SPHERICAL PELLETS CONTAINING COMMON CLAY PARTICULATE MATERIAL USEFUL AS A PROPPANT IN HYDRAULIC FRACTURING OF OIL AND GAS WELLS

Abstract

Ceramic propping agents include a plastic clay, aluminosilicate network modifier, strength enhancing agent, and binder. Usable strength enhancing agents can include nepheline materials having 0.1 to 5 percent iron oxide by weight. A resin coating can be used to encapsulate particles of the ceramic propping agent. The propping agent can be produced by grinding the components to the same approximate particle size, nucleating the particles by adding water, growing the resulting spherical pellets by adding additional particles that adhere to the surface of the spherical pellets, and vitrifying the pellets to form the propping agent.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of the prior-filed, co-pending United States Application for Patent having the application Ser. No. 13/924,049, filed Jun. 21, 2013, which in turn claims priority to the United States Provisional Application for Patent having the Application Ser. No. 61/664,591, filed Jun. 26, 2012. Both of the above-referenced applications are incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The present disclosure relates, generally, to the field of hydraulic fracturing, and more particularly, to propping agents (e.g., “proppant”) and related methods.

BACKGROUND OF THE INVENTION

Hydraulic fracturing, often referred to as “fracking” in the energy industry, is a stimulation technique utilized to increase the productivity of an oil and/or natural gas well.

The fracturing process involves injecting a fluid into rock formations at a high rate and pressure to widen existing openings in the rocks and/or create new cracks (e.g., fractures) in the formation. Once the cracks are created, fluid containing a particulate material, often referred to as a propping agent or “proppant,” is pumped into the newly created fractures to maintain the openings. This process increases the permeability of the tight underground rock, allowing for an easier and more efficient flow of oil and/or natural gas therethrough.

Hydraulic fracturing has been used with increasing frequency to improve the productivity of oil and/or natural gas wells in low permeability reservoirs. The list of raw materials previously used as proppants include: sand (the most common proppant), nut shells, aluminum and aluminum alloys, wood chips, crushed coke, granulated slag, pulverized coal, crushed rock, granules of metal such as steel, sintered bauxite, sintered alumina, refractories such as mullite, and glass beads.

As the technology associated with hydraulic fracturing has evolved and improved, those in the industry have recognized the benefit of manufacturing spherical shaped proppant bodies. Ceramic proppants in particular were manufactured with particulate material, processed by “dry” or “wet” manufacturing techniques.

Ceramic proppants have been found to yield more consistent and efficient production than some of the more common and inexpensive proppants. Ceramic proppants have been shown to have more advantageous characteristics due to their increased strength and uniformity of size and shape. However, ceramic proppants have not been utilized as commonly as other types of proppant due to various limitations.

Common mineral particulates historically used in the manufacture of ceramic proppants are characterized by a high alumina content. This has caused difficulty in the manufacturing process, as many mineral particulate deposits are limited in supply and only available in certain geographical locations. The scarcity of raw materials has led to manufacturing facilities located far from the oil and/or natural gas wells at which a manufactured proppant will be utilized, and therefore higher associated transportation costs of said proppants.

A need exists for a ceramic proppant that is stronger and able to be produced more efficiently and more cost-effectively than conventional counterparts.

BRIEF SUMMARY OF THE INVENTION

The present disclosure relates, generally, to ceramic propping agents (e.g., “proppant”) and related methods of use and/or manufacture.

For purposes of describing the following embodiments, the term “particulate ceramic” refers to a composition for utilization in oil and/or natural gas wells as a ceramic propping agent. The term “mineral particulate” refers to the raw materials from which a particular ceramic proppant can be made. One embodiment of a propping agent usable within the scope of the present disclosure can include a particulate ceramic made from raw materials which may comprise about: 10%-90% parts by weight of a naturally occurring mineral particulate, 30%-70% parts by weight of an aluminosilicate network modifier, 0.25%-20% parts by weight of a strength enhancer, and, typically, less than 10% by weight of a binder.

As described in one or more subsequent embodiments, common clay may be combined with other materials to enhance the crush strength of the particulate ceramic. The “aluminosilicate network modifier” may be selected from various modifiers including, but not limited to kaolin, metakaolin, bauxite, bauxitic clays, aluminum oxide, and/or other metal oxides. Some embodiments of the particulate ceramic may contain from about 30%-70% aluminosilicate network modifier by weight. In one embodiment, metakaolin serves as the aluminosilicate network modifier and nepheline syenite serves as a strength enhancer, as well as fluxing agent, the strength enhancer and fluxing agent comprising 0.25%-20% of the particulate ceramic by weight. The material particulate and aluminosilicate network modifier may be utilized in an un-calcined, partially calcined, or calcined form.

In one embodiment, the common clay can be ground and agglomerated with ground aluminosilicate network modifier, a strength enhancer, water, and, in some embodiments, a binder. In various embodiments, the binder may be chosen from, but not limited to cornstarch, polyvinyl alcohol (“PVA”), and/or cellulose gum (“CMC”). As a result of this process, the various components are formed into solid, spherical pellets (e.g., “green body” pellets) of a desired mesh size (e.g., a size suitable for use in the hydraulic fracturing of oil and/or natural gas wells). In some embodiments, the “green body” pellets are then fired in a kiln, or otherwise heated at temperatures ranging from about 1200° C. to about 1800° C., for periods ranging from about 30 minutes to about 60 minutes, with the soak time at peak temperature ranging from about 15 minutes to about 30 minutes.

In an embodiment, the clay utilized to form the proppant can include a Pennsylvanian age Strawn Group clay or “common red clay.” This dominantly siliceous clay/shale has thin lenses and layers (<5 feet) of calcareous, very fine-grained sandstones and fossil-rich clays. Recent X-ray diffraction (XRD) analyses have identified quartz, illite, chlorite, wustite, and kaolinite within the clay deposit. In this embodiment, common red clay can comprise from 10%-90% by weight of the particulate ceramic.

Common clay can include clay having an alumina content ranging from about 7% to 25% by weight, a silica content ranging from about 60% to 90% by weight, and a quartz content less than about 45%. Common clay is readily available in most markets and geographical areas and historically been used in the manufacture of ceramic bodies such as brick, tile, floor tile, pottery, and Portland cement.

In some embodiments, the mineral particulate can be ground such that about 95% of the ground mineral particulate has a particle size of less than 45 microns, and in some embodiments the particle size can be less than 10 microns. The mineral particulate may be un-calcined, partially calcined, or calcined. The ground mineral particulate can be mixed and agglomerated with a ground aluminosilicate network modifier(s), which can be ground to a particle size approximately equal to or less than that of the mineral particulate. In various embodiments, the aluminosilicate network modifier can include, without limitation, kaolin, metakaolin, bauxite, bauxitic clays, perlite, fly ash, volcanic ash, and/or alumina oxide sources. The strength enhancer can include, without limitation, nepheline materials and/or metal oxides such as iron, manganese, or dolomite. The mineral particulate and/or aluminosilicate network modifier(s) may be un-calcined, partially calcined, or calcined. In some embodiments, the common clay, aluminosilicate network modifier(s), and/or strength enhancer(s) can be combined into spherical pellets. Various methods of pellet formation can be used, one such method involving the use of an Eirich mixer.

The ground mineral particulate, aluminosilicate network modifier, and strength enhancer can be mixed with binder and water. Additional milled and/or ground mineral particulate can be added and mixing continues, forming spherical pellets. Dry powder may be continually added until the desired size of green pellets is reached. The green pellets can then be dried, in an embodiment to 1% moisture or less, and can be screened to eliminate pellets larger or smaller than the desired range of mesh size. In some embodiments, the screened green pellets are then sintered at about 1200° C. to about 1800° C. for about 30 minutes to about 60 minutes in a rotary kiln or similar device. In other embodiments, different temperatures, different times and/or a different heating mechanism may be used. In some embodiments, the time of the soak at peak temperatures can range from about 15 minutes to about 30 minutes. This process typically results in the formation of spherical ceramic pellets having a specific gravity of about 2.30 to about 3.40 g/cc, depending upon the mineral particulate content. Any binder that adequately holds the unfired pellet together and does not adversely affect the strength of the fired pellet may be used, such as PVA at 1% to 3% dry weight loadings. After firing, the particulate ceramic is generally suitable for use as a proppant.

In various embodiments, the particulate ceramic can be encapsulated in resin. For example, a phenolic or non-phenolic resin can be applied such that fines produced from portions of the particulate ceramic that become crushed are contained by the resin, rather than released into the adjacent subterranean fractures created by hydraulic fracturing.

In various embodiments, binders useful as raw materials can include, without limitation, PVA, bentonite such as sodium bentonite, sodium silicate, cellulose gum, vegetable starches, and/or sodium lignosulphonate.

Embodiments usable within the scope of the present disclosure can thereby include proppants having lower raw material costs than proppants manufactured from primarily bauxite, kaolin or kaloinitic clay, and/or montmorillonite-smectite clay; lower firing temperatures and thus lower energy costs for manufacture, when compared to sintered bauxite and proppants manufactured from bauxite, bauxitic clays, kaolin or kaolinitic clay, and/or montmorillonite-smectite clay; superior crush resistance when compared to to sand or resin coated sand; fracture conductivity which is superior to that of sand or resin coated sand; specific gravity lower than that of bauxite and nearly the same as that of sand; bulk density substantially lower than that of bauxite and lower than that of sand; lower transportation cost to an operational site (due to the fact that common clay is readily available in most areas where hydraulic fracturing occurs and manufacturing facilities can be built in close proximity); and, better delivery logistics than currently available ceramic proppants due to the ability to provide manufacturing plants within trucking distance of operational sites, eliminating the need for rail and/or other transshipment options for delivery logistics.

These and other aspects of the disclosed subject matter, as well as additional novel features, will be apparent from the description provided herein. The intent of this summary is not to be a comprehensive description of the subject matter, but rather to provide a short overview of some of the subject matter's functionality. Other systems, methods, features and advantages here provided will become apparent to one with skill in the art upon examination of the following FIGURES and detailed description. It is intended that all such additional systems, methods, features and advantages that are included within this description, be within the scope of the claims and any claims filed later.

BRIEF DESCRIPTIONS OF THE FIGURES

The novel features believed characteristic of the invention will be set forth in any claims appended hereto. The invention itself, however, as well as one or more preferred modes of use, further objectives, and advantages thereof, can be understood by reference to the following detailed description of one or more illustrative embodiments, when read in conjunction with the accompanying drawings and claims, wherein:

FIG. 1 is a 1×1 resolution depiction of an embodiment of the finished particulate ceramic with a mesh size ranging from −20/+40 of Example II;

FIG. 2 is a 3×1 resolution depiction of an embodiment of the finished particulate ceramic with a mesh size ranging from −20/+40 of Example II;

FIG. 3 is a 1×1 resolution depiction of an embodiment of the finished particulate ceramic with a mesh size ranging from −30/+50 of Example II;

FIG. 4 is a 3×1 resolution depiction of an embodiment of the finished particulate ceramic with a mesh size ranging from −30/+50 of Example II;

FIG. 5 is a 1×1 resolution depiction of an embodiment of the finished particulate ceramic with a mesh size ranging from −40/+80 of Example III;

FIG. 6 is a 3×1 resolution depiction of an embodiment of the finished particulate ceramic with a mesh size ranging from −40/+80 of Example III;

FIG. 7 is a 1×1 resolution depiction of an embodiment of the finished particulate ceramic with a mesh size ranging from −40/+80 of a resin coated version of Example III;

FIG. 8 gives the weight percent of common clay used in Examples I-IV;

FIG. 9 gives the characteristics of the fired particulate ceramic for examples I-IV at a mesh range of −40+70;

FIG. 10 gives the characteristics of the fired particulate ceramic for examples I-IV at a mesh range of −30+50;

FIG. 11 gives the characteristics of the fired particulate ceramic for examples I-IV at a mesh range of −20+40;

FIG. 12 gives the chemical composition of the mineral particulate, aluminosilicate network modifiers, and strength enhancers utilized to produce the particulate ceramics of Examples I-IV;

FIG. 13 gives the conductivity and permeability of the fired spheroids of Example II at a mesh range of −20+40;

FIG. 14 gives the conductivity and permeability of the fired spheroids of Example II at a mesh range of −30+50;

FIG. 15 gives the conductivity and permeability of the fired spheroids of Example II at a mesh range of −40+70;

FIG. 16 gives the conductivity and permeability of the fired spheroids of Example III, in a mesh range of −40/+80.

DETAILED DESCRIPTION

While the invention has been described with respect to a limited number of embodiments, the specific features of one embodiment should not be attributed to other embodiments of the invention. No single embodiment is representative of all aspects of the inventions. Moreover, variations and modifications therefrom exist. For example, the invention described herein may comprise other components. Various additives may also be used to further enhance one or more properties. In some embodiments, the inventions are substantially free of any additive not specifically enumerated herein. Some embodiments of the invention described herein consist of or consist essentially of the enumerated components. In addition, some embodiments of the methods described herein consist of or consist essentially of the enumerated steps.

Embodiments of particulate ceramics described herein may be made by a process in which mineral particulate material, aluminosilicate network modifier(s), binder(s), strength enhancer(s), and water are mixed and pelletized to form spheroid particles. An exemplary mineral particulate that may be utilized in such a process can include a non-kaolin, non-kaolinitic, non-smectite, non-montmorillonite-smectite, common illitic structural clay such as that found in the Strawn Formation from the Pennsylvania Shale era mined from a site in Brown County, Texas. Clays are generally classified into the following groups: kaolin group, which includes the minerals kaolinite, dickite, and nacrite; smectite group, which includes dioctahedral smectites such as montmorillonite and nontronite and triocatahedral smectites such as saponite; illite group, which includes clay micas where illite is the common mineral; chlorite group; and mixed-clay, which includes of combinations of the denoted groups. Clays are commonly referred to as 1:1 or 2:1, based on the arrangement of tetrahedral sheets and octahedral sheets therein. A 1:1 clay would include one tetrahedral sheet and one octahedral sheet (e.g., in alternation), and examples would include kaolinite and serpentine. A 2:1 clay would include an octahedral sheet sandwiched between two tetrahedral sheets, and examples are illite, smectite, attapulgite, and chlorite. Common clays can include 1:1 or 2:1 clays that are naturally occurring, fine-grained material composed primarily of hydrous aluminum silicates, often with significant impurities that distinguish them from substantially pure clay minerals or mixtures of substantially pure clay minerals. The term common clay encompasses a wide variety of clay types, including fine-grained rocks such as shale. Common clays suitable for formation of the particulate ceramics described herein can include 1:1 or 2:1 clays that are not identified as substantially pure kaolins or smectites. Other exemplary common clay types suitable for forming particulate ceramics can include Redart clay, which is mined in Ohio, Newman Red Clay, mind in California, and Lincoln Fire Clay, mined in California.

The mineral particulate material, aluminosilicate network modifier(s), and strength enhancer(s) can be ground prior to mixing, and in an embodiment, to the same approximate particle size. Using materials of approximately the same particle size facilitates even distribution of alumina throughout the particulate ceramic.

In some embodiments, an agglomeration process may be utilized where the particle size of the particulate material is coarser than that of the other materials in the composition and forms a core or seed. The other materials with higher alumina content can be ground to a finer particle size and agglomerate to the seed, forming a spheroid having higher alumina content within the outer portions and surface thereof.

Selecting the type of mixer used can impart various benefits and functionality to the process. For example, a suitable mixer can processes the mineral particulate material, aluminosilicate network modifier(s), and strength enhancer(s) into unfired spheroids having a high Krumbein roundness. In an embodiment, the mixer can provide a relatively high yield of particles in the range of 0.84 to 0.177 millimeters in largest dimension (20-80 mesh). Exemplary types of mixing apparatuses usable within the scope of the present disclosure can include balling pans or disk agglomerators, such as those used in the mining industry.

In various embodiments, high energy mix pelletizers can be used, two examples of such machines including the Littleford® mixer and the Eirich® Machine. Mixers of this type can include a rotatable cylindrical container, the central axis of which is at an angle to the horizontal, one or more deflector plates, and at least one rotatable impacting impeller, typically located below the apex of the path of rotation of the cylindrical container. The rotatable impacting impeller engages the material being mixed and may rotate at a higher angular velocity than the rotatable cylindrical container itself.

In an embodiment, the general steps that may be utilized in making the spheroids in a high energy mix pelletizer can include: (1) mixing ground/powdered dry mineral particulate, aluminosilicate network modifier(s), strength enhancer(s), and binder, each component being ground to the same approximate particle size, at high speed; (2) nucleation, at which time water is added to the region of the mix pelletizer near the impacting impeller to be dispersed as droplets to aid the formation of spherical pellets of the particulate ceramic; (3) growth of the spheroids (e.g., in the manner of a snow ball) with the added ground materials agglomerating on the previously-deposited grains, during which time the impacting impeller rotates at a slower speed than during the nucleation step; (4) addition of a dry mix of the ground components to adhere to the surface of the agglomerated mixture, resulting formation of spherical pellets; and (5) polishing and/or smoothing the surfaces of the spheroids by deactivating the impacting impeller while allowing the cylindrical container to rotate (e.g., similar to a balling pan).

Prior known processes include a “seed-shell” process where a mineral is ground to a coarser particle size than a strength enhancer, and serves as a seed on which the finer particles of strength enhancer agglomerate, building the spheroid having mineral particulates at the interior, coated with the strength enhancer at the surface. In contrast, embodiments described herein can include mineral particulates, strength enhancers, aluminosilocate network modifiers, and binders ground and agglomerated in a manner that causes all components to be generally evenly dispersed throughout the pellets.

In an embodiment, the binder can include a dry binder comprising about 0.25% by weight of the dry materials fed to the mix pelletizer, and an amount of liquid binder ranging from about 1% to about 3% by weight.

The wet spheroids, or prill, are discharged and/or otherwise removed from the mix pelletizer and can be dried at a temperature of about 120° C. to about 180° C. The dried spheroids may be screened to obtain a desired mesh size (e.g., 20/80 mesh—0.84 to 0.177 mm) for further processing. In an embodiment, the selected particle size can be larger than the desired size of the end product due to expected shrinkage of the spheroids during firing.

After removal from the mixer, the spheroids can be fed (e.g., using a vibratory feeder) to a rotary kiln. In an embodiment, a parting agent can be used to prevent the spheroids from agglomerating or sticking to the kiln walls.

It should be understood that while use of a rotary kiln is described herein, in various embodiments, the vitrification step, also called firing, may be performed statically. The residence time of the spheroids in the kiln can vary depending upon various parameters: kiln length, diameter, angle, rotational speed, feed rate to the kiln, temperature within the kiln, particle size of the spheroids, and shape of the particles. Residence time can be adjusted to achieve the desired properties for a given end use. For example a typical residence time in the kiln can be greater than or equal to 30 minutes, to facilitate subjecting all or the majority of the spheroids to a desired thermal history, thus imparting the desired strength thereto. A shorter residence time can lower the density of the final product, which may be desired in some cases, while a longer residence time can increase the crush strength of the product. A product can be formed using lower temperatures if longer residence times are used. In an embodiment, the time the product is exposed to peak temperature during firing can range from about 15 minutes to about 30 minutes.

In an embodiment, the kiln can initially be heated to a low temperature, then raised in stages at given times, until the desired crush strength is attained in the end product. This corresponds to the optimum firing condition.

The product from the kiln can be screened to obtain a desired particulate ceramic size fraction (e.g., about 20/80 mesh—0.84 to 0.177 mm). Before, during, or after screening, the spheroids can be subjected to vigorous agitation by air and/or other agitation methods to remove dust from the surfaces thereof (e.g., a “dedusting” step).

The alumina gradient within the spheroids may be achieved in several ways. The particulate mineral material can have an alumina content by weight ranging from about 7% to about 25%. Aluminosilicate network modifiers having a high alumina content can be added to achieve a blended alumina content sufficient to achieve a desired level of crush strength. Depending upon desired crush strength, the weight percent of the particulate mineral may range from 10% to 90%, with a lower weight percent of the mineral particulate (and thus a higher weight percent of the aluminosilicate network modifier) resulting in a higher crush strength at the expense of increased weight (measured as specific gravity). In an embodiment, the weight percent of the aluminosilicate network modifier can range from 30% to 70%. The weight percent of the strength enhancer can range from 0.5% to 20%, and the amount used will affect the specific gravity, strength, and firing temperature of the resulting product.

Methods for evaluating the properties of proppants may be found in American Petroleum Institute Publications such as: API RP 19C, Recommended Practice for Measurement of Proppants in Hydraulic Fracturing and Gravel-packing Operation, First Edition as well as the internal standard of ISO 13503-2:2006/Amd0.1:2009(E), which are incorporated herein by reference in their entirety. Two important parameters for evaluating proppants are crush strength, or crush resistance, and fracture conductivity. Crush strength indicates the extent to which the proppant material will perform the function of propping a rock formation (e.g., by retaining a fracture), and resisting the crushing pressure of the formation. Crush strength can be measured by placing a sample of proppant material into the internal diameter die cavity of a test apparatus. Typically, the test volume of the proppant sample is equivalent to the volume occupied by 4 pounds/ft.sup0.2 (1.95g./cm.sup0.2) of the desired mesh size proppant in the test cell. In use, a steel plunger or piston can apply pressure to the ceramic inside the cavity at a rate of 2000 lbs per minute to achieve the test pressure (e.g. 5,000 psi, 7500 psi, 10000 psi, 12500 psi or 15000 psi), and after 2 minutes at test pressure, the pressure can be released. The sample can then be screened between 20, 40 and 80 mesh screens for 10 minutes on a Ro-Tap® (a registered trademark of W.S. Tyler®) screen vibrator, and the percentage of fines less than the smallest mesh size is recorded. It is normally desirable to minimize the weight percent fines produced in the crush strength test.

Fracture conductivity is a measure of the flow rate of fluid which can be conducted through a fracture under given conditions. It can be measured in millidarcy-feet (md-ft) at various applied pressures. Both crush strength and fracture conductivity values typically decrease with increasing applied pressure. However, the relationship of this decrease with pressure varies significantly with the type of proppant used. Directly related to conductivity, permeability measures the ability of fluids to flow through rock or other porous media, such as a proppant pack in a hydraulically fractured oil or gas well. Permeability can be measured in Darcies (with each Darcy representing 1,000 millidarcies). Tests for proppant conductivity and permeability can be measured in a conductivity cell in accordance with ISO 13503-2:2006/Amd0.1:2009 (E).

Bulk density can be measured in accordance with ISO 13503-2:2006/Amd0.1:2009(E), for example, by using the described apparatus in FIG. 6 of the ISO standard.

In the hydraulic fracturing process, proppant is typically transported through the well bore to the fractures in a fluid or gel solution. A lower weight (e.g., lower specific gravity) proppant exhibits greater conductivity and transportability with lower pumping pressures and use of a less viscous fracturing fluid solution. Embodiments usable within the scope of the present disclosure can provide a lighter weight proppant without sacrificing consistent crush strength and conductivity.

The particulate ceramic examples, shown in FIGS. 1-7, are grouped into mesh size samples. End users can specify and purchase specified size groupings for various applications/operations. Screens can be used to separate particulate ceramics such that all particles than a first stated mesh number fall through the screen and are not retained in the size grouping. Particulate ceramic with diameters larger than the second stated mesh number are screened out and do not enter the subsequent mesh size grouping. By way of example mesh size groupings can be stated as 20/40 or −20/+40. In these examples, particulate ceramic in this size grouping would have a diameter of at least 20 mesh and no greater than 40 mesh. The correlative diameters of particulate ceramic expressed in mesh sizes are as follows:

U.S. MESH SIZE	MILLIMETERS	INCHES
20	.853	.0331
40	.422	.0165
50	.297	.0117
70	.211	.0083
80	.178	.0070

The disclosed subject matter will be further clarified by a consideration of the following examples, which are intended to be purely exemplary.

EXAMPLES

Examples I-IV

For Example III, a dry ceramic mix of:

• 4,400 grams of common red clay obtained from Brown County, Texas deposit (“BCH”); and
• 1,100 grams of three aluminosilicate network modifiers;
  were blended for two minutes in the pan of a mixer/granulator (may use Eirich Machines, Inc., Model RV02) with the cylindrical container rotating at about 30 hertz. The pan and rotor were engaged with a fast pan speed and a rotor speed of 40 hertz. Pan rotation was clockwise and rotor rotation was counter-clockwise. The impacting rotor impeller had vanes or deflecting blades of two sizes, 125 mm and 185 mm long. A mixture of 700 grams of water and binder, selected from among cornstarch, CMC, or PVA, was added over a period of about one minute. Speed was increased, immediately after the water and binder were added, to 70 hertz. At 4 minutes, pan is reduced to slow speed and 250 grams of dry retained mixed material were added. At 5 minutes total mixing time, the rotor speed was decreased to 50 hertz and retained mixed material was added. At 6 minutes total mixing time, the rotor speed was decreased to 40 hertz retained mixed material was added. At 7 minutes total mixing time the rotor speed was decreased to 30 hertz and retained mixed material was added. At 8 minutes, rotor speed was reduced to 20Hz and mixed for a time period of 1 to 5 minutes, dependent on desired size and spherical shape. Once desired results were achieved, the mixing unit was stopped and the finished batch of particulate ceramic was removed.

FIG. 8 indicates the weight percent of common clay used in each formulation, and FIGS. 9-11 indicate the characteristics of the fired particulate ceramic for examples I-IV. Bulk density may be measured in accordance with ISO 13503-2:2006/Amd0.1:2009(E), e.g., by using the mentioned apparatus in FIG. 6 of the ISO standard.

Alternatively or additionally, bulk density can be measured by pouring the material at a constant flow rate into a container of known volume, leveling off the top surface with a straight edge, and recording the weight.

The wet spheroids were removed from the mix pelletizer, placed into flat trays, and dried in an electric dryer (not equipped with a circulation fan) at a set point temperature of 250° F. until a moisture level of <1% was reached. Moisture was measured by a Moisture Analyzer, such as the ML-50 manufactured by A&D. The dried spheroids were screened using U.S. standard mesh full height screens manufactured by Hogentogler and W.S. Tyler. Screening was mechanically accomplished by using a W.S. Tyler Ro-Tap® Model RX-29 for 5 minutes. The large mesh opening screen was stacked on top of the small mesh opening screen with a catch pan in place on the bottom of the stack to obtain −40/+80 mesh (0.420−0.177 mm.) fractions.

The particulate ceramic was placed into crucibles of fireclay/alumina composition. The screen material was weighed prior to placement in the crucible. Filled crucibles were weighed prior to firing to allow for calculation of weight loss during firing. The crucibles were placed in a furnace for firing. Firing was done in an electrically heated furnace using either a Skutt Kiln model KM818-3 or Sentro Tech box furnace Model ST-V600C-666, operated at atmospheric pressure in air. The heating rate and peak temperature hold was controlled by a built in microprocessor controller with input from a standard thermocouple supplied by the furnace manufacturer. To confirm the amount of heat work (time and temperature relationship) a temperature uniformity tab, TempTAB, suitable for the planned peak temperature and manufactured by Orton Ceramic Foundation was placed on the top surface of one crucible, taking care not to embed the tab such that material penetrates the center hole of the tab. The firing temperature curve for this formulation was characterized by: start—temperature—ambient, heat to 2200° F. at 400 to 1000° F. per hour, hold peak temperature for 0.25 to 0.75 hours, and power off kiln and allow to cool in room temperature at an approximate cooling rate of 145° F. per hour. After the firing cycle was complete and samples had cooled to a temperature to allow handling, the crucibles were then removed from the kiln. The Temp TAB was removed, taking care to return to the crucible any material that adhered to the tab. The Temp TAB was measured with a micrometer. An equivalent firing temperature was obtained by using an equivalency chart provided by the Orton Ceramic Foundation. Comparison of TempTAB results to previous firing confirmed ongoing consistency of multiple firings and the accuracy of the firing procedure. Crucibles were weighed and loss on ignition was calculated by the formula: weight of material before firing less weight of material after firing divided by weight of material before firing.

Fired material was removed from the crucible and prepared for screening to desired size. Screen sizes depend on the intended purpose of the proppant. Three size range groupings were used in this example:

• −40 mesh+80 mesh—particulate ceramic diameters ranging from 0.177 to 0.420 MM
• −20 mesh+40 mesh—particulate ceramic diameters ranging from 0.420 to 0.840 MM
• −30 mesh+50 mesh—particulate ceramic diameters ranging from 0.297 to 0.590 MM

In each case, an identical screening procedure was used. The larger mesh screen was placed on top of the smaller mesh screen with a pan below the stack. The assembly was placed in a Ro-Tap® machine that was operated for 5 minutes. Material was retained on the smaller mesh screen and was removed by hand for further testing.

Screened material was tested for apparent specific gravity and crush strength. Five different force levels were used in testing: 5,000 lbs, 7,500 lbs, 10,000 lbs, 12,500 lbs, and, 15,000 lbs. The test procedures were identical in all cases, varying only in the load placed on the sample.

The equipment used for testing crush strength included a steel cylinder with piston of 1″ to 2″ in diameter, dependent on the volume of material for testing. The piston was free floating within the cylinder, and the cylinder had a removable base such that material may be placed inside the cylinder and force applied to the piston, creating stress and applying a crushing force to the material. The force was applied with a Carver Industries Model C bench top press equipped with force gauge calibrated in 200 lb increments and a manual hydraulic jack. The proper testing method was followed using the ISO 13503-2:2006/Amd0.1:2009(E) standard for comparable results.

A sample of the fired material of 20 grams was weighed and measured on an analytical balance within 0.01 grams of accuracy. This procedure was repeated two additional times to create 3 samples for measurement and averaging. The measured sample was carefully poured into the die with a 1 inch piston so that the material surface in the cylinder was as level as possible. The piston was inserted in the cylinder and lowered until contact with the material was made. The piston was rotated 180 degrees without applying force to the sample or disrupting the crush cell die set. The die set was then placed in the center of the press. Without making contact, the lower platen of the press was raised by operating the lever jack as close to the die as possible without contacting the piston. The lever jack was operated until the test force level was achieved. The pressure of the test force level was maintained for 2 minutes at which point the pressure was released. The die cylinder was removed and all contents were poured onto a screen mesh corresponding to the bottom range of the proppant distribution being tested. By way of example, if a 40/80 mesh proppant is being tested, an 80 mesh screen is used. A brush was used to gently remove any remaining sample that was left in the cylinder. Using a Ro-Tap® machine, the sample was sieved for 10 minutes. The material passing through the designated mesh screen was weighed and compared to the weight of the sample before stress was applied, thus calculating the percentage amount by weight of crushed fines that passed through the mesh screen. The test was repeated with the two remaining samples and averaged for reporting.

Apparent specific gravity was calculated using a 10 ml pycnometer with a perforated stem (item #330403889641 obtained from Avogadro's Lab Supply, Inc.), which was calibrated by weighing a clean, dry, empty flask, including the stem stopper, using an electronic scale capable of 0.01 gram precision. After the WF (weight of flask) was calculated, the flask was filled with deionized water to the halfway point of the pycnometer stem without a stopper in place. The stopper was inserted into the pycnometer, allowing water to be discharged from the opening off the stopper, thus providing a constant volume of water for future testing. The entire assembly of water and pycnometer was weighed and the weight recorded. The dry pycnometer weight was subtracted from the assembly weight and recorded. The difference in weight was calculated and represents the weight of the liquid (WL). Three ml of dry sample material were measured using a 10 ml graduated cylinder. The material was weighed and the weight recorded. This represents the solid weight of material whose specific gravity is to be determined (WS). The 3 ml of dry material was placed into an empty pycnometer. The pycnometer was filled approximately halfway up the stem of the pycnometer. Air bubbles were removed by gently tapping and rotating the pycnometer while holding it at an approximate angle of 45 degrees. The pycnometer was placed upright on a flat surface and the stopper was inserted, ejecting water from the opening of the stopper. The exterior of the pycnometer was dried of any excess water and the absence of any bubbles was confirmed. The assembly consisting of the pycnometer, 3 ml of material, and deionized water was weighed and the weight recorded (WT).

The specific gravity of the material was calculated using the formula: WT−WL−WS−WF=Weight of Water Displaced (WD). WD is a negative number. The following calculation was performed using the absolute value without regard to sign: WS/WD=Apparent Specific Gravity. Deionized water has a specific gravity of 1.0 gram/ml (specific gravity=1). The method for apparent specific gravity is also followed using the ISO 135032:2006/Amd0.1:2009(E) standard for comparable results.

IN the current example, the preferred mesh size of the sample proppant was −40 mesh+80 mesh, the specific gravity of the fired sample was 2.55, and the percentage of fines created at the noted crush pressures were as follows:

5,000 psi  0.7%
7,500 psi  2.0%
10,000 psi 3.9%

The same procedures as described above were used in the preparation and evaluation of all Examples. The dry weight material composition percentages and chemistry of the particulate ceramics of Examples I-IV are given in FIG. 8. The properties of the fired spheroids of Examples I-IV, specified by mesh size range, are given in FIGS. 9-11. The chemical composition of the mineral particulate, aluminosilicate network modifiers, and strength enhancers utilized to produce the particulate ceramics of Examples I-IV are given in FIG. 12. The conductivity and permeability of the fired spheroids of Example II, specified by mesh size range, are given in FIGS. 13-15. The conductivity and permeability of the fired spheroids of Example III, in a mesh range of −40/+80, are given in FIG. 16.

In addition to the above described embodiments, those skilled in the art will appreciate that this disclosure has application in a variety of arts and situations and this disclosure is intended to include the same.

Claims

1. A method for producing a ceramic propping agent, the method comprising:

grinding a mineral particulate, an aluminosilicate network modifier, a strength enhancer, and a binder to form particles having a same approximate particle size;

mixing said particles of mineral particulate, aluminosilicate network modifier, strength enhancer, and binder;

nucleating said particles by adding water thereto to form spherical pellets;

growing said spherical pellets by adding additional particles comprising said mineral particulate, said aluminosilicate network modifier, said strength enhancer, and said binder, wherein said additional particles adhere to a surface of said spherical pellets;

drying said spherical pellets; and

vitrifying said spherical pellets to form the ceramic propping agent.

2. The method of claim 1, wherein mixing said particles comprises mixing at a high speed using a mixer.

3. The method of claim 2, wherein using said mixer comprises processing said mineral particulate, said aluminosilicate network modifier, said strength enhancers, and said binder into spheroids having a high Krumbein roundness.

4. The method of claim 1, wherein nucleating said particles comprises adding said water proximate to an impeller of a mix pelletizer to be dispersed into droplets, thereby aiding in formation of the spherical pellets.

5. The method of claim 1, further comprising polishing the surface of said spherical pellets, smoothing the surface of said spherical pellets, or combinations thereof.

6. The method of claim 1, wherein vitrifying said spherical pellets comprises feeding said spherical pellets into a kiln.

7. The method of claim 1, further comprising screening said ceramic propping agent to obtain a desired particulate ceramic size fraction.

8. The method of claim 1, wherein drying said spherical pellets comprises applying a temperature ranging from 120 degrees Centigrade to 180 degrees Centigrade thereto.

9. A ceramic propping agent comprising:

a plastic clay;

an aluminosilicate network modifier;

a strength enhancing agent comprising nepheline materials, wherein the nepheline materials comprise from 0.1 percent to 5 percent iron oxide by weight; and

a binder.

10. The ceramic propping agent of claim 9, wherein said plastic clay comprises from 38% to 90% of the ceramic propping agent by weight.

11. The ceramic propping agent of claim 10, wherein said aluminosilicate network modifier comprises from 30% to 70% of the ceramic propping agent by weight, wherein said strength enhancing and flux agent comprises from 0.25% to 20% of the ceramic propping agent by weight, and wherein said binder comprises 10% or less of the ceramic propping agent by weight.

12. The ceramic propping agent of claim 9, wherein said plastic clay comprises a plurality of layers having a thickness of five feet or less.

13. The ceramic propping agent of claim 9, wherein said plastic clay comprises from 7% to 25% alumina by weight, from 60% to 90% silica by weight, and 45% or less quartz by weight.

14. The ceramic propping agent of claim 9, wherein said aluminosilicate network modifier is selected from the group consisting of: kaolin, metakaolin, bauxite, bauxitic clays, aluminum oxide, metal oxides, and combinations thereof.

15. The ceramic propping agent of claim 9, wherein said binder is selected from the group consisting of: cornstarch, polyvinyl alcohol, cellulose gum, bentonite, sodium silicate, vegetable starches, sodium lignosulphonate, and combinations thereof.

16. The ceramic propping agent of claim 9, further comprising a resin coating adapted to encapsulate particles of the ceramic propping agent.

17. A ceramic propping agent comprising:

a plastic clay;

an aluminosilicate network modifier;

a strength enhancing agent;

a binder; and

a resin coating adapted to encapsulate particles of the ceramic propping agent.

18. The ceramic propping agent of claim 17, wherein the strength enhancing agent comprises nepheline materials, and wherein the nepheline materials comprise from 0.1 percent to 5 percent iron oxide by weight.

19. The ceramic propping agent of claim 17, wherein said plastic clay comprises from 38% to 90% of the ceramic propping agent by weight.

20. The ceramic propping agent of claim 17, wherein said plastic clay comprises from 7% to 25% alumina by weight, from 60% to 90% silica by weight, and 45% or less quartz by weight.