BACKGROUND

[0001] Hydrophilic polymers are widely used in industry. They can be used to thicken, suspend or stabilize aqueous systems. These polymers can produce gels or act as emulsion stabilizers, flocculants, binders, film formers, lubricants and friction reducers. In each of these applications, the polymers are used to adjust and control the rheological properties of the aqueous system to which they are being added.

[0002] The addition of the polymers to water often results in the formation of lumps of unhydrated polymer. These lumps are gel-like substances, wet on the outside but dry on the inside, that form as a result of the polymer beginning to hydrate before the polymer molecules are dispersed. Once the outer layer of polymer is hydrated, the lump or fisheye often cannot be dispersed even with vigorous mixing. Removal of these lumps results in significant losses of time, material and polymer efficiency.

[0003] These lumps are particularly problematic in the oil and gas industry where water soluble polymers are used downhole during drilling, workover, completion, stimulation and reservoir flooding operations. These unhydrated lumps, inert to enzymes, chemical breakers and acids, cause a variety of problems including plugging of the well and permeability impairment of the oil bearing strata. In addition, when polymers are used they are typically added to water in a dilute solution. During this operation fugitive dust is often generated. To avoid lump or dust formation and its associated problems, the polymers can be added to the aqueous systems as liquid slurries.

[0004] Traditional slurry compositions contain a water-soluble polymer dispersed in an oil-based carrier medium, in combination with a suspension agent and a surfactant. Such oil-based compositions are not generally biodegradable and raise environmental concerns.

SUMMARY

[0005] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0006] In one aspect, embodiments of the present disclosure are directed to a slurry comprising at least one water-soluble dry polymer and a deep eutectic solvent composition.

[0007] In another aspect, embodiments of the present disclosure are directed to a method of producing a slurry, the method comprising providing a deep eutectic solvent composition, and mixing at least one water-soluble dry polymer, the deep eutectic solvent composition, and optionally, one or more additives.

[0008] In another aspect, embodiments of the present disclosure are directed to a well treatment fluid comprising a slurry comprising at least one water-soluble dry polymer and a deep eutectic solvent composition, and an aqueous medium.

[0009] In another aspect, embodiments of the present disclosure are directed to a method of treating a subterranean formation, the method comprising providing a deep eutectic solvent composition, mixing at least one water-soluble dry polymer, the deep eutectic solvent composition, and optionally, one or more additives to form a slurry; mixing the slurry with an aqueous medium to form a well treatment fluid; and pumping the well treatment fluid into at least a portion of the subterranean formation.

[0010] Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims.

DETAILED DESCRIPTION

[0011] Embodiments disclosed herein relate to slurry compositions using an aqueousbased carrier fluid, in contrast to conventional oil-based carrier fluids, thereby achieving an environmentally friendly delivery of a slurry of water-soluble polymer. Embodiments also relate to aqueous treatment fluids containing such slurry compositions as well as methods of treating a formation with such aqueous treatment fluid. In particular, the slurry compositions may include at least one water-soluble dry polymer, at least one deep eutectic solvent (DES) composition, and optionally, one or more additives to support suspension. One or more embodiments relate to aqueous slurry compositions for use in hydraulic fracturing as a friction reducer (FR) and high viscosity friction reducer (HVFR).

[0012] Advantageously, slurry compositions according to the present disclosure may utilize high concentration and high-density brine solution along with additives to suspend the polymer and provide long term stability for storage and transportation. As a result, the final slurry’s carrier fluid is aqueous based, environmentally friendly, low cost, and substantially oil free.

[0013] Water-Soluble Dry Polymer

[0014] In one or more embodiments, the water-soluble dry polymer may be a synthetic polymer or a natural polymer. The water-soluble dry polymer may be present in an amount ranging from 10 wt% to 70 wt% by weight of the slurry composition, for example, from a lower limit of any of 10, 20, or 30 wt% to an upper limit of any of 50, 60, or 70 wt%, where any lower limit can be used in combination with any upper limit. Further, the water-soluble dry polymer may be either crosslinked or non- crosslinked.

[0015] In one or more embodiments, examples of synthetic water-soluble dry polymer may include but are not limited to: polyacrylamide, polyacrylamide derivatives, such as n-methyl acrylamide and n,n-dimethyl acrylamide, polyacrylate, polyacrylate derivatives, poly2-acrylamido-2-methylpropane sulfonic acid and its salt form, polydiallyldimethylammoniumchloride, poly(dimethylaminoethyl acrylate methyl chloride quat), polyethylene oxide, polypropylene oxide, PE/PO copolymers, polyvinyl alcohol, and copolymers thereof and combinations thereof.

[0016] In one or more embodiments, examples of crosslinked synthetic water-soluble dry polymer may include but are not limited to: cross-linked polyacrylamide and its derivatives, cross-linked polyacrylate and its derivatives, cross-linked poly(dimethylaminoethyl acrylate methyl chloride quat), cross-linked polyethylene oxide, cross-linked polypropylene oxide, cross-linked EO/PO copolymers and combinations thereof.

[0017] In one or more embodiments, examples of natural water-soluble dry polymer may include but are not limited to: guar, guar derivatives, xanthan gum, gellan gum, welan gum, schleroglucan gum, starch, starch derivatives (chemically derivatized starch, such as hydroxypropyl starch, hydroxyethyl starch, carboxymethyl starch) cellulose, cellulose derivatives (chemically derivatized cellulose such as hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, dihydroxypropyl cellulose, or carboxymethyl cellulose), and combinations thereof.

[0018] In one or more embodiments, examples of crosslinked natural water-soluble dry polymer may include but are not limited to: crosslinked guar or other gums, crosslinked guar or other gum derivatives, crosslinked cellulose, crosslinked cellulose derivatives, and combinations thereof.

[0019] In one or more embodiments, slurry compositions according to the present disclosure may be free of underivatized cellulose. However, in embodiments using underivatized cellulose, the underivatized cellulose is post-pulping, such as in a dry powder form.

[0020] As mentioned, the water-soluble polymer is provided in a dry form, that is as a powder. The powder may have a particle size ranging from a lower limit of any of 200, 170, 140, 120, or 100 to an upper limit of 40, 45, 50, 60, 70, 80, or 100 mesh where any lower limit may be used in combination with any upper limit. For example, the particle size may be from 40 - 200 mesh.

[0021] Deep Eutectic Solvent Composition (DES)

[0022] Embodiments of the slurry composition include a deep eutectic solvent (DES) composition. Deep eutectic solvents are solutions of Lewis or Bronsted acids and bases that form a eutectic mixture. Deep eutectic solvents are classified into four types, and in accordance with one or more embodiments, the slurry compositions of the present disclosure may use any of Types LIV. Type I or III DESs, containing a quaternary ammonium salt with a metal halide and / or hydrogen bond donor may be particularly used.

[0023] Examples of type I eutectics include, in addition to the quaternary ammonium salt, various metal halides including, and the following metal halides: AgCl, CuCl, LiCl, CdCh, CuCh, SnCl ₂ , ZnCl ₂ , LaCl ₃ , YC1 ₃ , and SnCl ₄ . Examples of Type III eutectics include, in addition to the quaternary ammonium salt such as choline chloride, hydrogen bond donors such as amides, carboxylic acids, and alcohols. [0024] In one or more embodiments, the quaternary ammonium salt may be choline chloride. The metal halide salt may be selected from choline chloride, calcium chloride, calcium bromide, zinc chloride, zinc bromide, magnesium chloride, magnesium bromide, cesium chloride, cesium bromide, or combinations thereof. The hydrogen bond donor may be selected from urea or urea derivatives, such as amides, carboxylic acids and alcohols. The deep eutectic solvent composition may further comprise an aqueous medium, such as water.

[0025] In particular embodiments, choline chloride (provided in solution form) may be used in combination with at least one metal halide and urea, and the metal halide and urea may be dissolved in the choline chloride solution without additional aqueous medium such as water added thereto. Each of the quaternary ammonium salt, the metal halide, and the urea may be present in the aqueous medium in an amount ranging from 0.1 wt% to 90 wt%, for example from a lower limit of any of 0.1, 0.5, 1, 5, 10, 20, or 30 wt% to an upper limit of any of 30, 40, 60, or 90 wt%, where any lower limit may be used in combination with any upper limit. The amount of water present in the slurry may be selected so as to have an upper limit of 35 wt%. The amount of water present in the slurry may be in an amount ranging from a lower limit of any of 0.1, 0.5, 1, 2, or 5 wt% to an upper limit of any of 5, 10, 15, 20, 25, 30, or 35 wt%, where any lower limit may be used in combination with any upper limit.

[0026] In one or more embodiments, the DES may be present in the slurry in an amount ranging from 30 wt% to 90 wt% by weight of the slurry composition, for example from a lower limit of any of 30, 40, or 50 wt% to an upper limit of any of 70, 80, or 90 wt%, where any lower limit can be used in combination with any upper limit.

[0027] Advantageously, in addition to serving as a carrier for the water-soluble dry polymer, the deep eutectic solvent composition may also function as a clay- stabilizer upon incorporation into an aqueous treatment fluid that is pumped downhole.

[0028] Additives

[0029] In one or more embodiments, additives such as suspension agents may optionally be added to the slurry. Additives may include but are not limited to viscoelastic surfactants (VES); hydrophobically modified polyacrylamide and its derivatives; fumed silica; amorphous silica; activated alumina; polysaccharide and polysaccharide derivatives, such as xanthan gum; and organophilic phyllosilicates, such as Garamite® 7305 from BYK. It is also envisioned that combinations of such additives may be used in the slurry, such as, for example, xanthan and silica, silica and alumina, or organophilic phyllosilicates and alumina. The total amount of additives may be present in an amount ranging from 0.01 wt% to 10 wt%, for example from a lower limit of any of 0.01, 0.05, 0.1, 0.5, 1, 2, or 4 wt% to an upper limit of any of 5, 6, 8, or 10 wt%, where any lower limit may be used in combination with any upper limit.

[0030] Slurry Properties

[0031] In one or more embodiments, the slurry may be flowable. Flowability may be determined by measuring a pour point. The pour points were tested by PSL SYSTEMTECHNIK PPT 45150 following ASTM 20 method. This test method determines the no-flow point of products by detection of the crystal structure or viscosity increase, or both, in the sample that is sufficient to impede flow of the specimen. This test method includes the range of temperatures from -40 to +50°C.

[0032] In one or more embodiments, slurries may have a viscosity of up to 4000 cP, using a Brookfield viscometer at room temperature using Spindle #63 at 30 rpm). In embodiments, the slurry may have a viscosity of at most 500 cP, or 1000 cP, or 1500 cP, or 2000 cP, or 3000 cP, or even 4000 cP.

[0033] In one or more embodiments, the slurry may be stable for a period of at least 24 hrs. In one or more embodiments, the slurry may be stable for a period of at least 3 days, 1 week, 2 weeks, or even 1 month. A slurry is considered stable if the separation of the slurry in a volumetric cylinder is less than 2% and/or if no gel formation is observed.

[0034] In one or more embodiments, the slurry, specifically the water-soluble polymer, may function as a friction reducer. Upon incorporation into an aqueous treatment fluid, the water-soluble polymer (from the slurry) may exhibit a plateau friction reduction of up to 80%. Friction reduction is measured using a friction flow loop that has 1/2" outer diameter stainless steel tubing, approximately 10 feet in overall length. Test solutions were pumped out of the bottom of a tapered 5 gallon reservoir from fresh water up to high concentrations of brine (250,000 TDS). [0035] Moreover, as noted, use of a DES may result in an aqueous slurry composition. Advantageously, such slurry composition may be substantially free of an oleaginous liquid, for example, with less than 5 wt% of the slurry composition being an oleaginous liquid, or in more particular embodiments, less than 1 wt%, or less than 0.5 wt%.

[0036] Method of Producing Slurry

[0037] In an aspect, a method of making a slurry is provided. The method may include the general steps of: providing a deep eutectic solvent composition, mixing a water- soluble dry polymer with the deep eutectic solvent composition to form a slurry, and optionally, mixing the slurry with one or more additives.

[0038] In one or more embodiments, the mixing may be performed according to methods of mixing commonly known in the art, including simultaneous or sequential addition of components.

[0039] In one or more embodiments, the deep eutectic solvent composition may be prepared by providing a choline chloride solution, and mixing one or more halide salts and / or urea until dissolved. Additives may optionally be added to the deep eutectic solvent composition and mixed until dissolved.

[0040] The prepared deep eutectic solvent composition may be mixed with a water- soluble dry polymer until the water-soluble dry polymer is evenly dispersed in the deep eutectic solvent composition to form a slurry.

[0041] Well Treatment Fluid

[0042] In an aspect, one or more embodiments relate to a well treatment fluid. The well treatment fluid may comprise an aqueous medium and a slurry composition, the slurry including a deep eutectic solvent composition, at least one water-soluble dry polymer, and optionally additives. The slurry may be added to the aqueous treatment fluid in an amount ranging from 0.01 wt% to 1.5 wt%. For example, the slurry may be present in the well treatment fluid in an amount ranging from 0.01 wt% to 1.5 wt%, for example from a lower limit of any of 0.01, 0.05, 0.1, 0.3, or 0.5 wt% to an upper limit of any of 0.8, 1.0, 1.3, or 1.5 wt%, where any lower limit may be used in combination with any upper limit. [0043] The water-soluble polymers of this disclosure can be used in an aqueous treatment fluid, for example, to lower the pumping friction, to raise the low shear viscosity and control fluid loss to the formation, and enhanced oil recovery operations. The well treatment fluid may be used for the treatment of a subterranean formation. The polymers are also used in drilling muds, completion and work-over fluids, acidizing and fracturing fluids, in barrier fluids to control the water-oil ratio and in polymer flooding operations. Thus, the aqueous treatment fluid may include other components that are known to those skilled in the art. For example, when the slurry is used in a fracturing fluid, the aqueous treatment fluid may also include proppants. Suitable proppant materials may include sand, ceramic, plastic, and composite materials. However, it is also envisioned that one or more other additives may also be present such as antifoaming agents, surfactants, corrosion inhibitors, thickeners, bactericides, weighting agents, oxidizing agents, wetting agents, polymer stabilizers, clay stabilizers, scale inhibitors and dissolvers, wax inhibitors and dissolvers, asphaltene precipitation inhibitors, water flow inhibitors, fluid loss additives, chemical grouts, diverters, sand consolidation chemicals, proppants, permeability modifiers, viscoelastic fluids, gases (e.g., nitrogen and carbon dioxide), foaming agents, and the like.

[0044] In an embodiment, a method for fracturing a subterranean formation is provided, wherein the method includes the step of injecting a well treatment fluid of the present disclosure (containing the described slurry) into at least a portion of the subterranean formation at pressures sufficient to fracture the formation.

[0045] A well treatment fluid may be produced, for example, by providing a slurry according to the present disclosure and diluting the slurry with an aqueous medium, and optionally mixing one or more optional additives. The treatment fluid may be batch prepared or prepared by continuous mix processes from the slurry. For example, the treatment fluid may be first prepared in total, and then injected or otherwise introduced into a subterranean formation. This is referred to as a “batch mixing” process. In another embodiment, the treatment fluid may be prepared by continuous mix processes, wherein the treatment fluid components are mixed together while the fluid is simultaneously introduced into the wellbore. By “introduced” it is meant that a fluid may be pumped, injected, poured, released, displaced, spotted, circulated or otherwise placed within a well, wellbore, and/or formation using any suitable manner known in the art.

[0046] The aqueous medium of the well treatment fluid may be any suitable aqueous medium known in the art including, but not limited to, fresh water, acidified water having pH range from 1.0 to 3.0, brine, sea water, produced water, synthetic brine (such as 2% KC1), etc.

[0047] Examples

[0048] Slurries according to the present disclosure were prepared according to the amounts listed in Table 1. A DES composition is first formulated as shown below using a balance of water. The dry polymer is added into the DES composition in each of the below samples at approximately 40 wt% relative to the total formulation. Additives are added into the DES composition at the below-noted contents for the final formulation, with the balance being the DES composition. For the comparative example (Cl), dry polymer was added to water at approximately 40 wt% relative to the total formulation.

Table 1

Table 2

[0049] As shown in Table 1, the present formulations may provide a stable delivery system for dry polymer that is advantageously oil-free (thus avoiding the biodegradability and environmental concerns associated traditional oil-based slurries). Further, when the oil-free slurries in Examples 1-7 are combined with an aqueous fluid (both fresh water and high total dissolved solids water), they offer good hydration viscosity and friction reduction, confirming that the oil-free formulations may provide a slurry of the dry polymer for subsequent use such as a friction reducer. In fact, when added to water, the oil-free formulations achieve the same hydration viscosity as comparative examples of an oil-based polymer slurry. Thus, the formulations may provide long term stability for storage and transportation, but once added into an aqueous treatment fluid, the dry polymer may subsequently hydrate as desired. It is envisioned that different polymers may be selected for inclusion in the oil-free formulations with long term stability while also achieving the desired viscosity and friction reduction effect. Table 2 demonstrates the performance of slurries according to the present disclosure compared to a similar oil-based slurry, the separation level, and the slurry stability for slurries comprising the various additives.

[0050] Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. § 112(f) for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function.