RU2663753C2 - Proppant particles formed from slurry droplets and method of use - Google Patents

Abstract

FIELD: chemistry.SUBSTANCE: invention relates to a proppant for hydraulic fracturing. Method of preparing proppant particles comprises using a slurry of bauxite, the slurry containing a reactant comprising a polysaccharide, wherein the solids content in the slurry is from 25 wt% to 75 wt%, feeding the slurry through a nozzle positioned above the upper surface of the liquid, while simultaneously vibrating the slurry to form droplets, introducing said droplets into a reservoir containing a liquid, the liquid containing a coagulant which reacts with the reactant in the slurry and causing coagulation of the reactant in the droplets, transferring droplets from the liquid, drying the drops to obtain green granules, and sintering the green granules to obtain proppant particles having an adequate strength, wherein proppant particles have an adequate strength if the long-term permeability of the test particles, measured according to ISO 13503-5 at 250°F, decreases by less than 70% with an increase from 2000 psi to 14000 psi of stress applied to the test particles with the same composition obtained in the same manner as the proppant particles and having a size in the range of 20-40 mesh.EFFECT: proppant for hydraulic fracturing is used.13 cl, 13 dwg, 4 tbl

Description

Technical field

The present invention relates to hydraulic fracturing in the bowels of the earth. More precisely, sintered ceramic proppant particles have been proposed, which are formed as a result of vibration dropping from a nozzle of a droplet of a suspension of a finely dispersed ceramic material, as well as a method for their use.

State of the art

Hydraulic fracturing is a technology of injection with a high speed and under high pressure of a liquid into a layer lying in the bowels of the earth, as a result of which a crack forms in the thickness of the rocks around the well. After pumping a sufficient volume of fluid to properly wedge the crack, solid particles called a proppant are added to the fluid. Upon completion of the injection, hydrocarbon production from the well begins. After a fracture, well productivity usually increases significantly. Since the technology of hydraulic fracturing was first patented in 1949 (US patents 2596843 and 2596844), it has been significantly improved.

First, quartz sand was used as a proppant for hydraulic fracturing. With increasing depth of the wells, it was found that the sand does not have the proper strength. In deep wells, sand collapses under stress in the reservoirs and becomes less effective in terms of increasing well productivity.

To increase the strength of proppants, proppants based on synthetic materials have been created. The first synthetic sintered proppant was sintered bauxite. Recently, a variety of ceramic raw materials have been used to produce sintered ceramic proppants, including bauxite with lower alumina and clays such as kaolin. It was found that the strength of ceramic particles usually increases with increasing amount of alumina in the particles, with all other other unchanged parameters.

A general method for producing a particle of a synthetic proppant includes the use of ceramic raw materials, milling it into fine powder, forming granules (called "green" granules), and sintering green granules in an oven. The final product is ceramic granules with a size gradation acceptable for proppants, from about 70 mesh to 12 mesh (0.008 inch to 0.067 inch). Depending on the conditions in the well, granules of various sizes are used.

A variety of methods have been proposed for forming proppant granules. US Pat. No. 4,427,068 describes a method for forming sintered ceramic granules by adding dry powder clay and alumina, bauxite or a mixture thereof to a high-intensity mixer (hereinafter, the “dry mixing method”). The initial ceramic ingredients (ceramic raw materials), crushed into fine particles, are mixed to obtain a dry, homogeneous mixture. Then enough water is added to cause agglomeration of the small starting particles and the formation of composite spherical granules from the powder. Continuous mixing is provided so that the fine granules grow to the desired size. At the stage of granule formation, a granule with a wide gradation of sizes is obtained. A preferred mixer is an Eirich mixer manufactured by Eirich Machines, Inc. The obtained granules are dried and sintered to obtain finished proppant particles. Recently, in the manufacture of most proppants, this granule formation technology has been used. US Pat. No. 4,440,866 describes an alternative method for producing granules that are sintered to obtain high strength granules. Continuous spraying / granulation of an aqueous binder containing suspended alumina ore is used to form granules which are then sintered (hereinafter referred to as the "fluidized bed spraying method"). All stages of this method can be carried out continuously. An aqueous suspension containing ceramic raw materials is continuously sprayed and sent to a layer of already partially dried initial dust particles (often called grains), which are fluidized in a stream of hot drying air. An aqueous suspension of ceramic material is continuously sprayed onto the grains and dried until ready green granules of the desired diameter are obtained. The particles obtained by this method have a less wide gradation of sizes than the particles usually obtained by the dry mixing method according to the patent US 4427068, but with a sufficient dispersion, which requires additional processing. Particles are continuously removed from the layer and separated from fractions with sizes above and below the nominal. The material is continuously recycled into the drying air stream. This method of spraying in a fluidized bed is also used in industry to produce large quantities of ceramic proppants.

The described methods for the formation of granules have inherent disadvantages. Using the dry mixing method, green granules with a very wide gradation of sizes are obtained, which is explained by the random nature of mixing using a rotor and a bowl. By spraying in a fluidized bed, green granules are obtained with a slightly narrower size gradation, but significantly wider than desired. These methods require laborious screening and recycling throughout the manufacturing process. Under the best production conditions, about 30% of green particles should be recycled to the pellet formation process. Both in the case of dry mixing and spraying in a fluidized bed, granules with a random distribution of pore size are also obtained, including a small fraction of very large pores, which significantly reduce the strength of the granules. The strength of the sintered granules is of paramount importance, since in the case of destruction of the granules under the influence of strong stress in the crack, the throughput of the crack decreases, and hydraulic fracturing becomes less effective. Also important is the sphericity and smoothness of the surface of the particles obtained by these methods, while high sphericity and a very smooth surface are traditionally most desirable. All of these characteristics are greatly affected by the way granules are formed.

US 2006/0016598 provides a list of granule forming methods that can be used to produce a ceramic proppant, including agglomeration, spray granulation, wet granulation, extrusion and granulation caused by vibration, dripping according to US Pat. No. 5,500,162, the use of droplets formed by a spray nozzle, and selective agglomeration. US Pat. No. 5,500,162 describes the preparation of microspheres by vibration-induced dripping of a chemical solution through a nozzle plate, the falling droplets forming a shell surrounded on all sides by a stream of reactive gas. The liquid chemical solution does not contain or contains little (i.e. 20% or less) of solid particles at the entrance to the nozzle plate, at the exit of the nozzle plate and when passing through the first free fall zone. A chemically active gas is necessary to cause precipitation (gelation) of small solid particles (usually of submicron size) in the form of liquid droplets when falling through the second free fall zone and then falling into the reaction liquid with further transformation into a gel. A chemically active gas is required to partially convert the liquid from the gel before it enters the reaction liquid, while the droplets slow down in the liquid by directing the foam or reaction liquid onto the falling droplets tangentially in the direction of their fall. These two features, i.e. the passage of the falling droplets through the reactive gas and their slowing down by the foam are necessary to ensure the partial dropping of the droplets into a gel during the sol-to-gel conversion reaction and, accordingly, to prevent their deformation, for example, flattening upon impact with the reaction liquid. Reactive gas is aspirated from the inside or outside of the shell. This method can be used to obtain, for example, spheres of aluminum oxide with a diameter of up to 5 mm.

Vibration-induced runoff, referred to in the description as "drop casting," was originally designed to produce nuclear fuel pellets. Since then, it has been adapted to produce a wide variety of metal and ceramic microspheres, such as abrasive materials and catalyst supports. It is mainly used in food and pharmaceutical industries. The drip casting method is described on the website and in promotional materials of Brace GmbH. They also provide examples of "microspheres" formed by the drip casting method of various materials. US Pat. No. 6,197,073 describes a method for producing alumina pellets from a sol or suspension based on acidic alumina by feeding the suspension through a vibrating nozzle plate to form droplets that are pre-cured by ammonia gas and then coagulated in an ammonia solution. The mechanical strength of ceramic particles formed by sintering of particles obtained by drop casting does not matter in any of the sources cited.

It is known that in order to provide maximum strength of proppant ceramic particles for a given ceramic material, particles must have a minimum porosity, and existing pores should have a minimum size, since the particle strength of a given proppant is limited by the size of the largest pores. Thus, a method for forming green ceramic particles is required, in which pore size can be reduced by sintering and, accordingly, maximum strength is achieved for use as a proppant. The particles should preferably have a spherical shape, a smooth surface and the same size. Also required is a method of forming green particles without recycling a fraction of ceramic granules of an undesirable size.

SUMMARY OF THE INVENTION

A method for forming proppant granules from ceramic raw materials in the form of a suspension is proposed. The granules have a higher strength than the known proppant granules, which are obtained from various ceramic raw materials by known granule formation methods. One-dimensional spherical granules with a smooth surface can be manufactured in industrial quantities. They are used for hydraulic fracturing.

Brief Description of the Drawings

In FIG. 1 illustrates the principles of the device for forming proppant granules according to the present invention.

In FIG. 2 shows a nozzle for forming droplets from a suspension stream.

In FIG. 3 shows a multi-nozzle plate for forming droplets from a suspension stream.

In FIG. 4a shows an alumina particle obtained by the drip casting method.

In FIG. 4b shows an alumina particle obtained in an Eirich mixer.

In FIG. 4c shows a bauxite particle obtained by the drip casting method.

In FIG. 4g shows a bauxite particle obtained in an Eirich mixer.

In FIG. 4e shows a kaolin particle obtained by the drip casting method.

In FIG. 4e shows a kaolin particle obtained in a pilot plant for spraying a fluidized bed.

In FIG. 5 shows the long-term permeability as a function of the stress experienced by the alumina pellets obtained in the granule forming apparatus according to the invention and the known dry mixing method in an Eirich mixer.

In FIG. 6 is a pore size distribution diagram of kaolin particles obtained by the method of the invention and the known fluidized bed spraying method.

In FIG. 7 is a diagram of the long-term permeability of a proppant having different alumina contents and prepared by various methods.

In FIG. 8 is a diagram of the long-term permeability of a proppant having different alumina contents and prepared by various methods.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 shows a granule forming apparatus 10 having a single nozzle in order to illustrate the principles of the method according to the invention, commonly referred to as “drop casting”. In the nozzle 12 from the supply tank 14 enters the suspension 15, which contains suspended ceramic materials in water. Under pressure applied to the supply tank 14 by the pressure supply system 16, the suspension at a selected speed preferably in the form of a laminar flow flows through the nozzle 12. Under the nozzle 12 there is a coagulation tank 17 into which droplets enter. A vibrating device 18 is connected to the nozzle 12 for supplying pressure pulses to the nozzle or directly into the suspension flow through the nozzle. The suspension created through vibration of the flow through the nozzle causes the flow at the outlet of the nozzle 12 to break into droplets of the same size. When droplets fall into the coagulation tank 17 of them, spheres are formed under the influence of surface tension. For the formation of spherical particles, the reaction does not require the transformation of the sol into a gel, a free fall zone with a chemically active gas, a foamed layer of the reaction liquid or the direction of the reaction liquid into droplets before they enter the reservoir with the reaction liquid.

In FIG. 2 shows in detail the suspension 15 exiting the nozzle 12 and breaking into droplets. Due to the surface tension of the suspension, the droplets have a minimum surface area, which is achieved due to the spherical shape when they fall into the coagulation tank 17. The drop height is preferably chosen sufficient so that the droplets turn into spheres before they enter the reservoir 17 with liquid.

Suspension 15 from the supply tank 14 contains finely ground mineral or processed powder (with a particle size of 0.01-50 microns), by sintering of which a strong ceramic material can be obtained, the appropriate amount of dispersant, necessary so that the solid particles in the suspension remain well separated , water and a reagent, and which reacts with one of the components of the liquid 19 in the coagulation tank 17 and forms a semi-solid or insoluble compound. The solids content of the suspensions may be from about 25% to about 75%. Suspensions typically have a viscosity of 1 to 1000 centipoise, but may have a higher viscosity. The lower viscosity of the suspension contributes to the formation of droplets and spherical particles and is an essential feature of the claimed invention. Viscosity is reduced by optimizing the type and concentration of dispersant. Dispersants can be selected based on the cost, availability and effectiveness of reducing the viscosity of the selected suspension. Dispersants that can be used to reduce the viscosity of suspensions include sodium silicate, ammonium polyacrylate, sodium polymethacrylate, sodium citrate, sodium polysulfonate and hexametaphosphate.

The reagent widely used in suspension in the supply tank 14 is sodium alginate. It is a natural polysaccharide that is soluble in water as a sodium salt, but crosslinked and forms a gel like a calcium salt. Alginate is usually added to the suspension in an amount of from 0.1% to 1.0% (alginate solids based on the total weight of the suspension). Coagulation reservoir 17 typically contains coagulation fluid 19, which gel the reagent in suspension 15. The coagulation fluid commonly used for sodium alginate is a solution of calcium chloride in a concentration of from 0.5% to 10% by weight. A variety of reagents can be used in the suspension flowing through the nozzle 12 and the coagulation tank 17. These may include other polysaccharides and other cross-linking compounds, such as polyvinyl alcohol or liquid borates.

The diameter of the nozzle 12, the viscosity of the suspension 15, the content of ceramic particles in the suspension 15, the pressure of the suspension in the nozzle, as well as the frequency and amplitude of the vibration generated by the vibration source 18, are controlled so as to obtain droplets of the desired size. Constant values are preferably set for these parameters, and a batch of proppant granules is formed from the resulting spheres. Pellets from different lots can have different sizes. The granules from each batch preferably have the same dimensions (i.e., remain on the same sieve, for example, pass through a 20 mesh sieve, but remain on a 25 mesh sieve). The pressure used to feed the suspension into the nozzle is controlled in such a way as to create a laminar flow through the nozzle. The supply pressure can range from 1 to 50 psi. inch. The frequency for each set of suspension states is adjusted in such a way as to establish resonance in the suspension stream at the exit of the nozzle to then obtain spherical drops. The frequency can be from 10 to 20,000 Hz. Iteratively optimize pressure and frequency to create droplets of uniform spherical shape. The amplitude is adjusted so as to improve the uniform shape of the resulting spherical droplets. The flow rate of the suspension through the nozzle depends on the diameter of the nozzle, the supply pressure of the suspension and the properties of the suspension, such as viscosity and density. For example, the flow rate of suspensions of kaolin and alumina through nozzles with a diameter of up to 500 μm can be from 0.2 to 3 kg / h.

The distance between the nozzle 12 and the upper level of the liquid 19 in the coagulation tank 17 is chosen so that the droplets turn into spheres until the upper level of the liquid is reached. The distance can be from 1 to 20 cm, but more often from 1 to 5 cm in order to reduce the distortion of the shape of the droplets when they hit the surface of the liquid and thereby eliminate the need for a reactive gas, a foamed layer or tangentially directed reaction liquid before it arrives drops into the coagulation tank 17. The reagent in the drops of the suspension reacts with the coagulation liquid 19 in the coagulation tank 17, as a result of which a semi-solid surface is formed in the drops, helping to maintain a spherical shape and prevent agglomeration of the granules: The residence time of the granules in the coagulation tank 17 is preferably sufficient so that the granules become rigid enough to prevent deformation of the spheres when they are removed and dried, i.e. semi-rigid. In some embodiments, the granules can fall into a coagulation fluid solution flowing vertically upward, as a result of which the sedimentation of particles through the fluid is slowed down and the residence time in the coagulation reservoir is increased.

Particles obtained in the device shown in FIG. 1, washed to remove excess coagulant, and transferred to other devices in which they are dried and then sintered by methods well known in the art.

In FIG. 3 illustrates a multi-nozzle device necessary for implementing the method on an industrial scale. A plurality of nozzles 32 are housed in a pressure-controlled reservoir 30 for supplying slurry through nozzles. For the industrial production of proppant particles, a large number of nozzles are required. The reservoir 30 is vibrated to cause the nozzles to vibrate as described above. Alternatively, an alternating pressure may be created in the suspension to form one-dimensional drops. Drop collection is carried out as described previously.

Granules obtained by the method described with reference to FIG. 1-3 are almost the same size. For example, Table 1 compares the size distribution of granules of a proppant of sintered alumina proppant obtained by the dry mixing method and the drip casting method described in the invention without sifting green granules. The dry mixing method without sifting green granules produces fired proppant granules remaining during sifting on six sieves, while the drip casting method produces fired proppant granules that remain predominantly on one sieve. Accordingly, when a proppant is obtained by the drip casting method, sieving of green granules is not required in order to select the desired size gradation and recycling of green granule material beyond the selected size gradation. The size of the sintering granules of the proppant is selected by adjusting the diameter of the nozzle 12 or 32, the viscosity of the slurry 15, the content of ceramic particles in the slurry 15, the pressure at which the slurry is fed into the nozzle, and the frequency and amplitude of vibration communicated by the vibration source 18.

In FIG. 4a-4d show photographs of alumina, bauxite and kaolin particles obtained by the device shown in FIG. 1, and by known methods. In FIG. 4a shows alumina particles obtained by the drop casting method as shown in FIG. 1, and having high sphericity and a very smooth surface. In FIG. 4b shows alumina particles obtained in an Eirich mixer. Particles have rough surfaces and are generally flattened. In FIG. 4c shows bauxite particles obtained by the drop casting method, and FIG. 4g shows bauxite particles obtained by a known industrial method using an Eirich mixer (Carbo HSP manufactured by Carbo Ceramics Inc., Houston, Texas, USA). In FIG. 4e shows kaolin particles obtained by the drop casting method, and FIG. 4e shows kaolin particles obtained in a pilot plant in a fluidized bed.

The surface roughness of each solid granule shown in FIG. 4a-4e. A smooth convex perimeter was outlined around each granule, forming an average surface level as close as possible to the actual surface area of the granule, but retaining a convex shape. Then determine the discrepancy between the actual surface area and the smooth average surface area around the perimeter at intervals of 100 μm. At 100 times the magnification used in FIG. 4, the discrepancy could be determined with an accuracy of about 0.5 μm. The average measurement results around the entire perimeter reflect the surface roughness of the granule. Table 2 shows that the surface roughness of granules obtained by dry mixing and spraying in a fluidized bed is 3-7 times higher than the surface roughness of granules obtained by drip casting.

In FIG. 5 shows the comparative permeability of the granules obtained in the device shown in FIG. 1, and granules obtained by dry mixing. The granules obtained by both methods had the same size and, in both cases, the aluminas were made of alumina with a high degree of purity (more than 99%). The only difference is the way granules are formed. The permeability was determined according to ISO 13503-5, Procedures for Measuring the Long-Term Sustained Conductivity of Proppants, except that steel plates were used instead of sandstone plates. In the apparatus for measuring long-term steady conductivity described in ISO 13503-5, a steel cell was used to measure conductivity with an internal slot of 7 inches long and 1.5 inches wide. An open channel passed from each end of the slot to the outer surface of the cell to allow fluid to flow through the slot. Other channels passed along the length of the slot, also extending to the cell surface and used to measure the internal pressure in the slot. The upper and lower pistons were installed in the slot, extending in length beyond the cell, which made it possible to apply a load directly to the pistons using a hydraulic power frame. To apply a load to the cell for measuring conductivity, we first installed the lower piston in the cell so that it does not interfere with the flow of fluid through the discharge channels. An O-ring was installed to prevent leakage of pressure or fluid between the slot and the piston wall. Then placed on the lower piston a metal gasket according to the size of the slot and a sandstone plate. Alternatively, instead of a sandstone plate, a steel plate can be used (as in this case). Then, a predetermined amount of proppant was placed on the plate. In this case, two identical volumes of two proppants were placed, initially occupying a space of about 0.19 inches wide. The proppant leveled. Then a second steel plate, a metal gasket, an annular seal and an upper piston were placed over the proppant. An initial load was applied to the pistons, and a fluid medium was supplied through a proppant with simultaneous pressure measurement. The temperature of the fluid was maintained and the cell temperature was 250 ° F. By measuring the flow rate of the fluid and the pressure loss, the proppant conductivity was determined in millidars per foot. The permeability of the proppant was calculated by dividing the conductivity by the measured proppant width, which was about 0.16-0.19 inches, as shown in FIG. 5. As a fluid medium, a deoxygenated aqueous solution of 2% KCl saturated with silica was used. Conductivity was measured at voltages from 2,000 psi. inch to 20,000 psi increments of 2000 psi inch. In each case, voltage was maintained for 50 hours before the conductivity measurement. The proppant permeability decreased with an increase in the closure stress crack due to fracture of the proppant grains. Stronger granules had higher permeability. As shown in FIG. 5, the loss of permeability of the granules obtained by the dry mixing method (lines 2) was 78% with an increase in the fracture causing closure of the crack from 2000 psi. inch to 20,000 psi inch. In contrast, the loss of permeability of granules obtained in the device shown in FIG. 1 (line 1) amounted to only 31% or less than half the permeability loss of granules obtained by dry mixing. This higher permeability of the granules obtained in the device shown in FIG. 1, due to the higher strength of the granules. The strength of the proppant can be determined by the proppant crush resistance test method described in ISO 13503-2, "Measurement of the properties of proppants used in hydraulic fracturing and gravel pack installation." To do this, first proppant sample was sifted to remove small particles (granules or fragments smaller than the nominal size that may be present), and then placed its crushing chamber, in which using a piston created a limited crack closing stress, a certain amount exceeding the tensile strength a certain fraction of proppant granules. Then re-sieved the sample and determined the percentage by weight of small particles resulting from the destruction of the granules, as a percentage of crushing. To determine the relative strength, we compared the percentage crushing when testing two samples of granules of the same size. Crush Percentage at 15,000 psi the inch of the two granule samples used in the described conductivity test was 2.7% for granules obtained by the dry mixing method and 0.8% for granules obtained by the drip casting method. This once again proves that more durable granules are obtained by the drop casting method. The relative strength of the granules can also be determined by measuring the strength of the granules of the same type. The strength distribution of 40 granules of each of the two granule samples used in the described conductivity test was determined, tabulated and analyzed by the Weibull method to determine the standard strength. The standard strength determined in this way for granules obtained by the drip casting method was 184 MPa, and for granules obtained by the dry mixing method was 151 MPa.

According to the mechanics of fracture, the granules are destroyed under stress, starting from the weakest point. The weakest point in the proppant granules is presumably the largest pore. Accordingly, the fracture stress is inversely proportional to the square root of the area of the weakest point. Thus, the ratio (R) of the fracture stress of the proppant obtained by the drop casting method (DC) in the device according to the invention and the proppant obtained by conventional methods (dry mixing or spraying in a fluidized bed) (CONV) is:

R = (maximum pore size _DMP / maximum pore size _CONV ) ^1/2

Investigated granules obtained by the method of drop casting and known methods, the method of scanning electron microscopy (SEM) with a 500-fold increase. In order to determine the pore size distribution of particles, the SEM method was used to study cross sections of sintered granules of alumina, bauxite, and kaolin obtained by each method. A photograph of a randomly selected area of approximately 252 μm × 171 μm was obtained from each sample of granules of ten different types. The ten largest pores were measured at each site, and the above equation was used to calculate the theoretical ratio of the fracture stress of the granules obtained by the drip casting method and the granules obtained by traditional methods. The results are shown in Table 3. For example, the average maximum pore size of the aluminum oxide granules obtained by the drip casting method was 16.3 μm, and the average maximum pore size of the aluminum oxide granules obtained by the dry mixing method was 40.8 μm. Applying the equation, it was determined that the ratio of the fracture stress of the granules obtained by the drip casting method and the granules obtained by the dry mixing method is 1.6. Accordingly, the fracture mechanics shows that the pellets with a high content of alumina obtained by the drip casting method must withstand approximately 1.6 times greater stress without breaking than the granules obtained by the dry mixing method.

Additional measurements were carried out on samples of kaolin granules. At the same time, each visible pore was measured, and the combined data obtained in all ten sections, as well as the size of the largest pores from Table 3 were used to calculate the average pore size, standard deviation of pore size, and the number of pores per square millimeter. These data are summarized in Table 4, and in FIG. 6 shows plots of pore size distribution of kaolin granules obtained by the drop casting method (curve 1) and the spraying method in a fluidized bed (curve 2). On the microstructures illustrated in FIG. 4e, a small fraction of the very large pores generated by atomization in the fluidized bed, as shown in FIG. 6 (curve 2). Due to the absence of large pores, the material obtained by drop casting provides favorable strength, as described above.

The proppant from kaolin is more advantageous than proppants with a higher alumina content, which are obtained from more expensive ores with a higher percentage of alumina. For example, Carbo Ceramics (data from www.carboceramics.com, found 12/19/2011) offers four proppants on the market with three alumina intervals. Higher alumina proppants are generally sold at higher prices and have a higher cost to the manufacturer. The lowest alumina content is ECONOPROP and CARBOLITE, in which it is about 48% and 51%, respectively. CARBOPROP has a higher alumina content of about 72%. CARBOPROP is a more expensive product to manufacture mainly due to the higher cost of raw materials.

One of the properties of a proppant, which is most directly related to its effectiveness in hydraulic fracturing, is permeability under stress conditions. In FIG. 5 shows the long-term permeability of a proppant made from pure alumina obtained in a known manner and by the drop casting method according to the present invention. In FIG. 7 shows the long-term permeability data of a proppant having different alumina content and obtained by various methods, collected in the same ways as the data in FIG. 5. Curve 1 shows the nominal permeability of the 20/40 mesh proppant ECONOPROP (from kaolin with an alumina content of about 48%) obtained in an Eirich mixer as described above. Curve 2 shows the permeability of 20/40 mesh proppant CARBOPROP (from a mixture of ores with an alumina content of about 72%). Curve 3 shows the average permeability versus stress for 15 proppant samples (from kaolin with an alumina content of about 48%) obtained by the drip casting method according to the invention. The proppant method uses a kaolin proppant with approximately the same permeability under stress conditions as a more expensive product containing 72% alumina. The average long-term permeability of 15 samples, measured at a voltage of 10,000 pounds per square. an inch was 173 darcy. This significantly exceeds the nominal long-term permeability at a voltage of 10,000 psi. an inch (85 darcy) of a proppant (ECONOPROP) commercially available with approximately the same alumina content as can be seen from a comparison of curve 3 and curve 1.

In FIG. 8 shows the long-term permeability data of a proppant having different alumina content and obtained by various methods, collected in the same ways as the data in FIG. 5 and 7. Curve 1 shows the nominal permeability of the 20/40 mesh proppant CARBOPROP (from a mixture of ores with an alumina content of about 72%) obtained in an Eirich mixer, as described above. Curve 2 shows the permeability of the proppant (previously sieved through a 25 mesh sieve) obtained by the drop casting method according to the invention from bauxite with an alumina content of 70%. Curve 3 shows the permeability of the 20/40 mesh proppant granules obtained in an Eirich mixer with an alumina content of about 83%. The proppant obtained by the drip casting process with an alumina content of only 70% shows practically the same permeability characteristics as the known proppant obtained in an Eirich mixer with an alumina content of about 83%. Since alumina is a more expensive component of proppants, significant savings are achieved through the use of cheaper raw materials and the drip casting method according to the invention. A comparison of curves 1 and 2 shows the advantages of the drip casting method with approximately the same alumina content in the proppant.

It is understood that those skilled in the art may make changes to the invention without departing from the scope of the appended claims. In the description, all the embodiments envisaged by the invention were not described in detail, in which the solution of the problems of the invention is achieved. Other embodiments may be proposed without departing from the spirit and scope of the appended claims. Although the invention has been described with reference to specific details, it is intended that such details should not be construed as limiting the scope of the invention, as long as they are included in the appended claims.

Claims (19)

1. A method of producing particles of a proppant, including: using a suspension of bauxite, the suspension contains a reagent containing a polysaccharide, where the solids content in the suspension is from 25 weight. % to 75 weight. % feeding the suspension through a nozzle located above the upper surface of the liquid, while vibrating the suspension to form droplets, the entry of drops into the reservoir containing the liquid, the liquid contains a coagulant that reacts with the reagent in suspension and causes coagulation of the reagent in the drops, transfer of drops from a liquid, drying the drops to obtain green granules, and sintering green granules in order to obtain proppant particles having the proper strength, and proppant particles have the proper strength if the long-term water permeability of the test particles, measured according to ISO 13503-5 at 250 ° F, decreases by less than 70% with increasing 2,000 psi inch up to 14,000 psi an inch of voltage applied to the test particles with the same composition obtained in the same way as the proppant particles and having a size in the range of 20-40 mesh. 2. The method according to p. 1, where the particles of proppant have a long permeability exceeding 85 darsi at a voltage of 10,000 pounds per square. inch and temperature 250 ° F, as measured according to ISO 13503-5. 3. The method of claim 1, wherein the proppant particles have an average maximum pore size of 14.3 microns. 4. The method of claim 1, wherein the proppant particles have an average roughness of 1.6 μm. 5. The method according to claim 1, where the proppant particles are formed without the need to expose the droplets of the sol to gel reaction. 6. The method according to p. 1, where the particles are sintered at a temperature in the range from 1400 ° C to 1650 ° C. 7. The method of claim 1, wherein the polysaccharide is alginate. 8. The method of claim 1, wherein the suspension further comprises a dispersant and where the dispersant is ammonium polyacrylate. 9. The method of claim 1, wherein the coagulant is calcium chloride. 10. The method according to p. 1, where the reagent and coagulant react and form a semi-rigid material. 11. The method according to p. 1, where when the suspension flows from the nozzle, vibration is reported to it by vibration of the nozzle. 12. The method according to p. 1, where the proppant particles are formed without the need for exposure to drops by a free fall zone with a chemically active gas. 13. The method according to claim 1, wherein the proppant particles are formed without the need for subjecting the reaction drops to the sol to gel or exposing them to a free fall zone with a reactive gas.

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