Thickening of fluids

Abstract

An aqueous fluid, possibly a wellbore fracturing fluid, comprises an aqueous solution or dispersion of a first polymer, which may be polysaccharide, as a thickener and a cross linking agent to enhance the viscosity of the fluid by crosslinking the first polymer, wherein the crosslinking agent is a second polymer comprising at least one polymer chain with phenyl boronate groups distributed along the polymer chain and the phenyl boronic acid groups have nitrogen attached to the phenyl group at a position which is meta relative to the boronate group.

Claims

1. A wellbore treatment fluid comprising: an aqueous solution or dispersion of a first polymer to thicken the fluid; a cross-linking agent to increase viscosity of the fluid by cross-linking the first polymer, wherein the cross-linking agent is a second polymer comprising at least one polymer chain with phenyl boronate groups distributed along the polymer chain, and wherein each phenyl boronate group comprises a phenyl group and a boronate group and has a nitrogen atom attached to the phenyl group at a position which is meta relative to the boronate group; and a viscosity breaker to reduce viscosity of the fluid after a period of time.

2. The wellbore treatment fluid of claim 1, wherein each phenyl boronate group is attached to the polymer chain through the nitrogen atom.

3. The wellbore treatment fluid of claim 1, wherein the phenyl boronate groups have a nitro substituent on the phenyl group at a position meta to the boronate group.

4. The wellbore treatment fluid of claim 1, wherein the concentration of the first polymer is in a range from 0.5 to 5 g/liter.

5. The wellbore treatment fluid of claim 1, wherein the concentration of the first polymer is no more than 2 g/liter.

6. The wellbore treatment fluid of claim 1, wherein the first polymer is a polysaccharide or a chemically modified polysaccharide.

7. The wellbore treatment fluid of claim 1, wherein the content of boron in the fluid is between about 5 and about 25 ppm by weight elemental boron.

8. The wellbore treatment fluid of claim 1, wherein the cross-linking agent includes a colored or fluorescent material to act as a tracer.

9. A method of treatment of a wellbore or a formation penetrated by a wellbore, the method comprising: pumping into the wellbore a fluid comprising: an aqueous solution or dispersion of a first polymer; and a cross-linking agent to increase viscosity of the fluid by cross-linking the first polymer, wherein the cross-linking agent is a second polymer comprising at least one polymer chain with phenyl boronate groups distributed along the polymer chain, and wherein each phenyl boronate group comprises a phenyl group and a boronate group and has a nitrogen atom attached to the phenyl group at a position which is meta relative to the boronate group.

10. The method of claim 9, wherein the phenyl boronate groups are attached to the polymer chain through the said-nitrogen atom.

11. The method of claim 9, wherein the phenyl boronate groups have a nitro substituent on the phenyl ring at a position meta to the boronate group.

12. The method of claim 9, wherein a concentration of the first polymer in the fluid is in a range from about 0.5 to about 2 g/liter.

13. The method of claim 9, wherein the first polymer is a polysaccharide or a chemically modified polysaccharide.

14. The method of claim 9, wherein a content of boron in the fluid is between about 5 and about 25 ppm by weight elemental boron.

15. The method of claim 9, wherein the cross-linking agent includes a colored or fluorescent material to act as a tracer.

16. The wellbore treatment fluid of claim 1, wherein the fluid is a fracturing fluid and contains suspended proppant.

17. A wellbore treatment fluid comprising: an aqueous solution or dispersion of a first polymer to thicken the fluid; and a cross-linking agent to increase viscosity of the fluid by cross-linking the first polymer, wherein the cross-linking agent is a second polymer comprising at least one polymer chain with phenyl boronate groups distributed along the polymer chain, and wherein each phenyl boronate group comprises a phenyl group and a boronate group and has a nitrogen atom attached to the phenyl group at a position which is meta relative to the boronate group; wherein the wellbore treatment fluid is a gravel packing fluid and contains gravel.

18. A wellbore treatment fluid comprising: an aqueous solution or dispersion of a first polymer to thicken the fluid; a cross-linking agent to increase viscosity of the fluid by cross-linking the first polymer, wherein the cross-linking agent is a second polymer comprising at least one polymer chain with phenyl boronate groups distributed along the polymer chain, and wherein each phenyl boronate group comprises a phenyl group and a boronate group and has a nitrogen atom attached to the phenyl group at a position which is meta relative to the boronate group; and one or more of a corrosion inhibitor, a chelating agent, an electrolyte, or a friction reducer.

19. A wellbore treatment fluid comprising: an aqueous solution or dispersion of a first polymer to thicken the fluid; and a cross-linking agent to increase viscosity of the fluid by cross-linking the first polymer, wherein the cross-linking agent is a second polymer comprising at least one polymer chain with phenyl boronate groups distributed along the polymer chain, and wherein each phenyl boronate group comprises a phenyl group and a boronate group and has a nitrogen atom attached to the phenyl group at a position which is meta relative to the boronate group; wherein the wellbore treatment fluid is an energized fluid formed by injecting gas into a wellbore concomitantly with the wellbore treatment fluid.

20. A wellbore treatment fluid comprising: an aqueous solution or dispersion of a first polymer to thicken the fluid; and a cross-linking agent to increase viscosity of the fluid by cross-linking the first polymer, wherein the cross-linking agent is a second polymer comprising at least one polymer chain with phenyl boronate groups distributed along the polymer chain, and wherein each phenyl boronate group comprises a phenyl group and a boronate group and has a nitrogen atom attached to the phenyl group at a position which is meta relative to the boronate group; wherein the wellbore treatment fluid contains plugs to achieve zonal isolation or to prevent fluid loss.

21. A wellbore treatment fluid comprising: an aqueous solution or dispersion of a first polymer to thicken the fluid; a cross-linking agent to increase viscosity of the fluid by cross-linking the first polymer, wherein the cross-linking agent is a second polymer comprising at least one polymer chain with phenyl boronate groups distributed along the polymer chain, and wherein each phenyl boronate group comprises a phenyl group and a boronate group and has a nitrogen atom attached to the phenyl group at a position which is meta relative to the boronate group; and a fiber component to improve one or more of particle suspension, particle transport capabilities, or gas phase stability.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1 and 2 are graphs of viscosity of thickened guar at ambient temperature;

(2) FIGS. 3, 4 and 5 show viscosity of thickened guar as temperature is raised and lowered; and

(3) FIG. 6 is a graph of viscosity of guar in a salt solution.

EXAMPLE 1

(4) A number of crosslinking agents were made, starting from copolymers of styrene and maleic anhydride. This polystyrene-co-maleic anhydride copolymer has high water solubility and is known to react with nucleophiles such as hydroxyl or amines. The copolymer was reacted with an aminophenylboronic acid in anhydrous tetrahydrofuran (THF) under reflux conditions. In a second step, the crude polymer was redissolved in water/NaOH which opened any remaining maleic anhydride rings. This two step reaction is illustrated thus:

(5) ##STR00003##

(6) Commercially available polystyrene-co-maleic anhydrides with varying molecular weight and ratio of styrene/maleic units were used.

(7) Synthesis of Functionalised Polystyrene-Co-Maleic Anhydride

(8) 2 g of polystyrene-co-maleic anhydride terminated with cumene and having Mn=1600 (1.25103 mol, 5.8 maleic moieties per chain) and a chosen amount of 3-amino phenyl boronic acid were added to 80 ml of tetrahydrofuran. The solution was stirred at 60 C. for 24 h. The solvent was evaporated with a rotary evaporator and the solid was redissolved in water made alkaline to pH=11. Excess water was evaporated and the product polymer was freeze-dried for 48 h.

(9) This procedure was carried out using amino phenyl boronic acids as follows

(10) TABLE-US-00001 Equivalents per Acid polymer chain 3-amino phenyl boronic 621 mg 4.00 10.sup.3 mol 3 acid monohydrate 3-amino phenyl boronic 1242 mg 8.00 10.sup.3 mol 6 acid monohydrate 2-amino phenyl boronic 1096 mg 8.00 10.sup.3 mol 6 acid 4-aminophenyl boronic 1387 mg 8.00 10.sup.3 mol 6 acid hydrochloride

(11) This procedure was also carried out using 1 g of polystyrene-co-maleic anhydride Mn=5000 (2.010.sup.4 mol, 20 maleic moieties per chain) and 630 mg of 3-aminophenylboronic acid monohydrate.

(12) The same procedure was repeated using 2 g of polystyrene-co-maleic anhydride Mn=9500 (2.110.sup.4 mol) and amounts of amino phenyl boronic acid as in the following table

(13) TABLE-US-00002 Equivalents per Acid polymer chain 3-amino phenyl boronic 315 mg 2.04 10.sup.3 mol 10 acid monohydrate 3-amino phenyl boronic 630 mg 4.08 10.sup.3 mol 19 acid monohydrate

(14) For all of the polymers synthesized as above, the amount of boron within the polymer was measured by ICP-MS. Using solutions made with 150 mg of polymer in 2.50 ml of water and diluted 2000 times with 1% nitric acid. Calibration curves were obtained from boron standard solution (1000 ppmB). The results were

(15) TABLE-US-00003 Polymer Abbreviation Ratio of boron to polymer Ps-co-Ma 1600 3PBA 3eq Poly1600-3-3 13.0 1.3 mg/g Ps-co-Ma 1600 3PBA 6eq Poly 1600-3-6 24.5 1.2 mg/g Ps-co Ma 5000 3PBA 18eq Poly 5000-3-18 21.0 2.1 mg/g Ps-co-Ma 9500 3PBA 10eq Poly9500-3-10 8.1 0.8 mg/g Ps-co-Ma 9500 3PBA 20eq Poly 9500-3-20 10.1 1.2 mg/g Ps-co Ma 1600 2PBA 6eq Poly 1600-2-6 22.3 2.2 mg/g Ps-co-Ma 1600 4PBA 6eq Poly 1600-4-6 10.5 1.0 mg/g
Testing Under Standard Conditions

(16) Crosslinking agents prepared as above were tested for ability to crosslink unmodified guar. An aqueous guar solution containing guar at a concentration of 4 gm/liter, equivalent to 33 lbs per 1000 US gallons was first prepared by mixing guar powder with de-ionised water in a Waring blender for 30 minutes. Polymer, prepared as above, was added to a 15 ml aliquot of the guar solution in an amount to give a boron concentration of 60 ppm. As a comparison, inorganic borate was added to a quantity of the same guar solution so as to give a boron concentration of 60 ppm. Portions of each mixture were diluted so as to provide lower concentrations of guar and boron, with the same guar to boron ratio. The lowest guar concentration was 1 gm/liter containing 0.75 ppm boron as polymer or 15 ppm boron as borate.

(17) After mixing, the pH was raised above 9.5 to allow crosslinking and thickening to occur, and after a delay of 7 minutes, viscosities were measured at 25 C. at shear rates of 25 sec.sup.1.

(18) It was found that poly 1600-4-6 failed to cross link guar. Other results are shown in FIG. 1 and FIG. 2 where solid lines show data for crosslinking polymers and broken lines show the data points for inorganic borate.

(19) It can be seen from these graphs that the cross linking polymers made using 3-amino phenyl boronic acid achieved much higher viscosities than inorganic borate with the same concentrations of boron and guar, and were able to achieve similar viscosities to borate even when the amount of guar and boron was reduced to half.

(20) Testing Under Temperature

(21) An aqueous guar solutions containing guar at a concentration of 0.36 gm/liter, equivalent to 30 lbs per 1000 US gallons was thickened with poly 1600-3-3 in an amount to provide 60 ppm boron in solution. A similar solution was thickened with poly 9500-3-20 in an amount to provide 20 ppm boron in solution. After mixing, pH was raised to 11.4 to thicken the solutions. Viscosity was monitored as temperature was progressively increased and then reduced again, so as to find the melting temperature of the crosslinked gels. Results are shown in FIGS. 3 and 4.

(22) The solution of guar thickened with poly 1600-3-3 progressively lost viscosity at temperatures above about 150 F. and had little or no viscosity above 160 F. However, its viscosity recovered somewhat when temperature was reduced. The sample thickened with the higher molecular weight poly 9500-3-20 showed better stability of viscosity in the temperature range 100-150 F., lost viscosity when temperature was raised to 200 F. and also recovered viscosity on cooling.

(23) Testing in a Salt Solution.

(24) An aqueous guar solution containing guar at a concentration of 0.4 gm/liter (0.4 wt %) was made as above while also including 1 wt % potassium chloride. A portion of the solution was successfully thickened with poly 1600-3-3 in an amount to provide 60 ppm boron in solution. An attempt was also made to thicken another portion with poly 1600-2-3 (made as above from 2-amino phenyl boronic acid) but the viscosity at low shear was about 1000 times lower. Such a solution cannot be thickened with inorganic borate: precipitation occurs.

(25) Viscosity of the solution thickened with poly 1600-3-3 was measured at a range of shear rates at 20 C., then the solution was heated in stages to 80 C. and cooled in stages back to 20 C., with viscosity measured over the range of shear rates at each temperature step. These viscosity measurements are shown as FIG. 6.

EXAMPLE 2

(26) A cross linking polymer was made by reacting polybenzyl chloride with 3 amino phenyl boronic acid in tetrahydrofuran, thus.

(27) ##STR00004##

(28) The polybenzylchoride had a molecular weight of about 100,000 which corresponds to about 660 benzyl chloride groups in a polymer chain. The amount of 3-phenyl boronic acid was chosen to introduce about 500 phenyl boronate groups per polymer chain.

(29) A solution containing guar at a concentration of 0.36 gm/liter, equivalent to 30 lbs per 1000 US gallons was thickened with this cross linking polymer in an amount to provide 60 ppm boron in solution. The thickened solution was tested as in the previous example by monitoring viscosity as temperature was progressively increased and then reduced again. The results are shown as FIG. 5. It can be seen that substantial viscosity was maintained up to about 140 F. The viscosity reduced at higher temperatures but recovered when temperature was reduced.

(30) It will be appreciated that example embodiments such as described in detail above can be modified and varied within the scope of the concepts which they exemplify. Features referred to above or shown in individual embodiments above may be used together in any combination as well as those which have been shown and described specifically. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.