Hydrating and Dissolving Polymers

Abstract

Polyacrylamides, guar gum (sometimes guar), xanthan gum, carboxymethylcellulose, hydroxyethylcellulose, and other water-soluble polymers are dissolved and hydrated in aqueous solutions, including especially recycled drilling, fracturing, and other oilfield fluids having significant salt contents, by passing the water-soluble polymer together with the aqueous medium to a cavitation device including an integrated disc pump. The integration of a disc pump with the cavitation device reduces the risk of gumming by applying a negative pressure at the feed point. The ability to use water-soluble polymers with the salty recycled oilfield fluids has significant environmental benefits, namely (1) fresh water is not needed, (2) disposal of the environmentally undesirable returned fluids is not needed, (3) difficultly degradable synthetic polymers may not be needed, and, in particular, (4) the enhanced ability to use guar, which, being a natural product, is biodegradable, is environmentally favored. Although the invention is most beneficial for use with salt or brackish water, its high efficiency points to beneficial use where fresh water is the only available choice for the aqueous medium. Where dry polymer is used, the invention's benefits are especially realized in terms of logistics and handling, since viscous and bulky solutions need not be prepared and stored in advance, thus also minimizing health, safety and environmental risks

Claims

1-20. (canceled)

21. Method of hydrating water-soluble polymer in an aqueous medium comprising (a) adding said water-soluble polymer to said aqueous medium (b) flowing said aqueous medium and said polymer into an integrated cavitation disc pump, and (c) operating said integrated cavitation disc pump to intimately mix and heat said polymer and said aqueous medium.

22. Method of claim 21 wherein said integrated cavitation disc pump has at least two disc pump discs.

23. Method of claim 21 wherein said water-soluble polymer comprises a natural polymer.

24. Method of claim 23 wherein said natural polymer is guar.

25. Method of claim 21 wherein said water-soluble polymer comprises a synthetic polymer.

26. Method of claim 25 wherein said synthetic polymer comprises polyacrylamide.

27. Method of claim 21 wherein said aqueous medium comprises salt or brackish fluid.

28. Method of claim 27 wherein said salt or brackish fluid is a produced oil field fluid or a clear completion fluid.

29. Method of claim 21 including, during step (c), recycling a portion of said aqueous medium containing said added polymer by adding said portion to the aqueous medium and polymer of step (a).

30. Method of hydrolyzing and dissolving a water-soluble polymer comprising passing said polymer together with an aqueous medium through a plurality of operating integrated cavitation disc pumps.

31. Method of claim 30 including operating said integrated cavitation disc pumps in series.

32. Method of claim 30 including operating said integrated cavitation disc pumps in parallel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is a diagram of my invention apparatus for use with dry polymer.

[0021] FIG. 2 shows a variation of the invention to describe treating and recycling polymer solution.

[0022] FIG. 3 illustrates further versatility of the invention, showing two of my units arranged for operation in series or parallel.

[0023] FIG. 4 depicts an adaptation of FIG. 1 to illustrate the use of the cavitation pump to hydrate and dissolve polymers in accordance with the concept of this continuation-in-part application.

[0024] FIG. 5 depicts an adaptation of FIG. 2 to illustrate the use of the cavitation pump, with recycling, to hydrate and dissolve polymers in accordance with the concept of this continuation-in-part application.

[0025] FIG. 6 depicts an adaptation of FIG. 3 to illustrate the use of more than one cavitation pump to hydrate and dissolve polymers in accordance with the concept of this continuation-in-part application.

DETAILED DESCRIPTION OF THE INVENTION

[0026] Referring now to FIG. 1, my method will be discussed with respect to feeds of dry powdered or flake polymer and brackish or salt water. Dry guar gum, polyacrylamide or other water-soluble polymer 1 in hopper 2 is fed directly into eductor 3 having an inlet 4 for salt-containing water such as a recycled or produced oil field fluid, or ocean water, which enters inlet 4 from a source not shown. The dry polymer mixes with the salt-containing water immediately on contact in the eductor, which includes a venturi 5 as is known in the art. The mixture passes from the venturi 5 through inlet 6 of the generally cylindrical housing 7 of the integrated disc pump and cavitation device.

[0027] The disc pump portion of the integrated disc pump cavitation device comprises three discs 8, 9, and 10 in substantially parallel planes, each having a central orifice 11, 12, and 13. The discs 8, 9, and 10 are held in place by supports 14 and 15 so that they will rotate with cavitation rotor 16. Rotation of the discs 8, 9, and 10 will cause the mixture entering housing 7 to flow through the integrated disc pump cavitation device whether or not the salt-containing water at inlet 4 is under an external positive pressure.

[0028] The mixture follows the arrows within housing 7, ultimately leaving through exit 17. Cavitation rotor 16, mounted on shaft 20 connected to a motor not shown, has a plurality of cavities 18 on its cylindrical surface. In the restricted space 19 between the cylindrical surface and housing 7, the fluid tends to enter the cavities but is immediately flung out by centrifugal force, causing small vacuum effects in the cavities, which are immediately filled; this fairly violent mini-action accelerates the mixing and dispersion of the polymer in the water, enabling rapid hydration of the polymer.

[0029] I have illustrated the invention with three discs 8, 9, and 10, but one or two may be effective for some purposes, and there may be as many as eight or ten; I prefer at least two discs but, as a practical matter, if there are more than five or six discs, it may be beneficial to lengthen shaft 20 so that it will pass through all orifices 11, 12, and 13 and be steadied by a collar fixed centrally near inlet 6. This will add to the cost and may not be necessary especially if any of the product solution is to be recycled.

[0030] The same equipment can be used to further dissolve highly concentrated solutions of polymer rather than dry polymer. That is, the hopper 2 will contain a concentrated solution of polymer made elsewhere instead of dry polymer as described above with reference to FIG. 1. This concentrated solution in hopper 2 may be quite viscous, but can be fed into eductor 3 by gravity or with the aid of a negative pressure exerted by the disc pump comprising discs 8, 9, and 10. Aqueous fluid from inlet 4 immediately begins to dilute the solution as they are mixed in eductor 3, and further hydrates the polymer as it follows the turbulent paths around discs 8, 9, and 10. In the constricted area between the rapidly turning cylinder 16 and the closely conforming internal surface of housing 7, the solution and some partially hydrolyzed polymer are subjected to the cavitation effect, which heats them as well as thoroughly mixes them, causing a great increase in surface area contact between the solution and any remaining unhydrolyzed polymer.

[0031] Four experiments were performed in a cavitation device similar to FIG. 1. The produced water used was from the Permian Basin and contained 120,000 ppm chlorides. Viscosity measurements were done with a Fann 35 using a B2 bob at 300 rpm and viscosity measured in about 2 minutes.

Example 1

[0032] Guar and water were mixed in a pail in a ratio of 40 pounds dry guar to 1000 gallons water and then run through a cavitation device similar to that of FIG. 1. Viscosity of 22 cps in the pail was increased to 33 cps after exiting the cavitation device, a 50% increase.

Example 2

[0033] Produced water from an oil field was mixed with an equal amount of fresh water and this brackish water was mixed in a pail at a ratio of 40 pounds of dry guar to 1000 gallons of brackish water, then run through the cavitation device similar to FIG. 1. At 2 minutes the hydration, as measured by viscosity, was increased from 18 cps to 33 cps, an 83% increase; at 3 minutes the 22.5 cps viscosity in the pail was increased to 34.5 cps, a 53% increase.

Example 3

[0034] 100% produced water was mixed in a pail with dry guar, in a ratio of 25 pounds to 1000 gallons of water. After running through the cavitation device, the viscosity in the pail of 11 cps was increased to 21 cps, a 91% increase.

Example 4

[0035] 100% produced water was mixed in the pail with dry guar in a ratio of 40 pounds guar to 1000 gallons of water, and run through the cavitation device as in the other examples. A viscosity of 15 cps was increased to 32 cps, an increase of 113%.

[0036] The conclusion for the experiments was that controlled cavitation speeds up the hydration of dry guar, and the most dramatic increase is in salt waters. In 100% salt water, the guar hydrated and developed viscosity the same as in both fresh water and salt water diluted by 50%.

[0037] Whether hopper 2 contains dry polymer or a concentrated solution, the aqueous fluid fed through inlet 4 may be plain water, brackish or salt water. It can be added to plain water, brackish, or salt water to provide a solution of friction reducer, or it may be added to a used drilling or fracturing fluid to make a reconstituted drilling or fracturing fluid.

[0038] It should be understood that hopper 2 is illustrative. Any effective means or device for feeding polymer into eductor 3 may be used. A control valve may regulate the rate of feed of polymer into eductor 3, whether the polymer is dry or a concentrated solution. Likewise, the rate of intake of the aqueous solvent through inlet 4 may be regulated by any satisfactory means. Eductor 3 may be any convenient eductor having two inlets and a venturi.

[0039] Referring now to FIG. 2, it will be seen that the hopper 2 of FIG. 1 has been removed and replaced by a conduit 30 for introducing a concentrated solution of polymer from a source not shown into eductor 3 by way of inlet 31. The solution passes through a valve 33 which may be used to control the rate of introduction of the solution into eductor 3. Any other or additional control valves or devices may be used to regulate the introduction of the solution.

[0040] Also seen is conduit 34 at exit 17 of housing 7, taking the processed solution from housing 7 to valve 35, from which it may be conveyed through conduit 36 to be used or stored. Valve 35 may also direct a portion of the processed solution through conduit 37 back to valve 33 for recycling to eductor 3. The processed solution in conduit 37 may be mixed with the incoming concentrated solution in conduit 30 on its way to the eductor 3. A viscometer may be inserted in conduit 37 or elsewhere in the recycle loop to help determine the position of valves 35 and 33. If desired, the recycled processed solution in conduit 37 may be injected directly into the incoming salt water prior to entering inlet 4, instead of or in addition to adding it in conduit 30.

[0041] In FIG. 3, two units designated A and B, each similar to the apparatus of FIG. 2, are connected for hydrating, diluting or dissolving various materials, but operation will be described first for dissolving polymer in salt water. Shaft 20 of unit A is turned by a motor not shown, which rotates both the cavitation rotor 16 and discs 8, 9, and 10 of unit A. As explained with reference to FIG. 1, rotation of discs 8, 9, and 10 generates a pumping action which draws salt water from a source not shown through inlet 4 of eductor 3 of unit A. A polymer to be hydrated, dissolved, or diluted also is introduced to eductor 3 of unit A, by way of inlet 31. The polymer may be dry as in the hopper 2 of FIG. 1 or a concentrated solution, it being understood that by a concentrated solution of polymer I mean one which is quite viscous although it may contain only a very small amount of polymer. The concentrated solution may be introduced through conduit 40 and valve 41, or from conduit 42 having a source 43. The dry, concentrated, or partly dissolved polymer and the salt water are mixed and further dissolved within housing 7 of unit A as described with respect to FIGS. 1 and 2, leaving unit A from exit 17 into conduit 34.

[0042] For parallel operation of units A and B, valves 44 and 45 are adjusted to send the processed material from unit A through conduits 46 and 47. Normally, parallel operation means both units A and B will operate substantially identically. In this example, salt water from source 60 will enter unit B through its inlet 4 (by way of conduit 54) and dry polymer or concentrate will enter inlet 31 of unit B from source 48 or otherwise through conduit 49 into eductor 3 of unit B. Turning shaft 20 of unit B will induce the mixing materials from eductor 3 to be further mixed and subjected to the cavitation action of the cavitation device as described elsewhere. The thoroughly mixed materials, now hydrated, dissolved and/or diluted, emerge at exit 17 of unit B and are sent by valve 50 through conduit 51 to join the similar processed fluid from unit A at valve 45 to be sent to storage or use through conduit 47. Parallel operation has been described in the situation where both units A and B process the same materials, but it should be understood that different materials may be introduced into the two units and brought together at valve 45.

[0043] In series operation, the finished processed material from unit A is utilized as a feed material for unit B. The two materials mixed in eductor 3 of unit A, further mixed by the discs 8, 9, and 10 of unit A, and further processed by cavitation within housing 7 are sent by valve 44 through conduits 52, 53 and 54 to inlet 4 of eductor 3 of unit B, where it is mixed with one of the ingredients introduced in unit A or a third material, from conduit 49. Alternatively, the mixture in conduit 54 may become the source material 48. The new combination in eductor 3 of unit B is processed by unit B as previously described, emerging in conduit 34, from which it may be sent to conduit 47 for use or storage. In a variation of the series mode, part of the material in conduit 34 of unit A may be recycled to either conduits 48 and 49 of unit B or 43 and 42 of unit A and reprocessed as described with reference to FIG. 2.

[0044] Many different materials may be processed in my apparatus. For example, a water-soluble polymer could be crosslinked by sending a solution of polymer through one inlet of an eductor and a crosslinking agent could be introduced through the other. Forming a crosslinked polymer will in almost all cases substantially increase the viscosity of the solution, but the apparatus can readily handle it. As another example, fresh water may be used where I speak of salt water. The cavitation device being excellent for mixing and heating, various chemical reactions can be performed in my apparatus.

[0045] In either parallel or series operation, recycling may be performed within either unit A or unit B in the manner described with respect to FIG. 2, while also conducting either parallel or series operation. Parallel and series operation may be conducted with more than two units. Using three or more units, parallel and series operations can be combined.

[0046] A great advantage of my invention is that the cavitation action enables maximum hydration of the polymers even using very high concentrations of salts. Seawater, typically having about 35,000 milligrams per liter (mg/1) chloride, and produced waters (water removed from the earth in the hydrocarbon production process), not uncommonly having very high concentrations of chlorides up to 200,000 mg/1, are readily handled by the cavitation device operated to hydrate virtually any water soluble polymer. The polymers themselves tend to react differently to salt, but the mini-violent cavitation action can overcome any difficulties posed by a particular brine, including ones containing high concentrations of bromides, common in clear completion fluids. Thus my invention is applicable to the use of brackish fluids, sometimes defined as containing from 1000 to 5000 mg/l salt, as well as very high content salt water such as ocean water, seawater and gulf water as in the Gulf of Mexico, which may be slightly less salty than the open ocean because of significant fresh water from rivers. My use of the term salt water is intended to include brackish water as defined above as well as, in oil field terminology, produced water, meaning brackish water which emerges from wells along with produced hydrocarbons or as a consequence of producing the hydrocarbons, and clear completion fluids, which may contain significant quantities of bromides or formates. Clear completion fluids commonly also meet the definitions of salt water or brackish water. Having the ability to mix and heat means my invention is also applicable to the use of fresh water to conduct various chemical reactions.

[0047] Thus my invention includes a method of hydrating dry polymer in salt water comprising (a) contacting the dry polymer with the salt water in an eductor, (b) flowing the salt water and the polymer from the eductor into a rotating disc pump, (c) passing the salt water and polymer from the disc pump to a cavitation device, and (d) operating the cavitation device to intimately mix and heat the polymer and the salt water.

[0048] My invention also includes an apparatus for dissolving and hydrating water soluble polymer comprising (a) an eductor (b) a cavitation device having a cavitation rotor for rotation within a substantially cylindrical housing, and (c) a disc pump, the disc pump being adapted to receive a mixture comprising polymer and water from the eductor and pass it to the cavitation device, the disc pump also adapted to rotate with the cavitation rotor.

[0049] And, my invention includes a method of diluting a concentrated solution of water soluble polymer with salt water comprising (a) contacting the concentrated solution with the salt water in an eductor, (b) flowing the salt water and the concentrated solution from the eductor into a rotating disc pump, and (c) passing the salt water and concentrated solution from the disc pump to a cavitation device, and (d) operating the cavitation device to intimately mix and heat the concentrated solution and the salt water.

[0050] FIGS. 4, 5, and 6 relate to this continuation-in-part application. They are adapted from FIGS. 1, 2, and 3; therefore, wherever possible the reference numbers of FIGS. 1, 2, and 3 have been retained.

[0051] Referring now to FIG. 4, dry guar gum, polyacrylamide or other water-soluble polymer 1 in hopper 2 is fed directly into conduit 80 having an inlet 4 which may be for fresh or salt-containing water such as a recycled or produced oil field fluid, gulf or ocean water. The aqueous solution enters inlet 4 from a source not shown. The dry polymer 1, which may be in flake or other form, mixes with the aqueous medium immediately in conduit 80. The mixture then passes through inlet 6 of the generally cylindrical housing 7 of the integrated cavitation disc pump. I call the apparatus within housing 7 an integrated cavitation disc pump because the disc pump and the cavitation rotor are within the same housing and are mounted on a common shaft 20 which may be, and normally is, rotated by a motor, as further explained throughout the present application. A disc pump in a separate housing, even if on the same rotating shaft as the cavitation rotor, would not be able to establish the flow pattern described herein, delivering fluid to constricted space 19.

[0052] As in FIG. 1, the disc pump portion of the integrated disc pump of FIG. 4 comprises three discs 8, 9, and 10 in substantially parallel planes, each having a central orifice 11, 12, and 13. The discs 8, 9, and 10 are held in place by supports 14 and 15 so that they will rotate with cavitation rotor 16. Rotation of the discs 8, 9, and 10 will cause the mixture entering housing 7 to flow through the integrated disc pump whether or not the aqueous mixture at inlet 4 or inlet 6 is under an external positive pressure. The principle of the disc pump is well known and widely used after its original description more than 100 years ago in Tesla's U.S. Pat. No. 1,061,142. Rotation of the discs causes a pulling or inducting effect, drawing the fluid from inlet 4 into the housing 7. This negative pressure alleviates a tendency of polymers to gum up at the feed point when the sole fluid force is a positive one upstream of the feed point. It also insures against the highly undesirable backing up of fluid into the hopper or other source of polymer. The integrated cavitation pump is the subject of U.S. patent application Ser. No. 14/715,160 and its continuation-in-part Ser. No. 15/221,878, and is further described in those applications. Both application Ser. Nos. 14/715,160 and 15/221,878 are hereby incorporated herein by reference in their entireties.

[0053] The flow path of the mixture follows the arrows within housing 7, ultimately leaving through exit 17. Cavitation rotor 16, mounted on shaft 20, which is turned by a motor not shown, has a plurality of cavities 18 on its cylindrical surface. In using the term cavity, I employ the basic definition of a cavity as a hollowed out space; normally the cavities will be placed on the rotor 16 by boring to a desired depth. They are dead-end holes which may be called closed bores since they are normally made by drilling a short distance into the cylindrical surface of the cavitation rotor. In the restricted space 19 between the cylindrical surface and housing 7, the fluid tends to enter the cavities but is immediately flung out by centrifugal force, causing small vacuum effects in the cavities, which are immediately filled; this fairly violent mini-action accelerates the mixing and dispersion of the polymer in the water, enabling highly enhanced contact between the polymer and the water, resulting in rapid hydration of the polymer.

[0054] Following is a paraphrase of a passage in my U.S. Pat. No. 7,201,225 describing the action of the cavitation rotor on a different fluid, adapted to use reference numbers of FIG. 4: On passing into the space 19 between housing 7 and cavitation rotor 16, the solution quickly encounters cavities 18 and tends to fill them, but the centrifugal force of the rotation tends to throw the liquid back out of the cavities, which creates vacuum in them.

[0055] As applied to the use of the present application's cavitation pump, the vacuum in the cavities draws the liquid back into them, creating constant mini-violence in them, and causing intimate contact of the water with the hydratable sites of the polymer as they are constantly filled, emptied and filled again. Small bubbles are formed and instantly imploded. Heat is generated without the use of a heat transfer surface; the heat is beneficial to the hydrolyzing process and is largely retained in the liquid, minimizing dissipation into the metal parts.

[0056] I have illustrated the invention with three discs 8, 9, and 10, but one or two may be effective for some purposes, and there may be as many as eight or ten; I prefer at least two discs but, as a practical matter, if there are more than five or six discs, it may be beneficial to lengthen shaft 20 so that it will pass through all orifices 11, 12, and 13 and be steadied by a collar fixed centrally near inlet 6. This will add to the cost and may not be necessary especially if any of the product solution is to be recycled.

[0057] The system of FIG. 4 can be used to further dissolve previously made highly concentrated solutions of polymer rather than dry polymer. That is, the hopper 2 will contain a concentrated solution of polymer made elsewhere instead of dry polymer as described above with reference to FIG. 4. This concentrated solution in hopper 2 may be quite viscous, but can be fed into conduit 80 by gravity or with the aid of a negative pressure exerted by the disc pump comprising discs 8, 9, and 10. Aqueous fluid from inlet 4 immediately begins to dilute the solution as they are mixed in conduit 80, and further hydrates the polymer as it follows the turbulent paths around discs 8, 9, and 10. In the constricted space 19 between the rapidly turning cylinder (cavitation rotor) 16 and the closely conforming internal surface of housing 7, the solution and some partially hydrolyzed polymer are subjected to the cavitation effect described above, which heats them as well as thoroughly mixes them, causing a great increase in surface area contact between the solution and any remaining unhydrolyzed polymer.

[0058] In FIG. 5, it will be seen that the hopper 2 of FIG. 4 has been removed and replaced by a conduit 30 for introducing a concentrated solution of polymer, or an aqueous medium carrying dry or partially dissolved polymer from a source not shown into conduit 80 by way of inlet 31. The solution passes through a valve 33 which may be used to control the rate of introduction of the solution or mixture into conduit 80, which contains fresh water, salt water, brackish water, recovered oil field water, or other aqueous fluid from inlet 4 as described elsewhere herein. Any other or additional control valves or devices may be used to regulate the introduction of the aqueous material to the cavitation pump. Discs 8, 9, and 10 operate as described for FIGS. 1 and 4, and cavitation rotor 16 is also constructed as described in FIGS. 1 and 4. The cavitation pump comprising the discs and cavitation rotor 16 within housing 7 operate as described with respect to FIGS. 1 and 4, efficiently hydrating and dissolving the polymer in the aqueous carrier.

[0059] Also seen is conduit 34 at exit 17 of housing 7, taking the processed solution from housing 7 to valve 35, from which it may be conveyed through conduit 36 to be used or stored. Valve 35 may also direct a portion of the processed solution through conduit 37 back to valve 33 for recycling to conduit 80. The processed solution in conduit 37 may be mixed with the incoming concentrated solution in conduit 30 on its way to conduit 80. A viscometer may be inserted in conduit 37 or elsewhere in the recycle loop to help determine the position of valves 35 and 33. If desired, the recycled processed solution in conduit 37 may be injected directly into the incoming aqueous carrier prior to entering inlet 4, instead of or in addition to adding it in conduit 30.

[0060] FIG. 6 is adapted from FIG. 3; but conduits 80 are substituted for eductors 3. By appropriate operation of the valves as described in FIG. 3, the two cavitation pumps A and B can be arranged to treat incoming mixtures of polymer and aqueous carrier separately, in parallel, or in series, noting that in each case cavitation pumps A and B need not be served by an eductor, and that the invention is applicable to achieve the hydration and dissolution of a great variety of water-soluble polymers in a wide range of fresh water and salt waters, including water having high concentrations of bromides.