CONTROLLED RELEASE

FIELD OF THE INVENTION [0001 ] This disclosure relates to compositions and methods for different applications, particularly oilfield operations such as hydraulic fracturing. More particularly, this disclosure relates to the hydrophobic coating of scale inhibitors to control their release into a surrounding fluid.

BACKGROUND OF THE INVENTION [0002] Hydraulic fracturing is a technology commonly used to enhance oil and gas production from a subterranean formation. During this operation, a fracturing fluid is injected along a wellbore into a subterranean formation at a pressure sufficient to initiate fractures in the formation. Following fracture initiation, particulates, commonly known as proppants, are transported into the fractures as a slurry, that is, as a mixture of proppants suspended in fracturing fluid. At the last stage, fracturing fluid is flowed back to the surface leaving proppants in the fractures, forming proppant packs which prevent the fractures from closing after pressure is released. The proppant packs provide highly conductive channels through which hydrocarbons can effectively flow.

[0003] There are a number of different known proppants, including sands, ceramic particulates, bauxite particulates, glass spheres, resin coated sands, synthetic particulates and the like. Among them, sands are by far the most commonly used proppants. Proppants normally range in size between about 10 to about 100 U.S. mesh, which is about 2,000 pm to about 150 pm in diameter.

[0004] A vast majority of the fracturing fluids currently used are aqueous-based. Since proppants normally have a significantly higher density than water, for example the density of sand is typically about 2.6 g/cm ³ while that of water is 1 g/cm ³ , a high viscosity fluid is required to prevent the proppants from settling out of the slurry. For this purpose, viscosifiers such as water-soluble polymers or viscoelastic surfactants are commonly added to the slurry to increase the fluid viscosity. A cross-linked fluid having guar gum cross-linked by borates is a well-known example of this technology in the fracturing industry. In comparison with a fluid having a cross-linked gel, fluids comprising linear gels, i.e. , fluids containing enough polymer to significantly increase fluid viscosity without cross-linking, cause less formation damage and are more cost- effective, but they have relatively poor suspension capability compared to fluids having a cross-linked gel.

[0005]“Slick water” or simply“water” fracturing is a method of hydraulic fracturing that is widely used in fracturing shale or tight formations. In slick water fracturing, water containing a very small amount of a friction reducing agent is pumped into a formation at high rates to generate narrow, complex fractures. Pumping rates must be sufficiently high to transport proppant over long distances before entering the fracture. The fracturing fluid is pumped down the well-bore as fast as 100 barrels per minute (bpm) (or higher if acheivable), as compared to conventional (non-slick water) fracturing, where the top speed of pumping is around 60 bpm. A friction-reducing agent is added in water to suppress turbulence at high pumping rates thus reducing pumping pressure. Polyacrylamide-based friction reducing agents, which include polyacrylamides and polyacrylamide copolymers (which contain other monomers in addition to acrylamide monomers), are predominantly used in an amount between about 0.02 wt.% to about 0.05 wt.% of the fluid. Because of its low cost and its ability to create a complex fracture network leading to better production, slick water has recently become the“go-to” fluid for fracturing shale or tight formations.

[0006] After the well is put on production, crude oil and/or gas flows out of the well, often not as a single phase, but as a multi-phase flow, namely as a mixture of oil or gas and water. Further, crude oil itself is a complex mixture of different hydrocarbons ranging normally from butane to long chain paraffin wax, as well as asphaltene; while water is normally brine water comprising different amounts of inorganic ions including, but not limited to, K ⁺ , Ca ²⁺ , Mg ²⁺ , Cl , C0 ₃ ² and SO4 ² . During production, because of changes in temperature, pressure and other conditions, inorganic scales including carbonate salts, such as CaC0 ₃ or MgC0 _3, or sulphate salts, such as CaS0 ₄ , BaS0 ₄ or MgS0 _4, or silica can precipitate out of water and form inorganic scales. The formation of scale often occurs in both the subterranean formation and in the wellbore, and impedes production flow and worsens pipe corrosion. [0007] To mitigate scale formation, it is common to add chemical inhibitors known as scale inhibitors directly into the fracturing fluid during fracturing operations. Inhibitors used for preventing inorganic scale buildup include lignin amines, inorganic and organic polyphosphates, carboxylic acid copolymers, phosphinic polycarboxylates, sodium polyacrylates, polyepoxysuccinic acid, polyaspartates, sodium gluconate and sodium glucoheptonate.

[0008] Since a production well can last for decades and the formation of scale is a gradual process that accompanies its entire life cycle, it is highly desirable to keep the scale inhibitors active in a formation for as long as possible. Unfortunately, most of the scale inhibitors are water-soluble and will flow back with the fracturing fluid, after the fracturing treatment. To prolong their effectiveness, a few technologies have been developed to slowdown their release into water, for example, by forming complexes between phosphonic acid inhibitor with metal ions, as taught in U.S. Patent No. 5,207,919, by impregnating the inhibitor into pores of specially engineered ceramic proppants, as described in U.S. Patent No. 9,951 ,267, or adsorbing the inhibitors onto naturally occurring diatomaceous earth, such as clays, as described in U.S. Patent No. 3,179,170, or by adsorbing the inhibitors/metal complex onto water-insoluble adsorbents, as described in U.S. Patent No. 5,964,291 or by encapsulating the inhibitors with polymers such as a polyether, as described in U.S. Patent No. 6,380,136. One of the potential drawbacks of the technology of the‘291 patent is that ceramic proppants are very expensive compared to sand proppants and they only find limited applications in formations deeper than 4,000 meters, which excludes current shale formations. The‘170 patent provides a versatile method for adsorbing different additives and releasing them slowly into formations to prolong their effectiveness. Its drawback is that adding extra small particles, such as clay, into the formation may reduce conductivity of the proppant pack, which is vital for well production. Encapsulation with polymers is normally operationally costly.

[0009] There is a need for more efficient and cost-effective compositions and methods for the controlled release of inorganic scale inhibitors which may be used in different applications, including in water-treatment processes and in the oil and gas industry.

SUMMARY

[0010] Embodiments herein are compositions and methods for hydrophobic coating of scale inhibitors so that they are slowly released into surrounding aqueous fluid. This slow release promotes long lasting effects of the scale inhibitors and finds application in different oilfield operations including in hydraulic fracturing operations, and in water- treatment processes.

[0011 ] In at least one embodiment, methods according to present disclosure comprise preparing coated scale inhibitors by contacting uncoated solid inhibitors with a coating agent selected from the group consisting of: organosilanes, polysiloxanes, amine functionalized polyolefins, polymerizable natural oils and polyethylene-vinyl copolymers.

[0012] In at least one embodiment, methods according to present disclosure comprise preparing coated scale inhibitors by contacting uncoated solid inhibitors with an oil containing a small amount of a coating agent selected from the group consisting of: organosilanes, polysiloxanes, amine functionalized polyolefins, polymerizable natural oils and polyethylene-vinyl polymers.

[0013] In at least one embodiment, the contacting comprises spraying a liquid medium comprising the coating agent or an oil comprising the coating agent onto the solid scale inhibitor.

[0014] In at least one embodiment, methods according to present disclosure comprise preparing coated scale inhibitors by first adsorbing the liquid scale inhibitor onto a solid adsorbent and then coating the mixture of the adsorbent and the scale inhibitor with the coating agent. [0015] In at least one embodiment, methods according to present disclosure comprise preparing the coated scale inhibitors by first adsorbing the liquid scale inhibitor onto a solid adsorbent and then coating the mixture of the adsorbent and the scale inhibitor with an oil containing certain amount of the coating agent. [0016] In at least one embodiment, methods according to present disclosure comprise preparing the coated scale inhibitors by mixing the scale inhibitor with a polyvalent salt including one or more of Cu (II), Zn (II), Fe(lll), Ca (II), and Mg (II) salts and coating the mixture with the coating agent. In case where the scale inhibitor is a liquid, preferably, a solid anti-caking agent including a water-soluble salt and, optionally, fumed silica, is added to prevent clumping during preparation.

[0017] In at least one embodiment, methods according to present disclosure comprise preparing the coated scale inhibitors by mixing the scale inhibitor with a polyvalent salt including one or more of Cu (II), Zn (II), Fe(lll), Ca (II), and Mg (II) salts and coating the mixture with an oil containing the coating agent. In case where the scale inhibitor is a liquid, preferably, a solid anti-caking agent including a water-soluble salt and, optionally, fumed silica, is added to prevent clumping during preparation.

[0018] In one aspect, described herein is a method of hydraulic fracturing of a formation, comprising: a) preparing a hydraulic fracturing fluid by adding hydrophobically coated scale inhibitors into an aqueous fracturing fluid, and b) pumping the hydraulic fracturing fluid into the formation.

[0019] In a preferred embodiment the hydraulic fracturing fluid is a slick water fracturing fluid.

[0020] In preferred embodiments the coating agent is an organosilane such as an alkoxysilane, an organosiloxane, a polysiloxane, or mixtures thereof. In preferred embodiments the polysiloxane is an alkoxysiloxane. [0021 ] In preferred embodiments the coating agent is an organosiloxane, a polysiloxane, or mixtures thereof. In preferred embodiments the polysiloxane is a cationic polysiloxane.

[0022] In preferred embodiments the coating agent is a polyvinyl acetate or its copolymer, or mixtures thereof. In preferred embodiments the coating agent is a liquid polyethylene-vinyl acetate copolymer latex, more preferably water-based polyethylene- vinyl acetate copolymer latex.

[0023] In preferred embodiments the polysiloxane is a cationic polysiloxane. In preferred embodiments the coating agent is an oil containing a cationic polysiloxane or an amphoteric polysiloxane.

[0024] In preferred embodiments the coating agent is an oil containing an alkoxysilane.

[0025] In preferred embodiments the coating agent is an amine functionalized polyolefin, preferably mixed with an oil. In preferred embodiments the amine functionalized polyolefin agent is polyisobutylene amine. [0026] In preferred embodiments the coating agent is a polymerizable natural oil. In preferred embodiments the polymerizable natural oil is tung oil.

[0027] In preferred embodiments the scale inhibitor is phosphonic-based or polyacrylate-based. In preferred embodiments the scale inhibitor is diethylene triamine penta (methylene phosphonic acid) (DTPMP). [0028] In at least one embodiment the aqueous fluid is a hydraulic fracturing fluid. In a preferred embodiment the aqueous fluid is a slick water fracturing fluid.

[0029] In at least one embodiment the coating of the scale inhibitor comprises contacting uncoated solid inhibitors with the coating agent or an oil containing the coating agent. In a preferred embodiment the contacting comprises spraying a liquid medium comprising the coating agent onto the uncoated solid scale inhibitors. In another embodiment the contacting comprises mixing uncoated solid scale inhibitor with a liquid medium comprising the coating agent, and drying the coated inhibitor. [0030] In a preferred embodiment the coating of the scale inhibitor comprises mixing the scale inhibitor mixed with a polyvalent salt and an anti-caking agent and contacting, preferably by spraying, a coating agent. In a preferred embodiment the coating agent is a polysiloxane preferably an amino-polysiloxane, or an alkoxysilane; the scale inhibitor is DTPMP and the anti-caking agent is table salt (NaCI).

[0031 ] In a preferred embodiment the coating of the scale inhibitor comprises mixing the scale inhibitor mixed with a polyvalent salt and an anti-caking agent and contacting, preferably by spraying, an oil containing a coating agent. In a preferred embodiment the coating agent is a polysiloxane preferably an amino-polysiloxane, or an alkoxysilane; the scale inhibitor is DTPMP and the anti-caking agent is table salt (NaCI) and the oil is mineral oil.

[0032] In a preferred embodiment the coating of the scale inhibitor comprises mixing the scale inhibitor mixed with a polyvalent salt and an anti-caking agent and contacting, preferably by spraying, a coating agent. In a preferred embodiment the coating agent is tung oil; the scale inhibitor is DTPMP and the anti-caking agent is table salt (NaCI). In one embodiment the chemical additive is a scale inhibitor. In preferred embodiments the chemical additive is diethylene triamine penta (methylene phosphonic acid) (DTPMP).

[0033] In a preferred embodiment the coating agent is an organosilane. In a preferred embodiment the coating agent is alkoxysilane. In a preferred embodiment the coating agent is an oil containing an alkoxysilane.

[0034] In a preferred embodiment the coating agent is an amine functionalized polyolefin. In a preferred embodiment the coating agent is polyisobutylene amine.

[0035] In a preferred embodiment the coating agent is a polymerizable natural oil. In a preferred embodiment the coating agent is tung oil. [0036] In a preferred embodiment the chemical additive is a scale inhibitor. In a preferred embodiment the chemical additive is diethylene triamine penta (methylene phosphonic acid) (DTPMP). [0037] In all above, at least part of the solid scale inhibitor is coated with the coating agent.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1 is a graphical display of the percentage of polyacrylate scale inhibitor released as a function of effluent volume, with and without hydrophobic coating.

[0039] FIG. 2 is a graphical display of graphical display of the percentage of DTPMP scale inhibitor released as a function of effluent volume, with and without hydrophobic coating.

DETAILED DESCRIPTION [0040] For the purposes of understanding the specification and the claims appended hereto, a few terms are defined. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which embodiments of the disclosure pertain.

[0041 ] The singular forms "a," "an," and "the" include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to a composition containing "a compound" includes a composition having two or more compounds.

[0042] The term "about" as used herein can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1 % of a stated value or of a stated limit of a range. [0043] Values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a range such as from 1 to 6 should be considered to have specifically disclosed sub- ranges such as from 1 to 3, from 2 to 4, from 3 to 6 etc., as well as individual numbers within that range, for example, 1 , 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range. [0044] In the methods described herein, the steps may be carried out in any order, except when a temporal or operational sequence is explicitly recited. Furthermore, specified steps may be carried out concurrently unless explicit claim language recites that they be carried out separately. [0045] The term "substantially free" refers to a composition or mixture in which a particular compound is present in an amount that has no material effect on the composition or mixture. For example,“substantially free of a viscosifier” means that a viscosifier may be included in the composition or mixture an amount that does not materially affect the viscosity of the composition or mixture. It is within the ability of one skilled in the art with the benefit of this disclosure to determine if and whether an amount of a compound has a material effect on the composition. In embodiments, substantially free may be less than 2 wt.%, less than 1 wt.%, less than 0.5 wt.%, or less than 0.1 wt.%.

[0046] The term "fracturing" or“fracturing operation” refers to the process and method of breaking down a geological formation, e.g., the rock formation around a well bore, by pumping fluid at very high pressures, in order to increase production rates from a hydrocarbon reservoir. The fracturing methods disclosed herein use otherwise conventional techniques known in the art. The term“slick water fracturing” refers to a process of fracturing in which a low viscosity fluid (i.e., having a viscosity of less than about 10 cP at 511 sec ¹ at surface temperature), is injected into a formation at a flow rate of between about 60 and about 100 bpm, to generate narrow fractures with low concentrations of proppant.

[0047] The term "fracturing fluid" refers to fluids or slurries used in a formation, during a fracturing operation. The fracturing fluids encompassed herein include fluids comprising aqueous and/or non-aqueous liquids. Aqueous fracturing fluids are preferred, with slick water fracturing fluids being particularly preferred. There are several different types of fracturing fluids known to those of skill in the art, including viscosified water-based fluids, non-viscosified water-based fluids, gelled oil-based fluids, acid-based fluids and foam fluids. [0048] Viscosified water-based fracturing fluids include linear gel fluids which contain a gelling agent like guar, HPG, CMHPG, or xanthan, and have a viscosity of about 10 to about 30 cP at 511 sec ¹ at surface temperature, and crosslinked gel fluids which contain the gelling agents used in linear gel fluids plus a crosslinker such as boron (B), zirconium (Zr), titanium (Ti) or aluminum (Al). Cross-linked fluids have a higher viscosity of 100 - 1000 cP, at 100 sec ¹ at surface temperature. Linear gel fluids commonly include medium-size proppant, such as 30/50 size proppant, whereas crosslinked gel fluids commonly include large-size proppant, such as 20/40 size proppant.

[0049] A“slick water” fracturing fluid is a non-viscosified water-based fracturing fluid. These fluids are characterized in having a low viscosity, generally less than about 10 cP at 511100 sec ¹ at surface temperature, generally between about 2 and 3 cP at 100 sec ¹ at sub-surface temperature, and a friction-reducing agent in an amount that reduces friction pressure to between about 50% and about 80%, generally between about 60% and about 70%, as compared to fluids that do not have these agents. Common chemistries for friction reduction include polyacrylamide derivatives and copolymers added to the fracturing fluid at low concentrations, for example between about 0.02 wt.% to about 0.05 wt.% of the fluid. Accordingly, slick water fracturing fluids are commonly free, or substantially free, of viscosifiers such as natural or synthetic polymers and viscoelastic surfactants. [0050] The term “aqueous liquid” as used herein means water, solutions containing water, salt solutions, or water containing an alcohol or other organic solvents. The term “liquid medium” as used herein includes both aqueous and non-aqueous mediums. "Water" as used herein includes freshwater, pond water, sea water, salt water or brine source, brackish water and recycled or re-used water, for example, water recycled from previous or concurrent oil- and gas-field operations.

[0051 ]“Oil” as used herein refers to a neutral, nonpolar chemical substance that is hydrophobic (immiscible with water) and lipophilic (miscible with other oils). Some embodiments of the methods and compositions disclosed herein include an “oil promoter”, which differs from a polymerizable natural oil in being a petrochemical oil, an oil that is derived from petrochemicals, or a silicon oil. Representative non-limiting examples of an oil include hydrocarbon oils such as mineral oil, and silicone oils such as polydimethylsiloxane (PDMS).

[0052]“Scale inhibitor” as used herein refers to any suitable compounds used for the purpose of inhibiting inorganic scale deposition in well bore or water flowlines or water tanks on the surface in oilfields and beyond. Known inhibitors for preventing inorganic scale formation include lignin amines, inorganic and organic polyphosphates, carboxylic acid copolymers, phosphinic polycarboxylates, polyepoxysuccinic acid, polyaspartates, sodium gluconate, sodium glucoheptonate and sodium polyacrylates. Water soluble organic compounds containing carboxylic acid and/or phosphonic acid and/or sulphonic acid groups, either polymeric or monomeric, are commonly used as scale inhibitors. Examples of such compounds are 2-phosphonic -1 ,2,4-tricarboxylic acid, hydroxyethyl diphosphonic acid, and aminoalkyl phosphonic acids, hydroxy-substituted polyamino methylene phosphonates; ethylene diamine tetra (methylene phosphonate), diethylene triamine penta (methylene phosphonate) and salts of polyacrylate. Phosphonic-based and polyacrylate-based scale inhibitors are generally preferred.

[0053] The fluid compositions described herein can also include other agents, depending on the intended use of the fluid, and provided that these other agents do not adversely affect the composition. For example, polymers may be added to viscosify the fluid, crosslinkers may be added to change a viscous fluid to a pseudoplastic fluid, buffers may be used to control pH, surfactants may be used to lower surface tension, fluid-loss additives may be used to minimize fluid leakoff into a formation, stabilizers may be used to keep the fluid viscous, and breakers may be used to break polymers and crosslink sites. [0054] The term“coating agent” as used herein means a chemical compound that is able to coat particular surfaces, such as sand, glass or scale inhibitor surfaces, to make the surface hydrophobic, meaning the water contact on the surface is greater than about 60°, preferably greater than about 90°. When an interface exists between a liquid and a solid, the angle between the surface of the liquid and the outline of the contact surface is described as the contact angle Q. There are different methods for measuring contact angle. The contact angle can be measured by a contact angle goniometer using an optical subsystem to capture the profile of a pure liquid on a solid substrate. The angle formed between the liquid-solid interface and the liquid-vapor interface is the contact angle. In the methods and compositions contemplated herein, the contact angle is measured by placing a drop of water on the flat surface of a layer of compacted coated particulate. The flat surface of the layer of compacted coated particulate may be prepared by compacting coated particulate on top of another surface that is flat, for example, glass.

[0055] For clarity and convenience, coating agents contemplated herein are divided into four groups, A to D, as described below:

[0056] Group A) includes organosilanes, organosiloxanes and polysiloxanes modified with different functional groups, including cationic, amphoteric as well as anionic groups, fluorinated silanes, fluorinated siloxanes and fluorinated hydrocarbon compounds. In general, organosilanes are compounds containing silicon to carbon bonds. Polysiloxanes are compounds in which the elements silicon and oxygen alternate in the molecular skeleton, i.e., Si-O-Si bonds are repeated. The simplest polysiloxanes are polydimethylsiloxanes. Polysiloxane compounds can be modified by various organic substituents having different numbers of carbons, which may contain N, S, or P moieties that impart desired characteristics. For example, cationic polysiloxanes are compounds in which one or more organic cationic groups are attached to the polysiloxane chain, either at the middle or the end or both. The most common organic cationic groups are organic amine derivatives including primary, secondary, tertiary and quaternary amines (for example, quaternary polysiloxanes including, quaternary polysiloxanes including mono- as well as di-quaternary polysiloxanes, amido quaternary polysiloxanes, imidazoline quaternary polysiloxanes and carboxy quaternary polysiloxanes). Similarly, the polysiloxane can be modified by organic amphoteric groups, where one or more organic amphoteric groups are attached to the polysiloxane chain, either at the middle or the end or both, and include betaine polysiloxanes and phosphobetaine polysiloxanes. Among different organosiloxane compounds which are useful for the present compositions and methods are polysiloxanes modified with organic amphoteric or cationic groups including organic betaine polysiloxanes and organic amino or quaternary polysiloxanes as examples. One type of betaine polysiloxane or quaternary polysiloxane is represented by the formula

wherein each of the groups Ri to R ₆ , and R ₈ to Rio represents an alkyl containing 1-6 carbon atoms, typically a methyl group, R ₇ represents an organic betaine group for betaine polysiloxane, or an organic quaternary group for quaternary polysiloxane, and have different numbers of carbon atoms, and may contain a hydroxyl group or other functional groups containing N, P or S, and m and n are from 1 to 200. For example, in one type of quaternary polysiloxane R ⁷ is represented by the group

wherein R ¹ , R ² , R ³ are alkyl groups with 1 to 22 carbon atoms or alkenyl groups with 2 to 22 carbon atoms. R ⁴ , R ⁵ , R ⁷ are alkyl groups with 1 to 22 carbon atoms or alkenyl groups with 2 to 22 carbon atoms; R ⁶ is -O- or the NR ⁸ group, R ⁸ being an alkyl or hydroxyalkyl group with 1 to 4 carbon atoms or a hydrogen group; Z is a bivalent hydrocarbon group, which may have a hydroxyl group and may be interrupted by an oxygen atom, an amino group or an amide group; x is 2 to 4; the R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁷ may be the same or different, and X is an inorganic or organic anion including Cl and CH ₃ COO . Examples of organic quaternary groups include [R-N ⁺ (CH ₃ ) ₂ - CH ₂ CH(0H)CH ₂ -0-(CH ₂ ) ₃ -] (CH ₃ COO ), wherein R is an alkyl group containing from 1 - 22 carbons or a benzyl radical and CH ₃ COO an anion. Examples of organic betaine groups include -(CH ₂ ) ₃ -0-CH ₂ CH(0H)(CH ₂ )-N ⁺ (CH ₃ ) ₂ CH ₂ C00 . Such compounds are commercially available. It should be understood that cationic polysiloxanes include compounds represented by formula (II), wherein R ₇ represents other organic amine derivatives including organic primary, secondary and tertiary amines. [0057] Other examples of organo-modified polysiloxanes include di-betaine polysiloxanes and di-quaternary polysiloxanes, which can be represented by the formula

wherein the groups R ₁₂ to R ₁₇ each represent an alkyl containing 1-6 carbon atoms, typically a methyl group, the Rn and R _I8 groups represent an organic betaine group for di-betaine polysiloxanes or an organic quaternary group for di-quaternary, and have different numbers of carbon atoms and may contain a hydroxyl group or other functional groups containing N, P or S, and m is from 1 to 200. For example, in one type of di quaternary polysiloxane Rn and R _{I 8} are represented by the group

wherein R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , Z, X and x are the same as defined above. Such compounds are commercially available. Quaternium 80 (INCI) is one of the commercial examples.

[0058] Similarly, the polysiloxane can be modified by organic anionic groups, where one or more organic anionic groups are attached to the polysiloxane chain, either at the middle or the end or both, including sulfate polysiloxanes, phosphate polysiloxanes, carboxylate polysiloxanes, sulfonate polysiloxanes, thiosulfate polysiloxanes. The organosiloxane compounds also include alkylsiloxanes including hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, hexamethyldisiloxane, hexaethyldisiloxane, 1 ,3-divinyl- 1 , 1 ,3,3-tetramethyldisiloxane, octamethylthsiloxane, decamethyltetrasiloxane. The organosilane compounds include alkylchlorosilane, for example methylthchlorosilane, dimethyldichlorosilane, thmethylchlorosilane, octadecylthchlorosilane; alkyl- alkoxysilane compounds, for example methyl-, propyl-, isobutyl- and octyltrialkoxysilanes, and fluoro-organosilane compounds, for example, 2-(n-perfluoro- octyl)-ethyltriethoxysilane, and perfluoro-octyldimethyl chlorosilane. Other types of chemical compounds, which are not organosilicon compounds, which can be used to render proppant surfaces hydrophobic are certain fluoro-substituted compounds, for example certain fluoro-organic compounds including cationic fluoro-organic compounds. Further information regarding organosilicon compounds can be found in Silicone Surfactants (Randal M. Hill, 1999) and the references therein, and in United States Patent Nos. 4,046,795; 4,537,595; 4,564,456; 4,689,085; 4,960,845; 5,098,979; 5, 149,765; 5,209,775; 5,240,760; 5,256,805; 5,359, 104; 6, 132,638 and 6,830,81 1 and Canadian Patent No. 2,213, 168, all of which are incorporated herein by reference in their entirety. [0059] Organosilanes can be represented by the formula

RnSiX(4-n) (I) wherein R is an organic radical having 1 -50 carbon atoms that may possess functionality containing N, S, or P moieties that impart desired characteristics, X is a halogen, alkoxy, acyloxy or amine and n has a value of 1 -3. Examples of suitable organosilanes include: CH ₃ Si(OCH ₂ CH3)3, CH ₃ Si(OCH2CH ₂ CH3)3, CH ₃ Si[0(CH ₂ ) ₃ CH ₃ ] ₃ , CH ₃ CH ₂ Si(OCH ₂ CH ₃ ) ₃ , C ₆ H ₅ Si(OCH ₃ ) ₃ , C ₆ H ₅ CH ₂ Si(OCH ₃ ) ₃ , C ₆ H ₅ Si(OCH ₂ CH ₃ ) ₃ , CH ₂ =CHCH ₂ Si(OCH ₃ ) ₃ , (CH ₃ ) ₂ Si(OCH ₃ ) ₂ , (CH ₂ =CH)Si(CH ₃ ) ₂ CI, (CH ₃ ) ₂ Si(OCH ₂ CH ₃ ) ₂ , (CH ₃ ) ₂ Si(OCH ₂ CH ₂ CH ₃ ) ₂ , (CH ₃ ) ₂ Si[0(CH ₂ ) ₃ CH ₃ ] ₂ , (CH ₃ CH ₂ ) ₂ Si(OCH ₂ CH ₃ ) ₂ , (C ₆ H ₅ ) ₂ Si(OCH ₃ ) ₂ , (C ₆ H ₅ CH ₂ ) ₂ Si(OCH ₃ ) ₂ , (C ₆ H ₅ ) ₂ Si(OCH ₂ CH ₃ ) ₂ , (CH ₂ =CH) ₂ Si(OCH ₃ ) ₂ , (CH ₂ =CHCH ₂ ) ₂ Si(OCH ₃ ) ₂ , (CH ₃ ) ₃ SiOCH ₃ , CH ₃ HSi(OCH ₃ ) ₂ , (CH ₃ ) ₂ HSi(OCH ₃ ), CH ₃ Si(OCH ₂ CH ₂ CH ₃ ) ₃ , CH ₂ =CHCH ₂ Si(OCH ₂ CH ₂ OCH ₃ ) ₃ , (C ₆ H ₅ ) ₂ Si(OCH ₂ CH ₂ OCH ₃ ) ₂ , (CH ₃ ) ₂ Si(OCH ₂ CH ₂ OCH ₃ ) ₂ , (CH ₂ =CH) ₂ Si(OCH ₂ CH ₂ OCH ₃ ) ₂ ,

(CH ₂ =CHCH ₂ ) ₂ Si(OCH ₂ CH ₂ OCH ₃ ) ₂ , (C ₆ H ₅ ) ₂ Si(OCH ₂ CH ₂ OCH ₃ ) ₂ , CH ₃ Si(CH ₃ COO) _3, methyldiethylchlorosilane, butyltrichlorosilane, diphenyldichlorosilane, vinyltrichlorosilane, methyltrimethoxysilane, vinyltriethoxysilane, vinyltris(methoxyethoxy)silane, methacryloxypropyltrimethoxysilane, glycidoxypropyltrimethoxysilane, aminopropyltriethoxysilane, divinyldi-2-methoxysilane, ethyltributoxysilane, isobutyltrimethoxysilane, hexyltrimethoxysilane, hexydecyltriethoxysilane, hexydecyltrimethoxysilane, n-octyltriethoxysilane, dihexyldimethoxysilane, octadecyltrichlorosilane, octadecyltrimethoxysilane, octadecyldimethylchlorosilane, octadecyldimethylmethoxysilane. It is well known that some silanes, for example, alkoxy silanes, undergo hydrolysis in aqueous medium before reacting with hydroxyl groups (-OH) on the particulate surfaces, for example, sand surfaces. It is noted that further included in the term of organosilanes or organosiloxanes are silicone-modified polyolefin or polyacrylic and their respective copolymers, where silane such as hydrolysable silane including alkoxyl-silane group, or siloxane groups including cationic siloxane group, are attached to the polymer chain either at middle or end or both. Examples of silane-modified hydrophobic polymers, by way of illustration only, include: (a) silane-modified polyolefin including silane-modified polybutyl, silane-modified polyisobutylene, silane-modified polyethylenes, silane- modified olefin copolymer and silane-modified polypropylenes and the copolymers; (b) silane-modified styrene polymers; (c) silane-modified vinyl polymers; (d) silane-modified acrylate polymers including silane-modified poly(t-butyl methacrylate), poly(t- butylaminoethyl methacrylate); and (e) silane-modified polyesters. Especially preferred are silane-modified polyolefins including mono/homo and copolymers such as polyethylene and polypropylene, and copolymers of ethylene-propylene, ethylene- butene, ethylene-hexene, ethylene-vinyl-acetate, vinyl-acetate, ethylene-methyl- acrylate, ethylene-ethyl-acrylate and ethylene-butyl-acrylate. These silane-modified polymers and copolymers are known and have been disclosed, for example, in various patents including U.S. Pat. Nos. 3,729,438; 3,814,716; 6,455,637; 6,863,985 and 8,476,375, which are incorporated herein by reference in their entirety. Silane-modified polymers or copolymers, prepared as an aqueous dispersion, are disclosed, for example, in U.S. Pat. Nos. 3,729,438; 3,814,716 and 6,863,985, which are incorporated herein by reference in their entirety, and are especially preferred for use in the methods and compositions described herein.

[0060] Group B) includes amine functionalized polyolefins, which is a class of polymers or copolymers synthesized from simple olefin as a monomer and includes polybutyl amine, polyisobutylene amine, polyisobutylene succinimide, amine functionalized polyethylenes, amine-terminated olefin copolymers, amine functionalized polypropylenes and combinations thereof.

[0061 ] Group C) includes polymerizable natural oils such as tung oil or linseed oil which can coat and polymerise on particulate surfaces. A polymerizable natural oil, as used herein, is an oil that is extracted from a plant source, and that comprises unsaturated carbon-carbon double bonds that can be polymerized in the presence of oxygen.

[0062] Group D) includes polyvinyl acetate and its copolymers, for example, polyvinyl acetate latex or polyethylene-vinyl acetate copolymer latex.

[0063] The compounds of Groups A), B), C) and D) are further described and exemplified in the following references, all of which are incorporated herein by reference in their entirety: U.S. Patent Nos. 7,723,274, 8,236,738, 8,105,986; U.S. Patent Application Publication Nos. 20100256024, 20120322697, 2012267112, 2012067584, 20150252254, 20150307772, 20160017213; 20160222282; W02006/116868,

W02007/033489 and Canadian Patent No. 2,735,428.

[0064] The methods described herein contemplate coating the solid scale inhibitor with the coating agent, to generate coated inhibitors that are subsequently used in a number of different applications, including oilfield applications. The coating agent or an oil containing the coating agent is directly coated on the solid inhibitor making the surface of the coated scale inhibitor more hydrophobic. Without being limited to theory, Applicant believes that the coating not only provides a physical barrier between the inhibitor and the aqueous fluid but also the hydrophobic nature of the coating further reduces water contact which further delays the release of the scale inhibitor into the aqueous stream where scales predominantly form. Compared to encapsulation, the present invention provides a more cost-effective and operationally simpler approach. When combined with adsorption, as in the‘170 patent, or forming metal complex, as in U.S. Patent No. 5,207,919, the hydrophobic coating will further prolong the release of the inhibitors.

[0065] Applicant contemplates several embodiments of methods for coating solid scale inhibitors with a coating agent, thus delaying or prolonging its release into an aqueous stream. As used herein, a“coated scale inhibitor” is a scale inhibitor in its solid state, or a liquid adsorbed on a solid or a solid inhibitor/metal complex that has been coated with the coating agent or an oil containing the coating agent.

[0066] Alternatively, the solid scale inhibitor may be coated by contacting the solid scale inhibitor (for example by spraying or mixing them) with a liquid medium containing the coating agent, for example, an amino-polysiloxane or an alkoxysilane in an alcohol or an oil containing the coating agent, for example, an amino-polysiloxane or an alkoxysilane. The coated inhibitor may then be dried and stored for later use. The preferred liquid medium is alcohol or alcohol containing an amount of water.

[0067] The application of the coating agent may, in some embodiments, for example when silane-modified polyolefin is used as a coating agent, be accompanied by the use of heat, which speeds up the drying of the surface of the particulate, for example, in spray applications in a manufacturing plant.

[0068] In addition to the hydraulic fracturing operations, the coated scale inhibitor can also be used in other oilfield applications including gravel packing. In this application the coated inhibitors, may be pumped into a wellbore as a gravel pack, to prevent formation sands from migrating into the wellbore, while at the same time acting as a chemical source for treating the fluids, such as oil or water, flowing through the gravel pack. [0069] Alternatively, the coated scale inhibitor can be added into a water source, for example, a water tank, or water flowline to provide long-term inhibition for scale in other industries and applications.

EXAMPLES [0070] Having thus described the composition and method herein, specific embodiments will now be exemplified.

EXAMPLE 1

[0071 ] [Inorganic scale inhibitor sodium salt of polyacrylate with no coating, as control]

[0072] One gram of solid scale inhibitor powder Lubrizol Carbosperse K-759, which is sodium salt of polyacrylate, was mixed with 49 grams of 20/40 mesh sand. Then the mixture was packed in a glass column and tap water was flushed by hydrostatic pressure. The effluent was collected, and polymer concentration was determined by using an FT-IR spectrometer. It was found that after 100 mL, 0.98 gram of scale inhibitor was washed out, from the initial one gram added; this implies 2% of the initial scale inhibitor remains available on the proppant pack for further release. The results for this experiment are shown in FIG. 1.

EXAMPLE 2

[0073] [Inorganic scale inhibitor sodium salt of polyacrylate with hydrophobic coating]

[0074] Ten grams of solid scale inhibitor powder Lubrizol Carbosperse K-759, which is sodium salt of polyacrylate, was mixed with 2 milliliters of 10 wt% amino-polysiloxane (dimethyl, methyl(3-aminopropyl) siloxane, 3- aminopropylethoxymethylsiloxy- terminated) in mineral oil. The mixture was stirred for five minutes and then heated in an oven at 70 °C for one hour. The coated particulate showed water repellent, which is indicative of hydrophobicity. [0075] One gram of above particulate was mixed with 49 grams of 20/40 mesh sand.

Then the mixture was packed in a glass column and tap water was flushed by hydrostatic pressure. The effluent was collected, and polymer concentration was determined by using an FT-IR spectrometer. It was found that after 100 ml_, 0.81 gram of scale inhibitor was washed out, from the initial one gram added; this implies 19% of the initial scale inhibitor remains available on the proppant pack for further release. The results for this experiment are shown in FIG. 1.

[0076] FIG. 1 is a graphical display of the percentage of polyacrylate scale inhibitor released as a function of effluent volume, with and without hydrophobic coating as prepared in Examples 1 and 2.

EXAMPLE 3 [0077] [Inorganic scale inhibitor hepta sodium salt of diethylene triamine penta

(methylene phosphonic acid) (DTPMP Na7) with no coating, as control]

[0078] Six milliliters of 40 wt% DTPMP Na7 solution, which is a product of Shandong Taihe Water Treatment Technologies Co. Ltd., was added to a beaker containing 10 grams of sodium chloride and 2.1 grams of zinc chloride powders. The mixture was stirred for 5 minutes then heated in an oven at 70 °C for one hour.

[0079] One gram of above particulate was mixed with 49 grams of 20/40 mesh sand. Then the mixture was packed in a glass column and tap water was flushed by hydrostatic pressure. The effluent was collected, and phosphorus concentration was determined by using an Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES). It was found that after 300 mL, 0.79 gram of scale inhibitor was washed out, from the initial one gram added; this implies 21 % of the initial scale inhibitor remains available on the proppant pack for further release. The results for this experiment are shown in FIG. 2.

EXAMPLE 4 [0080] [Inorganic scale inhibitor hepta sodium salt of diethylene triamine penta

(methylene phosphonic acid) (DTPMP Na7) with hydrophobic coating] [0081 ] Six milliliters of 40 wt% DTPMP Na7 solution, which is a product of Shandong Taihe Water Treatment Technologies Co. Ltd., was added to a beaker containing 10 grams of sodium chloride and 2.1 grams of zinc chloride powders. The mixture was stirred for 5 minutes then heated in an oven at 70 °C for one hour. Afterward, one milliliter of 2 wt% hexadecyltrimethoxysilane in mineral oil was added and mixed for 15 minutes. The coated particulate showed water repellent, which is indicative of hydrophobicity.

[0082] One gram of above particulate was mixed with 49 grams of 20/40 mesh sand. Then the mixture was packed in a glass column and tap water was flushed by hydrostatic pressure. The effluent was collected, and phosphorus concentration was determined by using an Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES). It was found that after 300 mL, 0.57 gram of scale inhibitor was washed out, from the initial one gram added; this implies 43% of the initial scale inhibitor remains available on the proppant pack for further release. The results for this experiment are shown in FIG. 2.

[0083] FIG. 2 is a graphical display of graphical display of the percentage of DTPMP scale inhibitor released as a function of effluent volume, with and without hydrophobic coating as prepared in Examples 3 and 4.

Statements of the Disclosure [0084] Statements of the Disclosure include:

[0085] Statement 1 : A delayed-release scale inhibitor composition, the composition comprising a scale inhibitor composition; and a hydrophobic coating disposed on a surface of the scale inhibitor composition.

[0086] Statement 2: A composition according to Statement 1 , wherein the scale inhibitor composition comprises a scale inhibitor absorbed onto an absorbent.

[0087] Statement 3: A composition according to Statement 1 , wherein the scale inhibitor composition comprises a mixture of a scale inhibitor and a polyvalent salt. [0088] Statement 4: A composition according to Statement 1 , wherein the scale inhibitor composition comprises a mixture of a scale inhibitor and an anti-caking agent.

[0089] Statement 5: A composition according to Statement 1 , wherein the scale inhibitor composition comprises scale inhibitor and one or more of an absorbent, a polyvalent salt and an anti-caking agent.

[0090] Statement 6: A composition according to any one of Statements 2-5, wherein the scale inhibitor is a phosphonic-based scale inhibitor.

[0091 ] Statement 7: A composition according to Statement 1 , wherein the scale inhibitor composition comprises a phosphonic-based scale inhibitor. [0092] Statement 8: A composition according to Statement 6 or 7, wherein the phosphonic-based scale inhibitor is diethylene triamine penta (methylene phosphonic acid) (DTPMP).

[0093] Statement 9: A composition according to any one of Statements 2-5, wherein the scale inhibitor is a polyacrylate-based scale inhibitor. [0094] Statement 10: A composition according to Statement 1 , wherein the scale inhibitor composition comprises a polyacrylate-based scale inhibitor.

[0095] Statement 11 : A composition according to Statement 6 or 7, wherein the polyacrylate-based scale inhibitor is a polyacrylate sodium salt.

[0096] Statement 12: A composition according to any one of Statements 1 -11 , wherein the wherein the hydrophobic coating is selected from the group consisting of organosilanes, organosiloxanes, polysiloxanes, and any combination thereof.

[0097] Statement 13: A composition according to any one of Statements 1 -11 , wherein the hydrophobic coating is a polyvinyl acetate or copolymer thereof.

[0098] Statement 14: A composition according to any one of Statements 1 -11 , wherein the hydrophobic coating is an amine functionalized polyolefin. [0099] Statement 15: A composition according to any one of Statements 1 -11 , wherein the hydrophobic coating is a polymerized natural oil.

[00100] Statement 16: A method for the hydraulic fracturing of a formation, the method comprising combining a composition according to any one of Statements 1 -15 with a fracturing fluid to form a hydraulic fracturing fluid; and injecting the hydraulic fracturing fluid into a formation.

[00101 ] Statement 17: A method according to Statement 16, wherein the fracturing fluid is a viscosified water-based fracturing fluid.

[00102] Statement 18: A method according to Statement 16, wherein the fracturing fluid is a non-viscosified water-based fracturing fluid.

[00103] Statement 19: A method according to any one of Statements 16-18, wherein the hydraulic fracturing fluid is injected into the formation at a flow rate of between about 60 and about 100 barrels per minute (bpm).

[00104] Statement 20: A method of making a delayed-release scale inhibitor composition, the method comprising providing a scale inhibitor composition; and applying a hydrophobic coating agent on a surface of the scale inhibitor composition.

[00105] Statement 21 : A method according to Statement 20, wherein the scale inhibitor composition comprises a scale inhibitor absorbed onto a solid absorbent.

[00106] Statement 22: A method according to Statement 20, wherein the scale inhibitor composition comprises a mixture of a scale inhibitor and a polyvalent salt.

[00107] Statement 23: A method according to Statement 20, wherein the scale inhibitor composition comprises a mixture of a scale inhibitor and an anti-caking agent.

[00108] Statement 24: A method according to Statement 20, wherein the scale inhibitor composition comprises scale inhibitor and one or more of an absorbent, a polyvalent salt and an anti-caking agent. [00109] Statement 25: A method according to any one of Statements 21 -24, wherein the scale inhibitor is a phosphonic-based scale inhibitor.

[00110] Statement 26: A method according to Statement 20, wherein the scale inhibitor composition comprises a phosphonic-based scale inhibitor. [00111 ] Statement 27: A method according to Statement 25 or 26, wherein the phosphonic-based scale inhibitor is diethylene triamine penta (methylene phosphonic acid) (DTPMP).

[00112] Statement 28: A method according to any one of Statements 21 -24, wherein the scale inhibitor is a polyacrylate-based scale inhibitor. [00113] Statement 29: A method according to Statement 20, wherein the scale inhibitor composition comprises a polyacrylate-based scale inhibitor.

[00114] Statement 30: A method according to Statement 28 or 29, wherein the polyacrylate-based scale inhibitor is a polyacrylate sodium salt.

[00115] Statement 31 : A method according to any one of Statements 20-30, wherein the wherein the hydrophobic coating is selected from the group consisting of organosilanes, organosiloxanes, polysiloxanes, and any combination thereof.

[00116] Statement 32: A method according to any one of Statements 20-30, wherein the hydrophobic coating is a polyvinyl acetate or copolymer thereof.

[00117] Statement 33: A method according to any one of Statements 20-30, wherein the hydrophobic coating is an amine functionalized polyolefin.

[00118] Statement 34: A method according to any one of Statements 20-30, wherein the hydrophobic coating is a polymerizable natural oil.

[00119] Statement 35: A method according to any one of Statements 20-34, wherein the hydrophobic coating agent is placed in an oil prior to application on the surface of the scale inhibitor composition. [00120] Statement 36: A method according to any one of Statements 20-34, wherein the hydrophobic coating agent is placed in a liquid medium prior to application on the surface of the scale inhibitor composition.

[00121 ] All publications, patents and patent applications cited herein are hereby incorporated by reference as if set forth in their entirety herein. While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass such modifications and enhancements.