Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SSND.269919
HYDRAULIC FRACTURE COMPOSITION AND METHOD
RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No.
15/136,352, filed April 22, 2016, which is a continuation-in-part of U.S.
patent application Ser.
No. 15/011,111, filed January 29, 2016, which is a continuation-in-part of
U.S. patent application
Ser. No. 14/171,920, filed February 4, 2014, which is a continuation of U.S.
patent application
Ser. No. 13/418,227, filed Mar. 12, 2012, now U.S. Patent No. 9,057,014 issued
June 16, 2015;
which is a continuation-in-part of U.S. patent application Ser. No.
13/299,288, filed Nov. 17,
2011, now Patent No. 8,661,729 issued March 4, 2014; which is a continuation-
in-part of U.S.
patent application Ser. No. 12/789,177, filed May 27, 2010, now U.S. Pat. No.
8,341,881 issued
Jan. 1, 2013; which is a continuation of U.S. patent application Ser. No.
12/324,608, filed on
Nov. 26, 2008 now U.S. Pat. No. 7,726,070, issued Jun. 1, 2010; which claims
the benefit of
U.S. Provisional Patent Application Ser. No. 61/012,912, filed Dec. 11, 2007;
all of which are
hereby incorporated by reference in their entirety.
BACKGROUND
[0002] 1. The Field of the Invention
[0003] This invention relates to oil field and oil well development, and,
more
particularly, to novel systems and methods for fracturing and propping
fissures in oil-bearing
formations to increase productivity.
[0004] 2. The Background Art
[0005] Oil well development has over one hundred years of extensive
engineering and
chemical improvements. Various methods for stimulating production of well
bores associated
with an oil reservoir have been developed. For example, United States Patent
Application
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1
Publication US 2009/0065253 Al by Suarez-Rivera et al. and entitled "Method
and System for
Increasing Production of a Reservoir" is incorporated herein by reference in
its entirety and
provides a description of fracturing technology in order to increase
permeability of reservoirs.
Moreover, various techniques exist to further improve the fracture channels,
such as by acid
etching as described in U.S. Pat. No. 3,943,060, issued Mar. 9, 1976 to Martin
et al., which is
likewise incorporated herein by reference in its entirety.
[0006]
In general, different types of processes require various treatments. In
general, well
production can be improved by fracturing formations. Fracturing is typically
done by pumping a
formation full of a fluid, containing a large fraction of water, and
pressurizing that fluid in order
to apply large surface forces to parts of the formation. These large surface
forces cause stresses,
and by virtue of the massive areas involved, can produce extremely high forces
and stresses in
the rock formations. Accordingly, the rock formations tend to shatter,
increasing porosity an
providing space for the production oil to pass through the formation toward
the bore hole for
extraction. However, as the foregoing references describe, the chemistry is
not simple, the
energy and time required for incorporation of various materials into mixtures
is time, money,
energy, and other resource intensive.
[0007]
It would be an advance in the art if such properties as viscosity,
absorption,
mixing, propping, and so forth could be improved by an improved composition
and method for
introduction.
BRIEF SUMMARY OF THE INVENTION
[0008]
In view of the foregoing, in accordance with the invention as embodied
and
broadly described herein, a method, apparatus, and composition are disclosed
in certain
embodiments in accordance with the present invention, as including a substrate
that may be
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formed of sand, rock product, ceramic sand, gravel, or other hard and
structurally strong
materials, provided with a binder to temporarily or permanently secure a
hydrating polymer in
proximity to the substrated. When used herein any reference to sand or
proppant refers to any or
all of these used in accordance with the invention. In certain embodiments of
a method in
accordance with the invention, a composition as described may be mixed
directly into drilling
fluids, such as a fracturing fluid made up of water and other additives.
[00091
By virtue of the increased surface area and weight provided to the
polymeric
powders affixed to the substrate, the surface area, and consequently the
frictional drag, is greatly
increased, sweeping the material of the invention into a flow of fluid. This
greatly decreases the
time required to absorb polymers into the fluid.
[0010]
In fact, rather than having to wait to have the polymers thoroughly mixed,
or
absorb a full capacity of water, and thereby flow properly with the drilling
fluid or fracturing
fluid, a composition in accordance with the invention will sweep along with
the fluid
immediately, with the weight of the substrate submerging the polymer.
Meanwhile, the cross
sectional area presented results in hydrodynamic drag sweeps the composition
along with the
flow.
[0011]
Meanwhile, over time, the polymeric powder adhered to the substrate will
absorb
water, without the necessity for the time, energy, temperature, mixing, and so
forth that might
otherwise be required by surface mixing. Thus, the composition in accordance
with the invention
is immediately transportable and flows, relying on the drilling or fracturing
fluid as its carrier.
[0012]
Moreover, as the polymer tends to pick up more water, the density of the
granule
of substrate and polymer powder becomes closer to the density of water.
Accordingly, the size
increase and the density change tend to drive the particles of the composition
even more
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homogeneously with the flowing fluid. Thus, the sand does not settle out in
various eddies,
obstructions, and other locations of low velocity. Rather, the sand continues
to be carried with
the fluid, providing a double benefit. That is, the sand weight and area helps
to initially mix and
drive the particles (granules) with the fluid. Thereafter, the hydration of
the polymer tends to
increase the surface area and reduce the density of the granule or particle,
tending to make the
particles flow even better and more homogeneously with the surrounding fluid.
[0013]
Ultimately, as the particles (granules) of the composition flow into fracture
locations, they provide very small proppants as the substrate, such as sand,
becomes trapped and
lodged at various choke points. Nevertheless, because of the small size, the
sand or other
substrate acting as a proppant, simply needs to provide an offset, keeping
fractured surfaces from
collapsing back against one another. By providing the small, strong points of
separation, the
substrate provides a well distributed proppant, carried to maximum extent that
the fluids will
travel, and deposited in various traps, choke points, and the like.
[0014]
The net saving in time, money, energy for heating and pumping, and the like is
significant. Meanwhile, various technologies for reducing friction in the flow
of fluid pumped
into bore holes and other formation spaces is described in several patents,
including U.S. Pat. No.
3,868,328, issued Feb. 25, 1975 to Boothe et al. and directed to friction
reducing compounds, as
well as U.S. Pat. No. 3,768,565, issued Oct. 30, 1973 to Persinski et al. and
directed to friction
reducing, U.S. Patent Application Publication US 2001/0245114 Al by Gupta et
al. directed to
well servicing fluid, and U.S. Patent Application Publication US 2008/0064614
Al by Ahrenst et
al. and directed to friction reduction fluids, all described various
techniques, materials, methods,
and apparatus for developing, implementing, and benefitting from various well
fluids. All the
foregoing patent application publications and patents are hereby incorporated
by reference.
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[0015]
Similarly, the development of various chemicals has been ubiquitous in oil
field
development. For example, U.S. Pat. No. 3,442,803, issued May 6, 1969 to
Hoover et al. is
directed to thickened friction reducers, discusses various chemical
compositions, and is also
incorporated herein by reference in its entirety.
[0016]
In one embodiment of an apparatus, composition and method in accordance with
the invention, a method may be used for formation fracturing. The formation
may be in rock and
within or near an oil reservoir underground. One may select an oil field
region having a
formation to be fractured. Fracturing may be sought to increase production. By
providing a bore
into the formation and a pump, a carrier material, typically comprising a
liquid, and sometimes
other materials dissolved or carried therein may be pumped into the formation
through the bore.
[0017]
The carrier as a liquid, or slurry comprising a liquid, or otherwise
containing a
liquid may be driven by the pump to be pressurized into the formation.
However, the carrier may
be provided an additive formed as granules. Each granule may include a
substrate, such as a
grain of sand, ceramic sand, crushed rock, other rock products, or the like
having bonded thereto
many particles (e.g. powder) formed from a polymer.
[0018]
The polymer may be selected to have various properties, including lubricity,
water absorption, water solubility, or the like. This hydrophilic polymer may
be bonded
permanently, temporarily, or the like to secure to the substrate. Various
binders may be used
alone or in combination. These may range from a solvent (e.g., organic or
water) simply
softening the polymer itself to bond it, to glues, sugars, molasses, and
various other saccharides,
as well as other products, including starches, other polymers, and so forth.
[0019]
Thus, with some bonds, the polymer powder may be less permanent or attached to
have a bond that is less robust. Over time, the polymer powder so attached may
wear off, pull
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away, or otherwise remove from the substrate into the carrier fluid, and may
even act as a
viscous agent, lubricant, or the like in the carrier.
[0020]
The method may include introducing the additive directly into the carrier. The
more dense substrate will immediately submerge the granules in the carrier at
ambient
conditions. Thus heating, extensive mixing, waiting, and the like may be
dispensed with, as the
granules typically will not float or resist mixing once initial surface
tension is broken.
[0021]
Pumping the carrier toward the formation is possible immediately. The carrier
fluid carries the granules by the liquid dragging against the substrate (with
the particles of
polymer attached. The substrate's cross sectional area engages immediately the
surrounding
liquid, dragging it into the carrier to flow substantially immediately
therewith.
[0022]
Meanwhile, weighting, by the substrate of the polymer, permits the granules to
flow into and with the carrier independently from absorption of any of the
liquid into the
polymer. Nevertheless, over time, absorbing by the polymer a portion of the
liquid results in the
polymer expanding and providing by the polymer, lubricity to the carrier with
respect to the
formation;
[0023]
Creating fractures may be accomplished by pressurizing the carrier in the
formation. This creates fissures or fractures. Thus, flowing of the carrier
and particles throughout
the fractures or fissures in the formation results in lodging, by the
particles, within those
fractures or fissures. Unable to re-align, adjacent surfaces of rock, now
fracture cannot close
back together due to propping open the fractures by the substrate granules
lodging in the
fractures.
[0024]
The substrate is best if selected from an inorganic material, such as sand,
ceramic
sand, or other hard, strong, rock product. The polymer may be selected from
natural or
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synthetically formulated polymers. For example polymers of at acrylic acid,
acrylate, and various
amides are available. Polyacrylamide has been demonstrated suitable for all
properties discussed
above.
[0025]
In fracturing a rock formation, the method may include providing an additive
comprising a substrate formed as granules, each having an exterior surface,
particles formed of a
hydrophilic material, the particles being comminuted to a size smaller than
the size of the
granules and having first and second sides comprising surfaces. The granules
may each be coated
with the particles, the particles being dry and bonded to the exterior surface
by any suitable
binder, including the polymer softened with a solvent. The particles are each
secured by the first
side to the granules, the second side extending radially outward therefrom.
[0026]
Upon identifying a reservoir, typically far underground from thousands of feet
to
miles, perhaps, and extending in a formation of rock, one needs to provide a
bore into the
formation. Providing a carrier, comprising a liquid, and possibly other
materials known in the art,
is for the purpose of fracturing the formation. Introducing the additive
directly into the liquid at
ambient conditions is possible, because the substrate weighs the granules
down, and there is no
need for long mixing, heating or the like as in addition of polymers directly
to the carrier.
[0027]
Thus, pumping may continue or begin immediately to move the carrier and
additive down the bore and toward the formation. This results in exposing the
second sides of the
polymer powder particles directly to the liquid during transit of the carrier
and additive toward
and into the formation. The polymer particles thus begin absorbing, a portion
of the liquid,
typically principally water. Swelling of the polymer increases the size,
effective diameter, and
cross-sectional area, thus increasing the fluid drag on the granules.
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[0028]
Fracturing, typically by hydraulic pressure in the carrier creates
fissures in the
formation by fracturing the rock pieces in bending, or by layer separation,
with tensile stresses
breaking the rock. The resulting fissures allow carrying, by the carrier, of
the granules into the
fissures. However, fissures vary in size and path, resulting in lodging of
granules, within the
fissures. The granules do not settle out from the carrier, and thus may travel
far into the
formation and every fissure. However, each time a grain or granule is lodged
like a chock stone,
it obstructs the ability of the adjacent rock surfaces to close back with one
another.
[0029]
Thus, rather than the proppant (substrate) settling out ineffectually,
failing to prop
open the fissures, the granules are swept forcefully with the flow of the
carrier wherever the
carrier can flow, until lodged. Meanwhile, the lubricity of the polymer aids
the granules, and thus
the substrate from being slowed, trapped, or settled out by the slow flowing
boundary layer at the
solid wall bounding the flow.
[0030]
In summary, weighting, by the substrate, sinks the polymer into the
carrier readily
and independently from absorption of the liquid into the polymer. Mixing,
dissolving, and so
forth are unnecessary, as the substrate drags the polymer into the carrier,
and the carrier drags the
granule along with it in its flow path. Lubrication is provided by the polymer
between the
substrate of each granule and adjacent solid walls of the bore, passages
previously existing in the
formation, and the fissures formed by fracturing. Any separating, by some of
the powdered
polymer particles from the substrate, still reduces friction drag on passage
of the carrier and
particles within the formation.
[0031]
A composition for fracturing and propping a formation of rock may include
a
fluid operating as a carrier to be pumped into a rock formation, a substrate
comprising granules
of an inorganic material, each granule having an outer surface and a size
characterized by a
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maximum dimension thereacross, and all the granules together having an average
maximum
dimension corresponding thereto. A polymer comprising a hydrophilic material
selected to
absorb water in an amount greater than the weight thereof may be bound to the
substrate. The
polymer is comminuted to particles, each particle having a size characterized
by a maximum
dimension thereacross.
[0032] All the polymer particles may be characterized by an average
maximum
dimension, and an effective (e.g. hydraulic diameter). The average maximum
dimension of the
particles is best if smaller, preferably much smaller, than the average
maximum dimension of the
granules.
[0033] The particles of the polymer, bound to the substrate, will travel
with it in the fluid.
Particles of the polymer are thus further directly exposed to water in the
fluid during travel with
the fluid. The granules, flowing in the fluid, are carried by the hydrodynamic
drag of the fluid
against the cross-sectional area of the granules coated with the particles of
the polymer. The
polymer, selected to expand by absorbing water directly from the fluid,
increases the area and
drag, assisting distribution in the formation by the carrier fluid. The
polymer meanwhile operates
as a lubricant lubricating the motion of the substrate against the formation
during flow of the
granules against solid surfaces in the formation, bore, and fracture fissures.
[0034] The inorganic material, such as sand, ceramic sand, or the like is
typically sized to
lodge in fissures formed in the formation and has mechanical properties
rendering it a proppant
capable of holding open fissures formed in the formation.
[0035] In one embodiment, a method for making self-suspending proppant
particles is
provided. The method includes mixing a volume of substrate particles with a
liquid binder so
that at least a portion of the volume of substrate particles are at least
partly covered with the
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liquid binder on an outer surface, thereby forming binder-coated substrate
particles. The method
also includes using a water-in-oil emulsion to apply a first water-absorbing
polymer to at least a
portion of the binder-coated substrate particles so that the at least a
portion of the binder-coated
substrate particles are at least partly coated with the first water-absorbing
polymer, thereby
forming intermediate polymer-coated substrate particles. The method further
includes coating at
least a portion of the intermediate polymer-coated substrate particles with a
second water-
absorbing polymer to thereby form polymer coated substrate particles; and
drying the polymer
coated substrate particles to remove at least a portion of the water-in-oil
emulsion to thereby
form self-suspending proppant particles. Each of the self-suspending proppant
particles are at
least partly coated with the second water-absorbing polymer.
100361 In another embodiment, a method for making self-suspending
proppant particles
is provided. The method includes adding a volume of substrate particles to a
mixing vessel, the
substrate particles including sand particles. The method also includes
applying a first water-
absorbing polymer suspended in a liquid to at least a portion of the substrate
particles in the
mixing vessel, so that the at least a portion of the substrate particles are
at least partly coated
with the first water-absorbing polymer, thereby forming intermediate polymer-
coated substrate
particles. The first water-absorbing polymer includes an anionic
polyacrylamide. The method
further includes coating at least a portion of the intermediate polymer-coated
substrate particles
with a second water-absorbing polymer in powdered form to thereby form polymer-
coated
substrate particles; and drying at least a portion of the polymer coated
substrate particles to
remove at least a portion of the liquid thereby forming self-suspending
proppant particles.
100371 In yet another embodiment, self-suspending proppant particles are
provided. The
self-suspending proppant particles including substrate particles, the
substrate particles including
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sand. The self-suspending proppant particles further including an outer
polymeric coating
positioned on an outer surface of each of the substrate particles, the outer
polymeric coating
including at least one water-absorbing polymer in powdered form, where at
least a portion of the
outer polymeric coating is applied to each of the substrate particles using a
water-in-oil
emulsion.
[0038]
In another embodiment, a method for making self-suspending proppant particles
is provided. The method includes mixing substrate particles with a liquid
binder so that at least a
portion of the substrate particles are at least partly coated with the liquid
binder. The method
also includes applying one or more water-absorbing polymers to the at least a
portion of the
substrate particles that are at least partly coated with liquid binder to form
polymer-coated
substrate particles. The applying one or more water-absorbing polymers
includes applying a first
water-absorbing polymer in a first form, and applying a second water-absorbing
polymer in a
second form that is different from the first form, where the first and second
forms are selected
from a powder and an emulsion. Each of the first and second water-absorbing
polymers is about
20 mol. % anionic to about 50 mo. % anionic. The method further includes
exposing the
polymer-coated substrate particles to heat sufficient to cause crosslinking in
at least a portion of
the one or more water-absorbing polymers present on the polymer coated
substrate particles,
thereby forming self-suspending proppant particles.
[0039]
In yet another embodiment, a method for making self-suspending proppant
particles is provided. The method includes adding a volume of substrate
particles to a mixing
vessel, the substrate particles comprising sand. The method also includes
coating at least a
portion of the substrate particles with glycerol in the mixing vessel to form
binder-coated
substrate particles. Further, the method includes mixing a first water-
absorbing polymer with the
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binder-coated substrate particles in the mixing vessel. The first water-
absorbing polymer
includes a co-polymer of acrylamide monomers and acrylate monomers, where the
first water-
absorbing polymer is about 20 mol. % anionic to about 50 mo. % anionic, and
where the first
water-absorbing polymer is in powdered form. The method also includes,
subsequent to mixing
the first water-absorbing polymer with the binder-coated substrate particles,
mixing a second
water-absorbing polymer with first water-absorbing polymer and the binder-
coated substrate
particles to form polymer-coated substrate particles. The second water-
absorbing polymer
including a co-polymer of acrylamide monomers and acrylate monomers, where the
second
water-absorbing polymer is about 20 mol. % anionic to about 50 mo. % anionic.
The second
water-absorbing polymer is present in a water-in-oil emulsion, and each of the
polymer-coated
substrate particles includes a polymeric coating that includes the first water-
absorbing polymer
and the second water-absorbing polymer. The method further includes exposing
the polymer-
coated substrate particles to heat sufficient to cause crosslinking in the
polymeric coating present
on the polymer-coated substrate particles, thereby forming self-suspending
proppant particles.
[0040]
In yet another embodiment, self-suspending proppant particles are
provided. The
self-suspending proppant particles include substrate particles, the substrate
particles including
sand. The self-suspending proppant particles further include an outer
polymeric coating
positioned on an outer surface of each of the substrate particles, the outer
polymeric coating
including first and second water-absorbing polymers that are at least partly
covalently cross-
linked. Each of the first and second water-absorbing polymers include a co-
polymer of acrylate
monomers and acrylamide monomers, where a molecular weight of the first water-
absorbing
polymer is at least about 1 Million Daltons (g/mol) greater than a molecular
weight of the second
water-absorbing polymer. Each of the first and second water-absorbing polymers
is about 20
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MOI. % to about 50 mol. % anionic, where the first water-absorbing polymer was
applied to the
substrate particles in the form of an emulsion, and wherein the second water-
absorbing polymer
was applied to the substrate particles in powdered form. The self-suspending
proppant particles
remain suspended in a 1000 ppm CaCO3 aqueous solution for at least 30 minutes
at a
temperature of 170 F.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041]
The foregoing features of the present invention will become more fully
apparent
from the following description and appended claims, taken in conjunction with
the
accompanying drawings. Understanding that these drawings depict only typical
embodiments of
the invention and are, therefore, not to be considered limiting of its scope,
the invention will be
described with additional specificity and detail through use of the
accompanying drawings in
which:
[0042]
FIG. 1 is a schematic cross-sectional view of a material including a substrate
provided with a binder securing a hydrating polymer thereto in accordance with
the invention;
[0043]
FIG. 2 is a schematic block diagram of one embodiment of a process for
formulating and producing fluid additive particles in accordance with the
invention;
100441
FIG. 3 is a schematic diagram of the fluid-particle interaction in an
apparatus,
composition, and method in accordance with the invention;
[0045]
FIG. 4 is a chart illustrating qualitatively the relationship between
volumetric
increase over time at various temperatures, illustrating the improved
activation with minimum
mixing and temperature increase of particles in accordance with the invention;
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[0046]
FIG. 5 is a schematic diagram illustrating one embodiment of friction reducing
by
polymers used in compositions in accordance with the invention;
[0047]
FIG. 6 is a schematic diagram of the fracturing and proppant action of
particles in
accordance with a method and composition according to the invention;
[0048]
FIG. 7 is a schematic block diagram of a fracturing and propping process using
compositions and methods in accordance with the invention,
[0049]
FIG. 8 is an image of various self-suspending proppants in the presence of
various
flowing agents after being exposed to heat and humidity as described in
Example 3;
[0050]
FIG. 9 is an image of the various self-suspending proppants with various
flowing
agents of FIG. 9 after being exposed to additional heat and humidity as
described in Example 3;
[0051]
FIG. 10A depicts various self-suspending proppants with various flowing agents
after being centrifuged and inverted for an initial attempt to remove the
proppants from a
centrifuge tube as described in Example 3; and
[0052]
FIG. 10B depicts the self-suspending proppants of FIG. 10A after being removed
from the centrifuge tubes.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0053]
It will be readily understood that the components of the present invention, as
generally described and illustrated in the drawings herein, could be arranged
and designed in a
wide variety of different configurations. Thus, the following more detailed
description of the
embodiments of the system and method of the present invention, as represented
in the drawings,
is not intended to limit the scope of the invention, as claimed, but is merely
representative of
various embodiments of the invention. The illustrated embodiments of the
invention will be best
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understood by reference to the drawings, wherein like parts are designated by
like numerals
throughout.
[0054]
Referring to FIG. 1, a material 10 in accordance with the invention may
include a
substrate 12 formed of a suitable material for placement in the vicinity of a
fracture region. For
example, a substrate may be a particle of sand, ceramic sand, volcanic grit,
or other hard
material. In some embodiments, a substrate may be formed of organic or
inorganic material.
Nevertheless, it has been found effective to use sand as a substrate 12
inasmuch as it is
submersible in water and will not float as many organic materials will when
dry Likewise, the
sand as substrate 12 is comminuted to such a small size that interstices
between individual grains
of the sand substrate 12 provide ample space and minimum distance for water to
surround each
of the substrate 12 particles.
[0055]
In the illustrated embodiment, a binder 14 may be distributed as a
comparatively
thin layer on the surface of the substrate 12. Typical materials for binders
may include both
temporary and permanent binders 14. Permanent binders include many polymers,
natural and
synthetic. Temporary binders may be sugar-based or other water soluble
materials. For example,
corn syrup, molasses, and the like may form temporary binders. In the presence
of water, such
material may ultimately dissolve. Nevertheless, so long as the substrate 12 is
not turned, mixed,
or otherwise disturbed significantly, any other materials supported by the
binder 14 would not be
expected to dislocate.
[0056]
Otherwise, certain naturally or synthetically occurring polymers may also be
used
as a binder 14. Lignicite may be used as a binder 14. Lignicite is a byproduct
of wood, and
provides material having good adhesive properties, and substantial permanence
as a binder 14 on
a substrate 12. Any suitable insoluble polymer may be used for more permanent
binding.
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[0057]
Other polymers may be used to form a binder 14. For example, various
materials
used as glues, including mucilage, gelatin, other water soluble polymers
including, for example,
Elmer's.TM. glue, and the like may also operate as binders 14 to bind
materials to a substrate 12.
[0058]
In certain embodiments, the substrate 12 may be used in oil fields as a
substrate
12 for polymer additives to fracture fluids. In other situations, the
substrate 12 may be
implemented as a proppant.
[0059]
Pigment 16 may be implemented in any of several manners. For example, the
substrate 12 may have pigment 16 applied prior to the application of the
binder 14. In alternative
embodiments, the pigment 16 may actually be included in the binder 14, which
becomes a
pigmented coating on the substrate 12. In yet other embodiments, the pigments
16 may be added
to a hydration particle 18 either as a pigment 16 mixed therein, or as a
pigment 16 applied as a
coating thereto. Thus the location of the pigment 16 in the Figures is
schematic and may take
alternative location or application method.
[0060]
Particles 18 of a hydrophilic polymer material may be bonded to the
substrate 12
by the binder 14. Particles may be sized to substantially coat or periodically
coat the substrate 12.
[0061]
In certain embodiments, the hydrophilic material 18 may be a powdered
polymeric material 18 such as polyacrylamide or any of the materials in the
patent documents
incorporated by reference. In other embodiments, the particles 18 may actually
be organic
material having capillary action to readily absorb and hold water. In one
presently contemplated
embodiment of an apparatus in accordance with the invention, the particles 18
may be powdered
polymeric material in a dehydrated state, and having a capacity to absorb
water, typically many
times the weight (e.g., five to forty times) of a particular particle 18.
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[0062]
The substrate 12, in certain embodiments, may be some form of sand or
grannular
material. The sand will typically be cleaned and washed to remove dust and
organic material that
may inhibit the binder 14 from being effective Likewise, the substrate 12 may
be sized of any
suitable size. For example, sand particles may range from much less than a
millimeter in
effective diameter or distance thereacross to approximately two millimeters
across. Very coarse
sands or ceramic sands may have even larger effective diameters. Hydraulic
diameter is effective
diameter (four times the area divided by the wetted perimeter). However, in
one presently
contemplated embodiment, washed and dried sand such as is used in
construction, such as in
concrete, has been found to be suitable. Fine sands such as masonry sands tend
to be smaller, and
also can function suitably in accordance with the invention.
[0063]
Accordingly, the distance across each powder particle 18 may be selected to
provide an effective coating of powdered particles 18 on the substrate 12. In
one presently
contemplated embodiment, the effective diameter of the particles 18 may be
from about a 30
mesh size to about a 100 mesh size. For example, a sieve system for
classifying particles has
various mesh sizes. A size of about 30 mesh, able to pass through a 30 mesh
sieve, (i.e., about
0.6 mm) has been found suitable Likewise, powdering the particles 18 to a size
sufficiently small
to pass through a 100 mesh (i.e., about 0.015 mm) sieve is also satisfactory.
A mesh size of from
about 50 mesh to about 75 mesh is an appropriate material to obtain excellent
adhesion of
particles 18 in the binder 14, with a suitable size of the particles 18 to
absorb significant liquid at
the surface of the substrate 12.
[0064]
As a practical matter, about half the volume of a container containing a
substrate
12 as particulate matter will be space, interstices between the granules of
the substrate 12. One
advantage of using materials such as sand as the substrate 12 is that a
coating of the particles 18
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may provide a substantial volume of water once the particles 18 are fully
saturated. By contrast,
where the size of the particles 18 is too many orders of magnitude smaller
than the effective
diameter or size of the substrate particles 12, less of the space between the
substrate particles 12
is effectively used for storing water. Thus, sand as a substrate 12 coated by
particles 18 of a
hydrophilic material such as a polymer will provide substantial space between
the substrate
particles 12 to hold water-laden particles 18.
[0065]
The diameter of the particles 18, or the effective diameter thereof, is
typically
within about an order of magnitude (e.g., 10×) smaller than the
effective diameter of the
particles of the substrate 12. This order of magnitude may be changed. For
example, the order of
magnitude difference less than about 1 order of magnitude (i.e., 10×)
may still be effective.
Similarly, an order of magnitude difference of 2 (i.e., 100×) may also
function.
[0066]
However, with particles 18 too much smaller than an order of magnitude smaller
than the effective diameter of the substrate 12, the interstitial space may
not be as effectively
used Likewise, with an effective diameter of particles 18 near or larger than
about 1 order of
magnitude smaller than the size of the particles of the substrate 12, binding
may be less effective
and the particles 18 may interfere more with the substrate itself as well as
the flow of water
through the interstitial spaces needed in order to properly hydrate a material
10.
[0067]
Referring to FIG. 2, an embodiment of a process for formulating the material
10
may involve cleaning 22 the material of the substrate 12. Likewise, the
material of the substrate
12 may be dried 24 to make it more effective in receiving a binder 14. The
material of the
substrate 12 may then be blended 26.
[0068]
One embodiment, a ribbon blender provides an effective mechanism to perform
continuous blending as the binder 14 is added 28. Other types of mixers, such
as rotary mixers,
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and the like may be used. However, a ribbon blender provides a blending 26
that is effective to
distribute binder 14 as it is added 28.
[0069]
For example, if an individual particle of the substrate 12 receives too much
binder
14, and thus begins to agglomerate with other particles of the substrate 12, a
ribbon binder will
tend to separate the particles as a natural consequences of its shearing and
drawing action during
blending 26.
[0070]
As the binder 14 is added 28 to the mixture being blended 26, the individual
particles of the substrate 12 will be substantially evenly coated. At this
stage, the binder 14 may
also be heated in order to reduce its viscosity and improve blending.
Likewise, the material of the
substrate 12 or the environment of the blending 26 may be heated in order to
improve the
evenness of the distribution of the binder 14 on the surfaces of the substrate
12 materials or
particles 12.
[0071]
Blending 26 of the binder 14 into the material of the substrate 12 is complete
when coating is substantially even, and the texture of the material 10 has an
ability to clump, yet
is easily crumbled and broken into individual particles. At that point,
addition 30 of the
hydrophilic particles 18 may be accomplished.
[0072]
For example, adding 30 the particles 18 as a powder into the blending 26 is a
naturally stable process. Typically the particles 18 attach to the binder 14
of the substrate 12
particles, thus removing from activity that location. Accordingly, other
particles 18 rather than
agglomerating with their own type of material will continue to tumble in the
blending 26 until
exposed to a suitable location of binder 14 of the substrate 12. Thus, the
adding 30 of the
particles 18 or powder 18 of hydrophilic material will tend to be a naturally
stable process
providing a substantially even coating on all the particles of the substrate
12.
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[0073]
Just as marshmallows are dusted with corn starch, rendering them no longer
tacky
with respect to one another, the material 10 formulated by the process 20 are
dusted with
particles 18 and will pour freely. Accordingly, distribution 32 may be
conducted in a variety of
ways and may include one or several processes. For example, distribution may
include marketing
distribution from packaging after completion of blending 26, shipping to
distributers and
retailers, and purchase and application by users.
100741
An important part of distribution 32 is the deployment of the material 10. In
one
embodiment of an apparatus and method in accordance with the invention, the
material 10 may
be poured, as if it were simply sand 12 or other substrate 12 alone. Since the
powder 18 or
particles 18 have substantially occupied the binder 14, the material 10 will
not bind to itself, but
will readily pour as the initial substrate material 12 will.
[0075]
The material 10 may typically include from about 1 percent to about 20 percent
of
a hydrophilic material 18 or particles 18. The particles 18 may be formed of a
naturally occurring
material, such as a cellulose, gelatin, organic material, or the like.
[0076]
In one embodiment, a synthetic gel, such as polyacrylamide may be used for the
particles 18, in a ratio of from about 1 to about 20 percent particles 18
compared to the weight of
the substrate 12. In experiments, a range of from about 5 to about 10 percent
has been found to
be the most effective for the amount particles 18.
100771
Sizes of particles 18 may range from about 20 mesh to smaller than 100 mesh.
Particles 18 of from about 50 to about 75 mesh have been found most effective.
[0078]
The binder 14 may typically be in the range of from about in 1/4 percent to
about
3 percent of the weight of the substrate 12. A range of from about 3/4 percent
to about 11/2
percent has been found to work best. That is, with a binder such as lignicite,
1/4 of 1 percent has
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been found not to provide as reliable binding of particles 18 to the substrate
12. Meanwhile, a
ratio of higher than about 3 percent by weight of binder 14 to the amount of a
substrate 12, such
as sand, when using lignicite as the binder 14, tends to provide too much
agglomeration. The
pouring ability of the material 10 is inhibited as well as the blending 26,
due to agglomeration.
Other binders also operate, including several smaller molecules that are water
soluble. For
example, glues, gelatins, sugars, molasses, and the like may be used as a
binder 14. Insoluble
binders are also useful and more permanent.
[0079]
One substantial advantage for the material 10 in accordance with the present
invention is that the material remains flowable as a sand-like material 10
into the fluids to be
used in oil field fracturing. Thus, handling and application is simple, and
the ability of granular
material 10 to flow under and around small interstices of fractures provides
for a very effective
application.
10080]
Referring to FIG. 3, a formation 80 such as a reservoir area of an oil may
increase
large and small flows 82 in passages 84 formed in the rock 86 of the formation
80. Typically, the
flow 82 represented by arrows 82 indicating the development of flow at a
faster speed in center
of a passage 84, and the lower velocity near the wall 88 of the passage 84,
illustrates the flow 82
of fluid in the passage 84.
[0081]
In the illustrated embodiment, the granules 10 or large composite particles 10
or
the materials 10 formed as a granulated material 10, having the substrate 12
in the center column
with the polymer 18 adhered by a binder 12 on the outside thereof. This
material 10 may be
added to a flow 82 being pumped into a formation 80. Initially, a particle 10
will have an
effective diameter 90a. In this condition, the particle 10 of material 10 is
largely dependant on
the density of the substrate 12, which constitutes the majority of its volume.
Eventually, over
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time, with exposure to the liquid 82 or flow 82 and the water of that flow 82,
the polymer 18 will
absorb water, increasing in its effective diameter 90b. Ultimately, the
polymer 18 or the polymer
powder 18 will eventually become fully hydrated, increasing many times its
size, and beginning
to dominate the effective diameter 90c or hydraulic diameter 90c of the
particle 10.
[0082]
Initially, the diameter 90a reflects the comparatively smaller size and larger
density of the particle 10 dominated by the weigh of the substrate 12, such as
sand, ceramic sand,
or some other hard and strong material. Ultimately, the diameter 90a or
effective diameter 90a is
sufficient to provide fluid drag according to fluid dynamic equations, drawing
the particle 10 into
the flow 82.
[0083]
Meanwhile, the increase in diameter 90b and the ultimate effective diameter
90c
result in reduction of the density of the particle 10 as the polymer 18
absorbs more water,
bringing the net density of the particle 10 closer to the density of water.
Accordingly, the
particles 10 flow with the water exactly in sync, so to speak, rather than
settling out as a bare
substrate 12 would do.
[0084]
For example, in areas where eddies in the flow occur, such as corners,
crevices,
walls, and the like, heavy materials having higher density, such as sand and
the like, normally
will tend to drift out of the flow, toward a wall 88, and ultimately will
settle out. Instead, by
virtue of the large "sail" presented by the larger diameter 90c of a fully
hydrated polymer 18,
each particle 10 stays with the flow 82 in passage 84, providing much more
effective transport.
[0085]
Referring to FIG. 4, a chart 92 illustrates a volume axis 94 representing the
volume of a particle 10 or material 10 in accordance with the invention. The
volume axis 90 is
displayed orthogonally with respect to a time axis 96, representing the
passage of time of the
particle 10 submerged in a carrier 82 or flow 82 of fluid 82. Typically, at
different temperatures,
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illustrated by curves 98a-98e, with the temperature associated with curve 98a
being the coldest
and the temperature associated with the curve 98e being the hottest, one can
visualize how heat
added to a fluid flow 82 tends to increase the chemical activity and thus the
rate of absorption of
water into a polymer 18.
[0086]
In an apparatus and method in accordance with the invention, the particles 10
may
be added directly to a flow 82, without waiting for any significant time to
absorb water into the
polymer 18. Instead, the normal flow 82 will draw the particles 10 along in a
passage 84 while
exposing each individual particle 10 to surrounding fluid 82, thus promoting
maximum rates of
exposure and increased rates of absorption. Accordingly, the volume 94
increases, representing
an increase in the absorption of water into the polymer 18.
[0087]
In an apparatus and method in accordance with the invention, the curve 98a is
suitable because the entire travel within the well bore, and within the
formation 80 by the fluid
82 bearing the particles 10 is permissible and available as absorption time.
By contrast, prior art
systems rely on the increased temperature of curve 98e in order to provide the
time, temperature,
and mixing to work polymers into a flow 82 or liquid carrier 82.
[0088]
Referring to FIG. 5, in one embodiment of an apparatus, composition, and
method
in accordance with the invention, some of the polymer 18 may eventually be
scraped, sheared, or
otherwise removed from the particles 10. If bonded only by itself with a water
solvent, such a
separation may be easier than if bonded by a more durable polymer. Such a
release may even be
engineered, timed, controlled by a solvent, or the like.
[0089]
Thus, a certain amount of the polymer 18 may be released from the granule 10
into the carrier fluid 82 to flow with the fluid 82 and operate as a general
friction reducer or
provide its other inherent properties to the carrier fluid 82. By an
engineered process of bonding
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and un-bonding, the polymer powder may be less permanent or attached to have a
bond that is
less robust. Over time, the polymer powder so attached may release, tear, wear
off, pull away, or
otherwise remove from the substrate into the carrier fluid to act as a
viscosity agent, surfactant,
lubricant, or the like in the carrier, according to its known properties
available for modifying the
carrier 82.
[0090]
For example, a polymer 100 or polymer chain 100 may be captured on a corner
102 defining a passage 84 into which a flow 82 will proceed. Accordingly, the
corner 102
renders less of an orifice on the passage 84 against entry of the flow 82 by
virtue of the friction
reduction of the polymer 100 in the fluid, deposited temporarily or
permanently about a corner
102. Thus, other particles 10 passing the corner 100 may shear off a portion
of the polymer 18
carried thereby or may rely on the presence of the polymer 18 as a direct
friction reducing agent
on the particle 10 (granule) itself, permitting the particles 10 to pass more
easily with the flow 82
into the passage 84.
[0091]
Referring to FIG. 6, the fracture process is described in various literature,
including U.S. Patent Application publication US 2009/0065253 by Suarez-Rivera
et al.
incorporated herein by reference. In a fracturing process, the pressure
applied to a formation 80
tends to force apart large expanses of rock. As a result of that expansion of
passages 84 in a rock
formation 80, the rock is stressed. Pressure pumped into the fluid 82 flowing
in the passages 84
within the formation 80 results in bending stresses, tensile stresses, and so
forth in the formation
80.
[0092]
In FIG. 6, the forces 110 illustrated the effect of a large pressure applied
over a
large area. Since pressure multiplied by area equals force, applying an
elevated hydraulic
pressure to a large surface of a rock 86 or rock segment 86 within a formation
80 results in
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tensile forces. Compressive forces will not tend to break rock. However, a
tensile force, which
may be induced by bending, expansion, or the like, results in fracture of the
rock. The fracture of
the rock 86 thus results in condition shown in the lower view, in which the
passages 84 are mere
fissures within the rock 86.
[0093]
The inset of FIG. 6 magnifies the fissures 84 or passages 84 formed in the
rock 86
and immediately entered by the working fluid 82 being used for the fracture.
Having the particles
formed around substrates 12, the fluid 82 extends into each of the fissures
formed. Fissures 84
are simply passages 84. Some may be large, others small. Proppants 10 trapped
in a small
location may still maintain opened in another opening much larger elsewhere on
the rock 86.
They may also collect and fill larger spaces, eliminating the ability for
rocks 86 to return to
former positions.
[0094]
After fracturing rock 86 to form all of the fissures 84, the fluid 82 will
pass
through the fissures, carrying particles 10, which eventually collect in
cavities or reach choke
points. In the absence of the particles 10, fissures 84 could close back up
after the fracturing
water leaves. However, by containing the particles 10, the individual
substrates 12 are
themselves rock in the form of sand, ceramic sand, or the like. Thus, a
particle 10 need only
obstruct the ability of the fissure 84 to close, and it may "prop" open the
fissures 84 precluding
the rock 86 or the pieces of rock 86 from settling back into alignment with
one another.
[0095]
Thus, the particles 10 both alone and in collected piles act as proppants left
behind by the fluid flow 82, by virtue of the particles 10B captured. As a
practical matter, it is
only the substrate 12 that acts as a proppant. The polymer 18 may eventually
be worn off but can
easily be compressed, distorted, or cut. Regardless, as the fissures 84 open,
they are back filled
and close in at choke points and settling points collecting the substrate 12.
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[0096]
Referring to FIG. 7, a process 10 may include preparing 112 a fluid 82.
Processing 114 other additives other than the particles 10 may be done
according to any suitable
methods, including prior art processes. Adding 116 directly to the fluid 82,
the particles 10 as
described hereinabove, may be done in such a manner that the operators need
not wait for
absorption or any other processes to take place. Additional energy for
elevating temperature is
not required, neither mixing or the like, other than adding 116 directly
particles 10 in to the flow
82. The flow 82 will immediately grab the particles 10 according the
principles of fluid dynamics
in which fluid drag is dependent upon a shape factor of the particle 10, the
density of the fluid
82, the square of velocity of the fluid, and so forth, as defined in
engineering fluid mechanics.
[0097]
The fluid 82 now bearing the particles 10 would be immediately pumped 118 into
the formation 80 that is the reservoir 80 of 8 and oil field. Eventually,
pressurizing 120 the
reservoir by pressurizing the fluid 82 results in creating 122 fractures 84 or
fissures 84 within the
formation 80 by breaking up the rock 86 of the formation 80. A fracture 84
with enough
displacement may make a site for material 10 to stagnate and collect.
[0098]
Creating 122 fracture lines throughout the formation 80 is followed by
penetrating
124, by the particles 10 borne in the fluid 82 into the passages 84 or
fissures 84 in the rock 86 of
the formation 80. Whenever the flow 82 of fluid 82 carries a particle 10 to a
choke point 108 in a
passage 84, as illustrated in FIG. 6, a particle 10 will be lodged as
illustrated in the inset of FIG.
6, a particle 10 with its polymer 18 still secured and intact may be lodged.
Similarly, the
substrate 12 may be lodged 126 and the polymer 18 may stripped therefrom by
the consequent or
subsequent flowing of material in the flow 82. Likewise, piles of stagnant
particles 10 may
backfill spaces, precluding rock 86 settling back in.
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100991
After the lodging 126 or propping 126 of the fissures 84 by the substrate 12,
in the
particles 10, the passages 84 will remain open. These fissures 84 may then be
used to later
withdraw 128 the fluid 82 from the formation 80. Thereafter, returning 130 the
formation 80 to
production may occur in any manner suitable. For example, heat may be added to
the formation,
liquid may be run through the formation as a driver to push petroleum out, or
the like.
[00100]
As discussed above, the material 10 may be utilized as self-suspending
proppants
in hydraulic fracturing. As used herein, the material 10 may also be referred
to as self-
suspending proppants.
Methods for Forming Self-Suspending Proppant Particles
[00101]
In various embodiments, as discussed above, the self-suspending proppants
described herein may include a substrate, e.g., sand, having an outer
polymeric coating that is
water-absorbing. In such embodiments, a water-absorbing outer polymeric
coating comprises
one or more water-absorbing polymers, such as the water-absorbing polymers
discussed below.
In addition, in various embodiments, as discussed above, the self-suspending
proppants may
include a binder, which may aid in securing at least a portion of the water-
absorbing polymeric
coating to the substrate.
[00102]
In certain embodiments, the substrate can include frac sand. In one or more
embodiments, the frac sand can be graded as a 12-20 mesh frac sand, a 16-30
mesh frac sand, a
20-40 mesh frac sand, a 30-50 mesh frac sand, a 30-70 mesh frac sand, a 40-70
mesh frac sand,
or a 100+ mesh frac sand. In certain embodiments, a combination of various
grades of frac sand
can be used, such as a combination of the grades listed above. Such frac sands
and grades are
commercially available.
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,
,
Methods for Forming Self-Suspending Proppant Particles: Binder-Coated
Substrate Particles
[00103]
In embodiments, as discussed above, the self-suspending proppants can be
made
by first mixing a substrate with a binder to form binder-coated substrate
particles. In certain
embodiments, the binder may be a liquid binder, such as glycerol. Other liquid
binders are
described above.
[00104]
In one or more embodiments, when mixing a binder with a substrate, one may
add
at least about 0.05 wt. % binder, at least about 0.1 wt. % binder, at least
about 0.15 wt. % binder,
or at least about 0.2 wt. % binder; and/or less than about 3 wt. % binder,
less than about 2 wt. %
binder, less than about 1 wt. % binder, or less than about 0.5 wt. % binder.
In the same or
alternative embodiments, when mixing a binder with a substrate, one may add
about 0.25 wt. %
binder. As used herein, "wt. % binder" refers to the ratio of the weight of
the binder to the
weight of the substrate, multiplied by 100.
[00105]
In embodiments, the binder and substrate can be mixed using any
commercially
available mixing device or mixing vessel and a particular one can be chosen by
one skilled in the
art for a specific purpose. In certain embodiments, a ribbon mixer or paddle
mixer may be
utilized when mixing the binder and substrate.
[00106]
In certain embodiments, the binder and substrate may be mixed for a time
sufficient to substantially evenly apply the binder to the substrate
particles. In one or more
embodiments, the binder may be mixed with the substrate for at least about 1-2
minutes. In
certain embodiments, upon mixing the binder and substrate under the conditions
described
herein, a substantially portion, or substantially all of, the binder may be
coated onto the outer
surface of the substrate particles so that there is little to no excess free
binder.
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Methods for Forming Self-Suspending Proppant Particles: Intermediate Polymer-
Coated
Substrate Particles
[00107]
In embodiments, at least a portion of the binder-coated substrate particles,
or
substrate particles without binder, may be coated with one or more polymeric
materials, such as
water-absorbing polymers to form intermediate polymer-coated substrate
particles. In one or
more embodiments, the water-absorbing polymers utilized to form the
intermediate polymer-
coated substrate particles can include polyacrylamide, polyacrylates, or a
combination thereof.
In certain embodiments, the water absorbing polymers can include a co-polymer
of acrylamide
monomers and acrylate monomers. In such embodiments, the co-polymer of
acrylamide
monomers and acrylate monomers may be a random co-polymer of acrylate monomers
and
acrylamide monomers such that the acrylate monomers and the acrylamide
monomers are
randomly positioned within the co-polymer.
[00108]
In embodiments, any of the water-absorbing polymers disclosed herein may be
linear or cross-linked. As used herein, a polymer that is linear refers to a
polymer that is not
cross-linked with itself or another polymer by covalent bonds and/or ionic
bonds. In certain
embodiments, a polymer that is linear, while not being cross-linked, can
include simple linear
polymers and branched linear polymers. A simple linear polymer refers to a
polymer having a
single long chain, while a branched linear polymer refers to a polymer having
a long chain with
one or more shorter chains branched off from the long chain.
[00109]
In certain embodiments, the water-absorbing polymer can include an anionic
polymer, such as polyacrylamide or a co-polymer of acrylate monomers and
acrylamide
monomers. As discussed above, the polyacrylamide can include a linear
polyacrylamide. In
various embodiments, the anionic polyacrylamide or other anionic polymer, such
as an anionic
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µ
co-polymer of acrylamide monomers and acrylate monomers, can have an anionic
charge in an
amount of about 10 mol %, about 20 mol %, about 30 mol %, about 40 mol % or
about 50 mol%.
In embodiments, the anionic polymer or co-polymer can be about 10 mol % to
about 50 mol %
anionic, about 20 mol % to about 50 mol % anionic, or about 30 mol % ot about
40 mol %
anionic. In certain embodiments, within an anionic co-polymer of acrylate
monomers and
acrylamide monomers, the anionic content may substantially correlate to the
content of the
acrylate monomers in the co-polymer. For instance, in such embodiments, a co-
polymer of
acrylate monomers and acrylamide monomers that is about 20 mol % to 50 mol %
anionic, can
include about 20 mol % to about 50 mol % acrylate monomers.
[00110]
In various embodiments, a co-polymer of acrylate monomers and acrylamide
monomers may include neutral or non-ionic acrylamide monomers and anionic
acrylate
monomers. In such embodiments, the acrylamide monomers can be present in the
co-polymer in
an amount of at least about 50 mol %, at least about 60 mol %, at least about
70 mol %, or at
least about 90 mol %; or from about 40 mol % to about 90 mol %, or from about
50 mol % to
about 90 mol %, or from about 50 mol % to about 80 mol %. In the same or
alternative
embodiments, the water-absorbing polymer can include a non-ionic polymer,
cationic polymer,
anionic polymer, or a combination thereof. It is appreciated that one skilled
in the art is aware
that such types of water-absorbing polymers can be commercially obtained.
Representative
commercial vendors includes SNF and Evonik.
[00111]
In certain embodiments, utilizing water-absorbing polymers having the
anionic
content ranges described above can provide some advantageous functional
properties to the self-
suspending proppants. For example, in certain embodiments, utilizing water-
absorbing polymers
having the anionic content ranges described above can result in the effective
suspension of the
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self-suspending proppants in an aqueous fluid, including brackish water.
Further, in certain
embodiments, the anionic content of a water-absorbing polymer described herein
may affect the
molecular weight or size of the polymer, which may affect the ability of the
polymer to form a
polymer coating on the substrate particle. In such an embodiment, utilizing
water-absorbing
polymers having the anionic content ranges described above allows for the
appropriate molecular
weight of the water-absorbing polymer so that such a polymer can form an
effective polymer
coating on the substrate particles. These and other properties are discussed
further below.
[00112]
In embodiments, the water-absorbing polymer can have a molecular weight of at
least about 1 million Daltons (g/mol), at least about 5 million Daltons
(g/mol), at least about 15
million Daltons (g/mol), or at least about 20 million Daltons (g/mol). In the
same or alternative
embodiments, the water-absorbing polymer can have a molecular weight of about
40 million
Daltons (g/mol) or less, or about 30 million Daltons (g/mol) or less.
[00113]
In certain embodiments, coating the binder-coated substrate particles with one
or
more polymeric materials to form intermediate polymer-coated substrate
particles can include
applying one or more polymeric materials to a mixing vessel or device
containing binder-coated
substrate particles, such as the mixing devices discussed above.
[00114]
In certain embodiments, the water-absorbing polymers may be suspending in
liquid prior to being added to a mixing vessel containing the substrate
particles or binder-coated
substrate particles. In one or more embodiments, the water-absorbing polymer
may be present in
a water-in-oil emulsion (i.e., an invert emulsion). In such embodiments, the
water-in-oil
emulsion may include the water-absorbing polymer in the water or aqueous
phase, which is
emulsified in the larger oil phase, such as a mineral oil or other distillates
of petroleum. In
addition, in such embodiments, the water-absorbing polymer may be present in
the water-in-oil
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emulsion in an amount of about 15 wt. %, about 20 wt. %, about 25 wt. %, about
30 wt. %.,
about 40 wt. %, or about 50 wt. %. It is appreciated that one skilled in the
art understands that
water-in-oil emulsions comprising water-absorbing polymers can be commercially
obtained.
One such commercial vendor is SNF.
[00115]
In one or more embodiments, when a water-in-oil emulsion is utilized, the
emulsion can be added to the binder-coated substrate, or plain substrate, in
an amount of at least
about 0.1 wt. % emulsion relative to the weight of the substrate, at least
about 0.2 wt. %, at least
about 0.3 wt. %, at least about 0.4 wt. %, at least about 0.5 wt. %, at least
about 1 wt. %, at least
about 2 wt. %, at least about 2.5 wt. %, at least about 3 wt. %, at least
about 4 wt. %, at least
about 5 wt. %, or at least about 7.5 wt. %. In the same or alternative
embodiments, the emulsion
can be added to the binder-coated substrate, or plain substrate, in an amount
of less than about 20
wt. % emulsion relative to the weight of the substrate, less than about 15 wt.
%, or less than
about 10 wt. %. As used herein, "wt. % emulsion relative to the weight of the
substrate" refers
to the ratio of the weight of the emulsion to the weight of the substrate,
multiplied by100.
[00116]
In certain embodiments, the water-absorbing polymer may be mixed with the
binder-coated substrate particles, or substrate particles, for a time
sufficient to substantially
evenly apply the water-absorbing polymer, or the liquid or emulsion containing
the water-
absorbing polymer, to the substrate particles to form the intermediate polymer-
coated substrate
particles. In one or more embodiments, the intermediate polymer-coated
substrate particles can
be fully coated with water-absorbing polymer and/or the liquid or emulsion
containing the water
absorbing polymer. In one or more embodiments, the water absorbing polymer may
be mixed
with the substrate for about 1-0 minutes, or about 2-3 minutes.
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[00117]
Without being bound by any particular theories, in certain embodiments, it is
believed that the humectant properties of the binder, such as the humectant
properties of
glycerol, may attract the aqueous dispersion of water-absorbing polymer from
the water-in-oil
emulsion to the surface of the substrate particles resulting in the coating of
the water-absorbing
polymer onto the surface of the substrate particle. In such embodiments, the
binder can include
other humectants or hygroscopic compounds known to one skilled in the art.
[00118] In
alternative embodiments, the water-absorbing polymers may be in dried
powdered form prior to being added to a mixing vessel containing the substrate
particles or
binder-coated substrate particles. The dried powdered form of the water-
absorbing polymers can
include any or all of the features of the dried powdered form of water-
absorbing polymers
discussed below. For instance, the water-absorbing polymer in dried powdered
form can include
powder particles of less than about 300 microns, less than about 200 microns,
or less than about
100 microns. In one or more embodiments, the water-absorbing polymer in dried
powdered form
can include powder particles with a maximum dimension of less than about 300
microns, less
than about 200 microns, or less than about 100 microns. In the same or
alternative embodiments,
a water-absorbing polymer in powdered form refers to a dry powdered polymer
having a dry
content of: at least about 50%, at least about 75%, at least about 85%, at
least about 95%, or at
least about 99%; or a dry content of from about 75%-100% or about 88%-100%.
[00119] In
embodiments when the dried powdered form of the water-absorbing polymer is
added to a mixing vessel containing the substrate particles or binder-coated
substrate particles to
form intermediate-coated substrate particles, the water-absorbing polymer can
be added in an
amount of 0.01 wt. % water-absorbing polymer relative to the weight of the
substrate, at least
about 0.1 wt. %, at least about 0.25 wt. %, at least about 0.5 wt. %, at least
about 1 wt. %, at least
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,
about 1.5 wt. %, or at least about 2 wt. %; and/or less than about 10 wt. %,
less than about 7.5
wt. %, less than about 5 wt. %, or less than about 3 wt. %.
Methods for Forming Self-Suspending Proppant Particles: Polymer-Coated
Substrate Particles
[00120]
In various embodiments, the intermediate polymer-coated substrate
particles can
be coated with a second water-absorbing polymer to form polymer-coated
substrate particles.
In certain embodiments, the second water absorbing polymer can have any or all
of the
parameters and properties of the water-absorbing polymers described above. In
various
embodiments, the water-absorbing polymer applied to the intermediate polymer-
coated substrate
particles can include an acrylamide and acrylate co-polymer that is cross-
linked. In various other
embodiments, the water-absorbing polymer applied to the intermediate polymer-
coated substrate
can include a linear co-polymer of acrylate monomers and acrylamide monomers.
In the same or
alternative embodiments, the water-absorbing polymer applied to the
intermediate polymer-
coated substrate particles can include a linear polyacrylamide. In such
embodiments, the linear
polyacrylamide applied at this step may have an increased molecular weight
relative to the
water-absorbing polymer applied in forming the intermediate polymer-coated
substrate particles.
[00121]
In certain embodiments, a water-absorbing polymer utilized in an emulsion
can
have a greater molecular weight than a water-absorbing polymer utilized in
powdered form. In
such embodiments, the molecular weight of the water-absorbing polymer present
in an emulsion
can be at least about 1 million Daltons (g/mol), at least about 2 million
Daltons (g/mol), or at
least about 3 million Daltons (g/mol) greater than the molecular weight of the
water-absorbing
polymer present in powdered form.
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[00122]
In one or more embodiments, the polymer coated substrate particles can be
formed by applying the second water-absorbing polymer to the intermediate
polymer-coated
substrate particles in a mixing vessel, such as the mixing vessels discussed
above.
[00123]
In certain embodiments, the second water-absorbing polymer may be present in
powdered form when applying to the intermediate polymer-coated substrate
particles. In certain
embodiments, a water-absorbing polymer in powdered form refers to a dry
powdered polymer
with powder particles of less than about 300 microns, less than about 200
microns, or less than
about 100 microns. In the same or alternative embodiments, a water-absorbing
polymer in
powdered form refers to a dry powdered polymer having a dry content of: at
least about 50%, at
least about 75%, at least about 85%, at least about 95%, or at least about
99%; or a dry content of
from about 75%-100% or about 88%-100%. In embodiments, the processes described
above for
forming the intermediate polymer-coated substrate particles may result in the
intermediate
polymer-coated substrate particles having an outer wet surface, due to the
application of the
binder and/or the application of a water absorbing polymer in a liquid, such
as an emulsion
described above. In such embodiments, a dry powdered second water-absorbing
polymer may
adhere to the wet outer surface of the intermediate polymer-coated substrate
particles.
[00124]
In one or more embodiments, the second water-absorbing polymer may be applied
in an amount so as to not completely, or discontinuously, cover or coat the
outer surface of the
intermediate polymer-coated substrate particles. In alternative embodiments,
the second water-
absorbing polymer may be applied in an amount so as to substantially coat or
cover the outer
surface of the intermediate polymer-coated substrate.
[00125]
In certain embodiments, the second water-absorbing polymer may be applied in
an amount of at least about 0.01 wt. % water-absorbing polymer relative to the
weight of the
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substrate, at least about 0.1 wt. %, at least about 0.25 wt. %, at least about
0.5 wt. %, at least
about 1 wt. %, at least about 1.5 wt. %, or at least about 2 wt. %; and/or
less than about 10 wt. %,
less than about 7.5 wt. %, less than about 5 wt. %, or less than about 3 wt.
%. As used herein,
"wt. % water-absorbing polymer relative to the weight of the substrate" refers
to the ratio of the
weight of the second water-absorbing polymer to the weight of the substrate,
multiplied by 100.
[00126]
In embodiments, the second water-absorbing polymer may be mixed with the
intermediate polymer-coated substrate particles to form polymer-coated
substrate particles for a
time sufficient to evenly distribute the second water-absorbing polymer
amongst the volume of
intermediate polymer-coated substrate particles. In certain embodiments, the
second water-
absorbing polymer may be mixed with the intermediate polymer-coated substrate
particles for
less than about 5 minutes, less than about 4 minutes, less than about 3
minutes, less than about 2
minutes, or less than about 1 minute.
[00127]
In certain embodiments, the second water-absorbing polymer applied to the
binder-coated substrate particles to form intermediate-coated substrate
particles in this step can
be present in a liquid, such as an emulsion. In such embodiments, this water-
absorbing polymer
applied in a liquid can include any or all of the properties of the water-in-
oil emulsions discussed
above. Further, in such embodiments, this water-absorbing polymer in liquid
form can be
applied to the binder-coated substrate particles to form intermediate-coated
substrate particles in
this step in the amount of at least about 0.1 wt. % emulsion relative to the
weight of the substrate,
at least about 0.2 wt. %, at least about 0.3 wt. %, at least about 0.4 wt. %,
at least about 0.5 wt.
%, at least about 1 wt. %, at least about 2 wt. %, at least about 2.5 wt. %,
at least about 3 wt. %,
at least about 4 wt. %, at least about 5 wt. %, or at least about 7.5 wt. %.
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[00128]
As discussed above, the methods described herein can include two separate,
distinct applications of a water-absorbing polymer in different forms from one
another, such as
powdered form and in the form of an emulsion. In certain aspects, it may be
desirable to add the
water-absorbing polymer in powdered form prior to applying the water-absorbing
polymer in the
form of an emulsion, since this particular order of application can prevent or
reduce the water-
absorbing polymer in powdered from from clumping.
Methods for Forming Self-Suspending Proppant Particles: Optional Third
Application of Water-
Absorbing Polymer
[00129]
In one or more embodiments, a third application of water-absorbing polymer may
be optionally applied to the polymer-coated substrate particles. In such
embodiments, this
optional application of the water-absorbing polymer can include any or all of
the properties and
parameters discussed above in applying the water-absorbing polymer to the
binder-coated
substrate particles to form the intermediate polymer-coated substrate
particles. For example, in
various embodiments, this third application of water-absorbing polymer can
include mixing a
water-in-oil emulsion comprising a water-soluble polymer with the polymer-
coated substrates in
a mixing vessel for 2-3 minutes.
Methods for Forming Self-Suspending Proppant Particles: Drying the Polymer-
Coated Substrate
[00130]
In embodiments, the polymer-coated substrate, with or without the third
application of water-absorbing polymer, can be dried in order to form self-
suspending proppant
particles. In such embodiments, this drying step can remove at least a portion
of the liquid with
which the water-absorbing polymer was suspended during application of the
water-absorbing
polymer to the substrate, such as that described above with reference to the
formation of
intermediate polymer-coated substrate particles or the polymer-coated
substrate particles.
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[001311
In certain embodiments, the polymer-coated substrate can be exposed to mild
heat, such as a temperature of at least about 100 F, or at least about 150 F;
and/or less than about
300 F, less than about 250 F, or less than about 225 F. In embodiments, the
drying temperature
can be about 200 F or less than about 230 F. Any type of oven or drying
system, e.g., fluid bed
dryer, can be used to dry the polymer-coated substrate, and a particular
system can be chosen by
one skilled in the art for a specific purpose. The polymer-coated substrate
can be exposed to
mild heat for at least about 10 minutes, at least about 20 minutes, or at
least about 30 minutes.
[00132]
In certain embodiments, exposing the polymer-coated substrate particles to the
temperature ranges described above can be sufficient to cause cross-linking in
at least a portion
of the one or more water-absorbing polymers present on the substrate surface.
In such
embodiments, this method of cross-linking is referred to as thermal cross-
linking. Without being
bound by any particular theories, it is believed that, when the water-
absorbing polymer includes
a co-polymer of acrylate monomers and acrylamide monomers, the cross-linking
can comprise a
covalent cross-link that includes the carboxylate anion on the acrylate
monomers covalently
bonding to another portion of a water-absorbing polymer, such as an acrylamide
monomer.
Further, without being bound by any particular theories, it is believed that
this thermal cross-
linking facilitates the securing of the polymer coating around the substrate
particle. In certain
embodiments, prior to this thermal cross-linking, one or more of the water-
absorbing polymers in
the polymer-coated substrate particles is linear.
[00133]
In certain embodiments, the amount of cross-linking of the water-absorbing
polymers can be controlled by the temperature and time of heat exposure. In
such embodiments,
the polymer-coated substrate particles can be exposed to a temperature of at
least about 100 F
(38 C), or at least about 150 F (66 C); and/or less than about 250 F (121 C),
or less than about
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,
230 F (110 C); or a temperature of about 180 F (82 F) for a time period of at
least about 10
minutes, at least about 20 minutes, or at least about 30 minutes.
[00134]
In various embodiments, the amount of cross-linking of the water-
absorbing
polymers can be controlled by the anionic content of the water-absorbing
polymers present on
the polymer-coated substrate particles. In such embodiments, one or more of
the water-
absorbing polymers can be about 10 mol % to about 50 mol % anionic, or about
20 mol % to
about 50 mol % anionic. In certain embodiments, the water-absorbing polymers
present in the
self-suspending proppants produced according to the methods described herein
may be partially
cross-linked (e.g., not fully cross-linked). In such embodiments, this partial
cross-linking may
provide sufficient water swellability and suspension of the proppant while
still allowing for the
ability to settle out when exposed to a conventional breaker.
[00135]
In certain embodiments, by controlling the heating temperature, exposure
time to
the heat, and anionic content of the water-absorbing polymers on the outer
polymeric coating,
self-suspending proppants are formed that exhibit the desirable suspension
properties disclosed
herein, including the ability to remain suspending in brackish or salt water
conditions, while also
being able to settle out when exposed to a conventional breaker, as discussed
further below.
[00136]
In certain embodiments, two distinct applications of a water-absorbing
polymer in
powdered form and in the form of an emulsion can provide different coating
properties to the
self-suspending proppant, which can result in advantageous performance of the
self-suspending
proppants. For example, applying a water-absorbing polymer in an emulsion or
other liquid can
provide a substantially continuous or continuous coating of the water-
absorbing polymer to the
surface of the substrate particle, as the emulsion or liquid can evenly coat
the substrate particle.
Further, in certain embodiments, this substantially continuous coating, when
subsequently cross-
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linked, can form a cross-linked coating on the surface of the substrate
particle, effectively
locking the substrate particle inside this cross-linked polymeric coating.
Additionally, in certain
embodiments, the application of the water-absorbing polymer in dried powdered
form can
increase the water-absorbing polymer content in the self-suspending proppant's
polymer coating
(relative to a single application of the water-absorbing polymer in an
emulsion), which may aid
in the suspension ability, including in salt water, while still allowing for
polymer coating
removal from the substrate using conventional breakers.
[00137]
In certain embodiments, due to the size of the powdered particles of the
powdered
form of the water-absorbing polymer relative to the size of the substrate,
such as various grades
of frac sand, and due to the amount of powdered polymer added in the methods
described herein,
individual substrates may not be fully coated with powdered polymer particles.
Even though the
substrates may not be fully coated with the powdered polymer particles in
certain embodiments,
the self-suspending proppant can also include a coating of a water-absorbing
polymer that was
applied in an emulsion, which may substantially or entirely coat the outer
surface of the substrate
particle.
[00138]
Further, in certain embodiments, utilizing two distinct applications of the
water-
absorbing polymer where each application includes applying the water-absorbing
polymer in a
different form (e.g., one application with the water-absorbing polymer in
powdered form and
another application in an emulsion), allows for the modulation of the amount
of the water-
absorbing polymer present on the substrate particle in a production efficient
manner. For
instance, in such embodiments, an application of the water-absorbing polymer
in an emulsion
form can provide a high localized concentration of water-absorbing polymer to
the surface of the
substrate particles; however, the amount of water-absorbing polymer that may
be applied to the
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,
surface of the substrate particles may be limited, as only so much of the
emulsion can physically
coat onto the substrate particles without falling off. Thus in such
embodiments, an application of
the water-absorbing polymer in powdered form, in addition to the application
of a water-
absorbing polymer in an emulsion, can increase the water-absorbing polymer
content on the
substrate surface (relative to a single application of the water-absorbing
polymer in emulsion
form), which can result in advantageous self-suspending proppant performance,
such as an
enhanced salt water tolerance, and/or an enhanced suspension ability. Further,
this increase in
the water-absorbing polymer content on the substrate surface (relative to a
single application of
the water-absorbing polymer in emulsion form) can be achieved in a production
efficient
manner, e.g., utilizing a single vessel and a single drying and/or
crosslinking step (e.g., via heat
exposure).
Methods for Forming Self-Suspending Proppant Particles: Addition of a Flowing
Agent
[00139]
In various embodiments, once the polymer-coated substrate particles are
dried
thereby forming the self-suspending proppant particles, a flowing agent may be
added to the self-
suspending proppant particles to aid in handling and distribution of the self-
suspending proppant
particles in humid environments. In embodiments, the flowing agent can include
fumed silica,
sodium aluminosilicate, potassium aluminosilicate, calcium aluminosilicate,
synthetic zeolites,
natural zeolites, or a combination thereof. In one embodiment, the flowing
agent can include a
synthetic sodium aluminosilicate zeolite. In certain embodiments, other
commercially available
flowing agents can be used. A non-limiting list of other commercially
available flowing agents
includes potassium aluminum silicate, silicon dioxide, calcium silicate, and
powdered cellulose.
[00140]
In embodiments, at least about 0.05 wt. % flowing agent relative to the
weight of
self-suspending proppant particles can be mixed with or added to the self-
suspending proppant
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particles, at least about 0.1 wt. %, at least about 0.25 wt. %, at least about
0.5 wt. %, at least
about 0.75 wt. %, or at least about 1 wt. %, and/or less than about 5 wt. %,
less than about 4 wt.
%, less than about 3 wt. %, or less than about 2 wt. %. In certain
embodiments, about 0.1 wt. %
flowing agent relative to the weight of self-suspending proppant particles can
be added, about
0.25 wt. %, about 0.5 wt. %, about 0.75 wt. %, about 1 wt. %, about 2 wt. %,
about 3 wt. %,
about 4 wt. %, or about 5 wt. %.
Self-Suspending Proppant Particles
[00141]
As discussed above, the self-suspending proppant particles described herein
can
include a substrate, e.g., sand particle, having an outer polymeric coating.
In embodiments, the
outer polymeric coating can be discontinuous. As used herein a discontinuous
outer polymeric
coating refers to a polymeric coating on an outer surface of a substrate (that
is or is not coated in
binder) that covers less than about 80 % of the surface, less than about 70 %,
less than about 60
%, less than about 50 %, or less than about 25 %. In an alternative
embodiment, the outer
polymeric coating can be a continuous outer coating that covers at least about
50 % of the outer
surface of the substrate, at least about 60 %, at least about 70 %, at least
about 80 %, at least
about 90 %, at least about 95%, or at least about 99 %.
[00142]
In embodiments, the self-suspending proppant particles made according to the
methods described above can include more than one application of a water-
absorbing polymer to
form the outer polymeric coating. In certain embodiments, as discussed above,
the self-
suspending proppant particles can include a first water-absorbing polymer that
may be applied to
a substrate particle, or binder-coated substrate particle, and a second water-
absorbing polymer
that may be applied to the intermediate polymer-coated substrate particles.
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[00143]
In certain embodiments, the combined amount of the first water-absorbing
polymer applied to the binder-coated substrate particles and the second water-
absorbing polymer
applied to the intermediate polymer-coated substrate particles can provide an
outer polymeric
coating weight (or coat weight) to the self-suspending proppant particles of
at least about 0.5
wt.% coat weight, at least about 1.0 wt. %, at least about 1.5 wt. %, at least
about 2.0 wt. %, at
least about 2.5 wt. % or at least about 3.0 wt. %, and/or less than about 7.5
wt. %, less than about
5.0 wt. %, or less than about 4 wt. %. As used herein, wt. % coat weight
refers to the ratio of the
total weight of the water-absorbing polymer applied to substrate, to the
weight of the substrate,
multiplied by 100.
[00144]
In certain embodiments, depending on the application of a binder and one or
more
water-absorbing polymers, the outer polymeric coating of the self-suspending
proppant particles
can include glycerol, mineral oil, one or more water-absorbing polymers, or a
mixture thereof.
In such embodiments, the water-absorbing polymers can comprise, consist
essentially of, or
consist of one or more linear polyacrylamides. In certain embodiments, the one
or more linear
polyacrylamides can include two linear polyacrylamides having different
molecular weights
and/or different mol. % anionic charges.
[001451
In one or more embodiments, depending on the application of a binder and one
or
more water-absorbing polymers, the outer polymeric coating of the self-
suspending proppant
particles can include glycerol, mineral oil, one or more water-absorbing
polymers, or a mixture
thereof. In such embodiments, the water-absorbing polymers can comprise,
consist essentially
of, or consist of one or more of polyacrylamides, polyacrylates, or co-
polymers of acrylate
monomers and acrylamide monomers.
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[00146]
In various embodiments, the first and second water absorbing polymers can be
different from one another. For example, in one embodiment, the first and
second water
absorbing polymers can be different polyacrylamide polymers of different
molecular weights. In
such an embodiment, the second water-absorbing polymer, e.g., polyacrylamide
polymer, may
have a higher molecular weight than that of the first water-absorbing polymer,
e.g., a
polyacrylamide polymer.
[00147]
In certain embodiments, the first and second water-absorbing polymers can be
different types of polymers, or similar types of polymers with different
properties. For example,
the first and second water-absorbing polymers can be the same types of
polymers, e.g.,
polyacrylamides, but one may be a linear, non-cross-linked polymer, and the
other polymer may
be cross-linked. In another example, the first and second water-absorbing
polymers can be
different types of polymers, such as one being a polyacrylamide and the other
being a
polyacrylate or co-polymer of acrylate and acrylamide.
[00148]
In embodiments, the ability to vary the types or properties of the water-
absorbing
polymers applied to the substrate can impart various beneficial properties to
the self-suspending
proppant particles. For example, in certain embodiments, by using a cross-
linked water-
absorbing polymer for at least one of the water-absorbing polymers in the
outer polymeric
coating one can increase the ability for such a self-suspending proppant
particle to remain
suspending in brackish water conditions that may be found in various wells.
[00149]
In one embodiment, a self-suspending proppant having a first water-absorbing
polymer comprising linear polyacrylamide (which may be applied via a water-in-
oil emulsion)
and a second water-absorbing polymer comprising a crosslinked polymer, such as
crosslinked
polyacrylate or a crosslinked co-polymer of acrylamide and acrylate (which may
be applied by to
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the substrate in powdered form) can greatly increase the suspension of the
proppant in various
types of salt or brackish water.
[00150]
In another embodiment, a self-suspending proppant having a first water-
absorbing
polymer comprising a first linear polyacrylamide and a second water-absorbing
polymer
comprising a second linear polyacrylamide that is different from the first
linear polyacrylamide,
or is applied to the substrate differently than the first linear
polyacrylamide, can greatly increase
the suspension of the proppant in various types of salt or brackish water.
[00151]
In one or more embodiments, the self-suspending proppants made as described
herein may remain suspended in a 1000 ppm CaCO3 aqueous solution for at least
30 minutes, at
least 60 minutes, at least 90 minutes, or at least 120 minutes, at room
temperature or,
alternatively at a temperature of 170 F, after adding the self-suspending
proppant particles to the
salt solution and shaking to incorporate.
[00152]
In certain embodiments, a breaker, such as ammonium persulfate or sodium
chlorite, may be present at varying levels in a suspension test, such as that
described above. The
addition of a breaker may be utilized to determine if the proppant will become
suspended, or if
already suspended, to determine if the suspended proppant can be "broken" (and
settle out). In
embodiments, the breaker may be present in an amount of from 1-100 pounds per
thousand
gallons.
[00153]
In certain embodiments, by varying the types and/or properties of the first
and
second water-absorbing polymers utilized in forming the self-suspending
proppant particles one
may be able to tailor a particular type of self-suspending proppant particle
for a particular type of
water, such as water containing cations, chlorine, iron, or other ionic
components.
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1001541
The present invention may be embodied in other specific forms without
departing
from its spirit or essential characteristics. The described embodiments are to
be considered in all
respects only as illustrative, and not restrictive. The scope of the invention
is, therefore, indicated
by the appended claims, rather than by the foregoing description. All changes
which come within
the meaning and range of equivalency of the claims are to be embraced within
their scope.
[00155]
The concepts discussed herein will be further described in the following
examples, which do not limit the scope of various embodiments described in the
claims.
Examples
Example 1: Effect of Various Brackish Well Waters on Specific Self-Suspending
Proppants
[00156]
In this Example, various self-suspending proppants were made and analyzed
for
their ability to remain suspended in various brackish water samples from
fracking wells. Each of
the proppants tested in this method have been made according to the methods
described above.
For example, frac sand (40-70 mesh frac sand, unless otherwise noted below)
was added to a
mixing device, e.g., a kitchen mixer, and 0.20 wt. % glycerol was added and
allowed to mix for
two to three minutes. Then a water-in-oil emulsion containing a linear
polyacrylamide was
added and allowed to mix for two to three minutes, followed by the addition of
another linear
polyacrylamide in powder form, which was mixed in for a period of two to three
minutes. The
amounts of water-in-oil emulsion and powdered linear polyacrylamide that were
added in the
various samples are provided below in Table 1. The proppants were then dried
at about 230 F
for 15-20 minutes in an electric frying pan.
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Table 1: Water-absorbing polymers components in self-suspending proppant
samples
Amount of
Powdered
Water-absorbing Amount of
polyacrylamide
Sample polymer coat weight , Emulsion emulsion
(Hyperfloc AF
(wt. %)* (wt.%)
308 product)
(wt. %)
A 5
Hyperfloc AE
3.33 0.5
1. 873H
HyperflocCD AE
B 2.0 3.33 1.0
853H
C
(30-50 mesh 2.5 Hyperfloc0 AE 3.33 1.5
853H
frac sand)
Hyperfloc0 AE
D 2.0 3.33 1.16
852
Hyperflock AE
E 1.5 2.0 0.5
859
Hyperfloc0 AE
F 1.5 3 .33 0.66
872
* wt. % of coat weight refers to the ratio of the weight of the water
absorbing polymer added (from
both the emulsion and the powdered polyacrylamide) to the weight of the frac
sand, multiplied by
100. The weight of water absorbing polymer from the emulsion was determined
based on the
weight percent of polyacrylamide in the emulsion. The emulsions and powdered
polyacrylamide
were obtained from SNF.
[00157] 11.88
grams of each of the self-suspending proppants was added to 45 mL of
various test waters in a 50mL tube (2.2 ppg), capped, and then shaken by hand
vigorously for
thirty seconds. The shaken tubes were observed over time the settling of the
self-suspending
proppants. The results appear below in Tables 2-4.
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[00158] Table 2: Suspension results in brackish well water sample #1
Well water sample # 1: 11.73 mS conductivity and pH of 8.34
Sample First reading: Second reading: Third reading: Fourth reading: Fifth
reading:
Time and Time and Time and Time and Time
and
Suspension Suspension . Suspension Suspension
Suspension
Level* Level* Level* Level* Level*
A 0 min. ¨ 100% 5 min. ¨ 18 min. ¨ 60 min. ¨ 120
min. ¨
(6mL) 37 mL 42 mL 43 mL 44 mL
.
B 0 min. ¨ 100% 5 min. ¨ 10
min. ¨ 47 min. ¨ 107 min. ¨
(6mL) 22 mL 25 mL 27 mL 28 mL
C 0 min. ¨ 100% 58 min. ¨ n/a n/a n/a
(6mL) 28 mL
D 0 min. ¨ 100% 5 min. ¨ 10
min. ¨ 42 min. ¨ 102 min. ¨
(6mL) 20 mL 25 mL 28 mL 33.5
mL
E 0 min. ¨ 100% 5 min. ¨ 37
min. ¨ 97 min. ¨ n/a
(6mL) 31 mL 34 mL 35 mL
F 0 min. ¨ 100% 32 min. ¨ 92 min. ¨ n/a n/a
(6mL) 45 mL 46 mL
* Suspension level was visually determined based on the position of the top of
the suspended
proppants in the brackish well water sample #1. For example, 100 % suspended
refers to seeing no
settled proppant and the position of the top of the suspended proppants is
approximately at the 6 mL
level, as determined based on the graduations on the tube. 28 mL is determined
to be 50%
suspended.
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[00159] Table 3: Suspension results in brackish well water sample #2
Well water sample # 2: 1024 1.1S conductivity and pH of 7.83
Sample First reading: Second reading: Third reading: Fourth reading:
Time and Time and Time and Time and
Suspension Suspension Suspension Suspension
Level* Level* Level* Level*
A 0 min. ¨ 100% 44 min. ¨ 18 min. ¨ 60 min. ¨
(6mL) 10 mL 42 mL 43 mL
0 min. ¨ 100% 5 min. ¨ 49 min. ¨ n/a
(6mL) 6 mL 7 mL
0 min. ¨ 100% 7 min. ¨ 63 min. ¨ n/a
(6mL) 1 mL 15 mL
0 min. ¨ 100% 5 min. ¨ 53 min. ¨ n/a
(6mL) 6 mL 7 mL
0 min. ¨ 100% 5 min. ¨ 12 min. ¨ 60 min. ¨
(6mL) 8 mL 11 mL 28 mL
0 min. ¨ 100% 4 min. ¨ 11 min. ¨ 64 min. ¨
(6mL) 30 mL 33 mL 41 mL
* Suspension level was visually determined based on the position of the top of
the
suspended proppants in the brackish well water sample #2. For example, 100 %
suspended refers to seeing no settled proppant and the position of the top of
the
suspended proppants is approximately at the 6 mL level, as determined based on
the
graduations on the tube. 28 mL is determined to be 50% suspended.
1001601 Table 4: Suspension results in brackish well water sample #3
Well water sample # 2: 3.62 mS conductivity and pH of 8.27
Sample First reading: Second reading: Third reading: Fourth reading:
Time and Time and Time and Time and
Suspension Suspension Suspension Suspension
Level* Level* Level* Level*
0 min. ¨ 100% 3 min. ¨ 24 min. ¨ 92 min. ¨
(6mL) 21 mL 21 mL 26 mL
* Suspension level was visually determined based on the position of the top of
the
suspended proppants in the brackish well water sample #3. For example, 100 %
suspended refers to seeing no settled proppant and the position of the top of
the
suspended proppants is approximately at the 6 mL level, as determined based on
the
graduations on the tube. 28 mL is determined to be 50% suspended.
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[00161] Table 5: Suspension results in fresh water sample
Fresh Water Sample: 2.43 mS conductivity and pH of 8.05
Sample First reading: Second reading: Third reading:
Time and Time and Time and
Suspension Level* Suspension Level* Suspension
Level*
C 0 min. ¨ 100% 21 min. ¨ 90 min. ¨
(6mL) 16 mL 24 mL
* Suspension level was visually determined based on the position of the top
of the suspended proppants in the fresh water sample. For example, 100 %
suspended refers to seeing no settled proppant and the position of the top of
the suspended proppants is approximately at the 6 mL level, as determined
based on the graduations on the tube. 28 mL is determined to be 50%
suspended.
[00162] As can be seen in the above results, Samples B and C, which
included the same
water-absorbing polymers, just with varying coat weight, unexpectedly appeared
suspended
longer than the other samples (aside from Sample D). For example in brackish
water samples #1
and #2, at least 50 % of Samples B and C were suspended after about one hour
subsequent to
shaking. Further, Sample C performed equally as well in brackish water sample
#3 and the fresh
water sample. In any of the four water samples tested, Sample C was not
observed to be less
than 50 % suspended within the observed timeframe. Although Sample D stayed
almost 100%
suspended in brackish water sample #2 about 60 minutes after shaking, the same
sample was
observed to be less than 50 % suspended in brackish water sample #1 after
about 102 minutes.
Example 2: Self-Suspending Proppants in 1000 ppm CaCO3
[00163] In this Example, the suspension of various self-suspending
proppants were
analyzed in 1000 ppm CaCO3. In this Example two main samples were utilized, a
self-
suspending proppant having a cross-linked water-absorbing polymer and another
self-suspending
proppant with only linear water-absorbing polymers. The self-suspending
proppant having only
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linear water-absorbing polymers was made as described in Example 1 with
reference to Sample
B.
[00164]
For the self-suspending proppant having a cross-linked water-absorbing
polymer,
frac sand (40-70 mesh) was added to a mixing device, a kitchen mixer, and 0.26
wt. % glycerol
was added and allowed to mix for less than two minutes. Then 0.45 wt. % SNF
Hyperfloc0 AE
873H linear polyacrylamide emulsion was added and allowed to mix for two to
three minutes,
followed by the addition of 2 wt. % of an acrylamide and potassium acrylate co-
polymer, cross-
linked (Evonik Industries Stockosorbt S 18G) in powder form, which was mixed
in over a
period of about five minutes. Next an additional 0.45 wt. % % SNF Hyperfloct
AE 873H
linear polyacrylamide emulsion was added and allowed to mix for two to three
minutes. The
proppants were then dried at 200 F for 30 minutes in a conventional oven and
0.5 wt. % fumed
silica was added.
[00165]
Approximately the same amount of proppants were added to separate vials
containing a 1000 ppm CaCO3 solution and shaken vigorously for thirty seconds
and allowed to
sit in an oven at a temperature of 170 F for 75 minutes. An additional vial
contained the linear
polyacrylamide self-suspending proppant and the same 1000 ppm CaCO3 solution
along with a
breaker and was treated similarly. After 75 minutes at 170 F, both self-
suspending proppants
remained suspended in the brackish conditions. In addition, the vial
containing the linear
polyacrylamide self-suspending proppant and the breaker settled out,
suggesting that such an
outer polymeric coating can be "broken" with a breaker to settle out the
proppant. The cross-
linked self-suspending proppant was not exposed to the breaker.
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Example 3: Effects of Various Flowing Agents on Self-Suspending Proppants in
Humid
Conditions
[001661
In this Example, various flowing agents were tested with a self-suspending
proppant in humid conditions to test for flowability and water absorption.
Table 6 below lists the
various self-suspending proppant samples and the various flow treatments.
[001671 Table 6: Flowability Test Proppant Samples
Coating Flow
Mix sand
Base Sand
Sample (mesh) Mixture Drying Profile Flow Agent Agent
(wt.%)
(wt.%)
A 30/50 A-1.5% 220 F-15min None -
40/70-10%
B 30/50 A-1.5% 220 F-15min E-554
0.50% -
C 40/70 A-1.5% 220 F-15min DFC 0.17% -
D 40/70 A-1.5% None E-554 0.50% -
E 40/70 A-1.5% 220 F-15min Whey
1.00% -
F 30/50 A-1.5% 220 F-15min WPC 34 1.00% -
G 30/50 A-1.5% None Whey 1.00% -
H 40/70 A-1.5% None WPC 34
1.00% -
I 40/70 A-1.5% None E-554 1.00% -
J 40/70 A-1.5% None E-554 2.00% -
K 30/50 A-1.5% 220 F-15min None -
-
L 30/50 A-1.5% 220 F-15min E-554
1.00% -
M 40/70 A-1.5% 220 F-15min DFC 0.12% -
N 40/70 A-1.5% 220 F-15min Whey
1.50% -
O 40/70 A-1.5% 220 F-15min WPC 34
1.50% -
P 40/70 A-1.5% 220 F-15min F
0.10% -
4 40/70 A-1.5% 220 F-15min F 0.15% -
R 40/70 A-1.5% None None - -
[001681
The proppant samples listed in Table 6 were prepared as described above with
respect to sample A of Table 1 in Example 1 to give a coated sand with a 1.5%
by weight outer
polymeric coating. The same polyacrylamides utilized in sample A of Table 1 in
Example 1
were utilized. However, the drying protocol differed as described in Table 6,
for example some
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of the samples were dried with a standard temperature profile, while some were
not heat treated.
Some of the samples were treated with a flow agent product, as listed in Table
6. Some of the
samples were mixed with uncoated sand. The "E-554 (Zeolex 23A)" flow agent is
a sodium
aluminosilicate purchased from J.M. Huber Corporation. The "F" flow agent is
Aerosil R202
fumed silica purchased from Evonik Corporation. The "WPC 34" is a whey protein
concentrate
at 34% that is commercially available. The "whey" is commercially available.
DFC is a
proprietary coating utilized to provide a dust-free frac sand.
[00169]
First, the various proppant samples were exposed to a humidity chamber.
Specifically, the samples prepared as in Table 6 were added to an open vial
and weighed. Then,
the vials were exposed to 85 % relative humidity at 90 F for 15 minutes and
weighed thereafter.
The temperature and humidity were verified by sensor recordings. The results
are listed in Table
7 below.
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[00170] Table 7: Humidity Testing in vials
Weight
when Pre-Trial Post-Trial Trial
prepared Weight Weight Weight
Sample (g). ' (g) (g) Gain (g)
A 41.23 41.23 41.24 0.01
42.94 42.93 42.95 0.02
39.52 39.52 39.53 0.01
35.82 35.81 35.81 0
41.95 41.94 41.95 0.01
42.3 42.29 42.31 0.02
31.91 31.92 31.92 0
30.56 30.57 30.56 -0.01
36.74 36.74 36.74 0
39.63 39.62 39.63 0.01
40.65 40.65 40.65 0
41.05 41.04 41.06 0.02
M 43.13 43.11 43.11 0
41.61 41.6 41.62 0.02
O 39.02 39.02 39.04 0.02
P 38.01 38.02 38.02 0
Q 37.88 37.88 37.9 0.02
29.95 29.9 29.9 0
[00171] Next, the samples exposed to the humidity chamber as above were
tested for their
ability to flow out of a vial. Specifically, each sample vial was emptied into
the Petri dish. The
number of shakes/taps of the upside-down vial required to empty the sand from
the vial to the
Petri dish were recorded. Each time further agitation is required to break up
vial sand clumps
add 25 shakes/taps to the count. If the equivalent of 100 or more shakes are
required, record 100
shakes/taps and empty the remaining contents into the Petri Dish by any means.
4. If a surface
clump was formed on the top exposed surface of the vial, record the relative
size of the surface
clump. The level of bulk clumping visible in each sample, and whether the sand
of the sample is
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uniformly sticking together was recorded. The results appear in Table 8 below
and FIG. 9 shows
the images of the petri dishes.
[00172] Table 8: Flow testing from vials
Shake/Tap Surface
Sample Scale Clump Bulk Sticky
A 5 Medium
Medium
Medium Small
1 Small
5 Medium
2
100 Bulk Large Yes
75 Bulk Large Yes
0
0
3 Small Small
1
0 Small
2 Large
0 8 Large Small
1 Small
1 Small
100 Bulk Large Yes
[00173]
Next the petri dishes from FIG. 9 containing the samples A-R, were subjected
to
the humidity chamber again, this time for 60 minutes at 90 F with 85% relative
humidity. The
temperature and humidity were verified by sensor recordings. The petri dishes
were weighed
before and after this humidity chamber exposure. The results are listed in
Table 9 below.
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[00174] Table 9: Humidity testing in petri dish
Pre-Trial Post-Trial Trial
Weight Weight Weight
Sample (g) (g) Gain (g)
A 40.62 40.88 0.26
42.29 42.55 0.26
38.87 39.1 0.23
35.12 35.17 0.05
41.36 41.65 0.29
41.64 41.93 0.29
31.18 31.22 0.04
29.91 29.92 0.01
36.04 36.1 0.06
38.93 38.99 0.06
39.97 40.16 0.19
40.23 40.51 0.28
42.22 42.49 0.27
40.84 41.13 0.29
O 38.4 38.66 0.26
37.28 37.52 0.24
37.07 37.31 0.24
28.55 28.52 -0.03
[00175] The samples in the petri dish were dumped over onto white pieces
of paper and
are shown in FIG. 10.
[00176] Next the samples on the white pieces of paper were evaluated for
flowability by
being transferred back to their original vials using a plastic funnel.
Specifically, an empty funnel
was placed into the sample's original sample vial and the sand sample was slid
off the paper into
the sample funnel. The funnel was shaken vertically 15 times to break up the
sand sample in an
attempt to have the sand gravity flow into the sample vial. If the humidified
sand sample formed
a Petri dished shape clump when slid into the funnel, it was noted how easily
the clump breaks
up when during the shaking. Further, it was noted how easily the sample sand
flowed into the
vial from the funnel once the initial clump was broken up (if present). The
approximate fill
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volume of sample sand that was returned to each of the original sample vials
was recorded. The
overall flow and transfer of humid sand was scored according to the following
Table 10 and the
results are listed in Table 11.
'
[00177] Table 10: Scoring for the flow transfer return to vials
Points
Scored Clump Breakage Funnel Flow Vial Fill
20 No Clump
15 Very Easy Very Easy 90-110%
Easy Easy 75-90%
5 Slightly Difficult Slightly
Difficult 50-75%
2 Difficult Difficult 25%-50%
1 Very Difficult Very Difficult <25%
0 No Breakage No Flow 0%
[00178] Table 11: Flow transfer return
from vials
Sample Clump Breakage Funnel Loading Flow Vial
Fill Score
I No Clump Very easy 90-110% , 50
J No Clump Very easy 90-110% 50
D No Clump Easy 90-
110% 45
B Very Easy Easy ,
90-110% 40
L Very Easy Easy 90-
110% 40
P Very Easy Easy 90-
110% 40
Q Very Easy Easy 90-110% 40
K Easy Difficult 50-75%
17
O Slightly Difficult
Difficult 50-75% 12
A Difficult Difficult <25% 5
E Difficult Difficult <25%
5
F Difficult Difficult <25% 5
M Difficult Difficult <25% 5
N Difficult Difficult <25%
5
C Very Difficult Very Difficult <25% 3
G Very Difficult Very
Difficult <25% 3
H Very Difficult Very
Difficult <25% 3
R Very Difficult Very Difficult <25% 3
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[00179] Based on the above results from Tables 7-11 a humidity and flow
correlation
analysis was performed, which is shown in Table 12.
1001801 Table 12: Mixture variation performance analysis
Drying Profile
220 F-15min None
Flow Weight Tap Flow Weight Tap
Score Gain Scale Score Gain Scale
Flow Agents AVG AVG AVG AVG AVG AVG
E-554 40.0 0.79% 3 48.3
0.19% 0
sample B 40.0 0.74% 5
sample D 45.0 0.18% 1
sample I 50.0 0.21% 0
sample J 50.0 0.19% 0
sample L 40.0 0.84% 1
40.0 0.80% 1
sample P 40.0 0.79% 1
sample Q 40.0 0.80% 1
None 11.0 0.67% 4 3.0 -0.14% 100
sample A 5.0 0.77% 5
sample K 17.0 0.58% 3
sample R 3.0 -0.14% 100
WPC 34 8.5 0.83% 5 3.0 0.04% 75
sample F 5.0 0.84% 2
sample H 3.0 0.04% 75
sample 0 12.0 0.83% 8
Whey 5.0 0.85% 4 3.0 0.17%
100
sample E 5.0 0.84% 5
sample G 3.0 0.17% 100
sample N 5.0 0.86% 2
DFC 4.0 0.74% 5
sample C 3.0 0.72% 10
sample M 5.0 0.77% 0
Grand Total 18.1 0.78% 4 25.7 0.11% 46
[00181] Next various samples were subjected to centrifugal settling. The
proppant
samples are listed below in Table 13. The samples were made as discussed above
with respect to
the samples in Table 6.
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[00182] Table 13: Proppant samples for centrifugal compression
Flow Agent Added (/0 by weight)
Sample ID Base Preparation
E-554-sodium aluminosilicate
40/70, A-1.5% coat weight,
0.5%
Undried
40/70, A-1.5% coat weight,
X 1.0%
Undried
40/70, A-1.5% coat weight,
V 2.0%
Undried
[00183] For each of the above samples, a 2.1g standard method sample was
prepared of
40/70 mesh dried sand coated with the standard polymer mixture, dried using
the standard
temperature profile, and 0.1% weight percent of Product F (fumed silica)
added.
[00184] 2.1g of each of samples W, X, and V (and the standard samples) was
hydrated, by
placing it in 8m1 of water inside its own 15m1 centrifuge tube. Each tube was
then shaken
vigorously to mix the proppant and water mixture and then centrifuged at a low
speed for 2-5
minutes. A speed a 13% was used for this testing. The centrifuge was an IEC
International
Centrifuge Model HT. This centrifuge did not have working instrumentation to
show its
rotational speed. According to associated literature, this model centrifuge
should have a
maximum speed of 17,000 RPM and generate a relative centrifugal force of
34375. After
spinning at 20% speed the rotor RPM was tested with a separate instrument
which gave a value
of 3300 RPM. This is consistent with a maximum 100% speed of 17,000 RPM. After
centrifuging, the samples were removed and the settling of the materials was
compared.
[00185] No difference in settling was noted in the samples spun for 5
minutes. The
Sample X spun for 3 minutes showed slightly less settling than the standard
method sample. The
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undried samples with the sodium aluminosilicate had more opaque gel layer than
that of the
standard samples.
1001861 Finally, another centrifugal compression test was performed. The
samples for this
test were prepared according to the below Table 14.
1001871 Table 14: Centrifuge compression samples
Coating Flow Agent
Taps to
Sample Base Sand Mixture Drying Profile Flow Agent Amount
Mix Sand Remove
(mesh)
30/50 A-1.5% 220 F-15min E-554 0.50% 1
I 40/70 A-1.5% None E-554 1.00% 9
30/50 A-1.5% 220 F-15min None 40/70-20%
40/70 A-1.5% 220 F-15min F 0.15% 3
1001881 The samples were prepared as indicated in the Table 14 and
according to the
procedures set out with respect to Table 6. In this test, 5m1 of each sample
proppant was placed
into a 15ml centrifuge tube and centrifuged at a medium or high speed for
about 5 minutes (for
centrifuge force see the above description with respect to Table 13. The
samples were removed
and the compaction of the materials was compared. The samples were removed by
slowly
inverting the centrifuge tube above a white paper. If some compressed sand was
stuck in the
centrifuge tube, the tube was lightly tapped on the table until the sand was
removed. Any
required taps in recorded in the above Table 14. FIGS. 11A and 11B show the
results of the
initial dump (FIG. 11A) and the sand fully removed after tapping (FIG. 11B).
[00189] In view of these results of Example 3, the flowing agent that
worked the best to
promote flowability of the coated sand when exposed to high humidity
environments is the
sodium aluminosilicate (E-554). Unlike the fumed silica samples, the sodium
aluminosilicate-
containing samples showed unexpectedly beneficial properties, such as having
coated sand
product flowability even when added to product that was not heat treated with
a drying process.
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[00190]
The amount of water vapor absorbed by the coated sand mixtures was not
changed significantly by the flowing agents added. If the coated sand was not
heat treated by
drying after coating, it didn't absorb as much moisture in the humid
environment. When exposed
to an environment of 90 F and 85% relative humidity for 60 minutes the undried
samples
increased weight an average of 0.1% compared to an average weight increase of
0.8% for the
dried samples.
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