CA2198812C - Proppants with fiber reinforced resin coatings - Google Patents

Abstract

Coated particles made of particulate substrates having a coating of resin and fibrous material are provided for use in subterranean formations. The coated substrate particles are proppants useful to prop open subterranean formation fractures. The coated substrate particles are also useful for sand control, that is, acting as a filter or screen to prevent backwards flow of sand, other proppants or subterranean formation particles. Methods of making the coated particles are also disclosed.

Description

PROPPANTS WITH FIBER REINFORCED RESIN COATINGS
Background of the Invention 1. Field of the Invention The present invention is directed to particulate substrates coated with a resin comprising phenolic-aldehyde polymer or other suitable polymer. Depending upon the resin selected, the substrate selected and how the resin is combined with the substrate, the resulting resin coated particle is useful in either subterranean formations as a curable proppant or a precured proppant. The present invention also relates to methods of making or using the resins or coated substrates.

2. Description of Background Art The use of phenolic resin coated proppants is disclosed by U.S. Patent No.
5,218,038 to Johnson et al. In general, proppants are extremely useful to keep open fractures imposed by hydraulic fracturing upon a subterranean formation, e.g., an oil or gas bearing strata.
Typically, the fracturing is desired in the subterranean formation to increase oil or gas production. Fracturing is caused by injecting a viscous fracturing fluid or a foam at high pressure into the well to form fractures. As the fracture is formed, a particulate material, referred to as a "propping agent" or "proppant" is placed in the formation to maintain the fracture in a propped condition when the injection pressure is released. As the fracture forms, the proppants are carried into the well by suspending them in additional fluid or foam to fill the fracture with a slurry of proppant in the fluid or foam. Upon release of the pressure, the proppants form a pack which serves to hold open the fractures. The goal of using proppants is to increase production of oil and/or gas by providing a highly conductive channel in the formation. Choosing a proppant is critical to the success of well stimulation.

'Ihe propped fracture thus provides a highly conductive channel in the formation_ The de~ee of stimulation afforded by the hydraulic fracture treatment is largely dependent upon formation parameters, the fracture's permeability and the fracture's propped width. If the proppant is an uncoated substrate and is subjected to high stresses existing in a gas/oil well, the substrate may be crushed to produce fines of crushed proppant. Fines will subsequently reduce conductivity within the proppant pack. However, a resin coating will enhance crush resistance of a coated particle above that of the substrate alone.
Known resins used in resin coated proppants include epo.~cy, loran, phenolic resins and combinations of these resins. The resins are from about 1 to about 8 percent by weight of the total coated particle. The particulate substrate may be sand, ceramics, or~other particulate substrate and has a particle size in the range of USA Standard Testing screen numbers from about 8 to about 100 (i.e. saeen opening$ of about 0.0937 inch to about 0.0059 inch).
Resin coated proppants come in two types: precur~ed and curable. Precured resin coated proppants comprise a substrate coated with a resin which has been significantly I5 crosslinked. The resin coating of the precured proppants provides cn~sh resistance to the substrate. Since the resin coating is already cured before it is introduced into the well, even under high pressure and temperature conditions, the proppant does not a~olomerate. Such precured resin coated proppants are typically held in the well by the stress surrounding them In some hydraulic fracturing circumstances, the precured proppants in the well would flow back from the fracture, especially during clean up or production in oil and gas wells. Some of the proppant can be transported out of the fractured zones and into the well bore by fluids produced from the well. this transportation is known as flow back.
Flowing back of proppant from the fracture is undesirable and has been controlled to an extent in some instances by the use of a proppant coated with a curable resin which will consolidate and cure underground. Phenolic resin coated proppants have been commercially available for some time and used for this purpose. Thus, resin-coated curable proppants may be employed to "cap" the fractures to prevent such flow back. The resin coating of the curable proppants is not significantly crosslinked or cured before injection into the oil or gas well.
Rather, the coating is designed to crosslink under the stress and temperature conditions existing in the well formation. This causes the proppant particles to bond together forming a 3-dimensional matrix and preventing proppant flow-back.
These curable phenolic resin coated proppants work best in environments where temperatures are sufficiently high to consolidate and cure the phenolic resins. However, conditions of geological formations vary greatly. In some gas/oil wells, high temperature ( > 180°F) and high pressure ( > 6,000 psi) are present downhole. Under these conditions, most curable proppants can be effectively cured. Moreover, proppants used in these wells need to be thermally and physically stable, i.e. do not crush appreciably at these temperatures and pressures. Curable resins include (l) resins which are cured entirely in the subterranean formation and (ii) resins which are partially cured prior to injection into the subterranean formation with the remainder of curing occurring in the subterranean formation.
Many shallow wells often have downhole temperatures less than 130°F, or even less than 100°F. Conventional curable proppants will not cure properly at these temperatures.
Sometimes, an activator can be used to facilitate curing at low temperatures.
Another method is to catalyze proppant curing at low temperatures using an acid catalyst in an overflush technique. Systems of this type of curable proppant have been disclosed in U.S. Patent No.

4,785,884 to Armbruster. In the overflush method, after the curable proppant is placed in the fracture, an ~l acidic catalyst system is pumped through the proppant pack and initiates the coring even at temperatures as lo~.v as about 70°F. This causes the bonding of proppant particles.
Due to the diverse variations in geological characteristics of different oil and gas wells, no single proppant possesses all properties which can satisfy all operating requirements under various conditions. The choice of whether to use a precured or curable proppant or both is a matter of e,~cperience and knowledge as would be known to one skilled in the art.
In use, the proppant is suspended in the fracturing fluid. Thus, interactions of the proppant and the fluid will greatly affect the stability of the fluid in which the proppant is suspended. The fluid needs to remain viscous and capable of carrying the proppant to the fracture and depositing the proppant at the proper locations for use_ However, if the fluid prematurely loses its capacity to carry, the proppant may be deposited at inappropriate locations in the fracture or the well bore. 'Ibis may require extensive well bore cleanup and removal of the mispositioned proppant.
It is also important that the fluid breaks (undergoes a reduction in viscosity) at the appropriate time after the proper placement of the proppant_ After the proppant is placed in the fracture, the fluid shall become less viscous due to the action of breakers (viscosity reducing agents) present in the fluid_ This permits the loose and curable proppant particles to come together, allowing intimate contact of the particles to result in a solid proppant pack a$er curing. Failure to have such contact will a ve a much weaker proppant pack.
Foam, rather than viscous fluid, may be employed to carry the proppant to the fracture and deposit the proppant at the proper locations for use. The foam is a stable foam that can suspend the proppant until it is placed into the fiacture, at which time the foam breaks.
Agents other than foam or viscous fluid may be employed to carry proppant into a fracture where appropriate_ ~~9~ ~'~ ~
Also, resin coated particulate material, e.g., sands, may be used in a wellbore for ''sand control." In this use, a cylindrical structure is filled with the proppants, e_a., resin coated particulate material, and inserted into the welibore to act as a filter or screen to control or eliminate baciwvards flow of sand, other proppants, or subterranean formation particles.
Typically, the cylindrical structure is an annular structure having inner and outer walls made of mesh. 'The screen opening size of the mesh being sufficient to contain the resin .:oatee particulate material within the cylindrical structure and let fluids in the formation pass therethrouah.
While useful proppants are known, it would be beneficial to provide proppants having IO improved features such as reduced flow back, increased compressive strength, as well as higher long term conductivity, i.e., permeability, at the high closure stresses present in she subterranean formation. Reduced flow back is important to keep the proppant in the subterranean formation. Improved compressive strength better permits the proppant to withstand the forces within the subterranean forn~ation. Hid conductivity is important I5 because it directly impacts the future production rate of the well.
Objects of the Invention It is an object of the present invention to provide proppants coated with fiber-containing polymer.
It is another object of the present invention to provide curable proppants coated with 20 fiber-containing phenol-aldehyde novolac polymer.
It is another object of the present invention to provide precured proppants coated with fiber-containing phenol-aldehyde resole polymer.
It is another object of the present invention to provide methods of using proppant coated with a fiber-containing polymer.

It is another object of the present invention to provide methods of using proppant coated with a fiber-containing polymer.
These and other objects of the present invention will become apparent from the following specification.
Brief Description of the Drawings Fig. 1A shows a schematic drawing of a first embodiment of a resin coated particle of the present invention for use as a proppant.
Fig. 1B shows a schematic drawing of a second embodiment of a resin coated particle of the present invention for use as a proppant.
Fig. 2 shows plots of long term conductivity and permeability.
Summary of the Invention The invention provides an improved resin-coated proppant comprising a particulate substrate e.g., sand, and a fiber-containing resin. The resin may be any conventional proppant resin. A typical proppant resin is a phenolic novolac resin coating composition combined with IS hexamethylenetetramine (HEXA), formaldehyde, paraformaldehyde, oxazolidines, phenol-aldehyde resole polymers and/or other known curing agents as a cross-linking agent to achieve a precured or curable proppant.
The proppant resin comprises any of a phenolic novolac polymer; a phenolic resole polymer; a combination of a phenolic novolac polymer and a phenolic resole polymer; a precured resin made of cured furan resin or a combination of phenolic/furan resin (as disclosed by U.S. Patent No. 4,694,905 to Armbruster); or a curable resin made of furan/phenolic resin which is curable in the presence of a strong acid (as disclosed by U.S. Patent No. 4,785,884 to Armbruster).

., ~z~~~~~z The phenolics of the above-mentioned novolac or resole polymers may be phenolic moieties or bis-phenolic moieties.
The fibers may be any of various kinds of commercially available short fibers_ Such f bers include at Least one member selected from the eroup consisting of milled glass fibers, milled ceramic fiber, milled carbon fibers and synthetic fibers, having a softening point above typical starting sand temperature for coating, e. j., at least about 200°F so as to not degrade, soften or agglomerate.
The present invention achieves curable proppants having hi5her compressive streneths and thus reduced flow-back. These stronger fiber reinforced coated proppants will better withstand the closure stress exerted in the fracture. This will help in maintaining better conductivity and permeability of the formation for a longer time.
The present invention also provides precured proppant with better resistance to flow back. The resistance to flovwback is especially achieved where at least a portion of the fibers protrude from the resin coating to interlock with fibers of other proppant particles. An advantage of employing fiber-laden precured proppant, over curable coated proppant (which are fiber free) is that it works at any temperature. In contrasts curable resin coated sand only works where downhole temperatures are high enough to cure the resin or in the presence of added activators or acid catalyst (discussed above). Fiber-laden precured proppants are also different from, and better than, proppant systems of physical loose mi.of sand and fibers. Such physical mixtures may segregate and thus achieve reduced effectiveness. Also, because the precured resin is completely reacted, there is Less interaction of the resin with carrier fluid. This lack of interaction makes the fluid more stable and results in more predictable performance.

The invention also provides improved methods of using the above-described curable and/or precured proppants for treating subterranean formations.
When the method employs a precured coating composition on the proppant, the proppant is put into the subterranean formation without a need for additional curing within the formation.
When the method employs a curable coating composition on the proppant, the method may further comprise curing the curable coating composition by exposing the coating composition to sufficient heat and pressure in the subterranean formation to cause crosslinking of the resins and consolidation of the proppant. In some cases an activator, as discussed above, can be used to facilitate consolidation of curable proppant. In another embodiment employing a curable coating composition on the proppant, the method further comprises low temperature acid catalyzed curing at temperatures as low as 70°F. An example of low temperature acid catalyzed curing is disclosed by U.S. Patent No. 4,785,884.
Also, resin coated particulate material, e.g., resin coated sands, may be used by filling a cylindrical structure with the resin coated particulate material, i.e., proppant, and inserted into the wellbore. Once in place, the improved properties of this invention are beneficial because the proppant will cure and act as a filter or screen to eliminate the backwards flow of sand, other proppants, or subterranean formation particles. This is a significant advantage to eliminate the backflow of particulates into above ground equipment.
Detailed Description of the Preferred Embodiments The fibers of the present invention may be employed with any resin-coated particulate proppant material. The type of resin, particulate material and fiber making up the proppant will depend upon a number of factors including the probable closure stress, formation temperature, and the type of formation fluid.

The term resin includes a broad class of high polymeric synthetic substances.
Resin includes thermosetting and thermoplastic materials, but excludes rubber and other elastomers.
Specific thermosets include epoxy, phenolic, e.g., resole (a true thermosetting resin) or novolac (thermoplastic resin which is rendered thermosetting by a hardening agent), polyester resin, and epoxy-modified novolac as disclosed by U.S. Patent No. 4,923,714 to Gibb et al.
The phenolic resin comprises any of a phenolic novolac polymer; a phenolic resole polymer;
a combination of a phenolic novolac polymer and a phenolic resole polymer; a cured combination of phenolic/furan resin or a furan resin to form a precured resin (as disclosed by U.S. Patent No. 4,694,905 to Armbruster); or a curable furan/phenolic resin system curable in the presence of a strong acid to form a curable resin (as disclosed by U.S.
Patent No.
4,785,884 to Armbruster). The phenolics of the above-mentioned novolac or resole polymers may be phenol moieties or bis-phenol moieties. Novolac resins are preferred.
Specific thermoplastics include polyethylene, acrylonitrile-butadiene styrene, polystyrene, polyvinyl chloride, fluoroplastics, polysulfide, polypropylene, styrene acrylonitrile, nylon, and phenylene oxide. It is desired to use resin amounts of about 0.5 to about 8 % based on substrate weight, preferably about 0.75 to about 4 % .
A. Substrate Particulate material, i.e., substrate, includes sand, naturally occurring mineral fibers, such as zircon and mullite, ceramic, such as sintered bauxite, or sintered alumina, other non ceramic refractories such as milled or glass beads. The particulate substrate may be sand, ceramics, or other particulate substrate and has a particle size in the range of USA Standard Testing screen numbers from about 8 to about I00 (i_e. screen opening of about 0.0937 inch to about 0.009 inch). Preferred substrate diameter is from about 0.01 to about 0.04 inches.
Bau.Yite, unlike alumina, contains naturally occurring impurities and does not require the addition of sintering agents. The particles are typical proppant particles.
Thus, they are hard and resist deforming Deforming is different from crushing wherein the particle deteriorates.
B.
The fibers may be any of various kinds of commercially available short fibers.
Such fibers include at least one member selected from the soup consisting of milled glass fibers, milled ceramic fibers, milled carbon fibers, natural fibers, and synthetic fibers having a so$ening point above typical starting sand temperature for coating, e.g., at Least about Z00°F, so as to not decade, soften or agglomerate.
The typical glasses for fibers include E-glass, S-glass, and AR-glass. E-glass is a commercially available ~-ade of glass fibers typically employed in electrical uses. S-glass is used for its strength. AR glass is used far its allcali resistance. The carbon fibers are of graphitized carbon. The ceramic fibers are typically alumina, porcelain, or other vitreous material.
The fiber material should be inert to components in the subterranean forn~ation, e.g., well treatment fluids, and be able to withstand the conditions, e.g., temperature and pressure, in the well. Fibers of different dimensions and/or materials may be employed together. Glass ZO fibers and ceramic fibers are most preferred Typically the fiber material density is about that of the substrate, but this is not necessary.
The fiber material is preferably abrasion resistant to withstand pneumatic conveying.
It is important that the dimensions and amount of fibers, as well as the type and amount of resin coating, be selected so that the fibers are attached to the resin coating of the proppant rather than being loosely mixed with proppant particles. The attachment prevents loose particles from clogging parts, e.g., screens, of an oil or gas well. Moreover, the attachment prevents loose particles from decreasing permeability in the oil or gas well.
Resin coated curable proppants contain about 0.1 % to about 15 % fibers based on the substrate weight, preferably about 0.1 % to about 5 weight percent fibers, more preferably about 0.1 % to about 3 weight percent fibers.
Resin coated precurable proppants contain about 0.1 to about 15 weight percent fibers, based on substrate weight. To achieve enhanced permeability at low to moderate (less than about 4000 psi) closure stress levels, a fiber content of 0.25 to about 5 weight percent is typical. At fiber levels of about 5 to 15 weight percent the coating surface roughens. The roughened grains do not slide easily. Thus, this roughness diminishes flow-back. Also, to achieve enhanced flow-back resistance, by having fibers protrude from the coated fiber, a fiber content of about 10 to about 15 weight percent is preferred. The degree of roughness and/or fiber protrusion varies with parameters such as fiber loading levels, fiber length, resin loading levels, and substrate size and shape.
Fiber lengths range from about 6 microns to about 3200 microns (about 1/8 inch).
Preferred fiber lengths range from about 10 microns to about 1600 microns.
More preferred fiber lengths range from about 10 microns to about 800 microns. A typical fiber length range is about 0.001 to about 1/16 inch. Preferably, the fibers are shorter than the greatest length of the substrate. Suitable, commercially available fibers include milled glass fiber having lengths of 0.1 to about 1/32 inch; milled ceramic fibers 25 microns long;
milled carbon fibers 250 to 350 microns long, and KEVLART"' aramid fibers 12 microns long. Fiber diameter (or, for fibers of non-circular cross-section, a hypothetical dimension equal to the diameter of a hypothetical circle having an area equal to the cross-sectional area of the fiber) range from about I to about 20 microns. Length to aspect ratio (length to diameter ratio) may range from about 5 to about 175. The fiber may have a round, oval, square, rectangular or other appropriate cross-section. One source of the fibers of rectangular cross-section may be chopped sheet material. Such chopped sheet material would have 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 lengths of the shorter side to the longer side is typically about 1:2-10. The fibers may be straight, crimped, curled or combinations thereof.
Typical resin coated proppants have about 0.1 to about IO weight percent resin, preferably about 0.4 to about 6 weight percent resin, more preferably about 0.4 to about 5 wei~t percent resin, most preferably about 2.5 to about 5 weight percent resin. Potential hypothetical resin coated proppants include a conventional prappant substrate with any of the following resin levels and fibers. Resin levels of 0.75 to 3 wei~t percent, based on substrate weight, with 0.0001 to 1/32 inch long milled glass fiber at levels as low as 0.1 to 0 ~5 weight percent, based on substrate weight may be employed. In particular, resin levels of 2.5 to 3 weight percent, based on substrate weight, with 1/32 inch long milled glass fiber may be employed Resin levels of about 0.75 to about I weight percent, based on substrate weight, with 1/32 inch long milled glass fiber may be employed Resin levels of 2.5 to 3.0 weight percent, based on substrate weight, with ceramic fibers having Ienoths from 20 to 25 microns may be employed Resin levels of 1 to 1.5 wei~t percent, based on substrate weight, with ceramic fibers having lengths of 20 to 50 microns may be employed.
By employing fibers, the present invention achieves curable proppants having higher compressive strengths. These stronger fiber reinforced coated proppants will better withstand the closure stress of fracture and better resist flow-back. 'Ibis will help in maintaining better l~
conductivity and permeability of the proppant in the fracture for a longer time than conventional curable progpants employing the same resin in the absence of fibers.
The present invention also provides procured proppant with better resistance to flow back. Tne resistance to flow back is especially achieved where the fibers rou~en the resin coating surface and/or protrude from the resin coating. 'Ihe roughened surface and/or protruding fibers cause the coated proppant particEes to resist moving past one another to prevent ilow-back. An advantage of employing fiber-laden preeured proppant, over curable coated proppant (which are fiber free) is that it works at any temperature.
Curable resin coated sands only work where downhole temperatures are high enou~ to cure the resin.
Fiber-laden procured proppants are also different from, and better than, proppant systems of physical loose mixtures of sand and fbers. Such physical mixtures may se~egate and thus, achieve reduced effectiveness.
C. Phenol-~dehvde Novolac Polymer-Containing Resins An embodiment of the present invention is a resin coated particulate material wherein I~ the resin includes phenol-aldehyde novolac polymer. The novolac may be any novoIac employed with proppants. The novolac may be obtained by the reaction of a phenolic compound and an aldehyde in a strongly acidic pH region. Suitable acid catalysts include the strong mineral acids such as sulfuric acid, phosphoric acid and hydrochloric acid as well as organic acid catalysts such as oxalic acid, or para toluenesulfonic acid An alternative way to make novolacs is to react a phenol and an aldehyde in the presence of divalent inorganic salts such as zinc acetate, zinc borate, manganese salts, cobalt salts, ere.
'Ihe selection of catalyst may be important for directing the production of novolacs which have various ratios of ortho or para substitution by aldehyde on the phenolic rind e.g., zinc acetate favors ortho substitution. Novolacs enriched in ortho substitution, i.e.. hi~h-ortho novolacs, may be 15 preferred because of greater reactivity in further cross-linking for polymer development. High ortho novolacs are discussed by Knop and Pilato, Phenolic Resins, p. 50-51 (1985) (Springer Verlag). High-ortho novolacs are defined as novolacs wherein at least 60% of the total of the resin ortho substitution and para substitution is ortho substitution, preferably at least about 70%
of this total substitution is ortho substitution.
The novolac polymer typically comprises phenol and aldehyde in a molar ratio from about 1:0.85 to about 1:0.4. Any suitable aldehyde may be used for this purpose. The aldehyde may be formalin, paraformaldehyde, formaldehyde, acetaldehyde, furfural, benzaldehyde or other aldehyde sources. Formaldehyde itself is preferred.
The novolacs used in this invention are generally solids such as in the form of a flake, powder, etc. The molecular weight of the novolac will vary from about 500 to 10,000, preferably 1,000 to 5,000 depending on their intended use. The molecular weight of the novolacs in this description of the present invention are on a weight average molecular weight basis. High-ortho novolac resins are especially preferred.
The coating composition typically comprises at least 10 weight percent novolac polymer, preferably at least about 20 weight percent novolac polymer, most preferably about 50 to about 70 weight percent novolac polymer. The remainder of the coating composition could include crosslinking agents, modifiers or other appropriate ingredients.
The phenolic moiety of the novolac polymer is selected from phenols of Formula I or bisphenols of Formula II, respectively:
R R' I, and HO

X
HO ~OH
R and R' are independently alkyl, aryl, aryiaikyl or IT In Formula II, R and RE are preferably meta to the respective hydroxy soup on the respective aromatic rind. Unless otherwise defined, alkyl is defined as having 1 to 6 carbon atoms, and aryl is defined as having 6 carbon atoms in its ring. In Formula II, X is a direct bond, sulfonyl, alkytidene unsubstituted or substituted with halogen. cycloaikylidene, or haloQenated cycloallcylidene.
Alkylidene is a divalent organic radical of Formula III:
R' III.
~3 R
When X is alkylidene, RZ and R' are selected independently from I~ allcyl, aryl, arylalkyl; halogezrated alkyl, halogenated aryl and halogenated arylatkyl.
When X is halogenated alkyiidene, one or more of the hydrogen atoms of the allcyfidene moiety of Formula II are replaced by a halogen atom. Preferably the halogen is fluorine or chlorine.
Also, haiogenated cycIoalkylidene is preferably substituted by fluorine or chlorine on the cycioalkylidene moiety.
I~ A typical phenol of Formula I is phenol, per se.
Typical bisphenols of Formula II include Bisphenol A, Bisphenol C, Bisphenol E, Bisphenol F, Bisphenol S, or Bisphenol Z.
The present invention includes novolac polymers which contain any one of the phenols of Formula I, bisphenols of Formula II, or combinations of one or more of the phenols of ?0 Formula I and/or one or more of the bisphenols of Formula II. The novolac polymer may optionally be further modified by the addition of ViNSOL~, epoxy resins, bisphenol, waxes, or other known resin additives. One mode of preparing an alkylphenol-modified phenol novolac polymer is to combine an alkylphenol and phenol at a motar ratio above 0.05:1. This combination is reacted with a source of formaldehyde under acidic catalysis, or divalent metal catalysis (e.g, Zn, hfn). Dur;ng this reaction, the combination of allylphenol and phenol is present in molar excess relative to the formaldehyde present. Under acidic conditions, the polymerization of the methyloiated phenols is a faster reaction than the initial methylolation from the formaldehyde. Consequently, a polymer stn.~cture is built up consisting of phenolic and allylphenolic nuclei. linked together by methylene bridges, and with essentially no f=ee IO methylol groups. In the case of metal ion catalysis, the polymetiz~tion will lead to methylol and benzylic ethers, wfiich subsequently break down to methylene bridges, and the final product is essentially free of methylol groups.
j). (~rntslinking AaentS and Other Additives For practical purposes, phenolic novolacs do not harden upon heating, but remain I ~ soluble and fusible unless a hardener (crosslinking agent) is present.
Thus, in curing a novoiac resin, a crosslinking agent is used to overcome the deficiency of aikylene-bridgjng groups to convert the resin to an insoluble infusible condition.
Appropriate crosslinking agents include hexamethylenetetramine (HE~~A), parafomzaldehyde, oxazolidines, melamine resin or other aldehyde donors andlor phenol-20 aldehyde resole polyrners_ Each of these crosslinkers can be used by itself or in combinations with other crosslinkets. The resole polymer may contain substituted or unsubsrituted phenol.
The coating composition of this invention typically comprises up to about 25 wei jht percent HEXA and/or up to about 90 wei~t percent resole polymers based on the total weight of coating composition. 'Vhere HE~C.A is the sole crosslinking anent, the HEXA

comprises from about S to about 2S weight percent of the resin. Where the phenol-aldehyde resole polymer is the sole crosslinking agent, the resin contains from about 20 to about 90 weight percent of the resole polymer. The composition may also comprise combinations of these crosslinkers.
S The phenol-aldehyde resole resin has a phenol:aldehyde molar ratio from about 1:1 to about 1:3. A preferred mode of preparing the resole resin is to combine phenol with a source of aldehyde such as formaldehyde, acetaldehyde, furfural, benzaldehyde or paraformaldehyde under alkaline catalysis. During such reaction, the aldehyde is present in molar excess. It is preferred that the resole resin have a molar ratio of phenol to formaldehyde from about 1:1.2 to 1:2.5. The resoles may be conventional resoles or modified resoles.
Modified resoles are disclosed by U.S. Patent No. 5,218,038. Such modified resoles are prepared by reacting aldehyde with a blend of unsubstituted phenol and at least one phenolic material selected from the group consisting of arylphenol, alkylphenol, alkoxyphenol, and aryloxyphenol.
Modified resole resins include alkoxy modified resole resins. Of alkoxy modified resole 1S resins, methoxy modified resole resins are preferred. However, the phenolic resole resin which is most preferred is the modified orthobenzylic ether-containing resole resin prepared by the reaction of a phenol and an aldehyde in the presence of an aliphatic hydroxy compound containing two or more hydroxy groups per molecule. In one preferred modification of the process, the reaction is also carried out in the presence of a monohydric alcohol.
Metal ion catalysts useful in production of the modified phenolic resole resins include salts of the divalent ions of Mn, Zn, Cd, Mg, Co, Ni, Fe, Pb, Ca and Ba. Tetra alkoxy titanium compounds of the formula Ti(OR)4 where R is an alkyl group containing from 3 to ~ ~19~~~

8 carbon atoms, are also useful catalysts for this reaction_ A preferred catalyst is zinc acetate.
These catalysts we phenolic resole resins wherein the preponderance of the brides joining the phenolic nuclei are ortho-benzylic ether brides of the general formula -CH,(OCH,n where n is a small positive integer.
Additives are used for special cases for special requirements. The coating systems of the invention may include a wide variety of additive materials. The coating may also include one or more other additives such as a coupling went such as a silane to promote adhesion of the coating to substrate, a silicone lubricant, a wetting ~aent, a surfactant, dyes, flow modifiers (such as flow control agents and flow enhancers), and/or anti-static agents_ The surfactants may be anionic, nonionic, cationic, amphoteric or mixtures thereof. Certain surfactants also operate as flow control agents. Other additives include humidity resistant additives or hot strength additives. Of course, the additives may be added in combination or singly.
E. Method to Make NovoIac Polymer To make phenolic novolac polymers with one or more phenols of Formula I, the phenol is mixed with acidic catalyst and heated. Then an aldehyde, such as a ~0 weight solution of formaldehyde is added to the hot phenol and catalyst at elevated temperature.
Water made by the reaction is removed by distillation to result in molten novolac. The molten novolac is then cooled and flaked.
To make novolac polymers with bisphenols of Formula II, the bisphenol is mixed with a solvent, such as n-butyl acetate, at elevated temperature. An acid catalyst such as oxalic acid or methane sulfonic acid is then added and mixed with the bisphenol and then an aldehyde, typically fon~naldehyde, is added. The reactants are then refluxed_ It is noted that the preparation of the novolac resin can occur under acidic catalysis, or divalent metal 0 ~ 1g~ 8' ~

catalysis (e. j., Zn, NIn), wherein the bisphenol is present in greater than equimolar amount relative to the source of aldehyde. After reffux, water is collected by azeotropic distillation with n-butyl acetate. Afrer removal of the water and n-butyl acetate, the resin is flaked to yield resin products. Alternatively, the polymers can be made using water as a solvent_ F. Manufacturing of Resoles A typical way to make resoles is to put a phenol in a reactor, add an alkaline catalyst, such as sodium hydroxide or calcium hydroxide, and aldehyde, such as a ~0 weight solution of formaldehyde, and react the ingredients under elevated temperature until the desired viscosity or free formaldehyde is achieved. Water content is adjusted by distillation.
G. Reacting A_ldehvde Wth Phenyl-Aldehvde ~lovolacs or Bisphenol-Aldehv lie Novo acs Phenol-aldehyde novolacs or bisphenol-aldehyde novolacs may be modified by reacting these novolacs with an additional quantity of aldehyde using a basic catalyst.
Typical catalysts used are sodium hydroxide, potassium hydroxide, barium hydroxide, calcium l~ hydroxide (or lime), ammonium hydroxide and amines.
In the case of phenol-aldehyde polymers or bisphenol-aldehyde polymers, the molar ratio of added aldehyde to phenolic moiety, based on the phenolic moiety monomeric units in the novolac, ranges from 0.x:1 to 3:1, preferably from 0.8:1 to 2:1. This achieves a crosslinkable (reactive) polymer having different chemical structures and generally higher molecular weights than the resole polymers obtained by a single step process which involves initially mixing bisphenol monomers and aldehyde with an alkaline catalyst at the same molar ratio of the combined aldehyde and bisphenol. Furthermore, it is feasible to use different aldehydes at different stages of the polymer preparation.
These aldehyde-modified polymers are useful in coating compositions for oil field W proppants and foundry sands. These polymers can be used alone as a coating.
These ~~~9gg'~
polymers can also be used with other polymers, such as phenol-aIdehyde novolacs, bisphenol-aldehyde novoiac, or combinations thereof, as a crosslinking agent, or as a component of erosslinlsing agents. When the aldehyde-.modified polymers are employed as aosslinking agents, they may be used with other typical crosslinking agents such as those described above far novolac polymers.
H. Ntethod to Make Props t After making the resin, the crosslinking agent, resin. fibers, and particulate material are mixed at conditions to provide either a precured or curable coating composition, as desired. Precured or curable proppants can be made by coating particulate material, e.g., sand, with the coating composition and f bets. Whether a coating composition is of the precured or curable type depends upon a number of parameters. Such.parameters include the ratio of the novolac resin to the curing went; the acidity of the novoiac resin; the pH of the resole resin; the amount of the crosslinking agent; the time of mi.~cing the coating compositions, fibers, and particles; the temperature of the coating compositions, fibers, and 1~ particles during mi,~cin~ catalysts (if any) used during the particle coating; and other process parameters as known to those skilled in the art. Typically, the precured or curable proppants may have a coating which contains resole resin in the presence or absence of novolac resin.
The coating resin may be admixed to particulate material combined with fibers.
In an alternative method, the fibers (and optionally additional resin) are admixed to a resin coated particulate material. In another alternative method the particulate material is admixed to fibers and resin.
Typically, the resin is coated onto particulate material and fibers by a hot coat process or a warm coat process. The hot coat process includes adding the resin to hot sand, or other particulate material, which has been heated to a temperature above the resin's melting point.

'Then a crosslinking agent is added and the ingredients are stirred for the desired time to produce a particulate material coated with either a precured or curable resin as desired.
Typically, the mixing occurs in the presence of a coupling agent such as an organosilane and a lubricant, such as a silicone fluid, such as L-45T"" manufactured by Dow Corning Corporation, Midland, Michigan (materials of this type are discussed in U.S.
Patent No.
4,439,489 to Johnson, et al). The coated sand is then removed, cooled and sieved.
In the warm coat process, the resin is in a liquid form, e.g., solution, dispersion or suspension, preferably solution, when it is mixed with the particulate substrate, crosslinker or other appropriate ingredients. The carrier liquid, e.g., solvent, is then removed resulting in a free flowing proppant coated with curable resin.
Fig. 1A shows a proppant particle 10 comprising a substrate particle 20, a resin coating and fibers 18. The resin, crosslinking agent, fibers 18 and particle 20 are mixed to produce the proppant 10. The proppant 1U is prepared to comprise from about 1 to about 8 weight percent coating 15 as well as an amount of fibers 18 as disclosed above. Also, the particle 20 15 has a pre-coated size in the range of USA Standard Testing screen numbers from about 8 to about 100. A portion of the fibers 18 may protrude a distance D. Roughness or protruding fibers may prevent flow-back of curable proppant prior to completion of the curing process.
However, some of the fibers 18 may be totally embedded in the resin coating 15, e.g., fiber 24. Some fibers 22 may be curved. Moreover, some fibers 2b may curl sufficiently to hook both fiber ends into the coating 15.
Fig. 1B shows a coated proppant particle 110 wherein the fibers 24 are embedded in the resin coating 15 about the substrate particle 20, and the fibers 24 cause the proppant particle 110 to have a roughened surface 30.

The known hot coat or warm coat processes for making coated proppants may be modified by electrically charging the substrate and oppositeiy charging the fibers to encourage the fiber to orient orthogonal to the substrate and protrude from the coating.
The fibers provide the advantages of higher strength and reduced llow-back with curable resin-coated proppants. The protruding fibers improve the flow back resistance of precured resin-coated proppants because the fibers cause adjacent proppant particles to interlock Also; the precured, fiber-laden proppants improve the permeability of subterranean formations at closure stresses of up to about 4000 psi.
The foiloming parameters are useful when characterizing coated proppants of the present invention.
Compressive strength of curable proppants is defined as that measured according to the following procedure. A 2 weight percent KCl solution (doped with a small amount of detergent to enhance wetability) is added to proppant. The KCI solution and proppant are gently ao-itated to wet the proppant. Samples of the wet proppant will be cured at 1004 psi I~ or at atmospheric pressure. For wet proppant samples to be cured at- 1000 psi, the wet proppant is packed into steel tubes with a movable pIunQer. After packing the proppant, a load of 1,000 psi is applied using the plunger. For wet progpant samples to be cured at atmospheric pressure, the wet proppant is packed into a plastic tube. In either event, the samples are then heated to 200°F and held at 200°F for 24 hours to cure the samples. During the curing process, loose proppant particles become a consolidated mass. After 24 hours, the samples are removed as slugs. Both ends of each slug are smoothed to give flat surfaces and the slug are cut to about two inches in length. The slugs have a nominal one inch diameter.
Compressive strength tests of the slug are determined using a tensile tester manufactured by p~19~~12 Detroit Testing Machine Company and the results were reported Typical compressive stren~~ths of proppants of the present invention range from 50 to 3000 psi or higher.
Hot tensile strength of curable proppants is defined as that m~.sured by heating a two part bracket mold until it reaches a temperature of 450°F. Uncured resin coated sand is blown into the hot mold and the sand is kept at this temperature for 3 minutes to cure. After completion of curing time, tensile measurement are made automatically with a built-in tensile tester. Typical hot tensile strengths of proppants of the present invention range from 0 to 500 psi or higher.
Crush resistance of precured proppants is defined as that measured according to the following procedure. American Petroleum Institute RP 60 procedure, Section 7 (1989).
Lone term conductivity is defined as that measured by the "Proppant Consortium Baseline Procedure," developed by Stim-Lab, Inc., Duncan, Oklahoma.
Melt point of curable resin coated sand is defined as that determined using a melt point bar. A melt point bar is a brass metal bar ( 18 inches long and 2 inches wide} with an I S electric heating element at one end. Therefore, a temperature gradient can be established across the length of the bar and the temperature across tine bar is monitored with thermometers or thermocouples. Typically, the temperature is about 315 to about 330°F at the hottest end of the bar. Using a funnel, a uniform strip of resin coated sand is Iaid on the heated bar and cured for 60 seconds. Then an air jet at IO psi pressure is blown on the sand and any uncured sand will be blown off the bar. Melt point is the lowest temperature at which the resin coated sand forms a mass.
c a The following general coating procedures were followed to prepare fiber-laden curable proppants using HEXA as a crosslinlcin~ agent. Into a 3 quart mixing bowl was placed one kilogram of 20/40 mesh sand available from and an appropriate amount of fiber to achieve the desired weight percent fiber. 20/40 sand has 90% of its particles between 20 and 40 mesh (U. S.
Standard Sieve Series) per American Petroleum Institute RP-60 procedure, Section 4 ( 1989). The sand and glass fiber were stirred with a HobartTM C-100 mixer and heated with a gas flame to 280°F. 26.6 grams of EXS 150TM novolac resin (Borden, Inc.) and 0.4 grams of A-1100TM silane (Union Carbide Corporation) were added and mixed for 90 seconds. At this time 13.8 grams of 32.6% water solution of hexamethylenetetramine was added. Mixing was continued and at 96 seconds of total mixing time 8.1 grams of water was added. At 120 seconds of mixing time 1.0 gram of L-45 silicone was added. Mixing was continued for another 180 seconds.
At 300 seconds of total mixing time the coated sand was discharged from the bowl as a free flowing product consisting of individual sand grains coated with a curable resin coating. The stick melting point ofthis product was 232°F. A 3 minute, 450°F hot tensile strength test was run and produced a specimen with a hot tensile of 200 psi. The proppant was coated with Plasti FIakeTM
EX5150, a commercial phenol-formaldehyde novolac manufactured by Borden, Inc./
North American Resins, Louisville, Kentucky.
Comparative Example 1 The procedure generally such as that of Example 1 was repeated without fibers, with the same ingredients, except to make a conventional curable resin coated proppant.
Comparison of Curable Proppants of Example l and Comparative Example 1 The curable proppants of Example l and Comparative Example 1 were prepared with varying resin contents and added milled glass fibers, milled carbon fibers, milled ceramic fibers and KEVLAR aramid fibers at levels of 0%, 1/4%, 1/2%, 2%, 5% and 10 weight %
based on weight of 20/40 Brady sand. 20/40 Brady sand is available from Ogelby-Norton, Brady, Texas.
These laboratory prepared samples were evaluated for resin contents, melting point, hot tensile strength, and compressive strength. Tables I-6 summarize the results of these experiments. The proppants of Comparative Example 1 are listed as "Controls"
on Tables 1-6.
In the TABLES "Loss on Ignition" is defined as that measured after burning proppant at 1700°F for two hours and represents the amount of resin on the proppant. Table 7 employs 5 20/40 Brady sand with resin and fibers.
Table CURABLE
RESIN
WITH
1/16"
MILLED
GLASS
FIBER' AND 20!40 BRADY
SAND

Sample Control Control Number 1 1 2 2 3 4 5 6 7 8 9 Loss on 1.8 1.89 2.612.89 2.902.89 2.922.72 2.47 2.96 3.02 Ignition (wt%) Melting 246 257 260 239 238 235 252 >260 >260 252 262 Point (F) 15 Hot Tensile150 44 68 200 270 242 122 65 3 146 76 Strength (psi) Compressive388 135 127 747 518 470 482 119 5 497 181 Strength at Atm.

20 Pres./200F/

24 hrs (psi) Compressive675 384 561 946 19001895 975 455 68 978 830 strength 25 at 1,000 psi/200 F/

24 hrs (psi) Increase - - - - 100.8100.33.1 - - 3.4 -in Compressive Strength at looo psi/200F/

24 hrs Fiber 0 2 5 0 1/4 1/2 2 5 10 2 5 Load on Sand (%) ' Fibers are 1/16 inch long, 10 micron in diameter, made of E
glass, and available as MICR(~LASSTI"
milled fiber from Fibertec, Bridgewater, Massachusetts.

~1~~~~ 2 Table 2 CURABLE
RESIN
WITEi 1132"
WLLED
GLOSS
FIBERt BRADY
SAND

Conavl Sample 3 10 1 t2 Number I

Loss on t.8 1.781.691.53 Ignition (tt2%) Melting 246 >2~~No No Point (F?

StickSticfc Hot Tensilet~0 3a 0 0 Strength (~7 Compressive388 142 0 0 Strength at Arm Pre51200F/

24hr5 (psi) Compressive675 aDI 0 0 Strength at 1.000 psi!'L00FI

24hrs lncrcase - - - -in Cosnptessive Strength at 1000 psil200F/

24hts Fibertoad 0 2 5 !0 on Sand Tab le inued) (rnrrt Control Sample Numbar4 13 14 h 16 17 18 I9 Loss on IgnitionZ89 291 294 294 2.63 2.52294 3.02 (rrt%) j Melting Point~9 232 233 239 >235 >255242 >260 (F) Hot Tetuile 200 2I8 236 135 62 0 I13 83 Strength ~(Ps) Compressive 747 432 637 4-SZ128 7 480 257 Strrn~th a Atm Pres/200FI

j~ 24hs (psi) Compttssive 94b 197519001600499 127 12501050 Strcn~th at 1000 psir100FI

24hrs tpsy % Irse in - 108.8100.869.1- - 321 11.0 35 Compressive s~ts~ttt at 1000 psil200F/

2ahts Fiberload 0 1I4 1l2 2 5 10 2 S
on Sand (%) = FibetS ng. cis necer,c ss, ilableICROGL4$S
a2 1/32 16 in ttndof and as milled inca lo mictodiar ava M
gla fiber from gcwater,ssechtuctis.
Fioerrc~ Ma Br:d ~2~9~~12 Table CURABLE RESN 2"
WCn-I 1/3 ~~ID
1116"
MILLED
GLASS
FIBER

BRADY
SA~~lL7 Wch t/16"
1/32 Nlitled Nfilled Glass F~bcrz Glass Fbcr' Control Sample Number7 20 21 12 23 24 ~

Loss on Igution4.2 4.234.21 433 4.174.18 (wC'/) Melting Point230 ~4 244 >260240 240 (~

Hot Ttnsile 240 196 242 86 34b 142 Stttngth (pst) Compressive 1000 1367860 437 90Z 767 Strength at I O ~trt,.P~.rtooFr 24hts (psi>

Compnxsive 2300 30002525 ???5. 2875 Strength 2975 at 1000 psi/200F!

24hrs (psi) I J % Increase - 7. - - 6.3 27 in t Cotttptrssive Strength at 1000 psif200FI24hts 1 fiber Load0 2 5 IO Z 5 on Sand (%) ' See Table l 20 T See Tabte TaMe4 CURABLE
RESIN
WI'CH

MICRON
MILLED
CERAMIC
FIBER' AND 20!40 BRADY
SAND

SaTnple COIltf01 Number 6 25 26 27 28 29 30 Loss on 2.89 2.892.843.03 3.09 2.972.94 I ~tion wt%) Meking 224 235 240 242 ?260 240 245 Point (F

1 ~ Hot Tensile200 165 232 182 93 170 112 Stren i) Compressive747 860 843 603 293 467 288 Strength at Atm.Pres./

1 J~ 200 F/24hrs i) Compressive946 146713001575 1425 16251375 Strength at 1000 2~

F/
psi/200 24hrs i Increase - 55.037.466.5 50.6 71.845.3 in Compressive Strength 25 at loon pg;r 200F/24hrs Fiber 0 1/4 1/2 2 5 2 5 Load on Sand (%) Table 4 (continued) Control S !e Number 31 32 33 34 35 36 7 Loss on I 4.31 4.33 4.22 4.13 4.23 4.214.2 'tion (wtio Melon Point 220 220 232 255 240 240 230 (F) Hot'fensile 410 402 270 142 288 256 240 Strength i 35 Compressive 1133 1087 1113 863 1533 773 1000 Strength at Atm.Pres./200F/

24hrs (psi) Compressive 3100 2850 3725 3325 3350 33252800 Strength at 1000 i/200 F/24 si Inaease in 9.7 1.8 33.0 18.8 l9.fi18.8-Compressive Strength at 1000 si/200F/24hrs Fiber load I I Z 5 2 S 0 on Sand l4 /2 (%

45 ' Fibers are alumina ceramic, 20-25 microns long" 2-3 microns in diameter, and available as FIBERFRAXT"' from Carborundum C ., Nia a Falls, New York.

Tab1e 5 CURABLE RESIN
WITH KEVLAR
PULP FIBER"

SAND

Corrtrol S le Number 37 38 8 Loss of I 'lion3.553.51 2.89 wt%) Melon Point 250 ?260 224 F

Ho2 Tensile 125 0 200 Sven si Compressive 468 0 747 Strength at a200F/
Atrr 2 ~

Compressive 1725137 946 Strength at 1000 i/200F/24hrs i Increase in R2.3- -Compressive Strength at IS 1000 i/200F/24hrs Fiber Load on 1I2 2 0 Sand %

' Fibers have a length of 12 microns, a diameter of 2 miaons, are made of aramid fiber, and manufactured by E.I. duPont de Nemours &c Co., Wilmin on, Delaware.

20 Table CURABLE
RESIN
WITH

MILLED
CARBON
FIBERS

BRADY
SAND

Sample Control Control Number 25 ~ n Igmtaon2.89 5.98 4.52 5.636.77 4.2 (w1%) Melting 239 >255 >260 254 >260 230 Point (F) Hot Tensile200 55 0 205 46 240 Stren i) 30 Compressive747 310 10.3 101357 1000 Strength at Atm.Pres./

200F/24hrs si) 35 Co 946 795 SR 2625235 2800 tnpressive S

at 1000 psi/200F/

24hrs(psi) Fiber 0 2 5 2 5 0 Load on 40 sane (i) ' Fibers are made of g<aphitized carbon, have a length of 250 microns, a diam~er of about microns, and are FORTAFILTM
fibers, manufactured by Fortafil Fibers, Ine., Rockwood, Tennessee.

~~~9~~12 ~o Table CURABLE
R.LSM
WITH
FIBER
AND

EIICKORY
SAND

F~ER
LOAD
ON
SAND
Vs COIvtPRESSfVE
STRENGTH

A B C

,~ 20-ZS
Fiber vlicrc~n Load t/16" If32" Milled On iVfiiled Willed Ceramic SampicSand Glas.> Glass Fiber J Filler Fiber , tumber CompressiveCompressiveCompressive Strength Strengthstrength ( I OOOpsil200F/( 1000psi/200F!( 1000psi/200F!

24hrs) 24hrs) 24hr5) Control0 946 94b 946 A,B,C

43 O.IO 1078 963 1080 A,B,C

a.t 0.1251200 ( I50 1360 ,~B.C

to 45 o.25 1900 1975 1467 A.B,C

a6,~B,Co.5o Is9s 190o I,oo 47.4.B,C2.00 975 1600 1575 48 5.00 455 499 1425 A,B.C

49 10.0068 127 fI20 A.B,C

I ~ NOTE:
Fiber Specifications IvL(lcd Mtiled Glass Ceramic Fiber Fiber Fiber Fiber Fiber DiartxtetLrngdt Diameter Fiber (L~Gcron)(IvGcron)(Moron) Length (Inch) 1116 l0 (Avg) (Ave) 2~?5 2_3 (Avg.) (Avg.) II32 t6 (Avg) (Avg.) 20 To facilitate comparison of data, Table 7 repeats some of the data of Tables 1, 2 and 4 and includes additional data. The average L.O.I. of the samples of Table 7 is about 2.9.
~Amons all the samples whose results are listed on Tables 1-7, those curable (CR) samples containing milled Qlass fibers and milled ceramic fibers produced higher compressive strength than those of a contFOI when tested after curing under 1,000 psi at 200°F for 24 hrs.
25 Moreover, test results demonstrated good reinforcement capabilities of milled glass fibers and milled ceramic fibers. When tested after curing for 24 hours at 1,000 psi and 200°F, compressive strengths up to 1900 psi with 1/4% glass fiber loading and 1,600 psi with 2%
ceramic fibers loading (based on sand) were obtained (Tables I, 2 and 4). This translates as ____ p~~~~~~~

an increase in compressive strength of 100% and 69% respectively. The fiber loadinj level for curable products with loss on ignition (L.O.L) levels of about 3 appears to be desirable in the range of 1/=1 to 2% based on sand for milled glass fbers and lf~I% to 5% for milled ceramic fibers (Tables l, 2 and 4). At L.O.I. levels of about 4°/g the 2% and 5% levels of milled ceramic fibers indicated si~tificant increases in compressive stren5th when tested after curing at 1,000 psi and 200°F for 24 hrs (Table =1).
Attempts to add KEVLAR aramid fibers in the mia were not totally successful due to the difficulty of dispersion. Due to the tangled nature of the fibers, fiber separation and its full uniform distribution in the mi,~ were not achieved using our mixing and blending technique. Coated samples prepared with KEVLAR fibers when sieved produced many free fibers. Ivfieroscopic examination indicated that some of the fibers had been incorporated into the coating.
Data in Table 7 indicates jlass fiber levels of 0.1 to about 2, and ceramic fiber levels of 0.1 to 10, are desirable to increase compressive strength.
Example 2 - Preparation of Precured Resin/Fiber Coated Proppant In a 3 quart mixing bowl, 1 kilo~am of 20/40 mesh sand and an appropziate amount of fiber to achieve the weight percents of fber listed in the following Tables were added The sand was stirred with a Hobart C-100 mi,Yer and heated to 360°F.
4I.8 Barns of EX9100 resole resin (Borden, Inc., North American Resins) was added and mixed for 30 seconds. 0.4 of A-1100 silane (Union Carbide Corporation) was added. Mixing was continued and at ~0 seconds of mixing time the stirrer was shifted to high speed. At 100 seconds, 03 grams of betaine nonionic surfactant, cocamidopropyl hydroxysultaine, .vas added_ At I50 seconds the mixer was shifted to initial low speed. At 360 seconds mi.~cin~
time the coated sand was discharged from the bowl as a free flowing product. The product was post baked a2~~~~~2 3?
for 14 minutes in an oven at 360°F. Then the coated fiber-laden sand was cooled and sieved through an 18 mesh screen to eliminate aajlomerates.
~parative Exam A procedure generally such as that of E.~cample 2 was performed without fibers, to S make a conventional precured resin coated proppant Comparison of Precured Proppants of Example ? and Comparative Example 2 A number of samples were prepared for Example Z arid Comparative Example 2 at fiber toads of 0.25, 0.5, 2, ~ and 10% based on sand weight. These samples were then measured for Loss on Ignition and cnlsh resistance and the results listed on Tables 7-10. The sample numbers for Comparative Example 2 are listed as "Controls" on Tables ~-11.
Table ~CURFD
RES)I~
WITH
MILLm GLOSS
FIBER

AND
2(X40 BRADY
SAND

With f32:led Wth I MilGlass Ill6"
Fiber= Mtllexi Glazs Fiber' SampleControl Number12 50 51 52 53 54 53 56 57 58 59 Loan ? 48 2.62.782.42Z.p32.34266 268 2.~82.482.33 on Ignition (wP/o) Cncsh 11_38 17.214.9413. 9.7311.1915.4715.34l3. 9.8312_92 t3 l7 Rainartce at IO,OOOpsi Fibcr 0 Il41!1 2 5 10 1/4 1/Z 2 5 10 Load On Sand Rcsin is Oil Well Resole 9100.

' See Tahle 1.
-= Sec Table Z

-,-, Table PRECURED
RSB~f' WfTH
MILLED
GLASS
FIBER

AND ?0/40 BRADY
SAND

win wth Irz I/16 1v>iued Misled Glass Glass Fiber= Fiber' Conavt Samp(e (3 60 6I 62 63 Number Loss on 3.78 3.68 3.64 3.76 3.81 Igiition (wt%) Crush 3.92 5.a2 3.17 6.3 4.2 R~utance ac lo.ooo psi (%) Fiber 0 2 .l 2 l Load on 1~ ~d (%) ' Resin is Oil Well Resole 9100.

' See Table 1.

r Sec Table 2.

Table RESm wm-I
2o wc~oN
Mn.LED
cl;RAivac r-~ER~

BRADY
SAND
.

Cluable Curable Remn6 Rrnnr Sample Control C

Number 14 64 6i 66 67 IS 68 69 70 71 Loss on ? ? 2.63 272 2.813.78 3.713.773.98 3.93 I~ition (wr%) Crush 11.381? 13.7 14.3315.23.92 6.4 8.59.46 8.~3 Resistance at IO,OOQpsi(%) Fiber 0 2 5 1/Z 1/20 2 p 1/2 1/4 ?5 Load on Sand (%) ' See TabIC
4, however, only 20 micron length fibers erriployed '' Sr Table 7.

' Sce Table 8.

~~~9~~~~
Table II

PRECURED
RESIN
WCI~f-I

IvtICRON
&tILEFD
CARBON
FIBER' ArW ZOl40 BRADY
SAND

Prccutzd Procured Resinfi Resin' Sample Control Convol Number t6 i2 73 74 t7 75 76 L~s on 2.=t83.165.575.1 3.73 4.955.09 Imition (wt'/) Ctvsh I 9.33t8.218.23.92 6 129 E.33 5 1 Q ReSi~ance .
at t0.000ps1(%) Fiber 0 2 5 IO 0 2 Load on Sand (l) ' See Tabie 6.

I 5 see Tabte 7.

' See Table 8.

The data in Tables 8-10 indicates the fibers do not harm crush resistance.
Ie '' Procured proppants with fibers according to the description of Example 2 were 20 prepared Table 12 lists the precured samples of this e.~aznple. The ingredients of the same size and material are the same as in Example 2 unless otherwise indicated.
Varying amounts of different kinds of fiber were prepared to get products with roughened surfaces and/or protruding fibers. Observation of these samples under the microscope indicate that for milled glass fiber, the fibers start to protrude at the fiber Level of I3 to 15%.
Considerable amounts 25 of loose fbers were observed in the carbon filled samples at fiber levels of I4% and above.
Protruding fibers were not observed for milled ceramic fber filled samples because of the very small ceramic fiber size. However, the I4% milled ceramic fiber sample appeared to have a very rough surface.

~9~~~
3~
Table t2 ~! Fiber Fitxr SampleLoading FiberDiameter5ampie NumberOn FiberLrneth(Micron}L.O.I.Observation Sand 77 2 Milled1/16"10 -1% l~to fiber deICCICd on the sand Glass surface.

78 p " 1/16"10 " Very few fbers appeared on thr sand surface.

79 6.~ " 1/16"10 " Few fibers observed on the sand surface.

80 10 " t116"t0 " Some fibers appeared un the sand surface.

81 12 " 1/16"f0 " Some fibers appearzd on the sand surface.

82 13 " 1/16"10 " Whisker-like product with ~ some free ti6ers obtained IO 83 14 " I/I6"to Whisker-fike product with some freer fibers obtained.

84 l~ " II16"IO " Whisker-like product with a Iot oFtree fibers obtained 85 114 " 1116"14 -ZS% No fibs observed on the sand surface.

86 1!2 " U16 10 " No fiber observed on the sand surface.

87 2 " 1/16"10 ~ 1'io fiber obsrrved on the sand surface.

I 5 ' 88 2 " 1116"10 " No fiber observed on the sand surface.

89 Z ~ 1/16"IO No fiber observed on the _ sand surface.

90 p " 1/16"!0 " Few fibers observed on the sand surface:.

Table (continued) Fiber Fiber SampleLoading Fiber DiameterSample ~tumberC?n FibcxLength(VGcron)1_0.1.Obsen~ation Sand 9 t 10 " f/ 10 " Some fibers 16" obxrve d ~
IOgCIhGr tVllh SOfTK LGC

fibers.

j 92 I/4 Vlillcd!0-IS 2-3 --1% No fiber obxned on the CentmicMtcronVicron sand surface.

93 1/2 " " " " No Ether obsewed on the sand surface.

94 2 " " " " No fiber obxned on the sand surface.

95 j ~ " " No fiber observed on the sand swface.

96 ht " " No &ber obsmcd but coated sand siutace appeared ruin.

9~ In ~ " " No fiber vbxrved on the sand surface.

98 !l1 Milled20-25 2-~' -2.5"No fiber obsmed on the eerynicIvyQOrt" sand serctace.

99 2 ~ " " No fitxr observed on the sand stfffau.

I00 j .. .. ~ ~ ~ ~r obsmed, but coated sand surface appearzd roueh 101 2 bLlled2S0 7.3 -ZS Some 5bers obxrved on CarbonIvficronVfiann the sand surface.

1 J I02 5 " " " " Lot of fibers observed on the sand sti<face_ i03 10 " " " " Whisker like product with some &ee Fbers obtained.

104 Z , " -4% Sotrte fiber observed on the sand surface.

IOS 5 " " " " Lot of fibers appeat~d on the sand surface.
Some free fibers mere also prcsettt.

1e 4 A series of samples of fiber-laden curable and precured proppants was tested for 20/40 resin coated sand, at 250°F (121°C), for a flow rate of 2 lbm per ft , between Ohio Sandstone with 2% KCI. The samples employed resin and fibers coated on 20/40 Brady sand_ Sample 106 (Table 13) was curable proppant which employed EX-5150 resin, 1/4% by weight of substrate 1/32 inch long milled glass fibers (as in Table 2), and had a loss on ignition (LOI) of 2.91%. Sample 107 (Table 14) was a curable proppant which employed EX-5150 resin, 2% by weight of substrate 25 microns long ceramic fibers, and had a LOl of 2.97%.
Sample 108 (Table 15) was a precured proppant which employed OFR-9100TM resin manufactured by Borden, Inc./North American Resins, Louisville, Kentucky, 2% by weight of substrate 1/32 inch long milled glass fibers, and had a LOl of 2.42%. Control Sample 18 (Table 16) employed ACFRACTM PR 4000 precured proppant, manufactured by Borden, Inc., North American Resins, Louisville, Kentucky, and had a LOI of 2.32%. Ingredients of this Example having the same composition and size as in Examples 1-3 are the same unless otherwise indicated.
As shown by Fig. 2, both fiber filled curable proppants (Samples 106 and 107) performed significantly better than the curable control samples: ACFRAC CR 4000 and ACFRAC SB Ultra 6000TM. ACFRAC CR 4000 is a proppant of API high quality sand with a thermosetting fully curable phenolic/aldehyde resin with a LOI of about 2-2.6%. ACFRAC SB Ultra 6000 is a proppant of API high quality sand with a thermosetting partially-cured phenolic/aldehyde resin with a LOI of about 2.4-2.8. The resin of ACFRAC SB Ultra 6000 completes its curing during use.
As shown by Tables 15 and 16, fiber filled precured proppant (Sample 108) performed better than ACFRAC PR 4000 at stresses up to 4000 psi and performs about the same as ACFRAC PR 4000 at higher stresses.

Table Conductivity and Permeability of 2 Iblsq ft of Sample - (Curable Resin Coated Sand) Scztveen Ohio Sandstone with 2! KCi Tcmperuure 2~0F, 2 ml/min.

rlotrrs at ClosureConductivityWidthPcrfribbiliry Closure (pst)(rnd-ft)(in) (I?arurs) and Terr~erature 0 2000 4001 0.'~?d214 SO 2000 4b86 0.223252 0 :~ocx~4340 ~ z36 50 4000 3938 0.217218 0 6000 3588 0.216l99 50 6000 2872 0.21 160 ~

0 3000 2508 0.213141 ~0 8000 1570 0.20791 Table Conductivity and Permeability of 2 Iblsq ti of 2U~40 Sample - (Clireble Rsin Coated Sand) Betweat Ohio Sandstone with 2% KCl Temperature 250F, 2 rnUmiti Hours at ClosureConductivityWidthPetmesbility Closu2 (P~) (~-ft) (~) (~~) and T~~

0 2000 4260 0.?23Z'~9 p0 2000 4128 U.22_'~23 0 4000 3737 0.219205 50 4000 3W5 0.218197 0 6000 2899 0.216161 p0 6000 2432 0.213137 0 3000 2105 0.212119 p0 80t?0l4Zi 0.20683 Table h Conductivity and Prrmeabilitv of 2 Ih~sq ft of Sample.108 - (Procured Resin Coated Sand) Between Ohio 5and5tone with 2% KCl Temperature ?50'F.
2 rnl/min.

S Houa at Clo>ZUeConductivityWidthPermeability Closure (pst)(tnd-ft)(in) (Darcies) and Temperature 0 2000 4472 0.224240 i0 2000 4215 0.??3227 1~ 0 4000 3313 0.~?0183 50 4000 3014 0.217167 0 6000 1792 0.210102 50 6t>001275 0.20774 0 8000 849 0.20550 00 - S()DOW2 ~ 33 0.198 Table Conductivity and Permetbiliry of 2 l~sq ft of Samp(e Control (Pttautd Resin Coated Sand) Bawart Ohio Sandstone with 2% KCt Teinprrature Z50F, 2 tnUrnirt 20 Hours at ClosureConductivityWidthPerrrtrabiliry Closure (psi)(ind-ft)(in) (Darzics) and Tetr>paanue 0 2000 4082 0.224219 .0 2000 3918 O.Z3 211 0 4000 3359 0.219184 50 4000 2954 0.215165 0 6000 2002 0.211114 50 6000 1558 0.20890 0 8000 1129 0.20367 - 50 8000 791 0.199:18 Ii x Ie Procured proppants with fibers prepared according to the description of Example 2 were tested for angle of repose against procured proppants prepared without fibers as in Comparative Example 2. Table 17 shows the results of these tests. Samples made according 35 to Comparative Example 2 are listed as "Controls" on Table 17.

Table Nfeasurerrxnt Of The Lubriciry Cfu~r.~c:eriAia Of Fiber Reinforced Procured Proppanes Made of Brady Surd, Precrrrcd Resin' Arrd Milled Ghss Fiber Samplet~Liled Static Glaze Anele Fiber' Avg. Diameterof Repose Fiber % Fiber of the 0 Length Added Traced Circle (inch) (On Sand)(em) f 09 1116 1 p 10.85 30.6 110 1116 14 l0.05 32.7 111 1116 13 (0.60 313 112 1/16 1Z 11.15 29.9 Control- 0 11.60 28.8 PR - - t 1.9 2g 1 ' See Table I
' Sce Erample The results of these tests show the fiber laden proppants have a slightly higher angle 15 of repose. This implies the particles of proppants hold together better when they include fibers. Thus, the fiber laden proppant should have reduced flow back relative to the non-fiber-containing proppant_ While specific embodiments of the composition and method aspects of the invention have been shown and described, it should be apparent that many modifications can be made 20 thereto without departing from the spirit and scope of the invention.
Accordingly, the invention is not limited by the foregoing description, but is only limited by the scope of the claims appended thereto.

Claims (49)

1. ~A proppant particle comprising:
a particulate substrate; and a coating comprising resin and fibrous material, wherein the fibrous material is embedded in the coating to be dispersed throughout the coating.

2. ~The proppant particle of claim 1, wherein the particulate substrate is selected from the group consisting of sand particles, naturally occurring mineral fibers, ceramic particles, glass beads and mixtures thereof.

3. ~The proppant particle of claim 1, wherein the particulate substrate has a particle size in the range of USA Standard Testing screen numbers from about 8 to about 100.

4. ~The proppant particle of claim 1, wherein the fibrous material is 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 about 200°F.

5. ~The proppant particle of claim 1, wherein the coating comprises about 0.1 to about 15% fibrous material based on particulate substrate weight.

6. ~The proppant particle of claim 1, wherein the coating comprises about 0.1 to about 3% fibrous material based on particulate substrate weight.

7. ~The proppant particle of claim 1, wherein the fibrous material has length from about 6 microns to about 3200 microns and a length to aspect ratio from about 5 to about 175.

8. ~The proppant particle of claim 7, wherein the fibrous material has a round, oval, or rectangular cross-section transverse to the longitudinal axis of the fibrous material.

9. ~The proppant particle of claim 1, wherein the resin is present in an amount of about 0.1 to about 10 weight percent based on substrate weight.

10. ~The proppant particle of claim 1, wherein the resin is present in an amount of about 0.4 to about 6 weight percent based on substrate weight.

11. ~The proppant particle of claim 1, wherein the resin comprises a member selected from the group consisting of a novolac polymer, a resole polymer and mixtures thereof.

12. ~The proppant particle of claim 11, wherein the coating comprises a high ortho resin, hexamethylenetetramine, a silane adhesion promoter, a silicone lubricant, a wetting agent and a surfactant.

13. ~The proppant particle of claim 1, wherein the resin comprises a member of the group consisting of a phenolic/furan resin, a furan resin, and mixtures thereof.

14. ~The proppant particle of claim 1, wherein the resin comprises a bisphenolic-aldehyde novolac polymer.

15. The proppant particle of claim 1, wherein the resin comprises a cured resin.

16. The proppant particle of claim 1, wherein the resin comprises a curable resin.

17. The proppant particle of claim 1, wherein the fibrous material is dispersed within the resin.

18. The proppant particle of claim 1, wherein the fibrous material is completely within the resin.

19. The proppant particle of claim 1, wherein the fibrous material is partially embedded in the resin so as to extend from the resin.

20. A method of treating a hydraulically induced fracture in a subterranean formation surrounding a wellbore comprising introducing into the fracture proppant particles of claim 1.

21. The method of treating of claim 20, wherein the particulate substrate is selected from the group consisting of sand, ceramic particles, glass beads and mixtures thereof.

22. The method of treating of claim 20, wherein the particulate substrate has a particle size in the range of USA Standard Testing screen numbers from about 8 to about 100.

23. The method of treating of claim 20, wherein the fibrous material is 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 about 200°F.

24. The method of treating of claim 20, wherein the coating comprises about 0.1 to about 15% fibrous material based on particulate substrate weight.

25. The method of treating of claim 20, wherein the fibrous material has a length from about 6 microns to about 3200 microns and a length to aspect ratio from about 5 to about 175.

26. The method of treating of claim 20, wherein the resin is present in an amount of about 0.1 to about 10 weight percent based on substrate weight.

27. The method of treating of claim 20, wherein the resin comprises a member selected from the group consisting of a novolac polymer, a resole polymer and mixtures thereof.

28. The method of treating of claim 20, wherein the resin comprises a bisphenolic-aldehyde novolac polymer.

29. The method of treating of claim 20, wherein the fibrous material is dispersed within the resin.

30. The method of treating of claim 20, wherein the fibrous material is completely within the resin.

31. The method of treating of claim 20, wherein the fibrous material is partially embedded in the resin so as to extend from the resin.

32. ~A method of treating a subterranean formation having a wellbore to prevent particulates from the subterranean formation from flowing back into surface equipment comprising introducing into the wellbore particles of claim 1, comprising a particulate substrate and a coating, the coating comprising resin and fibrous material.

33. ~The proppant particle of claim 1, wherein the particle has an angle of repose of 29.9 ° to 33 °.

34. ~The proppant particle of claim 1, wherein the particle has an angle of repose of 29.9 ° to 32.7 °.

35. ~The proppant particle of claim 1, wherein the particle consists essentially of the particulate substrate and the coating comprising resin and fibrous material, the coating being on the outer surface of the substrate.

36. ~The proppant particle of claim 1, wherein the coating is on the outer surface of the substrate.

37. ~The proppant particle of claim 1, wherein the fibrous material is embedded in the coating.

38. ~The proppant particle of claim 1, wherein the fibrous material is embedded dispersed throughout the coating.

39. ~A proppant particle comprising:
a particulate substrate, and a coating comprising resin and fibrous material, wherein the coating consists essentially of a single layer.

40. ~The proppant particle of claim 1, wherein the proppant comprises at most one coating and said coating consists essentially of a single layer.

41. ~A method of making a proppant particle of claim 1 comprising the steps of:
providing a particulate substrate, a resin, and a fibrous material;
combining, the particulate substrate, the resin, and the fibrous material wherein the resin coat coats the substrate with a coating of the resin and fibrous material; and subsequent to the combining, solidifying the resin.

42. ~The method of claim 41, wherein the particulate substrate is combined with the fibrous material to form a mixture and then the resin is added to the mixture.

43. ~The method of claim 41, wherein the resin is coated onto the particulate substrate and then the fibrous material is added to the resin coated particulate substrate.

44. ~The method of claim 41, wherein the resin is added to sand heated to a temperature sufficient to melt the resin and form a mixture, and then a crosslinking agent is added to the mixture.

45. ~The method of claim 41, wherein the resin is mixed with a liquid to form a resin-containing mixture and the resin-containing mixture is mixed with the particulate substrate and a crosslinking agent to form a coating mixture, and then the liquid is removed from the coating mixture.

46. ~The method of claim 45, wherein the liquid is a solvent and a solution is formed by mixing the resin and the solvent such that the resin-containing mixture is a resin-containing solution, the resin-containing solution is mixed with the particulate substrate and the crosslinking agent to form the coating mixture, and then the solvent is removed from the coating mixture.

47. ~A method of treating a hydraulically induced fracture in a subterranean formation surrounding a wellbore comprising introducing into the fracture proppant particles of claim 39.

48. ~A method of treating a subterranean formation having a wellbore to prevent particulates from the subterranean formation from flowing back into surface equipment comprising introducing into the wellbore particles of claim 37, comprising a particulate substrate and a coating, the coating comprising resin and fibrous material.

49. ~A method of making a proppant particle of claim 37, comprising the steps of:
providing a particulate substrate, a resin, and a fibrous material;
combining, the particulate substrate, the resin, and the fibrous material wherein the resin coat coats the substrate with a coating of the resin and fibrous material; and subsequent to the combining, solidifying the resin.