparing a water-soluble cellulose ether containing pendent vic dihydroxy structure having or capable of assuming a cis geometry which comprises: (a) charging a cellulose ether starting material to a diluent system including water in an amount sufficient to swell the cellulose ether starting material to provide a slurry in an enclosed reaction vessel, (b) stirring the slurry while sparging the reaction vessel with an inert gas to remove entrained air, (c) adding an alkaline material in an amount sufficient to catalyze the reaction of the cellulose ether with a reactant capable of incorporating into said cellulose ether a pendent vic dihydroxy structure, (d) adding said reactant over a predetermined period of time in an amount sufficient to incorporate in the cellulose ether a predetermined degree of substitution of pendent vic dihydroxy structure, (e) continuing stirring the slurry while allowing the reaction to be completed, the total reaction time being at least about 2 hours, the temperature being maintained throughout in the range of from about ambient conditions to reflux of the diluent system, (f) adding acid in an amount sufficient to neutralize the resulting water-soluble cellulose ether product and (g) recovering same, said cellulose ether having, upon cross-linking, a shear-thermal stability characteristic of at least about 30 at 250° F. for a 0.6 percent by weight aqueous solution of said cellulose ether crosslinked by a polyvalent metal ion.

Claim 14

A process for preparing a water-soluble cellulose ether containing pendent vic dihydroxy structure having or capable of assuming a cis geometry which comprises: (a) charging a cellulose ether starting material to a diluent system including water in an amount sufficient to swell the cellulose ether starting material to provide a slurry in an enclosed reaction vessel, (b) stirring the slurry while sparging the reaction vessel with an inert gas to remove entrained air, (c) adding an alkaline material in an amount sufficient to catalyze the reaction of the cellulose ether with a reactant capable of incorporating into said cellulose ether a pendent vic dihydroxy structure, (d) adding said reactant over a predetermined period of time in an amount sufficient to incorporate in the cellulose ether a predetermined degree of substitution of pendent vic dihydroxy structure, (e) continuing stirring the slurry while allowing the reaction to be completed, the total reaction time being at least about 2 hours, the temperature being maintained throughout in the range of from about ambient conditions to reflux of the diluent system, (f) adding acid in an amount sufficient to neutralize the resulting water-soluble cellulose ether product and (g) recovering same, said cellulose ether having, upon cross-linking, a shear-thermal stability characteristic of at least about 30 at 250° F. for a 0.6 percent by weight aqueous solution of said cellulose ether crosslinked by a polyvalent metal ion.

Claim 15

The process of claim 12 wherein said cellulose ether is hydroxyethyl cellulose.

Claim 16

The process of claim 13 wherein said hydroxyethyl cellulose starting material has, as a 1 percent by weight solution in water, a Brookfield viscosity at 20° C. of at least about 2,500 centipoise.

Claim 17

The hydroxyethyl cellulose of claim 14 wherein said Brookfield viscosity is at least about 5,000 centipoise.

Claim 18

The process of claim 13 wherein said hydroxyethyl cellulose starting material is the purified product resulting from the etherification of a cellulosic source contained in the diluent system in which said product was prepared.

Claim 19

The process of claim 13 wherein the diluent is a member selected from the group consisting of acetone, isopropanol and t-butanol.

Claim 20

The process of claim 17 wherein the diluent is acetone.

Claim 21

The process of claim 18 wherein the water content of the diluent system is from about 5 to about 20 percent, based upon the total weight of acetone and water.

Claim 22

The process of claim 19 wherein the water content is in the range of about 7 to about 13 percent by weight.

Claim 23

The process of claim 13 wherein the weight ratio of the diluent to the hydroxyethyl cellulose starting material is in the range of from about 4:1 to about 25:1.

Claim 24

The process of claim 13 wherein the diluent to hydroxyethyl cellulose starting material weight ratio is in the range of from about 5:1 to about 10:1.

Claim 25

The process of claim 13 wherein said inert gas is nitrogen.

Claim 26

The process of claim 13 wherein said alkaline material is sodium hydroxide.

Claim 27

The process of claim 24 wherein the molar ratio of sodium hydroxide to said hydroxyethyl cellulose is in the range of from about 0.4:1 to about 1:1.

Claim 28

The process of claim 13 wherein said reactant is glycidol.

Claim 29

The process of claim 26 wherein said reactant is distilled glycidol.

Claim 30

The process of claim 26 wherein said reactant is crude glycidol.

Claim 31

The process of claim 13 wherein said reactant is 2,3-epoxy-1,4-butanediol.

Claim 32

The process of claim 13 wherein said reactant is added in an amount sufficient to provide a degree of substitution in the hydroxyethyl cellulose starting material in the range of from about 0.3 to about 1.3.

Claim 33

The process of claim 30 wherein said reactant is added in an amount sufficient to provide a degree of substitution in the range of from about 0.5 to about 1.2.

Claim 34

The process of claim 13 wherein said reactant is added over a period of at least one hour.

Claim 35

The process of claim 13 wherein the hydroxyethyl cellulose product recovered is washed to remove impurities and then dried.

Claim 36

A viscosified fluid comprising water, an effective viscosifying amount of a crosslinked water-soluble cellulose ether containing pendent vic dihydroxy structure having or capable of assuming a cis geometry, and a polyvalent metal cross-linker, said cellulose ether having a shear-thermal stability characteristic of at least about 30 at 250° F. for a 0.6 percent by weight aqueous solution of said cellulose ether crosslinked by a polyvalent metal ion.

Claim 37

A viscosified fluid comprising water, an effective viscosifying amount of a crosslinked water-soluble cellulose ether containing pendent vic dihydroxy structure having or capable of assuming a cis geometry, and a polyvalent metal cross-linker, said cellulose ether having a shear-thermal stability characteristic of at least about 30 at 250° F. for a 0.6 percent by weight aqueous solution of said cellulose ether crosslinked by a polyvalent metal ion.

Claim 38

The viscosified fluid of claim 34 wherein said fluid includes a proppant.

Claim 39

The viscosified fluid of claim 34 wherein said fluid includes a gravel pack material.

Claim 40

The viscosified fluid of claim 34 wherein said fluid includes an acid.

Claim 41

The viscosified fluid of claim 34 wherein the shear-thermal stability characteristic of said cellulose ether is at least about 60.

Claim 42

The viscosified fluid of claim 38 wherein the shear-thermal stability characteristic of said cellulose ether is at least about 90.

Claim 43

The viscosified fluid of claim 34 wherein said pendent vic dihydroxy structure is present in an amount to provide a degree of substitution of from about 0.3 to about 1.3.

Claim 44

The viscosified fluid of claim 40 wherein the degree of substitution is in the range of from about 0.5 to about 1.2.

Claim 45

The viscosified fluid of claim 34 wherein said pendent vic dihydroxy structure comprises the residue of glycidol.

Claim 46

The viscosified fluid of claim 34 which includes a buffer to maintain the pH in the range of from about 6 to about 9.

Claim 47

The viscosified fluid of claim 34 wherein said cellulose ether is a hydroxyethyl cellulose, a hydroxypropylhydroxyethyl cellulose, a carboxymethyl cellulose or a hydroxypropyl cellulose.

Claim 48

The viscosified fluid of claim 44 wherein said cellulose ether is hydroxyethyl cellulose.

Claim 49

The viscosified fluid of claim 45 wherein said water-soluble hydroxyethyl cellulose has, as a 1 percent by weight solution in water, a Brookfield viscosity at 20° C. of at least about 1,200 centipoise.

Claim 50

The viscosified fluid of claim 46 wherein said Brookfield viscosity is at least about 1800.

Claim 51

The viscosified fluid of claim 46 wherein said Brookfield viscosity is at least about 2500.