RU2621239C2 - Self-suspending proppants for hydraulic fracturing - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: modified proppant contains the particle of proppant substrate, coated with a polymer hydrogel, wherein the mentioned particle contains a resin-coated proppant and the adhesion promoter, bonding them. The manufacturing method of the mentioned proppant includes the provision of the substrate particle and a composition, containing the coating precursor, application of this coating to the substrate particle and polymerization, forming the mentioned proppant. The composition for hydraulic fracturing contains the above mentioned proppant and oxidating or enzymatic breaker fluid. The invention is developed in the formula dependent claims.

EFFECT: stability of proppant increase in the hydraulic fracturing.

15 cl, 59 ex, 30 tbl, 14 dwg

Description

FIELD OF TECHNOLOGY

[0001] This application generally relates to fracturing systems, compositions, and methods.

BACKGROUND

[0002] In the process of extracting oil and / or gas from a well, it often becomes necessary to intensify the flow of hydrocarbons by hydraulic fracturing. The term "fracturing" refers to the method of pumping fluid into a borehole until the pressure inside it reaches a level sufficient to destroy the underground geological formations in which the produced materials are enclosed. This process leads to the formation of cracks and faults, revealing the underlying layer, as a result of which the hydrocarbon product begins to flow more intensively into the wellbore. However, if pressure is not maintained, the newly formed passages close. In order to keep the inflow channel open, along with hydraulic fracturing fluid, a proppant or “proppant” is also fed into the well, which helps to maintain the open channel. As the fracture forms, proppants are fed into the drilling fluid, where they, after the hydraulic pressure is released, form a safety plug or proppant that keeps the cracks open.

[0003] To deliver proppant to a fracture, its particles are suspended in a fluid, which is then pumped to a predetermined location in the subterranean formation. To prevent sedimentation of particles, it is often necessary to use highly viscous media. The viscosity of the fluid is usually controlled by the introduction of synthetic or natural polymers. Three types of fluid systems with polymers are usually used to suspend and transport proppants during hydraulic fracturing operations: water with a small amount of cross-linked polymer; linear gel and crosslinked gel.

[0004] In water-based systems with the addition of a non-crosslinked polymer, anionic or cationic polyacrylamide is usually used as a friction reducer, which allows for maximum fluid flow with minimum pump power. Since the requirements for the power of the pumps used for hydraulic fracturing are quite high and amount to about 10,000-100,000 hp, the friction reducer is added to fluids with non-crosslinked polymer in order to ensure high performance of the pump unit and to avoid the need to use more powerful units. Despite the fact that these polymers are effective as friction reducers, their effectiveness as thickeners and suspending agents is low. Solutions with the addition of a non-crosslinked polymer usually contain 0.5-2.0 gallons of a friction reducing polymer per 1000 gallons of liquid, while the solutions are characterized by a low viscosity of about 3-15 cP. At such a low viscosity, under conditions of cessation of the turbulent regime of the suspension flow, suspended proppant particles can easily sediment. For this reason, fluids with the addition of a non-crosslinked polymer are used at fracturing stages in which proppant is either not used or proppant with a small particle size or under low proppant loads is used.

[0005] The second type of polymer fluid system is called linear gel systems. Linear gel systems typically contain carbohydrate polymers such as guar, hydroxyethyl cellulose, hydroxyethyl guar, hydroxypropyl guar and hydroxypropyl cellulose. Linear gel polymers typically have a flow rate of 10-50 pounds (4.5-22.7 kg) of polymer per 1000 gallons (3785 L) of linear gel fluid. Such polymer concentrations of the linear gel make it possible to obtain a liquid with higher proppant suspension characteristics compared to a liquid with the addition of an uncrosslinked polymer. Linear gel fluids are used to transport proppants at loading levels of 0.1 to 1 pound (45.4-454 g) of proppant per gallon (3.79 L) of liquid. Above the indicated proppant loading level, the resulting more viscous solution usually implies the use of a stable suspension.

[0006] Crosslinked gel is the most viscous type of fluid with polymer additives that are used to move proppant. In crosslinked gel systems, the linear gel fluid described above is crosslinked by the addition of reagents such as borate, zirconate and titanate in the presence of an alkali metal. As a result, the viscosity of the liquid obtained after crosslinking the liquid with a linear gel becomes significantly higher, which ensures effective suspension of proppants. Liquids with linear and crosslinked gel have certain advantages, but their preparation requires a high consumption of expensive polymer.

[0007] A preferred way to improve proppant performance in hydraulic fracturing systems would be to modify their particles. Firstly, if the proppant particles were more buoyant, it would be possible to use less viscous liquids to prepare the suspension, and the particles would be moved to the desired fracture zone with less effort. Secondly, it is desirable that, after injection into the fracture, the proppants remain in the laying areas throughout the entire life of the well. Changes within the formation during well operation can lead to proppant removal from their location, failure of process equipment and reduced permeability of the reservoir rock due to clogging of pores by displaced proppants. Thirdly, being placed in the wedging site, the proppants must be resistant to stresses that cause the crack to close. Closing stresses can vary from 1172 MPa (1700 psi) in shale gas wells to 10342 MPa (15000 psi) and higher for deep, high-temperature (“hot”) wells. Care must be taken, because under the influence of these stresses, proppants can be destroyed to the state of fine particles and taken to places in the well that are undesirable from the point of view of impact on the equipment. It is advisable that the proppant be resistant to the processes of transformation of the rock during operations on hydraulic fracturing. High pressures and temperatures in combination with hydraulic agents for fracturing fluids can adversely affect the properties of proppant particles, leading to their diagenesis and, over time, the formation of finely divided solid particles, their scaling, and lowering well productivity.

[0008] Modern proppants and fracturing fluids with polymer additives are designed to solve these problems; Thus, the proppants can be delivered to the place of laying with hydraulic fracturing fluids, remain at the place of laying after they are delivered to the desired location and withstand the stresses that cause fractures to close in the reservoir. One way to prepare the appropriate proppants is to coat the proppant particles with resins. The resin coated proppant may be fully cured or partially cured. When fully cured with resin, resistance to crushing of the proppant base is ensured by stress distribution between particles. In addition, a fully cured resin helps to reduce the migration of fine particles by encapsulating a proppant particle. The partially cured resin can be completely cured after being placed in the crack. The method may prove to be as effective as using a fully cured resin. At the same time, resins can reduce the permeability and transmittance of a crack even though proppants keep it open. In addition, resins can break down, which entails the loss of their benefits. Resin-based systems are usually quite expensive, and in suspension they tend to precipitate.

[0009] In addition, there are problems in the field of labor protection, safety and environmental protection related to the processing and manufacture of proppants. For example, in sand formations of natural origin, finely dispersed particles (“dust”) of crystalline silicon dioxide are often found. Fine particles of this substance, known as the respiratory fraction, can be obtained from the processing and production of granular sand for fracking. With prolonged exposure, such dust can be dangerous for workers, leading to severe pulmonary diseases such as silicosis, chronic obstructive pulmonary disease, lung cancer, etc. In addition to affecting human health, dust can also cause harmful effects such as equipment clogging and environmental pollution.

[0010] Another approach for obtaining proppant-appropriate tasks is to mix the additives with the proppant itself, such as fibers, elastomer particles, and the like. However, in this case, additives can negatively affect the rheological properties of the transporting solution, making it difficult to deliver proppants to the place of laying in the crack. In addition, the use of additives can create obstacles to evenly spread the proppant mixture at the fracture site. Despite the fact that methods are known in the art for limiting the harmful effects of proppants, certain problems still remain. Thus, in the technical field there is a need for more advanced proppant systems that would ensure their precise placement in the fracture, support permeability in the fracture after placement, maintaining well productivity and equipment life, simplify hydraulic fracturing operations, reduce environmental impact, and would contribute to improving occupational health and safety. In addition, it is desirable that such improved systems are also cost-effective.

SUMMARY OF THE INVENTION

[0011] The present invention relates to modified proppants consisting of proppant particles and a hydrogel coating, and characterized in that the hydrogel coating is localized on the surface of the proppant particles to form a modified proppant. The proppant particles can be solids, such as sand, bauxite, sintered bauxite, ceramic, or low density proppant. Alternatively or additionally, the proppant particle comprises a polymer coated substrate. Optionally, the modified proppant further comprises an adhesion promoter, optionally bonding a hydrogel coating to a polymer coated substrate. The hydrogel coating preferably contains a water swellable polymer. The hydrogel coating may be made of a water-soluble polymer. A preferred weight average molecular weight of the polymer is ≥ about 1 million g / mol, preferably ≥ about 5 million g / mol. Preferably, the proppant is dry, free-flowing in dry form and / or free-flowing after exposure to relative humidity of about 80% -90% for one hour at 25-35 ° C. The hydrogel coating is preferably wear resistant and has a shear ratio determined according to the analytical shear test, ≥0.6.

[0012] The present invention relates to methods for producing proppants and to proppants made by these methods. Preferably, the hydrogel coating is applied to the proppant particle in the form of a liquid coating composition that dries to form a substantially continuous film on the surface of the proppant particle. Modified proppant can be made by a reverse emulsion coating technique, according to which a particle of proppant substrate is combined with a reverse emulsion, in which the oil phase forms a continuous phase of the emulsion, and the solution or dispersion of the superabsorbent polymer in water forms a discrete, emulsified phase.

[0013] The hydrogel coating preferably contains a polymer selected from the group consisting of polyacrylamide, hydrolyzed polyacrylamide, copolymers of acrylamide with ionic comonomers containing ethylene unsaturation, copolymers of acrylamide with salts of acrylic acid, polyacrylic acid or its salts, carboxymethyl cellulose, hydroxy cellulose, hydroxy cellulose, hydroxy cellulose, hydroxy cellulose, hydroxy cellulose, hydroxy cellulose, hydroxy cellulose, hydroxy cellulose, hydroxy cellulose, hydroxy cellulose, hydroxy cellulose, hydroxy resins, carboxymethyl guar, carboxymethyl hydroxypropyl guar, hydrophobically associated swellable emulsion polymers and latex polymers. The amount of hydrogel coating may be less than about 5% of the mass. from the total dry weight.

[0014] The modified proppant is preferably self-suspending. Preferred proppants according to the present invention can undergo a volume expansion of at least 100%, preferably at least 500%, when hydrated with excess water.

[0015] Modified proppants may contain additional excipients, such as cationic / anionic polymer pairs containing a cationic polymer and a high molecular weight anionic polymer. The cationic polymer may be selected from the group consisting of ammonium polydiallyldimethyl dimethyl chloride (poly-DADMAC), linear polyethyleneimine (LPEI), bound polyethyleneimine (BPEI), chitosan and cationic polyacrylamide.

[0016] Modified proppants are preferably used in conjunction with and / or additionally comprise an oxidative gel destructor or an enzymatic gel destructor. The oxidative destructor may be selected from the group consisting of peroxides, magnesium peroxide, calcium peroxide, persulphates, nitrates, bromates, ozone and oxidizing compounds of chlorine. The oxidative destructor may be a cationically modified oxidative destructor capable of associating with a hydrogel through ionic interaction. The enzyme destructor may be a cationic enzyme destructor capable of associating with a hydrogel through ionic interaction. The modified proppant may further comprise a hydrophobic outer layer. For example, the hydrophobic outer layer may be selected from the group consisting of fatty acids, aliphatic amines, hydrophobic quaternary amines, aliphatic amides, hydrogenated oils, vegetable oils, castor oil, triacetin, waxes, polyethylene oxides and polypropylene oxides. Alternatively, the modified proppant may further comprise a hydration inhibitor, such as a surfactant with a low hydrophilic-lipophilic balance, a displacing agent capable of displacing a finishing surfactant, an ionic crosslinking agent, a covalent crosslinking agent and / or a monovalent crosslinking protective agent with salt. The modified proppant may further comprise an alcohol selected from the group consisting of ethylene glycol, propylene glycol, glycerol, propanol and ethanol. In one embodiment of claim 1, the modified proppant further comprises an anti-caking agent, such as a hydrophobic layer material, a finely divided material and / or a crosslinking agent. Examples of anti-caking agents include calcium silicate, calcium carbonate, talc, kaolin, bentonite, diatomaceous earth, silicon dioxide, colloidal silicon dioxide, microcrystalline cellulose and attapulgite. These agents may also include fumed silica, calcium silicate, calcium carbonate, kaolin, bentonite and attapulgite. The hydrogel coating may contain an additive, such as a chemical additive or a labeled substance.

[0017] The modified proppant preferably contains unmodified particles that are less finely dispersed than the proppant.

[0018] The present invention includes hydraulic fracturing compositions comprising a modified proppant according to the present invention and an oxidative destructor or enzymatic destructor. The present invention also includes methods of fracturing in a well. These methods preferably include the following steps:

obtaining a composition for hydraulic fracturing according to the present invention, and

the introduction of the specified composition for hydraulic fracturing in the well in a volume and at a pressure effective for hydraulic fracturing,

whereby a fracturing operation is performed in the well.

[0019] In embodiments of the invention, a fracturing method in a well includes:

obtaining a fracturing composition containing a modified proppant according to the present invention,

the introduction of the specified composition for hydraulic fracturing in the well in a volume and at a pressure effective for hydraulic fracturing,

providing the composition of the destructor containing the oxidative destructor or enzyme destructor, and

the introduction of the specified composition of the destructor into the well in a volume and at a pressure effective for hydraulic fracturing,

whereby a fracturing operation is performed in the well.

[0020] In the methods of the present invention, the composition of the destructor can be fed into the well before, during or after the composition for fracturing is supplied to the well. The composition of the destructor can be submitted in one or more stages.

[0021] In a fracturing method, a geological formation is exposed through a well through which proppant-containing fracturing fluid is injected into said geological formation under pulsating pressure, the present invention including a method of reducing the amount of thickening agent added to a fracturing fluid containing as proppant modified proppant according to the present invention. The modified proppants of the present invention are preferably hydrated substantially completely for 2 hours, such as, for example, 10 minutes after the first combination with the fracturing fluid.

[0022] Also, the present invention includes methods for producing a modified proppant. These methods may include the following steps:

providing particles of a proppant substrate and a liquid polymer coating composition; and

applying a liquid polymer coating composition to a proppant substrate particle;

optionally drying the resulting modified proppant;

where the liquid polymer coating composition contains a hydrogel polymer and the hydrogel polymer is localized on the surface of the proppant substrate particle to form a modified proppant. In the drying step, a liquid polymer coating can be dried to form a substantially continuous film on the surface of the modified proppant. This method can preferably be carried out at or near the place of use of the modified proppant, such as a place of production of sand, ceramics, low density proppant, a polymer coated substrate and / or bauxite. The method may further include adding an alcohol selected from the group consisting of ethylene glycol, propylene glycol, glycerin, propanol and ethanol, during or before the stage of mixing the particles of the proppant substrate and the liquid polymer coating composition.

[0023] The method preferably includes introducing an invert promoter in or after the step of mixing the particles of the proppant substrate and the liquid polymer coating composition and / or anti-caking agent.

[0024] Methods for preparing a hydrogel coated proppant may also include:

providing a proppant substrate particle and a composition comprising a coating precursor, said coating precursor being able to form a hydrogel coating on the surface of the proppant substrate particle by in situ polymerization;

applying said composition to a proppant substrate particle; and

polymerization of the coating precursor in direct contact with a particle of the coating substrate, with the formation of a hydrogel coated proppant.

[0025] This method preferably leads to the formation of a substantially continuous coating film on the surface of the proppant substrate particle.

BRIEF DESCRIPTION OF THE FIGURES

[0026] In FIG. 1 shows vessels with uncoated sand (left) and hydrogel coated sand (in the middle and right) in water.

[0027] FIG. 2A-2C show microphotographs of hydration over time of the hydrogel layer on the surface of the proppant particle.

FIG. 3 is a flow chart of a process for producing self-suspending proppants.

FIG. 4 (FIGS. 4A and 4B) are images obtained using a scanning electron microscope (SEM), proppant particles with a hydrogel coating, without the addition of glycerol (FIG. 4A) and with the addition of glycerin (FIG. 4B).

FIG. 5 is a SEM image of a dried hydrogel coating on the surface of a proppant particle.

FIG. 6 is a graph of layer thickness versus shear application time for three series of self-suspending proppant samples.

FIG. 7 is a graph of layer thickness versus mixing time for two series of self-suspending proppant samples.

FIG. 8 is a graph of layer thickness versus mixing time for two series of self-suspending proppant samples.

FIG. 9 is a graph of layer thickness versus mixing time for one series of samples of treated self-suspending proppants.

FIG. 10 is a graph of layer thickness versus various amounts of calcium silicate added to self-suspending proppant samples.

FIG. 11 is a graph of layer thickness versus drying time for one series of samples of preheated and unheated self-suspending proppants.

FIG. 12 is a graph of layer thickness versus drying time at various temperatures.

FIG. 13 is a graph of temperature versus mixing time for one series of samples of treated self-suspending proppants.

FIG. 14 is a graph of layer thickness and calcination loss (SPP) versus drying time.

DETAILED DESCRIPTION

1. Particles of modified proppant

[0040] This application describes systems and methods for the formation and use of proppant particles with a hydrogel surface layer that increases the hydrodynamic volume of proppant particles during fluid transportation and forms a more stable proppant suspension that is resistant to sedimentation, separation and proppant precipitation from the fracturing fluid until after the proppant reaches its intended destination in the fracture. Additional advantages of hydrogel-coated proppants described in this application include reduced equipment erosion, lower wet friction, good adhesion to other particles after laying at the fracture site, resistance to uncontrolled formation of thin particles, and protection properties from biological fouling associated with hydrophilic surface characteristics. In embodiments of the invention, the described proppant particle formation systems can be applied to substrate types of the most commonly used proppants, for example, sand, polymer coated sand, bauxite, low density proppants, and ceramic materials. In other embodiments of the invention, proppant particles can be obtained from a number of substrates containing fibrous materials available to those of ordinary skill in the art. In certain embodiments of the invention, the proppant particles can be made so that they are resistant to fracture or deformation, or displacement, or they can be suspended in less viscous carrier fluids for transport to the reservoir.

[0041] The present invention encompasses a modified proppant comprising a proppant particle and a hydrogel coating, characterized in that the hydrogel coating is localized on the surface of the proppant particle to form a modified proppant. In embodiments of the invention, self-suspending proppants are formed by modifying the substrate particles with a water-swellable polymer coating, such as a hydrogel. In embodiments of the invention, the substrate particle can be modified with a polymer coating before it is introduced into the fracturing fluid. In embodiments of the invention, the amount of hydrogel polymer coating may be about 0.1-10% relative to the weight of the proppant. In embodiments of the invention, the hydrogel layer applied to the surface of the proppant substrate may have a coating thickness of from about 0.01% to about 20% of the average particle diameter of the proppant substrate. After hydration and swelling of the hydrogel layer in the fracturing fluid, the hydrogel layer can continue to expand due to water, and thus, the thickness of the expanded hydrogel layer can increase from about 10% to about 1000% of the average particle diameter of the proppant substrate. In FIG. Figure 1 shows an image of three vessels, each of which contains the same amount of proppant in water, the vessel on the left containing proppant without hydrogel coating, the vessel in the center containing proppant with 1% hydrogel coating, and the vessel on the right containing proppant with 3% hydrogel coating. In each vessel, the proppant was mixed with water and left to settle for 24 hours without stirring. The volume of the deposited proppant layer with a hydrogel coating significantly exceeds the volume of the deposited proppant layer without coating, which indicates that the proppant with a hydrogel coating remains suspended in water. In FIG. 2A, 2B and 2C, respectively, three optical microscope images of the same hydrogel-coated proppant grain are shown, each of the images was obtained at different time intervals of hydration of the hydrogel-coated proppant in water. In FIG. 2A, a hydrogel coated proppant particle was in water for 15 seconds, in FIG. 2B, a hydrogel coated proppant particle was in the water for 45 seconds, in FIG. 2C, the hydrogel coated proppant particle was in water for 120 seconds. As can be seen in these figures, the hydrogel layer rapidly increases in volume and significantly increases in size as the hydration time increases.

[0042] Although it is known in the art to create hydrogel coatings on individual particles of proppant substrate by coating them with superabsorbent polymers (see, for example, US 2008/0108524), the compositions and methods described in this application differ from these technologies by important advantageous aspects . According to the present description, the applied hydrogel compositions have certain distinctive properties. More specifically, the compositions according to the present description contain hydrogels selected and applied to the proppant particle to form a modified particle, so that: (a) the proppant obtained is dry in bulk, and / or (b) when hydrated in water, the hydrogel coating is wear-resistant and / or the hydrogel coating expands in such a way that the volume of hydrated modified proppant is at least 20% greater than the volume of dry modified proppant, or greater than about 20% -50% of the volume of dry modified prop antler, or exceeds about 50% -100% the volume of dry modified proppant, or exceeds about 100% -200% the volume of dry modified proppant, or exceeds about 200% -400% the volume of dry modified proppant, or is more than about 400% volume of dry modified proppant.

[0043] With regard to the term "dry" in the present description, the modified proppant will be considered dry at a moisture content of 1% of the mass. or less. Preferably, the moisture content in the dry modified proppants according to the present description is ≤0.5% of the mass. or even ≤0.1% of the mass. In embodiments of the present invention, the thickness of the dried hydrogel coating on the modified proppant may be less than 10 microns, and often less than 2 microns. In embodiments of the present invention, hydration of the hydrogel polymers in the aqueous suspension is substantially complete within 2 hours, or within 1 hour, or within 30 minutes, or within 10 minutes, or within 2 minutes, or even within 1 minute at making contact with excess tap water at 20 ° C. In the present description, the designation of a hydrogel coated proppant as “substantially completely hydrated” means that the amount of increase in the volume of the hydrogel coated proppant is at least 80% of the total increase in the volume of the hydrogel coated proppant when fully hydrated in water.

[0044] In embodiments of the present invention, the modified proppants obtained in accordance with the described compositions and methods in dry form will be free flowing, any lumps or clumping will be easily removed by careful mixing. Modified proppants will still be considered free flowing if they exhibit some degree of clumping or clumping, provided that the clumps or clumping can be destroyed by careful mixing.

[0045] The proppant volumetric expansion can be measured using a Settled Bed Height Analytical Test. For example, in a 20 ml glass vessel, 1 g of the analyzed dry modified proppant is placed and 10 g of water (e.g. tap water) is added at a temperature of about 20 ° C. Then the vessel is stirred for about 1 minute (for example, repeatedly turning the vessel over) to wet the coating of the modified proppant. Then leave the vessel to stand without interference until the hydrogel polymer coating is hydrated. The height of the layer formed by the hydrated modified proppant can be measured using a digital caliper. Then divide the obtained layer height by the height of the layer formed by the dry proppant. The resulting number shows the coefficient (factor) of the volume expansion. Also, for convenience, it is possible to compare the height of the layer formed by hydrated modified proppant with the height of the layer formed by uncoated proppant, as shown in the following working example 5.

[0046] The wear resistance of the coating can be measured according to the Shear Analytical Test. For example, 1 liter of water (for example, tap water) is placed in a 1 liter square glass (such a glass has a total volume of about 1.25 liters, and is filled to the mark of 1 liter). The beaker is then placed in an EC Engineering CLM4 paddle mixer. The mixer speed is set to 300 rpm. After stirring is started, 50 g of the tested modified proppant in dry form is added to the beaker. After 30 seconds of stirring at 300 rpm, the stirring speed is reduced to 200 rpm and stirring is continued until the hydrogel polymer coating is hydrated. The mixture is then poured into a 1 L graduated cylinder and allowed to settle, after which the height of the deposited modified proppant layer is measured, as described above. The obtained height of the deposited layer (“the height of the deposited layer with a shift”) is then compared with the height of the deposited layer of the same amount of hydrated modified proppant that was not subjected to the described shear treatment (“the height of the deposited layer without a shift”). The amount by which shear treatment reduces the height of the deposited modified proppant layer is a measure of the wear resistance of said hydrogel coating. For the purposes of the present description, a hydrogel coating is considered wear resistant if the ratio of the height of the deposited layer with a shift to the height of the deposited layer without a shift (“shear ratio”) is at least 0.2. Modified proppants that exhibit shear ratios greater than 0.2, greater than or equal to 0.3, greater than or equal to 0.4, greater than or equal to 0.5, greater than or equal to 0.6, greater than or equal to 0.7, greater than or equal are desirable 0.8 or higher or equal to 0.9.

[0047] As indicated above, the type and amount of hydrogel polymer used in the modified proppants as described herein can be selected so that the volumetric expansion of the modified proppant, measured according to the above-described analytical test for the height of the deposited layer, increases by at least 1, 2 times. In specific embodiments of the present invention, as shown in Working Example 5, said coefficient may be greater than or equal to about 3, about 5, about 7, about 8, and even about 10.

[0048] Also, as described above, the modified proppants of the present invention are free-flowing in dry form. In specific embodiments, said modified proppants remain loose even when exposed to high humidity conditions, such as those observed in mid-summer in the southern United States. For this purpose, the test modified proppant can be tested in conditions of 80-90% relative humidity at 25-50 ° C for 1 hour. Modified proppant, still free-flowing after exposure to the specified humidity test conditions, is considered loose even after exposure to high humidity.

[0049] Methods for modifying proppant include spraying or impregnating the proppant substrate with a liquid polymer composition, followed by drying to remove water or other carrier liquids. The drying process can be accelerated by the application of heat or vacuum, as well as processing in a rotary drum or mixing a modified proppant during the drying process. Heating can be provided by forced hot air, convection, friction, heat transfer, combustion, exothermic reaction, microwave heating or infrared radiation. Stirring during the proppant modification process has an additional advantage, since a more uniform coating is formed on the surface of the proppant material.

[0050] In FIG. 3 is a flow diagram of a process for producing 100 self-suspending proppant 130 in accordance with the present invention. In the described embodiment, sand 132 (for example, dry sand with a residual moisture content of less than 0.1%) is conveyed by conveyor 122 into a mixer 124, and the liquid polymer composition 120 is sprayed onto the sand 132 on conveyor 122 through a spray nozzle 134. Sand 132, exposed to liquid polymer 120, enters a low-shear mixer 124, in which the components mix and form modified sand 128. After mixing, the modified sand containing liquid polymer is sent to dry a sludge device 126 for removing water and / or organic carrier liquids bound to the liquid polymer 120. After the drying step, the dry modified sand 132 goes through a finishing step 134, which may include processing in a vibrating screen and / or other sorting equipment, for example, a sieve for separating grains into fractions and removing agglomerates exceeding specified sizes. The final step 134 may also include treating the dry modified sand 132 in mechanical agitators, shear devices, crushing, crushing or the like apparatuses to break up coarse masses to materials with sizes corresponding to the size of the sieve. Finished material 130 is stored for subsequent shipment or use.

[0051] In embodiments of the invention, sand or another substrate used to make a self-suspending proppant is dried prior to modification with a hydrogel polymer to a moisture content of <1%, preferably <0.1%. In embodiments of the invention, the temperature of the sand or other substrate during mixing with the liquid polymer is in the range of about 10 to 200 degrees Celsius, preferably in the range of about 15 to 80 degrees Celsius, or 15 to 60 degrees Celsius.

[0052] In embodiments of the invention, the proppant substrate comes into contact with the liquid polymer composition by spraying or injection. The amount of liquid polymer composition n to be added is from about 1 to about 20%, preferably from about 2 to about 10%, by weight of sand. The proppant substrate and the liquid polymer are mixed for 0.1 to 10 minutes. In a preferred embodiment of the invention, the mixing equipment is a low shear mixer, such as a rotary drum, a vertical conical screw mixer, a conical body mixer, a double cone mixer, an auger mixer, a paddle mixer or a tape screw blade mixer. In embodiments of the invention, the mixing equipment may be equipped with a forced air supply, forced hot air supply, vacuum application, external heating, or other devices for evaporating carrier liquids.

[0053] In embodiments of the invention, the modified proppant substrate containing the liquid polymer is dried to remove water and / or organic carrier liquids bound to the liquid polymer. The drying equipment may be a conveyor oven, microwave or rotary type. In an embodiment, the drying step is performed such that the dried, modified sand contains less than 1% by weight of residual liquids, including water and any organic carrier liquids associated with the liquid polymer composition.

[0054] In embodiments of the invention, the same equipment can be used to mix the proppant substrate with a liquid polymer and dry the mixture in one processing step or in a continuous production line.

[0055] In other embodiments of the present invention, proppant modification methods include in situ synthesis of the hydrogel coating, or in the presence of a proppant particle, to form a hydrogel layer surrounding the surface of the proppant particle. For example, in situ hydrogel synthesis can be accomplished by combining proppant particles with monomers and / or macromonomers of a coating precursor, followed by a polymerization step. In other examples, the water-soluble polymer can be dispersed in monomers, with or without solvent, followed by polymerization in the presence of proppant particles to form interpenetrating cross-linked polymer structures to coat proppant particles. In other examples, the water-soluble polymer is dispersed in monomers, with or without a solvent, followed by polymerization to form proppant particles enclosed in a hydrogel consisting of particles of a water-soluble polymer entrapped in the newly formed polymer. Used monomers or macromonomers can be selected from monomers forming water-soluble polymers. In other examples, the particles may be enclosed in a water-insoluble polymer, which will then be modified or hydrolyzed to form a water-soluble hydrogel coating. As will be understood by a person skilled in the art, an encapsulating layer can be obtained using various polymerization techniques, with or without a solvent. The advantage of in situ polymerization of the polymer on the surface of the proppant grains may be to reduce or eliminate the drying steps.

[0056] As an example, water-soluble monomer (s) for hydrogel coating or in situ polymerization can be selected from the following monomers or their salts: acrylic acid, methacrylic acid, acrylamide, methacrylamide, and derivatives of these compounds, carboxyethyl acrylate, hydroxyethyl methacrylate (HEMA) , hydroxyethyl acrylate (NEA), polyethylene glycol acrylates (PEG acrylates), N-isopropyl acrylamide (NiPA), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), styrene sulfonate sodium salt, vinyl sulfonic acid, (meth) allyl new acid, vinylphosphonic acid, N-vinylacetamide, N-methyl-N-vinylacetamide, N-vinylformamide, N-methyl-N-vinylformamide, N-vinylpyrrolidone, N-butyrolactam or N-vinylcaprolactam, maleic anhydride, itaconic acid, vinyl acetate, dimethyldiallylammonium chloride; quaternized dimethylaminoethyl methacrylate (DMAEMA), (meth) acrylamidopropyl-trimethylammonium chloride, methyl vinylimidazolium chloride; 2-vinylpyridine; 4-vinylpyridine, and the like. The ratio of ionic monomers to nonionic monomers can be selected to obtain a hydrogel with different charge densities. In some cases, for example, it is desirable to obtain hydrogels with a higher charge, to obtain coatings with the properties of faster hydration or swelling. In one embodiment, the ion content or charge density of the hydrogel polymer is 10-70% of ionic monomers, in molar percent of all monomers, the rest are non-ionic monomers. In a preferred embodiment, the charge density of the hydrogel polymer is 25-55%, in mole percent. In other cases, ionizable monomers with higher or lower ionization constants can be selected to produce hydrogels that are more or less stable in the medium of saline solutions. Other beneficial properties can be imparted by the selection of appropriate charge densities.

[0057] In embodiments of the present invention, coating precursors may include polyfunctional monomers containing more than one polymerizable group that will introduce crosslinking or branch points into the hydrogel. Examples of these monomers are: pentaerythritol triallyl ether, PEG diacrylates and methacrylates, N, N'-methylene bisacrylamide, epichlorohydrin, divinyl sulfone and glycidyl methacrylate. If these monomers are used, the crosslinking monomer will be from 0.001 to 0.05% of the total monomer content. When choosing a range for adding cross-linking agents, one should beware of maintaining excessive amounts of cross-linking agent, for example, amounts in excess of 0.001-0.05% of the total monomer content, which can lead to the formation of brittle hydrogels that can break down or decompose under pressure. In embodiments, the introduction of crosslinking agents can lead to the formation of hydrogels, less prone to peeling from the surface of the particles in extreme conditions.

[0058] In embodiments, the monomers / macromonomers used are selected from those coating precursor monomers that will form a water-insoluble coating. After coating, it is subjected to further modification, which will lead to a water-swellable polymer. For example, you can create a polymer coating containing hydrolyzable groups, and subsequent hydrolysis will result in a hydrogel. Examples of monomers in this category are esters, anhydrides, nitriles and amides; for example, ester monomers methyl acrylate, tert-butyl acrylate can be used. As another example, a monomer containing vinyl functional groups can form a hydrogel by various polymerization techniques, with or without a solvent. Polymerization techniques include bulk polymerization, in suspension, in micelles and in solution.

[0059] In other embodiments, coating monomers or precursors may be selected to provide a self-suspending proppant with a hydrogel containing polyurethane or polyurea. The list of suitable monomers for preparing polymers with functional groups of polyurethane and / or polyurea includes: polyols such as ethylene glycol, propylene glycol, glycerin, trimethylolpropane, 1,2,6-hexanetriol, pentaerythritol, sorbitol, sucrose, a-methylglycoside, polyoxyalkylene, such as PEG, copolymers of PEG-PPG, Pluronics, Tetronics, polyamines, such as Jeffamines. Among the isocyanates, toluene diisocyanate, naphthalene diisocyanate, xylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, trimethylene diisocyanate, trimethylhexamethylene diisocyanate, cyclohexyl-1,2-diisocyanate, cyclohexyl-dihexylene are included. Other suitable polymers may include HYPOL® hydrophilic polyurethane prepolymers from Dow, DESMODUR® resins and MONDUR® from Bayer resins (2,4'-diphenylmethanediisocyanate, 4,4'-diphenylmethanediisocyanate, and mixtures thereof), and CONATHANE® (toluene diisocyanate prepolymers (polyol tetramethylene glycols) with polyisocyanate functional groups) from Cytec, and similar polymers.

[0060] Coating the proppant particle with a polyurethane (PU) hydrogel can be carried out by conventional methods. In an embodiment, the coating can be carried out in bulk without the use of solvents. For example, a conventional formulation for a crosslinked PU hydrogel can be obtained in a single-stage bulk polymerization process using diisocyanate, polyoxyalkylene and a multifunctional crosslinking agent. In embodiments, the composition will contain from 10 to 80% polyoxyalkylene with a molecular weight in the range from 200 to 25000.

[0061] Another in situ method for producing a hydrogel layer can be accomplished by dissolving or suspending a water-soluble polymer in the monomer, followed by polymerization of the monomer. Monomers may be selected from the previous list of water soluble monomers. In the event that the water-soluble polymer is dissolved in the monomer mixture, the resulting coating will consist of an interpenetrating hydrogel network of the starting water-soluble polymer and the polymer formed in situ. In the event that the water-soluble polymer is suspended in a monomer mixture, the resulting coating will consist of a hydrogel coating in which water-soluble particles are captured or enclosed. For example, said particles may be enclosed within a newly formed hydrogel coating, or said particles may be bound to a newly formed polymer. The water-soluble polymer may be dissolved or suspended in the monomer composition in the presence or absence of a solvent, and the polymerization can be carried out by various methods.

[0062] Suitable water soluble polymers for mixing with the monomers can be selected from the group consisting of polyacrylamide, polyacrylic acid, copolymers of acrylamide with salts of acrylic acid, polyethylene glycol, polyvinyl pyrrolidone, polyvinyl alcohol, carboxymethyl cellulose, hydroxy hydroxy hydroxy cellulose, hydroxy hydroxy hydroxy cell he hydrophobically associated swellable emulsion polymers, starches, latex polymers and similar polymers.

[0063] Another method for modifying proppant particles involves chemically grafting a particle of hydrophilic polymers. Grafting polymer chains onto the surface of a particle can be accomplished through reactions such as Husgen's cycloaddition and other coupling or addition reactions capable of immobilizing polymers on the surface of the particle.

[0064] The proppant particle used for these purposes can be selected so that functional groups such as epoxide, vinyl, amine, hydroxyl, etc. are located on its surface. These groups can then interact with polymers containing groups capable of interacting with functional groups on the particle surface. For example, proppant particles containing silica can be surface modified with silanes such as aminosilanes, vinylsilanes, epoxysilanes, etc.

[0065] In embodiments, the polymers that will interact with the functionalized particle are hydrophilic linear or branched polymers or copolymers. The polymer may contain one or more grafted fragments. In embodiments, the polymers may contain functional groups, such as an amino group, a carboxyl group or its salts, hydroxyl, thiol, acid anhydride, acid chloride and / or isocyanate group capable of covalently bonding to the functional groups of the particles. Examples of polymers that can be used to interact with a functionalized particle are: PEG, epoxide functionalized, amine PEG functionalized, PEG azide functionalized, polyethyleneimine, polyacrylic acid, polyvinyl alcohol, etc.

[0066] In embodiments, the resulting hydrogel, in addition to the ability to swell, may also be sensitive to temperature or pH. Thus, proppant behavior during swelling can be controlled. This is an additional advantage for feeding proppant into the well, since the temperature is lower in the early stages where the proppant is fed and full swelling is desired; higher temperatures are expected within the fractures, where less swelling of the hydrogel layer is desired to improve packaging. The monomers used to prepare the proppants coated with a temperature-sensitive hydrogel may be selected from N-isopropyl acrylamide (NiPA), ethylene oxide, propylene oxide, or macromonomers / polymers exhibiting lower critical dissolution temperatures (NCTR).

[0067] In an embodiment of the invention, the process of converting a substrate, such as sand, into a self-suspending proppant, can be carried out at the place of its use in preparation for or near the hydraulic fracturing, for example, at the location of an oil or gas well. This method has the advantage that a material of high consumption with a high total cost, such as sand, is subject to conversion into a special product with additional properties. Sand can be obtained from local sources or delivered directly from the place of its extraction or storage for subsequent modification at the place of use. This eliminates the initial transportation of sand to the mixing plant, and then ensures its delivery from the installation to the place of use. In the case of sand, transportation costs may be higher than the cost of raw materials, therefore, for the purpose of controlling the level of costs, it is advisable to avoid additional transportation costs.

[0068] In an exemplary manufacturing process, sand and modifying chemicals may be added to the continuous mixer. After mixing is complete, the composition may be (a) ready for use, or (b) sent for drying. The drying step may include a thermal or vacuum drying process, as well as the addition of anti-caking agents. The finished product can be stored in containers at the well site. An example of mixing equipment is a stirrer with a tape screw blade or a screw mixer. The drying step may be separate from the mixing process, with the aim of avoiding the application of excessive shear forces to the finished product, for example, in a conveyor or tunnel kiln for drying. Other types of dryers include rotary kilns, microwave, paddle and vacuum dryers.

[0069] Hydrogel polymers that can be used to modify proppants in accordance with the systems and methods described in the present invention, in variants of its implementation can be introduced in the form of oil-based emulsions, suspensions, water-based emulsions, latexes, solutions and variances. In embodiments of the invention, the hydrogel polymers can be introduced in the form of a distilled emulsion, for example, a hydrocarbon-based, evaporated to remove part of the carrier liquids. This can give the advantage expressed in lower requirements for drying compared to traditional emulsions. In embodiments of the invention, the hydrogel polymer may be an emulsion that swells under alkaline conditions, characterized in that the properties of the hydrogel-forming polymer before contact with alkali are not fully manifested. In this embodiment, an alkaline swelling emulsion can be applied to a proppant substrate to form a modified proppant, wherein the modified proppant can be suspended in a fracturing fluid in the presence of an alkaline material.

[0070] In embodiments of the invention, an additive, such as an alcohol selected from the group consisting of ethylene glycol, propylene glycol, glycerin, propanol and ethanol, can be added during or prior to the step of mixing the particles of the proppant substrate and the polymer coating fluid composition. In embodiments of the invention, invert activators suitable as additives to polymer coating compositions for self-suspending proppants may include surfactants with a high hydrophilic-lipophilic balance (HLB) such as surfactant polyethylene oxide lauryl alcohol (ETHAL LA-12 / 80% from ETNOX company), ethylene glycol, propylene glycol, water, sodium carbonate, sodium bicarbonate, ammonium chloride, urea, barium chloride and mixtures thereof. In embodiments, invert activators can perform a function that promotes the release of active polymer ingredients from the internal phase of the polymer oil emulsion into a (typically aqueous) process fluid being processed. Since this involves the conversion of the oily continuous polymer into an aqueous continuous medium, the described process can be defined as phase reversal.

[0071] In other embodiments, the proppant substrate may be modified by the composition of the polymer without using a drying step. This can be realized using a polymer composition without a solvent or a curable composition. In some simplified methods, the composition of the dry or liquid polymer can be applied to the proppant substrate by in-line mixing; The modified material prepared in this way can be used without further processing. The moisture content in the proppant substrate can be changed by adding or removing water or the addition of other liquids, which provides effective coating, processing and supply of the substrate to the fracturing fluid.

[0072] For effective dispersion in a fracturing fluid, the modified proppants can be further treated with a wetting agent, for example, a surfactant or other hydrophilic material. Hydrogel-modified proppants that are in suspension in a hydraulic fracturing fluid are considered self-suspending if low viscosity fluid is required to prevent precipitation of the solid phase from the suspension.

[0073] Modified proppants can be further modified to improve flowability and processing properties during processing, transportation, and storage. The hygroscopic surface of the modified proppants may in some cases have a negative effect on the flowability of the bulk material of the modified proppants, causing the adhesion of the modified proppants, especially noticeable in wet conditions and / or at high humidity. Modified proppants can be given anti-caking properties by additional modification, to reduce or eliminate caking by reducing the hygroscopicity of the modified proppants during processing, transportation and storage, or by reducing the interaction between adjacent surfaces of the modified proppants during processing, transportation and storage, or both of these methods. In embodiments, the anti-caking agent does not affect the expected processing characteristics of the modified proppants when introducing the modified proppants into the aqueous liquid in the targeted applications. Modified proppants can be treated with anti-caking agents, such as finely divided solids, or a second outer layer, or both. The second outer layer may have a low density of crosslinking with the surface of the modified proppant, or be a solid non-hygroscopic layer, or a layer of cationic salt, or an oil hydrophobic layer, or a combination of these options. Modified proppants with an anti-caking agent may have improved processing properties such as bulk properties, resistance to sticking, ease of movement, ease of dispensing, and ease of unloading from a storage or transportation container. In embodiments, modified proppants with anti-caking agents can have reduced drying requirements, so that a finished product can be produced with less energy, time and equipment.

[0074] In embodiments, the anti-caking agent is a finely divided solid, including clays, silicon materials, organic materials, metal oxides, or layers of fatty acids. In other embodiments, the anti-caking agent is a finely divided solid, such as calcium silicate, magnesium silicate, calcium carbonate, talc, kaolin, bentonite, attapulgite, diatomaceous earth, silicon dioxide, colloidal silicon dioxide, fumed silica, corn starch carbon black, microcrystalline cellulose, iron oxide, alumina, calcium stearate, magnesium stearate, or combinations thereof.

[0075] In embodiments, the anti-caking agent is a second outer layer formed by crosslinking the surface of the modified proppant. The introduction of compounds capable of crosslinking the swellable polymer on the surface of the proppant can effectively reduce the ability of the polymer layer to prematurely swell. Reducing the swelling of the polymer will reduce the tendency of the modified proppant to undergo caking or agglomeration during transportation and storage. In embodiments, crosslinking compounds are capable of forming a bond with a hydroxyl functional group, a carboxyl functional group, an amine functional group or an amide functional group. Crosslinking compounds can be selected from organic compounds containing aldehyde, amine, anhydride or epoxy functional groups. Crosslinking compounds can also be organometallic compounds. In embodiments, the crosslinking compounds form a bond that can be broken or removed by mechanical shear. Organometallic compounds capable of association and / or binding to hydroxyl and carboxy functional groups are examples of crosslinking compounds that form shear sensitive bonds. At high shear forces during pumping associated with hydraulic fracturing, polymer crosslinking can break and the polymer can swell indefinitely when a modified proppant is introduced into the hydraulic fracturing fluid.

[0076] In embodiments, the anti-caking agent is a thin second layer of solid non-hygroscopic material such as fatty acids, hydrogenated fatty acids, hydrogenated oils, waxes, polyethylene, polyethylene oxides, polypropylene oxides, copolymers of polyethylene oxide and polypropylene oxide, or combinations thereof. Examples of fatty acids suitable for use as a second layer include stearic acid, palmitic acid, lauric acid or tall oil fatty acids containing stearic acid, palmitic acid and / or lauric acid. Examples of hydrogenated oils suitable for use as a second layer include hydrogenated castor oil. Examples of waxes suitable for use as a second layer include paraffin, petroleum jelly, and gach. A thin dense layer can be applied to the surface of the modified proppant to create a barrier to preventing the swelling polymer layer from adhering to adjacent particles of the modified proppant during storage. The applied solid outer layer may consist of compounds that are soluble in water, insoluble in water, or both of these types. The solid outer layer is non-hygroscopic. The solid outer layer is selected to remain in the solid phase at temperatures below 38 ° C, and has a melting point in the range from 40 ° C to 120 ° C. In embodiments, the outer layer is selected so that the melting temperature is sufficiently low so that the outer layer is in the liquid phase during the drying process during the production of the modified proppant, but high enough so that the outer layer is in the solid phase during storage and transporting modified proppant. In the solid phase, the outer layer acts as a barrier to prevent / reduce caking of the modified proppant in wet conditions. The solid outer layer can be introduced into the modified proppant in the form of a fine powder, flakes, solution in an oil carrier or a warm liquid. The solid outer layer can be introduced into the modified proppant immediately before the polymer, simultaneously with the polymer, as a mixture with the polymer, or introduced at some point after the polymer is introduced, but before the drying process. Preferably, the solid outer layer of the anti-caking agent is introduced after thoroughly mixing the polymer with a modified proppant, but before drying the modified proppant.

[0077] In embodiments, the anti-caking agent is a second salt layer with a monovalent cationic charge that can be introduced into the modified proppant as a liquid or an oil solution at temperatures below 100 ° C, such as a cationic surfactant or hydrate monovalent salt. A cationic surfactant containing a quaternary amine with a hydrophobic tail, such as the commercially available Adogen 464 or Arquad 2HT-75 from Akzo Nobel, can be used as a second coating to impart a hydrophobic layer to the modified proppant, which also neutralizes the possible anionic charge of the polymer . Many salt hydrates, such as sodium acetate trihydrate and aluminum-sodium sulfate dodecahydrate, have melting points below 100 ° C and can be introduced into the modified proppant and melted as a second layer during drying of the modified proppant. Both in the case of a cationic surfactant and in the case of salt hydrate, a concentrated cationic charge layer is obtained on the surface of the modified proppant, which can reduce the swelling potential of the anionically charged polymer. When a modified proppant is introduced into the water stream, the monovalent salt is sufficiently diluted to allow the modified proppant to fulfill its intended function.

[0078] In embodiments, the anti-caking agent is a second layer of hydrophobic lubricating oil applied to a modified proppant, said oil being selected from the group consisting of organosilicon oils, mineral oils, petroleum jelly, triglycerides, or a combination of these oils. Examples of organosilicon oils suitable for use as a hydrophobic lubricating second layer include polydimethylsiloxane. Examples of triglycerides suitable for use as a hydrophobic lubricating second layer include corn oil, peanut oil, castor oil and other vegetable oils. Preferably, the hydrophobic lubricating oil has a smoke point and a boiling point higher than that used in the drying step in the production of the modified proppant. Preferably, the smoke temperature of the oil is more than 200 ° C. Preferably, the smoke temperature of the oil is at least 175 ° C.

[0079] According to the present invention and in contrast to the traditional approach of creating a homogeneous medium-viscosity fluid, the method of localizing the polymer concentrate on the surface of the proppant can be successfully used in hydrogel-modified proppants. The localized hydrogel layer allows more efficient use of the polymer, since a smaller amount of polymer can be used to prepare a proppant suspension compared to, for example, conventional fracturing fluids with polymer additives, such as water with non-crosslinked polymer additives, linear and crosslinked gels. Despite the fact that hydrogel-modified proppants are considered self-suspending, they can be used in combination with friction reducers, linear and crosslinked gels.

[0080] The hydrogel-modified proppants described in the present invention are characterized in that they have the advantage of feeding the friction reducing polymer to the fracturing fluid, and thus the need for other friction reducing polymers is either absent or significantly less if the operations hydraulic fracturing using proppants modified with hydrogel. In embodiments, a certain amount of hydrogel polymer can be desorbed from the proppant surface, leading to a predominant reduction in the friction or viscosity properties of the fracturing fluid. Although examples of embodiments of the present invention focus on the use of hydrogel-modified proppants for hydraulic fracturing purposes, other applications of hydrogel-modified proppants can be envisioned in which the ability of these proppants to retain water or reduce friction can be used. For example, hydrogel-modified proppants can be used to absorb water from wet environments by creating water-retaining particles that can be removed from the medium by removing unwanted moisture along with them. In another example, hydrogel-modified proppants can be used in situations where introducing water into the medium would be beneficial. Hydrogel-modified proppant can be saturated with water or an aqueous solution, and then used, for example, as an additive for soil remediation in dry conditions. Hydrogel-modified proppants can be made from sand or other substrates compatible with the soil, and they can be transported to the area of use in dry form; then they can be saturated with water and used as soil improver. In other embodiments, hydrogel-modified proppants can be used as a dry conditioner, while they can absorb and retain moisture from the environment, irrigation, rains, and the like. In these embodiments, it is possible to advantageously use the water-holding properties of the hydrogel-modified proppants. In embodiments, a hydrogel-modified proppant can be used to reduce erosion of the arable layer, seed bed, mixtures for hydroseeding, and similar applications. In embodiments, the hydrogel-modified proppant can be used as a carrier for introducing other compatible agents into the area, for example, into the soil. Hydrogel-modified proppants may contain additional formulations flowing from or through the hydrogel layer to the environment as the hydrogel breaks down or as the hydrogel absorbs moisture and expands. Examples of such formulations include fertilizers, seeds, plant growth regulators, herbicides, pesticides, fungicides, and the like. Other applications of hydrogel-modified proppants obtained according to the described compositions and methods can be assumed based on their properties described in the present description.

[0081] In embodiments of the invention, the hydrogel polymer used to prepare modified proppants may include polyacrylamide, copolymers of acrylamide with anionic and cationic comonomers, hydrolyzed polyacrylamide, copolymers of acrylamide with hydrophobic comonomers, (poly) acrylic acid, salts of (poly) acrylic acid, carboxymethyl, hydroxyethyl cellulose, hydroxypropyl cellulose, guar gum, alginate, carrageenan, fruit tree resin, carboxymethyl guar, carboxymethyl hydroxypropyl ApoB resin gidrofobnoassotsiirovannye swellable emulsion (HASE) polymers, latex polymers, starches and the like polymers. In embodiments, the hydrogel polymer may have a molecular weight (g / mol) of more than 1 million, for example, in the range of 10 million to 40 million Daltons. In embodiments, the hydrogel polymer may be a high molecular weight vinyl addition polymer soluble in water and having a linear structure.

[0082] In embodiments, the hydrogel polymer may be crosslinked as described above to improve the ability of the polymer to absorb water and swell. Crosslinking agents can be introduced as an element of the hydrogel base polymer, or they can be introduced as chemical modifiers of preformed polymers. Crosslinking compounds can be introduced directly into the polymer used to coat the proppant, introduced into the proppant simultaneously with the polymer when mixed, or introduced at some point after the polymer is introduced into the proppant, but before drying.

[0083] the Localization of the polymer around the surface of the proppant according to the method described in this application leads to more efficient use of the polymer and prevents the proppant from precipitating from the polymer solution. In embodiments of the invention, the polymer layer hydrates around the proppant, effectively preventing contact between the proppant particles. This is able to prevent the formation of a compact fixed proppant layer and, as a result, facilitates resuspension in fracturing fluid. The ability of a modified proppant to re-form a slurry is important in situations where fluid movement has been impaired during hydraulic fracturing operations. In this case, in order to avoid proppant loss or inadvertent blockage of the flow line when resuming movement, it is important that the proppant can be resuspended.

[0084] Modification of the polymer surface according to the method described in this application can lead to an increase in the effective hydrodynamic radius of the proppant particle during polymer swelling. This entails a delayed proppant movement as well as an effective change in the bulk density of the hydrogel / particle. Both that and another can cause a decrease in the sedimentation rate of proppant particles and a significant improvement in the transport properties of the fluid.

[0085] In the hydrogel-modified proppants of the present invention, localization of polymer concentration on the surface of the proppant can advantageously be used. Preferably, after hydration of the hydrogel with water and exposure to shear conditions, such as pumping through a pipeline, most of the hydrogel polymer remains bound to the proppant surface. In embodiments, a method for coating a substrate particle with a hydrogel polymer comprises physically or chemically attaching the polymer to the surface of the proppant. This attachment may be caused by entanglement of the polymer chains when the hydrogel film is dried, which leads to the formation of a hydrogel coating that resists desorption by shear in the hydrated state. In embodiments, entanglement of the polymer chains is facilitated by a chemical reaction or interaction between the polymer chains. In embodiments, a linear, non-crosslinked hydrogel polymer is used as a coating to allow linear polymer chains to become entangled in the formation of the polymer coating. In embodiments, entanglement of the polymer chains is facilitated through a drying process in production and through the use of coalescing additives. Coalescing additives are additives that cause the merging of individual droplets of the emulsion in the coating composition into a continuous film upon drying. In embodiments, the coalescing additive is an alcohol, such as propanol, glycerin, propylene glycol or ethylene glycol. In FIG. 4A and 4B show two images obtained using a scanning electron microscope (SEM), showing the effect of glycerol on the coalescence of the coating polymer to form a continuous film. In the image obtained using a scanning electron microscope, presented in FIG. 4A, the proppant was coated with a hydrogel composition from an anionic polyacrylamide emulsion without glycerol added, and then dried at 100 ° C for 1 hour. In the image shown in FIG. 4A, a complete coating of the surface of the proppant grain can be seen, but individual droplets of the emulsion with a diameter of about 1 micron still remain visible. In the SEM image shown in FIG. 4B, the proppant was coated with the same emulsion of anionic polyacrylamide, but with the addition of 10% of the mass. glycerol as a coalescing agent; and then dried at 100 ° C for 1 hour. The effect of the coalescing agent is clearly visible in the appearance of the dried film: the SEM image in FIG. 4B shows a substantially complete coating of proppant grain, in which case the emulsion droplets merged into a more continuous film. In FIG. 5 shows an SEM image of a dried hydrogel film obtained in the same manner as in FIG. 4B. The hydrogel film of FIG. 5 shows the good coalescence of the emulsion droplets in the film and the complete coating of the surface of the proppant grain.

[0086] In embodiments of the invention, polymer pairs may optionally be used in conjunction with an ionic combination to improve the retention of the hydrogel polymer on the surface of the proppant particles. For example, a cationic polymer is applied to the proppant as a first layer, which will “fix in place” a second layer containing a hydrogel, such as a high molecular weight anionic polymer, by ionic coupling. In embodiments of the invention, the cationic polymer may be ammonium polydiallyl dimethyl chloride (poly-DADMAC), linear polyethyleneimine (LPEI), branched polyethyleneimine (BPEI), chitosan, epichlorohydrin / dimethylamine polymer, ethylene dichloride dimethylamine polymer or cationic polyacrylamide. The cationic polymer layer can be applied to the proppant before or after surface modification by means of an anionic hydrogel layer. The ion-coupled interaction can act as a fixing mechanism and can help prevent desorption of the anionic polymer under high shear conditions, for example, passing through a pump or during injection into a borehole. The cationic polymer can also improve polymer retention by slowing down hydration and chain elongation of the anionic polymer. It is believed that during pumping, the shorter the polymer chain, the higher the degree of polymer retention on the proppant (i.e., the lower the desorption) during pumping.

[0087] In embodiments, covalent crosslinking of the hydrogel polymer layer on the proppant surface can improve polymer swelling and shear resistance, thereby preventing premature separation of the hydrogel from the proppant. Covalent crosslinking polymers may include the following functional groups: epoxides, anhydrides, aldehydes, diisocyanates, carbodiamides, divinyl or diallyl groups. Examples of such covalent crosslinkers are: PEG diglycidyl ether, epichlorohydrin, maleic anhydride, formaldehyde, glyoxal, glutaraldehyde, toluene diisocyanate, methylenediphenyl diisocyanate, 1-ethyl-3- (3-dimethylaminopropyl-amide-bis-carbides. Covalent crosslinking of the hydrogel polymer layer on the proppant surface can effectively create “polymer lattices” capable of swelling around the proppant. Covalent bonds prevent complete desorption of the polymer into the solution. The partially insoluble polymer layer has the ability to swell to form a hydrated polymer layer.

[0088] To further prevent the possible separation of the hydrogel from the surface of the particle, the proppant particle can be treated to introduce functional groups also involved in the polymerization process. For example, sand particles can be treated with silanes, with the formation of particles with vinyl functional groups, hydroxyl, epoxy, etc.

[0089] Slowed / controlled hydration of the polymer layer may be desirable to temporarily delay hydration and modify the polymer surface during proppant treatment and initial pumping of the wellbore. Environmental factors, such as humidity and rain, can cause premature hydration of the polymer coating, and, as a result, make it difficult to efficiently dispense the proppant supplied to the mixer during hydraulic fracturing operations. It is also believed that a fully hydrated polymer layer exhibits a greater tendency to desorption under conditions of high shear forces associated with pumping the fracturing fluid into the pipe. For this reason, it is advisable to create a surface-modified proppant with reduced or delayed hydration. In embodiments of the invention, delayed hydration can be achieved by adding surfactants with a low hydrophilic-lipophilic balance (HLB), with the exception of high surfactant high-HLB surfactants, solubility reducing comonomers, screening the charge with a monovalent salt, or by adding a hydrophobic layer, for example fatty acid or fatty alcohol.

[0090] In embodiments of the invention, hydrophobic groups may be introduced into the hydrogel polymer to provide hydrophobic interaction. This method allows to increase the salt tolerance of the hydrogel layer, despite the fact that the hydrogel layer retains the ability to swell even in an aqueous fluid with high salt concentrations.

[0091] Since the purpose of the hydrogel coating is to improve hydraulic proppant transfer, it is important that the hydrated hydrogel layer remains attached or localized to the surface of the proppant when shear is applied during transfer of the medium. However, when a hydrogel-coated proppant is placed in a fracturing well, the hydrogel polymer must break down or release to separate from the proppant grains to form a proppant pack with sufficient hydraulic conductivity to allow fluid production. The removal of the hydrogel layer from the proppant is caused by environmental factors such as elevated temperatures, exposure to microorganisms, the presence of destructors, saline solutions and / or hydrocarbons. In a preferred embodiment, after pumping the hydrogel coated proppant into the well, the hydrogel is destroyed, released, dissolved or separated by a destructor, such as an oxidizing agent or an enzyme. The oxidative type of destructor may be peroxides, magnesium peroxide, calcium peroxide, persulfate, sodium bromate, sodium hypochlorite, ozone, sodium nitrate, and the like. A mixture of the first oxidizing agent, which is activated at a lower temperature, such as ammonium persulfate, with the second oxidizing agent, which is activated at a higher temperature, such as magnesium peroxide, can improve the degradation of the hydrogel after delivery of the hydrogel coated proppant. Enzymatic destructors are known in the art and are widely used to reduce the viscosity of fluids injected into wells. Enzymes catalyze the destruction or cleavage of polymer bonds. In some cases, enzymatic destructors can provide more effective destruction, since they are aimed at bonds in the hydrogel polymer (s). Enzymatic destructors are usually more effective at low and moderate temperatures and can be combined with oxidizing agents activated at higher temperatures. Choosing a suitable enzyme destructor, which is made based on the nature of the hydrogel polymer and downhole conditions, can improve hydrogel disruption.

[0092] In addition, the present application describes a fracturing method in a well that uses proppant coated with a hydrogel in combination with a non-coated hydrogel proppant. For example, a hydrogel coated proppant may act as a suspending agent for a hydrogel coated proppant.

[0093] In specific embodiments, the hydrogel polymer is selected so that its hydration is substantially complete at least while the modified proppant carrying said hydrogel polymer reaches its destination. In embodiments, the destination in the downhole application is a portion of the well where the modified proppant enters the fractured geological formation, for example, where the direction of hydraulic fracturing fluid changes from vertical to horizontal, or where the direction of the drill string begins to change from vertical to horizontal. The self-suspending property of the preferred modified proppants of the present invention can be particularly useful in fracturing fluids moving in a substantially horizontal direction. In embodiments, the hydrogel polymer for the modified proppant is selected so that its hydration is substantially complete within 2 hours, within 1 hour, within 40 minutes, within 30 minutes, within 20 minutes, or even within 10 minutes after contact with excess tap water at 20 ° C.

[0094] In addition, the present application describes a method for increasing well productivity through an improved proppant packing method using hydrogel coated proppant. Hydrogel-coated proppant can be more effectively transferred to the far ends of the fractures, providing a higher debit of oil and gas from the well. Since the surface-modified proppants described in this application are less prone to falling out of the fluid, are easier to resuspend and transport in the fracture, it is believed that proppant packaging will be more efficient. The ability to transfer proppant in the fractures further can significantly increase the efficiency of the stimulation of hydraulic fracturing and provide the formation of a larger volume of fractures with high density. The resulting channels advantageously facilitate the flow of gas / condensate from the formation into the wellbore.

[0095] In addition, the present application describes an improved method for packaging proppant using low-viscosity fluid. The surface-modified proppants described herein provide a more efficient use of polymers for suspending / transporting proppant particles. Surface modification gives the proppant self-suspending properties, thereby reducing or eliminating the need for high viscosity fluids / gels to transport proppant. Thus, lower viscosity fluids can be used to transport proppant to cracks in combination with a surface-modified proppant. This advantageously simplifies fracturing gel compositions using proppants.

[0096] In addition, the present application describes a more effective method of hydraulic fracturing in the well, requiring less proppant. Since highly effective proppant packing in a fracture can be achieved using the easily transportable surface-modified proppants described in this application, it is anticipated that fewer fractions will be required for fracturing operations compared to systems using conventional proppants. Taking into account the growing demand for proppant / sand, the granulometric composition of which meets the requirements of hydraulic fracturing, and the reduction of sand reserves, preferred for use in proppant, it is advisable to develop systems and methods, such as described in this application, in which to achieve results comparable or superior to state of the art, less proppant can be used.

[0097] After pumping proppants coated with a hydrogel according to the present invention into the well, the hydrogel layer can degrade as a result of chemical, thermal, mechanical and biological mechanisms. In particular, the polymer modification of the proppant surface can be destroyed as a result of the action of chemical gel destructors (breakers), for example, ammonium peroxydisulfate, magnesium peroxide or other oxidizing agents. The polymer modification of the proppant surface can also be destroyed due to in-situ conditions, such as increased salt concentration, elevated temperature, and contact with hydrocarbons. The controlled destruction of the hydrogel layer after reaching the target temperature in the liquid or after a certain amount of time has passed can be used as a means of directly controlling the proppant placement in the desired location in the fracture. Degradation of the hydrogel layer is also beneficial to provide the required permeability of the wedged fracture after completion of hydraulic fracturing operations. In embodiments of the invention, the hydrogel layer may exhibit properties of different sensitivity to environmental factors, for example, swell in an aqueous medium under the influence of one set of conditions, such as a certain temperature or pH, and lose water, volume, thickness, or even collapse under the influence of another set conditions, i.e. different temperature or pH.

[0098] For example, in one embodiment of the invention, a heat-sensitive hydrogel is applied to proppants. A layer of thermosensitive hydrogel swells under the influence of water during the first set of conditions, for example, a water temperature of 50-100 degrees Fahrenheit (10-37.8 ° C), and then collapsed during a second set of conditions - a water temperature of 110-450 degrees Fahrenheit (43.3 -232.2 ° C). By implementing a mechanism of different sensitivity, a proppant coated with a thermosensitive hydrogel can exhibit self-suspending properties, while it is transported by a fracturing fluid at a certain initial temperature of water, for example, 50-100 ° F (10-37.8 ° C), to its location cracks. When the proppant in the area of the reservoir begins to experience a higher temperature, for example, 110-450 ° F (43.3-232.2 ° C), the hydrogel layer is destroyed, providing deposition and cementing of the proppant at the fracture site. The heat-sensitive hydrogel may be a water-soluble polymer or copolymer composition comprising hydrophobic monomers selected from the group of alkyl acrylate esters, N-alkyl acrylamides, propylene oxide, styrene and vinyl caprolactam. N-alkyl substituted acrylamides can be N-isopropyl acrylamide, N-butyl acrylamide, N-octyl acrylamide and the like. In alkyl acrylate esters, alkyl chains may contain from 1 to 30 carbon atoms. In a preferred embodiment, the thermosensitive hydrogel polymer comprises N-isopropyl acrylamide and comprises up to 90 percent units of the hydrophilic comonomer. The type and amount of the hydrophobic monomer substituent in the hydrogel polymer can be selected using experimental optimization methods to control the water solubility and heat-sensitive properties of the hydrogel polymer.

[0099] Furthermore, the present application describes a method for delivering additives, for example, chemical additives, to a proppant package by introducing said additives into the hydrogel layer of a modified proppant. Additives may include chemical additives that can be introduced into the hydrogel layer, for example, a scale inhibitor, a biocide, a destructor, a paraffin scavenger, an asphaltene scavenger, and markers. Chemical additives may be in the form of water-soluble materials, water-insoluble particles, fibers, metal powders or flakes and the like. Reagents can be selected so that slow dissolution or decomposition will initiate their chemical activity.

[00100] In embodiments of the invention, the chemical additives may be chemically bonded to the polymer in the hydrogel layer, for example, by covalent bonding, ionic bonding, hydrophobic association, hydrogen bonding, or encapsulation. Chemical additives can be added to the proppant separately from the hydrogel or as part of the hydrogel coating during the manufacture of the coated proppant. Destructive chemicals such as persulfates, peroxides, permanganates, perchlorates, periodates or percarbonates can be added by this indicated delivery method. The transfer and delivery of these hydrogel coated proppant reagents has the advantage of targeted delivery of these reagent chemicals to a fracture or proppant pack. The advantage of this method is the concentration of chemical additives in the place where their action is required, due to which the delivery of chemical additives is carried out more efficiently, more efficiently and in a lower concentration. In embodiments, desorption, oxidation, or degradation of the hydrogel polymer can result in a controlled release of chemical additives from the self-suspending proppant.

[00101] In embodiments, the fracturing operation may include multiple fracturing steps; proppants administered at each stage may contain unique chemical additives that act as labeled substances. Labeled substances commonly used in hydraulic fracturing include labeled substances that can be detected by high performance liquid chromatography (HPLC), gas chromatography (GC), absorption of ultraviolet or visible light, and measurement of a radioactive signal. An analysis of the fluid obtained from the fractured well may provide information on the relative productivity of each of the fracturing stages due to the presence and concentration of unique labeled substances corresponding to the stages. In other embodiments, additives acting as destructors may be enclosed in a hydrogel layer, for example, by physical bonding or incorporation into a polymer layer. In embodiments, the destructors can be modified by cationic coating of the surface to provide an attachment mechanism for attaching the destructors to the self-suspending proppant anionic hydrogel. For example, magnesium peroxide powder can be coated with a cationic polymer such as poly-DADMAC, and this cationically modified magnesium peroxide can be mixed with hydrogel-coated proppant before or after the proppant is introduced into the water stream for hydraulic fracturing. Using this approach, the destructors are transferred to the same place as the hydrogel-coated proppants, so that the destructor can effectively act on the hydrogel layer. Oxidative destructors may have enhanced activity at higher temperatures. Using this method, a destructor chemically incorporated into the hydrogel layer can become activated when placed in cracks, for example, by means of elevated temperatures in the oil reservoir.

[00102] In other embodiments, the destructors can be pumped into the subterranean formation before and / or after the introduction of hydrogel coated proppants. In the event that the destructor is pumped before the proppant, the fluid containing excess destructor will flow back through the proppant pack and be able to promote degradation of the hydrogel layer after the proppant has reached its destination. In the event that the destructor is pumped into the propped formation after the proppant, the destructor can seep into the proppant package and exert its effect on the destruction of the hydrogel layer. In embodiments, the destructor may be administered multiple times to facilitate destruction of the hydrogel layer. In embodiments, the destructors can be used in the form of a combination of several types, for example, a destructor activated at a lower temperature, such as ammonium persulfate, can be used for quick action, in combination with an encapsulated, longer-acting or activated at a higher temperature, destructor, such as magnesium peroxide, to obtain the delayed effect of the destruction of the hydrogel layer over time, before the fluids flow back and the well is put into operation.

[00103] In embodiments of the invention, the surface of the proppant substrate particles may be coated with the selected polymer either in a single layer or as a series of layers (multilayer coating). Under certain circumstances, a change in the properties of a coating (single layer or multi-layer) may be a switching nature. The terms “nature of switching” and “switching properties” as used in this application refer to a change in a set of properties / behavior depending on circumstances or conditions, for example, a change in one set of properties in the transport phase to another set when in a crack. The switching of properties, for example, is observed in the case when a particle exhibits hydrophilic properties while in a fracturing fluid and adhesive properties while in a fracture in the formation. Such behavior can be caused by circumstances such as high crack closing pressure in the fracture zone, while the outer coating layer is rebuilt and exhibits more preferred properties.

[00104] In an embodiment of the invention, under the influence of high pressure inside the crack, the properties of the coated particle could change from hydrophilic to hydrophobic. In an exemplary embodiment of the invention in the transport phase, when the hydrophilic coating of a particle was exposed to an aqueous fracturing fluid, it sought to expand completely. As a result, in this state, the coating layer acted as a lubricant for the particle, facilitating its movement in the proppant carrier fluid. After the particle has been transferred to the fracture at the fracture site, the high pressure in it allows to overcome the steric repulsion of the external hydrophilic polymer chains, leading to the reorganization of the outer layer and, thus, exposing the inner layer. In embodiments of the invention, the switching properties of the inner layer may be hydrophobic or adhesive, or both. The properties of the inner layer are manifested when exposed to the environment. For example, if the inner layer has adhesive properties, it bonds the particles to each other, which prevents their backflow. The inner layer can also be made in such a way that when proppant is destroyed it will capture fine particles. Moreover, residual intact hydrophilic groups present in the outer coating layer can provide a free flow of oil through the proppant pack.

[00105] In embodiments of the invention, coated proppant particles carrying subsequent coating layers can be prepared. First, a pressure-activated fixing polymer can be used to coat the proppant substrate. The coating layer can be elastomeric, thereby ensuring the strength of the proppant pack due to agglomeration of the proppant particles and the distribution of stresses between them. In addition, such a coating layer is able to encapsulate the particles of the substrate and retain the fine particles formed in the event of its destruction. Secondly, the block copolymer can be adsorbed or otherwise located on the first coating layer. The copolymer may have a site with high affinity for the first polymer layer, which provides strong interaction (hydrophobic interaction), and another site is hydrophilic, providing easy transportation of proppant in a liquid carrier medium.

[00106] In some embodiments, a stronger interaction between the first and second coating layers may be useful. For this purpose, the method of swelling-swelling can be applied. For example, a block copolymer can be adsorbed onto the surface of a particle coated with an elastomer. Then, the first coating layer can be swelled with a small amount of organic solvent, which allows the hydrophobic block of the copolymer to penetrate deeper into the first coating layer and to bond with the elastomeric coating. When the organic solvent is removed, the coated polymer composite material will swell, resulting in a stronger bond of the copolymer with the elastomer particle. An effective way to implement the swelling-swelling method is described in wSwelling-Based Method for Preparing Stable, Functionalized Polymer Colloids, ʺ A. Kim et al., J. Am. Chem. Soc. (2005) 127: 1592-1593), the contents of which are incorporated into this application by reference.

[00107] In embodiments of the invention, proppant systems utilizing the surface coatings described herein provide a reduction in the volume of aerosol particles associated with proppant production. For example, a respiratory fraction containing fine silica dust, the formation of which is associated with the processing and production of granular sand, can be trapped and retained by the coating layer during proppant treatment. In embodiments of the invention, coating agents may be added that are characterized by a specific affinity for aerosols in the environment that adversely affect the safety of workers or create problems in the operation of the equipment. In embodiments of the invention, the hydrogel coating of the proppant particles can serve as a binder or entrainment agent for mechanically capturing or adhering dusty particles.

[00108] Despite the fact that this application describes a two-layer coating system, it is also understood that the invention relates to multilayer (ie having more than two layers) coatings forming particles of composite proppant, with each individual coating layer having which - either all the characteristics of the two-layer coating described above, or one or more coating layers provide additional properties or features.

[00109] the Introduction of compounds capable of cross-linking the swellable polymer on the surface of the proppant, can effectively reduce the ability of the polymer layer to swell prematurely. Reduced swelling of the polymer can reduce the tendency of the polymer coated proppant to undergo caking during storage in wet conditions. In some embodiments, the crosslinking agent does not interfere with the hydration / swelling of the polymer coating when dispersing the polymer coated proppant in an aqueous fluid, such as a fracturing fluid. In embodiments, crosslinking compounds are capable of forming a bond with a carboxyl functional group, an amide functional group, or both of these groups. In some aspects, the crosslinking compounds form a bond that can be broken or removed by mechanical shear or by a chemical destructor. Crosslinking compounds can be introduced directly into the polymer used to coat the proppant, simultaneously with the polymer added to the proppant when mixed, or administered some time after the polymer is added to the proppant, but before drying.

[00110] The crosslinking compounds may be selected from organic compounds containing aldehyde, amine, anhydride or epoxy functional groups. Crosslinking compounds may also be an organometallic compound. Organometallic compounds capable of associating and / or binding to a carboxy functional group are examples of crosslinking compounds that form bond shear sensitive compounds. In such embodiments, organometallic compounds are capable of reducing the tendency to swell polymer coated proppant by crosslinking carboxyl groups before introducing the proppant into the fracturing fluid. Then, when the crosslinked polymer coating undergoes high shear forces during pumping associated with hydraulic fracturing, the polymer crosslinking can break, allowing the polymer to swell indefinitely when proppant is introduced into the hydraulic fracturing fluid.

[00111] In some embodiments, a thin, non-hygroscopic coating layer can be applied to the surface of the hydrogel-coated proppant to create a barrier to prevent the layers of swellable polymer from sticking to adjacent proppant particles during storage. The applied outer layer may consist of compounds soluble in water, insoluble in water, or both of these types. In embodiments, the composition of the outer layer may be such that it remains in the solid phase at temperatures below 40 ° C and has a melting point in the range from 40 ° C to 120 ° C. Preferably, the outer layer is of such a composition that its melting point is sufficiently low so that the outer layer is in the liquid phase during the drying process in the production of polymer coated proppant, but high enough so that the outer layer is in the solid phase during storage and transportation of the polymer coated proppant.

[00112] In these embodiments, the outer layer acts as a barrier to reduce caking of the coated proppant in a humid environment. As used herein, the term “caking” refers to the formation of lumps or solid masses by adhering loose granular material. Tracking of proppants during storage is undesirable from the point of view of handling the material. The hydrophobic outer layer can be introduced into the polymer coated proppant in the form of a fine powder or in the form of a liquid. In embodiments, the material of the outer layer can be melted before introduction into the coated proppant; in other embodiments, the material of the outer layer can be introduced in the form of a solid or waxy material that can melt during drying. The solid outer layer can be introduced into the proppant simultaneously with the polymer, or introduced some time after the polymer is added, but before drying. The outer layer may consist of fatty acids, hydrogenated oils, vegetable oils, castor oil, waxes, polyethylene oxides, polypropylene oxides and the like.

2. Materials of substrates in the form of particles

[00113] In accordance with these systems and methods, a wide variety of proppant substrate particles can be used to form composite proppant particles. Proppant substrate particles suitable for use according to the present invention may include sorted sand, polymer coated sand, bauxite, ceramic materials, silica materials, nutshells, polymeric materials, resinous materials and the like, and combinations thereof. The self-suspending proppant (SSP) described in this application can also be obtained using special proppants such as ceramic, bauxite and polymer coated sand. When combining sand SSP with special materials SSP, the resulting proppant can have favorable strength, permeability, suspending and transport properties. In embodiments of the invention, the substrates may include natural materials, for example, chopped, chopped, ground, or crumbled to the appropriate size nutshell (such as walnuts, pecans, coconuts, almonds, phytoteas, Brazil nuts and the like) or, for example chopped, chopped, chopped, or crushed to the appropriate size husks of seeds or fruit seeds (plums, olives, peaches, cherries, apricots, etc.), or, for example, crushed, chopped, or chopped materials of other plants, for example, corncob. In embodiments of the invention, the substrates can be obtained from wood or recycled timber, including without limitation, species such as oak, pecan, walnut, mahogany, poplar and the like. In embodiments of the invention, aggregates may be formed upon attachment or binding of inorganic and organic materials. Preferably, the particles of the proppant substrate include particles (individual substances or aggregates of two or more substances) of a size of the order of 4 to 100 (sieve number according to the American standard). Used in this application, the term "particle, in the form of particles" includes, without limitation, all known forms of materials, for example, spherical, elongated, polygonal, fibrous, irregular and mixtures thereof.

[00114] In embodiments of the invention, the substrate particles can be obtained in the form of a composite material from a binder and a filler material. Suitable fillers may include inorganic materials such as hard glass, glass microspheres, fly ash, silica, alumina, fine carbon, carbon black, graphite, mica, boron, zirconia, talc, kaolin, titanium dioxide, calcium silicate and the like. like that. In some embodiments of the invention, the proppant substrate particles can be reinforced to increase their resistance to high in-situ pressures, which, otherwise, can cause their destruction or deformation. Reinforcing agents may be selected from among materials capable of imparting additional structural strength to proppant substrate particles, for example, from high-strength particles such as ceramics, metal, glass, sand and the like, or other other materials capable of imparting to it in combination with a substrate particle extra strength.

[00115] In addition to unmodified or uncoated substrates, composite hydrogel-coated proppants can be made from pre-treated or coated substrates. For example, a number of polymer coated proppant particles are known to those skilled in the art. The coating compositions and methods described above are suitable for use with coated or treated proppant particles, including proppants coated with curable or pre-cured polymers.

[00116] In one embodiment for treating polymer coated sand, a swellable hydrogel layer, as described above, can be applied to polymer coated sand to improve its suspension characteristics. In embodiments, the introduction of compounds acting as adhesion promoters to attach the hydrogel to the polymer layer can be included. The adhesion promoters can be, for example, block copolymers consisting of hydrophobic and hydrophilic monomers. The block copolymer can be introduced after coating the sand substrate with the polymer or simultaneously with the polymer coating. In addition to the block copolymer, cationic compounds such as fatty amines, poly-quaternary amines and cationic surfactants can be used.

[00117] In some embodiments of the invention, the proppant substrate particle may be made in the form of an aggregate of two or more dissimilar materials providing its various properties. For example, a central particle of a substrate having a high compressive strength can be combined with a floating material with a lower density than the material of the central particle. The combination of these two materials in the form of an aggregate provides an appropriate level of strength for the central particle at a relatively lower density. As a particle with a lower density, it can be appropriately suspended in a less viscous fracturing fluid, which will allow it to be pumped at a lower cost; in addition, a higher degree of dispersion of proppants in the reservoir is achieved, since their promotion is carried out using less viscous fluid in more distant zones. High density materials used as proppant substrate particles, for example, sand, ceramics, bauxite and the like, can be combined with lower density materials such as hollow glass particles, other hollow particles, some polymeric materials and materials of natural origin (shell nuts, seed husks, fruit seeds, wood or other natural materials in chopped, chopped, crushed, or crumbled form), resulting in a less dense aggregate with sufficient compressive strength.

[00118] Aggregates suitable for use as proppant substrate particles can be formed using methods of binding the two components to each other. In accordance with one production method, proppant substrate particles can be mixed with a floating material whose particle size is similar to the proppant substrate particle size. The two types of materials were then mixed and bound by means of an adhesive substance, for example, wax, phenol-formaldehyde novolac resin and the like, so that a group of aggregated particles formed, while in one subgroup the proppant substrate particles were bound to other similar particles, in in the second subgroup, proppant substrate particles were associated with floating particles, and in the third subgroup, floating particles were associated with other floating particles. These three subgroups can be divided according to their difference in density: the first subgroup will sink in water, the second one will be in suspension in the liquid, and the third will remain on the surface.

[00119] In other embodiments, the proppant substrate particles can be made to have a lower density by coating the surface of the substrate particle with foam material. The thickness of the foam material can be calculated so that the resulting composite material will have neutral buoyancy. To obtain such a coated proppant particle, a particle having the required compressive strength may be coated with a substance involved in the foaming reaction, followed by exposure to another reagent. Initiation of foaming results in a proppant particle coated with a layer of foam material.

[00120] As an example, foaming of the polyurethane by the reaction of water can be used to form a coating around the particles to provide a lower overall bulk density of the particles. To create such a coated particle, it can be precoated with reagent A, for example, a mixture of one or more high molecular weight alcohols with an appropriate catalyst (for example, amine). The particle is then exposed to reagent B containing diisocyanate. The finished foam is formed on the particle, for example, as a result of steam treatment with simultaneous shaking, stirring protects the particles from agglomeration as foam forms on their surfaces.

[00121] In embodiments of the invention, along with BSC, fibers, including biodegradable, can be added to the fracturing fluid. Fibers, including biodegradable ones, can form a cross-linked structure that promotes the transfer of proppant by liquid. The types of fibers added to a fracturing fluid are known to those skilled in the art. Those skilled in the art will understand that the fibers added to the fracturing fluid can decompose in a well environment and voids will form in the proppant pack. The resulting voids provide higher permeability and a greater number of channels for the influx of hydrocarbons from the reservoir into the wellbore.

[00122] The term "fiber" may refer to synthetic or natural fibers. As used herein, the term “synthetic fibers” includes fibers or microfibers that are manufactured industrially in whole or in part. Synthetic ones include artificial chemical fibers in which the natural precursor source material is modified to form fibers. For example, cellulose (derived from natural materials) can be made into man-made fibers such as Rayon (Rayon, rayon) or Lyocell. Cellulose can also be converted to cellulose acetate fibers. These artificial fibers are examples of synthetic fibers. Synthetic fibers can be obtained from synthetic materials - organic or inorganic. Typical synthetic fibers can be obtained from materials such as substituted or unsubstituted lactides, glycolides, polylactic acid, polyglycolic acid, or copolymers thereof. As is known to those skilled in the art, other materials for making fibers contain glycolic acid polymers or copolymers formed therefrom.

[00123] As used in this application, the term "natural fiber" refers to fibers or microfibers obtained from natural sources without artificial modification. Natural fibers contain fibers of plant, animal and mineral origin. Among the fibers of plant origin, cellulose, i.e. fibers of cotton, jute, flax, hemp, Chinese nettle, bast fiber of sisal and the like. Fibers of plant origin may include fibers derived from seeds or seed bolls, such as cotton or kapok. Fibers of plant origin may include fibers derived from leaves, for example, sisal and agave. Fibers of plant origin may include fibers obtained from the outer layer, peel or bast surrounding the stem of the plant, for example, flax, jute, kenaf, hemp, Chinese nettle, rattan; soybean fibers, tree vines, jute, kenaf, industrial hemp, nettle, rattan, soybean fiber and banana fiber. Fibers of plant origin may include fibers obtained from the fruits of plants, for example, coconut fiber. Fibers of plant origin may include fibers obtained from the stem of a plant, for example, wheat, rice, barley, bamboo and herbs. Vegetable fibers may include wood fibers. Fibers of animal origin usually contain proteins such as wool, silk, mohair and the like. Fibers of animal origin can be obtained from the hairline of animals, for example, wool of sheep, goats, alpacas, horses, etc. Fibers of animal origin can be obtained from parts of the animal organism: intestines, veins and tendons, etc. Fibers of animal origin can be obtained from dried saliva or other secretions of insects, or their cocoons; for example, silk is produced from silkworm cocoons. Fibers of animal origin can be obtained from bird feathers. Fibers of mineral origin are obtained from mineral raw materials. Fibers of mineral origin can be obtained from asbestos. They can be obtained from glass or ceramics, for example, staple fiberglass, quartz filament, alumina, silundum, boron carbon and the like.

[00124] Preferably, the fibers can be selected or produced in such a way that their decomposition will occur at certain pH or temperature, or over time, and / or have chemical compatibility with special carrier fluids used in proppant transfer. Suitable synthetic fibers can be produced, for example, from solid cyclic dimers, or solid polymers of organic acids capable of hydrolyzing under specific or adjustable conditions of pH, temperature, time, and the like. Preferably, the fibers can be destroyed under predetermined conditions in the places where they were transferred. Preferably, when the destruction of the fibers of the decay products were environmentally friendly.

EXAMPLES

Materials

- Sand fraction 30/70 mesh

- Sand fraction 30/50 mesh

- Sand fraction 40/70 mesh

- Polydialldimethylammonium chloride (Aldrich, St. Louis, Missouri)

- LPEI 500 (Polymer Chemistry Innovations, Tucson, Arizona)

- Ethyl alcohol 200 Proof (Aldrich, St. Louis, Missouri)

- Hexane (VWR, Radnor, PA)

- FLOPAM EM533 (SNF)

- Polyethylene glycol diglycidyl ether (Aldrich, St. Louis, Missouri)

- Glyoxal, solution, 40% of the mass. (Aldrich, St. Louis, Missouri)

- HFC-44 (Polymer Ventures, Charleston, South Carolina)

- Carboxymethyl cellulose, sodium salt (Sigma-Aldrich, St. Louis, Missouri)

- Ammonium persulfate (Sigma-Aldrich, St. Louis, Missouri)

- Surfactant ethoxylated lauryl alcohol (Ethal LA-12/80%)) (Ethox Chemical Co, South Carolina)

- Glycerin (US Glycerin, Kalamazoo, Michigan)

- Potassium Chloride (Morton Salt, Chicago, Illinois)

- Fine Silica (Cabot, Boston, Massachusetts)

[00125] Example 1: Obtaining an inner polymer layer

[00126] A 100 ppm inner polymer layer was obtained on a sand sample by adding 200 g of 30/70 mesh sand to a long FlackTek Max 100 container. 85 g of tap water and 2 g of 1% solution of polydiallyldimethylammonium chloride (PDAC) were added to the sand. Then, the sample was manually shaken for approximately 5 minutes, filtered in a vacuum filter and dried in an oven at 80 ° C. A sand sample was removed from the oven and used in a subsequent test.

[00127] A method similar to the above was used to create the inner layer of the polymer coating at 10 ppm, with the exception that only 0.2 g of a 1% PDAC solution was used.

[00128] A method similar to the above was used to create the polymer inner layer with maximum polymer loading (“Max PDAC”), with the exception that 1 g of a 20% (wt.) PDAC solution was used. After processing, the sand was washed in an excess volume of tap water, filtered in vacuo and dried in an oven at 80 ° C. A sand sample was removed from the oven and used in a subsequent test.

[00129] Example 2: Obtaining an inner polymer layer

[00130] An inner polymer layer with a concentration of 100 ppm was obtained on a sand sample by dissolving 0.2 g of LPEI 500 in 10 g of ethanol to obtain a 2% solution of LPEI 500 in ethanol. To 70 g of ethanol in a 250 ml round-bottom flask was added 0.75 g of a 2% LPEI 500 solution. Then, 150 g of 30/70 mesh sand was added to the round-bottom flask. The solvent was removed using a rotary evaporator with a water bath heated to 65 ° C. Then the sample was removed from the flask and used in a subsequent test.

[00131] Example 3: Obtaining the outer polymer layer

[00132] The outer polymer layers were applied to sand samples by mixing sand with a Flopam EM533 liquid polymer under various conditions. In one coating method, a pure polymer product was added. In another coating method, the polymer product was diluted with hexane. For dilution with hexane, 10 g of polymer was added to 10 g of hexane in 40 ml glass vial and the mixture was brought to a homogeneous state using a vortex mixer. The polymer was then added to 30 g of 30/70 mesh sand samples in FlackTek Max 100 containers. Samples were placed in a FlackTek DAC150 SpeedMixer for about 25 seconds at 2600 rpm. After that, the samples were removed from SpeedMixer and dried in an oven at 80 ° C overnight.

[00133] Example 4: Properties of the outer polymer layer. Deposition time

[00134] The evaluation of the properties of the sand samples prepared in the previous example was made based on the sedimentation test. Before testing, all sand samples were sieved through a 25 mesh sieve. The deposition time was determined by adding 1 g of a sand sample to 100 ml of tap water placed in a 100 ml measuring cylinder. Then the graduated cylinder was inverted 8 times, after which the time required for all the sand to settle on the bottom of the graduated cylinder was fixed. For each sample, time was fixed three times. The deposition time is presented in Table 1.

[00135] Example 5: Properties of the outer polymer layer, the thickness of the deposited layer

[00136] The sand samples obtained in Example 3 with an external polymer layer were also evaluated by observing the thickness of the deposited layer in water. In a 20 ml glass vial, 1 g of a sand sample was added to 10 g of tap water. To properly hydrate the sand, the vials are turned 10 times. Then the vials were left in a relaxed state for about 30 minutes. To measure the thickness of the deposited sand layer in the vial, a digital caliper was used. The results are presented in Table 2.

[00137] Example 6: Ionic crosslinking of the outer polymer layer

[00138] 40 g of the sand sample of the 30/70 mesh fraction was treated with polymer for the outer layer, for which 1.3 g of Flopam EM533 polymer was added to 40 g of sand placed in a FlackTek Max 100 container, after which the container was shaken manually for 2 minutes. Then the sand was sieved through a 25 mesh sieve. In order to assess the degree of polymer retention in the sand under shear conditions, tests were performed, for which 10 g of treated sand was added to a 300 ml test beaker with 200 g of tap water with various PDAC levels. It is believed that the PDAC ionic interaction will stabilize the polymer layer in the sand. Then, using an overhead stirrer with a propeller-type blade, the suspension was stirred for 5 minutes at 900 rpm. After stirring was stopped, the samples were allowed to stand for 10 minutes. The viscosity of the supernatant was measured using a Brookfield DV-III + rheometer with an LV-II spindle at 60 rpm. The thickness of the layer deposited in a glass of sand was measured using a digital caliper. The results are presented in Table 3.

[00139] Example 7: Covalent crosslinking of the outer polymer layer — DHE PEG

[00140] Four sand samples of fraction 30/70 were treated with Flopam EM533, for which 0.66 g of polymer was added to 20 g of sand placed in a FlackTek Max 100 container, after which the container was manually shaken for 2 minutes. Then, various amounts of freshly prepared 1% solution of polyethylene glycol diglycidyl ether (DHE PEG) in deionized water were added to the treated sand samples. Then, the samples were again manually shaken for 2 minutes, after which they were placed in an oven at 100 ° C for 1 hour. Samples were removed from the oven and sieved through a 25 mesh sieve. The layer thickness for four samples was measured by the following procedure: 1 g of a sand sample was added to a glass vial with a volume of 20 ml to 10 g of tap water; to properly moisten the sand, the vials were turned about 10 times, and then left alone for about 10 minutes. The thickness of the layer was measured using a digital caliper. The results are shown in Table 4.

[00141] Example 8: Covalent crosslinking of the outer polymer layer - glyoxal

[00142] Four sand samples of fraction 30/70 were treated with Flopam EM533, for which 0.66 g of polymer was added to 20 g of sand placed in a FlackTek Max 100 container, after which the container was manually shaken for 2 minutes. A 1% solution of glyoxal in ethanol was prepared by adding 0.25 g of 40% (mass.) Glyoxal to a glass vial with a capacity of 20 ml, after which the solution was adjusted to 10 g with ethanol. Then, various amounts of a 1% glyoxal solution were added to the treated sand samples; samples were manually shaken for 2 minutes and placed in an oven at 100 ° C for 30 minutes. Samples were removed from the oven and sieved through a 25 mesh sieve. To measure the thickness of the deposited layer, 1 g of sand was added to a 20 ml glass vial with 10 g of tap water, the vial was inverted 10 times and allowed to stand for 10 minutes. The thickness of the layer was measured using a digital caliper. The results are shown in Table 5.

[00143] Example 9: Cationic anionic polymer treatment

[00144] Three 30/70 mesh sand samples weighing 30 g were treated with Polymer Ventures HCF-44 in a FlackTek Max 100 container. The container was shaken manually for 2 minutes. Then, Flopam EM533 was added to each sample. The container was again shaken for 2 minutes. Next, the samples were dried at 80 ° C overnight. Samples were removed from the oven and sieved through a 25 mesh sieve. To measure the thickness of the deposited layer, 1 g of sand was added to a 20 ml glass vial with 10 g of tap water, the vial was inverted 10 times and allowed to stand for 10 minutes. The thickness of the layer was measured using a digital caliper. The results are presented in Table 6.

[00145] Example 10: Sand coated with particles of a high molecular weight polymer

[00146] Sand 30/70 mesh fraction weighing 30 g was placed in a FlackTek Max 100 container. 0.3 g of paraffin wax was added to the sand. The sample was placed in a FlackTek DAC 150 SpeedMixer, where it was mixed at 2500 rpm for 2 minutes. After stirring, 1 g of carboxymethyl cellulose was added to the sample. Then the sample was again placed in a FlackTek DAC 150 SpeedMixer, where it was mixed at 2500 rpm for a minute. Sand was sieved through a 25 mesh sieve. To measure the thickness of the deposited layer, 1 g of sand was added to a 20 ml glass vial with 10 g of tap water, the vial was inverted 10 times and allowed to stand for 10 minutes. In this sample, sand was instantly aggregated and did not disperse in water, so an accurate measurement of the layer thickness could not be made.

[00147] Example 11: Test modified sand in a glass

[00148] Sand 30/70 mesh fraction weighing 30 g was added to the FlackTek Max 100 container. The sand was treated with Flopam EM533, for which 0.45 g of polymer was added to the container and shaken manually for 2 minutes. The sample was then dried at 80 ° C overnight. After drying, the sample was taken out of the oven and sieved through a 25 mesh sieve. Upon completion of sieving, four samples were prepared; for this, 1 g of treated sand was added to a 20 ml glass vial with 10 g of tap water. The vials were turned over 10 times and left to stand for 10 minutes. A 10% solution of ammonium persulfate was obtained by adding 2 g of ammonium persulfate to 18 g of tap water. Then, various amounts of the resulting solution were added to the sample vials. The vials with samples were turned over several times, after which they were placed in an oven at 80 ° C for 1 hour. After an hour, the samples were removed and the thickness of the deposited layer was examined. The results are shown in Table 7.

[00149] Example 12: Additives for emulsions

[00150] In order to determine the effect of emulsion additives on the properties of self-suspending proppant (SSP), glycerol and Ethal LA-12/80% were added to the emulsion polymer EM533, before applying proppant to granular sand. Three different polymer samples were prepared as follows:

- SSP polymer: 10 g EM533, no additives

- BSC + glycerin: 9 g EM533 and 1 g glycerol

- BSC + glycerin + Ethal: 9 g EM533 + 0.9 g glycerol +0.1 g Ethal LA-12/80%.

[00151] Each of the above samples was brought to a homogeneous state with a vortex mixer within 30 seconds. To prepare a modified proppant, 50 g of sand fraction 40/70 mesh was combined with 1.5 g of one of the samples of the above polymer and mixed for 30 seconds. Samples of modified proppant were evaluated for shear resistance during the test of 1 liter of suspension. To conduct this test, 50 grams of the modified proppant was added to 1 liter of water placed in a square plastic cup, and then mixed using a paddle / vibration mixer (EC Engineering, model CLM-4) at 200 rpm (corresponding to a shear rate of about 550 sec ^-1 ) for a different amount of time. Then, the shear test samples were poured into a 1000 ml graduated cylinder and left to sediment under their own weight for 10 minutes, after which the thickness of the deposited proppant sand layer was recorded. For comparison, unmodified proppant sand after mixing for an unlimited time leads to the deposition of a layer with a thickness of 10 mm Samples of self-suspending proppant, in comparison with unmodified, give a higher level of the layer due to the hydrogel layer, in which sand grains are enclosed. In general, an increase in shear rate or time may cause a decrease in the thickness of the self-suspending proppant layer due to desorption of the hydrogel layer from the surface of the modified proppant. For this reason, in this test, it is desirable that the thickness of the deposited layer be as large as possible, especially after shear. The results below show that the addition of glycerol improves the layer thickness and shear resistance of the product. The addition of glycerol and Ethal, while initially improving the layer thickness, leads to a slight decrease in shear resistance in the long term. These results are shown in the graph of FIG. 6.

[00152] Example 13: Glycerin and technological characteristics

[00153] This test was aimed at determining the degree of influence of glycerol and other additives on the performance of self-suspending proppants (hereinafter referred to as SSP). 1 kg of dry sand fraction 40/70 mesh was added to the bowl of a stationary mixer KitchenAid model KSM90WH, equipped with a blade nozzle. 3.09 g of glycerol was mixed with 27.84 g of EM533 emulsion polymer, after which the mixture was added over sand and allowed to soak for 1 minute. At time “0”, the mixer was started at a speed of “1” (initial rotation speed - 72 rpm). Samples were taken at intervals of 1-2 minutes and dried for one hour at 90 ° C. Then, each sample was subjected to a shear test with 1 liter of suspension, for which 50 g of BSC was added to 1 L of water and mixed at 200 rpm (approximately corresponds to a shear rate of 550 sec ^-1 ) for 20 minutes. After transferring the water / MSP mixture to a 1 liter measuring cylinder and 10 minutes of settling, the layer thickness was recorded. The test was repeated with a weighed emulsion polymer EM533 in 30.93 g, separately added to 1 kg of sand. The results are shown in FIG. 7. As can be seen from the graph, the glycerin additive significantly increased the thickness of the layer.

[00154] The performance difference became even more noticeable when the test was repeated with higher stirring speeds. In this case, the mixer was set to “4” (initial rotation speed - 150 rpm). With a short mixing time, the samples were not sufficiently mixed, which led to an incomplete coating of sand and rapid desorption of the polymer from the surface of the SSP during the shear test. With an increase in the mixing time during the coating process, the performance also improved until the ideal coating was achieved, at which the maximum thickness of the deposited layer corresponded to this sample. After that, with an increase in mixing time, an exponential deterioration (decrease) in the thickness of the deposited layer was observed, which is possibly the result of mechanical abrasion of the coating surface with prolonged mixing. At higher mixing speeds, this process was even faster, so that the processing time interval for only one emulsion polymer was less than one minute. With the addition of glycerol and the use of lower mixing speeds, this interval increased to almost 15 minutes. Compared to tests with emulsion polymer only, the use of glycerol led to an extension of the processing time interval, indicating that the production of BSC with glycerin is more functional. At the same time, glycerin provided a more complete inversion of the polymer emulsion, leading to the formation of a reliable coating and an increase in the thickness of the deposited layer. The results of experiments with combinations of glycerol and emulsion polymer EM533 at elevated mixing speeds are shown in FIG. 8.

[00155] Example 14: Modified proppant with anti-caking agent

[00156] For comparison purposes, samples of modified proppants were obtained with and without the use of an anti-caking agent. For sample A, 50 g of 40/70 fraction sand was placed in a FlackTek container. 1.5 g of EM533 emulsion polymer was added to the sand and mixed for 30 seconds. After stirring, 0.25 g of calcium silicate was added to the sample and stirring was repeated for 30 seconds. The sample was then dried for 1 hour at 85 ° C. After drying, the sample was poured into a 25 mesh sieve and lightly shaken for 30 seconds. Then measured the amount passed through a sieve of sand. For sample B, 50 g of 40/70 fraction sand was placed in a FlackTek container. 1.5 g of EM533 emulsion polymer was added to the sand and mixed for 30 seconds. The sample was then dried for 1 hour at 85 ° C. After drying, the sample was poured into a 25 mesh sieve and lightly shaken for 30 seconds. Then measured the amount passed through a sieve of sand. The results are shown in Table 8.

[00157] The results of fractionation by particle size show that the introduction of an anti-caking agent effectively improved the technological properties of the modified proppant.

[00158] Samples A and B were separately added to 1 L of water and mixed using an EC Engineering Mixer for 20 minutes at 200 rpm. The shear test samples were transferred to a 1 L graduated cylinder and allowed to sediment for 10 minutes. After that, the thickness of the deposited layer was measured. The measurements showed that a significant loss of shear resistance as a result of the introduction of an anti-caking agent did not occur. The results are shown in Table 9.

[00159] Example 15: Coating sand with a hydrogel by dissolving a water-soluble polymer in a monomer composition followed by polymerization of the monomers

[00160] 2.5 g of a mixture of acrylic acid (Aldrich 147230), polyethylene glycol methyl ether acrylate (Aldrich 454990) and polyethylene glycol dimethacrylate (Aldrich 437441) in a molar ratio: 0.5 / 0.4 / 0.1 were mixed with 7, 5 g of polyethylene glycol (Aldrich 202371) and 1% of the mass. ammonium persulfate. The solution was mixed with 100 g of 30/70 mesh sand in an atmosphere of nitrogen and allowed to react at an elevated temperature of 70 ° C for 5 hours. Then, the resulting solid was washed with methanol, filtered under vacuum and dried at 80 ° C.

[00161] Example 16: Sand Coating with Polyurethane Hydrogel

[00162] 100 g of sand fraction 30/70 mesh was placed in a Hobart mixer and heated to 120 ° C. Then 6 g of polyethylene glycol (Fluka 81190) was added and mixed for 1 minute. Then, 0.53 g of Desmodur N75 from Bayer was added. After stirring for another 1 minute, one drop of a 1,4-diazabicyclo [2.2.2] octane catalyst (Aldrich D27802) was added and the resulting mixture was allowed to react for another 5 minutes. The resulting solid was washed with methanol, filtered under vacuum and dried at 80 ° C.

[00163] Example 17: Shear Test

[00164] The coated sand samples obtained in Examples 15 and 16 were tested for shear resistance. In a square glass with a capacity of 1.25 liters with a mark at the level of 1 liter was placed one liter of tap water. The beaker was then placed in an EC Engineering CLM4 paddle mixer. The speed of the mixer was set to 300 rpm. As soon as mixing began, 50 g of the coated sand sample was added to the beaker. After 30 seconds of stirring at 300 rpm, the speed was reduced to 200 rpm and stirring was continued for another 20 minutes. At the end, the mixture was poured into a measuring cylinder with a capacity of 1 l and left for precipitation. After 10 minutes, the thickness of the deposited layer was fixed. The results are shown in Table 10. The greater the thickness of the deposited layer, the higher the performance of the proppant.

[00165] Example 18: Resistance to salts

[00166] In two vials of 20 ml was added 10 ml of tap water. Separately, 10 ml of a 1% KCl solution was added to two other vials of the same volume. 1 g of sand prepared in Example 15 was added to a test tube containing tap water, and 1 g to a test tube containing KCl. In addition, 1 g of sand prepared in Example 6 was added to a test tube containing tap water, and 1 g to a vial with KCl. The vials were turned over ~ 7 times and left to stand for 10 minutes. After that, the thickness of the deposited layer was measured. The results are shown in Table 11.

[00167] Example 19: Abrasion Test

[00168] In three glasses of 250 ml was added 50 ml of tap water. One aluminum disk weighing 5.5-6 g was placed in each glass. Also, one two-inch (5.1 cm) magnetic stirrer was placed in each glass. All three glasses were placed on their slabs of magnetic mixers, the speed of which was set at mark 5. Six grams of sand fraction 40/70 was added to one of the glasses. Six grams of sand prepared in Example 15 was added to another glass. No sand was added to the third glass. The contents of the glasses were mixed for 2 hours. After stirring, the aluminum disk was removed, washed and dried. After that, the disks were weighed again. The results shown in Table 12 show that, compared with unmodified sand, sand prepared in example 15, led to less abrasion of metal surfaces.

[00169] Example 20: Effect of glycerol on mixing

[00170] 1 kg of dry sand of a 40/70 mesh fraction was added to a bowl of a KitchenAid model KSM90WH stationary mixer equipped with a paddle. 3.09 g of glycerol was mixed with 27.84 g of emulsion polymer, after which the mixture was added over sand and allowed to soak for 1 minute. At time “0”, the mixer was started at a speed of “4” (initial rotation speed - 150 rpm). Samples were taken at intervals of 1-2 minutes and dried for one hour at 90 ° C. Then, each sample was subjected to a shear test, for which 50 g of BSC was added to 1 L of water and mixed at a shear rate of 550 sec ^-1 ) for 20 minutes. After 10 minutes of deposition, the layer thickness was recorded. The results of the shear test are shown in FIG. 9. The graph shows that both inadequate and excessive mixing can adversely affect the behavior of coated proppants, leading to the dissociation of the polymer from the sand during the shear test. For this example, the optimal mixing time was from 5 to 20 minutes. The influence of the duration of mixing on the performance characteristics suggests that the coating in the wet state is brittle and becomes more resistant after drying. Compared to testing the emulsion polymer alone, coatings with glycerin mixed in the emulsion extend the processing interval (for example, an acceptable mixing time). In addition, coatings with glycerin mixed in the emulsion appear to contribute to a more complete inversion, resulting in improved coating properties, such as the thickness of the deposited layer.

[00171] Example 21: Production of self-suspending proppant using a screw mixer

[00172] To prepare a batch of self-suspending proppant, a 3 cc screw type mixer was used. feet (0.085 cubic meters). About 50 pounds (22.7 kg) of 40/70 mesh sand was added to the mixer screw. 756 g SNF Flopam EM533 was added to a 1 L beaker, 84 g of glycerol was mixed into the polymer. The entire mixture was evenly distributed over the surface of the sand in the mixer screw. Then, the auger mixer was turned on at a speed of about 70 rpm. Samples were taken after 30, 60, 120, 180, 240, 300, 420 and 600 seconds from the start of mixing. Samples were dried for 1 hour. After drying, 50 g of each sample was added to 1 L of water and stirred for 20 minutes using an EC Engineering CLM4 mixer at 200 rpm. Then the samples were transferred to a 1 L graduated cylinder and left to settle for 10 minutes. After deposition, the layer thickness was measured. The results are shown in Table 13.

[00173] Example 22: Aging in a humid environment

[00174] 400 g of self-suspending proppant (CSP) was prepared as described in Example 15. 400 g of CSP were separated into 50 g samples and left in closed containers at room temperature. After drying with different durations, the samples were tested as described in example 21. The results are presented in Table 14.

[00175] Example 23: SSP + uncoated proppant

[00176] In a 20 ml vial, 10 ml of tap water was added. Then proppant sand was added to the vial - MPS prepared according to Example 15 and unmodified, fractions 40/70. The vials were turned over several times and left to settle for 10 minutes. After settling, the thickness of the deposited layer was measured. The results are shown in Table 15.

[00177] Example 24: Anti-caking agents added to the BSC

[00178] A 400 g batch of SSP was prepared as described in Example 15. The sample was divided into 50 g samples, after which 0.25 g of finely divided silica with a particle size of 80 nm was mixed into each sample. Then the samples were closed and aged at room temperature. Next, the samples were tested in accordance with the description in example 21. The results are shown in Table 16.

[00179] Example 25: Respiratory fraction

[00180] 200 g of samples of hydrogel coated sand and uncoated sand (40/70 mesh fraction) prepared in accordance with Example 15 were sieved through a 140 mesh sieve. Fine particles passing the sieve were collected and weighed. A hydrogel coated sand sample showed an 86% reduction in the amount of fine particles compared to an uncoated sand sample. The results are shown in Table 17.

[00181] Example 26: Anti-caking agents with different particle sizes

[00182] 50 g of sand fraction 40/70 mesh using a high-speed mixer was mixed with 2 g of SNF Flopam EM533 for 30 seconds at 800 rpm. Then 0.625 g of anti-caking agent was added and stirring was repeated for 30 seconds. Next, the samples were kept for 3 hours, after which they were subjected to a shear test for 20 minutes. Samples were left to settle for 10 minutes, and then the layer thickness was measured. The results are shown in Table 18. Anti-caking agents improved the layer thickness index after shear testing over a wide range of particle sizes.

[00183] Example 27: Chemical composition of anti-caking agents

[00184] A wide variety of anti-caking agents were tested (see Table 19). For each additive, 700 g of sand 40/70 fractions were mixed using a KitchenAid mixer with a mixture of 21.65 g of 10% glycerol and 90% EM533 at a speed of "1" (144 rpm). The mixture was divided into samples weighing 50 g, after which they were mixed with an appropriate amount of anti-caking agent in a high-speed mixer. Three samples that were mixed, respectively, with 1% calcium silicate, 1.5% diatomaceous earth and 1.5% kaolin were immediately subjected to shear tests; while the 7 remaining samples were dried for one hour in an oven at 80 ° C together with a control sample without the addition of an anti-sinter. All samples were tested by the method described in example 17. Table 19-A shows the results of measurements of the thickness of the deposited layer after shear testing of water-saturated (non-dried) samples with an anti-caking agent added. Table 19-B shows the results for dried (1 hour at 80 ° C) samples with a caking agent.

[00185] Example 28: Anti-caking agent: amounts needed upon drying

[00186] Seven samples of 40/70 sand weighing 50 g were placed in small plastic containers, followed by the addition of 2 g of a mixture of 10% glycerol / 90% emulsion polymer to each of them. After stirring rapidly for 30 seconds, 0.25 g, 0.375 g, 0.5 g, 0.675 g, 0.75 g, 1 g and 2.5 g of calcium silicate powder were added to the seven samples, after which the sand was again mixed for 30 sec Samples were sheared without a subsequent drying step, and the deposited layer was measured in mm. The results are shown in FIG. 10. A similar experiment was carried out using silica as an anti-caking agent. The test data showed that sand coated with a hydrogel layer can be treated with a caking agent, resulting in a product that does not require a separate drying step to obtain an acceptable thickness of the deposited layer after the shear test.

[00187] Example 29: Anti-caking agents based on silicon dioxide

[00188] 50 g of sand fraction 40/70 mesh was placed in a small container, followed by the addition of 2 g of a mixture of 10% glycerol with 90% EM533. The contents of the container were stirred at 800 rpm for 30 seconds, then the appropriate amount of finely divided silica was added (see Table 20) and stirred again for 30 seconds. The sample was subjected to a shear test for 20 minutes, after which the thickness of the deposited layer was measured. Drying in the oven was not used. The results are presented in Table 20.

[00189] A batch of coated sand was mixed in a KitchenAid mixer and divided into several 50 g samples. Then, 1% (mass) of finely divided silica with different particle sizes was added to each of the three samples, mixed and subjected to a shear test. The test results are shown in Table 21.

[00190] Example 30: Pre-heating sand

[00191] 500 g of sand fraction 30/50 was placed in an oven at 90 ° C for 1 hour and was mixed from time to time until the sand temperature reached equilibrium. Then the sand was mixed using a commercial planetary mixer until it reached the required preheating temperature (45 ° C, 60 ° C or 80 ° C), at which 20.8 g SNF Flopam EM533 was added to the sample and mixed for 7 minutes After that, the batch was separated and dried in an oven at 80 ° C with various lengths of time. For samples that did not undergo preheating, 500 g of sand of a 30/50 mesh fraction was placed in a mixer bowl with 20.8 g of a polymer emulsion, mixed for 7 minutes, and then dried with different lengths of time. All samples were shear tested using the following standard procedure: 50 g of sand was added to 1000 g of tap water, stirred at a shear rate of 550 sec ^-1 for 20 minutes, and then precipitated for 10 minutes in a 1 liter volumetric cylinder. The results are shown in FIG. 11. The results suggest that sand pre-heating to 45 ° C is acceptable, however, during shear tests at 60-80 ° C, the layer thickness was less.

[00192] Example 31: Active Ventilation Drying

[00193] 50 g of sand fraction 40/70 was mixed with 4% emulsion polymer (2 g), prepared by the method described in example 14 using a high-speed mixer for 30 seconds. The sample was transferred to a container equipped with a hot air gun, which was set at 90, 95 or 100 ° C. The sample was left under a hot air gun for a total of 30 minutes, while taking samples weighing 5 g after 5, 10, 15 and 30 minutes. Next, the samples were subjected to a short shear test, which was performed as follows: 100 ml of tap water in a 300 ml beaker, in which a two-inch (about 5.1 cm) magnetic stirrer was placed, began to mix at a speed of 500 rpm; 5 g of a sand sample was added to the beaker and subjected to shear for 3 minutes; then the whole solution was transferred to a 100 ml measuring cylinder, turned over once and left for 5 minutes to precipitate, the layer thickness was measured. The test results are shown in FIG. 12. As can be seen from the graph, an increase in the temperature of the injected air led to more complete drying and an increase in the layer thickness. To test the susceptibility of BSC to shear stress during drying by active ventilation, a laboratory rake with seven teeth was used, which mixed the sample, reproducing the effort of shear during drying. Two batches of SSP of 50 g each were obtained and dried in a stream of air at 110 ° C for 30 min. The first batch was in a completely stationary state, the second was constantly mixed with a rake during the entire 30-minute drying period. Both samples were subjected to a shear test for 20 minutes with 10 minutes of deposition. The thickness of the deposited layer of the sample dried in a static state was 100.63 mm; sample dried with gentle stirring - 109.49 mm

[00194] Example 32: Mixing with a vertical screw

[00195] A small vertical screw mixer was designed to conduct this test. Sand and organic polymer SNF Flopam EM533 were added to the container, which were then mixed by rotating the screw at a speed of 120 rpm. Then, the sample was divided into two parts of 50 g, one of which was dried in an oven at 80 ° C, and the other was mixed with 0.5 g (1% wt.) Of finely divided silica. Both samples were subjected to a shear test, as described in Example 17. The results of measurements of the thickness of the deposited layer were as follows: “Dried in the oven, 1 hour” had a thickness of the deposited layer of 101.34 mm; “Unsaturated, with 1% highly dispersed silica with a particle size of 7 nm” - 91.47 mm. Both oven drying and the addition of an anti-sinter to dry the product provided a significant layer thickness.

[00196] Example 33: Microwave Drying

[00197] 50 g of sand fraction 40/70 mesh was placed in a small plastic container, then mixed with 2 g of the composition containing 10% glycerol and 90% emulsion polymer in a high-speed mixer at 800 rpm for 30 seconds. The sample was placed in a 700 W microwave oven and heated at a maximum value of 45 seconds. The sample was sieved, cooled and then sheared in an EC Engineering CLM4 mixer at 200 rpm for 20 minutes. After stirring, the sample was transferred to a 1 L graduated cylinder and allowed to sediment for 10 minutes. After deposition, the layer thickness was measured in millimeters, which turned out to be 52.43 mm. Microwave drying provided acceptable results with a relatively short drying time.

[00198] Example 34: Mixing and heating with anti-caking agents

[00199] 500 g of sand fraction 40/70 was mixed using a KitchenAid mixer with 20 g of the composition (20% glycerol / 80% emulsion) for 8 minutes. Next, 0.44% of finely divided Cabot EN-5 silica was added and the product was stirred for 2 minutes, after which the sample was heated using a hot air gun. 50 gram samples were taken after 13, 18, 24 and 26 minutes from the time of mixing. Samples were sheared for 20 minutes; after which the layer thickness was recorded. The results are shown in FIG. 13. The combination of glycerol and silicon dioxide provided a longer treatment interval.

[00200] Example 35: Microwave Drying

[00201] 400 g of a 30/50 sand fraction was mixed with 16 g (4% by weight) of an emulsion polymer prepared as described in Example 14, and then mixed in a KitchenAid stationary mixer for 7 minutes. One 50 gram sample was dried in an oven at 80 ° C; the remaining 7 samples were placed in a 700 W microwave oven for 5, 10, 20, 30, 45, 60, and 120 seconds, respectively. A shear test (lasting 20 minutes) was carried out as described in example 12, after which the loss on ignition (SPP) of the samples was determined. The method for determining losses during calcination was to add 10 g of sand to a weighed crucible, which was then placed in an oven at 960 ° C for 1 hour. After heating for one hour, the crucible was cooled in a desiccator for 1 hour and then weighed. Drying time, layer thickness and SPP are shown in Table 22. The difference between the initial and final mass was expressed as a percentage of the total initial mass of sand, as shown in FIG. fourteen.

[00202] These tests suggest that the microwave drying method removes mainly water, rather than an oil component, from coated samples.

[00203] Example 36: Vacuum drying

[00204] 250 g of sand fraction 30/50 was mixed with 10 g of emulsion polymer, as described in example 14. The sand mixture was mixed in a stationary mixer KitchenAid at minimum speed for 7 minutes, then separated into samples weighing 50 g and dried in vacuum furnaces with a residual pressure of 24 inches (602.4 mm) of mercury and temperatures of 25 ° C, 50 ° C and 85 ° C for 1 hour, 1 hour and 30 minutes, respectively. Samples were cooled at room temperature, sieved and shear tested (as described in example 12) for 20 minutes. The results are shown in Table 23.

[00205] During the tests, not a single sample was completely dried, although a higher temperature may contribute to a more complete drying.

[00206] Example 37: Coating sand with a hydrogel using micellar polymerization

[00207] 250 g of sand fraction 30/70 was placed in 500 ml of a pre-degassed aqueous solution containing 0.6 mM hexadecyltrimethylammonium bromide surfactant (CTAB) (equivalent to 2/3 of the critical micelle concentration for CTAB), and 6 mM monomer ( a mixture of acrylic acid / acrylamide in a molar ratio of 30/70). The adsorption of CTAB and monomer on a sand particle was carried out with gentle stirring for 24 h at 25 ° C. Then 0.6 mM ammonium persulfate was added to the reactor and polymerization was carried out for 3 hours at 80 ° C. Excess polymer and surfactant were washed off with several volumes of water and the resulting sample was dried in a vacuum oven at 80 ° C overnight.

[00208] Example 38: Coating sand with a hydrogel using reverse slurry polymerization

[00209] 60 ml of DI water, 6.6 g of acrylamide, 3 g of acrylic acid, 2.4 g of N, N'-methylenebisacrylamide, 0.1 g of ammonium persulfate, 2.0 g of sodium chloride and 2 drops of N were placed in the flask. , N, N ', N'-tetramethylethylenediamine. To the resulting solution was added 200 g of sand fraction 30/70 and the temperature of the resulting mixture was maintained <10 ° C. 200 ml of cyclohexane was added to the mixture, and the resulting mixture was stirred vigorously under nitrogen. Then the temperature was raised to 60 ° C and the reaction was allowed to proceed for 6 hours. The resulting coated particles were filtered off, washed with hot water, acetone and dried at 45 ° C under reduced pressure.

[00210] Example 39: Coating Polymer

[00211] A proppant coating mixture was prepared by combining 10 g of glycerol and 90 g of Flopam EM533 in a glass vessel and mixing for 30 seconds using a vortex mixer. The resulting polymer mixture was used in the following examples.

[00212] Example 40: Obtaining a self-suspending proppant ("BSC") fraction 40/70

[00213] A 40/70 fraction BSC sample was prepared by adding 500 g of 40/70 sand to a KitchenAid mixer bowl. To the sand was added 20 g of the coating polymer of Example 39. The mixer was turned on in mode 1 and sand and polymer were mixed for 7 minutes. After stirring, the sample was dried for 1 hour at 85 ° C. After 1 hour, the sample was taken out of the oven and all the lumps were broken into separate grains.

[00214] Example 41: Obtaining a self-suspending proppant ("BSC") fraction 30/50

[00215] A 30/50 BSC sample was prepared by adding 500 g of 30/50 sand to a KitchenAid mixer bowl. To the sand was added 20 g of the coating polymer of Example 39. The mixer was turned on in mode 1 and sand and polymer were mixed for 7 minutes. After stirring, the sample was dried for 1 hour at 85 ° C. After 1 hour, the sample was taken out of the oven and all the lumps were broken into separate grains.

[00216] Example 42: Reduced fine content in a self-suspending proppant (“MOP”) compared to sand

[00217] A standard set of mesh screens was prepared with a 40 mesh sieve at the top, 70 mesh in the middle, and a tray at the bottom. The tare mass of each clean and dry sieve was measured and recorded. 50 g of BSC fraction 40/70 from Example 20 was placed on top of a set of sieves, and the set of sieves was shaken manually for five minutes. After shaking, each set was disassembled and weighed. The mass of the substance remaining on each sieve was calculated as a percentage of the initial mass of the sample, and the amount of sample remaining on the tray was a fine fraction determined by a transmission threshold of 70 mesh. The procedure was repeated, replacing the unmodified sand fraction 40/70 on MSP fractions 40/70. Table 24 shows the results of the distribution of particle sizes for SSP fraction 40/70. Table 25 shows an analysis of particle size distribution for unmodified sand fraction 40/70. The results show that the amount of material passing through a 70 mesh sieve is reduced for the BSC fraction 40/70 (1.2% compared to 4.8%). This shows that MSP may contain fewer fine particles than a sand sample.

[00218] Example 43: Friction Reduction

[00219] 1 L of tap water was placed in a square glass, and the glass was placed in an EC Engineering CLM-4 mixer. The mixer was turned on and a mixing speed of 200 rpm was set. To the tap water was added 120 g of BSC fraction 30/50 from Example 21. The suspension was stirred for 20 minutes, then transferred to a 1 L volumetric cylinder and allowed to sediment for 10 minutes. After precipitation, the supernatant was collected. This procedure was repeated until 2 L of supernatant was collected. The friction reduction in the collected fluid was measured using a closed loop apparatus. The closed loop consisted of a 0.12 inch (0.3 cm in. Diameter) stainless steel test tube and a length of 3 feet (91 cm) and a pump providing a constant flow rate of 55 gallons / hour (208 l / hour). These conditions corresponded to a Reynolds number of 23,000, which confirmed the turbulent flow of the liquid. The percentage reduction in friction (% CT) was determined experimentally by measuring the pressure at the inlet and outlet of the test tube at a constant flow rate. The percent reduction in friction was calculated according to the following equation:% CT = 100 * (1- (ΔP _i / ΔP ₀ )), where ΔP _i is the pressure drop along the test pipe when using supernatant fluid SSP, and ΔP ₀ is the pressure drop along the test pipes when using tap water. The pressure values were ΔP _i = 11.8 psi (81 MPa) and ΔP ₀ = 38.5 psi (265 MPa), which corresponded to a decrease in friction (% ST) of 69%. This shows that the SSP makes a significant contribution to reducing the pressure in the associated fluid, thereby reducing pump requirements.

[00220] Example 44: Hydraulic Conductivity Tests

[00221] To simulate hydraulic conductivity by simulating proppant packaging, 48 g of MSP fraction 30/50 from Example 21 was mixed with 1 L of water. Ammonium persulfate was added at a concentration of 0.1% and the resulting mixture was heated at 185 ° F (85 ° C) for 1 hour. After cooling to room temperature, the mixture was filtered through a column with an inner diameter of 2.25 inches (5.7 cm) with a 100 mesh sieve at the bottom to separate particles from the liquid. The particles formed a 0.5-inch (1.27 cm) layer on a 100 mesh grid, and the flow rate of various liquids through the layer was measured by flow under gravity. A layer of ordinary sand was made in a similar way and the costs were compared with the costs obtained for the layer of SSP. In this method, the costs obtained for SSP (yield 250 ml in 28 seconds) and ordinary sand (yield 250 ml in 25 seconds) were almost the same, showing that SSP, after treatment with oxidative destructors such as ammonium persulfate, does not have any undesirable impact on the hydraulic conductivity of the sand layer or imitation of proppant packing.

[00222] Example 45: Self-Suspending Proppants (“BSCs”) with anti-caking agents

[00223] In addition to the fact that anti-caking agents are capable of replacing the drying step, they can be used to generally improve the usability of the BSC. A number of different finely divided materials were tested as anti-caking agents, as shown in table 26 below. To prepare samples for each material, 800 g of 30/50 sand was mixed in a KitchenAid mixer at a speed of 1 (144 rpm) with 32 g of coating polymer according to Example 19. A 20 g sample was taken and mixed with the selected anti-caking agent in mixer, the dose of anti-caking agent was calculated as a percentage of the total sand content in the sample. The consistency of the sample was noted and recorded as “appearance before drying”, and then dried for 1 hour at 85 ° C. Consistency was noted again and recorded as “appearance after drying”. Then, the samples were subjected to 80% -90% relative humidity at 25-35 ° C for one hour to evaluate the anti-caking properties, and the consistency was noted and recorded as “appearance after exposure to humidity”. The results are shown in table 26 below and show that the anti-caking agent improves the handling comfort of the BSC, where flowability is a desirable feature.

[00224] Example 46: Processing of polymer coated sand SMA 4000i

[00225] The polymer coated sand was coated with an SMA 4000i by adding 25 g of polymer coated sand to a 250 ml round bottom flask. Separately, 0.25 g of SMA 4000i was dissolved in 3.57 g of tetrahydrofuran (THF) to give a 7% solution. Then, 1.43 g of a solution in THF was added to the polymer coated sand in a round bottom flask. More THF was added to the round bottom flask until the sand was coated. THF was then evaporated from the sample using a rotary evaporator.

[00226] Example 47: Processing of sand with a polymer coating SMA 4000i

[00227] The polymer coated sand was coated with an SMA 4000i by adding 25 g of polymer coated sand to a 250 ml round bottom flask. Separately, 0.25 g of SMA 4000i was dissolved in 3.57 g of tetrahydrofuran (THF) to give a 7% solution. Then, 0.72 g of a solution in THF was added to the polymer coated sand in a round bottom flask. More THF was added to the round bottom flask until the sand was coated. THF was then evaporated from the sample using a rotary evaporator.

[00228] Example 48: Processing of polymer coated sand SMA 2000i

[00229] The polymer coated sand was coated with an SMA 2000i by adding 25 g of polymer coated sand to a 250 ml round bottom flask. Separately, 0.25 g of SMA 2000i was dissolved in 3.57 g of tetrahydrofuran (THF) to give a 7% solution. Then, 1.43 g of a solution in THF was added to the polymer coated sand in a round bottom flask. More THF was added to the round bottom flask until the sand was coated. THF was then evaporated from the sample using a rotary evaporator.

[00230] Example 49: Processing of sand with a polymer coating SMA 2000i

[00231] The polymer coated sand was coated with an SMA 2000i by adding 25 g of polymer coated sand to a 250 ml round bottom flask. Separately, 0.25 g of SMA 2000i was dissolved in 3.57 g of tetrahydrofuran (THF) to give a 7% solution. Then, 0.72 g of a solution in THF was added to the polymer coated sand in a round bottom flask. More THF was added to the round bottom flask until the sand was coated. THF was then evaporated from the sample using a rotary evaporator.

[00232] Example 50: Treatment of polymer coated sand Pluronic L31

[00233] The polymer coated sand was coated with the Pluronic Surfactant L31 surfactant by adding 20 g of polymer coated sand to a small FlackTek container. 0.025 g of surfactant was added to the polymer coated sand. The sample was then mixed using a FlackTek Speedmixer at 800 rpm for 30 seconds.

[00234] Example 51: Treatment of polymer coated sand Pluronic L35

[00235] The polymer coated sand was coated with the Pluronic Surfactant L35 surfactant by adding 20 g of polymer coated sand to a small FlackTek container. 0.025 g of surfactant was added to the polymer coated sand. The sample was then mixed using a FlackTek Speedmixer at 800 rpm for 30 seconds.

[00236] Example 52: Treatment of polymer coated sand Pluronic L81

[00237] The polymer coated sand was coated with the Pluronic Surfactant L81 surfactant by adding 20 g of polymer coated sand to a small FlackTek container. 0.025 g of surfactant was added to the polymer coated sand. The sample was then mixed using a FlackTek Speedmixer at 800 rpm for 30 seconds.

[00238] Example 53: Processing of ARQUAD® 2HT-75 polymer coated sand

[00239] The polymer coated sand was coated with ARQUAD® 2HT-75 by adding 25 g of polymer coated sand to a 250 ml round bottom flask. Separately, 0.25 g of ARQUAD® 2HT-75 was dissolved in 3.57 g of IPA to give a 7% solution. Then, 0.72 g of a solution in IPA was added to the polymer coated sand in a round bottom flask. Another IPA was added to the round bottom flask until the sand was coated. Then, IPA was evaporated from the sample using a rotary evaporator.

[00240] Example 54: Processing of sand with a polymer coating ADOGEN® 464

[00241] The polymer coated sand was coated with ADOGEN® 464 by adding 20 g of polymer coated sand to a small FlackTek container. 0.025 g ADOGEN® 464 was added to the polymer coated sand. The sample was then mixed with a FlackTek Speedmixer at 800 rpm for 30 seconds.

[00242] Example 55: Polymeric coating mixture

[00243] 9 g of Flopam EM 533 (SNF) was combined with 1 g of glycerol in a 20 ml vessel. Then the vessel was stirred for 30 seconds in a vortex mixer.

[00244] Example 56: Hydrogel coating of sand samples

[00245] Sand samples were prepared by placing 20 g of the images obtained in Examples 46 through 54 into small FlackTek containers. 0.6 g of the coating mixture obtained in Example 35 was added to each container. The contents of the containers were mixed at 800 rpm using a FlackTek mixer. Then the samples were dried for 30 minutes at 100 ° C. After drying, 1 g of each sample was placed in a 20 ml vessel containing 10 ml of tap water. The vessels were gently mixed for 1 minute, and then allowed to stand for 10 minutes. After deposition, the layer thickness was measured to determine polymer hydration. The results are shown in table 27.

[00246] Example 57: Test for aging under wet conditions (metal chelating crosslinking agents)

[00247] Tyzor TE is a titanium and triethanolamine chelate, 80% solution in ethanol. Tyzor TEAZ is a 100% active chelate product of zirconium and triethanolamine. These metal chelates were dispersed in castor oil at various concentrations and applied to the proppant in a second additional step of the coating process. Coated proppant samples were prepared by adding 3 g of a mixture of Flopam EM533 and glycerol to 100 g of white sand proppant fraction 30/50 mesh in a FlackTek Max 100 container. Then the samples were mixed in a FlackTek Speedmixer mixer at 850 rpm for 30 seconds. Samples were then removed from the mixer and, in some cases, treated with a metal chelate / castor oil mixture. Then the samples were returned to the mixer and mixed at a speed of 850 rpm for 30 seconds. Then the samples were removed from the mixer, transferred to a watch glass and dried at 100 ° C for 30 minutes in a laboratory oven with forced air circulation. After drying, the samples were sieved through an 18 mesh sieve. For aging under wet conditions, 50 g of the finished samples were placed in Max 100 FlackTek containers and left in a humid chamber for 1 hour. Relative humidity in the chamber was maintained in the range of 60-70%. After exposure to moisture, the samples were tested in a Carver Press cell (internal diameter 2.25 inches — approximately 5.715 cm) with an applied load of 1000 l (454 kg) for 30 seconds. Tracking of the samples was evaluated visually and compared with the control (without a second addition). The degree of caking of the samples was evaluated from 1 to 4, with a rating of "1" denoted a solid piece, and a rating of "4" denoted a loose, non-caked material. The results are shown in table 28.

[00248] (Caking estimates for table 14: ʺ1ʺ - A hard piece that does not crumble during manipulations, ʺ2ʺ - An almost hard piece that begins to break during manipulations, '' 3 '' - A piece crumbles when removed from the press, ʺ4ʺ - There is no piece formation) .

[00249] Example 58: Test aging in wet conditions (powdered additives)

[00250] Coated proppant samples were prepared by adding 3 g of Flopam EM533 / glycerin mixture to 100 g of white sand proppant fraction 30/50 mesh. Samples were mixed in a FlackTek Speedmixer at 850 rpm for 30 seconds. Then the samples were removed from the mixer and in some cases treated with dry powder. Then the samples were returned to the mixer and mixed at a speed of 850 rpm for 30 seconds to uniformly distribute the powder in the sample. Then the samples were removed from the mixer, transferred to a watch glass and dried at 100 ° C for 30 minutes in a laboratory oven with forced air circulation. After drying, the samples were sieved through an 18 mesh sieve. For aging under wet conditions, 50 g of the finished samples were placed in Max 100 FlackTek containers and left in a humid chamber for 1 hour. Relative humidity in the chamber was maintained in the range of 60-70%. After exposure to moisture, the samples were tested in a Carver Press cell (internal diameter 2.25 inches — approximately 5.715 cm) with an applied load of 1000 l (454 kg) for 30 seconds. Tracking of the samples was evaluated visually and compared with the control (without a second addition). The degree of caking of the samples was evaluated from 1 to 4, with a rating of "1" denoted a solid piece, and a rating of "4" denoted a loose, non-caked material. The results are shown in table 29.

[00251] (The caking estimates for Table 15 are: ʺ1 Т - A hard piece that does not crumble during manipulations, ʺ2ʺ - An almost hard piece that begins to break when manipulated, ʺ3ʺ - A piece crumbles when removed from the press, ʺ4 Нет - There is no lump formation).

[00252] Example 59: Oil-based additives

[00253] Some oily or relatively hydrophobic materials were tested to determine their effectiveness in reducing caking of wetted samples of self-suspending proppant (BSC). Samples were prepared by mixing 300 g of sand fraction 30/50, pre-heated to 45 ° C, with 9 g of a mixture of 10% glycerol / 90% Flopam 533 in a KitchenAid mixer at a speed of 1. After 1 minute of mixing, a second additive (usually 0.2 % by weight of sand) and mixed for another minute. The sample was dried under medium shear conditions using a hot air gun and a KitchenAid mixer. Then the samples were placed in a chamber with a relative humidity> 50% for 1 hour. The caking behavior of the individual samples was then tested, subjecting them to a compression test. The specified test consisted of compression under pressure of 200 PSI (1379 MPa) for 30 seconds in the compression cell using Carver Press, then the sample was removed from the cell and examined. The resulting piece (see Table 16, compression test) was evaluated on the following scale: ʺ1ʺ - A solid piece that does not crumble during manipulations, ʺ2ʺ - An almost hard piece that begins to break down during manipulation, ʺ3ʺ - A piece crumbles when removed from the press, ʺ4ʺ - No the formation of a piece, as shown in table 30.

[00254] A sample treated with Adogen 464 had difficulty forming a lump in the present test, even at a lower dosage.

ANALOGUES AND EQUIVALENTS

[00255] Although specific embodiments of the invention are provided herein, the above description is illustrative and not limited. Although the invention has been described in detail and presented with reference to preferred embodiments thereof, one skilled in the art will understand that various changes in form and detail can be made without departing from the scope of the invention encompassed by the appended claims. After reading the present description, specialists in the art will be apparent numerous variants of the invention. Unless otherwise indicated, all numbers reflecting reaction conditions, amounts of ingredients and the like, and used in the present description and claims, should be understood as having in all cases the context of the term "about". Accordingly, unless otherwise indicated, the numerical parameters set forth herein are approximate and may vary depending on the properties, the acquisition of which is the purpose of the present invention.

[00256] Although the present invention has been specifically shown and described with reference to preferred embodiments of the present invention, one skilled in the art will recognize that various changes in form and detail can be made without departing from the scope of the present invention covered by the appended claims.

Claims (15)

1. A modified proppant containing a proppant substrate particle coated with a hydrogel-forming polymer, said proppant substrate particle comprising a resin-coated proppant and an adhesion promoter bonding the hydrogel coating to the resin-coated proppant. 2. The modified proppant according to claim 1, characterized in that said adhesion promoter is selected from the group consisting of a block copolymer containing simultaneously hydrophobic and hydrophilic monomers, a fatty amine, a poly-quaternary amine and a cationic surfactant. 3. The modified proppant according to claim 2, characterized in that said adhesion promoter is a block copolymer of styrene and maleimide. 4. Modified proppant according to any one of paragraphs. 1-3, characterized in that the type and amount of the hydrogel-forming polymer is selected so that the modified proppant is simultaneously self-suspending in a water-based hydraulic fracturing fluid and is wear-resistant from the point of view of maintaining self-suspension after shearing at a shear rate of about 550 s ^-1 for 20 minutes. 5. The modified proppant according to claim 4, characterized in that said proppant is free flowing after exposure to relative humidity of about 80% -90% for one hour at a temperature of from 25 ° C to 35 ° C. 6. Modified proppant according to any one of paragraphs. 1-3, characterized in that the hydrogel-forming polymer is selected from the group consisting of polyacrylamide, copolymers of acrylamide with anionic and cationic comonomers, hydrolyzed polyacrylamide, copolymers of acrylamide with hydrophobic comonomers, polyacrylic acid and salts of polyacrylic acid. 7. The modified proppant according to claim 6, characterized in that the hydrogel-forming polymer is an anionic polyacrylamide. 8. The modified proppant according to any one of paragraphs. 1-3, characterized in that the hydrogel-forming polymer is crosslinked in an amount sufficient to prevent premature hydration of the modified proppant due to moisture. 9. The modified proppant according to claim 8, characterized in that the cross-linking agent is covalent and selected from the group consisting of epoxide, anhydride, aldehyde, diisocyanate and carbodiamide. 10. Modified proppant according to any one of paragraphs. 1-3, characterized in that the hydrogel-forming polymer coating on the particle of the proppant substrate includes an alcohol selected from the group consisting of ethanol, propanol, ethylene glycol, propylene glycol and glycerol. 11. The modified proppant according to claim 1, further comprising a hydrophobic outer layer on said hydrogel coating, said hydrophobic outer layer selected from the group consisting of fatty acids, aliphatic amines, hydrophobic quaternary amines, aliphatic amides, hydrogenated oils, vegetable oils, castor oil oils, triacetin, waxes, polyethylene oxides and polypropylene oxides. 12. The modified proppant according to claim 11, characterized in that said hydrophobic outer layer contains a hydrophobic quaternary amine. 13. The modified proppant according to claim 1, characterized in that the type and amount of the hydrogel-forming polymer is selected so that the modified proppant is self-suspending in a water-based hydraulic fracturing fluid, said modified proppant being additionally combined with a sufficient amount of dry powder to substantially reduce the tendency modified proppant to caking when exposed to wet conditions. 14. The fracturing composition containing the modified proppant according to any one of paragraphs. 1-13 and an oxidative destructor or enzymatic destructor. 15. A method of producing a hydrogel coated proppant, comprising: providing a proppant substrate particle and a composition comprising a coating precursor, said coating precursor being able to form a hydrogel coating on the surface of the proppant substrate particle by in situ polymerization; applying said composition to a proppant substrate particle; and polymerizing the coating precursor in direct contact with the coating substrate particle to form a hydrogel coated proppant.

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