CA1330257C - Consolidation of partially cured resin coated particulate material - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A proppant composed of particulate material coated with a solid curable furan-phenolic or phenolic resin that can consolidate and cure at temperatures as low as about 60°F and as high as about 450°F. An acidic catalyst in a solvent system is used to cure the resin.

Description

` - 1 33~257 BAC~GROUND OF THE INVENTION
1. FIELD OF THB INVENTION
The present invention relates to a process for preparing particulate matter coated with a curable furan- ;
phenolic resin and utilizing the particulate material as a proppant or for sand control which is consolidated and cured underground.

2. DESCRIPTIO~ OF T~E PRIOR ART :~
Hydraulic fracturing is a technique $o-r stimulating ~-the production of subterranean formations. The technique normally involves (l) injecting a viscous llquid through a well and into a formation at a sufficient rate and pressure ,, - .. ...
to overcome the earth stresses and form a crack or fracture in the formation; and (2) placing a particulate material, referred to as a "propping agent" or "peoppant" in the formation to maintain the fracture in a propped condition when the injection pressure is released. ;~
The propped fracture thus provides a highly conductive channel in the formation. The degree of stimulation afforded by the hyaraulic fractu~e treatment i~
~ .
largely dependent upon the permeability and width of the propped fracture.
In hydraulic fracturing applications where proppants are used, proppant flow back can be a problem when the well , : .

:::
~, ' . ' 1 33025~
is put into operation. Some of the proppant can be transported out of the fractured zones and into the well ; -stem by fluids produced from the well.
This backflow is undesirable and has been controlled -S to an extent in some instances by the use of a proppant that -... . ,: . ~, ~
has been coated with a solid curable resin which will consolidate and cure underground. Phenolic resin coated proppants have been commercially available for some time and are used for thi~ purpose.
These curable phenolic resin coated proppants ~
work best in environments where temperatures are ~ -sufficiently high to consolidate and cure the phenolic resins. However, at underground temperatures below about 130F, these curable phenolic resin coated proppants are not -~ 1S useful because they do not consolidate and cure adequately ;~; to obtain sufficient compressive strength to prevent ~ flowback.
; ~ . .
Many shallow wells often have underground ~
:: ,.. ,.. ~,. .
temperatures of less than about 130F, and in some cases of ;-;~ 20 less than about 100F. At the present time there are no ~ ~;
commercially available curable free-flowing resin coated proppants which satisfactorily cure at these temperatures.
Curable free-flowing phenolic resin coated ~. . . . .
particulate material can also be used for sand :, :, . , . .. , . ~ .
'~

~ `

control. Wells that are placed in formations that contain poorly consolidated sand can produce sand along with the fluid. This is undesirable for a number of reasons. This ;~
3and production can be controlled by placing curable 5 phen~ilic resin coated particulate material around the well -~
stem, then curing it to form a consolidated sand filter to prevent loose formation sand or other debris from flowing into the well stem. As in fracturing the problem is that the phenolic resin coated sands do not operate satisfactorily at about below 130F.
An attempt to deal with thls sand control problem hais been with the use of liquid curable resins. In this approach, particles, usually coarse sand, are placed around the well bore and a liquid resin such as an epoxy or furan resin is pumped theough the sand in an effort to coat the liquid resin onto the sand. This is followed by contacting the liquid resin coated proppant with an overflush fluid containing a suitable catalyst, which is pumped into the proppant and retained there until the resin cures and consolidates the proppant.
In many cases it is preferable to utilize a proppant provided with a solid curable resin coating which can ~ ~
consolidate and cure at temperatures in the range of 60 to ~;
about 130F, rather than a liquid resin. The disadvantages of using liquid resins in these conditions is that it is difficult to control the amount of resin that coats the .

proppant. If too little resin is usedr flowback could occur If too much resin is used, the permeability could be too low. In additionr the liquid resin could enter the formation and seal it off. ~here is no way to as6ure that 5 the liquid resin completely and uniformly coats and bonds the sand around the well bore.
The patent literature dealing with this technology includes U.S. Patent 3r625r287 to Young which discloses the use of specific silane or organosilicon compounds added to a 10 liquid resin system can be used to conRolidate loose or incompetent ~-. - ~ :
sands to produce a stronger, stable product. The resin systems include furan resinsr phenolic resins, urea -;
formaldehyde resins, and epoxy resins.
U.S. Patent 3r419~073 to Brooks discloses the use of normal hexanol or a similar aliphatic alcohol containing from 5 to 10 carbon atoms, injected into an unconsolidated formation. The well is then shut for about one-half to about 120 hours, and a resin solution or mixture of resinous materials is thereafter injected, resulting in improved 20 strength and reductlon of permeability losses. Resins ~i useful in this process include epoxy resins, furfuryl ; -alcohol resins and urea formaldehyde resins.
U.S. Patent 3~4041735 to Young et al discloses a method for consolidating loose solids introduced into a well 2S by dispersing a predetermined amount of resin or consolidating fluid in an oil base liquid hydrocarbon.
' ' :~ ': ' ~ ~ 330257 : :
Sub~equently, a quantity of particulate material is introduced into the resin-oil diGpersion thereby coating the -~
solids with resin~ The oil-resin-solids mixture i8 then introduced through a well bore to a fracturing formation, 5 with injection continuing until a sand out or pack out -~
occurs and the desired amount of resin coated iqolids i~
deposited in the well bore. Excess solids are removed by reverse circulation, U.S. Patent 4,073,343 to l~arnsberger disclose~ a ;
10 method for treating an incompetent sand containing -underground formation by introducing specific amounts of ~-~
furfuryl alcohol, surfactant, water. silane coupling agent, catalyst and aromatic distillate in the formation sand to be consolidated.
U.S. Patent 3,393,736 to Goodwin discloses a method for controlling movement of sand in a well by pumping particulate matter coated with a resin-forming liquid or semi-liquid material, into the well. The liquid or semi-liquid resinous material also contains a catalyst which is capable of curing the resin. Suitable resins include furfuryl alcohol resins, urea formaldehyde resins, epoxy resins, phenol-formaldehyde resins and alkyd resins.
U.S. Patent 4,443,347 to Underdown et al discloses a method for peopplng a feactuee in a subtereanean well ;`' ~

1330257 ~; ~

formation which comprlses injecting a proppant composed of individual substrate particles having a thermoset coating.
The coating produce~ a charge wherein the conductivity ratio throughout a given closure stress range is greater than that of a charge of uncoated particles having substantially the same particle size distribution.
U.S. Patent 4,413,931 to McDonald discloses the treatment of subterranean geological formations such as those surrounding oil well bore holes by placing particulate lo material in or adjacent to ~he ormation. The particulate material is coated with a two-step, curable, novolac-type ~;
phenolic resin, which is thereafter cured in ~itu to bond the particulate matter together. In order to achieve the desired compressive strength, the resin must have an insolubility parameter of greater than about 1. This type of resin is not useful below about 130~.
U.S. Patent 4,336,842 to Graham et al, discloses curing a packed resole resin coated sand in a solution of a resin softening agent comprising alcohols such as 20 isopropanol, methanol or ethanol and nonionic surfactants. ~
It has been found that this resin system becomes tacky, but i ~ -~ .
does not satisfactorily cure at low temperatures. ~
. . .

SUMM~RY OF THE INVENTION
The present invention relates to a proppant composed of particulate material coated with a solid curable resin that can consolidate and cure at tempe~atures as low as about 60F and a~ high as about 450F. A process for preparing particulate material coated with the solid curable resin coating is also disclosed, and also a process for consolidating and curing particulate material coated with the resin.
:~ 10 DESCRIPTION OF T~E PREFERRED EMBODIMENTS
` ~ In accordance with the present invention, a proppant material coated with a solid curable coating of a furan~
phenolic resin or phenolic resin is consolidated with an acidic catalyst curing agent dissolved in a solvent system.
The solvent ~ystem is capable of softening the solid resin to the point where the resin can form bonds between and consolidate the individual proppant particles. The acidic ~` catalyst dissolved in the solvent system is capable of curing the resin in about 24 hours or less.
The proppant material can be any of the solid particulate materials normally used as propping agents.
Such materials include sand, sintered bauxite, zircon ceramic materials and glass beads. The proppant materials should be resistant to melting at temperatures below about ~5 450F. The proppant particles are preferably of a relatively uniform size. Particle sizes commonly employed vary from about lO and 100 mesh, U.S. Standard Screen size. -~` 1 330257 Sands which conform with the ~merican Petroleum Institute specifications Eor fracturing and/or sand control sands are particularly preferred as proppant materials.
The phenolic resins used in the practice of this invention are thermosetting resins made from phenol or substituted phenols and formaldehyde or other aldehydes.
The preferred substituted phenols are where either the two ortho, one ortho and the para, or the two ortho and the para po~itions are unsubstituted. In general, the phenols that can be used are those which are suitable for making phenolic resins. Phenol and formaldehyde are preferred materials. ~;
; Many of the phenolic resins suitable for use are called 'resolesll and can be either in a liquid or sOlia state.
A llresole" is the resin product of the partial ; 15 condensation of a phenol with an aldehyde in such proportions that the partial condensate is capable of ~-further condensation to an infusible or thermoset condition.
A "novolac" is the resin product of the substantially complete condensation of a phenol with an aldehyde in such proportions that condensation is not capable of proceeding to form an infusible product. The present invention also contemplates the use of resole~
novolac resin combinations that are capable of further -~
condensation to an infusible or thermoset condition.
The furan resins used in the practice of this invention are thermosetting resins made by reacting furfuryl alcohol with an aldehyde such as formaldehyde, or by the self-polymerization of furfuryl alcohol, or a combination of reacting furfuryl alcohol with formaldehyde and ~elf-polymerization.
Furfural can also be used in place of furfuryl ~ -alcohol. A terpolymer of phenol, furfuryl alcohol and formaldehyde can also be used in place of phenolic and furan resins.
The preferred curable resin used to coat the ~ 10 proppant material is a curable furfuryl alcohol-phenol--~ formaldehyde resin, especially that disclosed in Canadian patent No. 1,256,242 entitled "Phenol-Formaldehyde-Furfuryl j~ Alcohol Resins".

ccordingly, liquid phenol-formaldehyde-Eurfuryl lS alcohol resin is mixed with the proppant material at a -;~
temperature of about 225 to 450F until the resin partially cures to a state where it would solidify at room ;`~
temperature. The amount of time required to accomplish this depends on the sand temperature. Higher sana temperatures could shorten the time. ~ "working" length of time is needed jto coat the liquid resin on the sand and cure it to : :
the point where it would be a solid at room temperature.
Depending cn the mixing equipment, this time can range from about 30 seconds-to about 3 minutes or longer.

~ 9 ','~

~ 1 33~57 Water is then added to cool the mix and solidi~y the resin. The amount o resin can vary from about 1 to 8~ by weight o the particulate material. The amount of water i5 :
determined empirically. As a general rule suficient water is added to cool the resin-proppant mix to about 140 to 180F. When the mix i8 cooled to this temperature range in the mixer, it can break down to become a free-flowing product or it may be discharged from the mixer before it is free flowing as long as subsequent handling and cooling operations produce a free-flowing product. The important concern is that at ambient temperature the coated proppant be a free-flowing product composed of individual particles coated with a solid thermosetting resin.
Although it is possible to practice this invention without the use of a catalyst, it is preferred to use a curing catalyst which is sufficiently non-volatile at the operating temperatures, to accelerate the cure o~ the resin.
The curing catalyst can be incorporated into or premixed with the resin or added to the mixer after the ~
20 resin has been added and coated on the proppant. The ;~-.. ~
preferred method is to add it to the mixer after the resin ~-has been coated. As mixing is continued, the resin cures on ~ -the particulate matter to produce a free flowing product comprised of individual particles coated with the partially -cured resin. The advantage of the catalyst iB that its use ~` ` I 330257 can result in a lower coating temperature and/or faster processing time.
The catalyst can be used as is or dissolved in water or other suitable solvent system depending on the catalyst.
A strong acid catalyst must be diluted with water to prevent localized reaction of the catalyst with the resin before the catalyst has had a chance to mix with the resin. Solid catalysts that do not melt below the mixing temperature are preferably used in aqueous solution.
lo Specific catalysts include acids with a pKa of about 4.0 or lower, such as phosphoric, sulfuric, nitric, benzenesulfonic, toluenesulfonic, xylenesulfonic, sulfamic, oxalic, salicylic acid, and the like; water soluble multivalent metal ion salts such as the nitrates or ~15 chlorides of metals including Zn, Pb, Ca, Cu, Sn, Al, Fe, Mn, Mg, Cd and Co: and a~monia or amine salts of acids with a pRa of about 4.0 or lower, wherein the salts include the nitrates, chlorides, sulfates, fluorides, and the like.
The preferred class of catalyst is the ammonia salt~
of acids and the preferred catalyst is aqueous ammonium nitrate.
The amount of catalyst used can vary widely depending on the type of catalyst used, type of resin used, ~ ~-,, ., ~.

V .~l;' : 1 330257 mixing temperature and type of mlxer. In general, the amount of catalyst solids can range from about 0.2% to 10% ,,' based on the weight of the resin.
It is also desirable to include a silane additive to ', ensure good bonding between the resin and the particulate matter. The use of organofunctional silanes as coupling agents to improve interfacial organic-inorganic adhesion is especially preferred. These organofunctional silanes are characterized by the following formula:
~10 Rl-Si-(OR) where Rl represents a reactive organic function and OR
represents a readily labile akoxy group such as OCH3 or OC2H5.
Particularly useful for coupling phenolic or furan resins to silica are the amino functional silanes of which Union ' ' ' lS Carbide A1100 (gamma aminopropyltriethoxy) is an example.
The silane can be premixed with the resin or added to the '~
mixer.
It is desirable to add a lubricant to the sand ' ~' ,', mix after the cooling water has been added and before the , ~ , '' 20 mix breaks up,into free-flowing particles. The lubricant is ,;, ,~;`' ' preferably one that is liquid at the mixing temperature and `~
has a sufficiently high boiling point so that it is not lost , ';~
during the mixing process. Suitable lubricants include , ''~
liquid silicone such as Dow Corning Silicone 200, mineral ,~
'~ :' '~

12 , , ~ , oil, paraffin wax, petrolatum, and the like. The amount of lubricant can vary from about 0.03~ to about 0.5% by weight based upon the weight of the proppant material.
In preparing the proppant material coated with the curable phenol-ormaldehyde~furfuryl alcohol resin, the particulate material can be preliminarily coated with a cured resin that include~ furan-pheno]Lic resins, furan resins, phenolic resin~ or other type~ of re~ins such as epoxy resins. This can be desirable in situations where the lo proppant can benefit from the extra strength that results from this cured coating. The resin in the cured coating can vary from about 1 to 8% by weight of the proppant. The resin in the curable coating can vary from about 1 to 8% by weight o the proppant.
The proppant material coated with the curable phenol-formaldehyde-furfuryl alcohol resin can now be used : ~ .
as a proppant in a well fracture zone or for sand control.
It can be suitably dispensed therein and overflushed with a ~ -solvent system such as an acetone-water solution, which contains the acidic catalyst used to complete the cure of the curable resin, dissolved therein.
Any solvent system that is capable of softening the resin to the extent that the resin will become tacky and form bonds between the proppant particles and that is also , ~, ~' .

1 ~30257 capable of dissolving the acid used a~ the curing agent, is ~-suitable. The solvent3 used in this system include alcohols such as methanol, ethanol, propanol, phenol, and the like;
ketones such as acetone, methyl ethyl ketone, and the like;
5 esters such as dimethyl adipate, dimethyl succinate, amyl ~ ;~
acetate, butyl acetate, glycol ether acetates and the like, and other equivalent solvents such as the glycol etheræ, diacetone alcohol, tetrahydrofuran, dimethylformamide, and the like.
The solvent systems generally contain a solvent, water and an acid. However, it is not necessary that water be present in all solvent systems nor is it necessary that a solvent be present if the acid catalyst can also function as -the solvent. In this case, water may or may not be present.
: 15 The acid could comprise about 5 to 100% by weight of the ;
consolidating and curing system fluid. The amount of catalyst is not based directly on the amount of resin since the acid catalyst is used in an overflush. For example, a 3~ resin coating or a 4% coating could use the same overflush fluid.
Suitable acid catalysts include sulfuric acid, ;`~ ~;
benzene sulfonic acid, methane sulfonic acid, trichloroacetic acid, hydrochloric acid, hydrofluoric acid, ferric chloride, toluene sulfonic acid, chlorobenzene sulfonic, nitric acid, perchloric acid, and other equivalent ~ .

~--- 1 330257 acids. The prePerred systems aee acetone, sulfuric acid and water, or acetone, methanol, 8ulfuric acid and water.
The examples which follow serve to illustrate the present invention, and all part~ and percentages are by weight unless otherwise indicated, and all screen mesh sizes are U.S. Standard Screen sizes.
EXaMPLE 1 Into a 5 liter three necked flask equipped with a ~tirrer, theLmometer and reflux condenser were charged 1000 grams of phenol, llS0 grams of 50% formalin and 48 grams of 25% zinc acetate solution in water. The batch reached a maximum temperature of 99C and was reacted for 4 hours and 15 minutes. During this reaction the batch temperature ;~
gradually fell from 99C to 96C. At this time the batch ~ -~
~. ::
was cooled with cooling water and a sample checked for formaldehyde content which was 9.0% formaldehyde -corresponding to 377 grams of formaldehyde being reacted with the phenol. The batch was then vacuum dehydrated at about 50C to remove 558 grams of distillate. 1015 grams of furfuryl alcohol was then added to the flask and the reaction continued for 5 hours and 40 minutes at about 97C.
The batch was then cooled to give a product with the following properties: Viscosity: 1,650 centipoise at 25C; ~ -unreacted phenol: 6.7% unreacted furfuryl alcohol: ll.O~i.

EXAMPL~ 2 -Into a 3 quart mixing bowl was ~laced 1 kilogram of 20/40 mesh silica sand. The sand was stirred with a Hobart C-100 mixer and heated with a gas flame to 383F. 14 grams of resin from Example 1 was added and mixed for 20 seconds.
0.3 grams of AllO0 silane (Union Carbide Corporation) was added. Mixing was continued and at 40 second~ of total mixing time 0.5 milliliters of a 25% water solution of ammonium nitrate added. This catalyzed the cure of the resin and by 70 seconds of mixing time the sand had "broken down" to a free flowing mix of individual sand grains coated with cured resin. ~t 100 seconds of mixing time 45 grams o~
the aforesaid Example 1 resin was added to the sand as mixing continued. At 145 seconds about 0.15 milliliters of 25~ ammonium nitrate solution was added. ~t 130 seconds of : :
mixing time the sand was a tough dough-like mass and 45 milliliters of cooling water was added. ~t about 250 seconds of mixing time about 0.5 grams of L-45 silicone fluid (Union Carbide Corporationj was added to the mix. By ~ -300 seconds the sand had "broken down" to a free flowing mix. Mixing was continued to 380 seconds and stopped. ~t this time the sand temperature was 155F and the sand removed from the bowI and allowed to cool to room temperature. :
':, *Trade-mark '~ ^ 1 330257 The final product consisted o~ individually coated particles having a thin coating o cured resin adjacent to the sand grain su~face and over this cured coating was a coating of curable resin. The fact that the final coating 5 wa~ curable was evidenced when the sand was placed in a heated mold used to make 1/4" x 1" dogbone tensile strength specimens which were broken hot in the heated mold to determine the hot tensile strength of curable coated foundry sands. The coated sand fused and cured in 3 minutes at 450F to produce a specimen of 340 psi hot tensile strength.
E~MPL~ 3 In the same mixing equipment used in Example 1, 1 kilogram of 20/40 mesh sand was heated to 385F. 60 grams of Example 1 resin was added and mixed for 15 seconds at which time 0.3 grams of AllOO silane was added. ~ixing was continued and at 33 seconds of mixing time about 0.25 milliliters of a 50% ammonium nitrate solution was added.
At 130 seconds 40 milliliters of water was added. At 165 seconds 1 gram of L-45 silicone fluid was addedO At 210 seconds the mix broke down to a free flowing product. At-300 seconds mixing was stopped and the coated sand removed from the bowl. The sand temperature was 164F at 300 seconds mixing time and was allowed to cool to room temperatureO The final mix was a free flowing product ''".'.''' ~
~: -``'-,'''" ~
17 ~

comprised oE individual sand grains coated with a curable resin coating. A 3 minute, 450F hot tensile strength test was run as described in Example 2 and produced a specimen of -~
280 psi.
~Mpr~E 4 In the same mixing equipment used in Exa~ple 2, 1 kilogram of 20/40 mesh said was heated to 385F. 15 grams *
o EX5150 (Acme Resin Corp.) novolac flake resin was added and mixed for 30 seconds at which time 0.3 grams of AllO0 ~ 10 silane was added. Mixing was continued for an additional 20 ;~ seconds and 33 grams of EX9000 (Acme ~esin Corp.) resole was added to the sand. At 105 seconds of total mixing time, 30 milliliters of water was added to the mix. At 210 seconds the s~nd was removed from the bowl. The final product was a -lS free flowing product comprised of individual sand grains ; ~ coated with a curable p~lenolic resin coating.

In the same mixing equipment used in Example 2, 1 ~;
kilogram of 20/40 mesh sand was heated to 448F. 60 grams of Example 1 resin was mixed with 0.3 grams of AllO0 silane, ~` àdded to the sand and mixed for 80 seconds. At this time 65 milliliters of water was added followed by 1 gram of L-45 silicone at 100 seconds of mixing time. At 250 seconds of mixing time the coated sand was at a temperature of 155F ~ j : : :"
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1 330257 ~ ~
and was discharged from the bowl as a free flowing product consisting of individual sand grains coated with a curable resin coating. A 3 minute, 450F hot tensile strength test ; ~ ~
was run as described in Example 2 and produced a specimen o ~ -50 psi.
CONSOLIDATION OF CURABhE CQATE~ SAN~S
The curable coated sands of E~amples 2, 3, 4 'I~ 'S~.
and 5 were tested or their ability to bond, cure and consolidate in a consolidation fluid by the follo~ing method. A 4 inch by 1 inch inside diameter plastic test tube wa~ filled to about l/2 inch from the top with the coated sand. The consolidation fluid was added in a manner to aisplace all the air in the tube and wet and cover the coated sand. The tubes were stoppered and then placed in a .
40C oven for about 24 hours to cure and consolidate the ~; sand. The consolidated sand specimen was then removed from the tube and cut to a length of 2 inches to provide a testing specimen flat on both ends. The specimen was tested for the amount o~ compression strength needed to break the 20~ specimen, and the results are tabulated in Table I as follows~
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Claims (9)

1. In a method for propping a fracture or controlling sand in a subterranean formation comprising placing in said fracture particulate material coated with a solid curable resin and then curing said curable resin, wherein the improvement comprises using particulate material coated with a thermosetting resin, selected from furan-phenolic resin and phenolic resin, capable of curing with an acid catalyst from about 60 to 130°F and then curing said thermosetting resin by contacting it with an acidic catalyst dissolved in a solvent system capable of softening the resin.

2. The method of claim 1, wherein said thermosetting resin is selected from the group consisting of resoles and resole/novolac mixtures.

3. The method of claim 1, wherein said thermosetting resin is a furfuryl alcohol-phenol-formaldehyde resin, or furan/phenolic mixture.

4. The method of claim 1, wherein said curable resin cures in about 24 hours or less.

5. The method of claim 1, wherein said solvent system comprises a solvent selected from the group consisting of alcohols, ketones, esters, ethers and amides.

6. The method of claim 1, wherein said solvent system comprises acetone, sulfuric acid and water.

7. The method of claim 1, wherein said solvent system comprises methyl ethyl ketone, hydrochloric acid and water.

8. The method of claim 1, wherein said solvent system also includes methanol.

9. The method of claim 1, wherein said acidic catalyst is selected from the group consisting of benzene sulfonic acid, sulfuric acid, methane sulfonic acid, trichloroacetic acid, hydrochloric acid, hydrofluoric acid, ferric chloride, toluene sulfonic acid, chlorobenzene sulfonic acid, nitric acid and perchloric acid.