HK1030228B - Composite particle, preparing method thereof, method for treating fracture and method for water filtration - Google Patents

Description

Composite particle, preparation method thereof, crack treatment method and method for filtering water

Technical Field

The present invention relates to composite media used in filtration and composite proppants used in oil and gas production to "prop/prop" hydraulic fractures near a wellbore. The proppant keeps the hydraulic fractures open for oil and/or gas to flow in and can greatly improve the yield per well. More specifically, the present invention relates to composite proppants, as well as composite filter media, comprised of suitable fillers bonded together with organic and/or inorganic three-dimensional crosslinkers/binders. In addition, the invention also relates to a preparation method and application of the filter medium and the proppant.

Background

In general, proppants are extremely useful in order to keep open fractures created by hydraulic fracturing of a subterranean formation, such as a subterranean oil or gas formation. Often, cracks in the subterranean formation are desirable in order to increase oil or gas production. Fracturing is caused by injection of a viscous fracturing fluid or foam into the well under high pressure to form the fracture. When a fracture is formed, a particulate material, referred to as "proppant", is placed into the formation to maintain the fracture in a propped condition when the injection pressure is released. After the fracture is formed, when the pressure is released, the proppant forms a filler that props the fracture open. The proppant is introduced into the well by suspending it in a secondary liquid or foam to facilitate the filling of the fracture with the proppant slurry used in the liquid or foam. The purpose of using proppants is: oil and/or gas production is increased by providing open channels in the formation. In addition, the selection of proppant is also critical to the success of stimulation.

Thus, propped fractures provide highly conductive pathways in the formation. The extent of the stimulation provided by the hydraulic fracturing treatment depends primarily on: formation parameters, permeability of the fracture, and propped width of the fracture. If the proppant is an uncoated material, such as sand, and is subjected to the high stresses present in the gas/oil well, the material may fracture, forming debris that fractures the proppant. Subsequently, the debris will reduce the conductivity within the proppant pack. However, the resin coating will provide enhanced burst resistance of the coated particles over that of the proppant alone.

Glass beads have been used as support materials (see US4,068,718, which is incorporated herein by reference as prior art). The disadvantages include: the energy and production costs as previously described, and the severe reduction in permeability at high pressures (above about 35 MPa) due to excessive fragmentation under downhole conditions. Therefore, glass beads are currently not favored.

Three different support materials, proppants, are currently used.

The first type of proppant is sintered ceramic particles, typically alumina, silica or bauxite, often containing clay-like binders or doped with hard materials such as silicon carbide (see U.S. Pat. No. 8, 4,977,116; EP0087852, 0102761 or 0207668 to Rumpf et al, which are incorporated herein by reference). Ceramic particles have the following disadvantages: sintering must be carried out at high temperatures, which results in high energy costs. In addition, expensive raw materials will be used. They have a rather high bulk density and often have properties similar to those of carborundum abrasive materials, which cause great wear on the pumps and lines used to introduce them into the borehole.

The second type of proppant is made of a large number of known support materials (natural, relatively coarse sand) whose particles are approximately spherical and therefore they can produce significant flow (english "frac sand") (see prior art US5,188,175).

The third proppant comprises: the first and second samples may be coated with a layer of synthetic resin (U.S. Pat. No. 5,420,174 to Deprawshad et al; U.S. Pat. No. 5,218,038 to Johnson et al and U.S. Pat. No. 5,639,806 to Johnson et al (the disclosures of these three patents are incorporated herein by reference); EP 0542397).

Known resins used in resin-coated proppants include: epoxy resins, furan resins, phenolic resins, and mixtures of these resins. The resin comprises about 1-8 wt% of the total weight of the coated particle. The particulate material for the resin-coated proppant may be sand, ceramic, or other particles and have a particle size in the range of about 8-100 mesh number in the USA standard test (i.e., about 0.0937 inches to about 0.0059 inch mesh).

There are two types of resin-coated proppants: precured and curable. The pre-cured resin coated proppant comprises: coated with a substrate that has been significantly cross-linked with a resin. The resin coating of the pre-cured proppant will provide burst resistance to the substrate. Because the resin coating is cured prior to introduction into the well, the proppant does not aggregate even under high pressure and temperature conditions. The pre-cured resin coated proppant is typically fixed in the well by stresses around it. In some instances of hydraulic fracturing, the pre-cured proppant in the well may flow back through the fracture, particularly during cleanup or production of oil and gas wells. Some proppants will migrate fluids produced through the well out of the fracture zone and into the wellbore. This migration is called reflow.

Flowback of proppant from the fracture is undesirable and has been controlled to some extent in some instances by the use of proppants coated with curable resins that will consolidate and cure in the subsurface. Phenolic resin coated proppants have been sold for some time and used for such purposes. Thus, the resin-coated curable proppant may be used to "cover" the fracture, thereby preventing the noted flowback. The resin coating of the curable proppant does not significantly crosslink or cure prior to injection into the oil or gas well. More specifically, the coating is designed to crosslink under the stress and temperature conditions present in the well formation. This will bond the proppant particles together, forming a three-dimensional matrix and preventing the flowback of the proppant.

These curable phenolic resin coated proppants are best used in temperature environments up to the point where they can consolidate and cure the phenolic resin. However, the state of geological formations varies widely. In some gas/oil wells, high temperatures (< 82.2 ℃) and high pressures (< 6,000psi) exist downhole. Under these conditions, effective curing of most curable proppants will occur. In addition, the proppants used in these wells must be thermally and physically stable, i.e., not significantly fracture under these temperature and pressure conditions.

The curable resin includes: (I) a resin that is fully cured in the subterranean formation and (II) a resin that is partially cured prior to injection into the subterranean formation, with the remainder being cured in the subterranean formation.

The downhole temperature of many shallow wells is often below 54.4 c and even below 37.8 c. At these temperatures, conventional curable proppants will not cure properly. Sometimes, activators may be used to promote curing at low temperatures. The other method is as follows: in the post-flush process, the proppant is subjected to low temperature catalytic curing using an acidic catalyst. Such curable proppant systems are disclosed in U.S. Pat. No. 4,785,884 to Armbraster, which is incorporated herein by reference in its entirety. In the post-flush process, after the curable proppant is loaded into the fracture, an acidic catalyst system is pumped through the proppant pack and curing can be initiated even at temperatures as low as about 21.1 ℃. This will cause the proppant particles to bond.

Due to variations in the geological properties of different oil and gas wells, none of the proppants possess all the properties required to meet all the operating requirements under all conditions. The selection of pre-cured proppant or curable proppant, or both, is empirical and knowledge known to those of ordinary skill in the art.

In use, the proppant is suspended in the fracturing fluid. Thus, the interaction of the proppant and the fracturing fluid will significantly affect the stability of the liquid in which the proppant is suspended. The fracturing fluid needs to remain viscous and be able to bring the proppant into the fracture and deposit the proppant in the proper location for use. However, if the fracturing fluid loses its carrying capacity prematurely, proppant may be deposited in the fracture or in an inappropriate location in the well bore. This may require thorough cleaning of the wellbore and removal of the displaced proppant.

It is also important that the liquid separate (viscosity drop) at the appropriate time after the proppant is properly placed. After the proppant is placed in the fracture, the viscosity of the fluid will decrease due to the action of the demulsifier (viscosity-lowering agent) present in the fluid. This will cause the released, curable proppant particles to aggregate together, bringing the particles into intimate contact, thereby forming a solid proppant pack after curing. The absence of such contact would make the proppant pack very weak.

In addition to viscous liquids, foams may be used to bring the proppant to the fracture and deposit the proppant at the appropriate point of use. The foam is a stable foam that can suspend the proppant until it is placed in the fracture, where it will break. Other formulations besides foam or viscous liquids may be used to carry the proppant into the appropriate fracture.

Additionally, resin-coated particulate materials, such as sand, may be used in the wellbore for "sand control". In such applications, the cylindrical structure is filled with a proppant, such as a resin-coated particulate material, and inserted into the wellbore to act as a filter or screen to control or eliminate the flowback of sand, other proppants, or subterranean formation particulates. Typically, the cylindrical structure is: the net is made into a circular tube structure with an inner wall and an outer wall. The mesh has a mesh size sufficient to contain the resin-coated particulate material within the cylindrical structure and allow fluids in the formation to pass therethrough.

While useful proppants are known, it is beneficial to provide proppants that: the proppant has improved properties such as good flowback, good compressive strength, and good long term conductivity, i.e., permeability, at high closure stresses present in the formation. As described above, flowback involves retaining the proppant in the formation. Compressive strength relates to enabling the proppant to withstand forces in the formation. High conductivity directly affects the future production rate of the well. It would be particularly beneficial to provide such a proppant from a raw material that can be obtained and processed at relatively low and moderate cost, and to provide a method of producing such a proppant, with the result that the formed particles produce less wear in the equipment used to introduce the proppant into the borehole due to the low bulk density of the proppant and the smooth surface.

A separate field suggested for use is water filtration. In many industrial and non-industrial situations, it is desirable to be able to separate solids from a water stream. There are a number of filtration systems designed to meet these needs. Most of these systems use solid particles to form a filter plug through which a solids-containing water stream passes. The particles (filter media) retain the solids in the pores of the fill and allow water to pass through (at a lower solids content). The filter must be periodically back flushed to remove the captured solids so that the filtration process can continue. The filter medium should have the following characteristics:

high particle surface area so that there are many opportunities for solids to be captured.

As low a density as possible so that the weight required for filling the filter and the flow rate required for back flushing (process of expanding the volume of the filter charge) can be minimized.

Has acid/base/solvent resistance so that the integrity of the media is not affected by the presence of these materials.

Is non-toxic so that undesirable chemicals do not penetrate into the filtered water stream.

Can be made in a variety of sizes (20/40, 16/30, etc.) and densities so that the filter plug can be designed to separate a variety of particles.

Examples of filter media currently used are sand, ceramic, activated carbon, and walnut shells.

Disclosure of Invention

It is an object of the present invention to provide proppants comprising a finely divided mineral filler or a filler of finely divided mineral and fibers bound by a binder.

It is another object of the present invention to provide a filter medium for separating solids from an aqueous stream, said filter medium comprising a finely divided mineral filler or a filler of finely divided mineral and fibers bound with a polymer.

It is a further object of the present invention to provide a method of using a proppant or filter media comprising a finely divided mineral or a filler of finely divided mineral and a filler of fibers bound with a polymer.

These and other objects of the present invention will be apparent from the detailed description below.

Drawings

The drawings that accompany the present invention can be briefly described as follows, wherein like elements are denoted by like reference numerals.

FIG. 1 shows a flow diagram of a first embodiment of the process for the preparation of particles according to the invention.

Figure 2 shows a flow diagram of a second embodiment of the process for the preparation of the particles according to the invention.

Figure 3 shows a flow diagram of a third embodiment of the process for the preparation of particles according to the invention.

Figure 4 shows a flow diagram of the improved method of figure 3 including particle recycling.

Fig. 5 shows a first embodiment of proppant particles or filter media particles of the present invention.

Fig. 6 shows a second embodiment of proppant particles or filter media particles of the present invention.

Detailed Description

The present invention provides a composite particle for use in a proppant or filter media comprising filler particles, such as a finely divided mineral or a finely divided mineral and fibers, bound with a suitable organic or inorganic binder. One typical organic binder is a resole or novolac resin. Typical inorganic binders include: silicates, such as sodium silicate, phosphates, such as polyphosphate glass, borates, or mixtures thereof, such as a mixture of silicates and phosphates.

The filler particles can be any of a variety of commercially available finely divided minerals or finely divided minerals and short fibers. The finely divided mineral comprises at least one material selected from the group consisting of: silica (quartz sand), alumina, mica, metasilicate, calcium silicate, burnt lime, kaolin, talc, zirconia, borax, and glass. The fibers comprise at least one material selected from the group consisting of: milled glass fibers, milled ceramic fibers, milled carbon fibers, and synthetic fibers having a softening point above about 93 ℃ so as not to degrade, soften, or agglomerate during manufacture and use.

The composite particles of the present invention are substantially spherical. The sphericity of the composite particles is at least 0.7, preferably at least 0.85, most preferably at least 0.9, when measured according to API Method RP56, chapter 5 (API Method RP56Section 5).

The composite particles are prepared by mixing filler particles selected from at least one of finely divided minerals and optionally suitable short fibers with at least one binder. In particular, the composite particles are prepared by mixing filler particles with a first portion of a binder, thereby forming a particle core comprising a substantially uniform particulate product of the filler particles and the first portion of the binder. By "substantially uniform" is meant that the particle core is generally free of large substrate particles, such as particles of proppant used to coat sand. To reinforce the composite particle, a second portion of the binder may be applied to the particle core of the particulate product. The core binder, i.e. the first part of the binder, is preferably pre-cured. The overcoat resin, i.e. the second part of the binder, is curable or pre-cured.

For the purposes of this application, the terms "cured" and "crosslinked" are used interchangeably for the hardening that occurs in an organic binder. However, the term "curing" is also meant in its broader sense and generally includes the hardening of any organic or inorganic binder in order to form a stable material. For example, the final hardened form of the bonding material, which is formed by crosslinking, ionic bonding, and/or solvent removal, may be considered to be curing. Thus, removal of only the solvent from the organic binder prior to crosslinking will allow curing to occur, depending on whether the dried organic binder is in the final cured form.

The uncoated composite particles or coated proppant particles may optionally be dried, but not cured (e.g., crosslinked), and then the surface mechanically refined to be smooth and thus substantially spherical.

The composite particles described in the present invention have unique properties such as controllable plasticity and elasticity. Because of these unique properties, the composite particles can be used as the sole proppant in the form of 100% proppant pack (in fracking), or as a partial replacement for existing commercially available ceramic and/or sand-based proppants (resin coated and/or uncoated), or as a blend between these proppants. In addition, the composite particles can also be used as the sole filter medium in the form of 100% filter filler, or blended with other filter media.

The composite particles of the present invention used as proppants improve the backflow control of the pack when used, and will reduce the formation and generation of fines when used in composite packs that fill cracks at 100% or are combined with other commercially available proppants. When used, the composite particles will also greatly reduce the deleterious effects of potting, and the subsequent generation of debris (due to the potting effect) that is typically associated with the use of commercially available proppants. The reduction in potting will contribute to the elasticity of the composite particles and their ability to better distribute downhole stresses. The combination of all these properties of the composite particles will result in an increase in the conductivity/permeability of the filler.

The selection of the particular volume ratios of finely divided mineral and synthetic binder described below results in a surprisingly good flexural strength, which is also a measure of the impact (stressed) strength and hardness (brinell strength) of the steel ball. This is a very important factor for the use of the present material as proppant. Generally, when quartz sand is used as the mineral, the flexural strength is higher than when alumina is used.

Proppants according to the present invention have a higher resistance to compaction than certain ceramic proppants, and therefore less particle breakage. This will reduce point stress and produce less debris than previously tested (debris will destroy the conductivity of the fracture) and will also produce the desired absolute burst strength. In particular, preferred sphericity φ is greater than 0.9, due to the use of suitable post-treatment measures.

In addition, the present invention provides improved methods of using the above-described particles as water filtration media or as curable and/or pre-cured proppants for treating subterranean formations.

Detailed Description

The filler particles of the present invention can be used with any conventional proppant resin. The type of resin and filler from which the proppant is made will depend on many factors, including the likely closure stress, the formation temperature, and the type of formation fluid.

The term "resin" includes a wide range of polymeric synthetic materials. Resins include thermoplastic materials and thermoset materials. As disclosed in US4,923,714 to Gibb et al, specific thermosetting resins include: epoxy resins, phenolic resins such as resole (a true thermosetting resin) or novolak (a thermoplastic resin rendered thermosetting by a curing agent), polyester resins, and epoxy-modified novolak resins, which are incorporated herein by reference. The phenolic resin comprises: any of a novolac polymer, a resole polymer, a mixture of a novolac polymer and a resole polymer, a cured mixture of a phenolic/furan resin or a furan resin forming a pre-cured resin (as disclosed in U.S. Pat. No. 4,694,905 to Armbruster, incorporated herein by reference); or a curable furan resin/phenolic resin system which is curable in the presence of a strong acid to form a curable resin (e.g. US4,785,884 to Armbruster). The phenol in the above-described novolak or resole polymers may be a phenol moiety or a bisphenol moiety. Resol resins are preferred. Specific thermoplastic resins include: polyethylene, acrylonitrile-butadiene-styrene, polystyrene, polyvinyl chloride, fluoroplastics, polysulfides, polypropylene, styrene acrylonitrile, nylon, and phenylene oxide. Another typical type of resin is latex.

A.Filler particles

The filler particles should be inert to the components in the formation, such as the well treatment fluid, and be able to withstand the conditions in the well, such as temperature and pressure. Such filler particles may be used together, for example finely divided minerals of different sizes and/or materials or mixtures of finely divided minerals and fibres. The filler particles are preferably monocrystalline in order to be more wear resistant and thus enable the composite particles to undergo pneumatic transport. It is important that the size and amount of filler particles, as well as the type and amount of resin, be selected so that the filler particles remain within the resin of the proppant, rather than being loosely mixed with the proppant particles. The intermingled filler particles will prevent the loose particles from plugging the components, such as the screens of an oil or gas well. Furthermore, cementing will prevent loose particles from reducing permeability in an oil or gas well.

1.Finely divided minerals

The finely divided mineral comprises at least one material selected from the group consisting of: silica (quartz sand), alumina, mica, metasilicate, calcium silicate, burnt lime, kaolin, talc, zirconia, borax, and glass. Particularly preferred is microcrystalline silicon dioxide.

The finely divided mineral particles have a particle size of from about 2 to about 60 microns. D of the mineral particles₅₀Typically from about 4 to about 45 microns, preferably from about 4 to about 6 microns. Parameter d₅₀Is defined as: 50% by weight of the particles have a specific particle diameter. To minimize sharp edges in the shaped particle matrix, the preferred filler should be round, rather than angular or nearly angular. An example of such a preferred material is IMSIL microcrystalline silicon dioxide available from Unimim Specialty Minerals (Elco, Illinois).

The IMSIL microcrystalline silica filler is produced from an inert, naturally occurring alpha-quartz in the form of grapes. Such fillers may be wet and dispersed in solvent or water based systems. Table A lists the properties of the filler.

Fly ash, which typically contains 40-60 wt.% silica and 20-40 wt.% alumina, can also be used as a mineral for certain conditions in order to save material costs. The typical particle size (d) of such materials₅₀) Up to 35 microns and therefore still requires grinding to the preferred value of 4-6 microns. Fly ash should have a minimum content of carbon, the presence of which will weaken the proppant particles.

2.Fiber

The fibers may be any of the commercially available staple fibers. The fibers comprise at least one substance selected from the group consisting of: milled glass fibers, milled ceramic fibers, milled carbon fibers, natural fibers, and synthetic fibers, such as crosslinked novolac fibers, have a softening point above the usual starting temperature for mixing with the resin, such as at least about 93 ℃, so as not to degrade, soften, or aggregate.

Common glasses for fibers include: e-glass, S-glass and AR-glass. E-glass is a commercially available glass fiber commonly used in electrical applications. S-glass is used because of its strength. AR-glass is used because of its alkali resistance. The carbon fibers are graphitic carbon. The ceramic fibers are typically alumina, porcelain, or other glassy material.

The fiber length is from about 6 microns to about 3200 microns (about 1/8 inches). Preferred fiber lengths are from about 10 microns to about 1600 microns. More preferably, the fiber length is from about 10 microns to about 800 microns. Typical fiber lengths range from about 0.001 to about 1/16 inches. Preferably, the fiber length is shorter than the longest length of the substrate. Suitable commercially available fibers include: milled glass fibers having a length of from 0.1 to about 1/32 inches; 25 micron long milled ceramic fibers; 250-; and KEVLAR aramid fiber 12 microns long. The fiber diameter (or, for fibers of non-circular cross-section, assuming a size equal to the diameter of a hypothetical circle having the same cross-sectional area as the fiber) is from about 1 to about 20 microns. The aspect ratio (aspect ratio) may be from about 5 to about 175. The fibers may be circular, elliptical, square, rectangular, or other suitably shaped cross-sections. A rectangular cross-section fiber source may be shredded sheets having a length and a rectangular cross-section. The rectangular cross-section has a pair of shorter sides and a pair of relatively longer sides. The ratio of the length of the shorter side to the longer side is typically about 1: 2-10. The fibers may be straight, crimped, or a combination thereof.

B.Resin composition

1.Resol phenolic resin

The mole ratio of phenol-aldehyde in the resole resin is from about 1: 1 to about 1: 3, typically from about 1: 1 to about 1: 1.95. The preferred method of preparation of the resol resin is: phenol is mixed with an aldehyde source, such as formaldehyde, acetaldehyde, furfural, benzaldehyde, or paraformaldehyde, in the presence of a basic catalyst. In such reactions, the aldehyde is present in an excess molar amount. Preferably, the mole ratio of phenol to formaldehyde in the resole resin is from about 1: 1.1 to 1: 1.6. The resole may be a conventional resole or a modified resole. Modified resole resins are disclosed in US5,218,038, which is incorporated herein by reference in its entirety. The modified resol resin is prepared by the reaction of an aldehyde with a mixture of an unsubstituted phenol and at least one phenolic selected from the group consisting of arylphenols, alkylphenols, alkoxyphenols, and aryloxyphenols.

The modified resole resin comprises an alkoxy-modified resole resin. Among the alkoxy-modified resol resins, methoxy-modified resol resins are preferred. However, the most preferred resole resins are modified ortho-benzyl ether containing resoles prepared by the reaction of phenol with an aldehyde in the presence of an aliphatic hydroxyl compound containing two or more hydroxyl groups per molecule. In a preferred modification of the process, the reaction can also be carried out in the presence of a monohydric alcohol.

Metal ion catalysts for producing modified resole resins include: salts of divalent ions of Mn, Zn, Cd, Mg, Co, Ni, Fe, Pb, Ca and Ba. Formula Ti (OR)₄Also useful as catalysts for this reaction are tetravalent alkoxy titanium compounds of formula (I) wherein R is an alkyl group containing from 3 to 8 carbon atoms. A preferred catalyst is zinc acetate. These catalysts will give resols in which the bridging predominant portion linking the phenolic nucleus is of the formula-CH₂(OCH₂)_n-o-benzyl ether bridges, wherein n is a small positive integer.

2.Resins comprising novolak polymers

One embodiment of the present invention employs a resin comprising a novolac polymer. The novolac may be any novolac used with proppants. The novolak can be obtained by reacting a phenol compound with an aldehyde in a strongly acidic pH range. Suitable acidic catalysts include: strong mineral acids, such as sulfuric acid, phosphoric acid and hydrochloric acid, and organic acid catalysts, such as oxalic acid or p-toluenesulfonic acid. Another method for preparing the novolac is: the phenol is reacted with the aldehyde in the presence of a divalent inorganic salt such as zinc acetate, zinc borate, manganese salts, cobalt salts, and the like. For the direct production of novolacs having different proportions of ortho-or para-substituents on the phenol ring derived from the aldehyde, the choice of catalyst is important, for example zinc acetate favours ortho-substitution. Novolacs rich in ortho-substituents, i.e. high proportions of ortho-novolacs, are preferred due to their greater reactivity in further crosslinking of the polymer. Knop and Pilato inPhenolic resin(50-51 (1985, Springer-Verlag)) which is incorporated herein by reference. High ortho novolacs are defined as novolacs in which at least 60% of the total number of ortho and para substituents of the resin are ortho substituents, preferably at least 70% of the total number of substituents are ortho substituents.

The novolac polymer typically comprises: phenol and aldehyde in a molar ratio of from about 1: 0.85 to about 1: 0.4. Any suitable aldehyde may be used for this purpose. The aldehyde may be aqueous formaldehyde, paraformaldehyde, formaldehyde, acetaldehyde, furfural, benzaldehyde, or other aldehydes. Among them, formaldehyde is preferred.

The novolacs used in the present invention are generally solid, e.g., in the form of flakes, powders, and the like. The molecular weight is from about 500 to 10,000, preferably from 1,000-5,000, depending on the intended use of the novolac. In the present specification, the molecular weight of the novolak is in terms of weight average molecular weight. Particularly preferred is a high proportion of ortho-novolak resin.

The resin composition typically comprises at least 10 wt% of the novolac polymer, preferably at least 20 wt% of the novolac polymer, and most preferably from about 50 to about 70 wt% of the novolac polymer. The remainder of the resin composition may include: cross-linking agents, modifiers or other suitable ingredients.

The phenolic moiety of the novolac polymer is selected from a phenol of formula I or a bisphenol of formula II, respectively:

r and R¹Independently alkyl, aryl, aralkyl or H. In formula II, R and R¹The meta position is preferred for each hydroxyl group on each aromatic ring. Unless otherwise defined, alkyl is defined as alkyl of 1-6 carbon atoms, and aryl is defined as having 6 carbon atoms in its ring. In structure II, X is a linkage, sulfonyl, alkylene substituted or unsubstituted with halogen, cycloalkylene, or halocycloalkylene. Alkylene is a divalent organic radical of formula III:

when X is alkylene, R²And R³Independently selected from the group consisting of H, alkyl, aryl, aralkyl, haloalkyl, haloaryl and haloaralkyl. When X is a haloalkylene group one or more hydrogen atoms of the alkylene moiety of formula II are replaced by a halogen atom. Preferably halogen is fluorine or chlorine. Furthermore, the halogenated cycloalkylene group is preferably substituted on its cycloalkylene moiety by chlorine or fluorine.

A commonly used phenol of formula I is phenol itself.

Common bisphenols of formula II include: bisphenol A, bisphenol C, bisphenol E, bisphenol F, bisphenol S or bisphenol Z.

The present invention includes a novolak polymer comprising any of the phenols of formula I, the bisphenols of formula II, or a combination of one or more phenols of formula I and/or one or more bisphenols of formula II. The novolac polymer may also be prepared by addingEpoxy resins, bisphenols, waxes or other known resin additives. One method of preparing alkylphenol-modified novolak polymers is to combine the alkylphenol and phenol in a molar ratio of above 0.05: 1. This combination is a reaction with a source of formaldehyde in the presence of an acidic catalyst, or a divalent metal catalyst (e.g., Zn, Mn). During the reaction, the combination of alkylphenol and phenol is in molar excess with respect to the formaldehyde present. Under acidic conditions, the polymerization of hydroxymethylated phenols is a faster reaction than the hydroxymethylation from formaldehyde. Thus, the polymer structure is composed of phenolic and alkylphenol cores linked by methylene bridges and is substantially free of free hydroxymethyl groups therein. In the case of metal ion catalysis, the polymerization will form hydroxymethyl and benzyl ethers, which will subsequently decompose to methylene bridges, so that the final product is essentially free of hydroxymethyl groups.

C.Crosslinking agentAnd other additives

For practical purposes, the novolac resin does not cure upon heating, unless a curing agent (crosslinker) is present, it will remain soluble and fusible. Thus, when the novolac resin is cured, a cross-linking agent is used to overcome the defect of the alkylene bridge groups converting the resin into an insoluble infusible state.

Suitable crosslinking agents include: hexamethylenetetramine (HEXA), paraformaldehyde,Oxazoline, melamine resins or other aldehyde donors and/or the above-mentioned resol polymers. Each of these crosslinking agents may be used alone or in combination with other crosslinking agents. The resol polymer may comprise a substituted or unsubstituted phenol.

The resin composition of the present invention typically comprises about 25 wt.% of HEXA and/or up to 90 wt.% of resol polymer, based on the total weight of the coating composition. When HEXA is the sole crosslinking agent, HEXA comprises from about 5% to about 25% by weight of the resin. When the resol polymer is the only crosslinker, the resin comprises from about 20 wt.% to about 90 wt.% of the resol polymer. In addition, the composition may also comprise mixtures of these crosslinking agents.

The additives are used in specific applications for specific requirements. The resin system of the present invention may include a variety of additives. The resin may also include one or more other additives such as coupling agents, e.g., silanes to promote adhesion of the coating to the substrate, silicone lubricants, wetting agents, surfactants, dyes, flow modifiers (e.g., flow control agents and flow enhancers), and/or antistatic agents. The surfactant may be anionic, nonionic, cationic, amphoteric, or mixtures thereof. Certain surfactants may also be used as flow control agents. Other additives include moisture resistance additives or heat strength additives. Of course, these additives may be added in the form of a mixture or individually.

D.Preparation of resol resins

A common method of preparing resols is to charge phenol into a reactor, add a basic catalyst such as sodium or calcium hydroxide, and an aldehyde, such as a 50% by weight formaldehyde solution, and react the ingredients at elevated temperatures until free formaldehyde or the desired viscosity is achieved. The water content was adjusted by distillation. In addition, it is also possible to add an elastomer or plasticizer, such as bisphenol or cashew nut oil, to enhance the elasticity or plasticity of the binder. Other known additives may also be added.

E.Preparation method of novolac polymer

To prepare a novolak polymer containing one or more phenols of formula I, the phenol is mixed with an acidic catalyst and heated. Then, an aldehyde, such as a 50 wt% aqueous formaldehyde solution, is added to the hot phenol and catalyst at elevated temperatures. The water resulting from the reaction is removed by distillation to give a molten novolak. The molten novolac is then allowed to cool and pressed into flakes.

To prepare a novolak polymer from a bisphenol of formula II, the bisphenol is mixed with a solvent, such as n-butyl acetate, at elevated temperature. An acidic catalyst such as oxalic acid or methanesulfonic acid is then added and mixed with the bisphenol, followed by the addition of an aldehyde, typically formaldehyde. The reaction was then refluxed. It should be noted that the novolak resin can be prepared in the presence of an acidic catalyst or a divalent metal catalyst (e.g., Zn, Mn), wherein the bisphenol is present in an amount greater than the molar amount of the aldehyde source. After reflux, the water was collected by azeotropic distillation with n-butyl acetate. After removal of water and n-butyl acetate, the resin was flaked to give a resin product. Alternatively, water may be used as a solvent to prepare the polymer.

F.Reaction of aldehydes with novolaks or bisphenol-aldehyde varnishes

Novolacs or bisphenol-aldehyde novolacs can be modified by reacting these novolacs with additional amounts of aldehyde using an alkaline catalyst. The catalysts which are commonly used are: sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide (or lime), ammonium hydroxide, and amines.

In the case of phenol-aldehyde polymers or bisphenol-aldehyde polymers, the molar ratio of aldehyde to phenol moieties added, based on the monomer units of the phenol moieties in the novolak, is from 0.4: 1 to 3: 1, preferably from 0.8: 1 to 2: 1. This will result in a cross-linkable (living) polymer having a different chemical structure and generally a higher molecular weight than the resol polymer obtained by the one-shot process; wherein the one-step process comprises initially mixing the bisphenol monomer and the aldehyde with the basic catalyst in the same molar ratio of the combined aldehyde and bisphenol. Furthermore, different aldehydes may be used at different stages of polymer preparation.

These polymers may be used alone or together with other polymers such as phenol-aldehyde varnish, bisphenol-aldehyde varnish or mixtures thereof as crosslinking agents or as components of crosslinking agents. When aldehyde-modified polymers are used as the crosslinking agent, they may be used together with other commonly used crosslinking agents such as those described above for phenolic polymers.

G.Method for preparing proppant or filter medium

After the resin is prepared, the crosslinker, resin, and filler particles are mixed under conditions that provide the desired pre-cured or curable resin composition. Whether the resin composition is pre-cured or cured depends on a number of factors. The factors include: the ratio of novolac resin to curing agent; acidity of the novolac resin; the pH of the resole; the amount of cross-linking agent used; the mixing time of the resin composition and the filler particles; the temperature of the resin composition and the filler particles during mixing; the catalyst (if any) used during mixing, and other processing parameters known to those of ordinary skill in the art. Typically, the pre-cured or curable proppant may comprise a resole phenolic resin, with or without a novolac phenolic resin.

Figure 1 shows a simple flow diagram of a first embodiment of a method of making a proppant or filter media of the present invention. In this process, a binder stream 12 and a filler particle stream 14 are fed into a high intensity mixer 9 to produce a uniform slurry stream 5. Slurry stream 5 is fed to granulator 10 to produce granulated product stream 16. The binder stream 12 comprises resin, water and conventional additives. Typically, the resin is a resole resin and may act as its own cross-linking agent. Coupling agents are also commonly used additives. A commonly used pelletizer 10 is an Eirich R02 mixer (manufactured by Eirich Machines, inc., Gurnee, Illinois).

Typically, the granulator 10 is operated as a batch process and is operated according to the process generally described in EP308257 and us.re.34, 371, which are incorporated herein by reference. For example, EP308257 discloses the preparation of ceramic granules using an Eirich granulator described in US3,690,622. The pelletizer includes: a rotatable cylindrical vessel, a central shaft at an angle to the horizontal, one or more deflector plates, and at least one rotatable impact impeller mounted generally below the apex of the rotational path of the cylindrical vessel. A rotatable impact impeller feeds the material to be mixed (engage) and is able to rotate at a higher angular velocity than the rotating cylindrical vessel.

The following steps will be carried out in a mixing granulator (granulator 10): (1) nucleation or seeding upon addition of slurry near the impacting impeller; (2) growth of spheroids during which the impact impeller rotates at a lower rotational speed than during the nucleation step; and (3) polishing or smoothing the surface of the spherical body by turning off the impact impeller and rotating the cylindrical vessel.

The binder (resin) is typically used in an amount of from about 10% to about 30%, preferably from about 10% to about 25%, by weight of the total dry matter (resin, filler, etc.) added to the granulator 10. The amount of binder that is free of water is defined as the amount of resin, e.g. novolac and/or resole, other than water, and the amount of additives. Typically, the mixing is carried out in the presence of a coupling agent such as gamma/aminopropyltriethoxysilane. The coupling agent may be added to the mixer 9 first, or may be pre-mixed with the binder stream 12 and then added. Typically, 0-50% of the total binder stream 12 is water. At a rotation speed of 50-80 rpm and a chopping speed of 1400-1600 rpm, the mixing time is usually from 1-5 minutes. The granulation time (nucleation time) is from about 2 minutes to about 10 minutes using a vessel speed of 25-45 rpm and a chopping speed of 1400-1600 rpm. The smoothing action is also referred to as "shredding". The temperature of the granulator 10 during the above steps is between 10-40 ℃.

The prill stream 16 is then conveyed to a solidification apparatus 50. Typically, the solidification device 50 is a drying oven that operates at a residence time of the prill stream of from about 0.5 to about 2 hours and at a temperature of from about 90 ℃ to about 200 ℃, preferably from about 150 ℃ to about 190 ℃. This will produce a solidified granular product stream 52, which product stream 52 is sent to a screening device 80 to separate a proppant product stream 82 of a predetermined product size. The typical screening device 80 is a screen, such as a vibrating screen. Generally desired, d of the proppant particle₅₀Is from 0.4 to 0.8mm, or particle size is from 20 to 40 mesh (0.425 to 0.85mm) or 30 to 40 rpm.

Figure 2 illustrates a second embodiment of a method of making a proppant or filter media of the present invention. This embodiment is similar to the process of fig. 1, except that the prill stream 16 is delivered to a refining apparatus 15 in a dry, but uncured, manner to mechanically increase the sphericity of the prill to at least about 0.8, preferably at least about 0.85, more preferably at least about 0.9, and to produce a stream 17 of said mechanically treated material.

Said step consists in mechanically refining the surface of the granulated material so as to obtain an approximately spherical shape. For example, the mechanical refining step is generally carried out by: (1) the dried but uncured granules of figure 2 at 40 ℃ were placed in a granulation vessel at high inclination and high rotation speed for downhole processing; or (2) treating the particulate material in a SPHERONIZER apparatus (manufactured by Calvera Process Solutions Limited, Dorset, England) at 400-. The smoothing action is brought about by a cleaning process (grinding process) in which the particles in the shaped (profiled) rotating container are thrown against the cylinder wall and then rolled back onto the floor of the container.

In addition, the particles can be smoothed and compacted by tumbling before solidification.

Figure 3 shows a flow diagram of a third embodiment of a method of making a proppant or filter media of the present invention.

The process is similar to the process of fig. 2, except that the solidified granular product stream 52 is delivered to a coating device 60. Coating device 60 coats/impregnates the cured particulate material of stream 52 with additional resin from second binder stream 61. This will produce proppant particles having a resin and a filler core, wherein the core is coated with the resin. In particular, a solidified (or partially solidified) stream 52 of particle nuclei is discharged from the solidification apparatus 50 and then conveyed to the coating apparatus 60. The coating device 60 is typically a forming rotating drum or some form of batch mixer. The rotating drum means 60 rotates at a speed of 16-20 rpm. The second resin stream 61 is typically preheated to 50-60 ℃ and sprayed into the rotating drum device (containing the shaped particles) through an atomizing nozzle. The rotary drum device is operated in a batch process for about 5 to 20 minutes.

If Eirch mixer R02 is used as the coating device, it will operate under the following conditions: a vessel rotation speed of 20-40 rpm, preferably 30-35 rpm, a chopping speed of 700 rpm and 1100 rpm, preferably 800 rpm and 1000rpm, and a treatment time of 2-10 minutes, preferably 2-5 minutes.

The second binder stream 61 typically comprises a resin solution, water, and conventional resin additives. The dry weight ratio of binder stream 12 to second binder stream 61 is from about 70-60: 30-40. Second stream 61 and stream 52 are preferably conveyed to coating unit 60 to provide a weight ratio (on a water free basis) of second stream resin to uncoated proppant particles of about 1 to 10 parts resin: 95 parts of uncoated proppant particles. The resin in the first binder stream 12 may be the same as or different from the resin in the second binder stream 61. In addition, when a proppant having a curable resin in its core is desired, the drying oven 50 may only dry the coated proppant.

Preferably, stream 16 is added to a finishing unit (not shown), such as finishing unit 15 of fig. 2, prior to solidification/drying in unit 50.

The coated proppant is discharged from the coating apparatus 50 in the form of a coated proppant stream 62 and then conveyed to a curing apparatus 70.

The curing device 70 is typically: a chambered dryer (or may be a rotary dryer) that heats the proppant from about 20 ℃ to about 180 ℃ on a flat plate. Curing device 70 maintains the coated proppant at a suitable curing temperature, such as about 120 ℃ to about 180 ℃, for a suitable curing time, such as about 0.5 to about 2 hours or more. If a proppant with a curable coating is desired, the curing device 70 dries or partially cures the coating.

The solidified proppant is discharged from solidification device 70 in the form of a stream 72 of solidified proppant particles that are screened in screening device 80 to isolate a proppant product stream 82 of a predetermined particle size range. Typical predetermined particle sizes range from about 20 to about 40 mesh. The typical screening device 80 is a vibrating screen. Particles that exceed the predetermined size are discharged as stream 84.

Fig. 4 generally illustrates the method of fig. 3 with looping steps. Pellets are discharged from pelletizer 10 in stream 16 and conveyed to dryer 20. Dryer 20 is typically a chambered dryer that operates at about 30 c to 40 c for a sufficient time to remove moisture and dry the pellets without binding together. Typical drying times are about 0.5 to 2 hours. When the process of fig. 3 is utilized, a polishing step may also be employed on stream 16.

The dried granular stream 22 is then conveyed to a screen 30. The typical screen 30 is a vibrating screen. Screened particles of a predetermined size range are discharged in the form of screened stream 32. Particles having a particle size above the predetermined mesh range are discharged as a first recycle stream 34 which is passed to a crusher 40 and then recycled to the granulator 10. One typical predetermined core particle size is about 8-20 mesh. Another generally desirable size range is 20-40 mesh. Particles having a particle size less than the predetermined size are recycled to the granulator 10 as a second recycle stream 36.

Screened stream 32 is sent to curing unit 50. The curing apparatus 50 may be a chambered dryer that operates at a temperature of 120 c to 200 c, preferably from 150 c to 190 c, for a period of time to cure the material on a flat plate to produce the desired degree of cure. Typical curing times range from 0.5 to 2 hours. However, if the particles of the screened stream 32 have a sufficient degree of (or are not required to) solidification, this solidification step may be omitted and the particles merely dried.

A solidified (or partially solidified) stream 52 of proppant particles is discharged from the curing device 50 and conveyed to a coating device 60.

A general summary of the raw materials used in the process of figure 4 is shown in table 1.

The general operation of the method of fig. 4 is summarized as shown in table 2.

Alternatively, proppants can be prepared by modifying the above process by extruding pellets in an extruder and then mechanically pelletizing the pellets into round pellets (rather than pelletizing the pellets into round pellets in an Eirich mixer).

H.Proppant particles

Fig. 5 shows proppant particles 10 comprising filler particles 20, and resin 15.

Fig. 6 shows a coated proppant particle 110 having a core 112 of resin 15 and filler particles 24 coated with a second resin coating 25.

I.Parameters of the composite particles

The following parameters are useful when characterizing the composite proppant particles and composite filter media particles of the present invention.

The composite particles of the present invention generally have a lighter density than conventional sand. Preferably, the proppant particles have a bulk density of from 1.12 to 1.52g/cm³(70-95lbs/ft³). Their sphericity is greater than 0.7, preferably greater than 0.85, more preferably greater than 0.9. The volume percent of filler particles in the composite proppant is from 60 to 85%, preferably from about 60 to 75%, more preferably from about 65 to 75%. The weight percent of filler particles in the composite particles is from about 70% to about 90%. The weight percentage of filler particles in the core of the coated proppant particles is typically from about 80% to about 90%. D of the composite particles₅₀From about 0.4 to about 0.8 mm. For coated proppants, the dry weight ratio of the first portion of binder to the second portion of binder is 70-60: 30-40. The particle size of the composite particles is in the range of about 4 to about 100 mesh, based on the US standard series sieve, with a preferred particle size of 20/40 (0.425-0.85mm) based on API Method RP56Section 4.

Less than 4% of the fractured material of the pre-cured proppant at 4000psi closure stress was measured according to the following procedure, American Petroleum Institute Method RP56 procedure Section 8.

The dust amount was measured by API Method RP56Section 7 as turbidity.

Sphericity was measured by API Method 56Section 5.

The chemical inertness should be comparable to Jordan silica sand (20/40 mesh) in terms of resistance to hydrocarbon and sodium hydroxide solutions at pH 12. Acid resistance was measured by API Method RP56Section 6. Alkali resistance is measured as the tolerance to sodium hydroxide for 48 hours at pH12 and 93.3 ℃. The pH was maintained at 12 by the addition of sodium hydroxide if necessary. The performance and appearance of the proppant should not change when exposed to aliphatic or aromatic hydrocarbons at 93 ℃ for 96 hours. The hydrocarbons did not discolor during the test.

J.Use of composite particles

The composite particles described in the present invention have unique properties such as controllable plasticity and elasticity. Because of these unique properties, the composite particles can be used as the sole proppant in a 100% proppant pack (in a hydraulic fracture), or as a partial replacement for existing commercially available resin-coated and/or uncoated ceramic and/or sand-based proppants, or as a blend between these materials. The composite particles can also be used as the sole media in a 100% filter pack, or blended with other filter media.

When the method of the present invention is used with a pre-cured resin component, the proppant is placed into the formation without additional curing within the formation.

When the method uses a proppant having a pre-cured resin component, the method additionally includes curing the curable resin component by exposing the resin component to sufficient heat and pressure in the formation to crosslink the resin and cure the proppant. In some cases, activators may be used to promote curing of the curable proppant. In another embodiment of using a curable resin component on a proppant, the method further comprises: low temperature acid catalyzed curing at temperatures as low as 21.1 ℃. One example of low temperature acid catalyzed curing is disclosed in US4,785,884, which is incorporated herein by reference in its entirety.

Alternatively, the resin-containing particles may be used by filling the cylindrical structure with resin-containing particles, i.e., proppant, and inserting into the wellbore. Once placed, the improved performance of the present invention is beneficial because the proppant will solidify and act as a filter and screen to eliminate the flowback of sand, other proppants, or formation particulates. The elimination of backflow of particles into the surface equipment is a significant advantage.

The composite particles of the present invention are particularly advantageous due to their round shape. Whether the particles are used alone as proppants or in a multi-layer pack with other proppants, the rounded shape will increase their conductivity. By definition, the multilayer filling is not part of the single layer used in US3,659,651. In a partial monolayer, the particles in the well will contact the fracture walls, but not each other. In contrast, in a multilayer filler, the proppant fills the fracture and production is through the pores of the proppant.

Examples 1 to 12

The present invention will be explained in detail below using twelve compositions as exemplary embodiments, using the above-described process modifications of FIGS. 1-3. As mentioned above, the figures show:

FIG. 1: a first embodiment of the method of making the composite particles of the present invention.

FIG. 2: a second embodiment of the method of making composite particles of the present invention.

FIG. 3: a third embodiment of the method of making composite particles of the present invention.

Twelve compositions having the components listed in table 3 were prepared. The volume fraction refers to the final cured "composite proppant" and the weight refers to the composition prior to pelletizing. The silica content of the quartz sand (Q stands for quartz) is greater than 98.3%, the fineness of grinding d₅₀6 μm, density 2.63g/cm³. Al in alumina (represented by "A")₂O₃Content greater than 99%, fineness of grind d₅₀7.5um and a density of 3.96g/cm³. Liquid resol (denoted by "P") and viscous resol (denoted by "F") were used as synthetic resins, with water as the solvent. In the resol resins used in the process, the phenol: the ratio of formaldehyde is 1: 1.1 to 1: 1.9. The ratio is usually about 1: 1.2-1.5. In addition, the fineness D can also be used₅₀3-45 μm silica sand and other fillers.

Resol F was used in the same proportions as examples 1-6 to give the compositions of examples 7-12, respectively.

These compositions were first pressed at 53MPa into test strips of 5X 56mm and then placed in an oven at 160 to 240 ℃ and cured for 10 minutes. From a pelletizing capacity point of view, proppant pellets, typically having the highest flexural resistance, of a composition containing 65% by volume of minerals, with a particle size of from about 0.4 mm to about 0.8mm, (20/40 mesh), are preferably processed according to the process of fig. 1.

Examples 13 to 18

According to the process of fig. 2, the particles dried at 80 ℃, but not solidified, are subjected to a surface mechanical refining in order to smooth the surface and to make it approximately spherical. The mechanical refining step is carried out by: treating the granules in a granulation vessel at a high skew angle and a high rotational speed; or treating the particulate material in a SPHERONIZER apparatus at 400-. The smoothing action is brought about by a cleaning process (grinding process) in which the particles in the shaped (profiled) rotating container are thrown against the cylinder wall and then rolled back onto the floor of the container.

According to the process of fig. 3, the final cured particles were made with about 70 wt% of their final synthetic resin content and then surface coated with the remaining 30 wt% of the final synthetic resin content on a rotating disk.

The pellets, numbered in the order listed in Table 4, were produced and tested to determine the basic parameters, such as density, circularity and Brinell hardness.

The compositions of example 13, example 1 were prepared according to the method of figure 1.

The compositions of example 14, example 1 were prepared according to the process of figure 2, with subsequent smoothing in a speedizer apparatus.

The composition of example 15, example 1 was prepared according to the method of fig. 3, with a second cure in the oven.

The composition of example 16, example 1 was prepared according to the method of fig. 3, where the second cure was carried out in a rotary kiln.

The compositions of example 17, example 7 were prepared according to the method of figure 1.

The compositions of example 18, example 10 were prepared according to the method of figure 1.

Of these examples, example 15 was found to be particularly promising for the intended use and its features were discussed in detail. The following data in Table 5 are the effect of curing temperature on the flexural strength of the test piece of example 15 using a curing time of 30 minutes. They can also summarize other strength characteristics:

the samples of example 15 cured at 180 ℃ for 30 minutes can also be subjected to a fracture test according to the modified API RP56/60 as follows:

a) the crushing pool, 31mm in diameter, was filled with granules to a height of 10 mm.

b) The compression load was increased stepwise to about 100Mpa (14, 500psi) and the deformation of the particulate filler was recorded at two test temperatures, 20 c and 125 c.

The results are shown in Table 6:

the following values for tables 7 and 8 can also be measured for the same sample:

the acid solubility of example 15 was 4.4 wt% according to API RP 56/60.

Examples 19 to 21

Tables 9 and 10 show the recommended parameter values and actual parameter values for examples 19-21 made by the method of FIG. 3.

Table 11 shows conductivity and permeability data. Table 12 lists the test procedures for the properties listed for the proppants of the different examples.

While particular embodiments of the present compositions and methods have been shown and described, it will be understood that many modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims (39)

1. A composite particle comprising:

a substantially uniform shaped particle comprising:

a first portion of binder and filler particles distributed throughout said first portion of binder and optionally additives, wherein said first portion of binder is at least partially cured;

the filler particles have a particle size of from 0.5 to 60 microns, and the composite particles have a sphericity of at least 0.7; and

an optional second portion of binder and optional additives for coating the shaped particles;

60-85% by volume of said composite particles being said filler particles,

wherein the first part and the second part of the binder are each independently composed of at least one selected from the group consisting of: an inorganic binder, an epoxy resin, a novolac resin, and a resole resin, or each independently comprises one selected from the group consisting of: phenolic/furan resins, and mixtures thereof.

2. The composite particle according to claim 1, wherein the sphericity is at least 0.85.

3. The composite particle according to claim 1, wherein the sphericity is at least 0.9.

4. The composite particle according to claim 1, additionally comprising a substance selected from the group consisting of: milled glass fibers, milled ceramic fibers, milled carbon fibers, natural fibers, and synthetic fibers having a softening point of at least 200 ° F.

5. The composite particle of claim 1, wherein the composite particle has a bulk density of 70 to 95lbs/ft³。

6. The composite particles according to claim 1, additionally comprising an optional crosslinking agent.

7. The composite particle according to claim 1, wherein one or more substances selected from the group consisting of: hexamethylenetetramine, silanes to promote adhesion of the coating to the substrate, silicone lubricants, wetting agents and surfactants.

8. The composite particle according to claim 1, wherein the composite particle has a particle size of between 20 and 40 mesh and comprises a coating of a synthetic resin.

9. The composite particle according to claim 8, wherein the particle size of the composite particle is between 30 and 40 mesh.

10. The composite particle according to claim 1, wherein the composite particle has a particle size between 8 and 20 mesh and comprises a coating of a synthetic resin.

11. The composite particles according to claim 1, wherein the filler particles are finely divided minerals.

12. The composite particle according to claim 1, wherein the filler particle is present in an amount of 60% to 75% by volume of the composite particle.

13. The composite particle according to claim 1, wherein the filler particle is present in an amount of 65% to 75% by volume of the composite particle.

14. The composite particle according to claim 1, wherein the first portion of the binder comprises: resol modified with gamma-aminopropyltriethoxysilane, wherein the silane acts as a coupling agent between the filler and the resol.

15. The composite particles according to claim 1, wherein the first portion of the binder comprises a resole phenolic resin having a molar ratio of phenol to formaldehyde of from 1: 1.1 to 1: 1.95.

16. The composite particles according to claim 15, wherein the first portion of the binder comprises a resole phenolic resin having a molar ratio of phenol to formaldehyde in the range of from 1: 1.2 to 1: 1.6.

17. The composite particle according to claim 1, wherein the first portion of the binder is a cured binder.

18. The composite particle according to claim 17, wherein the first portion of the binder is a cured binder and the second portion of the binder is a curable binder.

19. The composite particle according to claim 1, wherein the filler particles are at least one mineral selected from the group consisting of: silica, alumina, mica, metasilicate, calcium silicate, burnt lime, kaolin, talc, zirconia, borax, and glass.

20. The composite particles according to claim 1, wherein the filler particles are at least one mineral selected from the group consisting of quartz sand and alumina.

21. The composite particle according to claim 1, wherein the filler particles comprise fly ash.

22. The composite particles according to claim 1, wherein the filler particles have a particle size d₅₀Is a mineral of 4-10 μm.

23. The composite particle according to claim 22, wherein the filler particles are of particle size d₅₀Is a mineral of 4-6 μm.

24. The composite particle according to claim 1, wherein the filler particles are mineral and are present in an amount of 70% to 90% by weight of the composite particle.

25. A method of preparing composite particles according to claim 1, comprising mixing filler particles, a first portion of binder, at least one member selected from the group consisting of water and organic solvents, and optionally additives, to form a mixture and adjusting the plasticity of the mixture; granulating the mixture in a plastic state to form shaped granules; and curing a first portion of the binder of the shaped particles, wherein after curing the first portion of the binder, the shaped particles are optionally coated with a second portion of the binder and then cured; or drying off the solvent after granulation, optionally coating the shaped particles with a second portion of binder after drying but before the first portion of binder is cured.

26. A method according to claim 25, wherein the shaped particles are smoothed and compressed by tumbling before the first portion of the binder cures.

27. Use of the composite particles of claim 1 for the treatment of a hydraulically induced fracture in a formation surrounding a wellbore, comprising introducing the composite particles of claim 1 into the fracture.

28. The use according to claim 27, wherein a multilayer filler comprising said composite particles is formed in a subterranean formation.

29. Use according to claim 27, wherein the first portion of the binder consists essentially of a resol resin.

30. The use according to claim 27, further comprising introducing into the fracture at least one particle selected from the group consisting of: sand, sintered ceramic particles, and glass beads.

31. Use according to claim 30, wherein the sand grains comprise resin-coated sand grains.

32. Use according to claim 27, wherein the composite particles have a sphericity of at least 0.85.

33. Use according to claim 27, wherein the composite particles have a particle size between 20 and 40 mesh and comprise a coating of synthetic resin.

34. A method according to claim 27, wherein the composite particles have a particle size of between 8 and 20 mesh and comprise a coating of synthetic resin.

35. Use according to claim 27, wherein the filler particles are finely divided minerals.

36. Use according to claim 27, wherein the proportion by volume of the filler particulate material is from 65% to 75% of the volume of the composite particle.

37. Use according to claim 27, wherein the filler particles comprise fly ash.

38. Use according to claim 27, wherein the filler particles are minerals having a particle size d₅₀Is 4-10 microns.

39. A method of filtering water comprising passing the water through a filter pack comprising the composite particles of claim 1.