Note: Descriptions are shown in the official language in which they were submitted.
PROPPANT WITH COMPOSITE COATING
FIELD OF INVENTION
[0001] The invention relates to a composition and method for the production
of
proppants having a coating that exhibits enhanced conductivity under medium
and high
pressure, downhole, fractured strata conditions.
BACKGROUND OF THE INVENTION
[0002] Coated proppants are often used in hydraulic well fracturing to
increase
production rate of the well. The commercial "standard" coatings are typically
a form of
phenolic thermoset coating. For high temperature wells, such as those with a
bottom hole
temperature above about 200 F (93 C), precured phenolic coatings are often
used due to
their high load-bearing properties. The high crack closure stresses are
usually above 6,000
psi, and often above 10,000 psi, so the proppant must resist such forces in
order to keep the
fracture cracks open and maintain fracture conductivity.
[0003] In practice, however, a variety of factors can adversely affect the
performance
of phenolic proppant coatings. The most important of these is premature curing
of the
partially cured phenolic resin in the coating due to exposure to high
temperatures before the
fractured strata has closed to the point that it forces particle to particle
contact. Even the
elevated, above-ground, temperatures found on loading docks and in shipping
containers can
be enough to effect curing of the coating long before it is desirable.
[0004] Recently, it has been discovered that cured, commercially acceptable,
coatings can be
applied to proppants using the polyurethane or polyurea reaction products of
polyols and
isocyanates. The details of these processes are disclosed in co-pending US
patent application
serial nos. 13/099,893 (entitled "Coated and Cured Proppants" and published as
U.S.
Application Publication No. 20120279703 on November 8, 2012); 13/188,530
(entitled
"Coated and Cured Proppants" and published as U.S. Application Publication No.
20120283153 on November 8,2012); 13/626,055 (entitled "Coated and Cured
Proppants" and
published as U.S. Application Publication No. 20130065800 on March 14, 2013);
13/224,726
(entitled "Dual Function Proppants" and published as U.S. Application
Publication No.
20130056204 on March 7, 2013); and 13/355,969 (entitled "Manufacture of
Polymer Coated
Proppants" and published as U.S. Application Publication No. 20130186624 on
July 25,
2013). Such polyurethane and polyurea-based proppant coatings are economically
and
environmentally desirable for a number of reasons. Importantly, each acts like
a fully cured
coating for purposes of handling, shipping and introduction into a fractured
field yet exhibit
the inherent ability to form interparticle bonds under downhole temperatures
and pressures
1
Date Recue/Date Received 2021-09-16
for enhanced conductivity and to minimize proppant flowback after the well is
put into
production. Commercially available proppants that use such coatings are
available under the
designations PEARL and GARNET from Preferred Sands, Inc. of Radnor, PA.
[0005] See also Tanguay et al. U.S. Application Publication No. 20110297383
for
high temperature proppant coatings made of a polycarbodiimide coating on sand
and
Tanguay et al. U.S. Application Publication No. 20120018162, which relates to
a polyamide
imide proppant coating for high temperature applications.
[0006] Despite the potential benefits of interparticle bonding seen in the
polyurethane
and polyurea proppant coatings, there exists a continuing need in the industry
for a proppant
coating that exhibits a higher crush strength and resistance to crack closure
stresses of 10,000
psi or more. The deformation of proppant coatings under the very high crack
closure stresses
that are found in high temperature/high pressure wells can be sufficient to
alter pore passages
and reduce the conductivity of the fractured strata.
[0007] It would also be even more desirable if proppants suitable for high
temperature/high pressure strata would also exhibit some level of
interparticle bond strength
without the use or introduction of bond formation or polymer softening agents
into the
fractured strata. Such interparticle bonding would provide a further effect
for retaining the
coated proppants within the fractured strata despite the outflow of fluids and
gases that can
dislodge the proppant particulates and flush them from the strata.
[0008] Others have considered the addition of various materials into the
coating on a
proppant core to address one or more issues. For example, US Patent No.
4,493,875 relates to
a composite proppant with a sand core and hollow, glass microspheres in an
"adhesive" that
bonds the microspheres to the core. A resole phenol/formaldehyde resin is used
in the
examples as a coating on the sand core of the proppant.
[0009] US Patent Nos. 5,422,183 and 5,597,784 teaches a proppant having a
substantially cured inner resin coating, an outer resin coating, and a
reinforcing agent
interspersed at the inner coating/outer coating boundary, which is used in the
propping of a
fracture in a subterranean formation. The core of the proppant is said to be
glass beads;
various organic materials such as walnut shells, pecan shells, and synthetic
polymers; or
metallic particulates such as steel or aluminum pellets.
[00010] US Patent No. 6,406,789 describes a proppant particle made with a
resin and
filler material. The disclosed resins include epoxy, phenolic, 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; or a curable furan/phenolic resin
system curable in
the presence of a strong acid to form a curable resin. The finely divided
minerals that can be
2
Date Recue/Date Received 2021-09-16
included in the resin include silica (quartz sand), alumina, mica, meta-
silicate, calcium
silicate, calcine, kaolin, talc, zirconia, boron and glass. Microcrystalline
silica is noted as
especially preferred.
[00011] US Patent No. 6,528,157 discloses a resin-coated proppant that
contains fibers
where at least a portion of the fibers protrude from the resin coating to
interlock with fibers of
other proppant particulates.
[00012] US Patent No. 7,490,667 describes a proppant having a water-soluble
external
coating on the proppant particle substrate and a microparticulate reinforcing
and spacing
agent at least partially embedded in the water-soluble external coating in a
manner such that
the microparticulate reinforcing agent is substantially released from the
proppant particle
substrate when the water-soluble coating dissolves or degrades.
[00013] US Patent No. 7,803,742 pertains to thermoset nanocomposite
particulates
made with carbon black, fumed silica, fumed alumina, carbon nanotubes, carbon
nanofibers,
cellulosic nanofibers, fly ash, polyhedral oligomeric silsesquioxanes, or
mixtures thereof.
[00014] US Patent Nos. 8,006,754 and 8,006,755 describe proppants coated by
a
material whose electromagnetic properties change at a detectable level under a
mechanical
stress such as the closure stress of a fracture. A preferred proppant is
described as a thermoset
nanocomposite particulate substrate where the matrix material comprises a
terpolymer of
styrene, ethylvinylbenzene and divinylbenzene, and carbon black particulates
possessing a
length that is less than 0.5 microns in at least one principal axis direction
incorporated as a
nanofiller. Over the proppant is a coating that comprises a PZT alloy
manifesting a strong
piezoelectric effect or Terfenol-D manifesting giant magnetostrictive behavior
to provide the
ability to track in a downhole environment.
[00015] US Patent No. 8,298,667 describes the use of two ceramic layers
that can
contain a reinforcing agent of carbon black, fiberglass, carbon fibers,
ceramic whiskers,
ceramic particulates, metallic particulates, or any combination thereof.
[00016] Published US Patent Application 2012/0277130 describes a proppant
made
from a ceramic matrix with inorganic reinforcing fibers such as wollastonite,
wollastonite
concentrate, synthetic wollastonite, beta-wollastonite, enstatite, dolomite,
magnesia,
magnesium silicates, forsterite, steatite, olivines, silicon carbide, silicon
nitride,
inorganic fibers, fibers produced from slugs, commercially available inorganic
crystalline fibers, alpha-alumina based fibers, alumina-silica based fibers,
glass fibers.
[00017] Published US Patent Application 2013/0045901 describes the addition
of
nanoscale carbon black, fumed silica, fumed alumina, carbon nanotubes, carbon
nanofibers,
cellulosic nanofibers, natural and synthetic nanoclays, finely divided grades
of fly ash, the
3
Date Recue/Date Received 2021-09-16
polyhedral oligomeric silsesquioxanes, and clusters of different types of
metals, metal alloys,
and metal oxides for nanocomposite proppants.
[00018] Despite the advances in the field of proppant technology, there
remains a need
in the industry for premium proppants for medium and high pressure fields that
can resist
deformation under the very high crack closure stresses that are found in high
temperature/high pressure wells
SUMMARY OF THE INVENTION
[00019] It is an object of the invention to provide a proppant exhibiting
an enhanced
level of hardness and crush resistance that is suited for fractured fields
exhibiting medium
and high crack closure stress levels.
[00020] In accordance with the above and other objects of the invention
that will
become apparent from the description herein, the present invention provides a
proppant
having a polymeric coating that is strengthened with reinforcing particulates
that are grafted
to or bonded to the polymeric proppant coating. Preferably, these particulates
are added into
and become part of the coating during the coating process. In one embodiment,
functionalized particulates are used that become grafted into the polymer of
the proppant
coating through the chemical functionality imparted to the particulates. If
non-functionalized
particulates are used, a coupling agent is preferably added to enhance the
bond strength
between the added particulates and the polymeric matrix of the proppant
coating.
[00021] The hard particulates that are integrated into the proppant coating
are
preferably chemically integrated and chosen to impart a greater hardness
and/or deformation
resistance to the coating. An increased hardness reduces agglomeration during
storage and
shipping and helps to mitigate dust. Reduced deformation of the proppant
coating avoids pore
closure due to coating deformation with the effect of maintained conductivity,
even in high
pressure wells. When functionalized particulates are used or if an adhesion
promoter is used
with non-functionalized particulates, the added chemical bonding helps the
particle to remain
in the coating and avoid the formation of microcrack defect sites that could
be initiation sites
for cracks leading to dusting and deterioration.
DETAILED DESCRIPTION OF THE INVENTION
[00022] The present invention relates to a coated proppant that
includes
particulates that are firmly bound to or grafted to the polymeric coating.
These particulates
impart enhanced hardness to the proppant coating and an internal reinforcing
agent linked to
4
Date Recue/Date Received 2021-09-16
the polymeric matrix of the coating that resists deformation of the composite
coating under
medium and high pressure stress.
[00023] The particulates added to the proppant coating in the present
invention
can be organic or inorganic. Preferred particulates for use in the present
composite proppant
coating are selected from among a wide variety of materials whose presence in
the coating
will enhance the overall strength and deformation resistance of the coated
proppant.
Reinforcing particulates can be used in any layer or layers applied to the
proppant core solid.
[00024] Organic particulates that are useful for the present invention
include
particulates that are relatively harder than the proppant matrix polymer and
may be pre-
reacted to include reactive functionalities for bonding with the polymeric
matrix of the
proppant coating or they may be non-reactive if a separate adhesion promoter
is added to the
composite to enhance bonding between the polymeric matrix and the added
particulates.
Suitable organic particulates include fullerenes, activated carbon, rubber,
rubber-reinforced
polymers, and other organic particulates sold as "impact modifiers" for
composites.
[00025] The preferred particulates for use in the present composite
coating
exhibit a wet glass transition temperature (Tg) for enhanced structural
reinforcement that is
greater than the glass transition temperature of the cured (or as
substantially fully cured as the
coating becomes in use) coating resin as well as the expected operating
temperature where
the proppant will be used. For enhanced impact resistance, the proppant
formulator would use
particulates with a Tg that is lower than that of the coating or lower than
the expected
operating temperature where the proppant will be used. Even more preferably,
the added
particulate is, or can be made to be, reactive towards the chemistry of the
resin coating so that
the particulate remains filinly attached and/or chemically grafted into or
onto the coating of
the proppant.
[00026] Suitable forms of particulate materials include dispersions,
short fibers
and powders (collectively referred to herein as "particulates") of finely
divided,
functionalized or non-functionalized metals, metal oxides, metalloids, and
ceramics e.g.,
silica, silicon carbide (particles, whiskers or milled whisker forms),
alumina,
aluminosilicates, spent cracking catalysts, bauxite, ceramics, and the like.
Especially
preferred inorganic materials are functionalized forms of silica or
dispersions or powders of
silica to which an external coupling agent has been added to enhance the bond
between the
added silica and the surrounding polymeric matrix of the proppant coating.
[00027] If used in the composite coating around the proppant core
solid
according to the invention, fibers may be any of various kinds of commercially
available
short fibers or crystalline whiskers. Such fibers include at least one type of
milled glass fiber,
Date Recue/Date Received 2021-09-16
milled ceramic fiber, milled carbon fiber, natural fiber, crystalline
inorganic forms including
forms having a ratio of length to diameter within the range of 1-100 (e.g.,
particles to
whiskers), and synthetic fibers, e.g., crosslinked novolac fibers, having a
softening point
above typical starting temperature for blending with resin, e.g., at least
about 93 C (200 F),
so as to not degrade, soften or agglomerate. The typical glasses for fibers
include E-glass, 5-
glass, and AR-glass. E-glass is a commercially available grade of glass fibers
typically
employed in electrical uses. S-glass is used for its strength. AR-glass is
used for its alkali
resistance. The carbon fibers are of graphitized carbon. The ceramic fibers
are typically
alumina, porcelain, or other vitreous material.
[00028] 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 or depth of the coating on the proppant. Suitable,
commercially available
fibers include milled glass fiber having lengths of 0.1 to about 1/32 inch.
Additional fibers
include milled ceramic fibers that are typically about 6 to 250 microns long,
milled carbon
fibers that are within the range of 50 to 350 microns long, and KEVLAR aramid
fibers of 6
to 250 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 1 to about 20 microns.
Length to aspect
ratio (e.g., length to diameter ratio) may range from about 5 to about 250.
The fiber may have
a round, oval, square, rectangular or other appropriate cross-section.
[00029] 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. See
McDaniels et al.
US Patent No. 6,632,527.
[00030] Functionalized inorganic particulates that are particularly
useful in the
present invention are prepared by reacting the inorganic particle with one or
more organic
agents that bond to the surface of the underlying particle and provide one or
more reactive
sites over the surface of the particle that can be used to bond or enhance the
bond between a
polymeric phase and the functionalized particulates dispersed therein. Silica
is one such
particle that has been functionalized in a variety of ways. See US Patent Nos.
5,168,082
(functionalizing group attached to the silica sol is a branched or straight
chain silane
6
Date Recue/Date Received 2021-09-16
including at one end a hydrophilic moiety and at another end a silicon anchor
group);
5,330,836 (polyfunctional silica particulates); 6,486,287 and 7,129,308
(functionalized
silicon for silica surfaces); 6,809,149 (silica with 3-methacryloxypropylsily1
and/or
glycidyloxypropylsilyl groups on the surface); and published US Patent
Application
Publication Nos. 2004/0138343 (colloidal silica functionalized with at least
one
organoalkoxysilane functionalization agent and subsequently functionalized
with at least one
capping agent); 2007/0238088 (functionalized silica compositions by reacting
acidic silica
particulates with hydrophilic organosilanes); 2008/0063868 (silica nano-sized
particulates
having polyethylene glycol linkages); and 2013/0005856 (amine-functionalized
silica particulates coupled to at least one group chosen from primary amines,
secondary
amines, tertiary amines, and quaternary ammonium groups).
[00031] For the present invention, finely divided particulates of
silica, alumina,
aluminosilicate, or ceramic particulates, whether functionalized or not
functionalized, are
preferred particulates for the composite coating. Through the hydrolysis of
tetraalkyl
orthosilicates, disperse particulates of colloidal silica can be prepared. The
surface of these
particulates has been modified to stabilize them in water or organic solvents.
Surface
modified colloidal silica particulates are referred to as functionalized, as
are the resulting
colloidal solutions, or sols. The surface of a formed alumina, or
aluminosilicate can also be
functionalized with a chemical moiety or chemical material, such as an organic
ligand, like a
surfactant, and can provide surface wetting properties which can assist in
grafting the added
particle into the polymer of the coating or providing bonding functionalities
that assist in
resilient incorporation of the particle into the proppant coating. Indeed,
particulates that have
been functionalized to include isocyanate-terminated moieties are useful to
add isocyanate
functionality to a polyurethane or polyurea-based polymer coating matrix.
[00032] If functionalized, the preferred functionalizing agents are
those that are
compatible with silica surfaces, such as the silicon compounds of US 6,486,287
and
7,129,308 that are made with a silicon compound comprising a silicon atom and
a
derivatizable functional group. In a preferred embodiment, the functionalized
silicon
compound is a functionalized silylating agent and includes an activated
silicon group and a
derivatizable functional group. As used herein, the term "derivatizable
functional group"
refers to a functional group that is capable of reacting to permit the
formation of a covalent
bond between the silicon compound and another substance, such as a polymer.
Exemplary
derivatizable functional groups include hydroxyl, amino, carboxy, thiol,
epoxy, amide, and
isocyano, as well as modified forms thereof, such as activated or protected
forms.
Derivatizable functional groups also include substitutable leaving groups such
as halo or
7
Date Recue/Date Received 2021-09-16
sulfonate. One preferred embodiment has a derivatizable functional group, such
as a hydroxyl
group, that is capable of reacting with the isocyanate (¨N=C=O) groups that
are found within
the polyurethane or polyurea-type coatings on the proppant. Another preferred
embodiment
uses a derivatizable group (e.g., ¨Si(OMe)3; ¨SiMe(OMe)2; ¨SiMeC12; SiMe(0E02;
SiC13 and ¨Si(0E03) that can react with hydroxyl functionalities found within
the
polyurethane, polyurea-type, furan, furyl alcohol and phenolic coatings on the
proppant.
[00033] If nonfunctionalized reinforcing particulates are used for the
present
composite proppant coating, an adhesion promoter is desirably used to enhance
the wetting
and/or surface bonding between the added particle and the polymeric coating.
The adhesion
promoter is preferably a silane or, more preferably, an organofunctionalized
silane.
[00034] Silanes are a particularly preferred type of adhesion promoter
agent
that improves the affinity of the coating resin for the surface of the
proppant core solid and is
particularly useful when sand is the proppant core. Adhesion promoters can be
used in an
outer layer portion of a proppant coating to provide bonding sites for
enhancing the
interparticle bonding of proppants bearing a similarly functionalized external
surface.
[00035] For the present invention, silanes can be mixed in as adhesion
promoters in the first step of the coating process, but can also be converted
chemically with
reactive constituents of the polyol component or of the isocyanate component.
Functional
silanes such as amino-silanes, epoxy-, aryl- or vinyl silanes are commercially
available. The
amino-silanes are preferred for silica-based core solids. For ceramic core
solids,
organofunctional zirconates or titanates are preferred, e.g., ethyltitanate.
[00036] Suitable organofunctional silanes for use in the present
invention as
adhesion promoters include those with the structure:
Si(R1)(R2)(R3)(R4),
in which R1, R2, R3, and R4 may the same or different and are independently
selected from
the group consisting of hydrogen, hydroxy, hydroxyalkyl, alkyl, haloalkyl,
alkylene, alkynyl,
alkoxy, alkynoxy, aryl, aryloxy, substituted aromatic, heteroaromatic, amino,
aminoalkyl,
arylamino, epoxide, thiol, and haloalkyl, ether, ester, urethane, amide,
provided that at least
one of R1, R2, R3, and R4 comprises an organic moiety. Preferably, the
oganofunctional
silane coupling agent includes an organic functionality selected from the
group consisting of
methyl, epoxide, epoxy/melamine, amino, mercapto, chloropropyl, methacryl,
methacryloxy,
vinyl, benzylamino, ureido, tetrasulfido, and Cl-C4 alkoxy groups.
8
Date Recue/Date Received 2021-09-16
Alternatively, the organofunctional silane is selected from the group
consisting of
mercaptosilanes possessing at least one hydroxyalkoxysilyl group and/or a
cyclic
dialkoxysilyl group, blocked mercaptosilane possessing at least one
hydroxyalkoxysilyl
group and/or a cyclic dialkoxysilyl group; mercaptosilanes in which the
silicon atoms of the
mercaptosilane units are bonded to each other through a bridging dialkoxy
group, each silane
unit optionally possessing at least one hydroxyalkoxysilyl group or a cyclic
dialkoxysilyl
group; blocked mercaptosilane dimers in which the silicon atoms of the blocked
mercaptosilane units are bonded to each other through a bridging dialkoxy
group, each silane
unit optionally possessing at least one hydroxyalkoxysilyl group or a cyclic
dialkoxysilyl
group; silane dimers possessing a mercaptosilane unit the silicon atom of
which is bonded to
the silicon atom of a blocked mercaptosilane unit through a bridging dialkoxy
group, each
silane unit optionally possessing at least one hydroxyalkoxysilyl group or a
cyclic
dialkoxysilyl group; mercaptosilane oligomers in which the silicon atoms of
adjacent
mercaptosilane units are bonded to each other through a bridging dialkoxy
group, the
terminal mercaptosilane units possessing at least one hydroxyalkoxysilyl group
or a cyclic
dialkoxysilyl group; blocked mercaptosilane oligomers in which the silicon
atoms of adjacent
blocked mercaptosilane units are bonded to each other through a bridging
dialkoxy group, the
terminal mercaptosilane units possessing at least one hydroxyalkoxysilyl group
or a cyclic
dialkoxysilyl group; and silane oligomers possessing at least one
mercaptosilane unit and at
least one blocked mercaptosilane unit, the silicon atoms of adjacent silane
units being bonded
to each other through a bridging dialkoxy group, the terminal silane units
possessing at least
one hydroxyalkoxysilyl group or a cyclic dialkoxysilyl group.
[00037] Specific examples of useful organofunctional silane coupling
agents
for use in enhancing the bond strength or wetting characteristics between
nonfunctionalized
reinforcing particulates and the polymeric coating of the proppants according
to the invention
include 3-glycidyloxypropyltrimethoxysilane, 3-
glycidyloxypropyltriethoxysilane, 2-(3,4-
epoxycyclohexyl)ethyltrimethoxysilane, and 2-(3,4-
epoxycyclohexyl)ethyltriethoxysilane; 3-
[2-(2-aminoethylamino)ethylamino] propyl-trimethoxysilane (CAS No. 35141-30-
1); 3-
mercaptopropyl-trimethoxysilane (CAS No. 4420-74-0); n-propyltrimethoxysilane
(CAS No.
1067-25-0); [3-(2-aminoethypaminopropylltrimethoxysilane (CAS No. 1760-24-3);
silane
n-dodecyltrimethoxysilane (CAS No. 3069-21-4); bis (trimethoxysilylpropyl)
amine (CAS
No. 82985-35-1); 1, 2-bis(trimethoxysilyl)ethane (CAS No. 18406-41-2);
vinyltri(2-
methoxyethoxy) silane (CAS No. 1067-53-4); n-octyltriethoxysilane (CAS No.
2943-75-1);
bis[3-(triethoxysily1) propyl] tetrasulfide (CAS No. 40372-72-3);
vinyltriethoxysilane (CAS
No. 78-08-0); 3-glycidoxypropyl-trimethoxysilane (CAS No. 2530-83-8); 3-
mercaptopropyl-
9
Date Recue/Date Received 2021-09-16
triethoxysilane (CAS No. 14814-09-6); 3-glycidoxypropyl-triethoxysilane (CAS
No. 2602-
34-8); 2-(3, 4-epoxycyclohexypethylltrimethoxysilane (CAS No. 3388-04-3); 3-
aminopropyltrimethoxysilane (CAS No. 13822-56-5); 2-(3, 4-
epoxycyclohexyl)ethyl
ltriethoxysilane (CAS No. 10217-34-2); 3-aminopropyltriethoxysilane (CAS No.
919-30-2);
3-glycidoxypropyl-methyldimethoxysilane (CAS No. 65799-47-5);
bis(triethoxysilylpropyl)amine (CAS No. 13497-18-2); 3-(2-aminoethylamino)
propyldimethoxymethylsilane (CAS No. 3069-29-2); N-(n-Buty1)-3-aminopropyltri-
methoxysilane (CAS No. 31024-56-3); n-propyltriethoxysilane (CAS No. 2550-02-
9);
vinyltrimethoxysilane (CAS No. 2768-02-7); 3-ureidopropyltriethoxy-silane (CAS
No.
23779-32-0); 3-methacryloxypropyl-trimethoxysilane (CAS No. 2530-85-0).
[00038] Another type of organofunctional silanes that are useful in
the present
invention are silane-terminated polymers, such as silane-terminated polyethers
and
polyurethanes. These polymers are formed by reaction of for instance a
polyether polymer
with isocyanate termination with aminosilanes or a polyether polymer with
amino
termination and/or hydroxyl termination with isocyanate-terminated silanes.
Reactions of the
reactive groups with other materials in the composition are also possible to
create other cross-
links. Silane-terminated polymers (STP) or silane- modified polymers (MS) can
be all pre-
polymers which at the chain ends - or laterally - carry silyl groups having at
least one
hydrolysable bond but which in the polymer framework, do not display the
siloxane bond
(SiR20)n that is typical of silicones. Two preferred silane-terminated
polymers are illustrated
by Formulas 1 (a dimethoxy(methyl) silylmethyl carbamate-terminated polyether)
and
Formula 2:
or OMe
MOO SI (CH;), C OARADdiedletwO¨C". -(CH2), Si tie
OM*H OMe
Formula 1
(CH):1*(ZH2),1
5i
(1\x kf X
Formula 2
Date Recue/Date Received 2021-09-16
[00039] Wherein for Formula 1: Polyether refers to a polyether chain
having 1-
200 carbon atoms. See also published US patent nos. 3,971,751 and 6,207,766 as
well as US
patent application publication number US 2007/0088137.
[00040] Wherein for Formula 2: R is an amine group; each X in Formula
5 can
each be independently selected from the group consisting of hydrogen, alkoxy,
halogen, and
hydroxyl; and n is an integer that is greater than zero. Such agents are
commercially available
from Wacker Chemie AG, Hanns-Seidel-Platz 4, 81737 Munchen, Germany under the
designation Geniosil 0 STP-E.
[00041] The dipodal silane-terminated polyether-based polymers of
Formulas 1
and 2 are compatible or miscible with polyether polyols that can be used as
the polyol
component for making a polyurethane proppant coating. Such silane-terminated
polyether-
based polymers are easily blended with polyether polyols as a last step top-
coat to provide an
adhesive coating layer for coated proppants according to the invention. The
dipodal amino
silane of Formula 4 in the form of bis(trimethoxysilylpropyl)amine has been
used as a
coupling agent in the proppants industry for "difficult" substrates. In the
present invention,
this silane could provide two silane, adhesive-like, functionalities for every
amine grafting
moiety.
[00042] The length of the carbon chain in the alkoxy moieties (e.g.,
methoxy
vs. ethoxy vs. propoxy vs. butoxy) determines the rate of hydrolysis of the
silane. So, the
choice of the length of the alkoxy carbon chain can be used to provide control
over the
resulting moisture and water resistance. Increasing resistance is seen as the
alkyl chain
increases. Longer carbon length chains will also delay the hydrolysis and,
therefore, the
bonding performance of the proppant in the fracture.
[00043] The size of the added particulates for the composite should be
selected
based on the coating thickness on the core solid of the proppant and can be in
the form of
sols, colloids, suspensions or dry powders. Preferably, the added particulates
do not extend
substantially above the upper surface of the coating or interfere with
handling, transport and
injection of the coated proppant. Suitable sizes are generally within the
range from about 5
nm to about 1500 nm. Preferably, the added particulates exhibit an average
particle size
within the range from about 5 nm to less than 1000 nm and more preferably
within the range
of about 8-20 nm. In one embodiment, the average particle size of the added
hard, crush-
resistant, inorganic particulates may be selected from the range of about 5 nm
to about 500
nm.
[00044] Preferably, the reinforcing particulates used in the present
invention
are added as an aqueous suspension as a separate stream or admixed with a
compatible
11
Date Recue/Date Received 2021-09-16
coating component. Water addition can be particularly useful for polyurethane
and polyurea-
based coatings. See copending US Patent Application serial no. 13/355,969
entitled
"Manufacture of Polymer Coated Proppants".
[00045] The amount of added functionalized inorganic particulates can
be
within a substantial range, depending on the polymer and coating thickness
used on the
proppant. In general, useful amounts are within the range of about 2-85 vol%
solids in the
proppant coating based on the volume of the coating. Preferred amounts are
within the range
of 2-65 vol% solids and even more preferably 5-30 vol% solids in the proppant
coating.
THE POLYMERIC COATING
[00046] A wide variety of polymers can be used as coating for
proppants of the
present invention. Indeed, the coating can be thermoset or thermoplastic and
may formed in
one or more layers that are the same, different, analogues or homologues of
the other and any
intervening proppant coating layers. Suitable polymeric coatings include
resins based on
polyurethane, polyurea-type, phenolic, epoxy, polycarbodiimide, or polyester
resins. A
preferred, multilayer proppant uses a first coating layer made from a precured
phenolic
coating with a second coating layer made with a polyurethane or polyurea-based
coating (for
providing interparticle bond strength). The reinforcing particulates of the
present invention
would be on or in the second coating layer.
[00047] The preferred proppant coatings for the present invention and
their
manufacture are described in co-pending US patent application serial nos.
13/099,893
(entitled "Coated and Cured Proppants" and published as U.S. Application
Publication No.
20120279703 on November 8, 2012); 13/188,530 (entitled "Coated and Cured
Proppants"
and published as U.S. Application Publication No. 20120283153 on November
8,2012);
13/626,055 (entitled "Coated and Cured Proppants" and published as U.S.
Application
Publication No. 20130065800 on March 14, 2013); 13/224,726 (entitled "Dual
Function
Proppants" and published as U.S. Application Publication No. 20130056204 on
March 7,
2013); and 13/355,969 (entitled "Manufacture of Polymer Coated Proppants" and
published
as U.S. Application Publication No. 20130186624 on July 25, 2013).
[00048] Particularly preferred proppant coatings as the inner and/or
outer layers
are those using polyurea-based or, with the use of a polyol, polyurethane-
based polymers. See
copending US patent application serial number 13/355,969, entitled
"Manufacture of Polymer
Coated Proppants" and published as U.S. Application Publication No.
20130186624 on July
25, 2013.
12
Date Recue/Date Received 2021-09-16
[00049] The polyurea-type coating is preferably formed on the proppant
from a
dynamically reacting mixture that comprises an isocyanate, water and a curing
agent
(preferably an aqueous solution containing a curing agent or catalyst) that
have been
simultaneous contacted and mixed in the presence of the proppant core. While
not wishing to
be bound by theory of operation, the controlled rates of substantially
simultaneous water and
isocyanate are believed to allow the water to form a reactive amine species
from the
isocyanate, which newly-formed amine then reacts with other, unconverted
isocyanate to
form the desired polyurea-type coating directly on the outer surface of the
proppant solid.
Thus, the simultaneous contact among the ingredients forms a reacting mixture
that
polymerizes to form a thin, hard, substantially foam-free coating directly on
the outer surface
of the proppant core. Indeed, the selection of different feed start times and
rate for the
isocyanate and water phase can be chosen to produce a gradient of polyurea-
type polymers
within in the coating. If the sand has been heated in advance of the contact,
the reaction can
proceed substantially to completion in less than about four minutes to form a
hard,
substantially fully-cured coating that does not require post-curing to form a
tack-free or
substantially tack-free outer surface.
[00050] Alternatively and less preferably, a polyurea-type coating can
be
formed on the proppant core by serially adding polyurea-type precursor
components to the
mixer. Such a process would likely need, however, sufficient agitation and
mixing to avoid
boundary layer effects from the first-added component that would cover the
surface of the
proppant core to a certain depth which might inhibit a complete reaction of
all of the first
material down to the surface of the proppant core solid. Sufficient agitation
would be used to
force the second component into the boundary layer of first component so that
the first
component boundary layer reacts downwardly from its outer surface towards the
outer
surface of the proppant core to form linkages that are tightly adhered to the
proppant core
surface.
[00051] Similar concerns would occur if the proppant core had been
stored
under external conditions and had become wet. It would be desirable to heat
the proppant
core above about 100 C, possibly less with moving air through the solids,
until the proppants
are substantially dry before they are first contacted with a reactable or
reacting mixture of
polyurea-type precursors. Such a drying process is commonly used in processing
even
uncoated sand proppants, the present coating process is preferably performed
in the same or
adjacent facility as the drying operation so that the sensible heat introduced
to the sand for
drying can also be used to facilitate the formation of cured coatings on at
least a portion of
the processed proppant sands.
13
Date Recue/Date Received 2021-09-16
[00052] Tests on the coating to determine its glass transition temperature
(Tg) when
exposed to water as well as laboratory-scale tests for bond strength, such as
conventional
UCS testing, or conductivity can be used to evaluate the suitability of any
particular coating
formulation that has been prepared by a particular coating method. In
particular, the Tg can
be used as a guide to foretell whether a thermoplastic coating (such as the
polyurethane and
polyurea-based coating layers of the present invention) is potentially useable
in the downhole
conditions of a given fractured stratum. It is desirable that the Tg of the
proppant coating be a
temperature that is less than that prevailing downhole so that the
thermoplastic coating has
the ability to soften under prevailing combination of temperature and
pressure. The Tg of the
reinforcing particulates should, however, be higher than the prevailing
downhole temperature
so that the particulate does not soften or lessen its reinforcing effects. For
the present
invention and for use in high temperature wells, the Tg of the proppant
coating is preferably
greater than about 75 C but less than about 200 C and even more preferably
within the
range from about 100-165 C. For lower temperature wells that have downhole
temperatures
within the range of 20 -52 C, the Tg of the proppant coating is desirably
within the range of
about 20 C to 60 C.
[00053] The Tg values that are described can differ if one is
describing a wet or
dry Tg test. See US Patent Nos. 3,725,358; 5,310,825; and 2010/0222461 for
testing to
determine the wet Tg of a resin or material, i.e., performing the
determination of Tg in a
thermomechanical analyzer with water added to the sample container. A dry Tg
could be in
the range of 130-160 C, but in a wet test, it is difficult to measure a Tg
that is above 110 C.
In the low temperature applications the wet Tg preferably falls into the
ranges described
above to promote interparticle bonding without the use of an external
activator.
[00054] A preferred testing method for proppant performance is
described in
ISO 13503-5:2006(E) "Procedures for measuring the long term conductivity of
proppants".
The ISO 13503-5:2006 provides standard testing procedures for evaluating
proppants used in
hydraulic fracturing and gravel packing operations. ISO 13503-5:2006 provides
a consistent
methodology for testing performed on hydraulic fracturing and/or gravel
packing proppants.
The "proppants" mentioned henceforth in this part of ISO 13503-5:2006 refer to
sand,
ceramic media, resin-coated proppants, gravel packing media, and other
materials used for
hydraulic fracturing and gravel-packing operations. ISO 13503-5:2006 is not
applicable for
use in obtaining absolute values of proppant pack conductivities under
downhole reservoir
conditions, but it does serve as a consistent method by which such downhole
conditions can
be simulated and compared in a laboratory setting.
14
Date Recue/Date Received 2021-09-16
THE ISOCYANATE COMPONENT
[00055] The isocyanate-functional component for the coatings of the
present
invention comprises an isocyanate-functional component with at least 2
reactive isocyanate
groups. Other isocyanate-containing compounds may be used, if desired.
Examples of
suitable isocyanate with at least 2 isocyanate groups an aliphatic or an
aromatic isocyanate
with at least 2 isocyanate groups (e.g. a diisocyanate, triisocyanate or
tetraisocyanate), or an
oligomer or a polymer thereof can preferably be used. These isocyanates with
at least 2
isocyanate groups can also be carbocyclic or heterocyclic and/or contain one
or more
heterocyclic groups.
[00056] The isocyanate-functional component with at least 2 isocyanate
groups
is preferably a compound, polymer or oligomer of compounds of the formula
(III) or a
compound of the formula (IV):
(R2)q
0 Ri - NC01
(III)
(R2)q (R2)q
(OCN¨R, r 0 R3 0 RI - NC 0)
s
(IV)
[00057] In the formulas (III) and (IV), A is each, independently, an
aryl,
heteroaryl, cycloalkyl or heterocycloalkyl. Preferably, A is each,
independently, an aryl or
cycloalkyl. More preferably A is each, independently, an aryl which is
preferably phenyl,
naphthyl or anthracenyl, and most preferably phenyl. Still more preferably A
is a phenyl.
[00058] The above mentioned heteroaryl is preferably a heteroaryl with
5 or 6
ring atoms, of which 1, 2 or 3 ring atoms are each, independently, an oxygen,
sulfur or
nitrogen atom and the other ring atoms are carbon atoms. More preferably the
heteroaryl is
selected among pyridinyl, thienyl, furyl, pyrrolyl, imidazolyl, pyrazolyl,
pyrazinyl,
pyrimidinyl, pyridazinyl, oxazolyl, isoxazolyl or furazanyl.
[00059] The above mentioned cycloalkyl is preferably a C3-10-
cycloalkyl, more
preferably a C5_7-cycloalkyl.
Date Recue/Date Received 2021-09-16
[00060] The above mentioned heterocycloalkyl is preferably a
heterocycloalkyl
with 3 to 10 ring atoms (more preferably with 5 to 7 ring atoms), of which one
or more (e.g.
1, 2 or 3) ring atoms are each, independently, an oxygen, sulfur or nitrogen
atom and the
other ring atoms are carbon atoms. More preferably the heterocycloalkyl is
selected from
among tetrahydrofuranyl, piperidinyl, piperazinyl, aziridinyl, acetidinyl,
pyrrolidinyl,
imidazolidinyl, morpholinyl, pyrazolidinyl, tetrahydrothienyl,
octahydroquinolinyl,
octahydroisoquinolinyl, oxazolidinyl or isoxazolidinyl. Still more preferably,
the
heterocycloalkyl is selected from among tetrahydrofuranyl, piperidinyl,
piperazinyl,
pyrrolidinyl, imidazolidinyl, morpholinyl, pyrazolidinyl, tetrahydrothienyl,
oxazolidinyl or
isoxazolidinyl.
[00061] In the formulas (III) and (IV), each le is, independently, a
covalent
bond or C1_4-alkylene (e.g. methylene, ethylene, propylene or butylene).
Preferably each R2
is hydrogen or a covalent bond.
[00062] In the formulas (III) and (IV), each R2 is each,
independently,
hydrogen, a halogen (e.g. F, Cl, Br or I), a C1_4-alkyl (e.g. methyl, ethyl,
propyl or butyl) or
C1-4-alkyoxy (e.g. methoxy, ethoxy, propoxy or butoxy). Preferably, each R2
is,
independently, hydrogen or a C1_4-alkyl. More preferably each R2 is hydrogen
or methyl.
[00063] In the formula (IV), R3 is a covalent bond, a C1_4-alkylene
(e.g.
methylene, ethylene, propylene or butylene) or a group ¨(CH2)R31-0-(CH2)R32-,
wherein R31
and R32 are each, independently, 0, 1, 2 or 3. Preferably, R3 is a -CH2- group
or an -0-
group.
[00064] In the formula (III), the average value of p is greater than
or equal to 2,
preferably greater than 2, and more preferably within the range of 2.05 and up
to 3.
[00065] In the formulas (III) and (IV), each q is, independently, an
integer from
0 to 4, preferably 0, 1 or 2. When q is equal to 0, the corresponding group A
has no
substituent R2, but has hydrogen atoms instead of R2.
[00066] In the formula (IV), each r and s are, independently, 0, 1, 2,
3 or 4,
wherein the sum of average values of r and s is greater than 2. Preferably,
each the average
of r and s are preferably greater than 2, and more preferably within the range
of 2.05 and up
to 3...
[00067] Examples of the isocyanate with at least 2 isocyanate groups
are:
toluol-2,4-diisocyanate; toluol-2,6-diisocyanate; 1,5-naphthalindiisocyanate;
cumo1-2,4-
diisocyanate; 4-methoxy-1,3-phenyldiisocyanate; 4-chloro-1,3-
phenyldiisocyanate;
diphenylmethane-4,4-diisocyanate; diphenylmethane-2,4-diisocyanate;
diphenylmethane-2,2-
diisocyanate; 4-bromo-1,3-phenyldiisocyanate; 4-ethoxy-1,3-phenyl-
diisocyanate; 2,4'-
16
Date Recue/Date Received 2021-09-16
diisocyanate diphenylether; 5,6-dimethyl-1,3-phenyl-diisocyanate;
methylenediphenyl
diisocyanate (including 2,2'-MDI, 2,4'-MDI and 4,4"-MDI); 4,4-diisocyanato-
diphenylether;
4,6-dimethy1-1,3-phenyldiisocyanate; 9,10-anthracene-diisocyanate; 2,4,6-
toluol
triisocyanate; 2,4,4'-triisocyanatodiphenylether; 1,4-tetramethylene
diisocyanate; 1,6-
hexamethylene diisocyanate; 1,10-decamethylene-diisocyanate; 1,3-cyclohexylene
diisocyanate; 4,4'-methylene-bis-(cyclohexylisocyanate); xylol diisocyanate; 1-
isocyanato-3-
methyl-isocyanate-3,5,5-trimethylcyclohexane (isophorone diisocyanate); 1-3-
bis(isocyanato-
1-methylethyl) benzol (m-TMXDI); 1,4-bis(isocyanato-1-methylethyl) benzol (p-
TMXDI);
oligomers or polymers of the above mentioned isocyanate compounds; or mixtures
of two or
more of the above mentioned isocyanate compounds or oligomers or polymers
thereof. A
variety of polymeric isocyanates can be used in the present invention.
Suitable examples
include polymers and oligomers of diphenylmethane diisocyanates (MDIs and
pMDIs),
toluene diisocyanates (TDIs), hexamethylene diisocyanates (HDIs), isophorone
diisocyanates
(IPDIs), and combinations thereof. The preferred polymeric isocyanate for use
in the present
invention is polymers and oligomers based on diphenylmethane diisocyanates.
[00068] Particularly preferred isocyanates with at least 2 isocyanate
groups are
toluol diisocyanate, methylenediphenyl diisocyanate, diphenylmethane
diisocyanate, an
oligomer based on toluol diisocyanate, an oligomer based on methylenediphenyl
diisocyanate
(poly-MDI) or an oligomer based on diphenylmethane diisocyanate and polymers
thereof.
THE POLYOL COMPONENT
[00069] A polyol component with polyhydroxy functionality is one of
the
components used in making a polyurethane coating on proppant solids in a
process according
to the invention, and it may be applied as the first component or the second
component. The
polyol component has two or more functional, hydroxyl moieties (such as diols,
tfiols and
higher polyol functionality based on starter molecules like glycerine,
tfimethylolpropane,
sorbitol, methyl glucoside and sucrose) excluding hydroxyl groups associated
with carboxylic
acids and may or may not have reactive amine functionality. Preferred
polyhydroxyl polyols
include polyethers (such as polyoxypropylene diols and triols), polyesters,
aliphatic polyols,
aromatic polyols, mixtures of aliphatic and aromatic polyols, synthetic
polyols,
polyhydroxyoligomers (see US 4554188 and 4465815), natural oil polyols (such
as cashew
nut oil and castor oil) and natural oils that have been treated to introduce
polyhydroxyl
content in place of unsaturated bonds such as oxidized soybean oil, oxidized
peanut oil, and
oxidized canola oil such as polyols produced from biomass.
17
Date Recue/Date Received 2021-09-16
[00070] A preferred polyurethane coating is made with a polyol mixture
that
includes 5-100 wt% of one or more polyether, polyester, aliphatic and/or
polyhydroxyoligomers polyols and 0-95 wt% of an aromatic polyol. An especially
preferred
polyol is a polyetherpolyol containing 0-5 wt% castor oil.
[00071] In a still further embodiment, the polyol component is a
phenol resin
with monomer units based on cardol and/or cardanol. Cardol and cardanol are
produced from
cashew nut oil which is obtained from the seeds of the cashew nut tree. Cashew
nut oil
consists of about 90% anacardic acid and about 10% cardol. By heat treatment
in an acid
environment, a mixture of cardol and cardanol is obtained by decarboxylation
of the
anacardic acid. Cardol and cardanol have the structures shown below:
OH OH
= C15 H31 _n I
5' '31 _n
HO
n=0,2,4,6 n=0,2,4,6
Cardanol Cardol
[00072] As shown in the illustration above, the hydrocarbon residue
(¨Ci5I-131-n)
in cardol and/or in cardanol can have one (n=2), two (n=4) or three (n=6)
double bonds.
Cardol specifically refers to compound CAS-No. 57486-25-6 and cardanol
specifically to
compound CAS-No. 37330-39-5.
[00073] Cardol and cardanol can each be used alone or at any
particular mixing
ratio in the phenol resin. Decarboxylated cashew nut oil can also be used.
[00074] Cardol and/or cardanol can be condensed into the above
described
phenol resins, for example, into the resole- or novolak-type phenol resins.
For this purpose,
cardol and/or cardanol can be condensed e.g. with phenol or with one or more
of the above
defined compounds of the formula (I), and also with aldehydes, preferably
formaldehyde.
[00075] The amount of cardol and/or cardanol which is condensed in the
phenol resin is not particularly restricted and preferably is from about 1 wt%
to about 99
wt%, more preferably about 5 wt% to about 60 wt%, and still more preferably
about 10 wt%
to about 30 wt%, relative to 100 wt% of the amount of phenolic starting
products used in the
phenol resin.
[00076] In another embodiment, the polyol component is a phenol resin
obtained by
condensation of cardol and/or cardanol with aldehydes, preferably
formaldehyde.
18
Date Recue/Date Received 2021-09-16
[00077] A phenol resin which contains monomer units based on cardol
and/or
cardanol as described above, or which can be obtained by condensation of
cardol and/or
cardanol with aldehydes, has a particularly low viscosity and can thus
preferably be
employed with a low addition or without addition of reactive thinners.
Moreover, this kind of
long-chain, substituted phenol resin is comparatively hydrophobic, which
results in a
favorable shelf life of the coated proppants obtained by the method according
to the present
invention. In addition, a phenol resin of this kind is also advantageous
because cardol and
cardanol are renewable raw materials.
[00078] Apart from the phenol resin, the polyol component can still
contain
other compounds containing hydroxyl groups. The other compounds containing
hydroxyl
groups can be selected from the compounds containing hydroxyl groups that are
known to be
useful for making polyurethanes, e.g., hydroxy-functional polyethers, hydroxy-
functional
polyesters, alcohols or glycols. One preferred compound containing hydroxyl
groups is, for
instance, castor oil. Compounds containing hydroxyl groups such as alcohols or
glycols, in
particular cardol and/or cardanol, can be used as reactive thinners.
CURING AGENTS AND CATALYSTS
[00079] The coatings of the invention can be cured with at least one
of a variety
of curing agents, including reactive, non-reactive (e.g., "catalysts") and
partially reactive
agents that facilitate the formation of polyurea-type linkages. Generally, the
preferred curing
agents are selected from the amine-based curing agents and are added to the
reacting mixture
of polyurea-type precursors at a total amount within the range from about
0.0001% to about
30 total wt%. The amine-based curing agents may also be used as a mixture of a
fast-acting
first curing agent and a second, latent curing agent if additional
crosslinking ability is desired
to take advantage of downhole heat and pressure conditions. Either of these
first and/or
second amine-based curing agents may be reactive, nonreactive or partially
reactive. If the
amine curing agent is reactive, however, the amine is preferably chosen to
favor the
formation of polyurea by reaction with the isocyanate.
[00080] Suitable single amine-based curing agents, catalysts or a
mixture of
amine-based curing agents for promoting the formation of polyurea can include,
but are not
limited to, 2,T-dimorpholinodiethyl ether; bis-dimethylaminoethylether ;
ethylene diamine;
hexamethylene di amine; 1-methyl-2,6-cyclohexyl diamine; 2,2,4- and 2,4,4-
trimethy1-1,6-
hexanediamine; 4,4'-bis-(sec-butylamino)-dicyclohexylmethane and derivatives
thereof; 1,4-
bis-(sec-butylamino)-cyclohexane; 1,2-bis-(sec-butylamino)-cyclohexane; 4,4'-
19
Date Recue/Date Received 2021-09-16
dicyclohexylmethane diamine; 1,4-cyclohexane-bis-(methylamine); 1,3-
cyclohexane-bis-
(methylamine), isomers, and mixtures thereof; diethylene glycol bis-
(aminopropyl)ether; 2-
methylpentamethylene-diamine; diaminocyclohexane, isomers, and mixtures
thereof;
diethylene triamine; triethylene tetramine; tetraethylene pentamine; propylene
diamine; 1,3-
diaminopropane; dimethylamino propylamine; diethylamino propylamine; imido-bis-
(propylamine); monoethanolamine, diethanolamine; triethanolamine;
monoisopropanolamine,
diisopropanolamine; isophoronediamine; 4,4'-methylenebis-(2-chloroaniline);
3,5-
dimethylthio-2,4-toluenediamine; 3,5-dimethylthio-2,6-toluenediamine; 3,5-
diethylthio-2,4-
toluenediamine; 3,5-di ethylthio-2,6-toluenediamine; 4,4'-bis-(sec-butylamino)-
benzene; and
derivatives thereof; 1,4-bis-(sec-butylamino)-benzene; 1,2-bis-(sec-
butylamino)-benzene;
N,N-dialkylamino-diphenylmethane; trimethyleneglycol-ci-p-aminobenzoate;
polytetramethyleneoxide-di-p-aminobenzoate; 4,4'-methylenebis-(3-chloro-2,6-
diethyleneaniline); 4,4'-methylenebis-(2,6-diethylaniline); meta-
phenylenediamine;
paraphenylenediamine; N,N'-diisopropyl-isophoronediamine; polyoxypropylene
diamine;
propylene oxide-based triamine; 3,3'-dimethy1-4,4'-ciaminocyclohexylmethane;
and mixtures
thereof. In one embodiment, the amine-terminated curing agent is 4,4'-bis-(sec-
butylamino)-
dicyclohexylmethane. Preferred amine-based curing agents and catalysts that
aid the ¨NCO-
and water reaction to form the polyurea-type links for use with the present
invention include
triethylenedi amine; bis(2-dimethylaminoethyl)ether; tetramethylethylenedi
amine;
pentamethyldiethylenetriamine; 1,3,5-tris(3-(dimethylamino)propy1)- hexahydro-
s-triazine
and other tertiary amine products of alkyleneamines.
[00081] Additionally, other catalysts that promote the reaction of
isocyanates
with hydroxyls and amines that are known by the industry can be used in the
present
invention, e.g., transition metal catalysts of Groups III or IV used for
polyurea-type foams.
Particularly preferred metal catalysts include duibutyltin dilaurate that can
be added to the
water or polyol feeds for co-introduction during the coating process.
[00082] Also preferred are catalysts that promote isocyanate
trimerization over
other reaction mechanisms. See, e.g., US Patent No. 5,264,572 (cesium fluoride
or
tetraalkylammonium fluoride), US Patent No. 3,817,939 (organic carbonate
salt), and US
Patent No. 6,127,308 (lithium salts, lithium hydroxide, allophane catalysts
such as tin-2-
ethylhexanoate or tin octoate, and organic compounds containing at least one
hydroxyl
group). Phosphorous-based catalysts have been used to promote the formation of
polycarbodiimides (see the examples in Tanguay et al. US 2011/0297383) and are
not
preferred for use in the present invention.
Date Recue/Date Received 2021-09-16
[00083] The amine-based curing agent may have a molecular weight of
about
64 or greater. In one embodiment, the molecular weight of the amine-curing
agent is about
2000 or less and is a primary or secondary amine. Tertiary amines will not
generally be used
as a reactant for forming polyurea-type coatings unless reactivity is provided
by additional
functionality, e.g., such as with triethanolamine.
[00084] Of the list above, the saturated amine-based curing agents
suitable for
use to make polyurea-type coatings according to the present invention include,
but are not
limited to, ethylene diamine; hexamethylene diamine; 1-methyl-2,6-cyclohexyl
diamine;
2,2,4- and 2,4,4-trimethy1-1,6-hexanediamine; 4,4'-bis-(sec-butylamino)-
dicyclohexylmethane; 1,4-bis-(sec-butylamino)-cyclohexane; 1,2-bis-(sec-
butylamino-
cyclohexane; derivatives of 4,4'-bis-(sec-butylamino)-dicyclohexylmethane;
4,4'-
dicyclohexylmethane diamine; 1,4-cyclohexane-bis-(methylamine); 1,3-
cyclohexane-bis-
(methylamine); diethylene glycol bis-(aminopropyl) ether; 2-
methylpentamethylene-diamine;
diaminocyclohexane; di ethylene triamine; triethylene tetramine; tetraethylene
pentamine;
propylene diamine; dipropylene triamine; 1,3-diaminopropane; dimethylamino
propylamine;
diethylamino propylamine; imido-bis-(propylamine); monoethanolamine,
diethanolamine;
monoisopropanolamine, diisopropanolamine; isophoronediamine; N,N'-
diisopropylisophorone di amine and mixtures thereof.
[00085] In one embodiment, the curative used with the prepolymer
include 3,5-
dimethylthio-2,4-toluenediamine,3,5-dimethyl-thio-2,6-toluenedi amine, 4,4'-
bis-(sec-
butylamino)-diphenylmethane, N,N'-diisopropyl-isophorone diamine;
polyoxypropylene
diamine; propylene oxide-based triamine; 3,3'-dimethy1-4,4'-
diaminocyclohexylmethane; and
mixtures thereof.
[00086] Because unhindered primary diamines result in a rapid reaction
between the isocyanate groups and the amine groups, in certain instances, a
hindered
secondary di amine may be more suitable for use. Without being bound to any
particular
theory, it is believed that an amine with a high level of stearic hindrance,
e.g., a tertiary butyl
group on the nitrogen atom, has a slower reaction rate than an amine with no
hindrance or a
low level of hindrance and further adds to the hydrolytic and thermal
stability of the final
product. For example, 4,4'-bis-(sec-butylamino)-dicyclohexylmethane (CLEARLINK
10000
from Huntsman Corporation in The Woodlands, Texas) may be suitable for use in
combination with an isocyanate to form the polyurea-type coating. In addition,
N,N'-
diisopropyl-isophorone diamine, also available from Huntsman Corporation,
under the
tradename JEFFLINKO, may be used as the secondary diamine curing agent.
21
Date Recue/Date Received 2021-09-16
[00087] In addition, a trifunctional curing agent can be used to help
improve
cross-linking and, thus, to further improve the chemical and/or abrasion
resistance of the
coating. In one embodiment, a diethylene triamine or triethylene tetramine are
both highly
reactive and are desirably added to the coating process with water.
[00088] The curing agents of the present invention can be added to the
coating
formulation simultaneously as any of these components or pre-coated on the
proppant.
Preferably, the curing agent and the reinforcing particulates are co-applied
with water at
substantially the same time that isocyanate is added to form the proppant
coating.
ADDITIVES
[00089] The proppant coating compositions of the invention may also
include
various additives that change its appearance, properties, handling
characteristics or
performance as a proppant or in fracturing or breaker fluids. For example, the
coatings of the
invention may also include pigments, tints, dyes, and fillers in an amount to
provide visible
coloration in the coatings. Other materials include, but are not limited to,
reaction rate
enhancers or catalysts, crosslinking agents, optical brighteners, propylene
carbonates,
coloring agents, fluorescent agents, whitening agents, UV absorbers, hindered
amine light
stabilizers, defoaming agents, processing aids, mica, talc, nanometer-sized
fillers that add an
additional function to the proppant, silane coupling agents (such as those in
US Patent No.
4,585,064), anti-slip agents, water affinity or repulsion components, water-
activated agents,
viscosifiers for the proppant coating operation or for release into a frac
fluid, flowaids,
anticaking agents, wetting agents, polymeric coating toughening agents such as
one or more
block copolymers, and components that act to remove at least some portion of
the heavy
metals and/or undesirable solutes found in subterranean groundwater. See,
copending US
patent application serial number 13/224,726 filed on 1 September 2011 entitled
"Dual
Function Proppants" and published as U.S. Application Publication No.
20130056204 on
March 7, 2013. The amount of any of these specific additives will be readily
determinable by
those skilled in the art with no more than routine tests. Preferably, they are
present in an
amount of about 15 weight percent or less.
[00090] Adhesion promoter agents can be used to increase the bond
strength
between the outer surface of the proppant core solid and any applied coating.
An adhesion
promoter can also be used at the outer surface or outside of the outermost
coating layer to
enhance adhesion between adjacent proppants. The adhesion promoter for
enhancing the
bond between the proppant core solid and the applied polymeric coating may be
the same or
22
Date Recue/Date Received 2021-09-16
different than the adhesion promoter that might be added to help bond the
added reinforcing
particulates into the polymeric coating. Preferably, they are the same or from
the same class
of compounds. The adhesion promoter for a nonfunctionalized particulate for
both the core-
polymer bonding as well as the polymer-reinforcing particulate bond can be
added at the
beginning of the coating process, throughout the coating process or towards
the end of the
coating process.
[00091] An especially preferred treatment for the cured proppant is to
use an
anticaking to enhance the handling characteristics of the proppants. Suitable
anticaking
agents include amorphous silica (e.g., silica flour, fumed silica and silica
dispersions) and
silica alternatives (such as those used in sandblasting as an alternative to
silica or
organofunctional silane like the DYNASYLAN fluids from Evonik Degussa
Corporation in
Chester, PA). These materials are applied to the outer surfaces of the coated
proppant solid to
prevent the formation of agglomerates during packing and shipping. Amorphous
silica is
preferably applied in an amount generally within the range from about 0.001
wt% to about 1
wt% based on the dry proppant weight.
[00092] An optional additional additive to the coating or in
particulates blended
with the proppants of the present invention is a contaminant removal component
that will
remove, sequester, chelate or otherwise clean at least one contaminant,
especially dissolved
or otherwise ionic forms of heavy metals and naturally occurring radioactive
materials
(NORMS), from subterranean water or hydrocarbon deposits within a fractured
stratum while
also propping open cracks in said fractured stratum. Preferably, the
contaminant removal
component is associated with the proppant solid as a chemically distinct solid
that is
introduced together with the proppant solid as: (a) an insoluble solid secured
to the outer or
inner surface of the proppant solid with a coating formulation that binds the
solids together,
(b) as a solid lodged within pores of the proppant solid or (c) as a chemical
compound or
moiety that is mixed into or integrated with a coating or the structure of the
proppant solid.
See copending US patent application serial number 13/224726 filed on 2
September 2011
entitled "Dual Function Proppants" and published as U.S. Application
Publication No.
20130056204 on March 7, 2013. Additional added functionality can also be in
the form of
fracture fluid breakers, de-emulsifiers, and bactericides.
[00093] The added functionality of an auxiliary particle to the
proppant may
also be in the form of an ion exchange resin that is pretreated or which
itself constitutes a
dissolvable solid for the slow release of corrosion or scale inhibitors. Such
slow release
materials could prove beneficial and advantageous to the overall operation and
maintenance
of the well.
23
Date Recue/Date Received 2021-09-16
PROPPANT CORE SOLIDS
[00094] The proppants can be virtually any small solid with an
adequate crush
strength and lack of chemical reactivity. Suitable examples include sand,
ceramic particulates
(such as aluminum oxide, silicon dioxide, titanium dioxide, zinc oxide,
zirconium dioxide,
cerium dioxide, manganese dioxide, iron oxide, calcium oxide, magnesium oxide,
or
bauxite), or also other granular materials.
[00095] Proppant sands are a preferred type of proppant for the
present
invention. Sand is mainly used in the hydraulic fracturing process of natural
gas and oil wells
to increase their productivity of valuable natural resources. Proppant sand is
monocrystalline
with a high silica content of at least 80 wt%, and more typically has a silica
content of greater
than about 97 wt% silica.
[00096] The American Petroleum Institute specifications place the
following
limitations on sieve distribution for proppants suitable for use in hydraulic
fracturing:
= At least 90% of material must fall between the two mesh sizes,
= No more than 10% of the material may be coarser than the largest mesh
size,
= No more than 0.1% of the material may be coarser than the next largest
mesh size,
e.g. for 20/40, up to 10% of the proppant may be between 16 and 20 mesh, but
no
more than 0.1% can exceed 16 mesh, and
= No more than 1% of material is permitted to fall onto the pan.
[00097] Proppants are divided into low-density, medium density, high-
density
when determined in bulk. Proppant crush strengths are divided into 52 MPa, 69
MPa, 86 MPa
and 103 MPa series. The size specifications of proppant sand are generally 12-
18 mesh, 12-
20 mesh, 16-20 mesh, 16-30 mesh, 20-40 mesh, between 30-50 mesh, 40-60 mesh,
40-70
mesh and smaller. The proppants to be coated preferably have an average
particle size within
the range from about 50 gm and about 3000 gm, and more preferably within the
range from
about 100 gm to about 2000 gm.
COATING METHOD
[00098] The coating process of the present invention preferably
produces a
polyurethane or polyurea-type coating on the proppant core solids that is
hard, durable and
resists dissolution under the rigorous combination of high heat, agitation,
abrasion and water
found downhole in a fractured subterranean formation. Preferably, the cured
coating exhibits
a sufficient resistance (as reflected by a 10 day autoclave test or 10 day
conductivity test) so
24
Date Recue/Date Received 2021-09-16
that the coating resists loss by dissolution in hot water ("LOT loss") of less
than 25 wt%, more
preferably less than 15 wt%, and even more preferably a loss of less than 5
wt%. The
substantially cured coating of the invention thus resists dissolution in the
fractured stratum
while also exhibiting sufficient consolidation and resistance to flow back
without the use of
an added bonding activator while also exhibiting sufficiently high crush
strength to prop open
the fractures and maintain their conductivity for extended periods.
[00099] The temperature of the coating process is not particularly
restricted
outside of practical concerns for safety and component integrity. The
preferred conditions for
the coating/curing step of the present invention are generally at conditions
within the range of
about 500 to about 225 C, more preferably at a temperature within the range
from about 75
C to about 150 C, and most preferably at a temperature within the range from
about 80 C to
about 135 C. As noted above, this temperature is conveniently achieved by
heating or using
heated proppant solids. The preferred temperature range avoids a number of
emissions issues,
reduces the amount of energy consumed in the coating process and also reduces
the cooling
time for the coated proppants for further handling and packaging.
[000100] Mixing can be carried out on a continuous or discontinuous
basis in
series or in several runs with a single mixer, but the specific mixer used to
coat the proppants
is not believed to be critical for the present invention. Suitable mixers
include tumbling-type
mixers, fluid beds, a pug mill mixer or an agitation mixer can be used. For
example, a drum
mixer, a plate-type mixer, a tubular mixer, a trough mixer or a conical mixer
can be used.
The easiest way is mixing in a rotating drum. As continuous mixer, a worm gear
can, for
example, be used.
[000101] A preferred mixer type is a tumbling-type mixer that uses a
rotating
drum driven by an electrical motor. The load on the motor can be used as a
measure of the
viscosity of the tumbling solids and the degree to which they are forming
agglomerates or
resinous deposits inside the mixer: the electrical load on the motor increases
as the
agglomeration and fouling increase. Adding water to the mixing solids or
adding one or more
of the polyurea precursor components in an aqueous solution, emulsion or
suspension can
help to reduce this load increase and retain the free-flowing nature of the
mixing solids,
thereby enabling even larger productivity from the mixer.
[000102] As noted above, water is preferably added to the isocyanate at
a rate
sufficient to form a reactive amine species which then reacts almost
immediately with
adjacent isocyanate to form polyurea. Preferably, water and an isocyanate-
containing
component are used in an amount within the range from about 5-30% water, 95-
70% ISO
consistent with the demands of the catalyst to promote the hydrolysis of the
ISO and
Date Recue/Date Received 2021-09-16
temperature of the substrate during the timed additions onto the proppant
substrate. The water
and isocyanate are added at a rate sufficient to maintain a proportion of 5-30
to 95-70 so as to
promote the in-situ formation of a reactive amine component from the
isocyanate which then
reacts with unconverted isocyanate to make the polyurea-type coating of the
present
invention. These ratios also control the ultimate nature of the polyurea
produced including
plastic flow, stress response and its ability to bond with other coated
particles.
[000103] Most of the components for the coating are preferably added
along
with either the water or the isocyanate to facilitate proper mixing and
metering of the
components. A silane adhesion promoter is added to the heated sand or among
the initial
steps of the coating process. A colorant is added during the coating process
by an injection
line into the coating mixer. A last step includes adding a suspension of
reinforcing
particulates as the polymeric components are reacting and curing. A surfactant
and/or flow
aid can be added after the proppants have been coated to enhance wettability
and enhanced
flow properties with lower fines generation, respectively.
[000104] The method for the production of coated proppants according to
the
present invention can be implemented without the use of solvents. Accordingly,
the mixture
obtained in step (a) in one embodiment of the method is solvent-free, or is
essentially solvent-
free. The mixture is essentially solvent-free, if it contains less than 20
wt%, preferably less
than 10 wt%, more preferably less than 5 wt%, and still more preferably less
than 3 wt%, and
most preferably less than 1 wt% of solvent, relative to the total mass of
components of the
mixture.
[000105] The coating is preferably performed at the same time as the
curing of
the coating on the proppant. In the present invention, the coated proppant
becomes free-
flowing at a time of less than 5 minutes, preferably within the range of 1-4
minutes, more
preferably within the range of 1-3 minutes, and most preferably within the
range of 1-2
minutes to form a coated, substantially cured, free-flowing, coated proppant.
This short cycle
time combines with the relatively moderate coating temperatures to form a
coating/curing
process that provides lower energy costs, smaller equipment, reduced emissions
from the
process and the associated scrubbing equipment, and overall increased
production for the
coating facility.
[000106] The coating material or combinations of different coating
materials
may be applied in more than one layer. For example, the coating process may be
repeated as
necessary (e.g. 1-5 times, 2-4 times or 2-3 times) to obtain the desired
coating thickness. Any
or all of these coatings may contain the reinforcing particulates of the
present invention.
26
Date Recue/Date Received 2021-09-16
[000107] Alternatively, the reinforced coating of the present invention
can be
applied as the outermost layer over, e.g., a precured or curable phenolic
coating, to take
advantage of the underlying properties of the phenolic coating while adding
the bonding
ability of the polyurethane or polyurea-type coating. Such an outer coating
would avoid the
need for an added activator or surfactant compounds that are typically
required for the
phenolic coatings and thereby also avoid the potential for chemical
incompatibility or
interference with the formulated fracturing or breaker fluids used in
hydraulic well fracturing.
A typical size range for the final, coated proppant is desirably within the
range of about 16 to
about 100 mesh.
[000108] The reinforced coating of the present invention can also be
applied to a
previously coated proppant or formed as an outermost "skin" layer of a
substantially
continuous coating. This skin layer of reinforced coating reduces any residual
surface
tackiness or unreacted moieties remaining after the coating reactions and
reduces deformation
of the resulting proppant coating. This skin is formed by waiting until less
than 20%,
preferably less than 10% of the time remaining in the coating and curing
process remains
before adding water to the process. See our copending US patent application
serial number
13/355,969 filed on 23 January 2012 entitled "Manufacture of Polymer Coated
Proppants"
and published as U.S. Application Publication No. 20130186624 on July 25,
2013. The
amount of added water, independent of any reinforcing particulates, should be
small, i.e., less
than 10 wt%, preferably less than 5 wt% of the total proppant mixture and just
enough to
maintain a free-flowing mixture without forming a slurry. In a polyurea-type
coating, the
small amount of water is believed to encourage remaining unreacted isocyanate
moieties to
react and form a polyurea-type skin coating on the surface of the underlying
proppant.
[000109] Similarly, utilizing the high reactivity of a polyurea system,
a polyurea
can be formed as the basecoat, followed by a reinforced topcoat of a phenolic,
or epoxy,
polyurethane or other coating. As noted above, any or all of these can include
functionalized
reinforcing particulates or, with an adhesion promoter, non-functionalized
particulates.
[000110] The amount of coating resin, that is, of the preferred
polyurethane or
polyurea-based components that are applied to a proppant, is preferably
between about 0.5
and about 10 wt%, more preferably between about 1% and about 5 wt%, resin
relative to the
mass of the proppant as 100 wt%. With the method according to the present
invention
proppants can be coated at temperatures between about 50 C and about 225 C,
preferably
within the range of about 750-1250 C and preferably in a solvent-free manner.
The coating
process requires a comparatively little equipment and if necessary can also be
carried out near
27
Date Recue/Date Received 2021-09-16
the sand or ceramic substrate source, near the geographically location of the
producing field
or at/near the well itself.
[000111] The coated proppants can additionally be treated with surface-
active
agents, anticaking agents, or auxiliaries, such as talcum powder or stearate
or other
processing aids such as fine amorphous silica to improve pourability,
wettability (even to the
extent that a water wetting surfactant can be eliminated), dispersability,
reduced static charge,
dusting tendencies and storage properties of the coated product.
[000112] If desired and by no means is it required, the coated
proppants can be
baked or heated for a period of time sufficient to further enhance the
ultimate performance of
the coated particulates and further react the available isocyanate, hydroxyl
and reactive amine
groups that might remain in the coated proppant. Such a post-coating cure may
occur even if
additional contact time with a catalyst is used after a first coating layer or
between layers.
Typically, the post-coating cure step is performed like a baking step at a
temperature within
the range from about 1000 - 200 C for a time of about 1 minute to 4 hours,
preferably the
temperature is about 125 - 200 C for about 1-30 minutes.
[000113] Even more preferably, the coated proppant is cured for a time
and
under conditions sufficient to produce a coated proppant that exhibits a loss
of coating of less
than 25 wt%, preferably less than 15 wt%, and even more preferably less than 5
wt% when
tested according to simulated downhole conditions under ISO 13503-5:2006(E).
Even more
preferably, the coated proppant of the present invention exhibits the low dust
and handling
characteristics of a conventional pre-cured proppant (see API RP 60) but also
exhibits a crush
test result at 10,000 psi of less than 10%, more preferably less than 5%, and
especially less
than 2%. The coated proppants of the invention preferably also have an
unconfined
compressive strength of greater than 20 psi and more preferably more than 500
psi with a
fracture conductivity at a given closure stress that is substantially equal
to, or greater than, the
conductivity of a phenolic coating used in the same product application range.
USING THE COATED PROPPANTS
[000114] The invention also includes the use of the coated proppants in
conjunction with a fracturing liquid to increase the production of petroleum
or natural gas.
Techniques for fracturing an unconsolidated formation that include injection
of consolidating
fluids are also well known in the art. See U.S. Patent No. 6,732,800.
Generally speaking, a
fluid is injected through the wellbore into the formation at a pressure less
than the fracturing
pressure of the formation. The volume of consolidating fluid to be injected
into the formation
28
Date Recue/Date Received 2021-09-16
is a function of the formation pore volume to be treated and the ability of
the consolidating
fluid to penetrate the formation and can be readily determined by one of
ordinary skill in the
art. As a guideline, the formation volume to be treated relates to the height
of the desired
treated zone and the desired depth of penetration, and the depth of
penetration is preferably at
least about 30 cm radially into the formation. Please note that since the
consolidation fluid is
injected through the perforations, the treated zone actually stems from the
aligned
perforations.
[000115] Techniques for hydraulically fracturing a subterranean
formation will
be known to persons of ordinary skill in the art, and will involve pumping the
fracturing fluid
into the borehole and out into the surrounding formation. The fluid pressure
is above the
minimum in situ rock stress, thus creating or extending fractures in the
formation. In order to
maintain the fractures formed in the formation after the release of the fluid
pressure, the
fracturing fluid carries a proppant whose purpose is to prevent the fracturing
from closing
after pumping has been completed.
[000116] The fracturing liquid is not particularly restricted and can
be selected
from among the fracturing liquids known in the specific field. Suitable
fracturing liquids are
described, for example, in WC Lyons, GJ Plisga, "Standard Handbook Of
Petroleum And
Natural Gas Engineering," Gulf Professional Publishing (2005). The fracturing
liquid can be,
for example, liquefied petroleum gas (LPG), water gelled with polymers, an oil-
in-water
emulsion gelled with polymers, or a water-in-oil emulsion gelled with
polymers. In one
preferred embodiment, the fracturing liquid comprises the following
constituents in the
indicated proportions: 1000 I water, 20 kg potassium chloride, 0.120 kg sodium
acetate, 3.6
kg guar gum (water-soluble polymer), sodium hydroxide (as needed) to adjust a
pH-value
from 9 to 11, 0.120 kg sodium thiosulfate, 0.180 kg ammonium persulfate and
optionally a
crosslinker such as sodium borate or a combination of sodium borate and boric
acid to
enhance viscosity.
[000117] In addition, the invention relates to a method for the
production of
petroleum or natural gas which comprises the injection of the coated proppant
into the
fractured stratum with the fracturing liquid, i.e., the injection of a
fracturing liquid which
contains the coated proppant, into a petroleum- or natural gas-bearing rock
layer, and/or its
introduction into a fracture in the rock layer bearing petroleum or natural
gas. The method is
not particularly restricted and can be implemented in the manner known in the
specific field.
The concentration of proppant in the fracturing fluid can be any concentration
known in the
art, and will typically be in the range of about 0.5 to about 20 pounds of
proppant added per
gallon of clean fluid.
29
Date Recue/Date Received 2021-09-16
[000118] The fracturing fluid can contain an added proppant-retention
agent, e.g.
a fibrous material, a curable resin coated on the proppant, platelets,
deformable particulates,
or a sticky proppant coating to trap proppant particulates in the fracture and
prevent their
production through the wellbore. Fibers, in concentration that preferably
ranges from about
0.1% to about 5.0% by weight of proppant, for example selected from natural
organic fibers,
synthetic organic fibers, glass fibers, carbon fibers, ceramic fibers,
inorganic fibers, metal
fibers and mixtures thereof, in combination with curable resin-coated
proppants are
particularly preferred. The proppant- retention agent is intended to keep
proppant solids in the
fracture, and the proppant and proppant-retention agent keep formation
particulates from
being produced back out from the well in a process known as "flowback."
EXAMPLE
Example 1 ¨ Polyurea-type Coatings with Reinforcing Functionalized Silica
[000119] Table 1 shows a sequence of actions, times of addition and
ingredients
for making a reinforced, urea-type proppant coating that takes advantage of
water used for
urea formation to incorporate a dispersion of functionalized silica into the
coating in a
substantially even distribution throughout the polymeric coating.
Table 1 - LAB CYCLE (Functionalized Silica Dispersion):
TIME(Start/Stop)(Min:Sec) STEP
0:00 2000g of preheated sand (208 F) is added to a lab mixer
0:00/0:05 2g of a silane possessing a reactive primary amino group
and
hydrolyzable ethoxysilyl groups is added with mixing over a 5
sec period as an adhesion promoter between the sand and the
polymeric coating
0:15/2:00 36.5g of poly-MDI is added over a 105 second period to
coat
the sand core solids
0:20/0:25 2g of an oil based colorant is optionally added over a 5
second
period
0:30/2:00 31.8g of an aqueous mix of 10.8g chemically
functionalized
silica (37-40 wt% solids), 20g water, and 1.0g of a tertiary
amine blowing catalyst are added over this 90 sec period to
react with the poly-MDI coated core sand solids and form a
polymeric coating with a substantially uniform dispersion of
chemically bonded silica particulates
2:30 Coated sand is discharged at 175 F
Date Recue/Date Received 2021-09-16
Example 2 - Polyurea-type Coatings with Reinforcing Non-Functionalized Silica
[000120] Table 2 shows a sequence of actions, times of addition and
ingredients
for making a reinforced urea-type proppant coating that takes advantage of
water used for
urea formation to incorporate a dispersion of non-functionalized silica into
the coating.
Table 2 - LAB CYCLE (Non-Functionalized Silica Dispersion):
TIME(Start/Stop)(Min:Sec) STEP
0:00 2000g of preheated sand (207 F) is added to a lab mixer
0:00/0:05 2g of a silane possessing a reactive primary amino group
and
hydrolyzable ethoxysilyl groups is added with mixing over a 5
sec period
0:15/1:45 36.5g of poly-MDI is added over a 90 second period
0:20/0:25 2g of an oil based colorant is added over a 5 second
period
0:30/1:45 31.8g of an aqueous mix of 10.8g non-functionalized
silica
(colloidal dispersion in water of amorphous silica 100 nm
spheres at 50 wt% concentration), 20g water, and 1.0g of a
tertiary amine blowing catalyst are added over this 90 sec
period
2:30 Coated sand is discharged at 176 F
[000121] Without wishing to be bound by a particular theory of
operation or
function, the use of the present invention enables chemical integration of
reinforcing
particulates into the proppant coating to form a reinforced, hybrid coating.
This hybrid should
be harder and outperform what might be expected by adding only a silica
"filler" into the
proppant coating that is merely dispersed in the coating but is not otherwise
grafted into the
polymer or chemically bound to it. This suggests that ability to adjust and
control the amount
of proppant deformation and conductivity characteristics that are exhibited by
the proppant to
more closely tailor the proppant to the demands of the fractured field with
only minor
adjustments to the coating process and formulation.
[000122] The advantages of using a waterborne dispersion of reinforcing
particulates include: (a) the tolerance of urea-type and polyurethane polymers
for the water
used in the dispersion, and (b) the benefit of dealing with discrete very
small, nanometer-size
particulates to provide high surface area for chemical interactions with the
developed and
reacting polymers of the coating.
31
Date Recue/Date Received 2021-09-16
[000123] Some possible reasons for how and/or why the invention works
as well
as it does might include:
1) The isocyanate and -NCO groups are hydrolyzed by the appropriate
selection of an active catalyst (usually tertiary amines) in combination with
water;
2) The amount of water used is determined by considering the efficiency
of the water/catalyst mix while also avoiding excessive cooling by water loss;
3) The reaction temperature is high enough to drive the reaction but low
enough to control removal of added water;
4) The isocyanate and water catalyst are fed simultaneously onto the
heated sands to create amines throughout the coating;
5) The generated amines react very fast with neighboring -NCO groups to
produce the urea and/or biuret-type linkages; and
6) Because the urea reaction accommodates the presence of water, it is
equally tolerant of a water dispersion containing other additives, such as
functionalized reinforcing particulates, especially silica, while the blowing
catalyst promotes the reaction of ¨NCO groups with hydroxyl functionalities
from the surface of hydrated or adhesively promoted silica or chemically
modified silica.
[000124] Once those skilled in the art are taught the invention, many
variations and
modifications are possible without departing from the inventive concepts
disclosed herein.
The invention, therefore, is not to be restricted except in the spirit of the
appended claims.
32
Date Recue/Date Received 2021-09-16
