Note: Descriptions are shown in the official language in which they were submitted.
CA 02308372 2005-10-12
FORMATION TREATMENT METHOD USING DEFORMABLE PARTICLES
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to subterranean formation treatments and,
more
specifically, to hydraulic fracturing treatments for subterranean formations.
In particular, this
invention relates to deformable particles mixed with fracturing proppants to
reduce fines
generation, improve fracture conductivity, and/or minimize proppant flowback..
2. Description of the Related Art
Hydraulic fracturing is a common stimulation technique used to enhance
production of
fluids from subterranean formations. In a typical hydraulic fracturing
treatment, fracturing
IS treatment fluid containing a solid proppant material is injected into the
formation at a pressure
sufficiently high enough to cause the formation or enlargement of fractures in
the reservoir.
During a typical fracturing treatment, proppant material is deposited in a
fracture, where it
remains after the treatment is completed. After deposition, the proppant
material serves to hold
the fracture open, thereby enhancing the ability of fluids to migrate from the
formation to the
well bore through the fracture. Because fractured well productivity depends on
the ability of a
fracture to conduct fluids from a formation to a wellbore, fracture
conductivity is an important
parameter in determining the degree of success of a hydraulic fracturing
treatment
One pmblem related to hydraulic fracturing treatments is the creation of
reservoir
"fines" and associated reduction in fracture conductivity. These fines may be
produced when
proppant materials are subjected to reservoir closure stresses within a
formation fracture which
cause proppant materials to be compressed together in such a way that small
particles ("fines")
are generated from the proppant material and/or reservoir matrix. In some
cases, production of
fines may be exacerbated during production/workover operations when a well is
shut-in and
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then opened up. This phenomenon is known as "stress cycling" and is believed
to result from
increased differential pressure and closure stress that occurs during fluid
production following a
shut-in period. Production of fines is undesirable because of particulate
production problems,
and because of reduction in reservoir permeability due to plugging of pore
throats in the
reservoir matrix.
Production of particulate solids with subterranean formation fluids is also a
common
problem. The source of these particulate solids may be unconsolidated material
from the
formation, proppant from a fracturing treatment and/or fines generated from
crushed fracture
proppant, as mentioned above. Production of solid proppant material is
commonly known as
"proppant flowback." In addition to causing increased wear on dowahole and
surface
production equipment, the presence of particulate materials in production
fluids may also lead
to significant expense and production downtime associated with removing these
materials from
wellbores and/or production equipment. Accumulation of these materials in a
well bore may
also restrict or even prevent fluid production. In addition, loss of proppant
due to proppant
flowback may also reduce conductivity of a fracture pack.
In an effort to control or prevent production of formation or proppant
materials, many
methods have been developed. For example, to address proppant flowback methods
utilizing
special types of proppants and/or additives to proppants have been employed to
help form a
fracture pack in the reservoir which is resistant to proppant flowback. One
well known method
of this type utilizes resin-coated proppant materials designed to help form a
consolidated and
permeable fracture pack when placed in the formation. Among the ways this
method may be
carried out are by mixing a proppant particulate material with an epoxy resin
system designed
to harden once the material is placed in the formation, or by the use of a pre-
coated proppant
material which is pumped into the formation with the fracturing fluid and then
consolidated
with a curing solution pumped after the proppant material is in place.
Although resin-coated
proppant techniques may reduce proppant flowback, they may also suffer from
various
problems, including incompatibility of resins with cross-linker and breaker
additives in the
fi~acturing fluid, and long post-treatment shut-in times which may be
economically undesirable.
Resin-coated proppants may also be difficult to place uniformly within a
fi~cture and may
adversely affect fracture conductivity. In addition, resin-coated proppants
are typically only
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added to the final stages of fracturing treatments due to their expense,
resulting in a fracture
pack that is consolidated only in a region near the well bore.
Recently, techniques employing a mixture of solid proppant materials designed
to
achieve proppant flowback control have been developed. In one technique, rod-
like fibrous
materials are mixed with proppant material for the purpose of causing particle
bridging within a
fracture proppant pack so as to inhibit particle movement and proppant
flowback. This
technique is believed to control proppant flowback by forming a "mat" of
fibers across
openings in the pack which tends to hold the proppant in place and limit
proppant flowback
during fluid production. However, in practice this method has proven to have
several
drawbacks, including reduction in fracture conductivity at effective
concentrations of fibrous
materials, and an effective life of only about two years due to slight
solubility of commonly
used fiber materials in brine. In addition, fiber proppant material used in
the technique may be
incompatible with some common well-treating acids, such as hydrofluoric acid.
In another recently developed method, thermoplastic material in the form of
ribbons or
flakes is mixed with proppant material in order to form a fracture proppant
pack that is resistant
to proppant flowback. The thermoplastic material is designed to intertwine
with proppant
particles and become "very tacky" at reservoir temperatures such as those
greater than about
220°F. In doing so, the materials are believed to adhere to proppant
material to form
agglomerates that bridge against each other and help hold proppant materials
in place. This
method of controlling proppant flowback suffers similar drawbacks as the fiber
proppant
additive method described above, most notably reduced conductivity. Therefore,
a method of
reducing fines creation while at the same time improving fracture conductivity
and reducing
pmppant flowback is desirable.
SUMMARY OF THE INVENTION
In one respect, this invention is a method of treating a subterranean
formation by
injecting into the formation a fracturing fluid composition that includes a
blend of a fracture
proppant material and a deformable beaded material.
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In another respect, this invention is a method of treating a subten-anean
formation by
injecting into the formation a blend of a fracture proppant material and a
deformable particulate
material. Individual particles of the deformable particulate material may have
a shape with a
maximum length-based aspect ratio of equal to or less than about 5.
In another respect, this invention is a method of treating a subterranean
formation by
injecting into the formation a blend of a fracture proppant material and a
deformable particulate
material having a shape that is at least one of beaded, cubic, bar-shaped,
cylindrical, or a
mixture thereof. Beaded or cylindrical shaped particulate materials may have a
length to
diameter aspect ratio of equal to or less than about 5, and bar-shaped
particulate material may
have a length to width aspect ratio of equal to or less than about 5 and a
length to thickness
aspect ratio of equal to or less than about 5.
In yet another respect, this invention is a method of treating a subterranean
formation by
injecting into the formation a fracturing fluid composition that includes a
blend of fracture
proppant material and deformable particulate material. In this method, the
fracturing fluid
composition is deposited in the subterranean formation so that the blend of
fracture proppant
material and deformable particulate material has an in situ conductivity
greater than an in situ
conductivity of either fracture proppant material or deformable particulate
material alone.
In yet another respect, this invention is a method of treating a subterranean
formation by
injecting into the formation a fracturing fluid composition that includes a
blend of fracture
proppant material and deformable particulate material. In this method, the
fracturing fluid
composition is deposited in the subterranean formation so that the blend of
fracture proppant
material and deformable particulate material has an in situ creation of fines
that is less than an
in situ creation of fines in said fracture proppant material alone.
In yet another respect, this invention is a composition for fracturing a
subterranean
formation that includes a blend of a fracture proppant material and a
deformable particulate
material. The deformable particulate material may have a particle size of from
about 4 mesh to
about 100 mesh, a specific gravity of from about 0.4 to about 3.5, and a shape
with a maximum
length-based aspect ratio of equal to or less than about 5.
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In yet another respect, this invention is a method of treating a subterranean
formation,
including the step of injecting a fracturing fluid composition into the
subterranean formation,
wherein the fracturing fluid composition includes a blend of a fracture
proppant material and a
deformable beaded material.
5 In yet another respect, this invention is a method of treating a
subterranean formation,
including the step of injecting a blend including a fracture proppant material
and a deformable
particulate material into a subterranean formation, wherein at least a portion
of the individual
particles of the deformable particulate have a shape with a maximum length-
based aspect ratio
of equal to or less than about S. The blend may include between about 1% to
about 50% by
weight deformable particulate material. Furthermore, at least a portion of the
individual
particles of the deformable beaded material may include two or more
components.
In yet another respect, this invention is a method of treating a subterranean
formation,
including the step of injecting a deformable particulate material into a
subterranean formation,
wherein at least a portion of the individual particles of the deformable
particulate material
include an agglomerate of substantially non-deformable material and
substantially deformable
material, a core of substantially non-deformable material surrounded by one
layer of
substantially deformable material, or a mixture thereof.
In yet another respect, this invention is a method of treating a subterranean
formation,
including the steps of injecting a fracturing fluid composition into the
subterranean formation,
wherein the fracturing fluid composition includes a blend of fracture proppant
material and
substantially deformable particulate material; and depositing the fracturing
fluid composition in
the subterranean formation, wherein an in situ conductivity of the blend of
fracture proppant
material and substantially deformable particulate material is greater than an
in situ conductivity
of either one of the fracture proppant material or substantially deformable
particulate material
alone; wherein at least a portion of the individual particles of the
deformable particulate
material include an agglomerate of substantially non-deformable material and
substantially
deformable material, a core of substantially non-defonmable material
surrounded by one layer
of substantially deformable material, or a mixture thereof.
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In yet another respect, this invention is a method of treating a subterranean
formation,
including the steps of injecting a fracturing fluid composition into the
subterranean formation,
wherein the fracturing fluid composition includes a blend of fracture proppant
material and
deformable particulate material; and depositing the fracturing fluid
composition in the
subterranean formation, wherein an in situ creation of fines in the blend of
fracture proppant
material and deformable particulate material is less than an in situ creation
of fines in the
fracture proppant material alone; wherein at least a portion of the individual
particles of the
deformable particulate material include an agglomerate of substantially non-
deformable
material and substantially deformable material, a core of substantially non-
deformable material
surrounded by one layer of substantially deformable material, or a mixture
thereof.
In yet another respect, this invention is a composition for fracturing a
subterranean
formation, the composition including a deformable particulate material,
wherein at least a
portion of the individual particles of the deformable particulate material
include a core of
substantially non-defornaable material surrounded by one layer of
substantially deformable
I S material.
In yet another respect, this invention is a composition for fracturing a
subterranean
formation, the composition including a blend of a fracture proppant material
and a deformable
particulate material, wherein the deformable particulate material has a
maximum length-based
aspect ratio of equal to or less than about 5.
In embodiments of the methods and compositions of this invention, deformable
beaded
material may have a Young's modulus of, for example, between about 500 psi and
about
2,000,000 psi at in situ formation conditions, between about 5000 psi and
about 200,000 psi at
in situ formation conditions, or between about 7000 psi and about 150,000 psi
at in situ
formation conditions. Deformable beaded material may be a copolymer, such as a
terpolymer,
which may be at least one of polystyrene/vinylldivinyl benzene, acrylate-based
terpolymer or a
mixture thereof. Deformable beaded material may also be polystyrene
divinylbenzene that
includes from about 4% to about 14% divinylbenzene by weight. At least a
portion of the
individual particles of the deformable beaded material may include two
components such as,
for example, a core of substantially non-deformable material surrounded by a
layer of
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substantially deforrnable material. In this regard, the core may include a
material selected from
at least one of silica, ceramics, synthetic organic particles, glass
microspheres, or a mixtm~e
thereof; and wherein the layer of substantially defontnable material includes
at least one of a
cross-linked polymer, plastic, or a mixture thereof. Alternatively, the core
may includes a
material selected from at least one of silica, ceramics, synthetic organic
particles, glass
microspheres, or a mixture thereof; the layer of substantially deformable
material may include
resin and make up greater than 8% by weight of the total weight of the
deformable beaded
particle. A deformable particle may also be an agglomerate of substantially
non-deformable
material and substantially deformable material with the substantially
deformable material
making up between about 5% and about 50% by volume of the total volume of each
of the
individual particles of the deformable beaded material; and the substantially
non-deformable
material making up between about 50% and about 95% by volume of the total
volume of each
of the individual particles of the deformable beaded material.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a representation of a uni-planar structural "mat" of fibers believed
to form
in situ using rod-like fibrous proppant additives of the prior art.
FIG. 2 is a representation of uni-planar agglomerate structures believed to
form in situ
using thermoplastic ribbon or flake proppant additives of the prior art.
FIG.3 is a representation of a substantially spherical deformable beaded
particle
according to one embodiment of the disclosed method.
FIG. 4 is a representation of one mechanism believed responsible for
deformation of the
substantially spherical particle of FIG. 3 due to contact with fracture
proppant under conditions
of formation stress.
FIG. 5 is a representation of a multi-planar hexagonal close-packed structure
believed
to form in situ using one embodiment of the disclosed method having a 7:1
ratio of fracture
proppant material to polystyrene divinylbenzene plastic beads.
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FIG. b is a simplified representation of one possible shape of a deformable
beaded
particle subjected to hexagonal contact with fracture proppant material.
FIG. 7 is a simplified representation of one possible shape of deformable
beaded
particle subjected to pentagonal contact with fracture proppant material.
FIG. 8 is a simplified representation of one possible shape of a deformable
beaded
particle subjected to tetragonal contact with fracture proppant material.
FIG. 9 is a simplified representation of one possible shape of a deformable
beaded
particle subjected to contact in two locations by fracture proppant material.
FIG.10 illustrates stress versus strain, and shows variation in Young's
modules of
elasticity for polystyrene divinylbenzene plastic beads.
FIG.11 illustrates volume compaction versus closure stress for polystyrene
divinylbenzene plastic beads.
FIG.12 illustrates linear compaction versus closure stress for polystyrene
divinylbenzene plastic beads.
FIG. I3 illustrates linear compaction versus closure stress for 20/40 mesh
Ottawa sand
at a pack density of 2 Ib/ft2.
FIG.14 illustrates permeability versus closure stress for plastic beads, 20/40
mesh
Ottawa sand, and 3:1 and 7:1 mixtures by volume of 20/40 plastic beads and
20/40 mesh
Ottawa sand according to embodiments of the disclosed method.
FIG.15 illustrates conductivity versus closure stress for 20/40 mesh Ottawa
sand, 20/40
mesh plastic beads, and 3:1 and 7:1 mixtures by volume of 20/40 mesh Ottawa
sand and 20/40
mesh plastic beads according to one embodiment of the disclosed method.
FIG.16 illustrates fines generation versus closure stress for 20/40 mesh
Ottawa sand
and 3:1 and 7:1 mixtures of 20/40 mesh Ottawa sand and 20140 mesh plastic
beads according to
embodiments of the disclosed method.
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FIG.17 illustrates three dimensional deformation of polystyrene divinylbenzene
particles after being subjected to stress in a simulated fracture proppant
pack.
FIG. 18 illustrates the flowback failure of an Ottawa sand proppant pack under
a
closure stress of greater than 1000 psi.
FIG.19 illustrates the flowback failure of a proppant pack containing a 3:1
mixture of
Ottawa sand to polystyrene divinylbenzene plastic beads under a closure stress
of greater than
1000 psi.
FIG. 20 illustrates the flowback failure of a proppant pack containing a 4:1
mixture of
Ottawa sand to polystyrene divinylbenzene plastic beads under a closure stress
of greater than
1000 psi.
FIG. 21 illustrates the flowback failure of a proppant pack containing a 5.7:1
mixture of
Ottawa sand to polystyrene divinylbenzene plastic beads under a closure stress
of greater than
1000 psi.
FIG. 22 illustrates drag force versus fracture width of a proppant pack
containing 20/40
mesh Ottawa sand.
FIG.23 illustrates drag force versus fracture width for a proppant pack
mixture
containing 20/40 mesh Ottawa sand and 15% by weight of 20 mesh polystyrene
divinyl
benzene plastic beads.
FIG.24 illustrates drag force versus fracture width for a proppant pack
mixture
containing 20/40 mesh Ottawa sand and 30 mesh silica/resin agglomerate beads.
FIG. 25 illustrates drag force versus flow rate for a proppant pack containing
20/40
mesh Ottawa sand and proppant pack mixtures containing 20/40 mesh Ottawa sand
and 15% by
weight of polystyrene divinyl benzene plastic beads of varying size.
FIG. 26 illustrates conductivity as a function of a closure stress for 20/40
mesh Ottawa
sand and a mixture containing 20/40 Ottawa sand and 15% by weight 20 mesh
polystyrene
divinylbenzene plastic beads.
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FIG. 27 is a representation of a layered deformable beaded particle including
a
substantially non-deformable core surrounded by a substantially deformable
coating or layer
according to one embodiment of the disclosed method.
FIG. 28 is a representation of a fracture proppant pack believed to form in
situ using
one embodiment of the disclosed method employing a mixture of layered
deformable beaded
particles and substantially non-deformable fracture proppant material.
FIG. 29 is a representation of a fracture proppant pack believed to form in
situ using
one embodiment of the disclosed method employing only layered deformable
beaded particles.
FIG. 30 is a representation of an agglomerated deformable beaded particle
including
substantially non-deformable components surrounded and intermixed with a coat
of
substantially deformable material according to one embodiment of the disclosed
method.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
In embodiments of the disclosed method, deformable particulate material {e.g.,
deformable particles) is added to and/or mixed with fracture proppant material
to enhance
conductivity and permeability of a fracture proppant pack, reduce fines
generation, and/or
minimize proppant flowback. By "deformable" it is meant that individual
particles of a
particulate material yield upon point to point stress with particles of
fracture proppant material
andlor deformable particulates present in a fracture pack. In connection with
the disclosed
method, the surprising discovery has been made that blends of fracture
proppants and
deformable particles according to embodiments of the disclosed method are
synergistic in that
combinations of fracture proppant material and deformable particles may
possess greater
conductivity andlor permeability than either material possesses alone. This
synergistic effect is
believed to result from a number of factors, including the in situ deformation
of the deformable
particles to form mufti-planar structures or networks that, among other
things, may cushion the
fracture proppant material.
Surprisingly, it has also been found that combinations of deformable particles
and
fracture proppants according to embodiments of the disclosed method typically
reduce fines
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generation as a result of closure stress applied on a proppant pack. In
embodiments of the
disclosed method, it is believed that deformable particulates act as a
"cushion" to prevent grain
to grain contact and absorb stress between particles of silica, synthetic or
other types of
proppants. It is believed that this cushion effect prevents proppant particles
from shattering or
breaking due to stress (including stress induced by stress cycling) and that
therefore less fines
are produced. When less fines are present to Iower pore space in a proppant
pack, porosity,
permeability and/or conductivity may be maintained. As demonstrated in Example
5 and
illustrated in FIG.16, this reduction in fines generation allows the extension
of the closure
stress range in which fracture proppant materials, such as sand, may be used.
This means that
lower cost proppants such as sand may be utilized in those applications where
more expensive
high strength proppants have been traditionally employed.
As an additional benefit, it has been found that combinations of deformable
particulate
and proppant material according to embodiments of the disclosed method rnay
also reduce
proppant flowback due to plastic deformation of deformable particles into
mufti-planar
structures. In the practice of the disclosed method, deformable particles
deform at formation
temperatures and with proppant contact as fracture closure stress is applied.
Previous methods
using fracturing treatment additive materials having fiber 2 or ribbon-like
(or flake) 4
geometries, are believed to address proppant flowback by creating uni-planar
structures with
proppant as shown in FIGS. 1 and 2. By "uni-planar" it is meant that the in
situ structures
created by these additives are believed to have geometries that extend vector
stress in one plane
of a pmppant pack. These structures are believed to exist as individual "mats"
or agglomerates
within a proppant pack. Unlike the previous methods and materials, embodiments
of the
disclosed method are believed to result in creation of mufti-planar structures
{or networks)
in situ that act to reduce or prevent proppant flowback by increasing particle
cohesion and
proppant pack stability. By "mufti-planar" it is meant that in situ structures
created by the
treatment additives of the disclosed method are believed to have geometries
that extend vector
stress in more than one plane of the proppant pack, i.e., in three dimensions.
Therefore,
structures formed in the practice of the disclosed method are believed to
exist as in situ
networks extending within, and forming part of, a fracture pmppant matrix.
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Particular embodiments of the disclosed method may offer further advantages.
For
example, when a substantially spherical deformable beaded material of the
disclosed method is
mixed with a relatively irregular or angular fracture proppant material such
as sand, greater
porosity and permeability may be achieved due to the creation of a pack
geometry, such as
hexagonal packing, that is superior to the pack geometry achieved by the
fracture proppant
material alone. In addition, even greater fracture conductivity may be
achieved using the
disclosed method by blending a fracture proppant material with a deformable
material having a
density less than that of the fracture proppant material, resulting in a
greater fractwe width per
unit mass.
An example of a substantially spherical deformable beaded particle 10
according to one
embodiment of the disclosed method is shown in FIG. 3. FIG. 4 illustrates one
possible
mechanism believed responsible for deformation of a substantially spherical
particle 10 of
FIG. 3 as a result of contact with individual particles of fracture proppant
material 20 under
conditions of formation stress. As seen in FIG. 4, proppant particles 20
create "dimpled"
impressions 30 in the sides 40 of deformable particle 10 in which proppant
particles 20 may
reside.
Although a substantially spherical deformable beaded particle is illustrated
in FIGS. 3
and 4, it will be understood with benefit of this disclosure that non-
spherical beaded particles as
well as non-beaded particle shapes may also be used successfully in the
practice of the
disclosed method. Examples of such non-spherical beaded particles include, but
are not limited
to, beaded particles having a shape that is elongated in one or more
dimensions, such as
particles that are oval shaped, egg-shaped, tear drop shaped, or mixtures
thereof. Examples of
such non-beaded particles include, but are not limited to, particles having a
shape that is cubic,
bar-shaped (as in a hexahedron with a length greater than its width, and a
width greater than its
thickness), cylindrical, multi-faceted, irregular, or mixtures thereof. In
addition, it will be
understood with benefit of the present disclosure that beaded or non-beaded
deformable
particles may have a surface that is substantially roughened or irregular in
nature or a surface
that is substantially smooth in nature. Moreover, it will also be understood
that mixtures or
blends of deformable particles having differing, but suitable, shapes for use
in the disclosed
method may be employed.
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When deformable particles having a cylindrical shape or an elongated beaded
shape
with a substantially uniform diameter are employed in the practice of the
disclosed method,
particles having a length to diameter aspect ratio of equal to or less than
about 5 are typically
employed (as used herein, "length" is measured along the axis of a particle
having the longest
dimension). More typically, cylindrical or elongated beaded particles having a
length to
diameter aspect ratio of equal to or less than about 3 are employed. Most
typically, cylindrical
or elongated beaded particles having a length to diameter aspect ratio of
equal to or less than
about 2 are used. Similarly, when deformable particles having a bar-shape are
employed, both
the length to width ratio and the length to thickness ratio of a given
individual particle are
typically equal to or less than about 5, more typically equal to or less than
about 3, and most
typically equal to or less than about 2. When deformable particles having
mufti-faceted or
irregular shapes, or shapes with tapered diameters are employed, the particles
typically have a
maximum length-based aspect ratio of equal to or less than about 5, more
typically equal to or
less than about 3, and most typically, equal to or less than about 2 As used
herein, "maximum
length based aspect ratio" means the maximum aspect ratio that may be obtained
by dividing
the length of a particle by the minimum (or shortest) dimensional value that
exists along any
other axis (other than the length axis) taken through the center of mass of
the particle. It will
also be understood with benefit of the present disclosure that particles of
any shape (including
any of the shapes described in this paragraph) may be employed in the
disclosed method when
such particles have a maximum length-based aspect ratio that is typically
equal to or less than
about 5, more typically equal to or less than about 3, and most typically
equal to or less than
about 2.
An example of a mufti-planar structure believed to form in situ from a mixture
of
deformable beaded particulate materials 10 and fracture proppant material 20
according to one
embodiment of the disclosed method having a 7:1 blend of fracture proppant
material to
deformable particulate material is shown in FIG. 5. However, a mufti-planar
pack may be
formed by other ratios of deformable material to fracture proppant material.
When deformable
particles are mixed with harder, non-deformable proppants, such as sand,
proppant packs may
be formed with proppant particles "locked" into deformed surfaces of the
deformable particles,
thus forming a stronger pack. However, no sticking or adherence between
deformable particles
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and fracture proppant material is required in order to obtain the benefits of
the disclosed
method. Beaded particulate material is believed to deform into different
shapes depending on
the packing geometry surrounding each bead. Just a few of these shapes are
illustrated in
simplified geometrical form in FIGS. 6-9.
Packing geometry is believed to be dependent on factors such as irregularity
of the
fracture proppant material, and a variety of geometries may exist in a single
fracture pack. For
example, FIGS. 6-8 illustrate approximate cuboidal and pyramidal shapes of
beaded particulate
material 10 that are believed to result from hexagonal (bead contacted by
proppant in six
locations), pentagonal (bead contacted by proppant in five locations), and
tetragonal (bead
contacted in four locations) packing, respectively. As shown in FIG. 9, where
a bead 10 is
contacted in only two locations by proppant, it may be deformed into a shape
resembling a "dog
bone." It will be understood with benefit of this disclosure that other
packing configurations,
mixtures of packing configurations, as well as numerous other shapes and
mixtures of shapes of
deformable particulate material are also possible.
1 S By having appendages in several planes, stresses on a given deformable
particle in one
plane provides additional stabilization to adjacent particles in other planes.
This effect is
believed to be squared by benefit of stresses in a second plane and cubed by
contributions of
stresses in a third plane. In addition to contributing to beneficial effects
not found in previous
methods, such as increased fracture conductivity and reduced fines creation,
this results in
superior stabilization of a fracture pack. In addition, the use of deformable
particle
embodiments of the disclosed method may allow a well to be put on production
faster than
resin coated sand methods which require shut-in time for resin curing, thus
providing a more
rapid return on investment.
Advantageously, embodiments of the disclosed method may be selected to be
chemically compatible with fracture fluid additives. In the practice of the
disclosed method,
deformable particles may be mixed with any substantially non-deformable
proppant suitable to
maintain a fracture in an oil, gas, geothermal, coalbed methane, water or
other subterranean
well. Such substantially non-deformable fracture proppant materials include,
for example,
silica (such as Ottawa, Brady or Colorado Sands), synthetic organic particles,
glass
SL~STtZLITE~MEET(RULE2~j
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WO 99/27229 PCTNS98/10735
microspheres, ceramics (including aluminosilicates such as "CARBOLITE,"
"NAPLITE" or
"ECONOPROP"), resin-coated sand (such as "ACME BORDEN PR 6000" or "SANTROL
TEMPERED HS"), sintered bauxite, and mixtures thereof. Typically, sand or
synthetic fracture
proppants are used. Most typically, sand is used as a fracture proppant.
5 In the practice of the disclosed method, any natural or synthetic
particulate material that
is substantially deformable under reservoir conditions in the presence of
fracture proppant
material to prevent formation of fines, improve fracture conductivity, and/or
reduce flowback of
proppant or formation materials may be employed. Examples of such
substantially deformable
particulate materials include, but are not limited to, those deformable
materials having a
10 Young's modulus of between about 500 psi and about 2,000,000 psi at
formation conditions,
more typically between about 5,000 psi and about 500,000 psi, more typically
between about
5,000 psi and 200,000 psi at formation conditions, and most typically between
about 7,000 and
150,000 psi at formation conditions. When used in the disclosed method,
substantially
deformable materials have a glass transition temperature that is greater than
the reservoir
15 temperature. Examples of such materials include, but are not limited to,
polymers, cross-linked
polymers and suitably deformable plastics. In this regard, with benefit of
this disclosure
defonmable materials having varying or increased glass transition temperatures
may be selected
by those of skill in the art. For example, polystyrene beads with greater
amounts of divinyl
benzene crosslinker tend to have increased hardness and glass transition
temperature.
Depending on formation conditions, materials that may be suitable in the
practice of the
disclosed method may include, but are not limited to cellulose acetate
butyral, polystyrene
acrylonitride, polytetrafluoroethylene, diglycol allyl carbonates, epoxy
resins, polyester, furan,
phenol formaldehyde, phenolic epoxy, urea aldehydes, silicones, acrylics,
vinyl acetates, casein,
and natural and synthetic rubbers. For example, at formation temperatures of
from about 50°F
to about 450°F, crosslinked elastomeric or polymeric materials are
typically employed.
Polymers that may be crosslinked for purpose of the disclosed method may
include, but
are not limited to, polystyrene, methylmethacrylate, nylon, polycarbonates,
polyethylene,
polypropylene, polyvinylchloride, polyacrylonitrile-butadiene-styrene,
polyurethane, or any
other suitable polymer, and mixtures thereof. For example, suitable
crosslinkers may include
sues nivrE sir tRU~ ~~
CA 02308372 2000-OS-OS
WO 99117229 PCTNS98/10735
16
divinylbenzene. Particularly suitable materials may include deformable
particles manufactured
of resin and/or those commercially available materials that do not
substantially interact
chemically with components of well treatment fluids and which are stable in a
subterranean
formation environment.
In the practice of the disclosed method deformable particles of crosslinked
polymers
may contain varying percentages of crosslinkers to produce proppant packs
having varying
stabilities and conductivities. In this regard, any amount of crosslinker
suitable for forming a
deformable particle may be employed. Percentages of crosslinker employed may
be selected on
many factors if so desired, such as the intended use of the deformable
particle, the specific
crosslinking agent, and other constituents which may optionally be present in
the deformable
particles. For example, changing the percentage of divinylbenzene crosslinker
present in
polystyrene divinylbenzene beads from about 14% to about 4% to about 0.5% to
about 0.3%
changes the confined Young's modulus at standard conditions from about 100,000
psi to about
70,000 psi to about 50,000 psi to about 30,000 psi, respectively.
In one embodiment of the disclosed method, polystyrene divinylbenzene plastic
beads
typically having between about 0.3% and about 55%, more typically between
about 0.5% and
about 20% by weight of divinylbenzene crosslinker are employed. For example,
in one
exemplary embodiment of the disclosed method typically employed at static
bottom hole (or
formation) temperatures of up to and including about 200°F, polystyrene
divinylbenzene plastic
beads having between about 0.5% and about 14% by weight of divinylbenzene
crosslinker are
employed. In this regard, divinylbenzene concentrations of polystyrene beads
employed in this
embodiment may be selected by those of skill in the art with benefit of this
disclosure
including, but not limited to, polystyrene divinyl benzene plastic beads
containing less than or
equal to about 14%, less than about 10%, less than about 5%, less than about
4%, less than
about 3%, less than about 2%, less than about 1%, less than about 0.5%, or
less than or equal to
about 0.3% by weight of divinylbenzene crosslinker. Still other exemplary bead
compositions
that that may be selected for use in this embodiment include, but are not
limited to, polystyrene
divinylbenzene plastic beads containing from about 0.1 % to about 14%, from
about 0.1 % to
about 10%, from about 0.2% to about 4%, from about 0.3% to about 4%, from
about 0.5% to
about 4%, from about 0.3% to about 2%, from about 0.3% to about 1 %, and from
about 0.3% to
~e~rr~u~rES~,.~rcRUr.~a~
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WO 99/2229 PCTIUS98/10735
17
about 0.5% divinylbenzene crosslinker by weight. Still other possible ranges
include, but are
not limited to, polystyrene divinylbenzene plastic beads containing respective
amounts of about
0.3%, about 0.4%, about 0.5% to about 4%, about 4%, about 10%, or about 14% by
weight
divinylbenzene crosslinker by weight. It will be understood with benefit of
this disclosure that
the preceding concentration ranges for use at temperatures of up to about
200°F are exemplary
only, and that polystyrene divinylbenzene beads containing greater than about
14% by weight
polystyrene divinylbenzene may also be employed at formation temperatures
within this range.
In another embodiment of the disclosed method typically employed at formation
temperatures of greater than about 200°F and more typically at greater
than about 200°F and up
to about 300°F, polystyrene divinylbenzene plastic beads having greater
than about 14% by
weight divinyl benzene crosslinker are employed. In this regard,
divinylbenzene concentration
of polystyrene beads employed in this embodiment may be selected by those of
skill in the art
with benefit of this disclosure including, but not limited to, polystyrene
divinyl benzene plastic
beads containing between greater than about 14% and about 55%, and between
greater than
about 14% and about 20% by weight of divinylbenzene crosslinker. It will be
understood with
benefit of this disclosure that the preceding concentration ranges for use at
formation
temperatures of greater than about 200°F are exemplary only, and that
polystyrene
divinylbenzene beads containing less than or equal to about 14% by weight
polystyrene
divinylbenzene may also be employed at formation temperatures within this
range.
However, notwithstanding the above, it will also be understood with benefit of
this
disclosure that polystyrene divinylbenzene beads having amounts of
divinylbenzene crosslinker
less than about 0.2% or less than about 0.1 % by weight may also be employed
at any given
formation temperature if so desired. Further, it will be understood that the
polystyrene
divinylbenzene beads disclosed herein may be employed at temperatures of
greater than about
300°F, if so desired.
It will be understood with benefit of the present disclosure that polystyrene
divinylbenzene plastic beads having the above-described concentration ranges
of
divinylbenzene crosslinker may be used under a wide variety of formation
conditions. For
example, it may be preferable to use beads containing less divinylbenzene
crosslinker at Iower
SUBS71TUTE SMEE1" (RULE 26)
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WO 99127229 PCTNS98J10735
18
formation closure stresses, as well as at lower temperatures. Thus, in one
exemplary
embodiment, polystyrene divinylbenzene plastic beads having from about 0.3% to
about 0.5%
by weight divinylbenzene crosslinker may optionally be employed in the
treatment of
formations having closure stresses of less than or equal to about 6000 psi. In
another
exemplary embodiment, polystyrene divinylbenzene plastic beads having greater
than or equal
to about 4% by weight divinylbenzene crosslinker may be employed in treatment
of formations
having closure stresses of greater than about 6000 psi. With benefit of this
disclosure, those of
skill in the art will appreciate that the exemplary embodiments given herein
only serve to
illustrate certain possible aspects of the disclosed method and therefore do
not limit the use of
various polystyrene divinylbenzene beads having these or other specific
concentration ranges of
divinylbenzene crosslinker at other closure stresses or ranges of closure
stresses than so
exemplified.
Many other deformable bead embodiments may also be employed in the practice of
the
disclosed method. For example, the polymer type and/or composition of a
deformable particle
may be varied in order to further tailor the characteristics of deformable
particles to anticipated
formation conditions and/or to optimize cost versus benefits of the disclosed
method, if so
desired. In this regard, deformable particles may be formulated to comprise co-
polymers for
use at higher formation temperatures, such as temperatures greater than about
300°F. For
example, terpolymer compositions (such those comprising
polystyrene/vinyl/divinyl benzene,
acrylate-based terpolymer, other terpolymers, etc.) may be employed.
For illustration purposes, Table I includes a partial listing of melting
point, glass
transition temperature and Young's modulus of elasticity values for some of
the polymer
materials listed above. In the practice of the disclosed method, polystyrene
divinylbenzene
particles are typically employed at formation temperatures from about
150°F to about 300°F,
and at formation stress values of from about 540 psi to about 12,000 psi. For
lower formation
temperatures, such as below about 150°F, materials such as rubbers or
non-crosslinked
polymers, including non-crosslinked species of those polymers described above,
may be
suitable. At higher formation temperatures, such as above about 300°F,
materials such as
polyvinylchloride or soft metals, including lead, copper, and aluminum, may be
employed. For
any given material, values of Young's moduIus may vary with in situ formation
conditions,
~~T17~T~fi~{~~~
CA 02308372 2000-OS-OS
wo ~ma~9 PCTmsmo~3s
19
such as temperature and pressure (or stress). As an example, FIG.10
illustrates the
relationship between values of Young's modulus and stress for polystyrene
divinylbenzene
beads.
TABLE I
_ Modulus
of Elasticity,
psi
Melting Glass
Point, TransitionLower Upper
olymer C Temp. C Range Range
polyacrylonitrile-butadiene- 90-120 ---
styrene
melamine-formaldehyde 1,300,0001,950,000
polystyrene 240 85-105 400,000 600,000
methylmethacrylate 100 350,000 500,000
polycarbonaxe 105 290,000 325,000
polyvinylchloride 285 75-105 200,000 600,000
high density polyethylene135 85,000 160,000
low density polyethylene115 35,000 90,000
polystyrene divinylbenzene 7,000 150,000
polypropylene 168 25 1,400 1,700
polyurethane 90-I OS
FIG. 5 illustrates just one embodiment of a mufti-planar structure believed to
be formed
in situ between beaded deformable particles and fracture proppant material in
the practice of the
disclosed method. In the disclosed method, deformable particles of any size
and shape suitable
for forming mufti-planar structures or networks in situ with fracture
proppants may be
employed, such as those particles having shapes as mentioned previously. This
also includes
any deformable particles suitable for forming mufti-planar structures or
networks that offer
improved fracture conductivity and/or reduced fines creation over conventional
proppant packs.
sues~rrurEtRU~~~
CA 02308372 2000-OS-OS
wo ~mzz9 Pcrmsmo~3s
Fracture proppant sizes may be any size suitable for use in a fracturing
treatment of a
subterranean formation. It is believed that the optimal size of deformable
particulate material
relative to fracture pmppant material may depend, among other things, on in
situ closure stress.
In this regard, deformable particles having a size substantially equivalent or
larger than a
5 selected fracture proppant size are typically employed. For example, a
deformable particulate
material having a larger size than the fracture proppant material may be
desirable at a closure
stress of about 1000 psi or less, while a deformable particulate material
equal in size to the
fracture proppant material may be desirable at a closure stress of about 5000
psi or greater.
However, it will be understood with benefit of this disclosure that these are
just optional
10 guidelines. Typically, a deformable particle is selected to be at least as
big as the smallest size
of fracture proppant being used, and may be equivalent to the largest fracture
proppant grain
sizes. In either case, all things being equal, it is believed that larger
fracture proppant and
deformable particulate material is generally advantageous, but not necessary.
Although
deformable particulate material smaller than the fractured proppant may be
employed, in some
15 cases it may tend to become wedged or lodged in the fracture pack
interstitial spaces.
Deformable particles used in the disclosed method typically have a beaded
shape and a size of
from about 4 mesh to about 100 mesh, more typically from about 8 mesh to about
60 mesh,
even more typically from about 12 mesh to about 50 mesh, even more typically
from about 16
mesh to about 40 mesh, and most typically about 20/40 mesh. Thus, in one
embodiment,
20 deformable particles may range in size from about 1 or 2 mm to about 0.1
mm; more typically
their size will be from about 0.2 mm to about 0.8 mm, more typically from
about 0.4 mm to
about 0.6 mm, and most typically about 0.6 mm. However, sizes greater than
about 2 mm and
less than about 0.1 mm are possible as well.
Deformable particles having any density suitable for fracturing a subterranean
formation
may be employed in the practice of the disclosed method. However, in one
typical
embodiment, the specific gravity of a deformable particulate material is from
about 0.3 to about
3.5, more typically from 0.4 to about 3.5, more typically from about 0.5 to
about 3.5, more
typically from about 0.6 to about 3.5, and even more typically from about 0.8
to about 3.5.
More typically a deformable particulate material having a specific gravity of
from about 1.0 to
about 1.8 is employed, and most typically a deformable particle having a
specific gravity of
SI~SST1't'IJTE SI~~T (~i~LE 2~)
CA 02308372 2000-OS-OS
WO 99!27229 PCT/US98/10~35
21
about 1.0 to about 1.1 is employed. In another specific embodiment, a
particular
divinylbenzene crosslinked polystyrene particle may have a bulk density of
from about 0.4 to
about 0.65, and most typically of about 0.6. In another specific exemplary
embodiment, a
particular divinylbenzene crosslinked polystyrene particle may have a specific
gravity of about
1.055. However, other specific gravities are possible. Advantageously, when
deformable
particles having a density less than that of a selected fracture proppant
material are employed,
reduced treating pressures and concentration levels of potentially formation-
damaging gelled or
viscous fluids may be employed. This may allow higher treating rates and/or
result in higher
formation productivity.
Deformable particles may be mixed and pumped with fracture proppant material
throughout or during any portion of a hydraulic fracturing treatment in the
practice of the
disclosed method. However, when deformable particulate material is mixed with
only a portion
of a fracture proppant material pumped into a formation, it is typically mixed
with proppant
during the latter stages of the treatment in order to dispose the deformable
particulate material
in the fracture pack at or near the point where the well bore penetrates a
subterranean formation.
In the practice of the disclosed method, it is also possible that mixtures of
deformable particles
and fracture proppant material may be pumped in any number of multiple stages
throughout a
fracture treatment job.
In the practice of the disclosed method, any suitable concentration of
deformable
particles may be mixed with fracture proppant material, with greater
concentrations of
deformable particles typically resulting in a greater reduction in fines
generation for a given
formation and proppant material. However, in one embodiment, ratio of
substantially non-
deformable fracture proppant material to deformable particulate material in a
deformable
particle/fracture proppant material mixture is from about 20:1 (or about 5% by
volume
deformable particulate) to about 0.5:1 (or about 67% by volume deformable
particulate) by
volume of total volume of deformable particle/fracture proppant mixture. In a
further
embodiment, a ratio of fracture proppant to deformable particulate material
may be from about
1:1 to about 15:1 by volume of total volume of deformable particle/fracture
proppant mixture.
More typically, a ratio of fracture proppant to deformable particulate
material is about 3:1 to
about 7:1. Most typically, a ratio of about 3:1 is employed. In another
embodiment of the
~~ET(RULE26)
CA 02308372 2000-OS-OS
WO 99117229 PCTIUS98110735
22
disclosed method, concentrations of deformable particulate material in a
deformable
particle/fracture proppant mixture may be from about 1 % to about 50% by
weight of total
weight of fracture proppant mixture, more typically from about 10% to about
25% by weight of
total weight of fracture proppant mixture, more typically from about 15% to
about 25% by
weight of total weight of fracture proppant mixture and most typically about
15% by weight of
total weight of fi actors mixture.
In the practice of the disclosed method, deformable particulate material may
be mixed
with a fracture proppant or mixture of fracture proppants in any manner
suitable for delivering
such a mixture to a subterranean formation. For example, deformable particles
may be mixed
with a fracture proppant prior to mixing with carrier fluid, or deformable
particles may be
mixed with carrier fluid before or after a carrier fluid is mixed with a
proppant. Deformable
particulate materials may also be mixed in a solution which is later added to
proppant or carrier
fluid as it is pumped. Additionally, mixtures or blends of deformable
particles and fracture
proppant may be injected into a subterranean formation in conjunction with
other treatments at
pressures sufficiently high enough to cause the formation or enlargement of
fractures, or to
otherwise expose the blend of deformable particles and fracture proppant
material to formation
closure stress. Such other treatments may be near wellbore in nature
(affecting near wellbore
regions) and may be directed toward improving wellbore productivity and/or
controlling the
production of fracture proppant or formation sand. Particular examples include
gravel packing
and "frac-packs."
In the practice of the disclosed method, any carrier fluid suitable for
transporting a
mixture of fracture proppant material and deformable particles into a
formation fracture in a
subterranean well may be employed including, but not limited to, carrier
fluids comprising salt
water, fresh water, liquid hydrocarbons, andlor nitrogen or other gases.
Suitable carrier fluids
include or may be used in combination with fluids have gelling agents, cross-
linking agents, gel
breakers, curable resins, hardening agents, solvents, surfactants, foaming
agents, demulsifiers,
buffers, clay stabilizers, acids, or mixtures thereof.
F~t~B$'IlME~ET (RUL.E ~6)
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WO 99/27229 PCT/US98/10735
23
Polystyrene divinylbenzene plastic beads for use with the disclosed methods
may be
prepared by methods that would be apparent to those of skill in the art or
purchased from
"DOW CHEMICAL."
Typically, cross-linked polystyrene beads having a specific gravity of from
about 1.0 to
about 1.8 are employed. In a most typical embodiment of the disclosed method,
20-40 mesh
polystyrene divinylbenzene copolymer plastic beads having a specific gravity
of about 1.0 are
mixed with 20/40 mesh Ottawa sand at a ratio of about 3:1 by weight. These
beads are
commercially available as a lubrication fluid from "SUN DRILLING PRODUCTS"
under the
brand name "LUBR.AGLIDE," or as ion exchange beads manufactured by "DOW
CHEMICAL." These beads offer crush resistance, are resistant to solvents, and
are
substantially round and smooth, having length to width and length to height
ratios of about 1:1.
Since the polystyrene divinylbenzene plastic beads of this embodiment have a
reduced bulk
density (i.e., about 0.64 gm/cm3), the beads may be suspended in frac fluids
with a significant
reduction in gelling agents. With a reduction in density, these plastic beads
require less packing
density (i.e., lb/ft2) to achieve the same fracture width. Test results
indicated that these plastic
beads are deformable under conditions of stress and relative to sand proppant.
Test results also
showed that these beads are compatible with oil field solvents and acids.
Favorable formation
treating characteristics offered by polystyrene divinylbenzene beads include,
among other
things, strength, crush resistance, chemical resistance, elasticity, high
glass transition
temperature. These beads are also "non-creeping" (i.e., resistant to slow
change in shape due to
constant force).
When plastic beads of this embodiment are mixed with substantially spherical
fracture
proppant material of substantially uniform size, a hexagonal-close-pack (HCP)
structure is
believed to be possible (i.e., typically generating six contact points for
each plastic bead). Each
contact point may generate a substantially flat face at higher stresses as the
plastic grains are
forced into a smaller volume, such as under conditions of closure stress.
Since plastic beads of
this embodiment of the disclosed method may deform to form substantially flat
surfaces on
multiple sides, Young's modulus for a proppant pack incorporating these beads
may be
increased, consequently increasing particle cohesion and proppant pack
stability, and
decreasing flowback of proppant. When plastic beads of this embodiment are
mixed with
SUBS'TI'~ SHEET (RULE 28)
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WO 99/27229 PCTNS98/10'735
24
harder, non-deformable proppants, such as sand, proppant packs may be formed
with proppant
particles "locked" into deformed surfaces of the plastic beads, thus forming a
stronger pack.
Although substantially spherical fracture proppant material of substantially
uniform size is
described in this embodiment, it will be recognized with benefit of this
disclosure that non-
spherical and/or non-uniformly sized fracture proppant material may also be
successfully
employed in the practice of the disclosed method.
In alternative embodiments of the disclosed method, mufti-component or
multiple
component deformable particles may be utilized. As used herein "mufti-
component" or
"multiple component" means a particle comprised of at least two materials
having different
deformation characteristics (such as differing values of elastic modulus).
Typically, at least one
component of such a mufti-component particle has the characteristic of being
substantially
deformable, and at least one other component of the particle has the
characteristic of being
substantially non-deformable relative to the deformable component. The two or
more materials
may be configured in virtually any manner desired to form mufti-component
particles, for
example, to achieve varying overall deformation characteristics of such
particles. Possible
particle configurations include, but are not limited to, layered particles
(such as concentrically
layered particles), agglomerated particles, stratified particles, etc. Such
mufti-component
deformable particles may be employed with substantially non-deformable
fracture proppant
material in any of the amounts described elsewhere herein for deformable
particles.
Furthermore, such mufti-component deformable particles may be employed alone
so as to make
up all, or substantially all, of a fracture pack with little or no
substantially non-deformable
fracture proppant material present in the pack.
In one such embodiment, layered mufti-component deformable particles may be
provided that comprise a substantially hard or non-deformable core surrounded
by one or more
layers of substantially deformable material. Although applicable for use over
a wide range of
fracture proppant conditions, such layered mufti-component deformable
particles may be
particularly desirable for use with higher anticipated formation temperatures
and/or higher
anticipated formation closure stresses due to the ability to provide
sufficient elasticity or
deformability of the surface of the particle without being susceptible to
excessive or total
8U8'SmL~'E~h~Elt~l.E26)
CA 02308372 2000-OS-OS
WO 99/27229 PCTIUS98/10735
deformation of the particles. This property is advantageously provided by the
substantially
hard core of the layered particle which resists excessive deformation.
In one exemplary embodiment depicted in FIG. 27, a layered mufti-component
deformable particle 200 may be provided using a proppant particle or other
substantially hard
5 or substantially non-deformable material core 202 coated by a substantially
deformable material
204. Advantageously, such a layered deformable particle may be formulated to
be capable of
withstanding total deformation, particularly at high formation temperatures
and formation
stresses (i.e., formation temperatures exceeding about 300°F and
formation stresses exceeding
about 6000 psi). A substantially hard core of such a layered deformable
particle may be
10 selected to provide sufficient strength or hardness to prevent total
deformation of the particle at
temperatures and/or formation closure stresses where substantially deformable
materials (such
as crosslinked polymers) generally become plastic. In this regard, it is
believed that total or
near-total deformation of a deformable particle in a proppant pack is
undesirable because it may
damage fracture proppant pack permeability when the amount of deformation
reaches levels
I S sufricient to plug proppant pack pore spaces.
Although a layered deformable particle having a substantially non-deformable
inner
core surrounded by a single layer of substantially deformable material is
depicted in FIG. 27, it
will be understood with benefit of this disclosure, that one or more layers of
deformable
materials may be utilized to provide a substantially deformable coating over a
substantially
20 non-deformable or hard inner core. Similarly, it will also be understood
that a substantially
non-deformable inner core may comprise more than one layer or thickness of
substantially non-
deformable material. Furthermore layers of such non-deformable and deformable
materials
may be alternated if so desired. In any case, a deformable coating is
typically provided in a
thickness or volume sufficient to allow adjacent and relatively hard fracture
proppant particles
25 in a fracture proppant pack to penetrate all or a portion of the deformable
coating so as to
provide one or more benefits of deformable particles as described elsewhere
herein, but without
substantially reducing porosity of a fracture pack due to excessive
deformation. In this regard,
a substantially non-deformable inner core acts to limit undesirable distortion
of the deformable
particle so as to prevent excessive damage to the conductivity of a fracture
proppant pack.
suesnrurs sir Cruz ~~
CA 02308372 2000-OS-OS
WO 99/27229 PGTNS98/10735
26
The deformable outer layers of a layered deformable particle acts to prevent
damage to
a proppant pack by preventing the creation of proppant fines that occur, for
example, when
increased stress is applied on a proppant pack and where uncoated fracture
proppant grains are
in point to point contact as stress is increased. FIG. 28 illustrates just one
possible embodiment
of a mufti-planar structure believed to be formed in situ between layered
deformable particles
200 and fracture proppant particles 206 in the practice of the disclosed
method. As with other
embodiments of the disclosed method, layered deformable particles of any size
and shape
suitable for forming mufti-planar structures or networks in situ with fracture
proppants may be
employed, including deformable particles having shapes as mentioned
previously.
Furthermore, layered deformable particles 200 may be utilized alone in well
stimulation
treatments to create proppant packs comprising only deformable particles 200
as depicted in
FIG. 29.
In the practice of the disclosed method, a layered deformable particle may
have one or
more layers or coatings of deformable material which may include any of the
deformable
materials mentioned elsewhere herein. In one exemplary embodiment, layered
deformable
particles include one or more coatings of crosslinked polymers. Suitable
crosslinked polymers
include, but are not limited to, polystyrene, methylmethacrylate, nylon,
polycarbonate,
polyethylene, polypropylene, polyvinylchloride, polyacrylonitrile-butadiene-
styrene,
polyurethane, mixtures thereof, etc. However, it will be understood with
benefit of the
disclosure that any other deformable material suitable for coating a
substantially hard proppant
core and having suitable deformable characteristics as defined elsewhere
herein may be
employed.
In the practice of the disclosed method, a core of a layered deformable
particle may
comprise any material or materials suitably hard enough to form a
substantially nondeformable
core about which one or more layers of deformable material may be disposed. In
this regard, a
core is typically a fracture proppant such as sand or any of the other
substantially non-
deformable fracture proppants mentioned elsewhere herein. For example, a
suitable core
material may be silica (such as Ottawa sand, Brady sand, Colorado sand, etc.
), synthetic organic
particles, glass microspheres, sintered bauxite (including aluminosilicates),
ceramics (such as
CARBOLITE from Carbo Ceramics, Inc., NAPLITE from Norton Alcoa, ECONOPROP,
from
8uesnrin~ sir ~RUr~ a.~~
CA 02308372 2000-OS-OS
WO 99!27229 PCT/US98/10735
27
Carbo Ceramics, Inc. etc. ), suitably hard plastic (such as nylon), suitably
hard metal (such as
aluminum), etc. In one embodiment a core material may have a Young's modulus
that is
suitably hard and non-deformable relative to the Young's modulus of layers of
deformable
material disposed thereabout. For example, in this embodiment a core material
may have a
Young's modules greater than about 500,000 psi, alternatively a Young's
modules between
about 500,000 psi and about 15,000,000 psi or alternatively a Young's modules
of between
about 2,000,000 psi and about 15,000,000 psi.
A deformable layer or coating around a substantially non-deformable particle
core may
be any thickness suitable for allowing deformation of the layer upon contact
with fracture
proppant materials under closure stress. However, typically thickness of such
layerls are
limited such that deformation under anticipated formation closure stress does
not result in
damage to conductivity due to excessive deformation and impingement into
fracture proppant
pack pore spaces. In this regard, a layers of deformable material typically is
thick enough to
provide a coating sufficient for reducing proppant flowback and/or fines
generation by allowing
adjacent relatively hard fracture proppant material to embed in the layers of
deformable
material without substantially reducing porosity or conductivity of the
proppant pack.
In one exemplary embodiment of the disclosed method, one or more layers of
deformable material comprise at least about 10% by volume or alternatively at
least about 20%
by volume of the total volume of the layered deformable particle. Alternately,
in this
embodiment one or more layers of deformable particulate material may comprise
respectively
from about 10% to about 90%, from about 20% to about 90%, from about 20% to
about 70%,
from about 40% to about 70%, or about 70% by volume of total volume of a
layered
deformable particle. However, it will be understood that one or more layers of
deformable
material may comprise less than about 10% by volume of the total volume of a
layered
deformable particle, and greater than about 90% by volume of the total volume.
of a layered
deformable particle. In yet another embodiment, one or more layers of
deformable material
may comprise greater than 8%, or alternatively greater than about 10%, by
weight of the total
weight of a layered deformable particle.
sue,~s~r'cRU~a~s~
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In another exemplary embodiment, the thickness of the outside layer or coating
of a two
component deformable particle may be substantially equivalent to the diameter
or thickness of
the particle core. As an example, a substantially hard core having a 40 mesh
size may be coated
with sufficient deformable material to produce a 20 mesh two-layer or two-
component
deformable particle. Although substantially spherical layered deformable
particles have been
described herein, it will be understood by those of skill in the art with
benefit of this disclosure
that non-spherical layered deformable particles having any of the deformable
particle shapes as
described elsewhere herein may also be employed.
In one embodiment employing a mixture of layered deformable particles and
fracture
i0 proppant material, the thickness of one or more outside layers or coatings
of deformable
material is typically equal to or greater than the non-deformable core
diameter for each particle.
In another embodiment employing all or substantially all layered deformable
particles to form a
fracture pack, the thickness of the one or more outside layers or coatings of
deformable material
is typically equal to or less than about 10% of the diameter of the non-
deformable core of each
particle. However, these are only exemplary embodiments and merely illustrate
that thinner
layers may be employed when deformable particles make up more or substantially
all of a
fracture pack, and that thicker layers may be employed when relatively greater
amounts of
substantially non-deformable fracture proppant materials are present in a
fracture pack.
Although any deformable material described elsewhere herein may be employed
for one
or more layers of a layered deformable particle, in one embodiment materials
having a modulus
of between about 500 psi and about 2,000,000 psi, or alternatively between
about 5,000 psi and
about 200,000 psi, may be employed. Typically such deformable materials are
selected to be
chemically resistant and substantially non-swelling in the presence of
solvents as described
elsewhere herein.
In one exemplary embodiment, a layered deformable particle comprises a silica
core
material surrounded by a single layer or coating of polystyrene divinylbenzene
co-polymer
(having from about 0.5% to about 20% by weight divinyl benzene cross-linker).
In this
embodiment the core material has a modulus of about 2,000,000 psi to about
5,000,000 psi and
the single layer coating has a modulus of about 70,000 psi. However, with
benefit of this
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disclosure, those of skill in the art will understand that core and layer
material selection may be
varied based on anticipated formation conditions such as temperature, pressure
and closure
stress, as well considerations of cost. In this regard, as with single
component deformable
particles, materials having relatively lower modulus values are typically
selected for use in
shallower and/or lower temperature and/or lower stress wells while deformable
materials with
relatively higher modulus values are selected for use in deeper and/or higher
temperature and/or
higher stress wells.
The disclosed layered deformable particles may be of any overall size suitable
for use in
a fracture proppant pack, either alone or in a mixture with fracture proppant
material, as well as
in sizes as described elsewhere herein. Typically, a layered deformable
particle for inclusion in
a mixture with fracture proppant is selected to have a size at least as large
as the smallest
fracture proppant particles being used. Alternatively, a layered deformable
particle for use in a
mixture with fracture proppant is selected to have a size equal to the largest
fracture proppant
particles. In one exemplary embodiment, a layered deformable particle has a
size typically
IS from about 4 mesh to about 100 mesh, more typically from about 12 mesh to
about 50 mesh,
and most typically about 20/40 mesh.
As described above, layered deformable particulate materials may be employed
alone as
a fracture proppant material (l. e. , without another type of fracture
proppant material), or may be
employed with mixtures of fracture proppant material as previously described
for single
component deformable particles. In this regard, layered deformable particles
may be mixed
with a fracture proppant material in any of the weight percentages or ratios
relative to fracture
proppant material as described elsewhere herein.
Although, embodiments of the disclosed method employing layered mufti-
component
deformable particles having two components or layers have been described and
illustrated
above, it will be understood that other configurations of layered mufti-
component deformable
particles may be employed. For example, layered particles may include a
substantially hard
core with two or more layers of deformable materials surrounding the core. Any
combination
of two or more deformable materials mentioned elsewhere herein may be employed
in multi-
component deformable particles having a core surrounded by two or more layers.
In this
StlB~t'1TUTE SHEET tRULE 26)
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regard, deformable particles having two or more layers of deformable materials
may be useful
for providing the desired degree of deformability in combination with other
desirable
properties. For example, a first layer of relatively soft defonnable material
may be surrounded
or covered by a second or outside layer of relatively hard, but chemical
resistant deformable
5 material. In this way sufficient particle deformability and chemical
resistance at high
temperatures may be provided simultaneously. In another example, a relatively
softer and more
chemical resistant second or outer layer of deformable material may surround a
first layer of
relatively harder, less chemical resistant deformable material. In one
particular exemplary
embodiment, a two-layer mufti-component deformable particle may include a
substantially hard
10 40 mesh Ottawa sand core surrounded by a first layer of substantially
deformable acrylate or
acrylic polymer and a second layer of substantially deformable polystyrene.
Such a particle
configuration provides deformability and strength over a larger range of
temperatures and
stresses.
In still another embodiment of the disclosed method, agglomerated mufti-
component
15 deformable particles may be employed. Such agglomerates may comprise one or
more
relatively hard or substantially non-deformable materials mixed or
agglomerated with one or
more relatively elastic or substantially deformable materials. One example of
such a particle
300 is illustrated in cross-section in FIG. 30. An agglomerated mufti-
component deformable
particle 300 may comprise one or more substantially non-deformable material
components 302,
20 such as one or more materials selected from the substantially non-
deformable materials
described elsewhere herein as suitable for a core material of a layered
deformable particle.
Such substantially non-deformable material components 302 may be coated with
or otherwise
intermixed with substantially deformable material 304 so that the deformable
material 304
functions to at least partially coat and/or fill pore spaces existing between
individual non-
25 deformable material components 302 as shown in FIG. 30. An outer layer of
deformable
material 304 may be present as shown in FIG. 30, although this is not
necessary. The
deformable components 304 of such an agglomerated mufti-component deformable
particle
300 may comprise any suitable substantially deformable materials, such as one
or more
materials selected from the substantially deformable materials described
elsewhere herein as
30 suitable for use in single component and/or layered deformable particles.
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In one embodiment of agglomerated mufti-component material, substantially non-
deformable material may be any substantially non-deformable granular material
less than about
100 microns in size, and substantially deformable material may be any
substantially deformabie
material suitable for encapsulating the substantially non-deformable material
in a matrix.
S Specific examples of substantially non-deformable material employed in this
embodiment
include, but are not limited to, at least one of silica, cristobalite,
graphite, gypsum, talc, or a
mixture thereof, and specific examples of substantially deformable material
employed in the
same embodiment include, but are not limited to, resins such at least one of
furan, furfuryl,
phenol formaldehyde, phenolic epoxy, or a mixture thereof. It will be
understood with benefit
of this disclosure by those of skill in the art that whenever resins are
utilized as substantially
deformable material in the practice of any of the embodiments of the disclosed
method that they
may be chemically modified, such as by inclusion of suitable plasticizers, to
render the resins
suitably deformable for individual applications. In this regard, plasticizer
may be incorporated
in all or a portion of the deformable material content of each particle. For
example, a
plasticizer may be incorporated into only an outer layer of an agglomerate
particle, or
alternatively throughout all of the deformable material of the agglomerate
particle.
It will be understood with benefit of this disclosure by those of skill in the
art that the amount
of deformable material relative to amount of substantially non-deformable
material may be
varied to change or modify the deformation characteristics of an agglomerated
multi-
component particle. In this regard, the amount of deformable material in such
an agglomerated
particle may vary from just greater than about 0% to just less than about 100%
by weight of the
particle. However, in one embodiment an agglomerated deformable particle
comprises from
about 5% to about 50%, alternatively from about 5% to about 25%, and in a
further alternative
from about 10% to about 20% by weight of substantially deformable materials,
with the
balance of the particle being composed of substantially non-deformable
materials. For
example substantially deformable material may make up between about 5% and
about 50% by
volume of the total volume of an agglomerated particle, and substantially non-
deformable
material may make up between about 50% and about 95% by volume of the total
volume of the
agglomerated particle.
SUB~TITt~TE't~LE26)
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In one exemplary embodiment, an agglomerated mufti-component particle may
comprise an agglomerated mixture of silica and resin. In this embodiment, a
resin component
may comprise any resin suitable for encapsulating the silica, including, but
not limited to,
epoxy resins, furan, phenol formaldehyde, phenolic epoxy, etc. Most typically,
such a particle
comprises about 10.5% by weight of phenolic resin mixed with particles of
silica having a size
of from about 6 to about 100 microns.
Whether agglomerated, layered or in other form, mufti-component deformable
particles
may be employed in any of the shapes and sizes described elsewhere herein as
being suitable
for other forms or embodiments of deformable particles. Moreover, such
particles may be
employed alone as a fracture proppant, or in mixtures in amounts and with
types of fracture
proppant materials as described elsewhere herein for other types of deformable
particles. It will
also be understood with benefit of this disclosure by those of skill in the
art that selection of
mufti-component deformabie particle characteristics may be made based on
anticipated
formation conditions such as formation temperature and/or formation closure
stress. Such
characteristics include, but are not limited to, core and layer materials of a
layered deformable
particle, layer and core thicknesses of a layered deformable particle, types
and relative
percentages of deformable and non-deformable materials employed in an
agglomerated multi-
component particle, etc.
EXAMPLES
The following examples are illustrative and should not be construed as
limiting the
scope of the invention or claims thereof.
Examples 1-3: Plastic Beads
Polystyrene divinylbenzene copolymer plastic beads with a 20/40 mesh size were
tested
alone (without other proppant materials) using modified API standards. These
beads contained
about 4% divinylbenzene by weight. These plastic beads used in this example
were found to
pass the standard API RP 56 test for roundness, sphericity, and acid
solubility (i.e., 0.5%).
Testing was also performed to determine if any swelling in solvents occurred.
The beads were
placed in xylene at room temperature and photographed over 65 hours. No
swelling occurred
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33
under these conditions. Standard API crush testing was also performed on the
beads at stresses
between 2000 and 8000 psi. It was found that plastic beads of this type
typically do not fracture
or shatter in a brittle manner to generate fines under stress, but instead
"plastically" deform to
form flat dimples on the round surface. Consequently, non-API tests were
performed to
S determine the crush properties of the beads.
Example 1 ~ API RP 56 Evaluation
The polystyrene divinylbenzene plastic beads of this embodiment had a
sphericity of 0.9
and roundness of 0.9 which is suitable for proppant use since it meets the
required minimum
value of 0.6 for each property. A sieve analysis of the material contained an
acceptable 93.8%
20/40 distribution with 6.1 % retained on the 50 mesh screen and 0.1 % fines.
The acid
solubility at 150°F was an acceptable 0.5% using a 12-3 HCI-HF acid.
Example 2: API Crush Testinr~
To measure propensity of polystyrene divinylbenzene plastic beads of this
embodiment
to generate fines under closure stress, the plastic beads were crush tested at
confining stresses of
2000, 4000, 6000 and 8000 psi using Equation 7.1 in API RP 60. An initial
starting mass of
15.71 gm for a measured bulk density of 0.636 gm/cm3 using a 2 inch diameter
crush cell was
calculated. The results of the crush test are given in Table II where the
weight percent of fines
are given for an initial 6.2% "fines" distribution material at zero stress.
The third column
estimates the fines less than 50 mesh by subtracting the initial 6.1 % 50 mesh
particles.
TABLE II
Weight Per Cent Fines for Plastic Bead Crush Tests
Crush Stress (psi) Fines (wt %) Fines (Less~Than 50 Mesh)
(wt%)
0 6.2 0,1
2000 6.9 0.7
400U 6.9 0.7
8000 S.0
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The results given in Table II indicate that the plastic particles are "crush
resistant" since
the percentage of fines are less than 14% at all stress levels.
Example 3: Non-API Crush Testing
To measure deformation properties of the polystyrene divinylbenzene beads of
this
embodiment, the plastic bead material was slowly (i.e., 2 minutes) stressed in
a 1-inch diameter
cell by computer control of the measured load while accurately monitoring the
change in
sample volume by using a sensitive linear variable differential transducer
(LVDT) calibrated to
0.001 inch accuracy.
In FIG.11, volume per cent change in plastic beads is plotted as a function of
closure
stress. At 2000 psi closure stress, 25% of the bulk bead volume has been lost
due to pore
volume changes. At 6000 psi closure stress, essentially all of the pore volume
is lost (i.e., 42%)
due to compaction, and the beads are essentially a conglomerate solid. This
large compaction
of plastic beads is shown in FIG. 12 where the change in fracture width is
plotted versus stress.
The change in fracture width is measured in the English unit mils (i.e., 1 mil
= 0.001 inches).
For comparison, the same measurements are shown in FIG. 13 for 20/40 mesh
Ottawa sand
proppant at 2 lb/ft2. At 4000 psi closure stress, the plastic beads are
compacted 210 mils.
Ottawa sand is compacted only 17 mils. The data in FIGS. 12 and 13 indicate
that the
compaction of plastic beads are a factor of 12 times larger than the
compaction of Ottawa sand.
For Ottawa sand, proppant crushing starts at about 4500 psi and increases
significantly for
stress greater than 6000 psi.
Examples 4-9: Plastic BeadlOttawa Sand Mixtures
Conductivity analyses were performed on combinations of plastic beads and
Ottawa
sand at 200°F. Results of these analyses are presented in Tables III
and IV, and graphically in
FIGS.14 and 15.
ExamQ,le 4: Conductivity Testing
Conductivity tests were performed on a combination of 20/40 mesh polystyrene
divinylbenzene plastic beads and combinations of 20/40 mesh Ottawa sand and
20/40 mesh
polystyrene divinylbenzene plastic beads according to the present embodiment.
Tests were
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performed using a "DAKE" hydraulic press having a "ROSEMOUNT" differential
transducer
(#3051 C) and controlled by a "CAMILE" controller. Also employed in the
testing was a
"CONSTAMETRIC 3200" constant rate pump. In addition to testing 20/40 plastic
beads alone,
a 7:1 mixture of 1.75 lbs/ft2 of 20/40 mesh Ottawa sand to 0.25 lbs/ft2 of
20/40 mesh plastic
5 beads, and a 3:1 mixture of 1.50 lbs/ft2 of 20/40 mesh Ottawa sand to 0.50
Ibs/ft2 of 20/40 mesh
plastic beads were also tested. Averaged test results are given in Tables IIi
and IV, as well as
FIGS. 14 and 15. For comparison purposes, conductivity and permeability data
for 20/40
Ottawa sand published by "STIMLAB" is also presented.
As shown in Tables III and IV, test results indicate that combinations of
plastic beads
10 and Ottawa sand according to this embodiment of the disclosed method may
have a positive
synergistic effect on permeability and conductivity.
TABLE III
Permeability at Varying Closure Stresses
Permeability,
Darcies
Closure Stress20/40 Mesh 20/40 Mesh 3:1 7:1
(psi) Ottawa Sand Plastic Beads CombinationCombination
1000 277 235 356
2000 248 99 272 262
4000 142 189 143
6000 45 120 52
8000 16 55 17
10000 9 36
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TABLE IV
Conductivity at Varying Closure Stresses
Conductivity,
md-ft
Closure Stress20/40 Mesh 20/40 Mesh 3:1 7:1
(psi) Ottawa Sand Plastic BeadsCombination Combination
1000 5135 7110 8355
2000 4340 3260 5778 5424
4000 2640 3013 2811
6000 1178 1310 977
8000 292 976 295 I
10000 164 639
II I I I I
As shown in Table III and FIG. 14, at a 3:1 mixture of 1.50 lbslft2 of 20/40
mesh
Ottawa sand to 0.50 lbs/ft2 of plastic beads there was a consistent increase
in permeability over
20/40 Ottawa proppant alone. At 2000 psi closure the increase in mixture
permeability over
Ottawa sand was approximately 10% (from about 250 darcy to about 270 darcy),
at 4000 psi
the increase was approximately 35% (from about 140 darcy to about 190 darcy),
and at 8000
psi, the increase was approximately 240% (from about 16 darcy to about 55
darcy).
Significantly, at 10,000 psi closure stress, the about 36 darcy permeability
of the 3:1
combination is approximately 300% greater than the about 9 darcies
permeability of Ottawa
sand alone. Among other things, this test demonstrated the ability of the
beads to reduce the
production of fines by Ottawa at higher closures stresses by preventing grain
to grain contact
between grains of proppant.
It may also be seen in Table III and FIG.14 that at 200°F a 7:1 mixture
of 1.75 lbs/ft2
of 20/40 mesh Ottawa sand to 0.25 Ibs/ft2 plastic beads yields permeability
values closer to
those of Ottawa sand alone than does a 3:1 mixture. However, Table IV and
FIG.15 show that
the 7:1 mixture yielded increased conductivity values over Ottawa sand for all
but the 6000 psi
test closure stress. Furthermore, for temperatures below 200°F, greater
permeability and
conductivity improvements may be expected with a 7:1 mixture. It will also be
understood
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with benefit of the present disclosure that mixtures of deformable particulate
material and
fracture proppant according to the disclosed method may be used to
successfully reduce fines
generation and/or proppant flowback independent of, or without, any associated
permeability or
conductivity improvement over fracture proppant alone.
S Referring again to FIG.11, deformation tests demonstrated that a deformable
particulate, in this embodiment a polystyrene divinylbenzene bead of 20/40
U.S. Mesh size and
containing about 4% divinylbenzene by weight, deforms to consume approximately
33% of the
existing pore space at 1000 psi closure stress. At 2000 psi closure
approximately 55%
deformation had occurred and at 8000 psi the pore space was essentially nil.
However, as
shown in FIG.15, when 20/40 mesh polystyrene divinylbenzene beads of this
embodiment are
combined with 20/40 mesh Ottawa fracturing sand in a 3:1 ratio by volume,
conductivity at all
stress values listed above is greater than either proppant alone. At 1000 psi
closure stress the
3:1 mixture had a conductivity of approximately 8355 md-ft while the
conductivity of 20/40
mesh Ottawa proppant alone is 5135 md-ft and conductivity of polystyrene
divinylbenzene
beads alone was found to be 7110 md-ft. At 2000 psi closure stress the
conductivity values are
5778 md-ft for the 3:1 mixture, 4340 md-ft for the 20/40 mesh Ottawa sand, and
3260 md-ft for
the plastic beads. At 6000 psi the 3:1 mixture gave 1310 md-ft while 20/40
mesh Ottawa sand
alone has a conductivity of 1178 md-ft. In FIG. 15, a similar effect may be
observed for the
7:1 mixture.
Example 5: Crush Testinsz
Reduction in fines generation using embodiments of the disclosed method is
evidenced
in crush tests performed on 3:1 and 7:1 by volume mixtures of 20/40 mesh
Ottawa sand and the
polystyrene divinylbenzene beads of the present embodiment. As shown in
FIG.16, the fines
generated as a percentage of pmppant (20/40 mesh Ottawa) decreases with
increasing
concentration of deformable plastic material. For example, at 6,000 psi
closure stress, 22%
fines were generated by 20/40 mesh Ottawa sand above. This level of fines
generation is above
the API recommended maximum fines generation of 14% for proppant applications.
For a 7:1
ratio of 20/40 mesh Ottawa sand to 20/40 mesh polystyrene divinylbenzene
beads,
approximately 13% fines were generated. For a 3:1 ratio of 20/40 mesh Ottawa
sand to 20/40
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mesh polystyrene divinylbenzene beads (4% divinylbenzene) only about 8% fines
were
generated. These levels of fines generation are well below the API recommended
maximum.
As seen in FIG.16, percentage reduction in fines for 20/40 mesh Ottawa
sand/20/40
mesh polystyrene divinylbenzene bead mixtures was even greater at higher
closure stresses.
For example, at 8,000 psi closure stress, approximately 33% fines were
generated for 20/40
mesh Ottawa sand alone, 22% fines for a 7:1 mixture and 13% fines for a 3:1
mixture. At
10,000 psi closure stress, 40% fines were produced for 20/40 mesh Ottawa sand,
29% for a 7:1
mixture and 15% for a 3:1 mixture. Significantly, the level of fines
generation for the 3:1
mixture remained 20%, even at 10,000 psi closure stress.
I0 These test results indicate that the fines reduction advantages of the
disclosed method
may be realized under a wide variety of closure stress conditions. These
results also
demonstrate that the useable range of fracture proppant materials, such as
Ottawa sand, may be
extended to higher stress levels using deformable particles of the disclosed
method.
Example 6: Packing Geometries
Referring to FIG. 17, photographs of polystyrene divinylbenzene beads obtained
from a
stereo microscope are shown. These beads were mixed with an Ottawa sand
fracture proppant
at a ratio of 3:1 to form a simulated proppant pack, and then subjected to a
stress of 10,000 psi.
Stress was then relieved and the deformed polystyrene divinylbenzene beads
photographed. As
shown in FIG.17, three dimensional structures were formed under stress between
deformable
polystyrene divinylbenzene beads 110 and 120 and fracture proppant particles
116, leaving
dimpled surfaces 114 and 124 on sides of beads 110 and 120, respectively,
without sticking or
adherence of the beads 110 and 120 to the fracture proppant particles 116. The
results of this
example indicate that embodiments of the disclosed method achieve three
dimensional multi-
planar structures when subjected to formation stress.
Example 7: Flowback Tests
Pmppant flowback failure was determined for Ottawa sand and mixtures of Ottawa
sand
to polystyrene divinylbenzene beads ranging from about 3:1 to about 6:1. For
comparison
purposes, proppant flowback failure was also determined for Ottawa sand alone.
The
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polystyrene divinylbenzene beads employed for these tests contained about 0.5%
divinylbenzene crosslinker by weight, had a Young's confined modulus of about
50,000 psi,
and had a size of about 20 mesh.
The proppant samples were loaded into a standard conductivity cell at 2
lbs/ft2. The
width of the pack was measured throughout the test using an LVDT. The
differential pressure
between the input and output flow of water through the pack was measured
employing a
Rosemount PD transducer and the rate of the flow was measured by a Micromotion
D6 mass
flow meter. Closure stress (approximately 1000 psi) was applied to the pack.
The end of the
conductivity cell was then removed to expose the proppant pack and replaced
with a Texan tube
filled with water. This allowed sand to flow into the tube at failure. Water
was then pumped
through the pack at flow rates increasing incrementally by 10 mUminute
intervals until pack
failure which was judged by width of the pack and the loss of differential
pressure. The
temperature of the water flowing into the pack and the cell were maintained at
between about
64°C to about 68°C.
As can be seen from FIGS. 18-21, compositions of Ottawa sand/polystyrene
divinylbenzene bead mixtures (FIGS. 19-21) failed at flow rates of greater
than approximately
110 mllmin while the Ottawa sand composition failed at flow rates of from
about 60 to 80
mUmin. Thus, the present invention allows for a significant improvement
(approximately
150%) in the stability of the pack while still improving the conductivity at a
closure stress of
about 1000 psi.
Example 8~ Resistance to Flowback
Resistance to flowback or measure of the force sufficient to move a proppant
particle
was determined for 20/40 mesh Ottawa sand and mixtures containing 20/40 mesh
Ottawa sand
and 15% by weight polystyrene divinyl benzene beads using the testing
procedure of Example
7. For comparison purposes, resistance to flowback was also determined for
20/40 mesh
Ottawa sand alone. The polystyrene divinyl benzene beads employed for these
tests contained
about 0.5% divinyl benzene crosslinker by weight, had a Young's confined
modulus of about
50,000 psi, and had a size of about 20 mesh.
~8~~1~t~LE2~~
CA 02308372 2000-OS-OS
PCT/US98/10735
WO 99127229
As can be seen in FIG. 25, proppants comprising a mixture of 20/40 Ottawa sand
and
polystyrene divinyl benzene beads exhibited maximum drag force ("Fd") or
resistance to flow
of from about 0.85 dynes for a mixture containing 40/60 mesh polystyrene
divinyl benzene
deformable beads to about 1.65 dynes for a mixture containing 20 mesh
polystyrene divinyl
5 benzene deformable beads. Higher maximum drag force values at higher flow
rates are an
indication of higher resistance to proppant movement for mixtures of
deformable beads and
sand as compared to sand alone. For example, 20/40 mesh Ottawa sand proppant
alone
exhibited a maximum drag force of about 0.65 dynes at a flow rate of about 70
ml per minute.
In contrast, mixtures of 40/60 mesh, 30/50 mesh, and 20 mesh polystyrene
divinyl benzene
10 beads with 20/40 Ottawa sand exhibited maximum drag force values of about
0.85 dynes at
about 80 ml per minute, 1.45 dynes at about 110 ml per minute, and about 1.65
dynes at about
120 ml per minute. These results illustrate the relationship between
deformable particle size,
fracture proppant material size, and the propensity of a fracture pack to
produce proppant. In
this example, combinations of deformable particles and Ottawa sand produced
more stable
15 packs than Ottawa sand alone. Increasing pack stability was also be noted
for those
combinations in which the size of deformable particles approached the size of
the Ottawa sand.
In this example, greatest stability of the tested size combinations was noted
where the
deformable particles had a size (20 mesh) that was as large as the maximum
mesh size of the
Ottawa sand (20/40 mesh).
20 FIGS. 22 and 23 represent resistance to flowback test data obtained at
varying fracture
widths for 20/40 mesh Ottawa sand and a mixture of 20140 Ottawa sand with 15%
by weight of
20 mesh polystyrene divinylbenzene beads containing 0.5% by weight
divinylbenzene
crosslinker, respectively. This data was generated under stepped flowrate
conditions up to
failure. As may be seen, the proppant mixture of Ottawa sand and polystyrene
divinylbenzene
25 beads exhibited a significantly higher Fd of about 1.3 to about 1.6 dynes
as compared to Fd of
the 20/40 Ottawa sand alone (about 0.60). Significantly, the Ottawa
sand/polystyrene
divinylbenzene also maintained this greater flowback resistance up to a
fracture width of about
0.235 inches as compared to a fracture width of about 0.205 inches for the
Ottawa sand alone.
This demonstrates the superior fracture pack stability provided by proppant
pack mixtures
30 containing the deformable particles of the present disclosure.
sus~murESH~'~RU~~~
CA 02308372 2000-OS-OS
WO 99/272Z9 PCTNS98110735
41
FIG. 24 represents resistance to flowback test data for a mixture of 20/40
Ottawa sand
with 25% by weight of 30 mesh agglomerate beads containing approximately 90% 6
micron
silica and 10% phenolic resin. This data was generated under stepped flowback
conditions up
to failure. As may be seen the combination of agglomerate beads and Ottawa
sand generated
even more resistance to proppant flowback than the Ottawa sand/polystyrene
divinyl benzene
mixture of FIG. 23. In other embodiments the phenolic resin may include a
plasticizer to make
the deformable layer more elastic.
Examvle 9- Cyclic Stress Tests
Conductivity measurements were made under conditions of cyclic stress on 20/40
mesh
Ottawa sand and a mixture containing 20/40 mesh Ottawa sand and 15%
polystyrene divinyl
benzene beads by weight of total proppant mixture. The polystyrene divinyl
benzene beads
employed in the mixture contained about 0.5% divinyl benzene crosslinker by
weight and had a
size of about 20 mesh.
The tests of this example were performed at a temperature of 150°F
using the procedure
of Example 4, with the exception that measurements were made under conditions
of cyclic
rather than static stress. Stress was increased from 2000 psi to 4000 psi and
held at 4000 psi
for one hour. The stress was then decreased to 2000 psi and held for one hour
before repeating
the cycle several times.
As can be seen in FIG. 26, at a closure stress of about 2000 psi, conductivity
of the
20/40 mesh Ottawa sand was about 900 millidarcy-feet {"md-ft") compared to a
conductivity of
about 2600 md-ft for the mixture of 20/40 Ottawa sand and polystyrene divinyl
benzene beads.
During closure stress cycling up to 4000 psi, the conductivity of the 20/40
mesh Ottawa sand
dropped from about 900 md-ft to about 750 md-ft. In comparison, the
conductivity of the 20/40
mesh Ottawa sand and polystyrene divinyl benzene bead mixture dropped from
about 2600 md-
ft to about 2200 md-ft. Results of this example indicate that the sand and
polystyrene divinyl
benzene bead mixture retains superior conductivity during and after stress
cycling when
compared to 20/40 mesh Ottawa sand alone.
8U88~1'NTES~T(R~~~
CA 02308372 2000-OS-OS
WO 99!27229 PCTIUS98/10735
42
While the invention may be adaptable to various modifications and alternative
forms,
specific embodiments have been shown by way of example and described herein.
However, it
should be understood that the invention is not intended to be limited to the
particular forms
disclosed. Rather, the invention is to cover all modifications, equivalents,
and alternatives
falling within the spirit and scope of the invention as defined by the
appended claims.
suBS~riu~ sir ~RU~ 2s~
