AUST RAL IA PATENTS ACT 1990 REGULATION 3.2 Name of Applicant: SAINT-GOBA N CERAMICS & PLASTICS, INC. Actual inventors; Walter T. Stephens; Kevin R, Dickson; Tihana Fuss; Ian Jaeger; Danny Louis Michelson; Suchira Sen; and Thomas Szymanski. Address for Service: E. F, WELLINGTON & CO, Patent and Trade Mark Attorneys, 312 St. Kilda Road, Melbourne, Southbank, Victoria, 3006. Invention Title: "CERAMIC PARTICLES AND METHODS FOR MAKING THE SAME" The following statement is a full description of this invention including the best method of performing it known to us.
CROSS-REFERENCE TO RELATED APPLICATION Tis application is a 'divisional' application derved from Australian Patent Application No. 2011216058 (PCT/UUS2O 1;023957: WO 2011;100203), claiming priority of US Application No. 6/303097, the entire contents of which are incorporated by reference herein. Each patent and patent applcation cited herein is also hereby incorporated by reference in its endrety BACKGROUND OF THE INVENTION Populations of ceramic particles may be used in a wide& variety of industrial processes and products including, for example abrasive media as a granular coating for asphalt based roofing shingle; asfltration mediumor liquids; as a substitute for sand in investment casting processes; and as proppants in a down hole driving operations where the ceranic particles may be rdfrred to as proppants. Proppants made frOm ceramic particles may be used in deep wells where the pressure exerted on the ceramic proppant exceeds the crush resistance of conventional pmppants such as sand and resin coated sand, Examples of patents and published patent applications directed to prppants include: US 376.930;US 4,632,876; US 067.445; US 752860%6 US 2006/0177661 and US 2008/000063&. SUMMARY Embodiments of the present i nvention include populations of particles having certain characteristics to improve crush strength conductivity and resistance to settling while aso lowering manufacturing cost for the producer of the ceramic particles Population of ceramic pardcles described herein can be created using Conventional equipment and raw materials. One enbodiment of the present invention comprises populations of ceramic panicles comprising a plurality of individ ual, free flowing particles. The plurality of particles having a total weight and particle size distribution including d 9 ) and d particle 2 sizes. The distribution has an effective width whichis the difference between the distribution's d9 5 and d- particle sizes. The distribution's effecike width exceeds 106 microns and comprises three abutting and non-overlappig regions including a first region, a second region, and a third region. The first reion abuts the second region and the second region abuts the third region. The width of the second region is at last 25% of the effective width. The weight of particles in the second region does not exceed 15% of the population's total weight and the weight of particles in the first region and the third region each exceed the weight of particles in the second gon Another embodiment of the present inventeion relies to a process for manufacturing a population of ceramic particles The process may include the following steps. Providing an iniial population of particles having a total weight and particle size distribution. Separating the initial population of particles into atleast three portions. identified herein as portion. A, portion B and porton C herein the d of portion. A is less than the d,, of portion B which isless than the d 5 a of portion C. Combining portion A and portion C thereby creating a final population of particles having a total weight and particle size distribution including dg and d 5 partide sies. The distribution'effective width is the difference between the distributon's digand d: particle sizes.he distributionseffective width exceeds 100 ntms and comprises thre abuttin and non overapping regions including a first region, a second region and a third region. The first region abuts the second region and the second reTgion abutsthe third region. The width of the second regim is at least 25% of the effective width. The weight of particles in the second region does not exceed i3% ofte final population's total weight and the weight of particles in the first region and the third region each exceed the weight of particles in the second region Another embodiment relates to another process for manufacturing population of ceramic particles.he process may comprise the tolowing steps. Providing a first population of particles and a second populaion of particles wherein the dg of the first population is less than the dje of the second population, Combining the first population and the second populationtereby creating a final population hainga total weight and particle size distribution including cb and d 5 particle sizes, The distribution has an effective width which is the difference between the distribution's d 0 and d. particle sizes, The distribution's effective with exceeds 100 microns and comprises three abutting and 31 noin-overlapping regions including a first region, a second region, and a third region. The first region abuts the second region and the second region abuts the third region. The width of the second region is at least 25% of the effective width. The weight of particles inthe second region does not exceed 15% of the final populationf total weight and the weight of particles in the frst rgion and the third region eachexceed the weight of particles in the second region BRFI DESCRIPTION OF THE DRAWINGS Fig. I is a firstgraph of weight percent versus particle diameter; Fig. 2 is a first process flow chart Fig. 3 is a second graph of weight percent versus particle diameter; and Fig. 4 is a second process flow chart. DETAILED DESCRIPTION As used herein, the phrase p opulation of ceramic partcles"is used as a general description of a phiaity of individual, free flowing ceramic particles. Terms such as proppant, abrasive grains and rooting granules describe populations of ceramic particles that are intended for use in specinc applications. As used herein, the terms "proppan or "proppants" may be used interchangeably to identify a large quantity of ceramic particles that are typically mixed with a fracturing fluid and then forcefully inserted into a well bore Te particle which nm have an average diameter between 200 microns and 2.4 mn, become lodged in fissures created in the geological formation by the fracturing fluid. After the fracturing fluid has been withdrawn, the particles remain in the fissures. As fluids located near the well bore drain through the fissures, into the well and are then pumped to the surface of the well, he individual particles prop open the passageways through the fissures thereby allowing additional fluids to fill the well Use of proppants may improve the economic performance of the well by enabling the Capture of more fluid than would be possible if proppants were not used on the same well. 4 in order to manufacture large quantities of ceramic particles such as proppants, commercial manufacturers of manmade proppants may use large rotating pan style mixers to mix dry ingredients with wet ingredients and then form a large quantity of manually deformable sphericaly shaped particles that may he referred to as greenware. The geenware, prior to anyfrder processing sh as sorting or heating, may be referred to herein as the original population of parties. With regard to the dry ingredients used to make the greenware. suitable starting materials include oxides such as aluninum oxides, siion oxides, magnesium oxides and mixtures thereof Other exemplary starting materials include clays (which are predominately hydrated alumina), such as kaolin, diaspore clay, budey clay, and flint Clay, bauxitic clays natural or synthetic bauxites, alumino-silicates, magnesium silicates, mixtures thereof and the like. Various sintering aidsnsuch as bentonite clay iron oxide, boron, boron carbide. ahluinUm diboride, horon nitride, boron phosphide other boron compounds, or fluxes, such as sodium carbonate, lithium carbonate, feldspar, manganese oxide. titania, and sodium silicates may be aked ianiounts up to about ten weight percent to aid sintering If desired a binder may be added to the mixture to improve particle formation and to increase the strength of the greeware Generally the binder is added at about 0-6 percent by weight based on the weight of the oxides. Suitable binder materials include starch, resin or wax, calcium carbonate, or a combination thereoF. The dry ingredient may be ground by bai milling or other attrition processes Prior to grinding, the dry ingredients may be dried to inprove the ease of grinding. in one embodiment, the dry ingredients nmy be combined with a wet ingredient, such as water and mixed in an intensive mixer having a rotatable containment vessel provided with a rotor table and a rotatable impacting impeller, such as an Eirne mixer The rotor table. or pan, rotates in an opposite direction to the impacting impeler The impacting impeller may be in the fonn of a disk with rods or bars attached to the dik and aligned generally parallel with the impelerI axis of rotation Sufcientater is needed to Cause essentially spherical particles of the mixture to fornt After such particles have formed, additional ceramic powder mia be added and the mixer may be further operated to cause accretion of the added material to the particles being fbrrmed Ihe resulting greenware is then dried, usaly in a dryer at between about I ) 0 Q and abothO3 to moisture content of less than about V) weight percent, 5 In conventional processes the distribution of particle diameters produced by the agglomerator is so vide that the distribution includes particles that are oversized and particles that are undersized as well as particles that are appropriately sized for use in a well bore. The oversized particles may be too large to function as a proppant because they are difficult to place in he geological formation. Te undersized proppants maybe too small to function as a proppant because they tend to fillthe voids between other appropriately sized proppant particles and thereby reduce the conductivty of a fluid through the proppant pack. Consequently/proppant manufacturers typically remove the oversized and undersized particles in order to produce a commercially viable proppant that has acceptable conductity and reistance to crushing, however, as the width of the particle size distribution is decreased by eliminating the oversized and undersized particles, the particles remaining in the distribution tend to form a monomodal di stribution with better conductivity than the original population but crushing may increase beyond an acceptable level. The oversized and undersized pariles are removed from the original population by allowing the particles to flow through a series ofscreens. Each screen contains a pluraity of uniformly shaped and sized holes that allow padres smaler than the screen's hole opening to flow through the screen and prevents particles larger than the screen's hole opening from passing therethrough As explained aboveif the pmppant manufacturing process cannot control the diameter of the individual proppant particles as closelas desired, the screening process may need to divert and then recycle large quantities of the original proppant population wh ich arc either too large or too small. In some commercial operations up to 30 weight percent of the proppants are removed during the screening process and then returned to the beginning of tproppat manufacturing process where they can be recovered. Proppant manufacturing processes that yield less than ' weight percent usable product on a single pass therethrough are known. While the recycled material nay be recoverable thereby avoiding a significant economic loss in material cost, the labor involved in manufacturing and recoering 30 weight percent of the greenware is an economic borden which ultimately increases the cost of producing the proppant The dried and screened greenware may then be heated in a tumace to an elevated temperature, such as 1 000C or higher, thereby sintering and/or bonding the agglomerated grains of dry ingredients to one another and forming porous, crush resistant proppant 6 particles. Suitable sintering temperatures are generally about 1 200"C and could be as high as 1509C As will be explained below, one embodiment of a process of this invention reduces the cost of producing the proppant by separating an initial quantity of particles into at least three portions which are identified herein as portion A, portion B, porton C, and then combining portion A with portion C thereby creating a final proppant population. Portion B may be sold as a separate product without further processing. The savings in labor costs associated withsubstantially improving the yield of the manufacturing process may significantly improve the economic performance of the proppant manufacturing process. Proppants may be characterized using one or more physical characteristics including particle size distribution. As used herein, particle size distribution is determined using a CAMS1ZER optical partial size analyzer which is manufactured by Retsch Technology in Germany. The particle size analyzer provides a gaph of particle size distribution which may indicate numerous particlesize metric, such as d 50 , which is used to indentify the particle diameter which is less than 50 percent of the particles diameters and greater than 50 percent of the particles diameters. Similarly d identifies the particle diameter which is less than 95 percept of the particles' diameters and greater than 5 percent. of the pa.-rticles' diameters. Fo~r any itrbtin sim1.ilar values canl be calculated for other particle size meinics such as d a d-. d 75 and d 0 . Another important physical characteristic used t describe proppants is conductivity which may be generally described as a measure of the resistance the proppant exerts on a fluid as the fluid moves through the proppant, Conductivity is determined using the procedure described in ISO 13503-5. Yet another important characteristic is a proppants ability to withstand crushing. Crush resistance is a term commonly used to denote the strength of a proppant and may be determined using ISO 13503-2. A strong proppant generates a lower weight percent crushed proppant than a weak proppant at the same closure stress. For example under the same test conditions, a proppant that has a 2 weight percent crushed proppant is censired to be a stron proppant and is ferred to a wak proppant that has a 10 wegtpe-rcent crushed proppanit.
When proppants are used in drilling operations, the particles are mixed with a fluid which is thenforcefuly pumped downhole. As the fluid and the particles entrained therein are pumped into the well, some of the particles tend to settle at a faster rate than other particles in the same population of particles. The depth of the well may impact the degree of separation with shallow wells (i.e. less than 2Q00 meters) experiencing less separation than deep wells (i.e. greater than 4000 meters) if the same mixture of fracturing fluid and proppant are used in each well. This phenomenon may be referred to herein as the 'proppant settling problem" which is a widely recognized and persistent problem for the companies that use proppants as part of their process to fracture geological formations. The proppant settling problem may lead to small particles accumulating in one location within the fracture zone while the large particles accumulate in a second location within the fracture zone. The uncontrolled settling of particles within the fracture zone may decrease the effectiveness of the proppant and thereby decrease the economic perfonnance of the well The inventors of th is invention recognized that this problem could be substantially reduced or eliminated by coordinating the selection of the proppants' physical characteristics, such as particle size distributions and specific gravity, and chemical compositions so that most of the particles settle at approximately the same rate. Mixing a first proppant population having a first average particle size and specific gravity with a. second proppant population having a different average particle size and specific gravity so that all of the particles in the final population of particles settle at approximately the same rate may Substantially remove the proppant sealing problem. T he inventors of this invention have also recognized that coordinating the selection of a first proppant population having a known particle size and specific gravity with a second proppant population having a known particle size and/or specific gravity that is different from the first proppant populations particle size and specific gravity can be used to intentionally create a spectrum of settling rates which can be used to cause a beneficial and controllable difference in the rates at which the particles settle, For example, small particles having a high specific gravity can he made to settle much more rapidly than large particles that have a low specific gravity. If desired, the difference in settling can be accentuated so that most of the small particles enter the fractures in the geological formation and travel as far as possible into the fissures before the larger particles can reach the opening of the fissure, Selectively inserting the smaller particles hi and then the larger particles may be desirable because it can lead to the prevention of particle back flow which is the undesired removal of partcles from fissures as the fracturing fluid is removed. Shown in Fig. I is graph of weight percent versus diameter for a population of ceramic particles of one embodient of this invention. The effective width of the distribution see arrow 28, is defined herein as the distance between particle size d see arrow 30, and particle size d, see arrow 32. As previously described, the particle size distribution's d 5 and dq5 may be determined using an optical particle size analyzer, Within the effective width there are at least three abutting and non-overlapping regions including first region 34, second region 36 and third region 38. The first region abuts the second region and the seCond region abuts the third The weight of particles in the first region and the weight of particles in the third regon each exceed the weight of particles in the second region. in Fig. , the weightof particles in the first and third regions is 40 percent of the population total weight and the weight of particles in the second region is 10 percent. With regard to the mean particle size, also referred to herein as the d, the d of the first region is iriherenti lessihan the ds of the second region which is inherently less than the d of the third region. Furthermore, the width of the second region, which is defined as the difference between particle size d.#, see arrow 40, and d,. see arrow 42. is approximately 25% of he width of effective width 28. With regard to the weight percentages of the first, second and third regions, a population of ceramic particles of this invention may have a first region and a third region that are individualy between 5 and 85 weight percent of t population's total weight provided the total of the first and third regions does not exceed 90% Thesecond reion does not exceed 15 weight percent of the population's total weight In some embodinents, the second region may account for no more than 10 weight percent, 5 weight percent or even 0 weight percent of the population's total weight. Weight percentages of the first or third regions been 5 and 5; such as 15. 35. 40.0, 63.5 and 75. are also feasible. Silarly, weight percentages of the second region between 0 and 5 such as 3,2, 9.5 and 12. 1 are feasible. The boundaries of the first, second and third regions shown in Fig I are defined for use herein as follows The first reion extends front the population's d to the second region's C The third region extends from the second regions da: to the populations 9 d.- T'he second region. exists between the first region and third region thereby occupying the region between the dQ and the dm, For a particular population of ceranic parcles, the d and the d. are the particle sizes that cooperatvely define a region which Simti haleoo:ly: occupies at least 25 % of the distribution's width between its d and d95 particle sizes; (2) the weight percent of the particles in he first region and third region each exceed the weight percent of particles in the second region; and (3) the weight percent of particles in the second region does not exceed 15 weight percent of the population's total weight. The boundaries of the second region (ie.te parties sizes corresponding to the de and the d,) may be determined by using a particle size analyzer to determine the particle diameters in the population of particles and then using sieves to determine the wAeight percent of particles between selected particle diameters, Shown in Fige. 2 is a flow char of a process that nay be used to produce an embodiment of a population of ceramic partcles o this invention. Step 50 represents providing an initial quantity of panicles that have a total weight and particle size distribution. The initial quantity may have a monomodal or multimodad particle size distribution and nay be produced using raw materials and conventional equipment. such as spray dryers. high intensity shear mixers and pan agglomerators which are known to those skills in the art of manufacturig proppant. in step 52, he initial quantity of particles is separated into portion A portion B and portion C which are identified in Fig 2 by part numbers 54, 56 and 5, respectively The d of portion A is less than the d' of portion B vhich is less than the ds, ofporton G Separating the initial quantity into three portions may be done using an air classification system, a cyclonic sepaevteror screening mechanism! Step 60 represents combining portion A with portion C to create a final population of ceramic panicles 62 that does not include portion B. -The particles in portion B may be sold without further screening or other modifiation thereby avoidig the costs associated with recovering 25 percent or more of the particles frm the initial quantity of ceramic particles. Fig. 3 discloses a hypothetical particle size distribution of a phraty of ceramic particles that could be manufactured by the process disclosed in Fig. 2 wherein, after the initial quantity of particles was divided into a portion A, portion B and portion C, portions A and C were combined thereby creating the fina population of ceramic particles having the particle size distribution disclosed in Fig The final population of ceramic particles has a total weight and a particle size distribution including dnand d 5 particle sizes. The distribution's effective wid, which is the differences between the distribution's dk and di particle sizes exceeds 100 microns and comprises three abutting and nom.-overlapping regions ininding fIrst region 34 which abuts second region36 which abuts third region 38. The width of the second region is at least 25% of the effective width and the weight of particles in the second region does not exceed 15% ofbe final population's total weight. Furthermore. the weight of particles in Ahe hrst region and the third region each exceed the weight of particles in the second region. Another process for manufacturing an embodiment of the applicant's invention will be described with reference to Fig. 4 wherein step 80 represents providing a first quantity of particles having a d particle size Step 82 represents providing a second quantity of particles having a particle size distribution having a do particle size, he first and second quantities of particles are selected so that the d% of the first quantity is less than the d of the second quantity in step 84 the firs and second quantities are then mixed to create a final population of ceramic partcles The final population has a particle size distribution including a d 5 and d 05 particle sizes. The distribution has an effective width whibc is the difference between the d and dA particle sizes; The effective width exceeds 100 microns and comprises three ab n. and non-overlapping regions including a frst region which abuts a second region which, in tun, abuts a third region. The weight ofpartiees in the first region and the third region each xceed thew t of particles in the second region The width of the second region's partile size distribution is at least 25% of the width of the nfial population'seffctiewidth With regard to the process disclosed in Fig 4, the first quantity of particles has an average specific gravity and particle siz distribution. The second quantity of particles has an average specific gravity and particle size distribution. isome embodinents, the average specific gravity ofhe particles in the second quantity may be at least 10% less than the average specific gravity of the particles in the first quantity, If desired, the average species gravity of the particles in the second quantity may be 15%, 20% or even 29% less than the average specific gravity of the particles in the first quantity. By coordinating the section of the particlesize distbutions and average specific gravities, the first quantity of particles can ben made to settle at approximately the same rate as the second quantity of particles. In some embodi nients, controlling the average specific gravity of the second quantity of particles to at least 10 weight percent less than the average specifc gravity of the first quantity of panicles will sussantially mitigate or prevent undesirable particle settling If as in the process disclosed in Fig 4 two different populations of particles are combined to manufacture an embodiment of a population of ceramic particles of this invention then both the physical (ie. specific gravity and particle size distribution) and chemical (i.e. compositions) characteristics of the first and second quantities may be independently selected to create a final population. For example, in one embodiment a population of ceramic particles of this invention may have a particle size distribution which has first region 34, second region 36 and third region 3$ as shown in Fig, 3. in this embodinent there are no particles in the second region. The parties in first region 34 may be chemically identical to particles in the third region 38 Alternatively, the particles in the first region may have a first chemical composition and the particles in the third region may have a second chemical composition which is chemically distinct from the first chemical composition. As used herein, two chemical compositions are considered to be"cheniaally distinct if: (1) the compositions do not contain at least one chemical compound in common; or (2)'if the compositions do contain at least one compound in common then there is at least a 10 weight percent difference, based on the total weight of the composition, between the amount of'the compound in the first cmposioin and the amount of the compound in the second composition. An x-ray fluorescent (XRF) ana Itical apparatus may be used to determine the quantities of compounds such as AbA and SiZh. For example, in a first embodiment, if the entire population of particles in the population of ceramic parties is made from auxte which has a first chemical composition that includes at least 30 weight percent Ah03 then the chemical compositions of the regions are not chemical distinct. Ina second embodiment if the particles in the first region are made from bauxite and the particles in the third region have a chemical composition that includes less than I weight percent A1 2 0 3 and at least >0 weight percent Si, then the compositions of the first and third regions are chemically distinct In the second emnbodinnen the particles in the third region may include sand in a third embodiment. if the particles in the first region are made from bauxite and thereby have 60 weight percent or more A103 while the particls in the third region are made 12 from clay that includes less than 50 weight percent Ah, then the compositions ofthe first and third regions are chemical distinct. With regard to the packing of proppant particles when they are inserted in a fissure in a geological formation the distribution of the proppant particles' diameters may impact the physical aragmeto the packed patileswich Could impactI the proppantis crush strength and conductivity. Consider, for example, a proppant pack that includes a mixture of three different size proppant particles havig average diameters of Dj, D2 and D 3 , respectively, wherein the smalest diameter particles have an average diameter equal to D, the medium diameter particles have an average diameter equal to D2 and the largest particles have an average diameter equal to D. Within the pack, the largest diameter particles may frequently abut one another thereby fonninga an essentially continuous matrix that defines numerous passageways there between. The medium size particles and smallest size particles may be selected to ready fil the passageways between the largest parices Because the largest diameter particles fnrm a matrix through the pack the cush resistance of the largest particles essentially determines the crush resistance of the proppant pack. Within the same pack, the smallest and medium diameter particles may have little impact on the proppant packs crush resistance because they fit within the voids created by the matrix but, ati same time, the small and medium size particles may reduce the conductivity of the proppait pack by filling the voids between the large particles thereby blocking the passageways through wvhichafluid could flow. I contrast, a distribution of proppant particles may be selected so that the smallest and/or medium diameter particles are too large to i within thevoids created by the large parties thereby forcing many of larger particles away from oneanother and reducing the nmnber of contact points between the large particles. This disruption to the packing patten of the large particles may be faciltated by selecting a population of particles wherein the ratio of the parties dd exceeds 0.2 Populations of particles that have a d:dratio greater than 0.30 or even 0.35are thasible. Populations of particles that have a d 5 :d 5 ratio greater than 022 may be advantageous for two reasons First, the disrupted packing pauern ray create many more points of contact between the largest particles and the smaller particles ihereby distributing the tOree applied to the pack over a broader area which results m improved resistance to crushing Second, the passageways defined by the largest particles are forced open by the medium and smallest diameter particles thereby 13 facilitating the flow of a fluid through the proppant pack, In certain embodiments, a proppant of this invention may contain a unique distribution of particle sizes that collectively provide resistance to crushing, resistance to settling during the fracturing process and cond uctiityoffluidtough the proppant These desirable performance characteristics are believed to be due at least in part to the particles' ability to pack in a disrupted packing pattern. EXAMPLES To illustrate an embodiment of a population ot ceramic particles of this invention, the inventors manflctured a population of proppants as follows. The starting raw materials included: 400 kg of Arkansas bauxite, which had been previously ground to an average particle size of about 10 mncrons; 7 kg of a commercially available corn starch binder; and 113 kg .250 lbs) of water added to a rotating Eirich mixer which is a well known agglomerator. The raw materials filled the chamber of the mixer approximately tio-thirds full. Rotation of the table and impeller were continued for approximately 1.5 minutes until particles of a suitable Size were formed. Approximately 100 kg of additional bauXite was slowly added thereby coating the previously formed particles with a layer of materiaL Rotation of the table and impeller were continued for approximately 4 minutes thereby resulting in the formation of spherical particles which may be referred to herein as greenware. The particles were then dried in a dryer at 2009C until the moisture content of the particles was less than 10% To achieve the desired density and strength, the dried parties were then heated to I 400"C for approximately one hour. The resulting particles had a splericity of about 0.9, as determined using the Krumbein and Sloss chart. The entire population of particles exiting the drying oven but prior to flowing through the turnace is defined herein as the parent populaton of parties. After heat treatment in a furnace at 1400*C, the parent populatio-n particles was screened by directing the particles to flow through a first commercial screening device which contained, i ar arrangement, a 14 mesh screen and thena 50 mesh screen. The first scening device removed particles that either (a) did not flow through the 14 mesh screen or (bj did flow the 50 mesh screen, thereby leaving a population of proppaits that were small enough to flow through a 14 mesh screen and too large to flow through a 50 mesh 14 screen. This population of particles isdefined herein as the initial population of particles and is designated Lot I in Table 1 Lot I was made to flow through a second screening process which included a commercial screening device that contained a 20 mesh screen and a5 mesh screen. The second screening device diverted and captured the particles into three separate portions. Portion A contained particles that had flowed through the 14 mesh screen in the first screening device bt were too large to flow through the 20 mesh screen. The particles in portion B were small enough to flow through the 20 mesh screen and too large to flow through the 35 mesh screen and are designated Lot 2 in Table 1. The particles in portion Cwere small enough to flow through the 35 mesh screen but too large to flow through the 50 mesh screen in the first screening device, *he particles in portion A and portion C w recombined thereby ceeating the final poppant population which is designated Lot 3 in Table 1. The particles in portion B were permanently separated from the finalproppant population. Shown below in Table I are the pertnew charcteristics of each proppant, All numerical values, except for percentages are in microns. Table I L Amount ' Width Sie % Region A -J _ ....... "' 1 4401 0 710 2 513 3 4 . 3 398 57% 80 1267 | 869 240 276 17.2 3.18 69 t EffectiveX Width is the difference between the distribution s doand ds. 2 Gap Size is the width ot the second region which is the difference between the distribution's de and de Gap % is the Gap Size divided by the E lkctiv W)idt. Amoum is the weight ot particles in each region divided by the weight of particles in the final population The daia clearly demonstrates that the population ofparticles of this invention, as represented by Lot 3n met the following criteria. First the populationswetivewdth exceeded 100 microns. Second, the width of the second region (i e. the Gap %) was at least 25% of the Effective Width Third the weightpercent of particles in the second region was less than 15% of the final population weight. Fou the weight percent of 15 particles in the first region and the third region each exceeded the weight percent of parties in the second region. To illustrate the advantage obtained by embodiment of a proppant of this invention, the crush resistance of the initial population, final population and proppant in region i were measured at pressures of 68.9 MIPa (10,000 psi 1034 MPa (15000 psi) and 137.9 MPa (20>000 psi) using the procedure described in ISO 13503-. Each of the crush resistance values in Table 2 represents an average ofthree samples, The crush resistance values are expressed as a weight percent of the samples starting weight The lower the number. the better the resistance to crushing. Table 2 Crush Resistance (weight percent) Lots 68.9 MPa 103,4 MIPa 13.9 MPa 5 (initial) .3 12.5 15 6 2(region II) 9.9 20.8 28 3(inai}. 0 12. 160 ( The data in abe 2 demonstrates that for an ermbodmennt of a proppant of this inention the final proppant population (i e Lot 3) had a cmsh resistance "uhic is both (a) approximately equivalnt to the crush resistance of thu initial proppant population (i.e. Lot 1) and (b) lower and thurefore better than the crush ruistance of the proppant in region ii (ime Lot 2) which were removed and available as a separate product in sharp contrast to conventional proppat manufacturing processes wherein onlythe proppants in region I were commercially valuable and the proppants in regions I and I were recycled, the proppants in regions I and Hl of this inventionrwere combined to create a final proppant with a crush resistance better than the proppants in region IL The abil H ito avoid the costs inherent in recycling large percentages of the initial proppant population may provide a dsn economic advantage to the proppant manufacurer The above deserption is considered that of panicular embodiments only. Modifications of the invemtion will occur to those skiIled in the art and to those who make or use the invention, Thereforeit understood that the embodiments shown in the drawings and described above are merely Or illustrative purposes and are not intended to limit the scope of the invention, which is deined by the flloigclaims as interpreted according to the principles of patent law including the Doctrine of Equivalents.
A reference herein to a patent document or other matter which is given as prior art is not taken as an admission that that document or prior art was part of common general knowledge at the priority date of any of the claims. With reference to the use of the words) "comprise" or "comprises" or "comprising" in the foregoing description and/or in the following claims, unless the context requires otherwise, those words are used on the basis and clear understanding that they are to be interpreted inclusively, rather than exclusively, and that each of those words is to be so interpreted in construing the foregoing description and/or the following claims.