HK1194450A - Self-suspending proppants for hydraulic fracturing - Google Patents
Self-suspending proppants for hydraulic fracturing Download PDFInfo
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Abstract
The present invention provides modified proppants, and methods for their manufacture. In embodiments, the modified proppant comprises a proppant particle and a hydrogel coating, wherein the hydrogel coating is applied to a surface of the proppant particle and localizes on the surface to produce the modified proppant. In embodiments, formulations are disclosed comprising the modified particles, and methods are disclosed for using the formulations.
Description
RELATED APPLICATIONS
This application claims the benefit of U.S. provisional application serial No. 61/529,600 filed on day 8/31 of 2011, U.S. provisional application serial No. 61/635,612 filed on day 4/19 of 2012, and U.S. provisional application serial No. 61/662,681 filed on day 6/21 of 2012. The above related applications are incorporated herein by reference in their entirety.
Technical Field
The present application relates generally to systems and methods for fragmentation techniques.
Background
During the process of obtaining oil and/or gas from a well, it is often necessary to stimulate the flow of hydrocarbons via hydraulic fracturing (fracturing). The term "fracturing" refers to a process of pumping fluid into a well until the pressure is increased to a level sufficient to fracture the subterranean geological formation containing the entrapped material. This process results in fractures and ruptures that damage the underlying layers to allow the hydrocarbon products to be carried to the well bore at a significantly higher rate. However, unless pressure is maintained, the newly formed orifice closes. To open the path and maintain the path, a propping agent or "proppant" is injected with the hydraulic fluid to create the support required to maintain the orifice. When a fracture is formed, the proppant is transferred in the slurry by the release of hydraulic pressure where it forms a pack or prop to hold open the fracture.
To accomplish placement of the proppant inside the fracture, these particles are suspended in a fluid and then pumped to a subterranean destination. To prevent settling of the particles, a high viscosity fluid is typically required to suspend the particles. The viscosity of the fluid is typically manipulated by the addition of synthetic or natural based polymers. There are three common types of polymer-enhanced fluid systems commonly used to suspend and transport proppant during hydraulic fracturing operations: sliding water (slickwater), linear gels and cross-linked gels.
In sliding water systems, anionic or cationic polyacrylamides are typically added as friction reducer additives (friction reducer additives), allowing maximum fluid flow with minimum pumping energy. Since the pumping energy requirements for hydraulic fracturing are high (around 10,000 and 100,000 horsepower), the addition of friction reducers to the sliding water fluid allows for high pumping rates while avoiding the need for even higher pumping energy. While these polymers are effective as friction reducers, they are not highly effective as tackifiers and suspending agents. The slip aqueous polymer solution typically contains 0.5-2.0 gallons of friction reducer polymer per 1000 gallons of slip aqueous fluid and the solution has a low viscosity, typically around 3-15 cps. At this low viscosity, the suspended proppant particles can easily settle out of suspension once the turbulent flow stops. For this reason, sliding water fluids are used in the fracturing stage with no proppant, with small particle size proppant or low proppant loading.
A second type of polymer-reinforced fluid system is known as a linear gel system. Linear gel systems typically contain carbohydrate polymers such as guar (guar), hydroxyethyl cellulose, hydroxyethyl guar, hydroxypropyl guar and hydroxypropyl cellulose. These linear gel polymers are typically added at a rate of use of 10 to 50 pounds of polymer per 1000 gallons of linear gel fluid. These concentrations of linear gel polymer result in fluids with improved proppant suspension characteristics relative to sliding aqueous fluids. The linear gel fluid is used to transport proppant at a load level of about 0.1 to 1 pound proppant per gallon of fluid. Beyond this proppant loading level, a more viscous solution is generally required to make a stable suspension.
Crosslinked gels are the most viscous types of polymer-reinforced fluids used to transport proppants. In a crosslinked gel system, a linear gel fluid as described above is crosslinked with added agents (e.g., borates, zirconates, and titanates) in the presence of an alkali metal. When a linear gel fluid is crosslinked into a crosslinked gel fluid, the viscosity is much higher and the proppant can be effectively suspended. Linear gels and crosslinked gel fluids have certain advantages, but they require high dosage rates of expensive polymers.
Modification of the proppant particles can be advantageously used to improve their performance in hydraulic fracturing systems. First, if the proppant particles are more buoyant, a less viscous suspension fluid may be used, which may still transport the particles to the target area, but is more easily pumped into the formation. Second, after the frac line has been injected, it is desirable for the proppant to remain where it is placed throughout the life of the well. If changes in the reservoir during production of the well force the proppant out of position, the production equipment may break and the conductivity of the reservoir formation may decrease as the reservoir pores become plugged with displaced proppant. Third, once they are placed in the fracture, the proppants in the system should be resistant to closure stresses. Closure stresses in certain shale gas wells can range from 1700psi up to and in excess of 15,000psi (for deep high temperature wells). Care must be taken that the proppants do not fail under this stress, so that they are not crushed into fine particles that can migrate to undesired locations in the well, thereby affecting production. Desirably, the proppant should resist diagenesis during the fracturing process. The combination of high pressure and temperature with chemicals used in fracturing fluids can adversely affect the proppant particles, causing their diagenetic effect, which over time can ultimately produce fine particulate matter that can go out of size range and reduce the productivity of the well.
Current proppant systems and polymer-enhanced fracturing fluids address these concerns so that the proppants can be carried by the fracturing fluid, can remain in place once they reach their target destination, and can resist closure stresses in the formation. One method of making suitable proppants includes coating the proppant material with a resin. The resin-coated proppant may be fully cured or partially cured. By helping to distribute stress in the grain particles, the fully cured resin can provide crush resistance to the proppant matrix. The fully cured resin can also help reduce fines (fine) migration by encapsulating the proppant particles. If initially partially cured, the resin may become fully cured once placed within the fracture. This process can yield the same benefits as using a fully cured resin at the beginning. The resin can reduce the conductivity and permeability of the fracture even when the proppant keeps it open. In addition, the resins may fail, so that their advantages are lost. Resin-based systems tend to be expensive and still tend to settle out of suspension.
Another method of making suitable proppants involves mixing the additive with the proppant itself (e.g., fibers, elastomeric particles, etc.). The additives can affect the rheological properties of the delivered slurry, making it more difficult to deliver the proppant to the desired location within the fracture. In addition, the use of additives can interfere with the uniform placement of the proppant mixture within the fracture site.
In addition, there are health, safety and environmental concerns associated with the processing of proppants. For example, fine particles ("fines"), such as crystalline silica dust, are commonly found in naturally occurring sand deposits. These fines may be released as respirable dust during handling and processing of the proppant sand. When exposed for long periods of time, the dust can be harmful to workers, resulting in various inhalation-related conditions, such as silicosis, chronic obstructive pulmonary disease, lung cancer, and the like. In addition to these health effects, fines can cause "nuisance dust" problems such as fouling of equipment and environmental pollution.
While there are known methods in the art to address the limitations of proppant systems, certain problems still exist. Accordingly, there is a need in the art for improved proppant systems that allow for precise placement, maintain fracture conductivity after placement, protect well production efficiency and equipment life, and promote worker health and safety. It is also desirable that such an improved system be cost effective.
Disclosure of Invention
In embodiments, disclosed herein is a modified proppant comprising a proppant particle and a hydrogel coating, wherein the hydrogel coating is applied to a surface of the proppant particle and localized on the surface to produce the modified proppant. The hydrogel coating may contain a water-swellable polymer. In embodiments, the hydrogel coating is applied as a liquid to a surface that may contain a solvent or carrier fluid; the liquid hydrogel coating may be changed to a dried hydrogel coating by removing the solvent or carrier fluid. In embodiments, the hydrogel coating comprises a water-swellable polymer that responds to elevated temperature or saline conditions by collapsing (collapsing) volume or thickness. In an embodiment, the hydrogel coating contains a hydrophobic comonomer selected from the group consisting of: alkyl acrylates, N-alkylacrylamides, N-isopropylacrylamide, propylene oxide, styrene and vinylcaprolactam. In embodiments, the dried hydrogel coating is capable of expanding in volume upon contact with an aqueous fluid to form a swollen hydrogel coating having a thickness of at least about 10% greater than the dried hydrogel coating. In an embodiment, the hydrogel coating comprises a polymer selected from the group consisting of: polyacrylamide, polyacrylic acid, copolymers of acrylamide and acrylate, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, guar gum, carboxymethyl hydroxypropyl guar gum, hydrophobically associating swellable emulsion polymers, and latex polymers. In embodiments, the hydrogel coating further comprises a chemical additive selected from the group consisting of: scale inhibitors (scale inhibitors), biocides (biocides), demulsifiers, wax control agents, asphaltene control agents, and tracers.
In embodiments, the modified proppant further comprises a cationic/anionic polymer pair comprising a cationic polymer and a high molecular weight anionic polymer; the cationic polymer may be selected from the group consisting of: poly-DADMAC, LPEI, BPEI, chitosan, and cationic polyacrylamide. In embodiments, the modified proppant further comprises a crosslinker; the crosslinking agent may contain a covalent crosslinking agent, and the covalent crosslinking agent may contain a functional group selected from the group consisting of: epoxides, anhydrides, aldehydes, diisocyanates and carbodiimides. In embodiments, the covalent cross-linking agent may 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) carbodiimide. In embodiments, the modified proppant may further contain a delayed hydration additive; the delayed hydration additive may be selected from the group consisting of: low hydrophilic-lipophilic balance surfactant, repellent capable of repelling modifying (finishing) surfactant, photo-ionic cross-linking agent, photo-covalent cross-linking agent and monovalent salt charge shielding agent. In embodiments, the modified proppant further comprises an alcohol selected from the group consisting of: ethylene glycol, propylene glycol, glycerol, propanol and ethanol. In an embodiment, the modified proppant further comprises an anti-caking agent.
Disclosed herein are hydraulic fracturing formulations containing the modified proppants described above. In embodiments, the formulation may also contain uncoated sand and/or fiber. In an embodiment, disclosed herein is a method for fracturing a well, the method comprising preparing a hydraulic fracturing formulation as described above, and introducing the hydraulic fracturing formulation into the well in an effective volume and at an effective pressure for hydraulic fracturing, thereby fracturing the well.
Also disclosed herein, in an embodiment, is a method of forming a modified proppant comprising providing a proppant particle; and applying the hydrogel coating to the surface of the proppant particle such that the hydrogel coating is localized on the surface. In embodiments, the hydrogel coating is applied to the surface as a liquid. The method may further comprise the step of drying the hydrogel coating on the surface by a drying process, which may comprise heating the hydrogel coating. In embodiments, the hydrogel coating contains a solvent or carrier fluid, and the hydrogel coating is dried on the surface by removing the solvent or carrier fluid to form a dried hydrogel coating. In embodiments, the method may further comprise the step of exposing the dried hydrogel coating to an aqueous fluid to form a swollen hydrogel coating, wherein the swollen hydrogel coating expands in volume to have a thickness that is at least about 10% greater than the thickness of the dried hydrogel coating.
Further, disclosed herein is a method for making a modified proppant comprising providing a proppant base particle and a fluid polymerized coating composition, applying the fluid polymerized coating composition on the proppant base particle, mixing the proppant base particle and the fluid polymer coating composition to form the modified proppant, and drying the modified proppant, wherein the fluid polymerized coating composition contains a hydrogel polymer, and wherein the hydrogel polymer localizes on the surface of the proppant base particle to produce the modified proppant. In embodiments, the manufacturing occurs at or near the point of use of the modified proppant. In an embodiment, the proppant substrate particle contains sand. In embodiments, the sand is obtained at or near the point where the modified proppant is used. The methods may further comprise adding an alcohol selected from the group consisting of: ethylene glycol, propylene glycol, glycerol, propanol and ethanol. These methods may further comprise adding a conversion (inversion) promoter during or after the step of mixing the proppant substrate particles and the fluid polymer coating composition. The methods may further comprise adding an anti-caking agent to the modified proppant.
Drawings
Fig. 1 is a flow diagram of a manufacturing process for self-suspending proppants.
Figure 2 is a graph of bed height versus shear time for three sets of self-suspending proppant samples.
Figure 3 is a graph of bed height versus mixing time for two sets of self-suspending proppant samples.
Figure 4 is a graph of bed height versus mixing time for two sets of self-suspending proppant samples.
Fig. 5 is a graph of bed height versus mixing time for a series of treated self-suspending proppant samples.
Figure 6 is a graph of bed height for different amounts of calcium silicate added to self-suspending proppant samples.
Fig. 7 is a graph of bed height versus drying time for a series of pretreated and non-pretreated proppant samples.
Figure 8 shows a graph of bed height versus drying time at various temperatures.
Figure 9 shows a plot of temperature versus mixing time for a series of treated self-suspending proppant samples.
Fig. 10 shows a graph of bed height and loss of ignition (LOI) versus drying time.
Detailed Description
1. Modified proppant particles
Disclosed herein are systems and methods for forming and using proppant particles with hydrogel surface layers to enhance the hydrodynamic volume of the proppant particles during fluid transport, resulting in a more stable proppant suspension that is resistant to settling, separation, and sifting out before the proppant can reach the intended target destination in the fracture. Other benefits of the hydrogel-coated proppants disclosed herein include a lower tendency to corrode equipment, a lower coefficient of friction in the wet state, good bond adhesion to each other after placement at the fracture site, resistance to uncontrolled fines formation, and anti-fouling properties attributable to the hydrophilic surface. In embodiments, the disclosed system for forming proppant particles may be applied to the most widely used types of proppant substrates, such as sand, resin coated sand, and ceramics. In other embodiments, the proppant particles can be formed from a variety of matrices, including fibrous materials, available to those of ordinary skill in the art. In certain embodiments, the proppant particles can be manufactured such that they are resistant to crushing or deformation, such that they are resistant to displacement, and such that they can be suspended in a less viscous fluid carrier for transport into the formation.
The invention includes 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. In embodiments, these self-suspending proppants are formed by modifying a particle matrix with a water-swellable polymer coating (e.g., a hydrogel). In embodiments, the particle matrix may be modified with a polymer coating prior to introducing the particle matrix into the fracturing fluid. In embodiments, the amount of hydrogel polymer coating may range from about 0.1% to about 10% based on the weight of the proppant. In embodiments, the hydrogel layer applied on the surface of the proppant substrate can have a coating thickness of about 0.01% to about 20% of the average diameter of the proppant substrate. Upon hydration and swelling of the hydrogel layer in the fracturing fluid, the hydrogel layer may be swollen by water such that the hydrogel layer thickness may be from about 10% to about 1000% of the average diameter of the proppant substrate.
Methods for modifying proppants include spraying or saturating a liquid polymer formulation on a proppant substrate followed by drying to remove water or other carrier fluid. The drying process may be accelerated by applying heat or vacuum, and by tumbling or agitating the modified proppant during the drying process. Heating may be applied by forced hot air, convection, friction, conduction, combustion, exothermic reactions, microwave heating, or infrared radiation. Agitation has the further advantage of providing a more uniform coating on the proppant material during the proppant modification process.
Fig. 1 schematically illustrates a manufacturing process 100 for preparing self-suspending proppant 130 according to the present disclosure. In the depicted embodiment, sand 132 (e.g., dry sand having less than 0.1% moisture) is transported into the mixing container 124 via the conveyor belt 122, and the liquid polymer composition 120 is sprayed on the sand 132 via the pump and spray nozzle apparatus 134 along the conveyor belt 122. Sand 132 exposed to liquid polymer 120 is reported (ports) to low shear mixing vessel 124 where the ingredients are further blended to form modified sand 128. After mixing, the modified sand containing liquid polymer is sent to a dryer 126 to remove water and/or organic carrier fluid associated with the liquid polymer 120. After the drying step, the dried modified sand 132 is subjected to a finalizing step 134, which may include a shaker and/or other size classification equipment, such as a screen, to remove oversized aggregates. The finalizing step 134 may also subject the dried modified sand 132 to a mechanical mixer, shearing device, grinder, crusher, etc. to break up the aggregate to allow the material to pass through a screen of appropriate size. The finished material 130 is then stored for shipping or use.
In embodiments, the sand used to produce the self-suspending proppant is pre-dried to a moisture content of <1%, and preferably <0.1%, prior to modification by the hydrogel polymer. In embodiments, the sand temperature ranges from about 10 ℃ to about 200 ℃, preferably from about 15 ℃ to about 80 ℃ when mixed with the liquid polymer.
In embodiments, the sand is contacted with the liquid polymer composition by spraying or injection. The amount of liquid polymer composition added ranges from about 1% to about 20% by weight of the sand, preferably from about 2% to about 10% by weight. The sand and liquid polymer are blended for a period of 0.1 to 10 minutes. In a preferred embodiment, the mixing device is a relatively low shear type mixer, such as an inverter, a vertical conical screw blender, a v-cone blender, a double cone blender, a kneading mill, a blade mixer, or a ribbon blender. In embodiments, the mixing device may be equipped with forced air, forced hot air, vacuum, external heating, or other means of causing evaporation of the carrier fluid.
In an embodiment, the modified sand containing the liquid polymer is dried to remove water and/or organic carrier fluid associated with the liquid polymer. The dryer apparatus may be of the conveyor oven, microwave or rotary kiln type. In one embodiment, the drying step is performed in a manner such that the dried modified sand contains less than 1 weight percent residual liquid, including water and any organic carrier fluid associated with the liquid polymer composition.
In embodiments, the same equipment may be used to blend sand with liquid polymer and dry the blended product in a single processing stage or in a continuous production line. In one embodiment, the process of converting a matrix (e.g., sand) into self-suspending proppant may be performed at or near the point of use, for example at an oil and gas well site in preparation for hydraulic fracturing. The method has the following advantages: high material handling costs (e.g., sand) are used to convert commodity materials into specialty materials with increased properties. Sand may be obtained from local sources or shipped directly from a sand production area or warehouse for modification at the point of use. This avoids having to ship the sand first to the blending facility and then second from the blending facility to the point of use. In the case of sand, shipping costs may be higher than material costs, so to control costs, it is desirable to avoid additional shipping.
In one exemplary manufacturing process, sand and modifying chemicals may be added to a continuous mixer. After mixing is complete, the mixture may be (a) ready for use or (b) sent to a drying step. The drying step may include a thermal drying process or a vacuum drying process, and it may include adding an anti-caking agent. The finished product may be stored in a container at the well site. An example of a mixing device is a continuous ribbon blender or a kneading mill. The drying step may be a separate process from the mixing, and the drying step may be designed to avoid over-shearing the finished product, such as a conveyor or tunnel dryer. Other types of drying mechanisms include rotary kilns, microwave dryers, blade dryers and vacuum dryers.
Hydrogel polymers that may be used to modify proppants in accordance with the systems and methods disclosed herein are incorporated, in embodiments, as oil-based emulsions, suspensions, water-based emulsions, latexes, solutions, and dispersions. In embodiments, the hydrogel polymer may be introduced as a distilled emulsion, such as an oil-based emulsion that has been partially evaporated to remove a portion of the carrier fluid. This may provide the advantage of reduced drying requirements compared to conventional emulsions. In embodiments, the hydrogel polymer may be an alkali swellable emulsion, wherein the hydrogel properties of the polymer do not fully develop until the polymer is contacted with the alkali. In this embodiment, the alkali swellable emulsion may be coated on a proppant substrate to form a modified proppant, and the modified proppant may be suspended in the fracturing fluid in the presence of the basic material.
In embodiments, during or prior to the step of mixing the proppant substrate particles and the liquid polymer coating composition, an additive such as an alcohol selected from the group consisting of: ethylene glycol, propylene glycol, glycerol, propanol and ethanol. In embodiments, in a polymeric coating formulation for self-suspending proppants, the conversion promoter that may be used as an additive may include a high HLB surfactant, such as polyoxyethylene lauryl alcohol surfactant (ETHAL LA-12/80%, from ETHOX), ethylene glycol, propylene glycol, water, sodium carbonate, sodium bicarbonate, ammonium chloride, urea, barium chloride, and mixtures thereof.
In other embodiments, the proppant matrix may be modified with a polymer formulation without the need for a drying step. This can be accomplished by using solvent-free polymer formulations or curable formulations. In certain simplified methods, dry or liquid polymer formulations can be applied on proppant substrates via in-line mixing, and the modified materials so prepared can be used directly without further processing. By adding or removing water, or adding other liquids, the moisture content of the proppant matrix can be altered to allow the matrix to be effectively coated, treated, and delivered into the fracturing fluid.
The modified proppant may also be modified with a wetting agent, such as a surfactant or other hydrophilic material, to allow for efficient dispersion in the fracturing fluid. Hydrogel-modified proppants are considered self-suspending when they are suspended in fracturing fluids if they require a lower viscosity fluid to prevent the particles from settling out of suspension.
The modified proppant may also be modified with an anti-caking agent (e.g., calcium silicate, magnesium silicate, colloidal silica, calcium carbonate, or microcrystalline cellulose) to improve the flowability and handling properties of the modified proppant material.
In contrast to conventional methods of making the overall fluid moderately viscous, the hydrogel-modified proppant of the present invention can advantageously use localized polymer concentrations on the proppant surface. The localized hydrogel layer may allow for more efficient use of the polymer, such that a lower total amount of polymer may be used to suspend the proppant, e.g., as compared to conventional polymer-reinforced fracturing fluids (e.g., sliding water, linear gels, and crosslinked gels). While hydrogel-modified proppants are believed to be self-suspending, they may be used in combination with friction reducers, linear gels, and crosslinked gels.
The hydrogel-modified proppants disclosed herein may have the following advantages: the friction-reducing polymer is delivered to the fracturing fluid such that when the hydrogel-modified proppant is used in a hydraulic fracturing operation, no or lesser amounts of other friction-reducing polymer may be needed. In embodiments, some of the hydrogel polymers may be detached from the surface of the proppant to deliver a friction-reducing benefit or viscosity characteristic to the fracturing fluid.
In embodiments, the hydrogel polymer used to make the hydrogel-modified proppant can contain polymers such as polyacrylamide, copolymers of acrylamide with anionic and cationic comonomers, copolymers of acrylamide with hydrophobic comonomers, polyacrylic acid, polyacrylates, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, guar gum, alginates, carrageenan, locust bean gum, carboxymethyl guar gum, carboxymethyl hydroxypropyl guar gum, Hydrophobically Associating Swellable Emulsion (HASE) polymers, latex polymers, starch, and the like. In embodiments, the hydrogel polymer may be crosslinked to enhance the water absorption and swelling properties of the polymer. The crosslinking agents may be incorporated as an element of the hydrogel-based polymer, or they may be incorporated as chemical modifiers for the preformed polymer.
Localizing the polymer around the proppant surface described herein can result in more efficient use of the polymer and can prevent the proppant from settling out of the polymer solution. In embodiments, the polymer layer hydrates around the proppant, effectively preventing proppant/proppant (inter-particle) contact. This may prevent the proppant from forming a dense settled bed and may result in proppant that is more easily resuspended in the fracturing fluid. Modifying the resuspension properties of the proppant may be important if fluid flow is interrupted during a hydraulic fracturing operation. Importantly, in such cases, the proppant can be resuspended as flow is restored to avoid loss of proppant or unexpected blockage of the fluid path.
The polymer surface modification described herein can cause the effective hydrodynamic radius of the proppant particle to increase when the polymer swells. This can result in increased drag (drags) on the proppant as well as effectively changing the overall hydrogel/particle density. Both can result in proppant particles with slower settling rates and good transport properties.
In embodiments, polymer pairing or ionic crosslinking may be used to improve retention (retention) of the hydrogel polymer on the surface of the proppant particle. For example, a cationic polymer may be deposited as a first layer on the proppant to "lock in place" a second layer containing a hydrogel (e.g., a high molecular weight anionic polymer). In embodiments, the cationic polymer may be polydiallyldimethylammonium chloride (poly-DADMAC), Linear Polyethyleneimine (LPEI), Branched Polyethyleneimine (BPEI), chitosan, epichlorohydrin/dimethylamine polymer, ethylene dichloride dimethylamine polymer, or cationic polyacrylamide. A cationic polymer layer can be placed on the proppant either before or after the proppant surface is modified with an anionic hydrogel layer. Ionic interactions can act as a crosslinking mechanism to help prevent anionic polymers from desorbing in a high shear environment, such as by a pump or during pumping through a wellbore. Cationic polymers may also improve polymer retention by causing delayed hydration and elongation of anionic polymer chains. It is believed that less polymer chain elongation during the pumping process will result in higher polymer retention (i.e., less desorption) on the proppant.
Covalently cross-linked hydrogel polymer layers on the surface of the proppant can improve the swelling properties and shear resistance of the polymer to prevent premature release of the hydrogel from the proppant. The covalent crosslinking agent may include the following functional groups: epoxides, anhydrides, aldehydes, diisocyanates, carbodiimides, divinyl or diallyl. Examples of such covalent crosslinking agents include: PEG diglycidyl ether, epichlorohydrin, maleic anhydride, formaldehyde, glyoxal, glutaraldehyde, toluene diisocyanate, methylene diphenyl diisocyanate, 1-ethyl-3- (3-dimethylaminopropyl) carbodiimide, and methylene bisacrylamide. Covalently cross-linked hydrogel polymer layers on the surface of the proppant can effectively create swellable "polymer cages" around the proppant. The covalent bonds prevent the polymer from fully desorbing into solution. The slightly insoluble polymer layer is capable of swelling and producing a hydrated polymer layer.
Delayed/controlled hydration of the polymer layer may be desirable to delay hydration of the polymer surface modification during treatment and initial pumping of the proppant through the wellbore. Environmental factors (e.g., humidity and rain) can cause premature hydration of the polymerized coating, which can make it difficult to effectively meter the proppant dose into the blender during a hydraulic fracturing operation. It is also believed that a fully hydrated polymer layer may be more susceptible to desorption under the high shear conditions associated with pumping down the tubular fracturing fluid. For these reasons, it may be advantageous to design surface-modified proppants with slower or delayed hydration properties. In embodiments, delayed hydration may be achieved by: by adding low hydrophilic-lipophilic balance (HLB) surfactants, repelling high HLB modified surfactants, ionic crosslinking, covalent crosslinking, charge shielding using monovalent salts, or by incorporating a hydrophobic layer (e.g., fatty acid or fatty alcohol).
In embodiments, hydrophobic groups may be incorporated into the hydrogel polymer to allow hydrophobic interactions. The method can improve the salt tolerance of the hydrogel layer such that the hydrogel layer remains swellable even in aqueous fluids containing elevated salt concentrations.
Also disclosed herein is a method of fracturing a well using a hydrogel-coated proppant in combination with a non-hydrogel-coated proppant. For example, hydrogel-coated proppants may use suspending agents that act on non-hydrogel-coated proppants.
Also disclosed herein is a method of improving well productivity through improved proppant placement using hydrogel-coated proppants. The hydrogel coated proppant can be more efficiently transported to the distal end of the fracture to ensure higher productivity of oil and gas from the well. It is believed that the proppant placement will be more effective because the surface-modified proppants disclosed herein may be less inclined to settle out of the fluid and more easily resuspend and transport through the fracture. The ability to transport proppant further into the fracture can significantly increase the effectiveness of the fracturing stimulation operation, resulting in a larger volume of higher density fractures. These fracture channels may advantageously allow gas/condensate to flow more easily from the reservoir into the wellbore.
Also disclosed herein is an improved method of proppant placement using a low viscosity fluid. The surface modified proppants disclosed herein more effectively utilize polymers to suspend/transport proppant particles. The surface modification renders the proppant self-suspending, thereby reducing or eliminating the need for highly viscous fluids/gels to transport the proppant. Thus, lower viscosity fluids may be used in combination with surface-modified proppants to transport the proppant into the fracture. This will advantageously simplify the formulation of broken gels for use with proppants.
Also disclosed herein are more efficient methods of fracturing a well using less proppant. Because a highly effective proppant placement can be achieved using the readily transportable surface-modified proppants disclosed herein, it is expected that a lesser amount of these surface-modified proppants will be required for any given fracturing operation than systems using conventional proppants. Due to the increased demand for fracture grade sand/proppant and the reduced supply of desired-shaped sand for proppant applications, it would be advantageous to provide systems and methods such as those disclosed herein, in which results comparable to or superior to those using current techniques can be achieved using less proppant.
After the hydrogel-coated proppant of the present invention has been pumped into a well, the hydrogel layer can degrade by chemical, thermal, mechanical, and biological mechanisms. In particular, modification of the polymerized surface on the proppant can be disrupted with the aid of chemical demulsifiers (e.g., ammonium persulfate, magnesium peroxide, or other oxidizing agents). Modification of the polymerized surface on the proppant can also be disrupted by means of environmental reservoir conditions (e.g., elevated brine content, elevated temperature) and contact with hydrocarbons. After a target temperature or amount of time is reached in the fluid, the controlled fracture hydrogel layer may serve as a means to guide placement of the proppant in a desired location in the fracture. Degradation of the hydrogel layer is also beneficial to ensure adequate conductivity of the propped fracture after completion of the hydraulic fracturing operation. In embodiments, the hydrogel layer may demonstrate a stimulus-responsive property such that it swells with water when exposed to a first set of conditions (e.g., certain first temperatures or pH) and loses water, loses volume, loses thickness, or even collapses when subjected to a certain set of conditions (e.g., a second temperature or pH).
For example, in one embodiment, a temperature-responsive hydrogel may be coated on the proppant material. The temperature responsive hydrogel layer may swell when exposed to water under a first set of conditions (e.g., water temperatures of 50-100F.) and may subsequently collapse when exposed to a second set of conditions (e.g., water temperatures of 110-450F.). Using this stimulus-response mechanism, temperature-responsive hydrogel-coated proppants can have self-suspending properties because the fracturing fluid carries them into the location of the subterranean fracture when at the initial water temperature (e.g., 50-100 ° F). When the coated proppant encounters higher temperature regions of the subterranean formation (e.g., 110 @and450F), the hydrogel layer may collapse, allowing the proppant to deposit and consolidate in the fracture. The temperature responsive hydrogel may be a water soluble polymer or copolymer composition containing hydrophobic monomers selected from the group consisting of: alkyl acrylates, N-alkylacrylamides, propylene oxide, styrene and vinyl caprolactam. The N-alkyl substituted acrylamide may be N-isopropylacrylamide, N-butylacrylamide, N-octylacrylamide, and the like. The alkyl acrylates may be substituted with alkyl chains having from 1 to about 30 carbons. In a preferred embodiment, the temperature responsive hydrogel polymer comprises N-isopropylacrylamide and contains up to about 90% hydrophilic comonomer units. The type and amount of hydrophobic monomer substituents in the hydrogel polymer can be selected by empirical optimization techniques to adjust the water solubility and temperature response properties of the hydrogel polymer.
Also disclosed herein is a method of delivering a chemical additive into a proppant package by incorporating or associating the chemical additive into the hydrogel layer of a modified proppant. Chemical additives that may be advantageously delivered via the hydrogel layer include scale inhibitors, biocides, demulsifiers, wax controls, asphaltene controls, and tracers. The chemical additives may be in the form of water-soluble materials, water-insoluble particles, fibers, metal powders or flakes, and the like. The chemical additives may be selected such that they slowly dissolve or disintegrate to release their chemical activity. In embodiments, the chemical additive may be incorporated into or associated with the hydrogel layer by physical entrapment, layer-by-layer decomposition, covalent attachment, ionic association, hydrophobic association, or encapsulation. Chemical additives may be added to the proppant separately from the hydrogel, or they may be combined with the hydrogel coating formulation in the manufacture of the coated proppant. Demulsifier chemicals such as persulfates, peroxides, permanganates, perchlorates, periodates, or percarbonates may be added to the delivery method. Delivery and delivery of these chemicals using hydrogel coated proppants has the advantage of targeting the chemicals to the fracture or proppant pack. This method provides the advantage of concentrating the chemical additives at the location where their function is required, thereby reducing the total amount of chemical additives required. Certain demulsifiers such as peroxides and persulfates have accelerated activity at higher temperatures. Using this method, the emulsion breaker chemicals incorporated in the hydrogel layer will be activated when placed in the crack by the elevated temperature of the reservoir carrying the oil.
In embodiments, the surface of the proppant particle substrate can be coated with the selected polymer, either as a single layer or as a series of multiple coatings. The coating (single or multiple layers) may in some cases exhibit switchable behavior. The term "switchable behavior" or "switching behavior" as used herein refers to a change in a property as a condition changes, for example, from one set of properties during a delivery phase to another set of properties inside a fracture. For example, the transformation behavior may be seen when the particles prove to have hydrophilic properties in the fracturing fluid and when placed within the fracture have adhesive properties. Such behavior can be triggered, for example, by high sealing pressures inside the fracture site, so that the outer layer of the coating rearranges itself to exhibit more favorable properties.
In one embodiment, the coated particles may convert from hydrophilic to hydrophobic when subjected to high pressure inside the fracture. In an exemplary embodiment, during the transport phase, the hydrophilic coating of the particles tends to fully swell when exposed to the water-based fracturing fluid. As a result, the coating can provide the particles with lubrication in this state, facilitating their movement through the proppant slurry. When the particles have been transported to their destination within fractures in the formation, the high pressure will overcome the steric repulsion of the external hydrophilic polymer chains, forcing the outer layer to rearrange itself, leaving the inner layer exposed. In embodiments, the switchable inner layer may be hydrophobic or adhesive, or both. When the inner layer is exposed, its properties may manifest themselves. If the inner layer has adhesive properties, for example, it may fix the particles to each other to prevent them from flowing back. The inner layer may also be configured to trap fines in the event of failure of the proppant particles. In addition, residual intact hydrophilic groups present in the outer coating may allow the oil to flow easily through the proppant package.
In embodiments, the coating-coated proppant particles carrying the following layers may be produced. First, pressure-activated fixative polymers may be used to coat the proppant substrate. The coating may be elastic, providing strength to the proppant package by helping aggregate proppant particles and distributing stress. In addition, the coating may encapsulate the matrix particles and retain any fines produced in the event of matrix failure. Second, the block copolymer may be adsorbed or otherwise disposed on the first layer of the coating. The copolymer may have a portion with a high affinity relative to the first polymerized layer, allowing for strong interactions (hydrophobic interactions), and may have another portion that is hydrophilic, allowing for easy transport of the proppant in the transport fluid.
In certain embodiments, a stronger interaction between the first coating and the second coating may be useful. To achieve this, a swell-deswell technique may be implemented. For example, the block copolymer may adsorb on the surface of the elastic-coated particle. Subsequently, the first coating can be swollen with a small amount of organic solvent that allows the hydrophobic block of the copolymer to penetrate deeper into the first coating and become entangled in the elastomeric coating. By removing the organic solvent, the layered polymerized composite will de-swell, resulting in a stronger interaction of the copolymer with the elastomeric particles. Useful methods for Swelling-deswelling techniques are described in "Swelling-based method for Preparing Stable, Functionalized Polymer Colloids" a.kim et al, j.am.chem.soc. (2005)127:1592-1593, the contents of which are incorporated herein by reference.
In embodiments, proppant systems using the coatings disclosed herein can reduce the amount of airborne particles associated with proppant manufacturing. For example, respirable dust (including fine crystalline silica dust) associated with handling and processing proppant sand may be captured and retained by the proppant coating during their processing. In embodiments, a coating agent having a specific affinity for particles in an environment that may adversely affect worker safety or create nuisance dust problems may be added. In embodiments, the hydrogel coating on the proppant particle may act as a binder or collector by mechanically entrapping or adhering to the dust particle.
While the systems described herein relate to a two-layer coating system, it is to be understood that there may be multiple (i.e., more than two) coatings forming the composite proppant particles disclosed herein, wherein each of the multiple coatings has some or all of the characteristics of the two coatings as described above, wherein one or more of the multiple coatings provides additional properties or characteristics.
2. Particle matrix material
Composite proppant particles according to these systems and methods can be formed using a wide variety of proppant matrix particles. The proppant particle matrix for use in the present invention may include degraded sand, resin coated sand, bauxite, ceramic materials, glass materials, walnut shells, polymeric materials, resin materials, rubber materials, and the like and combinations thereof. The self-suspending proppants ("SSPs") disclosed herein may also be prepared using specialized proppants, such as ceramics, bauxite, and resin coated sand. By combining sand SSP with a dedicated SSP, proppant injection can have favorable strength, permeability, suspension, and transport properties. In embodiments, the matrix may comprise naturally occurring materials such as nut shells (e.g., walnut, pecan, coconut, almond, ivory, brazil, etc.) that have been chopped, ground, pulverized, or crushed to a suitable size, or seed hulls or fruit pits (e.g., plum, olive, peach, cherry, apricot, etc.) that have been chopped, ground, pulverized, or crushed to a suitable size, or chopped, ground, pulverized, or crushed materials such as from other plants (e.g., corn cobs). In embodiments, the substrate may be derived from wood or processed wood, including but not limited to wood such as oak, pecan, walnut, mahogany, poplar, and the like. In embodiments, the aggregate may be formed using an inorganic material bonded or bonded to an organic material. It is desirable that the proppant particle matrix contain particles (whether individual species or aggregates of two or more species) having a size of about 4 to 100 mesh size (per standard number of screens). The term "particle" as used herein includes all known shapes of materials such as, but not limited to, spherical materials, elongated materials, polygonal materials, fibrous materials, irregular materials, and any mixtures thereof.
In embodiments, the particle matrix may be formed as a composite from a binder and a filler material. Suitable filler materials may include inorganic materials such as solid glass, glass microspheres, fly ash, silica, alumina, fumed carbon, carbon black, graphite, mica, boron, zirconia, talc, kaolin, titanium dioxide, calcium silicate, and the like. In certain embodiments, the proppant particle matrix may be reinforced to increase their resistance to high pressures of the formation, which may crush or deform them. The reinforcing material may be selected from those materials that add structural strength to the proppant particle matrix, such as high strength particles, e.g., ceramics, metals, glass, sand, etc., or any other material that can be combined with the particle matrix to provide additional strength.
In certain embodiments, the proppant particle matrix can be manufactured as an aggregate of two or more different materials that provide different properties. For example, a core particle matrix having a high compressive strength may be combined with a buoyant material having a lower density than a high-compressive-strength material. The combination of these two materials as an aggregate can provide core particles with a moderate amount of strength while having a relatively low density. As lower density particles, they may be sufficiently suspended in the less viscous fracturing fluid, allowing the fracturing fluid to be more easily pumped, and allowing the proppant to be more dispersed within the formation as they are pushed to more distant areas by the less viscous fluid. High density materials (e.g., sand, ceramics, bauxite, etc.) used as the proppant particle matrix may 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 shells, fruit pits, wood, or other naturally occurring materials that have been shredded, ground, pulverized, or crushed) to yield less dense aggregates that still have sufficient compressive strength.
Using techniques for attaching two components to each other, aggregates suitable for use as a proppant particle matrix can be formed. As a method of preparation, the proppant particle matrix may be mixed with a buoyant material having a particle size similar to the size of the proppant particle matrix. The two types of particles may then be mixed together and combined by a binder (e.g., wax, novolac resin, etc.) such that a population of paired aggregate particles is formed, one sub-population having a proppant particle matrix connected to another similar particle, one sub-population having a proppant particle matrix connected to buoyant particles, one sub-population having buoyant particles connected to another buoyant particle. The three populations can be separated by their density differences: the first sub-population sinks in the water, the second sub-population remains suspended in the liquid, and the third sub-population will float.
In other embodiments, the proppant particle matrix may be designed to be less dense by covering the surface of the particle matrix with a foam material. The thickness of the foam material can be designed to result in an effectively neutrally buoyant composite. To produce such coated proppant particles, particles having the desired compressive strength may be coated with a reactant for the foaming reaction, followed by exposure to other reactants. When foam formation is triggered, foam-coated proppant particles will be produced.
As one example, water-blown polyurethane foam may be used to provide a coating around the particles that will reduce the overall particle density. To prepare such coated particles, the particles may be initially coated with a reactant a, such as a mixture of one or more polyols and a suitable catalyst (e.g., an amine). The particles may then be exposed to a diisocyanate-containing reactant B. The final foam will form on the particles, for example when treated with steam under vibration; agitation will prevent the particles from agglomerating due to the formation of foam on their surface.
In embodiments, fibers (including biodegradable fibers) may be added to the fracturing fluid with the SSP. The fibers (including biodegradable fibers) may form a network of fibers that help the fluid carry the proppant. A variety of fiber types are familiar to those skilled in the art for adding to fracturing fluids. As understood by those skilled in the art, fibers added to the fracturing fluid may degrade under downhole conditions and form channels in the proppant package. The channels are highly permeable and therefore flow channels for the hydrocarbons traveling from the formation to the wellbore.
The term "fiber" may refer to synthetic or natural fibers. The term "synthetic fibers" as used herein includes fibers or microfibers that are manufactured in whole or in part. Synthetic fibers include man-made fibers where natural precursor materials are modified to form fibers. For example, cellulose (derived from natural materials) may be formed into man-made fibres, such as Rayon (Rayon) or Lyocell (Lyocell). Cellulose may also be modified to produce cellulose acetate fibers. These artificial fibers are examples of synthetic fibers. Synthetic fibers may be formed from inorganic or organic synthetic materials. Exemplary synthetic fibers can be formed from materials such as substituted or unsubstituted lactide, glycolide, polylactic acid, polyglycolic acid, or copolymers thereof. Other materials for forming the fibers include polymers of or copolymers with glycolic acid, as will be familiar to those skilled in the art.
The term "natural fiber" as used herein refers to fibers or microfibers that are derived from natural sources without artificial modification. Natural fibers include plant-derived (vegetable-derived) fibers, animal-derived fibers, and mineral-derived fibers. The plant-derived fibers may be primarily cellulosic, e.g., cotton, jute, flax, hemp, sisal, ramie, and the like. Plant-derived fibers may include fibers derived from seeds or seed husks, such as cotton or kapok. Plant-derived fibers may include fibers derived from leaves, such as sisal and agave. Plant-derived fibers can include fibers derived from the outer or bast surrounding the stem of a plant, such as flax, jute, kenaf, hemp, ramie, rattan, soybean fiber, vine fiber (vine fiber), jute, kenaf, industrial hemp, ramie, rattan, soybean fiber, and banana fiber. The plant-derived fibers may include fibers derived from the fruit of a plant, such as coconut fibers. Plant-derived fibers may include fibers derived from the stems of plants, such as wheat, rice, barley, bamboo, and grasses. The plant-derived fibers may include wood fibers. Animal-derived fibers typically contain proteins, e.g., wool, silk, mohair, and the like. Animal-derived fibers can be derived from animal hair, e.g., sheep wool, goat wool, alpaca, horsehair, and the like. Animal-derived fibers can be derived from animal body parts, e.g., catgut, tendon, and the like. Animal-derived fibers can be collected from dried saliva or other secretions of insects or their cocoons, e.g., silk derived from filarial cocoons. Animal-derived fibers may be derived from feathers of birds. Mineral-derived natural fibers are derived from minerals. The mineral-derived fibers may be derived from asbestos. The mineral-derived fibers can be glass or ceramic fibers, for example, glass wool fibers, quartz fibers, alumina, silicon carbide, boron carbide, and the like.
The fibers may be advantageously selected or formed such that they degrade at a specified pH or temperature, or over time, and/or are chemically compatible with a specified carrier fluid used for proppant delivery. Useful synthetic fibers can be made from solid polymers such as solid cyclic dimers or organic acids, which are known to hydrolyze under specific or adjustable conditions of pH, temperature, time, and the like. Advantageously, the fibers can be broken down at the location where they have been delivered under predetermined conditions. Advantageously, the decomposition of the fibers may result in environmentally friendly decomposition products.
Examples
Material
30/70 mesh fracturing sand
30/50 mesh fracturing sand
40/70 mesh fracturing sand
Polydiallyldimethylammonium chloride (Aldrich, St. Louis, MO)
·LPEI500(Polymer Chemistry Innovations，Tucson，AZ)
Ethanol, 200Proof (Aldrich, St. Louis, MO)
Hexane (VWR, Radnor, PA)
·FLOP AM EM533(SNF)
Polyethylene glycol diglycidyl ether (Aldrich, St. Louis, MO)
Glyoxal, 40% by weight solution (Aldrich, St. Louis, MO)
·HFC-44(Polymer Ventures，Charleston，SC)
Sodium carboxymethylcellulose (Sigma-Aldrich, St. Louis, MO)
Ammonium persulfate (Sigma-Aldrich, St. Louis, MO)
Ethoxylated lauryl alcohol surfactant (Ethal LA-12/80%) (Ethox chemical Co, SC)
Glycerol (US Glycerin, Kalamazoo, MI)
Potassium chloride (Morton Salt, Chicago, IL)
Fumed silica (Cabot, Boston, MA)
Example 1: preparation of the inner Polymer layer
An inner polymer layer of 100ppm concentration was prepared on the sand sample by adding 200g of 30/70 mesh frac sand to a FlackTek Max100 long tank. To the sand was added 85g of tap water and 2g of 1% polydiallyldimethylammonium chloride (PDAC) solution. The sample was then shaken manually for about 5 minutes, vacuum filtered, and dried in an oven at 80 ℃. The sand sample was then removed from the oven and used for subsequent testing.
The same method as described above was used to formulate a 10ppm internal polymer layer coating, except that only 0.2g1% PDAC solution was used.
At maximum polymer loading ("Max PDAC"), the inner polymer layer was formulated using the same method as described above, except that 1g20 wt% PDAC solution was used. After treatment, the sand was washed with excess tap water, vacuum filtered, and dried in an oven at 80 ℃. The sand sample was then removed from the oven and used for subsequent testing.
Example 2: preparation of the inner Polymer layer
An inner polymer layer of 100ppm concentration was prepared on the sand sample by dissolving 0.2g of LPEI500 in 10g of ethanol to form a 2% LPEI500 ethanol solution. In a 250mL round bottom flask, 0.75g of 2% LPEI500 solution was added to 70g of ethanol. 150g of 30/70 mesh frac sand was then added to the round bottom flask. The solvent was removed using a 65 ℃ water bath using a rotary evaporator. The sample was then removed from the flask and used for subsequent testing.
Example 3: preparation of the outer Polymer layer
The outer polymer layer was applied to the sand sample by mixing the sand with a liquid Flopam EM533 polymer under different conditions. In one coating method, the neat polymer product is added. In another coating process, the polymer product is extended by dilution with hexane. For hexane dilution, 10g of polymer was added to 10g of hexane in a 40mL glass bottle and mixed by vortexing until homogeneous. The polymer was then added to a 30g30/70 mesh frac sand sample in a FlackTek Max100 tank. The samples were placed in a FlackTek DAC150speedMixer at 2600rpm for about 25 seconds. The samples were removed from the SpeedMixer and dried in an oven at 80 ℃ overnight.
Example 4: properties of the outer Polymer layer, settling time
The performance of the sand samples prepared in the previous examples was evaluated in a sedimentation test. All sand samples were screened through a 25 mesh screen prior to testing. The settling time was obtained by adding a 1g sample of sand to 100mL of tap water in a 100mL graduated cylinder. The cylinder was then inverted about 8 times and the time required for all the sand to settle at the bottom of the cylinder was then recorded. Three recordings were made for each sample. Settling times are reported in table 1.
TABLE 1
Example 5: properties of the outer Polymer layer, settled bed height
The sand samples prepared in example 3 using the outer polymer layer were also evaluated by observing the height of the bed settled in water. In a 20mL glass bottle, a 1g sample of sand was added to 10g of tap water. The vial was inverted about 10 times to fully wet the sand treatment. The vials were then left undisturbed for about 30 minutes. A digital caliper was then used to record the height of the bed of sand in the bottle. The results are reported in table 2.
TABLE 2
Example 6: ionic crosslinking of the outer polymer layer
A 40g30/70 mesh frac sand sample was treated with the outer polymer layer by adding 1.3g Flopam EM533 polymer to 40g sand in a FlackTek Max100 tank and shaking the tank manually for 2 minutes. The sand is then screened through a 25 mesh screen. To evaluate polymer retention on sand under shear, testing was performed by adding 10g of treated sand to 200g of tap water with different levels of PDAC in a 300mL glass beaker. It is believed that the PDAC will stabilize the polymer layer on the sand by ionic interaction. The slurry was then stirred at 900rpm for 5 minutes using a flat propeller type mixing blade, using an overhead mixer. Mixing was then stopped and the sample allowed to settle for 10 minutes. The viscosity of the supernatant was then measured using a Brookfield DV-III + rheometer with LV-II rotor at 60 rpm. The bed height of the settled sand in the beaker was also recorded using a digital caliper. The results are reported in table 3.
TABLE 3
| Sample (I) | PDAC cone (ppm) | Viscosity (cP) | Bed height (mm) |
| 12 | 0 | 25 | 4.5 |
| 13 | 60 | 10 | 8.6 |
| 14 | 200 | 2.5 | 6.3 |
Example 7: covalently cross-linked outer polymer layer-PEGDGE
Four 30/70 mesh frac sand samples were treated with Flopam EM533 by adding 0.66g of polymer to 20g of sand in a FlackTek Max100 tank and shaking manually for 2 minutes. Different amounts of new 1% polyethylene glycol diglycidyl ether in deionized water were then added to the treated sand samples. The sample was again shaken manually for 2 minutes and then placed in an oven at 100 ℃ for 1 hour. The sample was then removed from the oven and sieved through a 25 mesh screen. Bed heights of four samples were measured as follows: the vial was inverted about 10 times by adding a 1g sample of sand to 10g of tap water in a 20mL glass vial to fully wet the sand and allow the vial to remain undisturbed for about 10 minutes. Bed height was then measured using digital calipers. The results are shown in Table 4.
TABLE 4
| Sample (I) | 1%PEGDGE(g) | Bed height (mm) |
| 15 | 0.1 | 9.3 |
| 16 | 0.2 | 8.8 |
| 17 | 1.0 | 6.2 |
| 18 | 0 | 12.7 |
Example 8: covalently cross-linked outer polymer layer-glyoxal
Four 30/70 mesh frac sand samples were treated with Flopam EM533 in a FlackTek Max100 tank by adding 0.66g of polymer to 20g of sand and shaking manually for 2 minutes. A 1% glyoxal ethanol solution was prepared by adding 0.25g40 wt% glyoxal to a 20mL glass bottle and diluting to 10g with ethanol. Different amounts of 1% glyoxal solution were then added to the treated sand samples, the samples were shaken manually for 2 minutes, and placed in an oven at 100 ℃ for 30 minutes. The sand sample was removed from the oven and sieved through a 25 mesh screen. For settled bed height measurements, 1g of sand was added to 10g of tap water in a 20mL bottle, inverted about 10 times, and held for about 10 minutes to settle. Bed height was measured using digital calipers. The results are shown in Table 5.
TABLE 5
| Sample (I) | 1% glyoxal g) | Bed height (mm) |
| 19 | 0.2 | 3.8 |
| 20 | 0.5 | 3.5 |
| 21 | 1.0 | 2.7 |
| 22 | 2.0 | 2.7 |
Example 9: cationic/anionic polymer treatment
Three 30g30/70 mesh frac sand samples were treated with Polymer ventures HCF-44 in a FlackTek Max100 tank. The jar was shaken manually for 2 minutes. Then, Flopam EM533 was added to each sample. The jar was shaken manually again for 2 minutes. The sample was then dried at 80 ℃ overnight. The sand sample was removed from the oven and sieved through a 25 mesh screen. For settled bed height measurements, 1g of sand was added to 10g of tap water in a 20mL bottle, inverted about 10 times, and held for about 10 minutes to settle. Bed height was measured using digital calipers. The results are given in table 6.
TABLE 6
| Sample (I) | HCF-44(g) | Flopam EM533(g) | Bed height (mm) |
| 23 | 0 | 0.45 | 10.26 |
| 24 | 0.07 | 0.38 | 8.08 |
| 25 | 1.0 | 0.35 | 5.08 |
| 26 | 1.5 | 0.30 | 3.94 |
Example 10: sand coated with macromolecular particles
A FlackTek Max100 tank was charged with 30g of 30/70 mesh frac sand sample. 0.3g of paraffin wax was added to the sand. The samples were placed in a FlackTek DAC150speedMixer and mixed for 2 minutes at 2500 rpm. After mixing, 1g of carboxymethyl cellulose was added to the sample. The sample was placed again in the FlackTek DAC150speedMixer and mixed at 2500rpm for 1 minute. The sand sample was screened through a 25 mesh screen. For settled bed height measurements, 1g of sand was added to 10g of tap water in a 20mL bottle, inverted about 10 times, and held for about 10 minutes to settle. The sand in this sample immediately coagulated together and did not disperse in water and the bed height could not be accurately measured.
Example 11: modified sand beaker test
A FlackTek Max100 tank was charged with 30g of 30/70 mesh frac sand sample. The sand was treated with Flopam EM533 by adding 0.45g of polymer to the jar and shaking manually for 2 minutes. The sample was then dried at 80 ℃ overnight. After drying, the samples were removed from the oven and sieved through a 25 mesh screen. After sieving, four samples were prepared by adding 1g of treated sand to 10g of tap water in 20mL bottles. The vial was inverted about 10 times and settled for 10 minutes. A10% ammonium persulfate solution was prepared by adding 2g of ammonium persulfate to 18g of tap water. Various amounts of 10% ammonium persulfate solutions were then added to the sample bottles. The sample was inverted several times to mix and then placed in an oven at 80 ℃ for 1 hour. After 1 hour, the sample was removed and the settled bed height was observed. Table 7 shows the results.
TABLE 7
| Sample (I) | 10%APS(μL) | Suspension of sand |
| 27 | 0 | Suspended in water |
| 28 | 180 | Sedimentation |
| 29 | 90 | Sedimentation |
| 30 | 18 | Sedimentation |
Example 12: emulsion additive
To determine the effect of the emulsion additive on self-suspending proppant ("SSP") performance, glycerin and cetyl alcohol (Ethal) LA-12/80% were added to the emulsion polymer EM533 prior to proppant sand application. Three different polymer samples were prepared as follows:
SSP polymers: 10g EM533, no additives
SSP + glycerol: 9g EM533 and 1g Glycerol
SSP + glycerol + cetyl alcohol: 9g EM533+0.9g Glycerol +0.1g cetyl alcohol LA-12/80%
Each of the above samples was vortex mixed for 30 seconds to ensure homogeneity. To prepare the modified proppant, 50g40/70 sand was combined with 1.5g of one of the above polymer samples followed by mixing for 30 seconds. Shear stability of the modified proppant samples was evaluated in a 1 liter shear test. The test consists of adding 50g of modified proppant to 1 liter of water in a square plastic beaker, followed by 200rpm (corresponding to about 550 s) on a blade/jar mixer (ECengineering, model CLM-4)-1Shear rate) for different amounts of time. The sheared sample was then poured into a 1000mL graduated cylinder and settled by gravity for 10 minutes, after which the bed height of settled proppant sand was recorded. For comparison, unmodified proppant sand would yield a bed height of 10mm after mixing in any amount. Due to the hydrogel layer encapsulating the sand grains, the self-suspending proppant sample will produce a higher bed level relative to the unmodified proppant. Generally, increasing the shear rate or time may cause the bed height of the self-suspending proppant to decrease as a result of desorption of the hydrogel layer from the surface of the modified proppant. For this reason, it is desirable that the bed height in this test is as high as possible, especially after shearing. The following results show that the addition of glycerol improves bed height and shear stability of the productAnd (5) performing qualitative determination. Glycerol and cetyl alcohol were added, although improving the initial bed height, the long term shear stability was slightly reduced. These results are illustrated graphically in fig. 2.
Example 13: glycerin and processability
This experiment sought to determine the effect of glycerin and other additives on the performance of self-suspending proppants (hereinafter denoted by SSP). To the drum of a kitchen aid bench mixer of model KSM90WH fitted with blade attachment was added 1kg dry 40/70 sand. 3.09g of glycerol was mixed with 27.84g of EM533 emulsion polymer, then the mixture was added to the top of the sand and soaked for 1 minute. At time 0, the mixer was started at speed 1(72rpm primary rotation). Samples were collected at 1-2 minute intervals and dried at 90 ℃ for 1 hour. Subsequently, each sample was subjected to a 1 liter shear test, in which 50g of SSP was added in 1L of water and at 200rpm (about 550 s)-1Shear rate of (d) for 20 minutes. After transferring the water/SSP mixture to a 1 liter graduated cylinder and settling for 10 minutes, the bed height was recorded. The experiment was repeated using 30.93g of EM533 emulsion polymer added separately to 1kg of sand. These results are shown in FIG. 3. As shown in the figure, the glycerol additive significantly increased the bed height.
The performance difference was even more pronounced when the experiment was repeated at higher mixing speeds. The mixer was set to speed 4(150rpm primary rotation) at this time. At low mixing times, the samples were not well mixed, resulting in incomplete coating of sand and polymer being easily desorbed from the surface of the SSP during shear testing. As the mixing time of the coating process is increased, the performance also increases until the desired coating is achieved, resulting in the maximum bed height for the sample. Subsequently, at higher mixing times, increasingly worse (lower) bed heights are seen, possibly as a result of coating wear during prolonged mixing. At higher mixing speeds, this process occurs even faster, such that the processing window of the emulsion polymer alone is less than 1 minute. With the addition of glycerol and the use of lower mixing speeds, the process window widens to nearly 15 minutes. Glycerol caused a broadening of the processing window compared to the test using emulsion polymer alone, indicating that SSP preparations with glycerol were more robust. At the same time, the glycerin allows the polymer emulsion to invert more completely, resulting in better coating and increased bed height. At higher mixing speeds, testing with a combination of glycerol and emulsion polymer EM533 gave the results shown in fig. 4.
Example 14: modified proppant with anti-caking agent
Samples of modified proppant were prepared for comparison with and without the use of an anti-caking agent. For sample A, 50g of 40/70 sand was added to the FlackTek tank. To the sand was added 1.5g of the EM533 emulsion polymer and the sample was mixed for 30 seconds. After mixing, 0.25g of calcium silicate was added to the sample, and the sample was mixed again for 30 seconds. The sample was then dried at 85 ℃ for 1 hour. After drying, the sample was poured on top of a 25 mesh screen and shaken gently for 30 seconds. The amount of sand passing through the screen is then measured. For sample B, 50g of 40/70 sand was added to the FlackTek tank. To the sand was added 1.5g of the EM533 emulsion polymer and the sample was mixed for 30 seconds. The sample was then dried at 85 ℃ for 1 hour. After drying, the sample was poured on top of a 25 mesh screen and shaken gently for 30 seconds. The amount of sand passing through the screen is then measured. Table 8 shows the results.
TABLE 8
| Sample (I) | Total mass of sample, g | Mass through the sieve, g | % pass through sieve |
| Sample A | 50.5 | 50.16 | 99.3% |
| Sample B | 50.5 | 15.71 | 31.1% |
The results of the screen tests show that the incorporation of an anti-caking agent is effective in improving the handling properties of the modified proppant.
Samples A and B were added separately to 1L of water followed by shearing in an EC Engineering mixer at 200rpm for 20 minutes. After shearing, the sample was transferred to a 1L graduated cylinder and settled for 10 minutes. After settling, the bed height was measured and showed no significant loss in shear stability as a result of the incorporation of the anti-caking agent. Table 9 shows these results.
TABLE 9
| Sample (I) | Bed height, mm |
| Sample A | 56.21 |
| Sample B | 59.67 |
Example 15: coating proppants with hydrogel layers
The coating composition was prepared by combining 10g of glycerol and 90g of Flopam EM533 in a glass bottle and mixing for 30 seconds using a vortex mixer. Next, 400g of 40/70 mesh proppant sand was added to the KitchenAid mixer drum. 16g of the coating composition was added to the KitchenAid mixer drum. The mixer was then turned on to the minimum setting and mixed for 7 minutes. After mixing, the sand was divided into 50g samples and placed in a forced air oven at 80 ℃ for 1 hour. After drying, the modified proppant was screened through a 25 mesh screen.
Example 16: coating proppants with hydrogel layers
400g of 40/70 proppant sand was added to the KitchenAid mixer drum. To the KitchenAid mixer bowl was added 16g of SNF Flopam EM 533. The mixer was then turned on to the minimum setting and mixed for 7 minutes. After mixing, the sand was divided into 50g samples and placed in a forced air oven at 80 ℃ for 1 hour. After drying, the modified proppant was screened through a 25 mesh screen.
Example 17: shear stability test
The coated sand samples prepared in examples 15 and 16 were tested for shear stability. 1L of tap water was added to a square 1L beaker. The beaker was then placed in an EC Engineering CLM4 blade mixer. The mixer was set to mix at 300 rpm. Once mixing started, a 50g sample of coated sand was added to the beaker. After mixing at 300rpm for 30 seconds, the mixing was reduced to 200rpm and continued for 20 minutes. At the end of this mixing, the mixture was poured into a 1L graduated cylinder and allowed to settle. After 10 minutes, the height of the settled bed was recorded as shown in table 10. A higher bed height indicates better proppant performance.
Watch 10
| Sand sample | Bed height, after shearing, mm |
| Untreated 40/70 sand | 13.24 |
| Example 2 | 70.4 |
| Example 3 | 57.64 |
Example 18: salt water tolerance
Two 20mL bottles were filled with 10mL of tap water. Separately, another two 20mL bottles were filled with 10mL of 1% KC1 solution. To a bottle containing tap water was added 1g of the sand prepared in example 15, and to a bottle containing 1% KC1 was added 1 g. In addition, 1g of the sand prepared in example 6 was added to a bottle containing tap water, and 1g was added to a bottle containing 1% KC 1. All four bottles were inverted about 7 times and then allowed to settle for 10 minutes. After settling, the bed height was measured. The results are shown in Table 11.
TABLE 11
| Sand sample | Height of tap water bed, mm | 1% KCl bed height, mm |
| Example 2 | 10.39 | 5.02 |
| Example 6 | 17.15 | 9.23 |
Example 19: wear testing
Three 250mL beakers were filled with 50mL of tap water. An aluminum plate having a mass of about 5.5-6g was placed in each beaker. A 2 inch stir bar was also placed in each beaker. All three beakers placed their own magnetic stir plate and the plate was set to speed setting 5. 6g40/70 sand was added to a beaker. In a second beaker were placed 6g of the sand prepared in example 15. The third beaker did not add sand at all. Each beaker was allowed to stir for 2 hours. After stirring, the aluminum pan was removed, washed, and then dried. The mass is then measured again. The results shown in table 12 indicate that the sand prepared in example 15 caused less wear of the metal surface when contacted compared to unmodified sand.
TABLE 12
| Initial mass, g | Mass after 2 hours, g | Total loss, g | % loss | |
| Without sand | 5.62 | 5.612 | 0.008 | 0.14% |
| 40/70 sand, uncoated | 6.044 | 6.027 | 0.017 | 0.28% |
| Example 15 Sand | 5.673 | 5.671 | 0.002 | 0.04% |
Example 20: effect of Glycerol on mixing
To the drum of a kitchen aid bench mixer of model KSM90WH fitted with blade attachment was added 1kg dry 40/70 sand. 3.09g of glycerol was mixed with 27.84g of the emulsion polymer, then the mixture was added to the top of the sand and soaked for 1 minute. At time 0, the mixer was started at speed 4(150rpm primary rotation). Samples were collected at 1-2 minute intervals and dried at 90 ℃ for 1 hour. Subsequently, each sample was subjected to a shear test, in which 50g SSP was added to 1L water and at 550s-1Shearing for 20 minutes. After settling for 10 minutes, the bed height was recorded. The results of these shear tests are shown in figure 5. This figure demonstrates that both under-mixing and over-mixing can affect the behavior of the coated proppant, resulting in shear testingDuring which the polymer dissociates from the sand. In this example, the optimum amount of mixing is about 5-20 minutes. The effect of mixing duration on performance indicates that the coating is brittle when wet and more durable once it is dried. Coatings with emulsions blended with glycerin appear to cause a broadening of the processing window (i.e., an acceptable amount of mixing time) compared to coating tests using emulsion polymer alone. In addition, the emulsion coating of the blended glycerol appeared more fully inverted, resulting in better coating properties, such as increased bed height.
Example 21: production of self-suspending proppants using kneading mill
A 3 cubic foot kneader type mixer was used to prepare the batch of self-suspending proppant. About 50lbs of 40/70 mesh sand was added to the kneading mill. In a 1L beaker, add about 756g SNFFlopam EM533 and mix 84g glycerol into the polymer. The entire mixture is then poured evenly on top of the sand in a kneading mill. The kneading mill was turned on and mixed at about 70 rpm. Samples were taken after mixing for 30, 60, 120, 180, 240, 300, 420 and 600 seconds. The sample was dried for 1 hour. After drying, 50g of each sample was added to 1L of water and mixed in EC Engineering CLM4 for 20 minutes at 200 rpm. After mixing, the sample was poured into a 1L graduated cylinder and settled for 10 minutes. After settling, the bed height was measured. The results are shown in Table 13.
Watch 13
| Kneading and milling machine mixing time (second) | Bed height, mm |
| 30 | 29.34 |
| 60 | 23.49 |
| 120 | 48.9 |
| 180 | 57.58 |
| 240 | 55.71 |
| 300 | 44.88 |
| 420 | 57.21 |
| 600 | 57.25 |
Example 22: wet aging (Wet aging)
A 400g sample of self-suspending proppant (SSP) was made in the same manner as in example 15. 400g of SSP were divided into 50g samples and placed in closed containers and kept at room temperature. After drying for various amounts of time, the samples were tested in the same manner as in example 21. The results are shown in Table 14.
TABLE 14
| Aging time in hours | Final bed height, mm |
| 0 | 10.1 |
| 2 | 26.63 |
| 4 | 60.16 |
Example 23: SSP plus uncoated proppant
10mL of tap water was added to a 20mL bottle. Proppant sand, SSP and unmodified 40/70, both prepared according to example 15, were then added to the bottles. The bottle was inverted several times and then settled for 10 minutes. After settling, the bed height was measured. The results are shown in Table 15.
Watch 15
| SSP，g | 40/70 sand, g | Height of settled bed, mm |
| 0.5 | 0.5 | 5.46 |
| 0.75 | 0.25 | 5.71 |
| 0.9 | 0.1 | 8.23 |
Example 24: adding an anti-caking agent to SSP
A400 g batch of SSP was produced in the same manner as described in example 15. The samples were divided into about 50g sub-samples and then 0.25g fumed silica with aggregate size 80nm was mixed in each sample. The samples were subsequently coated and aged at room temperature. The samples were tested in the same manner as described in example 21. The results are shown in Table 16.
TABLE 16
| Hour, aging | Height of settled bed, mm |
| 18 | 57.3 |
| 24 | 41.28 |
| 42 | 44.29 |
| 48 | 44.76 |
| 72 | 45.48 |
Example 25: respirable dust
A 200g sample of uncoated and hydrogel-coated sand (40/70 mesh) prepared according to example 15 was sieved using a 140 mesh sieve, and the fine particles that passed through the 140 mesh sieve were collected and weighed. The coated sample of sand demonstrated an 86% reduction in the amount of fine particles relative to the uncoated sand sample. The results are shown in Table 17.
TABLE 17
| Weight of sample | Weight of dust | Total percentage of dust | |
| Uncoated samples | 200.011g | 0.0779g | 0.03895% |
| Coated sample | 200.005g | 0.0108g | 0.00540% |
Example 26: anti-caking agent with different particle sizes
50g of 40/70 mesh sand was mixed with 2g of SNFFlopam EM533 at 800rpm for 30 seconds using a speed mixer. 0.625g of an anti-caking agent was then added and the materials were mixed again in the speed mixer for 30 seconds. The samples were allowed to stand for 3 hours, then tested in a 20 minute shear test, allowed to settle for 10 minutes, and the bed height was measured. The results are shown in Table 18. The anti-caking agent improved the bed height after using a broad particle size shear test.
Watch 18
| Anti-caking agent | Particle size | Bed height (mm) |
| Talc (magnesium silicate) | 12 micron | 16.76 |
| Calcium silicate | 1-3 micron | 39.78 |
| Fumed silica | 80nm | 73.87 |
Example 27: chemical composition of anti-caking agent
Various anti-caking agents as listed in table 19 were tested. For each reagent tested, 700g of 40/70 sand was mixed with 21.65g of a 10% glycerol/90% EM533 mixture in a KitchenAid mixer at speed 1(144 rpm). A50 g sample was isolated and mixed in a speed mixer with the appropriate amount of anti-caking agent. Three samples mixed with 1% calcium silicate, 1.5% diatomaceous earth and 1.5% kaolin respectively were immediately tested in the shear test, while the other 7 samples were dried in an oven at 80 ℃ for 1 hour together with the control sample without anti-caking agent. The samples were tested in the same manner as in example 17. Table 19-a shows the bed height after shear testing of wet (non-dried) samples with applied anti-caking agent. Table 19-B shows the bed height after shear testing for the dried (1 hour at 80 ℃) samples with the applied anti-caking agent.
TABLE 19-A
| Anti-caking agent | Measurement of | Bed height (mm) |
| Calcium silicate | 0.5g(1%) | 30.26 |
| Diatomite (DE) | 0.75g(1.5%) | 12.95 |
| Kaolin clay | 0.75g(1.5%) | 18.46 |
TABLE 19-B
| Anti-caking agent | Measurement of | Bed height (mm) |
| Is free of | -- | 85.9 |
| Sodium bicarbonate | 0.5g(1%) | 56.97 |
| Corn starch | 0.5g(1%) | 32.29 |
| Babies' powder (Talc) | 0.5g(1%) | 84.83 |
| Dry-flocculate AF (hydrophobic starch) | 0.5g(1%) | 32.24 |
| Cassava starch maltodextrin | 0.5g(1%) | 27.08 |
| Microcrystalline cellulose | 0.5g(1%) | 40.12 |
| Baking powder | 0.5g(1%) | 39.88 |
Example 28: anti-caking agent: amount required for drying
Seven 50g40/70 sand samples were added to small plastic tanks followed by 2g each of a 10% glycerol/90% emulsion polymer mixture in each tank. After 30 seconds of speed mixing, 0.25g, 0.375g, 0.5g, 0.675g, 0.75g, 1g and 2.5g of calcium silicate powder were added to the seven samples and the sand was mixed again for 30 seconds. Without further drying step, the sample was shear tested and the settled bed height (in mm) was recorded. The results are shown in FIG. 6. Similar experiments were performed using silicon dioxide as an anti-caking agent. These tests show that the hydrogel coated sand can be treated with an anti-caking agent to yield a product that does not require a separate drying step to produce an acceptable bed height after the shear test.
Example 29: silicon dioxide anti-caking agent
To the canister was added 50g40/70 sand followed by 2g of 10% glycerol/90% EM 533. The cans were speed mixed at 800rpm for 30 seconds and then the appropriate amount of fumed silica was added and mixed for another 30 seconds as described in table 20. The samples were subjected to a 20 minute shear test and the bed height was recorded. No oven drying was used. The results are shown in Table 20.
Watch 20
| Name of Compound | Chemical characteristics | Amount of addition | Height of bed |
| EH-5 | Amorphous fumed silica | 1% | 136.25mm |
| M-5 | Untreated fumed silica | 1% | 123.52mm |
| TS-720 | Treated fumed silicas, siloxanes, and silicones | 1% | 26.21mm |
| PG001 | 30% anionic colloidal silica, 25.9% solids | 1% solids | 15.30mm |
The batch of coated sand was mixed in a KitchenAid mixer and separated into several 50g samples. 1 weight percent of fumed silica of various sizes was then added to each of the 3 samples, mixed, and shear tested. The results of these tests are shown in Table 21.
TABLE 21
| Powder of | Approximate size | Amount of addition | Height of bed |
| Aldrich fumed silica | 7nm | 1% | 48.86mm |
| Aldrich silica nanopowder | 10nm | 1% | 35.48mm |
| Cabot EH-5 | 80nm aggregates | 1% | 59.10mm |
Example 30: preheating sand
500g of 30/50 sand are placed in an oven at 90 DEG CLeft for 1 hour with occasional stirring until the temperature of the sand equilibrates. The sand was then mixed in a commercial planetary mixer until it reached the desired pre-heat temperature (45 ℃,60 ℃ or 80 ℃), at which point 20.8g of SNF Flopam EM533 was added and the sample was mixed for 7 minutes. The batch was then separated and dried in an oven at 80 ℃ for a certain time. For the non-pretreated samples, 500g30/50 sand was placed in the mixer drum along with 20.8g polymer emulsion, mixed for 7 minutes, and then dried for various amounts of time. All samples were shear tested using standard procedures: 50g of sand was added to 1000g of tap water for 550s-1Was stirred for 20 minutes and subsequently settled for 10 minutes in a 1L graduated cylinder. The results are shown in FIG. 7. These results show that preheating the sand to 45 ℃ is acceptable, but 60-80 ℃ results in a lower bed height in the shear test.
Example 31: forced air drying
Using a speed mixer, 50g of 40/70 sand was mixed with 4% emulsion polymer (2g) prepared according to example 14 for 30 seconds. The samples were transferred to a vessel equipped with a hot air gun set at 90 ℃, 95 ℃ or 100 ℃. The sample was allowed to stand in the heat gun for a total of 30 minutes, and 5g of the sample was taken at the 5 minute, 10 minute, 15 minute and 30 minute marks. These samples were then tested using a small shear test, performed as follows: 100mL of tap water was set to be stirred in a 300mL beaker using a 2 inch stir bar rotating at 500 rpm; adding a 5g sample of sand to the beaker and shearing for 3 minutes; the entire solution was transferred to a 100mL graduated cylinder, inverted once, settled for 5 minutes, and the bed height was measured. The results of these tests are shown in figure 8. As shown in the figure, the higher temperature of the incoming forced air results in more complete drying and better bed height. To test the sensitivity of SSP to shear when using forced air drying, a seven-prong rake was pulled back and forth through the sample to simulate light shear when drying. Two 50g batches of SSP were prepared and dried at 110 ℃ for 30 minutes in air. The first was completely static, while the second was constantly raked during the 30 minute drying time. Two samples were tested for 20 minutes using the high shear test with a settling time of 10 minutes. Statically dried samples gave a settled bed volume of 100.63 mm; while using light to shear the dried sample gives a settled bed volume of 109.49 mm.
Example 32: mixing using vertical screws
A small scale vertical screw blender was constructed. Sand and SNF Flopam EM533 were added to the vessel, followed by mixing using a screw rotating at about 120 rpm. The sample was then divided into two 50g portions, one dried in an oven at 80 ℃ and the other mixed with 0.5g (l wt.%) fumed silica. Both were then subjected to mid shear testing as described in example 17. The results of the bed height measurements were as follows: oven drying for 1 hour to give a bed height of 101.34 mm; undried, to which 1% of 7nm fumed silica was added, gave a bed height of 91.47 mm. Both oven drying and addition of an anti-caking agent to dry the product gave high bed heights.
Example 33: microwave drying
50g of 40/70 sand was added to a small plastic jar which was then mixed in a speed mixer at 800rpm with 2g of the blend containing (10% glycerol/90% emulsion polymer) for 30 seconds. The sample was placed in a 700W microwave oven and heated on a high fire for 45 seconds. The sample was sieved and cooled, then sheared in an ECengineering CLM4 mixer at 200rpm for 20 minutes. After mixing, the sample was transferred to a 1L beaker and settled for 10 minutes. After settling, the bed height (in mm) was measured, giving a bed height of 52.43 mm. Microwave heating results in an acceptable bed height with a relatively short drying time.
Example 34: mixing with anticaking agent and heating
500g of 40/70 sand was mixed with 20g (20% glycerol/80% emulsion) in a KitchenAid mixer for 8 minutes. 0.44% Cabot EH-5 fumed silica was then added and mixed for 2 minutes, after which the sample was heated using a heat gun. At 13, 18, 24 and 26 minutes mixing time, 50g samples were collected. These shears were tested for 20 minutes and the bed height was recorded. The results are shown in FIG. 9. The combination of glycerin and silica allows for a longer processing window.
Example 35: microwave drying
400g of 30/50 sand were combined with 16g (4% by weight) of the emulsion polymer prepared according to example 14 and mixed for 7 minutes in a kitchen aid bench mixer. One 50g sample was dried using an oven (80 ℃) and the other 7 samples were placed in a 700W microwave oven for 5, 10, 20, 30, 45, 60 and 120 seconds, respectively. The samples were subjected to shear testing (20 minutes long) and Loss On Ignition (LOI) as described in example 12. The LOI test involves adding 10g of sand to a tared crucible, which is placed in an oven at 960 ℃ for 1 hour. After heating for 1 hour, the crucible was cooled in a desiccator for 1 hour, followed by weighing. The drying time, bed height and LOI are shown in table 22. The difference between the initial weight and the final weight is expressed as a percentage of the total initial sand weight, as shown in fig. 10.
TABLE 22
| Drying method | Drying time | Bed height (mm) | LOI(%) |
| Baking oven | 1 hour | 41.36 | 1.8 |
| Microwave oven | 5 seconds | 15.54 | 3.33 |
| Microwave oven | 10 seconds | 16.14 | |
| Microwave oven | 20 seconds | 24.68 | |
| Microwave oven | 30 seconds | 39.99 | 2.929 |
| Microwave oven | 45 seconds | 53.31 | |
| Microwave oven | 60 seconds | 49.84 | |
| Microwave oven | 120 seconds | 57.81 | 2.279 |
These tests show that the microwave drying technique removes mainly water, not oil, from the coated sample.
Example 36: vacuum drying
250g of 30/50 sand was combined with 10g of an emulsion polymer as described in example 14. The sand mixture was stirred in a KitchenAid bench mixer at the slowest speed for 7 minutes, then divided into 50g samples and dried in a vacuum oven at 24 inches Hg vacuum at 25 ℃, 50 ℃ and 85 ℃ for 1 hour, 1 hour and 30 minutes respectively. The samples were cooled to room temperature, sieved, and shear tested (as described in example 12) for 20 minutes. The results are shown in Table 23.
TABLE 23
| Sample # | Temperature (. degree.C.) | Time of day | Bed height (mm) |
| 1 | 25 | 1 hour | 16.79 |
| 2 | 50 | 1 hour | 17.34 |
| 3 | 85 | 30 minutes | 18.04 |
During these tests, no sample was completely dried, although other tests may show that higher temperatures may achieve more complete drying.
Equivalents of the same
Although specific embodiments of the invention have been disclosed herein, the foregoing description is illustrative and not restrictive. While this invention has been particularly shown and described with references to 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 encompassed by the appended claims. Many variations of the invention will become apparent to those skilled in the art upon review of this specification. Unless otherwise indicated, all numbers expressing reaction conditions, amounts of ingredients, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that may vary depending upon the desired properties sought to be obtained by the present invention.
Claims (36)
1. A modified proppant comprising a proppant particle and a hydrogel coating, wherein the hydrogel coating is applied to the surface of the proppant particle and localized on the surface to produce the modified proppant.
2. The modified proppant of claim 1, wherein the hydrogel coating comprises a water-swellable polymer.
3. The modified proppant of claim 1, wherein the hydrogel coating is applied to the surface as a liquid.
4. The modified proppant of claim 3, wherein the hydrogel coating comprises a solvent or carrier fluid, and wherein the liquid hydrogel coating becomes a dried hydrogel coating by removal of the solvent or carrier fluid.
5. The modified proppant of claim 4, wherein the dried hydrogel coating is capable of expanding in volume upon contact with an aqueous fluid to form a swollen hydrogel coating having a thickness of at least about 10% greater than the dried hydrogel coating.
6. The modified proppant of claim 1, wherein the hydrogel coating comprises a water-swellable polymer that responds to elevated temperature or brine conditions by collapsing volume or thickness.
7. The modified proppant of claim 1, wherein the hydrogel coating comprises a hydrophobic comonomer selected from the group consisting of: alkyl acrylates, N-alkylacrylamides, N-isopropylacrylamide, propylene oxide, styrene and vinylcaprolactam.
8. The modified proppant of claim 1, wherein the hydrogel coating comprises a polymer selected from the group consisting of: polyacrylamide, polyacrylic acid, copolymers of acrylamide and acrylate, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, guar gum, carboxymethyl hydroxypropyl guar gum, hydrophobically associating swellable emulsion polymers, and latex polymers.
9. The modified proppant of claim 1, wherein the hydrogel coating further comprises a chemical additive selected from the group consisting of: scale inhibitors, bactericides, demulsifiers, wax control agents, asphaltene control agents and tracers.
10. The modified proppant of claim 1, wherein the modified proppant further comprises a cationic/anionic polymer pair comprising a cationic polymer and a high molecular weight anionic polymer.
11. The modified proppant of claim 10, wherein the cationic polymer is selected from the group consisting of: poly-DADMAC, LPEI, BPEI, chitosan, and cationic polyacrylamide.
12. The modified proppant of claim 1, wherein the modified proppant further comprises a crosslinker.
13. The modified proppant of claim 12, wherein the crosslinker comprises a covalent crosslinker.
14. The modified proppant of claim 13, wherein the covalent crosslinking agent comprises a functional group selected from the group consisting of: epoxides, anhydrides, aldehydes, diisocyanates and carbodiimides.
15. The modified proppant of claim 13, wherein the covalent crosslinking agent is 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) carbodiimide.
16. The modified proppant of claim 1, wherein the modified proppant further comprises a delayed hydration additive.
17. The modified proppant of claim 16, wherein the delayed hydration additive is selected from the group consisting of: low hydrophilic-lipophilic balance surfactant, repellent agent capable of removing modified surfactant, photo-ionic cross-linking agent, photo-covalent cross-linking agent and monovalent salt charge shielding agent.
18. The modified proppant of claim 1, wherein the modified proppant further comprises an alcohol selected from the group consisting of: ethylene glycol, propylene glycol, glycerol, propanol and ethanol.
19. The modified proppant of claim 1, wherein the modified proppant further comprises an anti-caking agent.
20. A hydraulic fracturing formulation comprising the modified proppant of claim 1.
21. The formulation of claim 20, wherein the formulation further comprises uncoated sand.
22. The formulation of claim 20, wherein the formulation further comprises fiber.
23. A method of forming a modified proppant, the method comprising:
providing proppant particles; and
applying the hydrogel coating to a surface of the proppant particle such that the hydrogel coating is localized on the surface.
24. The method of claim 23, wherein the hydrogel coating is applied to the surface as a liquid.
25. The method of claim 23, further comprising the step of drying the hydrogel coating on the surface by a drying process.
26. The method of claim 25, wherein the hydrogel coating contains a solvent or carrier fluid, and wherein the hydrogel coating is dried on the surface by removing the solvent or carrier fluid to form a dried hydrogel coating.
27. The method of claim 25, wherein the drying step comprises heating a hydrogel coating.
28. The method of claim 26, further comprising exposing the dried hydrogel coating to an aqueous fluid to form a swollen hydrogel coating, wherein the swollen hydrogel coating expands in volume to have a thickness at least about 10% greater than the thickness of the dried hydrogel coating.
29. A method of fracturing a well, the method comprising:
preparing the hydrocracked formulation of claim 20, and
introducing the fracking formulation into the well in an effective volume and at an effective pressure for fracking,
thereby breaking the well.
30. A method of making a modified proppant, the method comprising:
providing proppant substrate particles and a fluid polymerized coating composition;
applying the fluid polymerized coating composition on the proppant substrate particles;
mixing the proppant substrate particles and a fluid polymer coating composition to form a modified proppant; and
(ii) drying the modified proppant(s),
wherein the fluid polymerized coating composition contains a hydrogel polymer, and wherein the hydrogel polymer is localized on the surface of the proppant matrix particles to produce a modified proppant.
31. The method of claim 30, wherein the manufacturing occurs at or near the point of using the modified proppant.
32. The method of claim 30, wherein the proppant substrate particle comprises sand.
33. The method of claim 32 wherein the sand is obtained at or near the point of use of the modified proppant.
34. The method of claim 30, further comprising adding an alcohol selected from the group consisting of: ethylene glycol, propylene glycol, glycerol, propanol and ethanol.
35. The method of claim 30, further comprising adding a conversion promoter during or after the step of mixing the proppant substrate particles and the fluid polymer coating composition.
36. The method of claim 30, further comprising adding an anti-caking agent to the modified proppant.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US61/529,600 | 2011-08-31 | ||
| US61/635,612 | 2012-04-19 | ||
| US61/662,681 | 2012-06-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| HK1194450A true HK1194450A (en) | 2014-10-17 |
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