MX2014012609A - Self-suspending proppants for hydraulic fracturing. - Google Patents

Abstract

The invention encompasses a modified proppant comprising a proppant particle and a hydrogel coating, wherein the hydrogel coating localizes on the surface of the proppant particle to produce the modified proppant. The invention also encompasses formulations comprising the modified proppant as well as methods for the manufacture and methods for the use of the modified proppant.

Description

SELF-SUSPENSION SCREWS FOR HYDRAULIC FRACTURATION RELATED REQUESTS This application claims the benefit of the provisional application of the United States of America Series No. 61 / 635,612 filed on April 19, 2012, of the provisional application of the United States of America Series No. 61 / 662,681, filed on September 21, June 2012, of the provisional application of the United States of America Series No. 61 / 725,751, filed on November 13, 2012, and of the provisional application of the United States of America Series No. 61 / 764,792, filed on April 14, 2012 February 2013. The complete contents of the above-mentioned applications are incorporated by reference here.

FIELD OF THE APPLICATION This application generally refers to the systems and methods for fracturing technologies.

BACKGROUND In the process of fracturing oil and / or gas from a well, it is often necessary to stimulate the flow of hydrocarbons through hydraulic fracturing. The term "fractural" refers to the method of pumping a fluid inside a well until the pressure increases to a level that is sufficient to fracture the underground geological formations that contain the trapped materials. This process results in cracks and breaks that disrupt the underlying layer to show the product of. hydrocarbon to be taken to the hole in the well at a significantly higher rate. Unless the pressure is maintained, however, the newly formed openings close. In order to open a trajectory and maintain this, a proppant or "proppant" agent is injected together with the hydraulic fluid to create a necessary support to preserve the opening. When the fissure is formed, the proppers are delivered in a solution where, with the release of the hydraulic pressure, the proppers form a package that serves to keep the fractures open.

To achieve the placement of the proppant within the fracture, these particles are suspended in a fluid that is then pumped to the underground destination. To prevent the particles from settling, a high viscosity fluid is frequently required to suspend them. The viscosity of the fluid is typically handled by the addition of synthetic polymers or natural base. These are three common types of polymer-enhanced fluid systems in general use for suspending and transporting proppant during fracture operations: oily water, linear gel and crosslinked gel.

In oily water systems, an anionic or cationic polyacrylamide is typically added as a friction-reducing addictive, allowing maximum fluid flow with minimal pumping energy. Since the pumping energy requirements of hydraulic fracturing are high, in the order of 10,000 to 100,000 horsepower, a friction reducer is added to the oily water fluids to allow for high pumping rates while avoiding the need of even higher pumping energy. Although these polymers are effective as friction reducers, they are not highly effective as viscosifiers and suspending agents. Oily water polymer solutions typically contain 0.5 to 2.0 gallons of friction reducing polymer per 1,000 gallons of oily water fluid, and solutions have a low viscosity, typically in the order of centipoise to 15 centipoise. At this low speed, the suspended propping articles can easily settle out of the suspension as soon as the turbulent flow is stopped. For this reason, oily water fluids are used in fracturing phases that do not have either proppant, proppant with a small particle size, or have low proppant charges.

The second type of fluid system improved with polymer is known as a linear gel system. The Linear gel systems typically contain carbohydrate polymers such as guar, hydroxyethyl cellulose, guar hydroxyethyl, guar hydroxypropyl, and hydroxypropyl cellulose. These linear gel polymers are commonly added at a usage rate of 10 pounds to 15 pounds of polymer per 1,000 gallons of linear gel fluid. These concentrations of linear gel polymer result in a fluid with improved proppant suspension characteristics against the oily water fluid. Linear gel fluids are used to transport the proppant at load levels of about 0.1 pounds to 1 pound proppant per gallon of fluid. Above the proppant loading level, a more viscous solution is typically required to make a stable suspension.

The crosslinked gel is the most viscous type of polymer enhanced fluid used to transport the proppant. In crosslinked gel systems, the linear gel fluid as described above is crosslinked with added reagents such as borate, zirconate, and titanate in the presence of alkali. With the crosslinking of the linear gel fluid in a crosslinked gel fluid, the viscosity is much higher and the proppant can be effectively suspended. Linear gel and crosslinked gel fluids have certain advantages but they require a high dose rate of expensive polymer.

The modifications of propping particles can be used advantageously to improve their performance in hydraulic fracturing systems. First, if the proppant particles were more floating, a less viscous suspension fluid could be used, which would still carry the particles to the target area but which would be easier to pump into the formation. Secondly, it is desirable that the proppant remain where they are placed through the life of the well after they have been injected into the fracture line. If changes within the reservoir during the production of the well force the proppers out of position, the production equipment can be damaged, and the conductivity of the reservoir formation can be lessened by clogging the pores of the reservoir by displacing the reservoirs. propping up Third, the proppers in the system must be resistant to the closing tension once they are placed in the fracture. The closing voltages can vary from 1,700 pounds per square inch in certain shale gas wells, up to and exceeding 15,000 pounds per square inch for deep high temperature wells. Care must be taken that the proppant does not fail under these stresses, unless they are crushed into fine particles that can migrate to undesirable locations in the well, thereby affecting production. Desirably, a proppant must resist diagenesis during fracture treatment. The high pressures and temperatures combined with the chemicals used in s Fractal fluids can adversely affect propping particles, resulting in their diagenesis, which can eventually produce fine particle matter that can scale out and decrease well productivity over time.

The current proppant systems and the polymer-enhanced fracturing fluids are intended to address these concerns, so that the proppant can be carried by the fracturing fluids, can remain in place once they reach their target destination, and can withstand the closing stresses and stresses in the formation. One approach to preparing suitable proppant includes coating the propping materials with resins. A proppant coated with resin can be either fully cured or partially cured. The fully cured resin can provide crush resistance to the proppant substrate by helping to distribute the stresses between the grain particles. A fully cured resin can also help reduce the migration of fines by encapsulating the proppant particle. If it is partially cured initially, the resin can be completely cured once it is placed inside the fracture. This approach can give the same benefits as the use of a resin that is completely cured initially. The resins, although they can decrease the conductivity and the permeability of the fracture, even when the proppant are maintaining their opening. Also the resins can fail, so that their advantages are lost. Resin-based systems tend to be expensive and are prone to settle out of suspension.

In addition, these are health, safety and environmental concerns associated with the handling and processing of the proppant. For example, fine ("thin") particles, such as crystalline silica dust, are commonly found in naturally occurring sand deposits. These fines can be released as a powder that can be breathed during the handling and processing of the proppant sand. With chronic exposure, this dust can be harmful to workers, resulting in various conditions associated with inhalation such as silicosis, chronic obstructive pulmonary disease, lung cancers and the like. In addition to these health effects, fines can cause a "noisy dust" problem such as equipment fouling and environmental contamination.

Another approach to preparing suitable proppant involves mixing additives with proppant itself, such as fibers, elastomeric particles and the like. The additives, however, can affect the rheological properties of the transport solution, making it more difficult to deliver the proppant to the desired locations within the fracture. In addition to the use of additives can interfere with the uniform placement of the proppant mixture inside the fracture site. Although there are methods known in the art to refer to the limitations of propping systems, there are still some problems. There is therefore a need in the art for improved proppant systems that allow precise placement, preserve fracture conductivity after placement, protect well production efficiency and equipment life, simplify hydraulic fracturing operations, reduce environmental impact and promote the health and safety of the worker. It is even more desirable that such improved systems be cost effective.

SYNTHESIS Embodiments of a modified proppant, comprising a proppant particle and a hydrogel coating, wherein the hydrogel coating is located on the surface of the proppant particle to produce the modified proppant are described herein. In the incorporations, the proppant particles comprise sand or comprise a substrate coated with resin. In additional incorporations, the proppant particle comprises bauxite, sintered bauxite, ceramic or lower density materials. In embodiments, the modified proppant further comprises an adhesion promoter, wherein the adhesion promoter fixes the hydrogel coating to the resin coated substrate. In some embodiments, the hydrogel coating comprises a polymer swellable in water. In embodiments, the hydrogel coating comprises a polymer selected from the group consisting of polyacrylamide, poly (acrylic acid), carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, guar gum, carboxymethyl guar, carboxymethyl hydroxypropyl guar gum, hydrophobically swellable emulsion polymers. associates, and latex polymers. In some embodiments, the modified proppant further comprises a pair of cationic / anionic polymer comprising a cationic polymer and a high molecular weight anionic polymer. In some embodiments, the cationic polymer is selected from the group consisting of poly-DADMAC, LPEI, BPEI, chitosan, and cationic polyacrylamide. In some embodiments, the modified proppant further comprises a cross-linking agent. The cross-linking agent may comprise a covalent cross-linked linker. The covalent crosslinker may comprise a functional group selected from the group consisting of an epoxide, an anhydride, an aldehyde, a diisocyanate and a carbodiamide. The covalent crosslinker can be selected from the group consisting of polyethylene glycol, diglycidyl ether, epichlorohydrin, maleic anhydride, formaldehyde, glyoxal, glutaraldehyde, toluene diisocyanate, and methylene diphenyl diisocyanate, 1-ethyl-3- (3-dimethylaminopropyl) carbodiamide. In some embodiments, the cross-linking agent comprises an organometallic compound. In additions, the modified proppant also comprises a hydrophobic layer, the which can be selected from the group consisting of fatty acids, hydrogenated oils, vegetable oils, castor oil, waxes, polyethylene oxides, and polypropylene oxides. In some embodiments, the modified proppant comprises a chemical breaker, for example an oxidative breaker. In additions, the modified proppant also includes a delayed hydration addictive. The delayed hydration additive can be selected from the group consisting of a low hydrophobic-lipophilic balance surfactant, an exclusion agent capable of excluding a finished surfactant, a light ionic cross-linking agent, a light covalent cross-linking agent, and a monovalent salt charge protector. In some embodiments, the modified proppant further comprises an alcohol which can be selected from the group consisting of ethylene glycol, propylene glycol, glycerol, propanol and ethanol. In some additions, the modified proppant also comprises an agent against glazing. In some embodiments, the hydrogel coating comprises an additive, which can be a chemical additive. In some additions, the additive is an indicator or chemical breaker. In some additions, the modified proppant contains less fines than a proppant particle that is not modified. In the incorporations, the hydrogel coating comprises an additive, which may be a chemical additive or an indicator.

The invention further encompasses a hydraulic fracturing formulation comprising a modified proppant particle described herein.

In addition, formulations comprising a modified proppant as described herein are described herein. Also described herein are methods for fracturing a well, comprising preparing the hydraulic fracture formulation as described herein, and introducing the hydraulic fracturing formulation into the well in an effective volume and at an effective pressure to hydraulically fracture, thus fracturing the water well.

Also described herein are methods for making a modified proppant, comprising providing a proppant substrate particle and a fluid polymer coating composition; applying the fluid polymeric coating composition on the proppant substrate particle, wherein the fluid polymeric coating composition comprises a hydrogel polymer and wherein the hydrogel polymer is located on the surface of the proppant substrate particle to produce the proppant modified. In some embodiments, the fluid polymeric coating comprises a kind of cross-linking. In some embodiments, the method further comprises the step of drying the modified proppant. In some additions, manufacturing takes place at or near the point of use of the modified proppant. In some additions, the proppant substrate particle comprises sand, which can be obtained at or near the point of use for the modified proppant. In some embodiments, the method further comprises the step of adding an alcohol selected from the group consisting of ethylene glycol, propylene glycol, glycerol, propanol, and ethanol during or before the step of applying the fluid polymeric coating composition on the substrate particle. proppant In some embodiments, the method further comprises a step of adding an inversion promoter during or after the step of mixing the proppant substrate particles and the fluid polymer coating composition. In additions, the method further comprises the step of adding an agent against apastelation to the modified proppant.

Also described herein are methods for making a hydrogel-coated proppant, comprising providing a proppant substrate particle and a formulation comprising a coating precursor, wherein the coating precursor is capable of forming a hydrogel coating on the particle. proppant substrate by in situ polymerization; apply the formulation to the proppant substrate particle; and polymerizing the coating precursor in juxtaposition to the proppant substrate particle to form the hydrogel-coated proppant.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a flow chart of a manufacturing process for self-supporting proppant.

Figure 2 is a graph of bed height (millimeters) versus cut-off time (minutes) for self-supporting proppant, auto-suspension proppant + glycerol and auto-suspension proppant + etal.

Figure 3 is a graph of bed height (millimeters) versus cut-off time (minutes) for samples with glycerol and without glycerol.

Figure 4 is a graph of bed height (millimeters) versus cut-off time (minutes) for glycerol and glycerol-free samples.

DETAILED DESCRIPTION 1. Modified Fixed Particles The systems and methods for forming and using the proppant particles having a hydrogel surface layer to improve the hydrodynamic volume of the proppant particles during the transport of fluid are described herein, creating a more stable proppant suspension that resists sedimentation, separation and sandblasting before the proppant can reach the target destination attempted in the fracture. Additional benefits of the hydrogel-coated proppant as described herein include a lower tendency to erode the equipment, a lower coefficient of friction in the wet state, a good bonding bond with one another after placement in a site of fracture, a resistance to the formation of uncontrolled fines, and properties against soiling attributable to the hydrophilic surface. In some embodiments, the systems described for forming proppant particles can be applied to the most widely used types of proppant substrates, for example, sand and ceramics. In other embodiments, the proppant particles can be formed from a variety of substrates, including fibrous materials, as will be available to those having ordinary skill in the art. In certain embodiments, the proppant particles can be manufactured so that they can withstand crushing or deformation, so that they resist displacement, and so that they can be suspended in less viscous fluid carriers for transporting into the formation.

In some additions, these self-supporting proppant are formed by modifying a particle substrate with a polymer coating inflatable in water such as a hydrogel. In some embodiments, the particle substrate can be modified with the polymer coating before the particle substrate is introduced into the fracturing fluid. In some embodiments, the amount of hydrogel polymer coating may be in the range of about 0.1 about 10 percent based on the weight of the proppant. In some embodiments, the hydrogel layer applied on the surface of the proppant substrate may be of a coating thickness of about 0.01 percent to about 20 percent of the average proppant substrate diameter. With the hydration and swelling of the hydrogel layer in the fracturing fluid, the hydrogel layer can be made to be expanded with water, so that the thickness of the hydrogel layer can be made from about 10 percent to about 1,000 percent of the average diameter of the proppant substrate.

Methods for modifying proppant include spraying or saturation of a liquid polymer formulation on the proppant substrate, followed by drying to remove water or other carrier fluids. The drying process can be accelerated by the application of heat or vacuum, and by flipping or stirring the proppant modified during the drying process. The heating can be applied by forced hot air, by connection, friction, conduction, combustion, exothermic reaction, microwave heating or infrared radiation. Agitation during The proppant modification process may have an additional advantage of providing a more uniform coating on the proppant material.

Figure 1 shows an example of a manufacturing process for self-suspending proppant using dried sand and a liquid polymer. In the embodiment shown, the sand is carried into a mixing vessel, and a liquid polymer composition is sprayed through a pump and spray nozzles onto the sand along the conveyor belt. The sand and the liquid polymer report to a mixing container, low cut, where the ingredients are also mixed. After mixing, the modified sand containing the liquid polymer is sent to a dryer to remove the water and / or the organic carrier fluids associated with the liquid polymer. After the drying step, the modified sand is passed through a size sorting equipment, such as a screen, to remove the larger agglomerates. Mechanical mixers, cutting devices, mills or grinders can be used to break the aggregates to allow the material to pass through the appropriately sized screen. The finished material is then stored for shipping or use.

In some additions, the sand that is used to produce the self-supporting proppant is pre-dried at a moisture content of < 1 percent, and preferably < 0.1 percent before being modified with a hydrogel polymer. In some embodiments, the sand temperature at the time of mixing with the liquid polymer is in the range of about 10 degrees centigrade to about 200 degrees centigrade, and preferably in the range of about 15 degrees centigrade to about 60 degrees centigrade. .

In some embodiments, the sand is brought into contact with the liquid polymer composition by means of spraying or injection. The amount of liquid polymer composition added is in the range of from about 1 to about 20 percent, and preferably from about 2 to about 10 percent by weight of the sand. The sand and liquid polymer are mixed for a period of about 0.1 to about 10 minutes. In a preferred embodiment, the mixing equipment is a type of relatively low cutting mixer, such as a tumbler, a vertical cone screw mixer, a V-cone blender, a double cone blender, a ribbon blender. In some additions, the mixing equipment can be equipped with forced air, hot forced air, vacuum, external heating or other means to cause the evaporation of the carrier fluids.

In some additions, the modified sand containing the liquid polymer is dried to remove the water and / or the organic carrier fluids associated with the polymer liquid. The dryer equipment that can be a transport oven, a microwave or a type of rotary oven. In one embodiment the drying step is carried out in a manner such that the modified and dried sand contains less than 1 weight percent residual liquids, including water and any organic carrier fluids associated with the liquid polymer composition.

In some additions, the same equipment can be used to mix the sand with the liquid polymer and to dry the mixed product in a single processing phase, or in a continuous production line.

In other embodiments, methods for proppant modification include the synthesis of a hydrogel coating at the site, or in the presence of the proppant particle, resulting in a hydrogel layer that encapsulates the surface of the proppant particle. As an example, the in situ synthesis of the hydrogel can be achieved by combining proppant particles with coating precursor monomers and / or macromonomers followed by the polymerization step. In other exemplary cases, a water-soluble polymer can be dissolved in monomers, with or without a solvent, followed by polymerization in the presence of proppant particles, resulting in the formation of interpenetrating polymer networks as a coating on the proppant. In other example cases, the soluble polymer in Water is dispersed in the monomers with or without solvent, and the subsequent polymerization will result in proppant encapsulated by a hydrogel consisting of water-soluble polymer particles fixed by the newly formed polymer. The monomers or macromonomers used can be selected from monomers that result in water soluble polymers. In other exemplary cases, the particles may be encapsulated by a polymer not soluble in water which will then be modified or hydrolyzed to give the water-soluble hydrogel coating. As understood by those of ordinary skill in the art, the encapsulation layer can be formed by different polymerization techniques, with or without solvents. The in situ polymerization of the polymer on the surface of the proppant grains can have the advantage of reducing or eliminating the drying steps.

By way of example, a water-soluble monomer or monomers can be chosen from the following monomers or salts thereof: acrylic acid, methacrylic acid, acrylamide, methacrylamide, and their derivatives, carboxyethyl acrylate, hydroxyethyl methacrylate (HEMA), hydroxyethyl acrylate (HEA), polyethylene glycol acrylates (PEG-acrylates), N-isopropyl acrylamide (NiPA), 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS), sodium salt of styrene sulfonate, vinyl sulfonic acid, acid ( Meth) allylsulfonic, vinyl phosphonic acid, N-vinylacetamide, N-methyl-N-vinylacetamide, N-vinylformamide, N-methyl-N- vinylformamide, N-vinyl pyrrolidone, N-butyrolactam or N-vinylcaprolactam, malic anhydride, itaconic acid, vinyl acetate, dimethyldiallylamino chloride, quaternized dimethylaminoethyl methacrylate (DMAEMA), (meth) acrylamido propyl trimethylammonium chloride, methyl vinyl chloride imidazolium, 2-vinyl pyridine, 4-vinyl pyridine, and the like The proportion of ionic to non-ionic monomers can be selected to give hydrogels with different charge densities In some cases, for example, it is desirable to have hydrogels with a charge higher in order to give coatings with a more rapid hydration or swelling property In other cases the ionizable monomers can be selected to have higher or lower ionization constants to give the hydrogels more or less a stable condition in brine environments Other advantageous properties can be imparted by selecting appropriate loading densities.

In some embodiments, the coating precursors may include polyfunctional monomers that contain more than one polymerizable group and that will introduce cross-linking or branch points in the hydrogel. Examples of these monomers are pentaerythritol triallyl ether, PEG-diacrylates and methacrylates, α, β-methylenebisacrylamide, epichlorohydrin, divinyl sulfone, and glycidyl methacrylate. When such monomers are used, the crosslinked monomer will be in the range of 0.001 to about 0.5 percent of the monomer content total. In the selection of a range to cross linkers, one should be aware that adding excessive amounts of crosslinker can form brittle hydrogels that can fracture or degrade under pressure and add insufficient amounts of crossed linkers can form hydrogels that are easily detached from the surface particle under extreme conditions.

In some embodiments, the monomers / macromonomers used are selected from coating precursor monomers that will form a coating not soluble in water. After the coating is applied, its further modification will result in the water-swellable polymer. As an example, a polymeric coating containing hydrolyzable groups can be formed, and subsequent hydrolysis will give the hydrogel. Examples of the monomers that fall into this category are esters, anhydrides, nitriles and amides; for example the methyl acrylate monomers, T-butyl acrylate can be used. As another example, a monomer containing vinyl functionalities can form the hydrogel by different polymerization techniques with or without solvents. Polymerization techniques include volume, suspension, admixing, and solution polymerization.

In other embodiments, the coating monomers or precursors can be selected to form a self-supporting proppant with a hydrogel comprising a polyurethane or polyurea. A list of suitable monomers for forming polymers with polyurethane and / or polyurea functionalities are: polyols such as ethylene glycol, propylene glycol, glycerin, trimethylol propane, 1,2,6-hexanetriol, penteritritol, sorbitol, sucrose, methyl glycoside, polyoxyalkylenes such as PEG, copolymers of PEG-PPG, Pluronics, Tetronics, polyamines such as JEFFAMINE® polyetheramines. The isocyanates include toluene diisocyanate, naphthalene diisocyanate, xylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, trimethylene diisocyanate, trimethyl hexamethylene diisocyanate, cyclohexyl-1,2-diisocyanate, cyclohexylene-1, 4 -diisocyanate and the like. Other suitable polymers may include HYPOL® hydrophilic polyurethane prepolymers from Dow, DESMODUR® and MONDUR® resins from Bayer (2, '-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate and mixtures thereof), and CONATHANE® (functionalized polyisocyanate prepolymers). of toluene diisocyanate and poly (tetramethylene glycols)) of Cytec and the like.

The coating of proppant particles with polyurethane hydrogel (PU) can be carried out by conventional methods. In one embodiment, the coating can be carried out in volume without the use of solvents. For example, a typical formulation for a polyurethane hydrogel Cross-linked can be prepared in a single-pass volume polymerization process using a diisocyanate, a polyoxyalkylene, and a cross-linked multifunctional agent. In one embodiment, the formulation will contain from 10 to 80 percent of the polyoxyalkylene having the polyoxyalkylene molecular weight of between 200 and 25,000.

Another method for forming the hydrogel layer in situ can be carried out by dissolving or suspending a water soluble polymer in a monomer formulation followed by the polymerization of the monomer. The monomers can be selected from the previous list of water soluble monomers. In the case that the water soluble polymer is dissolved in the monomer mixture, the resulting coating will consist of an interpenetrating hydrogel network of the initial water soluble polymer and the polymer formed in situ. In the case where the water-soluble polymer is suspended in the monomer mixture, the resulting coating will consist of a hydrogel coating in which the water-soluble particles are fixed or entrapped. For example, these particles can be trapped within the newly formed hydrogel coating or these can be attached to the newly formed polymer. The water soluble polymer can be dissolved or suspended in the monomer formulation in the presence or in the absence of a solvent and the polymerization can be carried out by different techniques.

Suitable water-soluble polymers can be mixed with monomers and can be selected from the group consisting of polyacrylamide, polyacrylic acid, copolymers of acrylamide with acrylic acid salts, polyethylene glycol, polyvinyl pylorridone, polyvinyl alcohol, carboxymethyl cellulose, hydroxyethyl cellulose , hydroxypropyl cellulose, guar gum, carboxymethyl guar, carboxymethyl hydroxypropyl guar gum, hydrophobically associable swellable emulsion polymers, starches, latex polymers and the like.

Another method for modifying the proppant particles includes hydrophilic graft polymers on the particle. The grafting of polymer chains on the surface of the particle can be done by reactions such as Huisgen cycloaddition and other addition or coupling reactions that can immobilize the polymers on the particle surface.

The proppant particle used for these purposes can be selected to have surface functional groups such as epoxy, vinyl, amine, hydroxyl, etc. These groups can still react with the polymers having groups capable of reacting with the functional groups on the particle surface. For example, proppant particles comprising silica can be modified from surface by silanes such as aminosilanes, vinylsilanes, epoxysilanes, and the like.

In some embodiments, the polymers that will react with the functionalized particle are linear or branched hydrophilic polymers or copolymers. The polymer may have one or more graft halves. In some embodiments, the polymers may have functional groups such as amino, carboxyl or salts thereof, hydroxyl, thiol, acid anhydride, acid chloride and / or diisocyanate groups capable of covalent attachment to the functional groups of the particle. Examples of the polymers that can be used to react with the functionalized particle are: functionalized PEG epoxide, functionalized PEG amine, functionalized PEG azide, polyethylene imine, polyacrylic acid, polyvinyl alcohol, and the like.

In some embodiments, the resulting hydrogel, in addition to having inflatable properties, may have pH response or temperature response properties. The resulting inflatable proppant properties can therefore be refined. This is an added benefit for transporting the proppant to the hole in the well, since temperatures are lower in the early phases in which the proppant is transported and the complete inflation behavior is desirable; the higher temperatures are expected within the fractures where the swelling more low of the hydrogel layer is desirable for a packing improvement. The monomers used to make the hydrogel-coated proppant that respond to temperature can be selected from N-isopropylacrylamide (NiPA), ethylene oxide, propylene oxide, or polymers / macromonomers that exhibit a lower critical solution temperature (LCST). .

In one embodiment, the process of bringing a substrate such as sand into a self-suspending proppant can be conducted at or near the point of use, for example, to an oil or gas well site in preparation for hydraulic fracking. . The method may have the advantage of converting a comfort material with high materials handling costs, such as sand, into a specialized material having added characteristics. The sand can be purchased from local sources or it can be sent directly from a sand beneficiation site or a warehouse, for modification at the point of use. This avoids having to send the sand first into a mixing plant and then sending it in a second time from the mixing plant to the point of use. In the case of sand, the shipping costs may be higher than the costs of the material, so avoiding extra shipping is desirable to control costs.

The hydrogel polymers that can be used to modify the proppant according to the systems and methods described herein can be introduced, in some incorporations, such as oil-based emulsions, dispersions, water-based emulsions, latex solutions, and dispersions. In some embodiments, the hydrogel polymer may be an alkali swellable emulsion, wherein the hydrogel properties of the polymer are not fully developed until the polymer is brought into contact with the alkali. In this embodiment, the alkali-swellable emulsion can be coated on the proppant substrate to form a modified proppant, and this modified proppant can be suspended in a fracturing fluid in the presence of an alkaline material.

In some additions, an additive such as an alcohol selected from the group consisting of ethylene glycol, propylene glycol, glycerol, propanol and ethanol can be added during or before the step of mixing the proppant substrate particles and the liquid polymer coating composition. In some embodiments, the investment promoters useful as additives in the polymer coating formulations for the self-suspending proppant can include the high lipophilic hydrophilic balance surfactants, such as the polyethylene oxide lauryl alcohol surfactant, (ETHAL LA-12/80% of ETHOX), ethylene glycol, propylene glycol, water, sodium carbonate, sodium bicarbonate, ammonium chloride, urea, barium chloride, and mixtures thereof. In some additions, investment promoters can serve the function of facilitating the release of the active polymer ingredients from the internal phase of an oil-based emulsion polymer into the process fluid (typically aqueous) to be treated. Since this process converts a continuous oil polymer into a continuous water environment, it can be characterized as a phase inversion.

In other embodiments, the proppant substrate can be modified with a polymer formulation, without the need for a drying step. This can be achieved by the use of a solvent-free polymer formulation, or a curable formulation. In certain simplified methods, a dry or liquid polymer formulation can be applied to the proppant substrate through in-line mixing, and the modified material thus prepared can be used without further processing. The moisture content of the proppant substrate can be modified by the addition or removal of water, or the addition of other liquids, to allow the substrate to be effectively coated, handled and delivered into the fracturing fluid.

The modified proppant can also be modified with a wetting agent such as a surfactant or other hydrophilic material to allow effective dispersion in the fracturing fluid. When the proppant modified with hydrogel are suspended in a fracturing fluid, they are considered to be self-regulating. suspension if these require a lower viscosity fluid to prevent particles from settling out of the suspension.

The modified proppant can also be modified with an anti-glaze agent such as calcium silicate, calcium carbonate, talc, kaolin, bentonite, diatomaceous earth, silica, colloidal silica, or microcrystalline cellulose to improve flow properties and handling of the proppant material modified. The anti-glaze agent-modified proppant can have improved handling properties, such as free-flowing properties, resistance to lumping, ease of transport, ease of dosing and ease of discharge from a storage or transport container. In some additions, the proppant modified with the agent or agents against the glaze may have reduced drying requirements, so that the finished product can be produced with a reduced amount of energy, a reduced amount of time and equipment.

The hydrogel-modified proppant of the invention can advantageously use a concentration of polymer located on the surface of the proppant, in contrast to the traditional approach of making the medium viscous full fluid. This localized hydrogel layer can allow a more efficient use of the polymer, so that a The lower total amount of the polymer can be used to suspend proppant, in comparison, for example, with conventional polymer-enhanced fracturing fluids such as oily water, linear gel and crosslinked gel. Although the hydrogel-modified proppant is considered to be self-suspended, it can be used in combination with friction reducers, linear gels and cross-linked gels.

The hydrogel-modified proppant as described herein may have the advantage of delivering the friction reducing polymer into the fracturing fluid, so that other friction reducing polymers may not be required or may be required in smaller quantities when the proppant modified with hydrogel They are used in hydraulic fracturing operations. In some embodiments, some of the hydrogel polymer can be desorbed from the proppant surface to deliver friction reduction benefits or viscosity characteristics to the fracturing fluid. Even though the example incorporations here focus on the use of hydrogel-modified proppant for hydraulic fracturing purposes, other uses for hydrogel-modified proppant can be provided, when their water retention or friction reduction capabilities can be exploited. For example, the proppant modified with hydrogel can be used to absorb water from humid environments, form water retention particles that can be removed from the environment, carry with them undesirable moisture. As another example, hydrogel-modified proppant can be used in situations where adding water to the environment can be advantageous. A hydrogel-modified proppant can be saturated with water or an aqueous solution and can then be used, for example, as a soil remedy additive in a dry environment. The proppant modified with hydrogel can be formed of sand or other substrates that are compatible with the sand and these can be transported to the area of interest in dry form; these can then be saturated with water and used as an environmental modification. In other embodiments, the hydrogel modified proppant can be used as a modification of the earth in dry form, where they can absorb and retain moisture from the environment, irrigation, falling rain and the like. In these embodiments, the moisture retention properties of the hydrogel-modified proppant can be advantageously used. In some embodiments, the modified proppant with hydrogel can be used to reduce erosion of the upper soil, seed beds, mixtures of hydrosemillas, and the like. In some additions, the hydrogel modified proppant can be used as a vehicle to introduce other compatible agents into the region, for example on the ground. The hydrogel-modified proppant may include additional formulations that are released outside or through of the hydrogel layer inside the environment, either as the hydrogel degrades or as it absorbs moisture and expands. Examples of these formulations include fertilizers, seeds, plant growth regulators, herbicides, pesticides, fungicides, and the like. Other uses for the hydrogel-modified proppant according to these formulations and methods can be provided which are consistent with their properties described herein.

The hydrogel polymer used for the preparation of hydrogel-modified proppant can, in embodiments, comprise polymers such as polyacrylamide, copolymers of acrylamide with anionic and cationic comonomers, copolymers of acrylamide with hydrophobic comonomers, poly (acrylic acid), poly ( acrylic acid), carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, guar gum, alginate, carrageenan, locust bean gum, carboxymethyl guar gum, carboxymethyl hydroxypropyl guar gum, hydrophobically-binding swellable emulsion polymers (HASE), latex polymers, starches, and similar. In some embodiments, the hydrogel polymer can be crosslinked to improve the water absorbency and swelling properties of the polymer. The crosslinkers can be introduced as an element of the hydrogel-based polymer or these can be introduced as chemical modifiers for the preformed polymers.

The location of the polymer around the proppant surface as described herein can result in a more effective use of the polymer and can prevent the proppant from sitting out of the polymer solution. In some additions, the polymer layer hydrates around the proppant effectively avoiding proppant / proppant (interparticle) contact. This can prevent the proppant from forming a compact seated bed and can result in a proppant that is easy to resuspend in the fracturing fluid. The resuspension properties for modified proppant can be important if fluid flow is interrupted during hydraulic fracturing operations. In this case, when the flow is summarized, it is important that the proppant can be suspended again to prevent proppant loss or unintended blockage of the fluid path.

The polymer surface modifications as described herein can cause an increase in the hydrodynamic radius of the proppant particle when the polymer swells. This can result in an increased drag on the proppant as well as an effective change of the hydrogel / general particle density. Both can result in a proppant particle with a slower settling rate and superior transport properties.

In some embodiments, the polymeric or ionic crosslinking can be used to improve the retention of hydrogel polymer on the surface of the propping particles. For example, a cationic polymer can be deposited on the proppant as a first layer to "fix in place" a second layer containing a hydrogel such as a high molecular weight anionic polymer. In embodiments, the cationic polymer may be polydiallyldimethylammonium chloride (poly- (DADMAC), linear polyethylene imine (LPEI), branched polyethylene imine (BPEI), chitosan, epichlorohydrin / dimethylamine polymer, ethylene dichloride, dimethylamine polymer, or cationic polyacrylamide. The cationic polymer layer can be placed on the proppant either before or after the modification of the proppant surface with the anionic hydrogel layer.The ionic interaction can act as a cross-linking mechanism to help prevent the polymer Anionic is desorbed in high cut environments such as going through a pump or pumping down the well bore.The cationic polymer can also improve polymer retention by causing a delay in hydration and extension of the anionic polymer chains.It is believed that less polymer chain extension during the process Pumping will give a higher polymer retention on the proppant (for example less desorption).

The covalent cross-linking of the hydrogel polymer layer on the proppant surface can improve the polymer swelling properties and the cut tolerance to prevent premature release of the hydrogel from the proppant. The covalent crosslinkers may include the following functional groups: epoxides, anhydrides, aldehydes, diisocyanates, carbodiamides, divinyl or diallyl groups. Examples of these covalent cross-linked linkers include: PEG diglyceryl ether, epichlorohydrin, maleic anhydride, formaldehyde, glyoxal, glutaraldehyde, toluene diisocyanate, methylene diphenyl diisocyanate, l-ethyl-3- (3-dimethylaminopropyl) carbodiamide, methylene bis acrylamide . The covalent cross-linking of the hydrogel polymer layer on the proppant surface can effectively create a "polymer cage" swellable around the proppant. The covalent bonds prevent the polymer from being completely desorbed inside the solution. The lightly insoluble polymer layer is capable of swelling and producing a layer of hydrated polymer.

To further avoid the possible release of the hydrogel from the surface of the particle, the proppant particle can be treated to impart functionalities that will also take part in the polymerization process. For example, sand particles can be treated with silanes to give particles with functionalities of vinyl, hydroxyl, epoxy, etc.

Delayed / controlled hydration of the polymer layer may be desirable to delay hydration of the polymer surface modification during proppant handling and initial downward pumping through the well bore. Environmental factors such as humidity and rain can cause premature hydration of the polymer coating, which can make it difficult to effectively measure the proppant dose inside the mixer during a hydraulic fracturing operation. It is also believed that a fully hydrated polymer layer may be more prone to desorption under the high cut conditions associated with the pumping of a fracturing fluid below the tubular. For these reasons, it may be advantageous to design a modified surface proppant having slower or delayed hydration properties. In other embodiments, delayed hydration can be achieved by the addition of a low hydrophilic-lipophilic balance surfactant (HLB), the exclusion of a high hydrophilic-lipophilic balance termination surfactant, ionic crosslinking, covalent crosslinking, shielding loading using a monovalent salt or by incorporating a hydrophobic layer such as a fatty acid or a fatty alcohol.

In some embodiments, hydrophobic groups can be incorporated into the hydrogel polymer to allow hydrophobic interactions. This method can improving the tolerance of the salt of the hydrogel layer so that the hydrogel layer remains inflatable even in an aqueous fluid containing high salt concentrations.

Also described herein is a method for improving well productivity by placing improved proppant using a hydrogel-coated proppant. The hydrogel coated proppant can be more effectively transported in the far end of the fractures to allow superior oil and gas productivity from a well. Because the surface modified proppant described herein may be less inclined to settle out of the fluid and more easily re-suspended and transported through the fracture, it is believed that proppant placement will be more effective. The ability to transport the proppant additionally within the fractures can significantly increase the effectiveness of a fracture stimulus operation, resulting in a larger volume of higher density fractures. These fracture channels can advantageously allow the gas / condensate to flow more easily into the well orifice from the reservoir.

An improved method for proppant placement using a low viscous fluid is also described herein. Modified surface proppant as described here uses polymers more effectively to suspend / transport the proppant particles. Surface modification makes proppant auto-suspension, thus reducing or eliminating the need for highly viscous gels / fluids to transport the proppant. Therefore, the lower viscosity fluids can be used in combination with the modified surface proppant to transport the proppant inside the fractures. This will advantageously simplify the formulation of fracturing gels for use with proppant.

A more efficient method to fracture a well using less proppant is also described here. Due to the highly effective proppant placement that can be achieved with the easily transportable surface modified proppant as described herein, it is anticipated that a smaller amount of these modified surface proppant will be required for a given fracturing operation, compared to the systems using traditional proppant With an increased demand for fracturing-grade proppant / sand, and a decreased supply of sand in a desirable manner for proppant use, it would be advantageous to provide systems and methods such as those described herein where less proppant can be used to achieve results. comparable to or superior to the results using current techniques.

After the hydrogel coated proppant of the invention has been pumped into a well, the hydrogel layer can be degraded by chemical, thermal, mechanical and biological mechanisms. Specifically, the modification of the polymer surface on the proppant can be broken with the help of chemical breakers, for example, ammonium persulfate or other oxidants. The controlled disruption of the hydrogel layer upon reaching a target temperature or a time amount in the fluid can be used as a means to direct the placement of the proppant at the desired location in the fractures. The degradation of the hydrogel layer is also beneficial to ensure the adequate conductivity of the proppant fracture after completing the hydraulic fracturing operations.

As described herein is also a method of delivering additives, for example chemical additives into the proppant pack, by incorporating the additives into the hydrogel layer of the modified proppant. The additives may include chemical additives that can be delivered advantageously in the hydrogel layer, for example, a scale inhibitor, a bioside, a breaker, a wax control, an asphaltene control, and indiciators. In some additions, these chemical additives can be chemically bonded to the polymer in the hydrogel layer. for example, by covalent bonding, ionic bonding, hydrophobic association, hydrogen bonding, and the like. After placement in a package proppant, the desorption, oxidation or degradation of the hydrogel polymer can result in a controlled release of chemical additives from the self-suspending proppant. In some additions, a hydraulic fracturing operation may have multiple phases of fracturing; the proppers injected in each phase may contain unique indicators. The analysis of the fluids produced from the fractured well can provide information about the relative productivity of each fracturing phase by the presence and concentration of the unique indicators that correspond to the phases. In other embodiments, the additives, for example, the particulate additives, can be physically bound or entangled in the polymer layer.

In some embodiments, the surface of the proppant particle substrate can be coated with a selected polymer, either as a single layer or as a series of multiple coating layers. The coating (either a single layer or multiple layers) may show a changeable behavior under certain circumstances. As used here, the term "changeable behavior" or "behavior that can change" refers to a change in properties with a change in circumstances, for example, a change of one set of properties during the transport phase and another set of properties. properties within the fracture. The behavior of change can be seen, for example, when a Particle demonstrates hydrophilic properties in fracturing fluid and adhesive properties when in place within fractures. Such behavior can be triggered by circumstances such as high closing pressures within the fracture site so that the outer layer of the coating arranges itself to exhibit more advantageous properties.

In one embodiment, the coated particle can change from hydrophilic to hydrophobic when subjected to high pressures within the fractures. In an exemplary embodiment, during the transport phase, when the hydrophilic cover of the particle is exposed to the water-based fracturing fluid, it will tend to be completely distended. As a result, the coating can provide the particle with lubrication in this state, facilitating its movement through the proppant solution. When the particle has been taken to its destination within the fractures in the formation, the high pressures will overcome the steric repulsions of the outer hydrophilic polymer chains, forcing the outer layer to rearrange itself so that the inner layer is exposed. In some embodiments, the changeable inner layer may be hydrophobic or adhesive, or both. By exposing the inner layer, its properties can manifest themselves. If the inner layer has adhesive properties, for example, it can fix the particles to each other to avoid the return flow. This inner layer it can also be configured to capture the fines in case the proppant particle fails. In addition, residual intact hydrophilic groups present in the outer coating can allow an easy flow of the oil through the proppant package.

In some embodiments, a coated proppant particle can be produced which supports the following coating layers. First, a pressure-activated fixative polymer can be used to coat the proppant substrate. This coating layer can be elastomeric, providing overall strength to the proppant pack by helping to agglomerate the proppant particles and to distribute the stress. In addition to this, the coating layer can encapsulate the substrate particles and retain any fines produced in the event of substrate failure. Second, a block copolymer can be adsorbed or otherwise placed on the first coating layer. The copolymer can have a section with a high affinity for the first polymeric layer, allowing a strong interaction (hydrophobic interaction), and can have another section that is hydrophilic, allowing easy transport of the proppant in the transport fluid.

In certain embodiments, a stronger interaction between the first and second coating layers may be useful. To achieve this, a swelling technique- deflation can be imp1emented. For example, the block copolymer can be adsorbed onto the surface of the elastomeric coated particle. Thereafter, the first coating layer can be rinsed with small amounts of an organic solvent which allow the hydrophobic block of the copolymer to penetrate deeper into the first coating layer and become entangled in the elastomeric coating. By removing the organic solvent, the layered polymeric compound will be deflated, resulting in a stronger interaction of the copolymer with the elastomeric particle. A method for the inflation-deflation technique can be useful and is established in the work "Swelling-based Method for Preparing Functionalized and Stable Polymer Colloids" by A. Kim et al., American Chemical Society (2005) 127: 1592- 1593, whose contents are incorporated here by reference.

Although the systems described herein refer to a two-layer coating system, it is understood that there may be multiple coating layers (for example more than two) forming the composite propping particles described therein, with each of the multiple coating layers. possessing some or all of the attributes of the two coating layers described above, or with one or more of the multiple coating layers providing additional characteristics or properties.

The addition of a species capable of cross-linking the swellable polymer onto the proppant surface can effectively reduce the ability of the polymer layer to swell prematurely. The decreased deflation of the polymer can reduce. the tendency of the polymer-coated proppant to undergo apastallation during storage under wet conditions. As used herein, the term "apastelation" refers to the formation of clods or solid masses by the adhesion of the loose granular material. The matting of the proppant during storage is undesirable for the purposes of handling the material. Preferably, the crosslinker will not prevent hydration / swelling of the polymer coating once the polymer coated proppant is dispersed in an aqueous fluid such as a hydraulic fracturing fluid. In some embodiments, the cross-linking species have the ability to form a linkage with the carboxyl functional group, an amide functional group or both. Preferably, the cross-linked looper forms a joint that can be broken or removed under a mechanical cut or by the action of a chemical breaker. The cross-linking species can be added directly into the polymer used to coat the proppant, they can be added simultaneously to the proppant with the polymer while it is maximized or added some time after the addition of the proppant polymer but before drying.

Cross-linking species can be chosen from organic compounds containing aldehyde, amine, anhydride, or epoxy functional groups. Cross-linking species can also be an organometallic compound. The organometallic compounds capable of associating and / or of binding with the carboxyl functional groups are an example of a kind of crosslinking which forms cut-sensitive bonds. In such embodiments, the organometallic compound is capable of reducing the swelling tendency of the polymer-coated proppant through the cross-linking of the carboxyl groups before the introduction of the proppant into the hydraulic fracturing fluid. Then, when the crosslinked polymer coating encounters the high pumping shear forces associated with hydraulic fracturing, the crosslinking on the polymer can be degraded allowing the polymer to be able to swell without damage when the proppant is introduced into the hydraulic fracturing fluid.

In certain embodiments, a thin, non-hydroscopic coating layer can be applied to the surface of a hydrogel-coated proppant to create a barrier that prevents the swellable polymer layer on the adjacent proppant particles from adhering during storage. The outer layer used may be composed of compounds that are water soluble, insoluble in water or both. In some additions, the outer layer may be formulated so that it remains in a solid phase at temperatures below 40 degrees centigrade and has a melting point in the range of 40 degrees Celsius to 120 degrees Celsius. Preferably, the outer layer is formulated so that the melting point is sufficiently low so that the outer layer will be in the liquid phase during the drying process in the manufacture of the polymer coated proppant, but is sufficiently high so that the outer layer will exist in the solid phase during storage and transport of the polymer-coated proppant.

In these additions, the outer layer acts as a barrier to reduce the weathering of the coated proppant in wet environments. The hydrophobic outer layer can be added to the polymer coated proppant as a finely divided powder or as a liquid. In some embodiments, the outer layer material may be melted before addition to the coated proppant. In other embodiments, the outer layer material can be added as a solid or wax material, which can be melted during the drying process. The solid outer layer can be added to the proppant simultaneously with the polymer or it can be added sometime after the addition of the polymer but before the drying process. The outer layer may be composed of fatty acids, hydrogenated oils, vegetable oils, castor oils, waxes, polyethylene oxides, polypropylene oxides, and the like. 2. Particle Substrate Materials The proppant particles compounded according to these systems and methods can be formed using a wide variety of proppant substrate particles. Substrating particle substrates may include for the present invention a graded sand, resin coated sand, bauxite, ceramic materials, glass materials, nut shells, polymeric materials, resinous materials, rubber materials and the like. In some additions, the substrates may include naturally occurring materials such as, for example, walnut shells that have been crushed, ground or crushed to a suitable size (eg, walnuts, walnut, coconut, almond, tagua, and Brazil nut). and the like), or for example seed husks or fruit bones that have been chipped, ground, pulverized or crushed to a suitable size (for example, plum, olives, peach, cherries, apricots, etc.) or for example splintered, ground, pulverized or crushed materials from other plants such as corn cobs. In some embodiments, the substrates may be derived from wood or processed wood, including but not limited to woods such as oak, walnut, walnut, mahogany, poplar, and the like. In some additions, the aggregates can be formed using a bonded inorganic material or coupled to an organic material. Desirably, the proppant particulate substrates will be composed of particles (either single substances or aggregates of two or more substances) having a size in the order of the mesh size of 4 to 100 (standard sieve numbers of the United States of America). ). As used herein, the term "particle" includes all known forms of materials without limitation, such as spherical materials, elongate materials, polygonal materials, fibrous materials, irregular materials, and any mixture thereof.

In some embodiments, the particulate substrate can be formed as a composite of a binder and a filler material. Suitable fillers may include inorganic materials such as solid glass, glass microspheres, fly ash, silica, alumina, smoked coal, carbon black, graphite, mica, boron, zirconia, talc, kaolin, titanium dioxide, silicate calcium, and the like. In certain embodiments, the proppant particle substrate may be reinforced to increase its resistance to high formation pressure which may otherwise crush or deform it. The reinforcing materials can be selected from those materials which are capable of adding structural strength to the substrate of propping particles, for example, high strength particles such as ceramics, metal, glass, sand and the like, or any other materials capable of being combined with a substrate in particles to provide this with additional resistance.

In addition to bare or uncoated substrates, the composite hydrogel-coated proppant can be formed from substrates that have undergone treatments or coatings. For example, a variety of resin-coated proppant particles are familiar to skilled artisans. The formulations and methods described above for the coating are suitable for use with coated or treated proppant particles, including pre-curable and curable resin-coated proppant.

In an embodiment for treating resin coated sand, an inflatable hydrogel layer, as described above, can be applied to the resin coated sand to improve its suspension characteristics. In some embodiments, one may include the addition of the species that act as an adhesion promoter to attach the hydrogel to the resin layer. Adhesion promoters can be, for example, block copolymers composed of both hydrophilic and hydrophobic monomers. The block copolymer can be added after the substrate sand is coated with resin or at the same time as the resin coating. In addition to block copolymers, cationic species can be used such as fatty amines, polyquaternary mines and cationic surfactants.

In certain embodiments, the proppant particulate substrate may be manufactured as an aggregate of two or more different materials providing different properties. For example, a core particle substrate having a high compressive strength can be combined with a floating material having a lower density than the high compressive strength material. The combination of these two materials as an aggregate can provide a core particle having an appropriate amount of strength, while having a relatively lower density. As a particle of lower density, it can be adequately suspended in a less viscous fracturing fluid, allowing the fracturing fluid to be pumped more easily, and allowing a greater dispersion of the proppant within the formation as these are driven by less viscous fluid in more distal regions. High density materials used as proppant particle substrates, such as sand, ceramic, bauxite, and the like, can be combined with lower density materials such as hollow glass particles, other hollow core particles, certain polymeric materials , and naturally occurring materials (nut shells, seed husks, fruit bones, woods, or other naturally occurring materials that have been chipped, ground, pulverized, or crushed), giving a less dense degree that will still possess a resistance to the proper compression.

Suitable aggregates for use as proppant particle substrates can be formed using techniques for joining the two components to one another. As a method of preparation, a substrate of proppant particles can be mixed with the floating material having a particle size similar to the size of the proppant particle substrates. The two types of particles can then be mixed together and be joined by an adhesive, such as wax, a phenol-formaldehyde novolac resin, etc., so that a population of aggregate pair particles are formed, a subpopulation having a substrate of proppant particles attached to another similar particle, a subpopulation having a substrate of propping particles attached to a proppant particle, and a subpopulation having a floating particle attached to another floating particle. The three subpopulations can be separated by their difference in density: the first subpopulation will sink in the water, the second subpopulation will remain suspended in the liquid and the third subpopulation will float.

In other embodiments, a proppant particle substrate can be designed so that it is less dense by covering the surface of the particle substrate with a foaming material. The thickness of the foaming material can be designed to give a compound that is effectively neutrally floating. To produce such proppant coated particle, a particle having a desirable compressive strength can be coated with a reagent for a foaming reaction, followed by exposure to another reagent. With the activation of the foam formation, a proppant particle coated with foam will be produced.

As an example, a water-blown polyurethane foam can be used to provide a coating around the particles that will lower the particle density in general. To make such a coated particle, the particle can be initially coated with a reagent A, for example a mixture of one or more polyols with a suitable catalyst (for example, an amine). This particle can then be exposed to a reagent B containing a diisocyanate. The final foam will be formed on the particle, for example when it is treated with steam while it is being stirred; the agitation will prevent the particles from agglomerating as the foam forms on their surfaces.

The cross-linked species can be added directly into the polymer used to coat the proppant, added simultaneously to the proppant with the polymer while blending is performed, or added some time after the addition of the proppant but before drying.

EXAMPLES materials Sand frac 30/70 mesh Fractal sand 40/70 mesh Polydiallyldimethylammonium chloride (Aldrich, St. Louis MO) LPEI 500 (Polymer Chemistry Innovations, Tucson, AZ) Ethyl alcohol, 200 grade (Aldrich, St. Louis MO) Hexane (V R, Radnor, PA) FLOPAM EM533 (SNF) Polyethylene glycol diglycidyl ether (Aldrich, St. Louis, MO) Glioxal, 40 percent by weight solution (Aldrich, St Louis, MO) HFC -44 (Polymer Ventures) Carboxymethyl cellulose, sodium salt (Sigma-Aldrich, St. Louis, MO) Ammonium persulfate (Sigma-Aldrich, St. Louis, MO) Surfactant of ethoxylated lauryl alcohol (Ethal LA 12/80%)) (Ethox Chemical Co., SC) Fractal sand coated with phenolic resin from a commercial source SMA 4000i, from Sartomer • SMA 2000i, from Sartomer • Pluronic L31 Surfactant, from BASF, Florham Park, NJ • Pluronic L35 Surfactant, from BASF, Florham Park, NJ • Pluronic L81 Surfactant, from BASF, Florham Park, NJ • ARQUAD® 2HT-75, from Sigma Aldrich, St. Louis, MO • ADOGEN® 464, from Sigma Aldrich, St. Louis, MO • Isopropanol (IPA), manufactured by Sigma Aldrich, St. Louis, MO • Tetrahydrofuran (THF), manufactured by Sigma Aldrich, St.

Louis, MO • Glycerol, manufactured by Sigma Aldrich, St. Louis, MO • White sand of 30/50 mesh • Thixcin-R (Elementis Specialties) • Castor oil (J. T. Baker) • Stearic Acid Powder (J. T. Baker) • Tyzor TE (Dorf Ketal) • Tyzor TEAZ (Dorf Ketal) Example 1: Preparation of Internal Polymer Layer An inner polymer layer of a concentration of 100 parts per million was prepared on a sand sample by adding 200 grams of sand mesh frac 30/70 to a long flask FlackTek Max 100. To the sand were added 85 grams of tap water and 2 grams of 1 percent of a solution of polydiallyldimethylammonium chloride (PDAC). The sample was then shaken by hand for approximately 5 minutes, filtered under vacuum and dried in an oven at 80 degrees centigrade. The sand sample was then removed from the furnace and used in a subsequent test.

An identical method was used as described above to formulate an inner polymer layer coating of 10 parts per million with the exception that only 0.2 grams of a 1 percent solution of polydiallyldimethylammonium chloride was used.

An identical method was used as described above to formulate an inner polymer layer at a maximum polymer load ("PDAC Max") with the exception that 1 gram of a 20 weight percent solution of polydiallyldimethylammonium chloride was used. . After the treatment, the sand was washed with excess tap water, vacuum filtered and dried in an oven at 80 degrees centigrade. The sand sample was then removed from the furnace and used in a subsequent test.

Example 2: Preparation of Inner Polymer Coating An inner polymer layer of a concentration of 100 parts per million was prepared on a sand sample by dissolving 0.2 grams of LPEI 500 in 10 grams of ethanol to form a 2 percent solution of LPEI 500 in ethanol. To 70 grams of ethanol in a 250 milliliter round bottom bottle were added 0.75 grams of a 2 percent solution of LPEI 500. Then 150 grams of sand frac of a 30/70 mesh was added to the round bottom bottle . The solvent was removed using a rotary evaporator with a water bath of 65 degrees Celsius. The sample was then removed from the bottle and used in a subsequent test.

Example 3: Preparation of Exterior Polymer Layer The outer polymer layers were applied to the sand samples by mixing sand with the liquid Flopam EM533 polymer under different conditions. In a coating method, the polymer product was pure aggregate. In another coating method the polymer product was extended by dilution with hexane. For the hexane dilution, 10 grams of polymer were added to 10 grams of hexane in a 40 milliliter glass vessel and swirled until they became homogeneous. The polymer was then added to mesh frac sand samples of 30/70 of 30 grams in flasks FlackTek Max 100. The samples were placed in a mixer FlackTek DACI 50 of speed mixer at 2600 revolutions per minute for about 25 seconds. The samples were removed from the speed mixer and allowed to dry in an oven at 80 degrees Celsius overnight.

Example 4: Performance of Outer Polymer Layer, Settlement Times The sand samples prepared in the previous example were evaluated for performance in a settlement test. Before the test, all sand samples were screened through a 25 mesh grid. Settling times were obtained by adding one gram of sand sample to 100 milliliters of tap water in a 100 milliliter graduated cylinder. The graduated cylinder was then inverted for about 8 times and then the time required for all of the sand to settle to the bottom of the graduated cylinder was recorded. Three times were recorded for each sample. The settlement times are reported in Table 1.

Table 1 Settlement Times Example 5: Performance of Exterior Polymer Layer, Seated Bed Height The sand samples prepared in Example 3 with the outer polymer layer were also evaluated by observing the bed height seated in water. In a 20 milliliter glass container, one gram of a sand sample was added to 10 grams of tap water. The containers were inverted for about 10 times to Properly wet sand treatments. The containers were then allowed to settle undisturbed for about 30 minutes. A digital meter was then used to record the height of the sand bed in the container. The results are reported in Table 2.

Table 2 Seated Bed Heights Exterior 40 grams of a sample of 30/70 mesh frac sand were treated with an outer polymer layer by adding 1.3 grams of Flopam EM533 polymer to 40 grams of sand in a FlackTek Max 100 flask and the vial was shaken by hand for 2 hours. minutes The sand was then screened through a 25 mesh grid. To evaluate the retention of the polymer on the sand under cut, the tests were carried out by adding 10 grams of treated sand to 200 grams of tap water with different levels of PDAC in a 300 milliliter glass beaker. It is believed that the PDAC will interact ionically to stabilize the polymer layer on the sand. The solutions were then agitated at 900 revolutions per minute with superior mixing using a propeller style mixing blade for 5 minutes.

The mixing was then stopped and the samples were allowed to settle for 10 minutes. The viscosity of the supernatant was then measured using a Brookfield DV-III + rheometer with an LV-II spindle at 60 revolutions per minute. The bed height of the sand seated in the beaker was also recorded using a digital meter. The results are reported in Table 3.

Table 3 Polymer Retention Example 7: Covalent Cross Linkage of Outer Polymer Layer-PEGDGE Four frac sand samples from a 30/70 mesh were treated with Flopam EM533 by adding 0.66 grams of polymer to 20 grams of sand in a FlackTek Max 100 flask and shaking by hand for 2 minutes. Then several amounts of 1 percent fresh polyethylene glycol diglycidyl ether solution in deionized water were added to the treated sand samples. The samples were again shaken by hand for 2 minutes and then placed in an oven at 100 degrees centigrade for 1 hour. The samples were then removed from the oven and screened through a 25 mesh grid. Bed heights were measured for all four samples by adding 1 gram of the sand sample to 10 grams of tap water in a 20-milliliter glass container, inverting the containers approximately 10 times to properly wet the sand and allow the containers to settle undisturbed for around 10 minutes. The bed heights were then measured with a digital meter. The results are listed in Table 4.

Table 4 Outer Polymer Layer Treated with PEGDGE Example 8: Covalent Cross Linkage of Polymer Layer Exterior-Glioxal Four frac sand samples from a 30/70 mesh were treated with the Flopam EM533 by adding 0.66 grams of polymer to 20 grams of sand in a FlackTek Max 100 flask and shaking by hand for 2 minutes. A 1 percent solution of glyoxal in ethanol was formulated by adding 0.25 grams of 40 percent by weight glyoxal to a 20 milliliter glass container and diluting to 10 grams with ethanol. The variable amounts of the 1 percent glyoxal solution were added to the treated sand samples, and the samples were shaken by hand for 2 minutes and placed in an oven at 100 degrees centigrade for 30 minutes. The sand samples were removed from the furnace and screened through a 25 mesh grid. For the seated bed height measurements, 1 gram of sand was added to 10 grams of tap water in 20 milliliter containers, inverted by about 10 times and given around 10 minutes for settlement. Bed heights were measured with a digital meter. The results are listed in Table 5.

Table 5 Outer Polymer Layer Treated with Glioxal Example 9: Cationic / Anionic Polymer Treatments Three samples of 30 grams of frac sand from a 30/70 mesh were treated with Ventures HCF-44 polymer in a FlackTek Max 100 flask. The flask was shaken by hand for 2 minutes. The Flopam EM533 was then added to each of the samples. The jars were again shaken by hand for 2 minutes. The samples were then dried at 80 degrees Celsius overnight. The sand samples were removed from the furnace and screened through a 25 mesh grid. For measurements of the bed height seated 1 gram of sand was added to 10 grams of tap water in containers of 20 milliliters, were inverted for about 10 times and were given around 10 minutes for settlement. The bed height was measured with a digital meter. The results are given in Table 6.

Table 6 Cationic / Anionic Polymer Treatment Example 10: Coated Sand with Macromolecular Particles A sample of 30 grams of 30/70 mesh frac sand was added to a FlackTek Max 100 bottle. 0.3 grams of paraffin wax were added to the sand. The sample was placed in a FlackTek DAC 150 speed mixer and mixed at 2, 500 revolutions per minute for 2 minutes. After mixing, 1 gram of carboxymethyl cellulose was added to the sample. The sample was again placed in a FlackTek DAC 150 speed mixer and mixed at 2,500 revolutions per minute for 1 minute. The sand sample was screened through a 25 mesh grid. For measurements of seated bed height 1 gram of sand was added to 10 grams of tap water in a 20 milliliter container, inverted by about 10 times and given about 10 minutes for settlement. The sand in this sample stuck together immediately and did not disperse in the water and an exact measurement of the bed height could not be obtained.

Example 11: Modified Sand Precipitation Tumbler Test A sample of 30 grams of 30/70 mesh frac sand was added to a FlackTek Max 100 bottle. The sand was treated with Flopam EM533 by adding 0.45 grams of the polymer to the bottle and shaking by hand for 2 minutes. The sample was then dried at 80 degrees centigrade during the night. After drying, the sample was removed from the oven and screened on a grid of 25 malls. After the screening, four samples were prepared by adding 1 gram of the treated sand to 10 grams of tap water in a 20 milliliter container. The containers were inverted for about 10 times and allowed to settle for 10 minutes. A 10 percent solution of ammonium persulfate was added by adding 2 grams of ammonium persulfate to 18 grams of tap water. The varying amounts of the 10 percent ammonium persulfate solution were then added to the sample vessels. The samples were inverted several times for mixing, and then placed in an oven at 80 degrees centigrade for 1 hour. After 1 hour the samples were removed and the seated bed heights were observed. Table 7 shows the results.

Table 7 Precxpitations Glass Test Example 12: Emulsion additives To determine the effect of the emulsion additives on the performance of self-supporting proppant ("SSP"), glycerol and Ethal L-12/80 percent were added to emulsion polymer E 533 before coating proppant sand . Three different polymer samples were made as follows: • Auto-suspension proppant polymer: 10 grams of EM533, without additive • Self-suspension bracket + glycerol: 9 grams of EM533 and 1 gram of glycerol • Self-suspended stanchion + glycerol + Ethal: 9 grams EM533 + 0.9 grams of glycerol + 0.1 grams of Ethal LA- 12/80 percent.

Each of the previous samples was mixed with a swirl for 30 seconds to ensure homogeneity. To make the modified proppant, 50 grams of 40/70 mesh sand were combined with 1.5 grams of one of the polymer samples above and then mixed for 30 seconds. The samples of modified proppant were evaluated with respect to the cut stability in the 1 liter cut test. This test involves the addition of 50 grams of modified proppant to 1 liter of water in a square plastic beaker followed by mixing on a bottle / pallet mixer (model EC Engineering CLM-4) at 200 revolutions per minute for different amounts of time. The cut samples are then poured into a graduated cylinder of 1,000 milliliters and allowed to settle by gravity for 10 minutes, after which the bed height of the seated proppant sand was recorded. For comparison, an unmodified proppant sand will produce a bed height of 10 millimeters after any amount of mixing. Samples of proppant self-suspension will produce a level of upper bed against proppant unmodified due to the layer of hydrogel that encapsulates the grams of sand. Generally, increasing the cutting rate or time may cause the bed height of the self-suspending proppant to decrease as a result of the desorption of the hydrogel layer from the surface of the modified proppant. For this reason, it is desirable that the bed height be as high as possible in this test, especially after cutting.

The results shown below indicate that the addition of glycerol improves the bed height and the cutting stability of the product. The addition of glycerol and Ethal, even when it improves the initial bed height, the stability of long-term cutting is slightly diminished. These results are illustrated in Figure 2.

Example 13: Glycerol and Processing This experiment sought to determine the effect of glycerol and other additives on the performance of self-supporting proppant (denoted as SSP below). 1 kilogram of dry 40/70 mesh sand was added to the container of a KitchenAid pedestal mixer, model KS 90WH, which was equipped with a paddle attachment. 3.09 grams of glycerol were mixed with 27.84 grams of EM533 emulsion polymer, then the mixture was added to the top of the sand and allowed to soak for 1 minute. At time 0, the mixer was turned on at speed 1 (72 revolutions per minute of primary rotation). Samples were collected at 1-2 minute intervals and dried for 1 hour at 90 degrees centigrade. Afterwards, each sample was subjected to a 1-liter cutting test, where 50 grams of auto-suspension proppant was added to 1 liter of water and cut at 200 revolutions per minute (a cut-off rate of approximately 550 s). 1) for 20 minutes after transferring the auto-suspension / water proppant mixture to a graduated cylinder of 1 liter and settlement for 10 minutes, bed heights were recorded. The experiment was reported with 30.93 grams of EM533 emulsion polymer added to only 1 kilogram of sand. These results are shown in Figure 3. As shown in Figure 1, the glycerol additive significantly increased bed heights.

The difference in performance was then more marked when the experiment was repeated at higher mixing speeds. Here the mixer was set at speed 4 (150 revolutions per minute of primary rotation). At low mixing times, the samples were insufficiently mixed, leading to an incomplete coating of the sand and a rapid desorption of the polymer from the self-suspending proppant surface during the cutting test. When the time of the coating process was increased also the performance, until an ideal coating was reached, giving a maximum bed height for that sample. After that, the increase in worst (lower) bed heights was seen at higher mixing times, possibly as a result of coating abrasion during extended mixing. At higher mixing speeds, this process happened even faster so that the processing window for the emulsion polymer was only less than 1 minute. With the addition of glycerol and the use of lower mixing speed, this processing window was extended to almost 15 minutes. Compared to the tests with the emulsion polymer alone, glycerol caused the processing window to expand, indicating that self-supporting proppant preparation with glycerol is more robust. At the same time, glycerol allowed the polymer emulsion to reverse more completely, leading to better coatings and increased bed heights. The test with combinations of glycerol and emulsion polymer EM533 at a higher mixing speed gave the results shown in Figure 4.

Example 14: Modified Marker with an Agent Against Tampering The modified proppant samples were made with and without agent against the apalast for comparison. For sample A, 50 grams of 40/70 mesh sand was added to a FlackTek flask. 1.5 grams of EM533 emulsion polymer were added to the sand and the sample was mixed for 30 seconds. After mixing, 0.25 grams of calcium silicate was added to the sample and the sample was mixed again for 30 seconds. The sample was then dried for 1 hour at 85 degrees centigrade. After drying, the sample was poured on a 25 mesh grid and stirred slightly for 30 seconds. The amount of sand that passed through the screen was measured. For sample B, 50 grams of 40/70 mesh sand were added to the FlackTek flask. 1.5 grams of EM533 emulsion polymer were added to the sand and the sample was mixed for 30 seconds.

The sample was then dried for 1 hour at 85 degrees centigrade. After drying, the sample was poured on a 25 mesh grid and stirred slightly for 30 seconds. The amount of sand that passed through the screen was then measured. Table 8 shows the results.

Table 8 The results of the screening test indicated that the incorporation of an agent against the apastelage was effective to improve the handling properties of the modified proppant.

Samples A and B were prepared and added separately to 1 liter of water and then cut in the EC Engineering mixer for 20 minutes at 200 revolutions per minute. After cutting, the samples were transferred to a 1 liter graduated cylinder and allowed to settle for 10 minutes. After settling, bed heights were measured, they did not show a significant loss in shear stability as a result of the incorporation of an agent against apaselation. Table 9 shows these results.

Table 9 Example 15: Sand Hydrogel Coating by Dissolving a Water Soluble Polymer in a Monomer Formulation followed by Polymerization of the Monomers 2. 5 grams of a mixture of acrylic acid (Aldrich 147230), poly (ethylene glycol) methyl ether acrylate (Aldrich 454990), and polyethylene glycol dimethacrylate (Aldrich 437441) in a molar ratio: 0.5 / 0.4 / 0.1 can be mixed with 7.5 grams of polyethylene glycol (Aldrich 202371) and 1 percent by weight of ammonium persulfate. The solution can be mixed with 100 grams of 30/70 mesh sand under nitrogen and can be allowed to react by increasing the temperature to 70 degrees centigrade for 5 hours. Then the solids obtained are washed with methanol, filtered with vacuum and dried in an oven at 80 degrees centigrade.

Example 16: Sand Polyurethane Hydrogel Coating 100 grams of 30/70 mesh frac sand were added to a Hobart type mixer and heated to 120 degrees Celsius. Then 6 grams of polyethylene glycol (Fluka 81190) will be added and allowed to mix for 1 minute.

After 0.53 grams of Desmodur N75 from Bayer will be added. After mixing for 1 more minute, a drop of 1,4-Diazabicyclo [2.2.2] octane catalyst (Aldrich D27802) will be added and the mixture will be allowed to react for a further 5 minutes. The solid obtained is washed with methanol, filtered with vacuum and dried in an oven at 80 degrees centigrade.

Example 17: Coating of sand hydrogel by admixing polymerization 250 grams of 30/70 mesh frac sand can be added to 500 milliliters of a previously degassed aqueous solution containing 0.6 mM of hexadecyltrimethylammonium bromide surfactant (C ) (equivalent to 2/3 of the critical micelle concentration of C ), and 6 mM monomer (mixture of acrylic acid / acrylamide in a molar ratio of 30/70). The adsorption of CTAB and monomer onto the sand particle can be carried out under gentle agitation for 24 hours at 25 degrees centigrade. Then, 0.6 mM of ammonium persulfate can be added to the reactor and the polymerization will take place for 3 hours at 80 degrees Celsius. The excess polymer and the surfactant can be rinsed with several volumes of water and the sample will be dried overnight in a vacuum oven at 80 degrees centigrade.

Example 18: Hydrogel coating with sand by reverse suspension polymerization To one bottle can be added 60 milliliters of deionized water, 6.6 grams of acrylamide, 3 grams of acrylic acid, 2.4 grams of N, N'-methylenebisacrylamide, 0.1 grams of ammonium persulfate, 2.0 grams of sodium chloride and 2 drops of? ,?,? ' ,? ' -tetramethylethylenediamine. To this solution 200 grams of 30/70 mesh frac sand can be added and the entire mixture will be maintained at a temperature of < 10 degrees Celsius. 200 milliliters of cyclohexane can be added to the mixture and the entire mixture can be vigorously stirred under nitrogen. Then the temperature can be increased to 60 degrees centigrade and the reaction is allowed to proceed for 6 hours. The resulting coated particles can be filtered and washed with hot water, with acetone and dried at 45 degrees centigrade under reduced pressure.

Example 19: Coating polymer A mixture to coat proppant was made by mixing SNF Flopam EM 533 and glycerol in a ratio of 9: 1. The polymer mixture is used in the following examples.

Example 20: Preparation of 40/70 mesh self-suspension proppant ("SSP") A sample of 40/70 mesh size self-supporting proppant was prepared by adding 500 grams of 40/70 frac sand to the container of a KitchenAid mixer. 20 grams of the coating polymer of example 19 were added to the sand. The mixer was fired at a setting of 1 and the sand and the polymer mixture were combined for 7 minutes. After mixing, the sample was dried for 1 hour at 85 degrees centigrade. After 1 hour, the sample was removed from the oven and any lumps were broken into individual grains.

Example 21: Preparation of a 30/50 mesh self-suspension proppant ("SSP") A sample of 30/50 mesh size self-supporting proppant was prepared by adding 500 grams of 30/50 mesh frac sand to a container of the KitchenAid mixer. 20 grams of the coating polymer of example 19 were added to the sand. The mixer was turned on and put on placement 1 and the sand and polymer mixture were combined for 7 minutes. After mixing, the sample was dried for 1 hour at 85 degrees centigrade. After 1 hour, the sample was removed from the oven and any lumps were broken into individual grains.

Example 22: Reduced thin content of self-supporting proppant ("SSP") against sand A stack of standard mesh screens was prepared with 40 meshes in the upper part, 70 meshes in the middle part, and a tray in the bottom. The tare weight of each clean / dry screen was measured and recorded. 50 grams of the 40/70 mesh self-suspending proppant of example 20 were added to the top of the screen stack, and the stack was shaken by hand for 5 minutes. After stirring, a pile was disassembled and each screen was weighed. The mass retained in each screen was calculated as one percent of the original sample mass, and the amount of the remaining sample in the tray represented the fraction of fines, as defined by a 70 mesh cut. The procedure was repeated substituting 40/70 mesh frac sand not modified by the 40/70 mesh self-supporting proppant. The results in Table 10 show the particle size distribution for the 40/70 mesh self-suspension proppant. Table 11 contains the particle size analysis for unmodified 40/70 mesh frac sand. The results showed that the amount of material passing through the 70-mesh grid was reduced in the 40/70 mesh self-suspension proppant (1.2 percent vs. 4.8 percent). This showed that the self-suspending proppant can contain a reduced amount of fine particles than a sand sample.

Table 10: 40/70 mesh auto proppant proppant particle size analysis Sample: 49,516 grams of 40/70 mesh self-supporting proppant Table 11: Analysis of white sand particle size of unmodified 40/70 mesh Sample: 50,974 grams of white sand 40/70 Example 23: Reduction of Friction 1 liter of tap water was added to a square beaker and the beaker was placed in an EC Engineering GLM-4 mixer. The mixer was turned on and set at a mixing speed of 200 revolutions per minute. 120 grams of the 30/50 mesh self-suspending proppant of example 21 was added to the tap water. The solution was mixed for 20 minutes, then it was transferred to a 1 liter graduated cylinder and allowed to settle for 10 minutes. After settlement, the supernatant was collected. This procedure was repeated until 2 liters of supernatant fluid were collected. The friction reduction of the collected fluid was then determined using a flow circuit apparatus. The flow circuit consists of a stainless steel test tube of 0.12 inches (ID) per 3 feet and a pump that delivers a constant flow rate of 55 grams per hour. These conditions correspond to a Reynolds number of 23, 000, confirming that the fluid is a turbulent flow. The percent reduction of friction (% friction reduction) was determined experimentally by measuring the pressures at the inlet and outlet of the test pipe at a constant flow rate. The following equation to calculate the friction percent reduction:% FR = 100 * (1- (??? / ?? 0)) where ??? is the pressure drop across the test pipe using supernatant proppant self-suspending fluid and 0 is the pressure drop through the test pipe using tap water. The pressure values were ??? = 11.8 pounds per square inch and 0 = 38.5 pounds per square inch, corresponding to a friction reduction (% FR) of 69 percent. This shows that the self-suspending proppant contributes significantly to the friction reduction of the associated fluid, representing a reduction in pumping requirements.

Example 24: Hydraulic conductivity tests To model the hydraulic conductivity of a simulated proppant package, 48 grams of self-suspending proppant of 30/50 mesh size from example 21 were mixed in 1 liter of water. Ammonium persulfate was added at a level of 0.1 percent and the mixture was heated to 185 degrees Fahrenheit for 1 hour. After cooling to room temperature, the mixture was filtered through a 2.25 inch ID column with a 100 mesh screen at the bottom, separating the particles from the fluid. The particles formed a bed depth of 0.5 inches over the 100 mesh grid, and the flow rates of various fluids through the bed were measured by gravity flow. A simple sand bed was built in a similar manner and the flow rates were compared with the bed derived from self-supporting proppant. Using this method, the efflux rates obtained by proppant of self-suspension (250 milliliters of efflux in 28 seconds) and single sand (250 milliliters of efflux in 25 seconds) were almost identical, showing that proppant self-suspension, a Once treated with oxidizing breakers such as ammonium persulfate, it does not have a deleterious effect on the hydraulic conductivity of a sand bed or a simulated proppant pack.

Example 25: Self-suspension ("SSP") stanchions with anti-glare agents In addition to anti-glaze agents being able to replace a drying step, these can be used to generally improve handling properties for self-suspending proppant. A number of different particulate materials were tested as anti-glaze agents, as set forth in Table 12 below. To prepare the samples for each material, 800 grams of 30/50 mesh sand was mixed in a KitchenAid mixer at a speed of 1 (144 revolutions per minute) with 32 grams of coating polymer from Example 19. Samples of 20. grams were taken and mixed with an agent against selected apastelation in a mixer, with the doses of anti-glaze agent calculated as a percent of total sand in the sample. The consistency of the samples was observed and recorded as "appearance before drying" and then they were dried for 1 hour at 85 degrees centigrade. This consistency was again observed and recorded as "appearance after drying". The samples were then subjected to relative humidity conditions of 80 percent-90 percent at 25-35 degrees Celsius per 1 hour to evaluate their properties against apaselation, and consistency was observed and recorded as "appearance after exposure. to moisture. " The results are shown in Table 12 below indicating that the anti-glaze agent improves the self-suspending proppant handling properties, where free flow is a desired feature.

Table 12: Evaluation of self-suspending proppant samples with anti-aggregates agents added Example 26: Sand Coated Resin Treatment with SMA 4000Í The resin coated sand was coated with SMA 4000i by adding 25 grams of resin coated sand in a 250 milliliter round bottom bottle. Separately, 0.25 grams of SMA 4000i were dissolved in 3.57 grams of tetrahydrofuran (THF) to make a 7 percent solution. 1.43 grams of the THF solution were then aggregates to the resin coated sand in the round bottom bottle. An additional THF was added to the round bottom bottle until the sand was covered. The THF was then evaporated out of the sample using a rotary evaporator.

Example 27: Sand Coated Resin Treatment with SMA 4000Í The resin coated sand was coated with SMA 200Oi by adding 25 grams of resin coated sand in a 250 milliliter round bottom bottle. Separately, 0.25 grams of SMA 2000i were dissolved in 3.57 grams of THF to make a 7 percent solution. 0.72 grams of the THF solution were then added to the resin coated sand in the round bottom bottle. The additional THF was added to the round bottom bottle until the sand was treated. The THF was then evaporated out of the sample using a "rotary evaporator.

Example 28: Sand Coated with Treatment Resin with SMA 2000Í The resin coated sand was coated with SMA 2000i by adding 25 grams of resin coated sand in a 250 milliliter round bottom bottle. Separately, 0.25 grams of SMA 4000Í were dissolved in 3.57 grams of THF to make a 7 percent solution. 1.43 grams of the THF solution were then added to the resin coated sand in the round bottom bottle. The additional THF was added to the round bottom bottle until the sand was treated. The THF was then evaporated out of the sample using a rotary evaporator.

Example 29: Sand Coated Resin Treatment with SMA 2000Í The resin coated sand was coated with SMA 2000i by adding 25 grams of resin coated sand in a 250 milliliter round bottom bottle. Separately, 0.25 grams of SMA 2000i were dissolved in 3.57 grams of THF to make a 7 percent solution. 0.72 grams of the THF solution was then added to the resin coated sand in the round bottom bottle. The additional THF was added to the round bottom bottle until the sand was treated. The THF was then evaporated out of the sample using a rotary evaporator.

Example 30: Resin Coated Sand Treatment with Pluronic L31 The resin-coated sand was coated with Pluronic L31 surfactant by adding 20 grams of resin-coated sand in a small FlackTek flask. 0.025 grams of the surfactant were added to the coated sand resin. The sample was then mixed using a FlackTek speed mixer at 800 revolutions per minute for 30 seconds.

Example 31: Resin Coated Sand Treatment with Pluronic L35 The resin-coated sand was coated with the Pluronic L35 surfactant by adding 20 grams of the resin-coated sand into a small FlackTek flask. 0.025 grams of the surfactant were added to the resin coated sand. The sample was then combined using the FlackTek speed mixer at 800 revolutions per minute for 30 seconds.

Example 32: Resin Coated Sand Treatment with Pluronic L81 The resin-coated sand was coated with the Pluronic L81 surfactant by adding 20 grams of resin-coated sand in a small FlackTek flask. 0.025 grams of the surfactant were added to the resin coated sand. The sample was then mixed using a FlackTek speed mixer at 800 revolutions per minute for 30 seconds.

Example 33: Resin Coated Sand Treatment with ARQUAD® 2HT-75 The resin-coated sand was coated with ARQUAD® 2HT-75 by adding 25 grams of resin-coated sand to a 250 milliliter round bottom bottle. Separately, 0.25 grams of ARQUAD® 2HT-75 were dissolved in 3.57 grams of IPA to make a 7 percent solution. 0.72 grams of the IPA solution were then added to the resin coated sand in the round bottom bottle. The additional IPA was added to the round bottom bottle until the sand was treated. The IPA was then evaporated out of the sample using a rotary evaporator.

Example 34: Coated Resin Sand Treatment with ADOGEN® 464 The resin-coated sand was coated with ADOGEN® 464 by adding 20 grams of resin-coated sand in a small FlackTek flask. 0.025 grams of ADOGEN® 464 was added to the resin coated sand. The sample was then combined using a FlackTek speed mixer at 800 revolutions per minute for 30 seconds.

Example 35: Mixture of Coating Polymer 9 grams of Flopam EM 533 (SNF) were combined with 1 gram of glycerol in a 20 milliliter container. The vessel was then mixed for 30 seconds with a swirl mixer.

Example 36: Hydrogel Coating of Sand Samples The sand samples were prepared by placing 20 grams of the samples prepared in example 26 to example 34 and were added to small FlackTek flasks. 0.6 grams of the coating mixture prepared in example 35 were added to each flask. The contents were then mixed at 800 revolutions per minute for 1 minute using a FlackTek speed mixer. The samples were then dried for 30 minutes at 100 degrees centigrade. After drying, 1 gram of each sample was added to a 20 milliliter container containing 10 milliliters of tap water. The containers were then mixed gently and allowed to settle for 10 minutes. After settling, the bed height was measured to determine the hydration of the polymer. The results of the test are shown in Table 13.

Table 13: Seated bed heights Example 37: Moisture Aging Test (Cross-Linked Metal Chelate Linkers) Tyzor TE is an 80 percent solution of titanium chelate triethanolamine in ethanol. Tyzor TEAZ is a 100 percent active zirconium triethanolamine chelate product. These metal chelates were dispersed in castor oil at different concentrations and applied to a proppant in the second editing step during the coating process. Samples of the coated proppant were prepared by adding 3 grams of a mixture of Flopam EM 533 and glycerol to 100 grams of white proppant sand of 30-50 mesh in a FlackTek Max 100 flask. The samples were then combined in a FlackTek speed mixer at 850 revolutions per minute for 30 seconds. The samples were then removed from the speed mixer and in some cases treated with a combination of castor oil / metal chelate. The samples were then returned to the speed mixer and combined at 850 revolutions per minute for 30 seconds. The samples were then removed from the speed mixer, transferred to a glass vessel and dried at 100 degrees centigrade for 30 minutes in a forced air laboratory oven. After drying, the samples were screened through a grid of 18 mesh. For wet aging 50 grams of the formulated samples were placed in the Max 100 FlackTek bottles and allowed to settle in a humidity chamber for 1 hour. The relative humidity of the chamber was maintained between 60-70 percent. After humification, samples were tested in a Carver press cell (2.25 inches I.D.) with an applied load of 1,000 pounds for 30 seconds. The matting of the samples was visually evaluated and compared to the control (no second addition). The extent to which the samples matched was rated from 1 to 4 with a rating of "1" indicating a solid pie and a "" rating indicating a non-fluffy free-flowing material. The results are shown in Table 14.

Table 14: Appearance Results with Quelate Aggregate Metal (Pastel ratings for Table 14: "1" - Solid cake that can be handled without separating and falling off, "2" - Nearly solid cake that begins to break when handled, "3" - Cake that crumbles in the cell press, "4" there is no cake formation).

Example 38: Moisture aging test (powder additives) Samples of coated proppant sand were formulated by adding 3 grams of Flopam EM 533 glycerol mix to 100 grams of a 30/50 white proppant sand. The samples were combined at 850 revolutions per minute for 30 seconds in a FlackTek speed mixer. The samples were then removed from the speed mixer and in some cases treated with a dry powder. The samples were then returned to the speed mixer and mixed at 850 revolutions per minute for 30 seconds to evenly distribute the powder through the sample. The samples were then removed from the speed mixer and transferred to a glass container, and dried at 100 degrees centigrade for 30 minutes in a forced air laboratory oven. After drying, the samples were screened through a grid of 18 mesh. For moisture aging around 50 grams of the formulated samples were placed in FlackTek Max 100 bottles and allowed to settle in a humidity chamber for 1 hour.

The relative humidity of the chamber was maintained between 60-70 percent. After humification, samples were tested in a Carver press cell (2.25 inches I.D.) with an applied load of 1,000 pounds for 30 seconds. The maturation of the samples was visually evaluated and compared to the control (no second addition). The extent to which the samples were matted was rated 1 to 4 with the rating of "1" indicating a solid pie and a "4" rating. "indicating a non-fluff material of free flow, as shown in Table 15.

Table 15: Pallet Facing Results Coated with Powder Additive (Match ratings for Table 15: "1" - Solid cake that can be handled without separating, "2" - Almost solid cake that begins to break when handled, "3" - Cake that crumbles out of the press cell , "4" without cake formation).

Example 39: Oil-Based Additives The various oil-based or relatively hydrophobic materials were tested to determine their effectiveness in decreasing apassing in the wetted samples of self-supporting proppant (SSP). The samples were prepared by mixing 300 grams of sand 30/50, preheated to 45 degrees Celsius, with 9 grams of a mixture of 10 percent glycerol / 90 percent Flopam 533 in a KitchenAid mixer at speed 1. After of 1 minute of mixing, the second additive (usually 0.2 percent by weight of sand) was introduced and the mixture was combined for another minute. The sample was dried under medium cut conditions using a hot gun and a KitchenAid aid. The samples were then subjected to > 50 percent relative humidity in a humidity chamber for 1 hour. These were then individually tested with respect to the sealing behavior by undergoing the compression test. This consisted of being compressed at 200 pounds per square inch for 30 seconds in a compression cell using a Carver press, and then removed from the cell and observed. The resulting cake (see Table 16, compression test) was graded on the following scale: "1" - solid cake that can be handled without separating, "2" - almost solid cake that begins to break when handled, "3" -pastel that is crumbling out of the cell dam, "4" -without cake formation, as established in Table 16.

Table 16: Results of Antiapastelamiento de Apuntalante Covered with Additives based on Oil The sample treated with Adogen 464 barely formed a cake in this test, even at lower doses.

EQUIVALENTS Although the specific embodiments of the invention have been described herein, said prior description is illustrative and not descriptive. Even though the invention has been particularly shown and described with references to Preferred embodiments thereof, it is understood by those skilled in the art that various changes in shape and features can be made therein without departing from the scope of the invention encompassed by the appended claims. Many variations of the invention will become apparent to those skilled in the art of reviewing this disclosure. Unless otherwise specified, all numbers express reaction conditions, amounts of ingredients and others as used in this description and in the claims and should be understood as being modified in all cases by the word "around". Therefore, unless otherwise indicated, the numerical parameters set forth herein are approximations that may vary depending on the desired properties sought to be obtained by the present invention.

Although the invention has been particularly shown and described with references to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention covered in the clauses. annexes.

Claims (35)

R E I V I N D I C A C I O N S

1. A modified proppant comprising a proppant particle and a hydrogel coating, wherein the hydrogel coating is located on the surface of the proppant particle to produce the modified proppant.

2. The modified proppant as claimed in clause 1, characterized in that the proppant particle comprises sand.

3. The modified proppant as claimed in clause 1, characterized in that the proppant particle comprises bauxite, sintered bauxite, ceramic or materials of lower density.

4. The modified proppant as claimed in clause 1, characterized in that the proppant particle comprises a substrate coated with resin.

5. The modified proppant as claimed in clause 4, further characterized in that it comprises an adhesion promoter, wherein the adhesion promoter fixes the hydrogel coating to the resin coated substrate.

6. The modified proppant as claimed in clause 1, characterized in that the hydrogel coating comprises a water swellable polymer.

7. The modified proppant as claimed in clause 1, characterized in that the hydrogel coating comprises a polymer selected from the group consisting of polyacrylamide, hydrolyzed polyacrylamide, copolymers of acrylamide with ethylenically unsaturated ionic comonomers, acrylamide copolymers and acrylic acid salts , poly (acrylic acid) or salts thereof, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, guar gum, carboxymethyl guar, carboxymethyl hydroxypropyl guar gum, hydrophobically bound swelling emulsion polymers, and latex polymers.

8. The modified proppant as claimed in clause 1, further characterized in that it comprises an anionic / cationic polymer pair comprising a cationic polymer and a high molecular weight anionic polymer.

9. The modified proppant as claimed in clause 7, characterized in that the cationic polymer is selected from the group consisting of poly-DADMAC, LPEI, BPEI, chitosan and cationic polyacrylamide.

10. The modified proppant as claimed in clause 1, further characterized in that it comprises a chemical breaker.

11. The modified proppant as claimed in clause 10, characterized in that the chemical breaker is an oxidative breaker.

12. The modified proppant as claimed in clause 1, further characterized in that it comprises a hydrophobic outer layer.

13. The modified proppant as claimed in clause 12, characterized in that the hydrophobic outer layer is selected from the group consisting of fatty acids, hydrogenated oils, vegetable oils, castor oil, triacetin, waxes, polyethylene oxides, and oxides of Polypropylene .

14. The modified proppant as claimed in clause 1, further characterized in that it comprises a delayed hydration additive.

15. The modified proppant as claimed in clause 14, characterized in that the delayed hydration additive is selected from the group consisting of a low hydrophilic-lipophilic balance surfactant, an exclusion agent capable of excluding a finished surfactant, an ion cross-linking agent, a covalent cross-linking agent and a monovalent salt-loading protector.

16. The modified proppant as claimed in clause 1, further characterized in that it comprises an alcohol selected from the group consisting of ethylene glycol, propylene glycol, glycerol, propanol and ethanol.

17. The modified proppant as claimed in clause 1, further characterized in that it comprises an anti-glaze agent.

18. The modified proppant as claimed in clause 1, characterized in that the hydrogel coating comprises an additive.

19. The modified proppant as claimed in clause 18, characterized in that the additive is a chemical additive.

20. The modified proppant as claimed in clause 19, characterized in that the additive is an indicator.

21. The modified proppant as claimed in clause 19, characterized in that the additive is a chemical breaker.

22. The modified proppant as claimed in clause 1, characterized in that the modified proppant contains less fines than a proppant particle which is not modified.

23. A hydraulic fracturing formulation comprising the proppant modified in clause 1.

24. A hydraulic fracturing formulation comprising the proppant modified in clause 21.

25. A method to fracture a well, comprising: prepare the hydraulic fracturing formulation of clause 23 or clause 24; and introduce the hydraulic fracturing formulation into the well in an effective volume and at an effective pressure for hydraulic fracturing, therefore fracturing the well.

26. The method as claimed in clause 25, characterized in that it comprises: prepare the hydraulic fracturing formulation of clause 24, Treat the modified proppant with a chemical breaker after the step of introducing the hydraulic fracturing formulation into the well.

27. A method for manufacturing a modified proppant comprising: provide a proppant substrate particle and a fluid polymeric coating composition; applying the fluid polymeric coating composition on the proppant substrate particle; wherein the fluid polymeric coating composition comprises a hydrogel polymer and wherein the hydrogel polymer is located on the surface of the proppant substrate particle to produce the modified proppant.

28. The method as claimed in clause 27, further characterized in that it comprises the step of drying the modified proppant.

29. The method as claimed in clause 27, characterized in that the fabrication takes place at or near the point of use for the modified proppant.

30. The method as claimed in clause 27, characterized in that the proppant substrate particle comprises sand, ceramic, low density proppant, a substrate coated with resin and / or bauxite.

31. The method as claimed in clause 30, characterized in that the proppant substrate particle is obtained at or near the point of use for the modified proppant.

32. The method as claimed in clause 26, further characterized in that it comprises adding an alcohol selected from the group consisting of ethylene glycol, propylene glycol, glycerol, propanol and ethanol during or before the step of applying the fluid polymeric coating composition on the proppant substrate particle.

33. The method as claimed in clause 27, further characterized in that it comprises adding a Investment promoter during or after the step of mixing the proppant substrate particles and the fluid polymer coating composition.

34. The method as claimed in clause 27, further characterized in that it comprises the addition of an anti-glaze agent to the modified proppant.

35. A method for manufacturing a hydrogel coated proppant comprising: providing a proppant substrate particle and a formulation comprising a coating precursor, wherein the coating precursor is capable of forming a hydrogel coating on a surface of the proppant substrate particle by in situ polymerization; apply the formulation to the proppant substrate particle; Y polymerizing the coating precursor in juxtaposition to the proppant substrate particle to form the hydrogel-coated proppant. SUMMARIZES The invention encompasses a modified proppant comprising a proppant particle and a hydrogel coating, wherein the hydrogel coating is located on the surface of the proppant particle to produce the modified proppant. The invention also encompasses a formulation comprising the modified proppant as well as methods for the manufacture and methods for the use of the modified proppant.