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WO2018052495A1 - Particules revêtues et leurs procédés de production et d'utilisation - Google Patents

Particules revêtues et leurs procédés de production et d'utilisation Download PDF

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Publication number
WO2018052495A1
WO2018052495A1 PCT/US2017/033753 US2017033753W WO2018052495A1 WO 2018052495 A1 WO2018052495 A1 WO 2018052495A1 US 2017033753 W US2017033753 W US 2017033753W WO 2018052495 A1 WO2018052495 A1 WO 2018052495A1
Authority
WO
WIPO (PCT)
Prior art keywords
particle
coating
biopolymer
cross
charge
Prior art date
Application number
PCT/US2017/033753
Other languages
English (en)
Inventor
Ryan Nicholas CHAN
Drew Williams
Caleb MEREDITH
Charlotte HOLT
Hasan SADEGHIFAR
Original Assignee
Tethis, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from PCT/US2016/062773 external-priority patent/WO2017091463A1/fr
Application filed by Tethis, Inc. filed Critical Tethis, Inc.
Priority to US16/462,049 priority Critical patent/US20230138358A1/en
Publication of WO2018052495A1 publication Critical patent/WO2018052495A1/fr

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D103/00—Coating compositions based on starch, amylose or amylopectin or on their derivatives or degradation products
    • C09D103/04—Starch derivatives
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
    • C08B31/00—Preparation of derivatives of starch
    • C08B31/003—Crosslinking of starch
    • C08B31/006—Crosslinking of derivatives of starch
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
    • C08B31/00—Preparation of derivatives of starch
    • C08B31/08—Ethers
    • C08B31/12—Ethers having alkyl or cycloalkyl radicals substituted by heteroatoms, e.g. hydroxyalkyl or carboxyalkyl starch
    • C08B31/125—Ethers having alkyl or cycloalkyl radicals substituted by heteroatoms, e.g. hydroxyalkyl or carboxyalkyl starch having a substituent containing at least one nitrogen atom, e.g. cationic starch

Definitions

  • the present invention generally relates to coated particles, such as, for example, proppants comprising a coating, and to methods of making and using the same.
  • RCP Resin coated proppants
  • One aspect of the present invention is directed to a particle comprising a core and a coating on, surrounding, and/or adhered to at least a portion of a surface of the core, the coating comprising a biopolymer (e.g., a modified biopolymer).
  • a biopolymer e.g., a modified biopolymer
  • the particle is a self-suspending particle when in a solution having a salinity in a range of about 50 ppm to about 100,000 ppm and/or having a hardness in a range of about 1 ppm to about 150,000 ppm.
  • the particle and/or coating swells upon contact with a solution having a salinity in a range of about 50 ppm to about 100,000 ppm and/or having a hardness in a range of about 1 ppm to about 150,000 ppm.
  • the amount of swelling may vary by less than 50% over a salinity concentration in a range of about 50 ppm to about 100,000 ppm and/or a hardness concentration in a range of about 1 ppm to about 150,000 ppm.
  • the particle is for use in fracking and/or is used in a method of fracturing a well and/or in a method of fracturing a geological formation.
  • a further aspect of the present invention is directed to a plurality of particles comprising a particle of the present invention.
  • a settled bed height and/or volume of the plurality of particles is achieved that is about 0.5 to about 4 times greater than a settled bed height and/or volume of a plurality of uncoated particles under the same conditions.
  • Another aspect of the present invention is directed to a method of preparing a cross- linked, coated particle, the method comprising combining a biopolymer with a core to form a coating comprising the biopolymer on the core; and cross-linking the biopolymer on the core, thereby preparing the cross-linked, coated particle.
  • a further aspect of the present invention is directed to a method of preparing a cross- linked, coated particle, the method comprising extruding a melt extrudate comprising a biopolymer into and/or onto a mixture comprising a plurality of cores and a cross-linking agent, thereby preparing the cross-linked, coated particle.
  • Another aspect of the present invention is directed to a method of preparing a cross- linked, coated particle, the method comprising combining a cross-linking agent with a biopolymer to form a mixture (e.g., a melt extrudate); and combining the mixture and a plurality of cores, thereby preparing the cross-linked, coated particle.
  • a cross-linking agent e.g., a melt extrudate
  • Fig. 1 is a graph of the percent of swelling versus the ion concentration for a cationic biopolymer coated particle according to embodiments of the present invention upon exposure to a solution comprising CaCl 2 , an amphoteric biopolymer coated particle upon exposure to a solution comprising CaCl 2; and a synthetic commercial coated particle upon exposure to a solution comprising CaCl 2 .
  • Fig. 2 is a photograph that illustrates how the height of the swollen bed of sand was measured compared to a gel fraction (free of sand).
  • Fig. 3 is a photograph of certain samples as they appeared for measurement of Settled Bed Height (SBH) in 10% CaCl 2 , which, from left to right, are uncoated sand, synthetic commercial coated particle control, and modified biopolymer coated particle.
  • SBH Settled Bed Height
  • FIG. 4 is an illustration of an extruder screw configuration used in Example 3.
  • FIG. 5 is an illustration of an extruder screw configuration used in Example 4D.
  • Fig. 6 is an illustration of an extruder screw configuration used in Example 4E.
  • Fig. 7 is an illustration of an extruder screw configuration used in Example 5A.
  • Fig. 8 is a comparison of SEM micrographs showing relative coating uniformity of a coated particle (right) compared to that of uncoated sand (left).
  • Fig. 9 is an illustration of a reaction scheme in an extruder in which a cross-linker is introduced following mixing of an ionized biopolymer and charge modifier, where (1) refers to the catalyst, (2) refers to the charge modifier, and (3) refers to the cross-linker.
  • Fig. 10 is an illustration of a reaction scheme in an extruder in which a charge modifier is introduced into an extruder prior to a catalyst, where (1) refers to the catalyst, (2) refers to the charge modifier, and (3) refers to the cross-linker.
  • Fig. 11 is an illustration of a reaction scheme in an extruder in which a catalyst and a charge modifier are combined prior to introducing them into an extruder, where (1) refers to the catalyst, (2) refers to the charge modifier, and (3) refers to the cross-linker.
  • the transitional phrase “consisting essentially of (and grammatical variants) is to be interpreted as encompassing the recited materials or steps "and those that do not materially affect the basic and novel characteristic(s)" of the claimed invention. See, In re Herz, 537 F.2d 549, 551-52, 190 U.S.P.Q. 461, 463 (CCPA 1976) (emphasis in the original); see also MPEP ⁇ 2111.03. Thus, the term “consisting essentially of as used herein should not be interpreted as equivalent to "comprising.”
  • the terms “increase”, “improve”, and “enhance” refer to an increase in the specified parameter of greater than about 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 125%, 150%, 175%, 200%, 250%, 300% or more.
  • a coated particle of the present invention comprises a core and a coating that is on, surrounding, and/or adhered to at least a portion of a surface of the core.
  • the coating circumferentially overlies the core.
  • the coating comprises a biopolymer (e.g., a modified biopolymer).
  • the coating may comprise a hydrogel-forming polymer and/or a superabsorbent polymer (SAP).
  • a hydrogel-forming polymer may be a polymer that forms a hydrogel upon contact with water.
  • a SAP and/or coating comprising a SAP may absorb a fluid in an amount of about 10 times or more (e.g., 15x, 20x, 30x, 40x, 50x, l OOx, 150x, 200x, 250x, 300x, etc.) relative to its weight.
  • a SAP and/or coating comprising a SAP may absorb a 10% saline solution in an amount of about 10 times or more (e.g., 15x, 20x, 25x, 30x, 35x, 40x, 45x, etc.) at room temperature and/or a 10% CaCl 2 solution in an amount of about 10 times or more (e.g., 15x, 20x, 25x, 3 Ox, 35x, 40x, 45x, etc.) at room temperature and neutral pH.
  • a hydrogel-forming polymer may be an SAP
  • the coating and/or coated particle may be biodegradable. In some embodiments, all or a portion of the coating and/or coated particle may undergo structural and/or chemical decomposition when exposed to heat, moisture, light, pH changes, and/or microbial enzymes. In some embodiments, a coated particle of the present invention will swell in solution (e.g., an aqueous solution) to reduce the specific gravity and/or increase the buoyancy of the coated particle, and may do so in a solution having a hardness in which multivalent cations (e.g., divalent cations) are present in a range of about 1 ppm to about 150,000 ppm or greater.
  • solution e.g., an aqueous solution
  • multivalent cations e.g., divalent cations
  • a coated particle of the present invention may have any suitable dimensions.
  • a coated particle of the present invention may have a diameter, on average, in a range of about 0.01 mm to about 20 mm.
  • a coated particle of the present invention may have an average diameter of about 0.01, 0.025, 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1 , 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 1 1, 1 1.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20 mm or more.
  • the coating on a particle of the present invention may have a uniform thickness on and/or surrounding a core.
  • the coating may have a thickness in a range of about 0.5 microns to about 50 microns, and the thickness may vary by about 20% or less.
  • a plurality of coated particles may be prepared and the thickness of the coating on and/or surrounding a respective core, on average, may vary by about 20% or less for the plurality of coated particles.
  • the coating on a coated particle of the present invention may have a thickness of about 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 11 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50 microns or more.
  • a coating may be applied to a particle, on average, in the amount of about 0.1% to about 20% by weight relative to the particle or more.
  • a coated particle of the present invention may have a coating, on average, of about 0.1%, 0.25%, 0.5%, 0.75%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or more by weight relative to the particle.
  • the coating on a coated particle of the present invention may comprise one or more (e.g., 1, 2, 3, 4, 5, 6, 7, or more) layers, which may be the same and/or different.
  • a coated particle may comprise a base coating layer adjacent to a surface of the core.
  • the base coating layer may provide and/or maintain strength (e.g., sand crush strength) and/or may bind to the surface of the core.
  • the base coating layer may encapsulate fines during fracture and/or pieces of the core that break off, such as, e.g., when the particle is exposed to shear and/or agitation.
  • One or more additional coating layers may overlie (e.g., circumferentially overlie) the base coating layer and/or core.
  • a base coating layer adjacent to a surface of the core may comprise a resin coating (e.g., an epoxy or vinyl coating).
  • one or more layers of an anionic coating e.g., an anionic SAP coating
  • a cationic coating e.g., a cationic SAP coating
  • one or more layers of an amphoteric coating e.g., an amphoteric SAP coating
  • a coated particle of the present invention may comprise alternating layers of an anionic and cationic coating.
  • a coated particle of the present invention may be a proppant.
  • the proppant may be a self-suspending proppant.
  • a self-suspending proppant may have a specific gravity that is less than the specific gravity of an uncoated proppant and/or the volume of the proppant, upon exposure to water, may be greater than that of a dry and/or uncoated proppant.
  • a coated particle (e.g., proppant) of the present invention may be used in a fracking application and/or method.
  • a coated particle of the present invention may swell greater than 0.5x in volume relative to an uncoated particle, such as, for example, lx, 1.5x, 2x, 2.5x, 3x, 3.5x, 4x, 4.5x, 5x or more.
  • the solution may have a hardness in a range of 1 ppm to about 150,000 ppm.
  • swelling of the coated particle as measured by volumetric change upon contact with a solution may represent a surrogate metric for increased proppant volume and/or reduced proppant specific gravity.
  • a coated particle of the present invention may swell greater than 4 times in volume upon contact with a solution.
  • the swelling may be independent of hardness.
  • the coated particle may swell greater than 0.5 times (e.g., lx, 2x, 3x, etc.) in volume upon contact with a solution having a hardness in a range of 1 ppm to about 150,000 ppm or greater.
  • a solution may comprise one or more dissolved minerals and/or multivalent ions (e.g., calcium and/or magnesium) in an amount of about 1, 10, 100, 500, 1,000, 5,000, 10,000, 15,000, 20,000, 25,000, 30,000, 35,000, 40,000, 45,000, 50,000, 55,000, 60,000, 65,000, 70,000, 75,000, 80,000, 85,000, 90,000, 95,000, 100,000, 120,000, 150,000, ppm or more.
  • multivalent ions e.g., calcium and/or magnesium
  • calcium and/or magnesium may be present in a solution in an amount of about 1, 10, 100, 500, 1,000, 5,000, 10,000, 15,000, 20,000, 25,000, 30,000, 35,000, 40,000, 45,000, 50,000, 55,000, 60,000, 65,000, 70,000, 75,000, 80,000, 85,000, 90,000, 95,000, 100,000, 120,000, 150,000, ppm or more.
  • the thickness of the coating on a coated particle of the present invention prior to swelling may be about 0.01% to about 20% of the average diameter of the coated particle prior to swelling.
  • the coating may have a thickness of about 10% to about 300% of the average diameter of the coated particle prior to swelling.
  • a coated particle of the present invention may have increased swelling compared to an uncoated core (e.g., uncoated sand) and/or a current commercial coated particle and/or proppant, such as, for example, an acrylate (e.g., polyacrylate) and/or acrylamide (e.g., polyacrylamide) coated particle and/or proppant.
  • An acrylate coated particle and/or proppant may have an anionic charge and an acrylamide coated particle and/or proppant may have a neutral charge and/or anionic charge.
  • the coated particle may have an amount of swelling that is increased by at least about 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 150%, 200%, or more compared to an uncoated core and/or a current commercial coated particle and/or proppant.
  • a coated particle of the present invention may swell at least two times greater (e.g., 2, 3, 4, 5, or more) than an uncoated core and/or a current commercial coated particle and/or proppant.
  • the coated particle may swell at least two times greater in a solution (e.g., an aqueous solution) having a salinity in a range of about 50 ppm to about 100,000 ppm and/or having a hardness in a range of about 1 ppm to about 150,000 ppm compared to an uncoated core and/or a current commercial coated particle and/or proppant.
  • a solution e.g., an aqueous solution
  • a solution e.g., an aqueous solution having a salinity in a range of about 50 ppm to about 100,000 ppm and/or having a hardness in a range of about 1 ppm to about 150,000 ppm compared to an uncoated core and/or a current commercial coated particle and/or proppant.
  • the solution may have a salinity of about 50, 100, 500, 1 ,000, 5,000, 10,000, 15,000, 20,000, 25,000, 30,000, 35,000, 40,000, 45,000, 50,000, 55,000, 60,000, 65,000, 70,000, 75,000, 80,000, 85,000, 90,000, 95,000, 100,000 ppm or more and/or may comprise one or more dissolved minerals and/or multivalent ions (e.g., calcium and/or magnesium) in an amount of about 1, 10, 100, 500, 1 ,000, 5,000, 10,000, 15,000, 20,000, 25,000, 30,000, 35,000, 40,000, 45,000, 50,000, 55,000, 60,000, 65,000, 70,000, 75,000, 80,000, 85,000, 90,000, 95,000, 100,000, 120,000, 150,000, ppm or more.
  • the coating when exposed to an aqueous solution, the coating may form a swollen gel, optionally a hydrogel.
  • Settled bed height may be used as a volumetric measure of swelling for a coated particle of the present invention.
  • SBH may be determined by exposing a given amount of coated particles to a solution, mixing and/or shaking the solution comprising the coated particles, and measuring the bed height of the plurality of particles after a given amount of time.
  • the bed height of the plurality of coated particles may be compared to the bed height of uncoated particles (e.g., the uncoated core of the coated particles) under the same or similar conditions to provide the percent of swelling.
  • a plurality of coated particles of the present invention may swell to provide an increase in settled bed height and/or volume when the plurality of coated particles is exposed to a solution, such as, e.g., an aqueous solution having a salinity in a range of about 50 ppm to about 100,000 ppm and/or a hardness in a range of 1 ppm to about 150,000 ppm, compared to a plurality of uncoated cores and/or a current commercial coated particle and/or proppant under the same or similar conditions.
  • a solution such as, e.g., an aqueous solution having a salinity in a range of about 50 ppm to about 100,000 ppm and/or a hardness in a range of 1 ppm to about 150,000 ppm
  • the increase in settled bed height and/or volume may be at least about 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 150%, 200%, 250%, 300%, or more compared to an uncoated core and/or a current commercial coated particle and/or proppant.
  • a settled bed height and/or volume may be achieved that is about 0.5 to about 4 times greater than the settled bed height and/or volume of a plurality of uncoated cores (e.g., uncoated cores that are the same as the core used in the coated particle) and/or a plurality of current commercial coated particles and/or proppants under the same or similar conditions.
  • a plurality of uncoated cores e.g., uncoated cores that are the same as the core used in the coated particle
  • a plurality of current commercial coated particles and/or proppants under the same or similar conditions.
  • the bed height and/or volume for a plurality of coated particles may show approximately equivalent values/heights when exposed to a range of hardness and/or salinity.
  • a plurality of coated particles may exhibit a 3x change in volume and/or settled bed height in an aqueous solution containing 200 ppm Ca 2+ and a 3x change in volume in an aqueous solution containing 2000 ppm Ca 2+ .
  • the degree of swelling for a coated particle of the present invention in an aqueous solution having a hardness in a range of about 150 ppm to about 150,000 ppm may change by less than about 40% (e.g., less than about 35%, 30%, 25%, 20%, 15%, 10%, 5%, etc.) compared to the coated particle in an aqueous solution having a hardness in a range of less than 150 ppm.
  • the settled bed height and/or volume for a plurality of coated particles of the present invention may change by less than about 40% (e.g., less than about 35%, 30%), 25%, 20%, 15%, 10%, or 5%) after multiple shaking and/or shear cycles.
  • the settled bed height and/or volume may change by less than about 40% (e.g., less than about 35%, 30%, 25%, 20%, 15%, 10%, or 5%) after exposing the coated particle to shear in a range of about 40 s "1 to about 600 s "1 , such as, e.g., about 40 s "1 to about 100 s "1 or about 170 s "1 to about 550 s "1 for about 1 minute to about 1 hour (e.g., about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60 minutes).
  • the plurality of coated particles may have a settled bed height and/or volume that is about 60% or more (e.g., 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98%, 100%, 1 10%, 120%, 150%, or more) of the settled bed height and/or volume prior to exposing the particles to shear.
  • a coated particle of the present invention may have an improved uniformity in swelling performance over a broad range of total dissolved solids (TDS) conditions compared to a current commercial coated particle and/or proppant.
  • TDS total dissolved solids
  • the degree of volumetric swelling for a plurality and/or bed of coated particles of the present invention in distilled water may change by about 50% or less (e.g., about 45%, 40%, 35%, 30%, 25%, 20%), 15%, 10%, 5%, etc.) compared to the degree of volumetric swelling for the plurality and/or bed of coated particles in an aqueous solution having a salinity in a range of about 50 ppm to about 100,000 ppm and/or a hardness in a range of 1 ppm to about 150,000 ppm.
  • the degree of volumetric swelling for a coated particle of the present invention may change by about 50% or less as ion concentration increases. In some embodiments, as the ion concentration increases, the amount of volumetric swelling for the coated particle changes by about 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, or less. In some embodiments, a coated particle of the present invention may have an increased amount of swelling at a particular ion concentration compared to a current commercial coated particle and/or proppant. For example, as shown in Fig.
  • a coated particle according to embodiments of the present invention may have a 1.5x - 3x increase in volumetric swelling and/or performance compared to a commercial polyacrylate or polyacrylamide coated particle and/or proppant upon exposure to a solution comprising of NaCl and/or CaCl 2 in concentrations greater than 1,000 ppm.
  • the coating on a coated particle of the present invention and/or a portion of the coating may remain present on, around, and/or adhered to the core ⁇ e.g., sand) during and/or after the presence and/or application of shear (e.g., dry and/or wet solution shear such as, for example, seen in shipping and tracking operations) and/or agitation.
  • shear e.g., dry and/or wet solution shear such as, for example, seen in shipping and tracking operations
  • the coated particle may be given sufficient time to settle, and after which the presence of a gel layer may become visible.
  • volumetric swelling behavior is retained after a relevant degree of shear.
  • a coated particle of the present invention may be a shear stable particle.
  • a coated particle of the present invention may be resistant to shear inherent to and/or caused by a pumping process, such as, for example, a pumping process used in a fracking operation, such that the coating may remain present on, around, and/or adhered to the core.
  • shear may be induced to and/or experienced by a coated particle of the present invention in solution via shaking vigorously by hand.
  • a coated particle of the present invention may be exposed to a solution and shaken for about one minute followed by allowing the coated particle to settle for about 5 minutes.
  • the coated particle may be additionally shaken and allowed to settle repeatedly, for example twice, three times, or more, with a less than about 20% change in the degree of swelling compared to initial measurements (Fig. 2).
  • the coating on a coated particle of the present invention may remain present on, around, and/or adhered to the core after one or more hours (e.g., 1, 2, 3, 4, 5, 6, or 7 hours) of exposure to and/or contact with an aqueous solution, optionally in the presence of shear and/or agitation.
  • the aqueous solution may have a temperature from about 28°F to about 350°F.
  • the aqueous solution may have a temperature of about 30°F, 50°F, 75°F, 100°F, 125°F, 150°F, 175°F, 200°F, 225°F, 250°F, 275°F, 300°F, 325°F, 350°F or more.
  • the aqueous solution may have a salinity in a range of about 50 ppm to about 100,000 ppm and/or a hardness of about 1 ppm to about 150,000 ppm.
  • the coating on a coated particle of the present invention may be insoluble in water.
  • the coating on a coated particle of the present invention may be resistant or substantially resistant to water hardness.
  • the performance of the coating e.g., a SAP coating
  • the gel strength and/or permeability of a swollen plurality and/or bed of particles of the present invention may be controlled by the cross-link density of the biopolymer (e.g., modified biopolymer) making up the coating.
  • the coating may be "breakable" (i.e., deswelled, unswollen, and/or degraded) in the presence of a breaking agent.
  • Breaking agents can include, for example, oxidizers (e.g., oxidizing agents), acids, and/or enzymes.
  • oxidizers e.g., oxidizing agents
  • primary oxidative breakers include, but are not limited to, persulfates and/or peroxides.
  • breaking agents include, but are not limited to, hydrochloric acid, ammonium persulfate, sodium peroxide, and/or magnesium peroxide.
  • the breaker or breaking agent can be added in concentrations of about 0.05 pounds to about 20 pounds per thousand gallons (pptg) for time lengths of about 0.1 hours to about 48 hours at temperatures of in a range of about 25°C to about 350°C.
  • a coated particle of the present invention may swell to a given degree (e.g., a maximum swelling amount) faster than a current commercial coated particle and/or proppant swells to the same or a similar degree.
  • the coated particle may swell to a given degree faster by about 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 150%, 200% ?
  • a coated particle of the present invention may swell to a given degree (e.g., the maximum swelling amount) in about 30 minutes to about 60 minutes.
  • a coated particle of the present invention may swell to a given degree in about 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 minute or less.
  • a coated particle of the present invention may swell to a given degree (e.g., a maximum swelling amount) in about 10 seconds to about 60 seconds.
  • a coated particle of the present invention may swell to a given degree (e.g., a maximum swelling amount) slower than a current commercial coated particle and/or proppant to the same or a similar degree.
  • the coated particle may swell to a given degree slower by about 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 150%, 200%, 250%, 300%, 350%), 400%), 450%), 500%» or more compared to a current commercial coated particle and/or proppant to the same or a similar degree.
  • a coated particle of the present invention may swell to a given degree in about 1 hour or more, whereas a current commercial coated particle and/or proppant may swell to the same degree in about 30 minutes to 60 minutes.
  • a coated particle of the present invention may swell to a given degree (e.g., a maximum swelling amount) in about 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8 hours or more.
  • a coated particle of the present invention may swell to a given degree (e.g., a maximum swelling amount) in about 2 hours to about 8 hours.
  • any suitable substrate and/or material may be used as a core.
  • at least a portion of a surface of the core is compatible with the coating, such that the coating may adhere to this portion of the surface of the core.
  • Example substrates and/or materials that may be used as the core include, but are not limited to, sand, resin coated sand, bauxites, low density proppants, ceramics, kaolinites, clay, particles formed from fibrous materials, glass materials, nut shells, ground or crushed nut shells, seed shells, ground or crushed seed shells, fruit pit pieces, ground or crushed fruit pits, processed wood, composite particulates prepared from a binder with filler particulate including silica, fumed silica, alumina, fumed carbon, carbon black, graphite, mica, titanium dioxide, meta-silicate, calcium silicate, kaolin, talc, zirconia, boron, fly ash, hollow glass microspheres, solid glass, fibers, textiles (nonwoven
  • the core may comprise a material and/or substrate used as a proppant and/or in a tracking application and/or method.
  • the core may comprise a lightweight proppant and/or the coating around a core may include additives such as, e.g., a traceable and/or slow release material, which may allow for a traceable proppant and/or carrier for viscosifying agent, respectively.
  • the core comprises sand.
  • the core comprises one or more (e.g., 2, 3, 4, 5, 6 or more) particles (e.g., sand particles) that may or may not be bound together. The coating, thus, may encapsulate one or more particles to form a larger particle.
  • a coating of the present invention may comprise a biopolymer, such as, for example, a modified biopolymer.
  • a "modified biopolymer” as used herein refers to a biopolymer that is modified chemically and/or physically, such as, for example, charge-modified and/or cross- linked, optionally by a method described herein.
  • the coating comprises a modified biopolymer, such as, but not limited to, a cross-linked, charge-modified biopolymer.
  • a cross-linked, charged-modified biopolymer of the present invention may comprise one biopolymer that has been charge-modified and cross-linked.
  • the coating of a coated particle of the present invention comprises one biopolymer that has been charge-modified and cross-linked.
  • the coating of a coated particle of the present invention comprises a biopolymer and the biopolymer consists of a cross-linked, charge-modified biopolymer.
  • a cross-linked, charged-modified biopolymer of the present invention may comprise two or more different biopolymers that are cross-linked and at least one of the biopolymers has been charge-modified. The two or more different biopolymers may be cross-linked with each other.
  • a cross-linked, charge-modified biopolymer may comprise two different biopolymers that are cross-linked and both of the biopolymers may be charge- modified.
  • a coating of the present invention comprises a biopolymer that is plasticized and/or gelatinized. Gelatinization may be determined by measuring the presence of crystallinity qualitatively (e.g., via birefringence) and/or quantitatively (e.g., via x-ray diffraction).
  • a coating of the present invention may comprise one or more additives, such as, but not limited to, one or more hydrophobic agents, viscosifying additives, flowability agents, binding agents, surfactants, leavening agents, and/or linker molecules.
  • additives such as, but not limited to, one or more hydrophobic agents, viscosifying additives, flowability agents, binding agents, surfactants, leavening agents, and/or linker molecules.
  • the coating of a coated particle of the present invention may comprise a modified biopolymer (e.g., a charge modified and/or cross-linked biopolymer) that has a degree of crystallinity that is and/or has been decreased compared to the biopolymer prior to modification (e.g., prior to a method of the present invention) and/or compared to a modified biopolymer prepared using a conventional method and/or compared to a known coating.
  • a modified biopolymer e.g., a charge modified and/or cross-linked biopolymer
  • the coating of a coated particle of the present invention may comprise a modified biopolymer that has a degree of crystallinity that is and/or has been decreased by at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 150%, 200%, or more compared to the biopolymer prior to modification (e.g., prior to a method of the present invention) and/or to a modified biopolymer prepared using a conventional method and/or compared to a known coating.
  • a modified biopolymer that has a degree of crystallinity that is and/or has been decreased by at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 150%, 200%, or more compared to the biopolymer prior to modification (
  • the coating of a coated particle of the present invention may comprise a modified biopolymer (e.g., a charge modified and/or cross-linked biopolymer) that has a glass transition temperature that is and/or has been decreased compared to the biopolymer prior to modification (e.g., prior to a method of the present invention) and/or compared to a modified biopolymer prepared using a conventional method and/or compared to a known coating.
  • a modified biopolymer e.g., a charge modified and/or cross-linked biopolymer
  • the coating of a coated particle of the present invention may comprise a modified biopolymer that has a glass transition temperature that is and/or has been decreased by at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or more compared to the biopolymer prior to modification (e.g., prior to a method of the present invention) and/or to a modified biopolymer prepared using a conventional method and/or compared to a known coating.
  • a modified biopolymer that has a glass transition temperature that is and/or has been decreased by at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or more compared to the biopolymer prior to modification (e.g., prior to a method of the present invention) and/or to a modified
  • a coated particle of the present invention may comprise a modified biopolymer (e.g., a cross-linked, charged modified biopolymer) and/or coating that is insoluble in an aqueous solution.
  • the coating and/or modified biopolymer is insoluble in an aqueous solution having a salinity in a range of about 50 ppm to about 150,000 ppm and/or having a hardness in a range of about 1 ppm to about 150,000 ppm.
  • At least a portion (e.g., about 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98%, or 100%) of the coating and/or modified biopolymer may remain present on, around, and/or adhered to a core for at least about 30, 45, or 60 minutes, or 1.5, 2, 2.5, 3 hours or more when in contact with and/or exposed to an aqueous solution (e.g., an aqueous solution having a salinity in a range of about 50 ppm to about 150,000 ppm and/or having a hardness in a range of about 1 ppm to about 150,000 ppm).
  • an aqueous solution e.g., an aqueous solution having a salinity in a range of about 50 ppm to about 150,000 ppm and/or having a hardness in a range of about 1 ppm to about 150,000 ppm.
  • a biopolymer e.g., a native biopolymer
  • modified biopolymer may be used to prepare a coating of the present invention.
  • a "biopolymer” as used herein refers to a polymer produced by a living organism or a derivative thereof.
  • a biopolymer has at least one free amine and/or hydroxyl group present on a majority of the monomeric units of the polymer.
  • a free amine and/or hydroxyl group may be present on each of the monomeric units of the polymer backbone.
  • Example biopolymers include, but are not limited to, proteins, polyamino acids, and/or polysaccharides.
  • a biopolymer may be synthetically obtained (e.g. , through laboratory synthesis) and/or obtained and/or derived from nature (e.g., from a living or previously living organism). Therefore, the biopolymer may be the same as a polymer found in nature (i.e., a native biopolymer) or may be a derivative thereof.
  • a biopolymer of the present invention may be a derivative of a polymer produced by a living organism, the derivative caused by the synthetic method used to obtain or isolate the biopolymer from nature.
  • a biopolymer may be a polymer produced by bacteria and/or microbes. The biopolymer may be biorenewable and/or biodegradable.
  • biopolymers include, but are not limited to, starches (including amylose and/or amylopectin), flours, chitosans, hemicelluloses, lignins, celluloses, chitins, alginates, dextrans, pullanes, polyhydroxyalkanoates, fibrins, cyclodextrins, proteins (e.g., soy protein), polysaccharides (e.g., pectin), poly amino acids (e.g., gamma-polyglutamic acid) and/or poly lactic acids.
  • starches including amylose and/or amylopectin
  • flours including amylose and/or amylopectin
  • chitosans hemicelluloses
  • lignins hemicelluloses
  • celluloses chitins
  • alginates dextrans
  • pullanes polyhydroxyalkanoates
  • fibrins cyclodextrins
  • proteins e.
  • a biopolymer and/or modified biopolymer used in a method of the present invention may have a moisture content of about 20% by weight or less. In some embodiments, the biopolymer and/or modified biopolymer may have a moisture content of about 20%, 15%, 10%, 5%, or less by weight. In some embodiments, the biopolymer and/or modified biopolymer may have a moisture content in a range of about 5% by weight to about 20% by weight or about 10% by weight to about 15% by weight. In some embodiments, a method of the present invention utilizes a biopolymer, such as, for example, starch, having a moisture content of about 20% by weight or less, and the biopolymer may be in powder form.
  • a biopolymer such as, for example, starch
  • a biopolymer and/or modified biopolymer used in a method of the present invention when soluble, may have a solution viscosity of about 2 cP or more.
  • a solution comprising the biopolymer and/or modified biopolymer dissolved in the solution in an amount of about 1% by weight of the solution may have a viscosity of about 2 cP to about 5,000 cP or more.
  • the biopolymer when only one biopolymer is used to prepare a modified biopolymer of the present invention (e.g., a charge-modified biopolymer and/or a cross- linked, charge-modified biopolymer), the biopolymer may have a molecular weight of greater than about 50,000 Daltons.
  • the biopolymer when two or more different biopolymers are used to prepare a modified biopolymer of the present invention (e.g., a cross-linked, charge-modified biopolymer), at least one of the two or more different biopolymers may have a molecular weight of about 10,000 Daltons or more, such as, for example, about 20,000; 30,000; 40,000, 50,000 Daltons or more.
  • a modified biopolymer of the present invention may be prepared using a biopolymer having a molecular weight of greater than about 50,000 Daltons optionally with a second different biopolymer having a molecular weight of greater than about 10,000 Daltons.
  • the biopolymer and/or modified biopolymer may be polydisperse.
  • the biopolymer and/or modified biopolymer used in a method of the present invention may be a starch.
  • Example starches include, but are not limited to, potato starch, wheat starch, tapioca starch, cassava starch, rice starch, corn starch, waxy corn starch, waxy wheat starch, waxy rice starch, waxy sorghum starch, waxy cassava starch, waxy barley starch, and/or waxy potato starch.
  • the starch may have an amylopectin content of about 70% w/w or more and an amylose content of about 30% w/w or less.
  • the starch may have an amylopectin content of about 70%, 75%, 80%, 85%, 90%, 95% w/w or more and an amylose content of about 30%, 25%, 20%, 15%, 10%, 5% w/w or less. In some embodiments, the starch may have an amylopectin content of less than 90%, such as, for example, about 85%, 80%, 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%o, 30%, 25%, 20%), 15%), 10%, etc.
  • starch may have an amylopectin content in a range of about 10%» to about 85%, such as, for example, about 25%) to about 85%) or about 50% to about 80%».
  • the starch may be dissolvable in water (e.g., pre-gelatinized starch).
  • the starch may be steam exploded to form a pre-gelatinized starch.
  • a starch used in a method of the present invention may have a reduced degree of crystallinity compared to a native starch.
  • the biopolymer and/or modified biopolymer used in a method of the present invention may be a flour.
  • Example flours include, but are not limited to, potato flour, wheat flour, tapioca flour, cassava flour, rice flour, corn flour, pre-gelatinized potato flour, pre-gelatinized wheat flour, pre-gelatinized tapioca flour, pre-gelatinized cassava flour, and/or pre-gelatinized rice flour.
  • the flour may have a starch content of about 85% or more. In some embodiments, the flour may have a starch content of about 85%), 90%, or 95%). In some embodiments, the flour may have a protein content of about 15%) or less. In some embodiments, the flour may have a protein content of about 1%, 5%>, 10%), or 15%.
  • the starch may be steam exploded to form a pre-gelatinized flour.
  • the biopolymer and/or modified biopolymer used in a method of the present invention may be a chitosan.
  • the chitosan may have a degree of deacetylation of about 50% to about 100%.
  • the chitosan may have a degree of deacetylation of about 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%.
  • the chitosan may have a degree of deacetylation in a range of about 70%> to about 100% or greater than about 80%.
  • the chitosan may have a molecular weight of greater than about 80,000 Daltons.
  • the biopolymer and/or modified biopolymer used in a method of the present invention may be a hemicellulose. In some embodiments, the biopolymer and/or modified biopolymer used in a method of the present invention may be a cellulose, hemicellulose, chitosan, lignin, pectin, and any combination thereof.
  • a biopolymer used in a method of the present invention may be charge-modified according to a method described herein (e.g., by reacting the biopolymer with a charge- modifying agent in a homogeneous reaction blend) to prepare a modified biopolymer.
  • a biopolymer may naturally carry a charge (i.e., the biopolymer may natively be charged in that the charge is present on the biopolymer not through a method of the present invention).
  • a method of the present invention may change the charge present on a biopolymer (e.g., type and/or amount of charge).
  • a charge-modified biopolymer of the present invention may be soluble (e.g., partially or fully soluble) in a polar solvent, such as, for example, water and/or a polar organic solvent at room temperature and/or a non-polar solvent at room temperature.
  • a charge-modified biopolymer of the present invention may be at least 70% soluble in a polar and/or non-polar solvent at room temperature. Solubility may be used as an indication and/or characteristic of the degree of charge modification.
  • Charge-modifying agent refers to a molecule or compound comprising one moiety that may react with a reactive group of the biopolymer (e.g., an amine and/or hydroxyl group) and a second moiety that may be positively charged or negatively charged under suitable conditions, such as, for example, at a certain pH.
  • a reactive group of the biopolymer e.g., an amine and/or hydroxyl group
  • a second moiety that may be positively charged or negatively charged under suitable conditions, such as, for example, at a certain pH.
  • Moiety refers to a portion of a molecule or compound having a particular functional or structural feature.
  • a moiety may comprise a functional group or a reactive portion of a compound.
  • a strong acidic moiety e.g., - S0 3 H
  • a weak acidic moiety e.g., -COOH
  • a strong basic moiety e.g., -OH
  • a weak basic moiety e.g., -NH + 4
  • the charge-modifying agent may comprise at least one moiety that may be a positively charged group, such as, but not limited to, a primary amine, secondary amine, tertiary amine, quaternary ammonium, sulfonium, and/or phosphonium group.
  • a positively charged group such as, but not limited to, a primary amine, secondary amine, tertiary amine, quaternary ammonium, sulfonium, and/or phosphonium group.
  • Example charge-modifying agents that can have a positively charged moiety include, but are not limited to, ethylene imine, N-(2-hydroxyethyl) ethylene imine, cyanamide, beta- morpholinoethylchloride, beta-diethyl aminoethylchloride, S-diethyl amino 1,2- epoxypropane dimethyl aminoethyl methacrylate, epoxy 3 -methyl ammonium, glycidyltrimethylammonium chloride (e.g., QUAB® 151), N-(2,3-epoxypropyl) trimethyl ammonium chloride, (4-chlorobutene-2) trimethyl ammonium chloride, 2-chloroethyl methyl ethyl sulfonium iodide, and/or Z-chloroethyl tributylphosphonium chloride.
  • the charge-modifying agent comprises a tertiary amino alkyl group, a hydroxyalkyl
  • a positively charged moiety may be introduced into and/or onto a biopolymer by reacting the biopolymer and charge-modifying agent in a homogeneous reaction blend, optionally in the presence of a catalyst.
  • This reaction may be a dry melt process and/or may be an etherification or esterification reaction.
  • a positively charged moiety may be introduced into and/or onto a biopolymer via reactive extrusion.
  • a cationic agent may be used such that it is converted into a reactive form via reactive extrusion (e.g., converting reagent in a chlorohydrin form to epoxide form).
  • the charge-modifying agent may comprise at least one moiety that may be a negatively charged group, such as, but not limited to, a carboxyl, sulfonate, sulfate, and/or a phosphate group (e.g., sodium tripolyphosphate).
  • a negatively charged group such as, but not limited to, a carboxyl, sulfonate, sulfate, and/or a phosphate group (e.g., sodium tripolyphosphate).
  • Example charge-modifying agents that can have a negatively charged moiety include, but are not limited to, acids (e.g., citric acid, glacial acetic acid, ethylenediaminetetraacetic acid (EDTA), and/or diethylene triamine pentaacetic acid (DTP A)); mono-halogen substituted fatty acids (e.g., monochloroacetic acid); acetates (e.g., sodium monochloroacetate); anhydrides (e.g., succinic anhydride, maleic anhydride, citraconic anhydride, and/or octenyl succinicanhydride); alkyl esters of acrylic acid, crotonic acid or itaconic acid (e.g., methyl and ethyl esters of acrylic acid, crotonic acid or itaconic acid); acrylonitrile; sodium periodate; sulfones; and/or sulfonic acids (e.g., halo alkane sulfonic
  • a negatively charged moiety may be introduced into a biopolymer by reacting the biopolymer and charge-modifying agent in a homogeneous reaction blend in the presence an alkaline catalyst.
  • the charge- modifying agent may be acrylonitrile and the reaction of the biopolymer and acrylonitrile in the presence of an alkaline catalyst may be followed by hydrolysis of the cyanoethyl groups.
  • the charge-modifying agent is sodium periodate
  • the reaction with the biopolymer may be followed by a treatment to transform the carbonyl groups into carboxyl groups, such as, but not limited to, by treating with sodium chlorite, and/or by a treatment with sodium bisulfite and/or potassium bisulfite.
  • both carboxyl and sulfonate groups may be introduced into a biopolymer by reacting the biopolymer with an anhydride of an unsaturated acid (e.g., maleic acid) and a bisulfite.
  • the bisulfite may be reacted with the unsaturated bond of the polysaccharide half ester.
  • the charge-modifying agent may react with an amine and/or hydroxyl group of a biopolymer to provide a charge-modified biopolymer.
  • the charge- modified biopolymer may be cationic (i.e., have a net positive charge) or may be anionic (i.e., have a net negative charge).
  • the charge-modified biopolymer may contain both positively and negatively charged moieties.
  • a biopolymer and/or modified biopolymer used in a method of the present invention may be cross-linked by reacting a cross-linking agent with the biopolymer and/or modified biopolymer and optionally with at least one different biopolymer that may optionally be charge-modified.
  • a cross-linking agent may be reacted with at least one charge-modified biopolymer.
  • Cross-linking agent refers to a compound that links two or more biopolymer chains and/or portions of the biopolymer together, the biopolymer optionally being charge-modified.
  • the linkage may be achieved via a covalent bond or an ionic bond.
  • the linkage may be through a moiety or group of the biopolymer or different biopolymers.
  • Example cross-linking agents include, but are not limited to, epichlorohydrin, glutaraldehyde, citric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, fumaric acid, maleic acid, malic acid, tartartic acid, sodium trimetaphosphate, sodium tripolyphosphate, ionic cross-linkers (e.g., calcium chloride, calcium hydroxide, etc.), ethylene glycol diglycidyl ether (EDGE), poly(ethylene glycol) diglycidyl ether (PEGDE), poly(propylene glycol) diglycidyl ether (PPGDE), and/or an anhydride, such as, for example, succinic anhydride and maleic anhydride.
  • the cross-linking agent is non-toxic.
  • a cross-linked, charge-modified biopolymer may have a net positive charge (i.e., is cationic) or a net negative charge (i.e., is anionic), when exposed to a solution.
  • a cross-linked, charge-modified biopolymer is a polyampholyte.
  • the cross-linked, charge-modified biopolymer may be a polyelectrolyte, which may be hydrophilic (e.g., due to the number of ionizable groups present on the modified biopolymer).
  • a cross-linked, charge-modified biopolymer may be a superabsorbent.
  • a cross-linked, charge-modified biopolymer of the present invention is charge-modified and/or cross-linked in an extruder.
  • Some embodiments of the present invention may provide a cross-linked, charge-modified biopolymer in a one step extrusion process.
  • a method of the present invention may provide a cross-linked, charge-modified biopolymer and/or charge-modified biopolymer having the charge modification substantially uniformly distributed throughout the bulk of the modified biopolymer.
  • the cross-linked, charge-modified biopolymer and/or charge-modified biopolymer may have a substantially uniform charge density.
  • the uniformity of the charge density of a modified biopolymer of the present invention may be determined by evaluating the presence of insoluble materials after exposure of the modified biopolymer to a solvent, such as, for example water. Observation of particles (such as, for example, 1 -10 ⁇ particles) may indicate the lack of charge modification within the particles and/or modified biopolymer.
  • charge density distribution on a modified biopolymer may be determined and/or evaluated using one or more spectrographic analytical techniques such as, but not limited to, EDS, EPS, and/or TOF-SIMS of the charged moiety's counter ion.
  • spectrographic analytical techniques such as, but not limited to, EDS, EPS, and/or TOF-SIMS of the charged moiety's counter ion.
  • an uneven distribution of counter ions and/or the presence of particles (e.g., 1-10 ⁇ particles) lacking the counter ion indicates non- uniformity and/or inhomogeneity in regard to the distribution of the charge on the modified biopolymer.
  • a cross-linked, charge-modified biopolymer and/or charge- modified biopolymer of the present invention may have an increased charge density and/or degree of cross-linking compared to a modified biopolymer (e.g., a cross-linked, charge- modified biopolymer) prepared using a conventional method and/or compared to a known coating.
  • a modified biopolymer e.g., a cross-linked, charge- modified biopolymer
  • Conventional method as used herein in reference to a method for preparing a modified biopolymer refers to a method for preparing a modified biopolymer in which the biopolymer is a solid (e.g., a particulate) and a reaction of the biopolymer with at least one reactant in the method occurs at a solid interface of the biopolymer.
  • a conventional method may be a method that does not involve forming a homogeneous reaction blend and/or that does not involve a melt extrusion process, such as a reactive extrusion process.
  • a conventional method may be a semi-dry process, a multiphase process, a process having a liquid interface with a solid material, and/or a heterogeneous process.
  • a conventional method may be a heterogeneous wet chemistry method and/or a multi-phase process.
  • a modified biopolymer of the present invention may have a charge density and/or degree of cross-linking that is increased by at least about 5% or more compared to a modified biopolymer prepared using a conventional method and/or compared to a known coating.
  • the modified biopolymer may have a charge density and/or degree of cross-linking that is increased by at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 150%, 200%, or more compared to a modified biopolymer prepared using a conventional method and/or compared to a known coating.
  • a modified biopolymer of the present invention may be prepared and/or formed in less time compared to the time to prepare and/or form a modified biopolymer using a conventional method.
  • the modified biopolymer may be prepared and/or formed in about 60 minutes or less, such as, e.g., 45, 30, 20, 10, 5, 4, 3, 2, 1 minutes or less compared to multiple hours, such as, e.g., in conventional, solution-based methods.
  • the degree or amount of cross-linking present in a cross-linked, charge-modified biopolymer may provide mechanical rigidity to the modified biopolymer and/or correlate with the degree of mechanical rigidity in the modified biopolymer.
  • a modified biopolymer of the present invention may have a degree of substitution (DS) of about 0.01 or more, such as, for example, in a range of about 0.01 to about 0.3.
  • the modified biopolymer may have a degree of substitution of about 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, or more.
  • a modified biopolymer may have a degree of substitution in a range of about 0.09 to about 0.3 or about 0.1 to about 0.25.
  • the degree of substitution may be measured by nitrogen content and/or titration.
  • a coating of the present invention may comprise a chemically and/or physically modified biopolymer, such as, for example, a chemically and/or physically modified starch and/or hemicellulose.
  • the chemically and/or physically modified biopolymer e.g., chemically and/or physically modified starch
  • a modified biopolymer that is used to prepare a coated particle of the present invention may be prepared as described in U.S. Patent No. 8,975,387 and/or U.S. App. No. 14/728,240, the contents of each of which are incorporated herein by reference in their entirety.
  • a method of preparing a modified biopolymer and/or coating of the present invention includes preparing a homogeneous reaction blend.
  • a homogeneous reaction blend is a melted blend of all the components in a single phase.
  • a homogeneous reaction blend may be obtained using an extruder.
  • a homogeneous reaction blend may be obtained using a reactive extrusion process in an extruder.
  • the homogeneous reaction blend may be in the form of a single liquid phase.
  • a homogeneous reaction blend may provide a uniform distribution of the components or reactants as compared to a conventional method.
  • a method of the present invention may provide a chemical reaction that occurs more uniformly and/or completely due to the formation of a homogeneous reaction blend as compared to a conventional method.
  • the biopolymer in the homogeneous reaction blend may be a melted thermoplastic.
  • a biopolymer may react thermo-mechanically and/or chemically with one or more reagents to form a modified biopolymer of the present invention, which may be thermoplastic and/or a viscoelastic material.
  • a method of the present invention removes hydrogen bonding and/or crystalline domains present in a biopolymer. This may allow for all or substantially all portions of the biopolymer to be available for chemical reaction, such as, for example, charge-modification and/or cross-linking.
  • a homogeneous reaction blend may contain a plasticized biopolymer, which may allow for greater access to moieties throughout the biopolymer.
  • a heterogeneous phase reaction for example, in which modified biopolymers are synthesized by a coating process, in a diluted suspension, or with a concentrated gel solution
  • moieties e.g., free hydroxyls
  • the reaction thus may be carried out on the surface of the solid granule, such as, for example, by direct conversion of either the semi-crystalline granules in aqueous suspension or as a dry process.
  • a biopolymer in the presence of a plasticizer, may be plasticized in a homogeneous phase reaction to obtain thermoplastic behavior. Under the action of thermo-mechanical energy, the biopolymer granule will melt.
  • the plasticizer may be adsorbed to the biopolymer by heating the mixture and destruction of the granule structure of the biopolymer may occur with the introduction of mechanical and heat energy.
  • biopolymer granules may be transferred to a continuous phase and moieties (e.g., hydroxyl free groups) may be available to react with the reagent.
  • a homogeneous reaction blend may aid in distributing a modification (e.g. a charge-modification) along a biopolymer chain and/or more uniformly throughout a biopolymer in contrast to a conventional method, such as, for example, one in which the modification is only achieved at the surface (e.g. at the surface of a solid biopolymer granule).
  • the coating of a coated particle of the present invention comprises a charge-modified biopolymer that is cross-linked.
  • the coating of a coated particle of the present invention may be covalently cross-linked, which may "lock" the coating onto and/or around the core even though the modified biopolymer may not be chemically bonded onto the core.
  • the coating may be cationic, anionic, or a polyampholyte.
  • the coating of a coated particle of the present invention comprises a cationic biopolymer.
  • the coating of a coated particle of the present invention comprises a covalently cross-linked cationic hydrogel upon contact with an aqueous solution (e.g., in a solution having a salinity in a range of about 50 ppm to about 100,000 ppm and/or a hardness of about 1 ppm to about 150,000 ppm).
  • the coating may comprise a charged-modified biopolymer, a cross-linker and/or a catalyst.
  • a method of the present invention may provide a cross-linked, charge-modified biopolymer (e.g., cross-linked, cationic starch) in the form of a coating on a core, such as, e.g., sand.
  • a method of the present invention may be a solution based process and/or a melt based process.
  • a method of the present invention may comprise a reactive extrusion process and/or step, such as, e.g., as described in U.S. App. No.
  • a reactive extrusion process and/or step may be performed in line with a step and/or method of the present invention (e.g., a coating operation), which may allow for a continuous process for preparing a coated particle of the present invention, optionally with the coating comprising a cross-linked, charge-modified biopolymer that may be a super absorbent polymer.
  • a reactive extrusion step and/or process may allow for the use of an inexpensive biopolymer (e.g., a native biopolymer such as native starch and/or a starch flour such as corn flour) as the raw material.
  • the reactive extrusion step and/or process may modify the raw material (e.g., covalently cross-link the biopolymer and may form a hydrogel coating) and may modify the raw material continuously in-line with a proppant coating step and/or process.
  • a method of the present invention provides a coated particle that is a self-suspending proppant that may perform in high salinity and/or high hardness conditions.
  • a method of the present invention may comprise providing a charge modified biopolymer ⁇ e.g., a cationic biopolymer).
  • a method of the present invention may comprise preparing the charge modified biopolymer.
  • a charge modified biopolymer may be produced by reacting a biopolymer (e.g., a native biopolymer), a charge modifying agent, catalyst, and/or a plasticizer, optionally in a reactive extrusion process (REX).
  • a plasticizer may be used to facilitate the process.
  • a cross-linking agent may be added to and/or combined with the mixture comprising the native biopolymer and/or the modified biopolymer to produce a cross-linked, charge modified biopolymer.
  • the cross-linked, charge modified biopolymer may form a coating on a core.
  • a native biopolymer e.g., starch
  • plasticizer e.g., polyethylene glycol
  • a cationic charge modifying agent e.g., polyethylene glycol
  • a catalyst e.g., a catalyst
  • An in-line method may be used to produce charge modified biopolymer (e.g., cationic starch), which may be used to produce a melt coating.
  • a cross-linking agent may be added at one or more different times in the method.
  • a cross-linking agent may be combined with a charge-modified biopolymer before, during, and/or after the charge- modified biopolymer is combined with a core.
  • a cross-linking agent may be combined with a composition comprising a core (e.g., uncoated sand) prior to coating with the charge modified biopolymer.
  • a charge-modified biopolymer e.g., a cationic starch
  • plasticizer and/or catalyst may be fed into an extruder and mixed to form an extrusion mixture, and a cross-linking agent may be added into the extrusion mixture.
  • a cross-linking agent may be combined with a composition comprising the core coated with the charge-modified biopolymer.
  • a method of the present invention comprises introducing (e.g., injecting and/or adding) a catalyst into an extruder prior to a charge modifier.
  • the introduction (e.g., injection) of the catalyst may allow for the mixing and/or ionization of the biopolymer (e.g., starch) prior to charge modification.
  • the cross-linker may be subsequently introduced following mixing of the at least partially ionized biopolymer with the charge modifier.
  • An illustration of the reaction scheme can be seen in Fig. 9 where (1) refers to the catalyst, (2) refers to the charge modifier, and (3) refers to the cross-linker.
  • a method of the present invention may comprise introducing a charge modifier into an extruder prior to a catalyst as can be seen in Fig. 10 where (1) refers to the catalyst, (2) refers to the charge modifier, and (3) refers to the cross-linker.
  • a method of the present invention may comprise combining (e.g., mixing) a catalyst and a charge modifier together prior to introducing them into an extruder as can be seen in Fig. 11 where (1) refers to the catalyst, (2) refers to the charge modifier, and (3) refers to the cross-linker. Combining the catalyst and charge modifier prior into introduction into the extruder may provide the benefit of possessing a greater residence time for charge modification within the extruder.
  • a method of the present invention may comprise introducing a cross-linker prior to a catalyst and a charge modifier.
  • Mixing such as, e.g., mixing in an extruder, may be performed in a method of the present invention at one or more times during the method. In some embodiments, mixing may be performed following the introduction of a catalyst to assist in the ionization and/or gelatinization of the biopolymer. Mixing may be performed in a method of the present invention following a charge modifier and/or cross-linker to promote uniform distribution of the reagents on the biopolymer backbone.
  • the water content in a method of the present invention may be considered to be the total plasticizer content.
  • the amount of water present in a method and/or composition of the present invention may be the amount within points (1), (2), and (3) as shown in Figs. 9-11.
  • the total water content in a method and/or composition of the present invention may be dictated by the minimum water content required for obtaining a melt flow, such as, for example, greater than about 75 % by weight relative to a biopolymer (e.g., a charge modified biopolymer).
  • the concentration of water at one or more steps and/or locations may be dictated by the pH of the catalyst solution.
  • the pH is sufficiently high to induce ionization of the biopolymer and to initiate charge modification downstream while low enough to prevent degradation of the biopolymer and low enough to prevent the initiation of side reactions of charge modifier.
  • a modified biopolymer (e.g., a charge modified biopolymer and/or cross-linked, charge-modified biopolymer) may be applied to a core using a solution based coating process.
  • a modified biopolymer may be applied to a core using a melt from a REX process.
  • a wetting agent may be added to the composition comprising the modified biopolymer and/or to the composition comprising the uncoated core.
  • a wetting agent may improve the wetting of the core with the modified biopolymer (e.g., a hot extrudate comprising the modified biopolymer) and/or may produce a more uniform coating on the core.
  • the coating addition level may impact performance whereby increased coating level correlates to increased volumetric swelling. This correlation may hold true up until a coating level where shear stability is no longer present (e.g., the coating of the coated particle begins to fracture off after shearing). In application, there may be a financial and/or performance optimum coating level point where increases in coating content result in a diminished return on increased performance and cost.
  • the amount of water present in a composition comprising a modified biopolymer and/or core and/or used in a method of the present invention may be adjusted. In some embodiments, the amount of water included in a composition and/or used in a method of the present invention may be reduced and/or minimal compared to conventional coating compositions and/or methods. In some embodiments, the amount of water included in a composition may be greater than the amount of water included in a conventional extrusion method. In some embodiments, the amount of water used in a reactive extrusion method may be greater than the amount of water used in a traditional extrusion method, but less than a conventional coating method (e.g., a solution based coating method).
  • a conventional coating method e.g., a solution based coating method
  • a drying step may be reduced and/or eliminated, which may improve the process economics and/or increase manufacturing process throughput.
  • the water level may be adjusted such that the resultant extrudate has a viscosity suitable for a coating process.
  • the water level may be increased to improve coating uniformity.
  • the amount of water in a composition and/or used in a method of the present invention may be controlled through raw material feed rates via extrusion.
  • a viscosity for uniform coating of a core may be determined by measuring melt viscosity of the extrudate inline during extrusion and/or externally using a rheometer.
  • a method of the present invention may comprise applying a coating comprising a modified biopolymer to a core, wherein the modified biopolymer may not be cross-linked or may be partially cross-linked.
  • the coating may be applied to a core prior to the modified biopolymer being fully cross- linked.
  • the modified biopolymer may be applied to the core directly from an extruder.
  • cross-linking of the biopolymer may be completed and/or aided by performing a thermal treatment. The thermal treatment may drive off and/or remove water, such as, for example, water used to plasticize the extrusion mixture.
  • a composition comprising a plurality of cores prior to applying the coating to a core, may be heated to a temperature above room temperature, such as, for example, a temperature in a range of about 50°C to about 200°C. Heating the core prior to coating with the modified biopolymer may prevent premature cooling and/or may improve the uniformity of the coating on the core.
  • the core may be heated in the presence of a cross-linking agent and then a composition comprising the modified biopolymer (e.g., a melt extrudate) may be applied onto the plurality of cores, to form a mixture of coated cores.
  • the mixture of coated cores may be mixed in a mixer (e.g., an orbital mixer).
  • a cross-linking agent may be contacted (e.g., sprayed) onto a plurality of cores at substantially the same time as a melt extrudate is added to the plurality of cores and/or a cross-linking agent may be contacted onto the outside of the coated cores. Heating may aid in drying a coated particle and/or in curing the coating of the coated particle.
  • a method of the present invention may include a cross-linking agent and/or cross-linking step during an extrusion process and/or after an extrusion process.
  • a cross-linking agent may be contacted (e.g., applied, sprayed, injected, and/or the like) to a core prior to, during, and/or after contact with a composition comprising a modified biopolymer of the present invention (e.g., a melt extrudate).
  • a cross-linking agent may be present in a composition comprising a modified biopolymer of the present invention (e.g., a melt extrudate) that is contacted to a plurality of cores.
  • the cross-linking agent may be combined with, mixed with, and/or injected into the composition, optionally in the extruder.
  • the cross-linking agent may be combined with a composition comprising a modified biopolymer of the present invention (e.g., a melt extrudate) prior to, during, and/or after the composition is contacted to a plurality of cores.
  • a cross-linking agent may be contacted to plurality of coated cores (e.g., cores coated with a charge-modified and/or cross-linked biopolymer).
  • a method of the present invention provides cross-linking on a surface of a coated particle.
  • a method of the present invention may comprise two or more (e.g., 2, 3, 4, or more) cross-linking steps, which may use the same and/or different cross-linking agents.
  • a cross-linking agent may be included in a composition comprising a modified biopolymer of the present invention (e.g., a melt extrudate) that is contacted to a plurality of cores to provide coated particles and the coated particles may subsequently be contacted with a cross-linking agent.
  • a cured coated particle of the present invention may be contacted with a cross-linking agent.
  • the coating of the cured coated particle may or may not comprise a cross-linking agent prior to contacting the cured coated particle with the cross- linking agent.
  • the coating of the cured coated particle does not comprise a cross-linking agent.
  • the coating of the cured coated particle comprises a cross-linking agent that is in an extrudate that is applied to a core to form the coated particle and/or the cross-linking agent is contacted to a core prior to and/or while an extrudate is applied to the core to form the coated particle.
  • the cross-linking agent is provided in a composition (e.g., an aqueous solution) comprising the cross-linking agent in an amount of about 0.5% to about 10% or 20% by weight relative to the weight of the coating on the coated particle to which the composition is contacted.
  • the cross-linking agent may be present in a composition and/or coating of the present invention in an amount of about 0.1%, 0.25%, 0.5%, 0.75%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 15%), 20%) by weight of the composition and/or coating or more.
  • cross-linking a cured coating on a coated particle of the present invention may increase the swelling rate of the coated particle and/or the settled bed height of a plurality of coated particles when exposed to a solution.
  • the swelling rate and/or settled bed height may be increased by about 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 125%, 150%, 175%, 200%, 250%, 300% or more compared to an uncoated core, a current commercial coated particle and/or proppant, and/or a coated particle of the present invention that does not cross-link the cured coating.
  • a coated particle of the present invention may be "pre- swollen" during processing and/or a method of the present invention and may not require drying.
  • a pre-swollen coated particle may be prepared on site and pumped directly into a formation without drying and/or curing.
  • the coated particles may be heated to a temperature above room temperature, such as, for example, a temperature in a range of about 25°C to about 200°C for a period of time, such as, for example, in a range of about 1 minute to about 3 hours. In some embodiments, the coated particles may be heated to a temperature of about 180°C for about 10 minutes. Thermally treating the coated particles may aid and/or complete the cross-linking process and/or the charge modifying process. Heating the coated particles may cure the coating and/or dry the coated particles. In some embodiments, a thermal post-treatment may reduce the amount of residual solvents and/or plasticizers present in the coating and/or coated particle. In some embodiments, a coated particle may be agitated and/or shaken during heating, which may prevent caking and/or agglomeration and/or improve heating efficiency (e.g., through treatment via fluidized bed drying or curing).
  • a temperature above room temperature such as, for example, a temperature in a range of about 25°C to about 200°
  • the coated particles may be allowed to cool. Agglomerates may be broken up, such as, for example, by agitation, grinding, and/or sifting (e.g., sifting through a sieve), which may provide a mixture of coated particles having a substantially uniform particle size.
  • the thermal treatment method may maintain a plurality of separate and/or discrete particles during curing such that subsequent size reduction and/or sizing may be minimized and/or eliminated.
  • the particle size of a plurality of coated particles varies by about 20% or less (e.g., 15%, 10%, 5% or less) (Fig. 8).
  • a method of the present invention may be referred to as a solution coating method (e.g., a static coating method or a dynamic coating method) or may be referred to as an extrusion coating method (e.g., a melt flow coating method).
  • Example process parameters for these methods may be as provided in Table 1.
  • Table 1 Example processing ranges for static, dynamic, and melt flow coating methods
  • a charge modified biopolymer may be charge-modified prior to extrusion or during extrusion.
  • Example process parameters for these methods may be as provided in Table 2.
  • Tabic 2 Melt flow coating method processing comparison for charged modified biopolymer precursor vs. extrusion charge modification.
  • a coated particle of the present invention may be prepared using a melt flow coating method.
  • a melt flow coating method may comprise adding a biopolymer (e.g., starch or corn flour) into an extruder and adding a catalyst into the extruder.
  • the biopolymer is a charge modified biopolymer (e.g., cationic starch).
  • the catalyst may be added to the extruder and/or present in a composition of the present invention in an amount of about 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 1 1%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21% 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or 50% by weight relative to the biopolymer.
  • the biopolymer may be charged modified during a method of the present invention, and the method may comprise adding a charge modifying agent to the biopolymer and/or catalyst.
  • a charge modifying agent may be added to the extruder and/or present in a composition of the present invention in an amount of about 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or 75% by weight relative to the biopolymer.
  • a plasticizer may be used in a method of the present invention and/or present in a composition of the present invention. In some embodiments, a plasticizer is present at one or more steps in a method of the present invention.
  • a plasticizer may be added before, during, and/or after a biopolymer, catalyst and/or charge- modifying agent is/are added to an extruder.
  • the total amount of plasticizer used in a method of the present invention and/or present in a composition of the present invention may be about 75%, 100%, 125%, 150%, 175%, 200%, 225%, 250%, 275%, 300%, 325%, 350%, 375%, 400%, 425%, 450%, 475%, or 500% by weight relative to the biopolymer.
  • a method of the present invention may comprise adding a cross-linking agent to a composition comprising a charge-modified biopolymer.
  • the composition may be in the form of a melt extrudate.
  • the charge-modified biopolymer may have a degree of substitution in a range of about 0.05, 0.1 , 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, or 0.8.
  • the cross-linking agent is added to the composition comprising the charge-modified biopolymer prior to, during and/or after contacting the composition comprising the charge-modified biopolymer to a core.
  • the charge-modifying agent may be present in an amount of about 0.1 %, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% by weight relative to the biopolymer.
  • composition comprising the charge-modified biopolymer and optionally a cross- linking agent may be contacted to (e.g., combined, mixed, etc.) a plurality of cores, with the composition being in an amount of about 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15% by weight relative to the uncoated cores.
  • the composition is a melt extrudate.
  • One or more steps in a method of the present invention may each be carried out at a temperature of about 60, 65, 70, 75, 80, 85, 90, 95, 100, 125, 150, or 160°C.
  • one or more steps in a method of the present invention may each be carried out with a mixing time of about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 , 1.5, 2, 2.5, or 3 minutes.
  • one or more steps in a method of the present invention may each be carried out in an extruder with a rpm of about 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1 150, 1200, or 1250.
  • a step of combining (e.g., mixing) one or more components in an extruder may be carried out at a temperature in a range of about 60°C to about 160°C for about 0.1 to about 3 minutes with a rpm of about 50 to about 1250.
  • a linker molecule may be present in a coated particle of the present invention.
  • the linker molecule may be added to and/or mixed with a core prior to and/or during mixing of the core with a modified biopolymer.
  • a linker molecule may be bound to reactive moieties on a surface of the core and to residual, unreacted functional groups (e.g., ⁇ — OH groups) on the charge modified biopolymer to form a chemical bond between the core and modified biopolymer.
  • a linker molecule may improve the adhesion of the coating to the surface of the core, which may result in increased shear stability of the coated particle compared to a coated particle without a linker molecule.
  • one or more binding agents and/or performance enhancing agents may be present in a coated particle of the present invention.
  • a binding agent and/or performance enhancing agent may be added to and/or mixed with a core prior to and/or during mixing of the core with a modified biopolymer.
  • an organosilane may be present in a coated particle and may be used to promote chemical adhesion between the coating and a core (e.g., a sand substrate).
  • An organosilane may be mixed with water and/or an acid in order to undergo hydrolysis prior to and/or during mixing with a core and then may be heat treated.
  • the organosilane may then undergo condensation to form a linkage with the core and biopolymer (e.g., modified biopolymer).
  • This condensation reaction may be expedited by residual catalyst from the biopolymer and/or by addition of a slightly basic solution. Additional thermal treatment after mixing of the organosilane, core, and biopolymer may aid in the efficiency of the linkage. Without chemical bonding, delamination may be more likely to occur under high shear conditions, surface stress conditions, etc. Improved adhesion may not directly yield a response in settled bed height; however, it may yield a response in shear stability in some cases.
  • organosilanes include, but are not limited to, glycidoxypropyltrimethoxysilane, chloropropyltrimethoxysilane, chloropropyltriethoxysilane, and/or methacryloxypropyltrimethoxysilane.
  • glycidoxypropyltrimethoxysilanes may be used due to the presence of an epoxy organic reactivity group which parallels the functionality of certain cross-linking agents, such as, for example poly(ethylene glycol) diglycidyl ethers.
  • a surfactant may be added to a composition comprising a biopolymer and/or modified biopolymer prior to, during, and/or after extrusion.
  • a surfactant may be used to improve the mixing of a composition and/or wetting of a melt extrudate on uncoated cores.
  • a surfactant may improve polymer distribution on a core and/or improve coating uniformity.
  • Other methods of improving uniformity may include reducing melt viscosity and/or increasing shear during mixing. Coating uniformity may be qualitatively shown though SEM analysis.
  • a hydrophobic surfactant may be used and may increase the rate at with the coating swells when exposed to a solution.
  • the rate at which a coated particle (e.g., proppant) swells within solution is a parameter that affects operational efficiency. In some embodiments, it may be desirable to have the coated particle reach close to full/maximum swelling in about 12 minutes or less (e.g., about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 minutes).
  • a surfactant may be applied to the surface of a coated particle to reduce surface tension amongst particles and/or improve gel bed permeability, which may result in faster swelling rates.
  • surfactants examples include, but are not limited to, siloxanes and silicones such as poly(dimethylsiloxane), functional silanes such as octodecyltrichlorosilane, and/or fatty acids such as lauric acid.
  • a silane based coupling agents may be used due to their relatively low cost and their ability to form weak links with the biopolymer coating. While not wishing to be bound to any particular theory, it is believed that these weak links enable a solution to fully penetrate into the bed of coated particles and subsequently penetrate into the coating itself (i.e., allow for swelling of the coating).
  • a viscosifying agent may be included in a composition of the present invention and/or used in a method of the present invention.
  • a viscosifying agent may be used in conjunction with a coated particle of the present invention in order to affect settling rate of the coated particle after agitation.
  • Example viscosifying agents include, but are not limited to, guar, carboxymethyl cellulose, charge modified starch, and any combination thereof.
  • a viscosifying agent may be added directly onto a coated particle of the present invention, may be included in an extrudate comprising a biopolymer, and/or may be mixed with a composition comprising the coated particles.
  • a viscosifying agent may be added to a composition comprising the biopolymer and/or modified biopolymer prior to, during, and/or after extrusion.
  • a leavening agent may be included in a composition of the present invention and/or used in a method of the present invention.
  • a leavening agent may be included in a coating on a particle of the present invention and/or may be used in a method of preparing a coated particle of the present invention, which may improve swelling performance of the coated particle.
  • inclusion of a leavening agent in a method of preparing a coated particle of the present invention and/or in a coating on a particle of the present invention may increase the swelling rate of the coated particle and/or the settled bed height of a plurality of coated particles when exposed to a solution.
  • the swelling rate and/or settled bed height may be increased by about 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 125%, 150%, 175%, 200%, 250%, 300% or more compared to an uncoated core, a current commercial coated particle and/or proppant, and/or a coated particle of the present invention that does not include a leavening agent in the coating and/or that does not include a leavening agent in the method to prepare the coated particle.
  • Example leavening agents include, but are not limited to, sodium bicarbonate; monocalcium phosphate; a gas such as, e.g., carbon dioxide, nitrogen, nitric oxide, oxygen, and/or air; a nucleating such as, e.g., calcium carbonate, calcium hydroxide and/or silicate; and any combination thereof.
  • the leavening agent is baking powder and/or baking soda.
  • the leavening agent is sodium bicarbonate and monocalcium phosphate.
  • one or more compounds that produce a gas such as, e.g., carbon dioxide, nitrogen, nitric oxide, and/or oxygen, in the coating and/or composition of the present invention are used as the leavening agent.
  • the leavening agent is a foaming agent.
  • sodium bicarbonate is used as the leavening agent in combination with and/or in the presence of a weak acid, and/or sodium bicarbonate is used as the leavening agent in an acidic composition.
  • a leavening agent may be added directly onto a coated particle of the present invention (optionally in the presence of a solvent, such as, e.g., water), may be included in an extrudate of the present invention, and/or may be included in a composition comprising coated particles of the present invention.
  • a leavening agent may be added to a composition comprising a biopolymer and/or modified biopolymer prior to, during, and/or after extrusion.
  • a leavening agent may be present in a composition and/or coating of the present invention in any suitable amount.
  • the leavening agent may be present in a composition and/or coating of the present invention in an amount of about 0.1%, 0.25%, 0.5%, 0.75%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 15%, 20% by weight of the composition and/or coating or more.
  • a leavening agent is used and/or incorporated in an amount relative to the weight of the coating.
  • a leavening agent may be present in a composition (e.g., an aqueous composition) that is contacted to and/or with a coated particle of the present invention.
  • the leavening agent may be present in the composition in an amount of about 0.1% to about 20% by weight relative to the weight of the coating on the coated particle to which the composition is contacted.
  • the coated particles may be added to, sprayed with, mixed with, and/or the like, the composition.
  • additives and/or excipients may be added to and/or present in a coated particle and/or composition of the present invention, and/or used in a method of the present invention.
  • charged entities e.g., anionic and/or amphoteric compounds
  • anti-clumping agents e.g., anti-clumping agents
  • anti-caking agents e.g., anti-caking agents
  • REX reactive extrusion
  • a charge modifier may be reacted with a biopolymer in the initial zone(s) of an extruder and followed by a cross-linking reaction in later zone(s) of the extruder and/or in subsequent mixing steps. Additional reaction and/or physical modification steps may be included along the length of the extruder, such as removal of volatile compounds via vacuum, addition of water for reduced viscosity, size reduction at the output of the extruder, and more. Examples of processes of the present invention are provided below.
  • Example 1 Hydrogels from modification of commerciallv-sourced anionic starch
  • REX may be used to induce a cross-linking (XL) reaction so that the output material is a hydrogel and/or SAP.
  • Poly(ethyleneglycol)diglycidylether (PEGDE, Sigma Aldrich: 475696 , St. Louis, MO) may be used as cross-linker, and sodium hydroxide (NaOH, GFS Chemicals: #630, Powell, OH) may be used as catalyst to induce cross-linking with the anionic starch in the presence of plasticizer (DI water).
  • Extrusion composition and process parameters are given in Table 3, and the extruder configuration is shown in Fig. 4.
  • Table 3 Extrusion composition and process parameters for producing an anionic SAP by reacting a commercially- sourced anionic starch, sodium hydroxide (NaOH), water (H 2 0), and poly(ethyleneglycol)diglycidylether (PEGDE).
  • Example IB Hydrogels from cross-linkinfi and anionic modification of native starch
  • Table 4 Extrusion composition and process parameters for producing an anionic SAP by reacting native starch, sodium chloroacetate (SCA), sodium hydroxide (NaOH), water (H20), and poly(ethyleneglycol)diglycidylether (PEGDE). Corn starch and SCA were mixed in the dry form and subsequently fed in Zone 1.
  • SCA sodium chloroacetate
  • NaOH sodium hydroxide
  • H20 water
  • PEGDE poly(ethyleneglycol)diglycidylether
  • Example 1C Hydrogels from modification of commercially-sourced cationic starch
  • Table 5 Extrusion composition and process parameters for producing a cationic SAP by reacting a commercially-sourced cationic starch, sodium hydroxide (NaOH), water (H20), and poly(ethyleneglycol)diglycidylether (PEGDE).
  • Table 6 Extrusion composition and process parameters for producing a cationic SAP by reacting native starch, (3-chloro-2-hydroxypropyl)trimethylammonium chloride (Quab 188), sodium hydroxide (NaOH), water (H20), and poly(ethyleneglycol)diglycidylether (PEGDE).
  • Test Metrics/Data Free Swelling Capacity (FS) data for Examples 1A-1D is shown in Table 7. Swelling performance data is shown in various solutions relevant to a range of applications. DI water corresponds to pure water (ideal conditions for conventional hydrogel materials), 0.9% NaCl corresponds to biological solutions, and 10% CaCl 2 corresponds to extreme hardness conditions. Hardness conditions are of particular interest as they relate to oil and gas ⁇ e.g., hydraulic fracturing) operations. Additional test metrics for SAP (i.e., CRC, AUL, permeability, etc.) may be conducted but are not included here.
  • CRC CRC
  • AUL permeability
  • Table 7 Swelling performance of samples prepared according to Examples 1A-1D in various solution conditions
  • anionic charged materials typically show reduced performance in divalent solutions (CaCl 2 )
  • additional features of a starch backbone are believed to contribute to a performance that is greater than that of their commercial counterparts (i.e., commercial anionic SAP materials) in divalent solutions.
  • Tethex modified SAPs formed using a REX process were prepared in-line with existing extrusion processes (Examples IB and ID), and native starch is a significantly more economical raw material.
  • REX other processes such as batch solution processes may be utilized. Although these processes may prove economical at very large economies of scale, they also may utilize large amounts of water and/or solvent ( ⁇ 1000's of percent or more relative to polymer), and typically have relatively long reaction/residence times ( ⁇ hours or more).
  • comparative processes for reactive extrusion of biopolymers can utilize as low as ⁇ 20% water or solvent and have residence times as low as a few seconds. Furthermore, the scalability and relative low profile of extrusion allows for distributed manufacturing.
  • Example 2 describes techniques for coating these hydrogel materials on to sand or proppant materials.
  • Example 2A - Using a static method and modified biopolymer to coat proppants (cationic charge)
  • the reagent and catalyst were combined in solution. In other embodiments, separate solutions of one or both components were made and added separately. When all components were combined in the petri dish, the sample is placed in a forced air oven at desired times and temperatures to initiate reactions and dry the material prior to grinding. Resulting material was ground in a mortar and pestle to separate sand particles prior to testing. [0137] The process disperses sand in the slurry at a controlled sand/polymer ratio. Although this demonstrates application of a swelling material on sand substrate, the method inherently yields a non-uniform coating and can generate unbound polymer, relative to methods below.
  • the first solution contained polymer and catalyst dissolved into water
  • the second solution contained cross-linker dissolved into water.
  • Compositions for solutions are shown in Table 8.
  • Table 8 Static coating method components and concentrations used in Example 2 A
  • coated proppant materials may by tested for volumetric swelling via a version of a settled bed height test, where 1 gram of material was placed in a 15 mL round glass vial with an outer diameter of 20.5 mm. 15 mL of test solution was added to the vial and followed with vigorous shaking for 5 seconds. After 1 hour, the bed height of the swollen sand was measured using digital calipers. Any visible gel layer (translucent layer) was considered free polymer and not counted in the following measurements. This initial measurement is termed "pre-shear height". Following measurement, the vial was then shaken vigorously for an additional 5 seconds and allowed to settle for 15 minutes to demonstrate shearing conditions.
  • post-shear height A second measurement is taken and termed "post-shear height". The measurements were used to calculate a percent (%) increase in height over that of 1 g of an uncoated sand material ( ⁇ 4mm). Initially relevant solutions are: 0.9% NaCl, 10% NaCl, 0.9% CaCl 2 , 10% CaCl 2 . The performance for samples coated via the static coating method is shown in Table 13.
  • Example 2B - Using a static method and modified biopolymer to coat proppants (anionic charge)
  • Example 2B focuses on the utilization of a cationic hydrogels for proppant coating
  • the example below demonstrates the variety of modified biopolymers that may be utilized as coatings. Feasibility of using anionic starch to create a hydrogel and/or SAP is demonstrated in the example below.
  • Materials utilized follow those in Example 1. Material preparation and coating methods follow static coating methods described in Example 2A. Compositions and components are shown in Table 9. The performance for samples described here is shown in Table 13, below.
  • Example 2C Using a dynamic method and cationic-modified biopolymer to coat proppants
  • Table 10 Example of compositions for solutions and components for a dynamic coating method
  • a 25 mL cross-linker solution was made according to parameters in described in Table 10, above. While the solution was stirring, 8g of sand was suspended into the solution and allowed to stir for 2 minutes. 6.4 grams of the polymer/catalyst solution was then added and allowed to stir for an additional 2 minutes. The temperature of the solution was then heated to 60°C and allowed to mix in an open container for 40 minutes.
  • a unique method for coating substrates includes submitting a commercial cationic starch and cross-linker to REX where the extrudate is immediately used for coating.
  • This method may be termed a melt coating method.
  • a viscous melt containing all necessary reagents is extruded into a planetary mixer containing heated sand.
  • the melt method may allow for improved process control which may provide more precise manipulations of polymer :reagent: catalyst: sand ratios.
  • This method may be directly translatable to a continuous, large-scale process where REX may be utilized in line with existing proppant processing equipment.
  • the continuous nature of this process also for more uniform and shear stable materials compared to that of alternative methods, including static and dynamic coating methods, described above. Additionally, water and solvent requirements are drastically reduced (> ⁇ 50% solids) resulting in improved efficiency, and reduced raw materials and capital costs.
  • An example of a melt coating process is described below. Compositions and process configurations used for Example 2D are given in Tables 11 and 12 and the extruder configuration is shown in Fig. 7.
  • the specified cross-linking solution was mixed with the heated sand in an orbital mixer until a uniform coating/consistency was observed. All other reagents were fed into the extruder according to parameters specified above. Using the dry feed rate for commercial cationic starch, extrudate was applied to sand to achieve a 5 wt. % polymer coating for 500 grams of sand. The components were again mixed until a uniform coating/consistency was observed. Samples were then heat treated and tested according to methods described above. The performance for samples coated via the melt coating method is shown in Table 13.
  • Example 1 The above examples demonstrate that materials, such as those described in Example 1, may be used to coat proppants and that the coating may be performed using different methods.
  • Static method was initially used to demonstrate swelling of a given polymer system when combined with sand.
  • SBH performance is maintained by changing coating methods.
  • properties such as coating uniformity may be improved from static to dynamic methods (Examples 2A-2C) as well as from dynamic to melt-coating methods (Examples 2C-2D).
  • the melt coating method may lend itself better to scaling from both a cost and throughput perspective.
  • EXAMPLE 3 Use of REX for inline biopolymer modification and proppant coating
  • a melt coating process utilizing REX is used to demonstrate inline starch modification with a coating process.
  • Example 3 focuses on starch cationization via reactive extrusion; however, additional biopolymer modification systems may similarly be used.
  • Example 2D A system as described in Example 2D was modified and used to demonstrate inline processing of cationic starch via a melt coating process. Here, glycidyltrimethylammonium chloride was included to charge modify starch during extrusion. Compositions and process configurations are given in Tables 14 and 15, and the extruder configuration is shown in Fig. 6.
  • Table 14 Extrusion composition and process parameters for producing cationic proppant coating by reacting native starch, sodium hydroxide (NaOH), glycidyltrimethylammonium chloride (Quab 151), and water (H20) and subsequently reacting the product with PEGDE (Table 15).
  • Cross-linking solution was mixed with the heated sand in an orbital mixer until a uniform coating/consistency was observed. Parameters for the cross-linking solution are shown in Table 15. Using dry feed rate (starch), extrudate was applied to sand to achieve a 4 wt. % starch coating for 500 grams of sand. The components were again mixed until a uniform coating/consistency was observed. Relative to Example 2, the extrusion screw configuration was modified to accommodate for injection of catalyst and charge modifier as shown in Fig. 5. Samples were then heat treated according to methods described in Example 2D.
  • An alternative cationic reagent may include (3-chloro-2-hyroxypropyl) trimethylammonium chloride (Quab 188, Sigma Aldrich #348287, St. Louis, MO), a precursor reagent used in Example 3A.
  • a catalyst NaOH
  • this chlorohydrin form of cationic reagent may be converted to the epoxide form in one or more zones of the extruder.
  • reactions may continue as described in Example 3A, above.
  • Compositions and process configurations are given in Tables 16 and 17. The extrusion screw configuration was equivalent to that seen in Fig. 6.
  • Table 16 Extrusion composition and process parameters for producing a cationic proppant coating by reacting native starch, sodium hydroxide (NaOH), (3-chloro-2- hyroxypropyl)trimethylammonium chloride (Quab 188), and water (H20) to produce a cationic starch and subsequently reacting the cationic starch with PEGDE (Table 17) to produce the cationic SAP.
  • Example 3B An alternative to Example 3B may be to convert the chlorohydrin form of the cationic reagent to its epoxide form external to REX.
  • catalyst sodium hydroxide
  • 3-chloro-2-hyroxypropyl)trimethylammonium chloride prior to injection.
  • reaction efficiency and solubility of the extrudate may be increased due to an increased residence time during REX.
  • Example 3A Compositions and process configurations are given in Tables 18 and 19. The extrusion screw configuration is equivalent to that seen Fig. 6.
  • Table 20 Extrusion composition and process parameters for producing an amphoteric proppant coating by reacting native starch, sodium chloroacetate (SCA), sodium hydroxide (NaOH), glycidyl trimethylammonium chloride (Quab 151), and water (H20) to produce an amphoteric starch, and subsequently reacted with PEGDE (Table 21) to produce the amphoteric SAP
  • REX may additionally be utilized to induce cross-linking during a melt coating process.
  • cross-linker is injected in the extruder so that the cross-linking reaction occurs in the extruder and/or in a thermal post treatment/drying step.
  • PEGDE polyethylene glycol
  • a starch, charge modified starch, or otherwise modified starch may be cross- linked in the extruder, resulting in a hydro gel.
  • native starch is injected, followed by subsequent injection of catalyst and further subsequent injection of cationic reagent and cross-linker into one or more zones of the extruder to result in a cationic, cross-linked starch.
  • Compositions and process configurations are given in Table 22. The extrusion screw configuration is equivalent to that seen in Fig. 4.
  • Table 22 Extrusion composition and process parameters for producing a cationic proppant coating by reacting starch, Quab 188, sodium hydroxide (NaOH), water (H20), and poly(ethyleneglycol)diglycidylether (PEGDE).
  • This process may lead to a more uniform distribution of cross-linking and may allow for consolidation of process steps. Although this method consolidates all reaction and reagent injection processes to extrusion, viscosity of resultant extrudate is slightly increased, resulting in reduced coating uniformity.
  • biopolymer feedstocks such as cellulose, hemicellulose, pectin, potato starch, tapioca starch, corn flour, potato flour, and others may similarly be utilized in an REX melt coating process.
  • corn flour is used in place of corn starch as the primary biopolymer for charge modification and cross-linking.
  • Other reagents and process parameters follow those described in Example 3B. Compositions and process configurations are given in Tables 23 and 24. The extrusion screw configuration was equivalent to that seen in Fig. 6.
  • Table 23 Extrusion composition and process parameters for producing a cationic proppant coating by reacting corn flour, sodium hydroxide (NaOH), (3-chloro-2- hyroxypropyl)trimethylammonium chloride (Quab 188), and water (H20) to produce a cationic starch and subsequently reacting the cationic starch with PEGDE (Table 24) to produce the cationic SAP.
  • Example 3 demonstrates a variety of inline starch modification techniques that may be used in conjunction with a melt coating process.
  • Materials shown here demonstrate significant ion tolerance in both NaCl and CaCl 2 .
  • Various reagents and reaction pathways may be utilized to achieve desired properties.
  • a mixture of anionic and cationic charges (amphoteric nature) is believed to demonstrate tunable ion tolerance for a given condition.
  • various raw material inputs may be modified via REX to achieve desired swelling properties.
  • EXAMPLE 4 Process configurations for coating a proppant using a polymer melt
  • Example 3E demonstrated including cross-linking during the REX process.
  • multiple points in which cross-linker can be added to the polymer system are described and demonstrated.
  • Example 4A Sand and cross-linker mixing prior to extrudate melt coating
  • cross-linker is injected into a mixer with sand prior to the addition of polymer melt.
  • the cross-linker is uniformly distributed on the sand in the first stage, and then coated by polymer melt in a second stage.
  • Method results in a gradient of cross- linker density where polymer closest to the substrate is preferentially cross-linked.
  • Compositions and process configurations are shown below in Tables 26 and 27. The extrusion screw configuration is equivalent to that used in Examples 3A-D.
  • Table 26 Extrusion composition and process parameters for producing a cationic proppant coating by reacting a commercially-sourced cationic starch, sodium hydroxide (NaOH), and water (H20), extruding the product and reacting the product with PEGDE (Table 27).
  • Table 29 Extrusion composition and process parameters for producing a cationic proppant coating by reacting a commercially-sourced cationic starch, sodium hydroxide (NaOH), and water (H20), extruding the product and reacting with PEGDE (Table 30).
  • Example 4C Inline biopolymer modification, sand coating, and well injection
  • Example 3B Native starch based cationic starch (chlorohydrin form)
  • Example 3B Native starch based cationic starch (chlorohydrin form)
  • a viscous melt containing all necessary reagents was extruded into a planetary mixer containing heated sand.
  • the sand was then thermally treated for varying times and temperatures as seen in Table 34.
  • Compositions and process configurations used for Example 4C are given in Tables 32 and 33 and the extruder configuration is shown in Fig. 6.
  • Table 32 Extrusion composition and process parameters for producing a cationic melt coating by reacting native starch, sodium hydroxide (NaOH), (3-chloro-2- hyroxypropyl)trimethylammonium chloride (Quab 188), and water (H20) to produce a cationic starch and subsequently reacting the cationic starch with PEGDE.
  • Table 34 Thermal treatment variation of 5% cationic coating produced via melt coat method of native starch with the chlorohydrin form cationizing reagent. Percent volumetric swelling increase is given is relative to uncoated sand.
  • Degree of coating is represented by total amount of polymer relative to sand (in wt. %) as measured by loss on ignition (LOI), also known as ash testing.
  • LOI loss on ignition
  • materials are placed in a muffle furnace at 575°C for 5 hours. At this temperature, all organic materials are degraded and the difference in weights prior to and after exposure to temperature may be used to calculate %coating as a percentage of initial sample weight. Furthermore, the percent coating as a percentage of applied polymer (dry weight of applied polymer) is termed "coating efficiency".
  • Theoretical degree of substitution of charge modifier is determined from the concentration of the charge modifying reagent relative to the concentration of starch. In extrusion, this relative ratio of reagent to starch is given by the injection flow rates, density, and purity of reagents and is given by the following equation:
  • p r is the density of the charge modifying reagent.
  • Q r and Q s are the flow rates of the reagent and starch, respectively.
  • M r and M s are the molar mass of reagent and starch, respectively.
  • l r and l s are the indices of purity for the reagent and starch, respectively.
  • the efficiency of the charge modification is dependent upon the extrusion and thermal treatment operating parameters (temperature, residence time, SME) as well as the catalyst concentration. It is consequently necessary to measure the resultant DS.
  • the achieved DS is calculated through elemental analysis, where %N in a polymer sample may be used to calculate DS through the following equation:
  • DS is the measured degree of substitution and %N is the measured nitrogen content.
  • a baseline of 0.002 is subtracted from %N measurements to normalize against native starch.
  • Examples of varied percent coating and varied DS are shown in Examples 5 A and 5B respectively. All of the samples described in Example 5 utilize an external cross- linker injection prior to extrudate (see Example 4 A for reference). Compositions and process configurations are given in Table 35 and the extruder screw configuration is shown in Fig. 6. Here, the cross-linking solution was mixed with the heated sand in an orbital mixer until a uniform coating/consistency was observed prior to the extrudate melt coating.
  • extrusion dry feed rate starch
  • extrudate was applied to sand to achieve a desired percent coating for 500 grams of sand.
  • the components were again mixed until a uniform coating/consistency was observed.
  • catalyst and reagent compositions may be modified to control resulting DS.
  • Table 35 Cross-linking solution parameters for injection into the sand prior to applying and mixing the extruded melt. Composition and concentrations are consistent for Examples 5A and 5B.
  • Example 5A Fixed DSTH with varied % coating
  • Extrusion composition and process parameters are given in Table 36. Secondary processing (mixing order, thermal treatment) are equivalent to that seen in Example 3A. Performance characterization methods are equivalent to that seen in Example 3A.
  • Table 36 Extrusion composition and process parameters where native starch is charge modified by Quab 151 and subsequently reacted with PEGDE (Table 34) to create cationic proppant coating.
  • Cross-linking solution was mixed with the heated sand in an orbital mixer until a uniform coating/consistency was observed.
  • dry feed rate starch
  • extrudate was applied to sand to achieve a 4, 6 and 8 wt. starch % coating, respectively for 500 grams of sand.
  • the components were again mixed until a uniform coating/consistency was observed. Samples were then heat treated according to conditions as described in Example 3A.
  • Example 5B Fixed % coating with varied DS TH
  • Extrusion composition and process parameters are given in Table 37. Secondary processing (mixing order, thermal treatment) are equivalent to that seen in Example 3A. Performance characterization methods are equivalent to that seen in Example 3 A.
  • Table 37 Extrusion composition and process parameters where native starch is charge modified by Quab 151 and subsequently reacted with PEGDE (Table 35) to create cationic proppant coating.
  • the primary factor which affects SBH is coating content relative to the proppant. Increases in coating percentage result in significant increases in corresponding SBH for all solutions. Increases in charge modification also result in an increase in SBH for all solutions. It is significant to note that for Examples 5A and B, the coating content is kept constant for the starch rather than for the total material coating ⁇ i.e., starch + charge modifier + catalyst).
  • extrudate was applied to sand to achieve a 5 wt. % coating for 500 grams of sand. The components were again mixed until a uniform coating/consistency was observed. Samples were then heat treated according to conditions provided in Example 3A.
  • Table 39 Extrusion composition and process parameters for producing a cationic melt coating by reacting native starch, sodium hydroxide (NaOH), (3-chloro-2- hyroxypropyl)trimethylammonium chloride (Quab 188), and water (H20) to produce a cationic starch and subsequently reacting the cationic starch with PEGDE.
  • Table 42 Extrusion composition and process parameters for producing a cationic proppant coating by reacting corn flour, sodium hydroxide (NaOH), (3-chloro-2- hyroxypropyl)trimethylammonium chloride (Quab 188), and water (H20) to produce a cationic starch and subsequently reacting the cationic starch with PEGDE (Table 43) to produce the cationic SAP.
  • Example 6 Use of a wetting agent for improved coating uniformity
  • Example 4 A A system as described in Example 4 A was used with the addition of glycerol to investigate the effects of alternative plasticizers and binding agents.
  • Commercial cationic starch, catalyst, and glycerol was extruded and immediately mixed with sand in an orbital mixer.
  • Cross-linker was subsequently injected into the sand/extrudate mixture and mixed again.
  • Compositions and process configurations are given in Tables 45 and 46.
  • the extruder configuration used is given in Fig. 4.
  • Table 45 Extrusion composition and process parameters for producing a cationic proppant coating by reacting a commercially-sourced cationic starch, sodium hydroxide (NaOH), glycerol, and poly(ethyleneglycol)diglycidylether (PEGDE).
  • Example 6B Demonstration of breakability for a modified biopolymer coating
  • Breaking of the proppant coating is a necessary step in order to regain conductivity of the proppant pack [SSP Transport Technology, Goldstein].
  • SSP Transport Technology, Goldstein In order to demonstrate breakability of the proppant coating, samples were exposed to HC1 and amylase.
  • the base coating material was a 5% cationic melt coating and equivalent to that seen in Example 4C with a thermal treatment of 120°C for 60 minutes.
  • the samples were crushed and sieved through 25/40 mesh and 35 grams was placed into the bottle as described for SBH testing. The samples were shaken for two minutes, allowed to settle for five minutes, and the SBH was subsequently recorded. After recording SBH, the samples received three different breaking conditions:
  • Control Using a bottle as described in the bottle shake test above (35 grams of sample in 84 mL of 10% CaC12 dihydrate), a control sample was shaken vigorously for two minutes. The same bottle was then heated at 80°C in a convective oven with no added breaking agent for one hour. After the hour at set temperature, the sample was removed and vigorously shaken for two minutes, allowed to settle for five minutes, and the new SBH was recorded. 2. Acid Breaking: Using a bottle as described in the bottle shake test above (35 grams of sample in 84 n L of 10% CaC12 dihydrate), -0.5 grams of 6 M HCl was slowly pipetted into the bottle to achieve a pH ⁇ 1. The bottle was shaken vigorously for two minutes and subsequently heat treated according to the same protocol as the control (Example 6C.1). The sample was subsequently shaken vigorously for two minutes, allowed to settle for five minutes, and the new SBH was recorded.
  • Example 6C Demonstration of biodegradability for a modified biopolymer coating
  • the biodegradability of the proppant coating is attributed with a structural decomposition of the biopolymer backbone. This decomposition can be seen in the viscosity reduction of a solubilized modified starch before and after treatment with an enzyme.
  • Cationic starch was created from native starch with a chlorohydrin form cationizing reagent.
  • the extrusion composition and operating conditions can be seen in Table 49.
  • the extrusion screw profile can be seen in Figure 6.
  • Table 49 Extrusion composition and process parameters for producing a cationic starch by reacting native starch, sodium hydroxide (NaOH), (3-chloro-2- hyroxypropyl)trimethylammonium chloride (Quab 188), and water (H20).
  • the viscosity of the 1% cationic starch so ution without enzyme treatment was 1300 cp
  • Example 6D Demonstration of flowability for a proppant coated with modified biopolymer
  • the described proppant coating is a starch based superabsorbent
  • the material tends to be hygroscopic. This hygroscopic nature may pose an issue for material handling and transport. Flowability tests were consequently completed for the material with and without anticaking agents. Additionally, uncoated sand was used as a reference measurement. The coating material used is equivalent to that seen in Example 3A with a post treatment temperature of 120°C and time of 60 minutes. The samples were crushed and sieved through 25/40 mesh. For samples with an anticaking additive, the already crushed and sieved coated proppant was simply hand mixed with the additive until a uniform mixture was observed.
  • a plastic funnel with a stem inner diameter of 1.0 mm, top diameter of 9.0 mm, height of 10.0 mm, and 30% inclination angle was placed within a ring stand above a 250 mL glass beaker.
  • the funnel was filled with 300 grams of material (sand or coated sand) while the bottom was covered.
  • a stopwatch was used to measure the time for the funnel to empty to the nearest hundredth of a second. The test was repeated six times for each sample and the average is reported in Table 51.
  • the coating or additive's effect on flowability can be determined by the relative difference between the coated and uncoated sample.
  • Table 51 Flowability for uncoated proppant, coated proppant, and coated proppant with an anticaking agent, sodium trisilicate (NaSilicate)
  • Example 6E Demonstration of use of hydrophobic additives for improved gel permeability and swelling rate
  • hydrophobic agent additives were utilized to improve gel bed permeability and swelling rate.
  • Coated sand materials as described in Example 4C were used as starting points for additional processing.
  • Polydimethylsiloxane (PDMS) was used as the hydrophobic reagent where three solutions of PDMS and deionized water were prepared and used to coat the materials as described in Table 52, below.
  • Table 52 Amount of hydrophobic coating (PDMS) added to coated proppant sample.
  • the solutions were mixed with the coated sand materials using an orbital mixer. Samples were then dried overnight in a forced air oven at 55°C. Samples were tested according to a modified SBH procedure where height measurements are recorded at designated times using the same bottle described in Example 3A. Here, the SBH was recorded every 30 seconds for up to 5 minutes following the initial 1 minute of shearing to the testing vials. The samples were all tested in 10% CaCl 2 . Results are outlined in Table 53.
  • Table 53 Swelling rates in PDMS coated samples compared to control sample with no PDMS coating
  • Results indicate improvement to swelling behavior for samples utilizing a hydrophobic additive.
  • Results indicate a 5-6 mm improvement in bed height over that of materials without hydrophobic coatings. Improved performance is attributed to reduction of gel blocking effect during swelling.
  • the additives may be included in line with the melt coating process whereby the PDMS solutions may be coated on to sand following polymer coating and preceding heat treating. Samples were then heat treated and tested according to Example 3E, above. PDMS concentrations are shown in Table 54 and performance is listed in Table 55, below.
  • Example 6F Demonstration of use of viscosifying agents for modified supernatant viscosity
  • Additives such as viscosifying agents may be utilized to include additional features on a coated particle.
  • Coated sand materials as described in Example 3C were used as starting base materials for additional processing.
  • guar is included as a viscosifying agent via a secondary coating, in line with a melt coating process. Process conditions are shown in Table 56 and performance is listed in Table 57, below.
  • Results show increased supernatant viscosity for materials with guar additives, demonstrating ability to modify settling rate for coated particles.
  • agent additive and degree of shear viscosity may be modified up to multiple orders of magnitude.
  • Including additives in a proppant coating may allow for reduction in use of viscosifying agents on site.
  • EXAMPLE 7 Example method of cross-linking a charged starch melt coating
  • a method of preparing a surface cross-linked particle incorporates a cross-linking agent into fully coated and cured particles via a fluidized bed or similar aeration processing technique.
  • a cationic charged modified starch is created using reactive extrusion and the compositions and process configurations are given in Table 58.
  • dry feed rate Starch + Quab 188 + NaOH
  • extrudate was applied to heated sand (180°C) to achieve a 5 wt. % dry coating for 500 grams of 20/40 sand.
  • the components were mixed in an orbital mixer until a uniform coating/consistency was observed.
  • the coated sand was then heat treated to finish curing and crushed to size (20/40 mesh) to provide the base sample.
  • Table 58 Extrusion composition and process parameters for producing a cationic SAP by reacting native starch, sodium hydroxide (NaOH), (3-chloro-2- hyroxypropyl)trimethylammonium chloride (Quab 188), and water (H 2 0) to produce a cationic starch and subsequently reacting the cationic starch with PEGDE (Table 59) to produce the cationic SAP.
  • Table 60 Fluidized bed operating conditions for cross-linking solution injection.
  • sample settled bed height (SBH) was tested in 10% CaCl 2 .
  • the performance of the base sample as well as the fluidized bed cross-linked sample is given in Table 61. Results show effective cross linking via fluidized bed or similar aeration processing technique.
  • a cationic charged modified SAP is created using reactive extrusion and the compositions and process configurations are given in Table 62.
  • dry feed rate Starch + Quab 188 + NaOH
  • extrudate was applied to heated sand (180°C) to achieve a 5 wt. % dry coating for 500 grams of 20/40 sand.
  • the extrudate, sand, and a crosslinking solution were mixed in an orbital mixer until a uniform coating/consistency was observed.
  • the coated sand was then heat treated to finish curing and crushed to size (20/40 mesh) to provide the cross-linked base sample.
  • Table 62 Extrusion composition and process parameters for producing a cationic SAP by reacting native starch, sodium hydroxide (NaOH), (3-chloro-2- hyroxypropyl)trimethylammonium chloride (Quab 188), and water (H20) to produce a cationic starch, and PEGDE (Table 59) to produce the cationic SAP.
  • Table 64 Cross-linking solution parameters for injection into the fluidized bed.
  • sample SBH was tested in 10% CaCl 2 .
  • the performance of the cross-linked base sample as well as the twice cross- linked sample is given in Table 65. Results show improved swelling performance for surface crosslinked particles such as those cross linked via a fluidized bed or similar aeration processing technique.
  • Table 65 Volumetric swelling percent increase relative to uncoated proppant for cross- linked base sample and cross-linked base sample with crosslinker addition in fluid bed
  • a leavening agent sodium bicarbonate and monocalcium phosphate
  • sodium bicarbonate and monocalcium phosphate were used as an additive to boost swelling performance.
  • the leavening agent gives added product value by releasing carbon dioxide gas into the wet coating mixture to form a porous structure, which is subject to increased surface area for contact with solution and resultantly may increase the swelling rate of the coating.
  • Example 4C Using extrusion processing and coating methods as described in Example 4C, a coated proppant was dried and sized to 20/40 mesh particles. A solution of Rumford baking powder (sodium bicarbonate, monocalcium phosphate, corn starch, and water) was then added to the dry coated proppantand mixed thoroughly by hand until a homogenous mixture was observed. The concentrations of additives are provided in Table 63. The sample was subsequently heat treated in a convective oven at 100°C for one hour. The resultant SBH can also be seen in Table 66 where the SBH testing procedure is equivalent to that described in Example 4C.
  • Rumford baking powder sodium bicarbonate, monocalcium phosphate, corn starch, and water

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Abstract

La présente invention concerne des particules revêtues, telles que, par exemple, des agents de soutènement comprenant un revêtement. Une particule revêtue de la présente invention peut gonfler au contact d'une solution présentant une salinité comprise dans une plage allant d'environ 50 ppm à environ 100 000 ppm et/ou présentant une dureté comprise dans une plage allant d'environ 1 ppm à environ 150 000 ppm. L'amplitude de gonflement peut varier de moins de 50 % sur une concentration de salinité comprise dans une plage allant d'environ 50 ppm à environ 100 000 ppm et/ou une concentration de dureté comprise dans une plage allant d'environ 1 ppm à environ 150 000 ppm. L'invention concerne également des procédés de production des particules revêtues et leurs procédés d'utilisation.
PCT/US2017/033753 2015-11-23 2017-05-22 Particules revêtues et leurs procédés de production et d'utilisation WO2018052495A1 (fr)

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