Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02738978 2012-11-26
1
PREVENTION OF WATER INTRUSION INTO PARTICULATES
BACKGROUND
[0003] The present disclosure relates to treatments and compounds
useful in subterranean formations, and, at least in some embodiments, to
treatments
and compounds wherein particulates may be subject to water intrusion.
[0004] In the production of fluids, such as hydrocarbons or water, from
a subterranean formation, the subterranean formation should be sufficiently
conductive to permit the flow of desirable fluids to a well bore penetrating
the
formation. Among others, hydraulic fracturing may be a useful treatment for
increasing the conductivity of a subterranean formation. Hydraulic fracturing
operations generally may involve pumping a treatment fluid (e.g., a fracturing
fluid or
a "pad fluid") into a well bore that penetrates a subterranean formation at a
sufficient
hydraulic pressure to create or enhance one or more pathways, or "fractures,"
in the
subterranean formation. Enhancing a fracture generally involves extending or
enlarging a natural or pre-existing fracture in the formation. These fractures
generally
increase the permeability of that portion of the formation. The treatment
fluid may
comprise particulates, including proppant particulates that are deposited in
the
resultant fractures. The particulates are thought to help prevent the
fractures from
fully closing upon release of the hydraulic pressure, forming conductive
channels
through which fluid may flow between the formation and the well bore.
[0005] It is generally believed that the surfaces of particulates
generally comprise minerals, which may react with other substances (e.g.,
water,
minerals, treatment
CA 02738978 2011-03-25
WO 2010/041031 PCT/GB2009/002422
2
fluids, and the like) that reside in the subterranean formation in chemical
reactions caused, at
least in part, by conditions created by mechanical stresses on those minerals
(e.g., fracturing
of the mineral surfaces or the compaction of particulates). These reactions
are herein referred
to as "stress-activated reactions" or "stress-activated reactivity." One type
of these stress-
activated reactions may be diageneous reactions. As used herein, the terms
"diageneous
reactions," "diageneous reactivity," and "diagenesis" include chemical and/or
physical
processes that, in the presence of water, move a portion of the mineral in a
particulate and/or
convert a portion of the mineral in a particulate into some other form. A
mineral that has
been so moved or converted is herein referred to as a "diageneous product" or
"diagenic
product." Any particulate comprising a mineral may be susceptible to these
diageneous
reactions, including natural silicate minerals (e.g., quartz), man-made
silicates and glass
materials, metal oxide minerals (both natural and man-made), and the like.
[0006] Two of the principal mechanisms that diagenesis reactions are thought
to involve are "pressure dissolution" and "precipitation processes." Where two
water-wetted
mineral surfaces are in contact with each other at a point under strain, the
localized mineral
solubility near that point may increase, causing the minerals to dissolve.
Minerals in solution
may diffuse through the water film outside of the region where the mineral
surfaces are in
contact (e.g., the pore spaces of a particulate pack), where they may
precipitate out of
solution. The dissolution and precipitation of minerals in the course of these
reactions may
reduce the conductivity of a particulate pack, inter alia, by clogging the
pore spaces in the
particulate pack with mineral precipitate and/or collapsing the pore spaces by
dissolving solid
mineral in the "walls" of those pore spaces. In other instances, minerals on
the surface of a
particulate may exhibit a tendency to react with substances in the reservoir,
formation, and/or
treatment fluids that are in contact with the particulates, such as water,
gelling agents (e.g.,
polysaccharides, biopolymers, etc.), and other substances commonly found in
these fluids.
Molecules from such substances may become anchored to the mineral surface of
the
particulate. These types of reactivity may further decrease the conductivity
of a subterranean
formation, inter alia, through the obstruction of conductive fractures in the
formation by any
molecules that have become anchored to the particulates resident within those
fractures. Both
types of reactions may generally require the presence of a fluid, such as
water, to occur to any
significant extent.
CA 02738978 2012-11-26
3
SUMMARY
[0007] The present disclosure relates to treatments and compounds
useful in subterranean formations, and, at least in some embodiments, to
treatments
and compounds wherein particulates may be subject to water intrusion.
[0008] One embodiment of the present invention provides a method.
The method comprises providing a plurality of particulates, wherein at least a
first
portion of the particulates comprise a diffusion barrier. The method further
comprises
introducing the plurality of particulates into a subterranean formation. The
method
further comprises allowing an aqueous fluid to flow through the plurality of
particulates. The method further comprises allowing the diffusion barrier to
impede
aqueous fluid interactions between the aqueous fluid and the plurality of
particulates.
[0009] Another embodiment of the invention provides another method.
The method comprises providing a plurality of particulates. The method further
comprises providing a diffusion barrier initiator. The method further
comprises
introducing the plurality of particulates into a subterranean formation. The
method
further comprises introducing the diffusion barrier initiator into the
subterranean
formation. The method further comprises allowing an aqueous fluid to flow
through
the plurality of particulates. The method further comprises allowing the
diffusion
barrier initiator to form a diffusion barrier for at least a portion of the
plurality of
particulates. The method further comprises allowing the diffusion barrier to
impede
aqueous fluid interactions between the aqueous fluid and the plurality of
particulates.
[0010] Yet another embodiment of the invention provides yet another
method. The method comprises providing a plurality of particulates. The method
further comprises providing a coating material. The method further comprises
allowing the coating material to form a diffusion barrier for at least a first
portion of
the plurality of particulates.
[0011] The features and advantages of the present invention will be
apparent to those skilled in the art.
CA 02738978 2011-03-25
WO 2010/041031 PCT/GB2009/002422
4
DESCRIPTION OF PREFERRED EMBODIMENTS
[0012] The present disclosure relates to treatments and compounds useful in
subterranean formations, and, at least in some embodiments, to treatments and
compounds
wherein particulates may be subject to water intrusion.
[0013] The term "coating" as used herein refers to at least a partial coating
of
some or all of the particulates. Neither complete nor substantial coverage of
the particulates
or mix of particulates is implied by the term "coating." Rather, a particulate
may be coated if
it has, for example, at least a partial coating.
[0014] The term "derivative" is defined herein to include any compound that
is made from one of the listed compounds, for example, by replacing one atom
in the listed
compound with another atom or group of atoms, rearranging two or more atoms in
the listed
compound, ionizing one of the listed compounds, or creating a salt of one of
the listed
compounds. A derivative of a material may include, but is not limited to, a
compound
composition based on a plurality of base materials, a composite material, or
an aggregated
material of various compositions.
[0015] As used herein, the terms "diageneous reactions," "diageneous
reactivity," and "diagenesis" include chemical and physical processes that, in
the presence of
water, move a mineral and/or convert a mineral into some other form. Examples
of such
minerals include, but are not limited to, oxides or hydroxides of zirconium,
magnesium,
aluminum, titanium, calcium, strontium, barium, radium, zinc, cadmium, boron,
gallium,
iron, or any other element suitable for forming a diagenic product. Such
minerals may be
found in a particulate, in a formation, and/or introduced into a formation as
"diagenesis
source material." A mineral that has been so moved or converted is herein
referred to as a
"diageneous product" or "diagenic product."
[0016] As used herein, the term "aqueous fluid interaction" includes a variety
of possible interactions between an aqueous fluid and a particulate. Such
interactions may
include infiltration of the aqueous fluid into the particulate, for example,
by infiltrating pores,
voids, crevices, cracks, and/or channels at or near the surface of the
particulate. Such
interactions may also include diagenesis.
[0017] As used herein, the term "diffusion barrier" includes any sort of
material, including a coating, on or proximate to a particle that impedes
and/or prevents
aqueous fluid interaction with the particle. For example, some diffusion
barriers fill or coat
CA 02738978 2011-03-25
WO 2010/041031 PCT/GB2009/002422
pores, voids, crevices, cracks, or channels at or near the particle's surface
to impede and/or
prevent infiltration by the aqueous fluid. As another example, some diffusion
barriers
impede and/or prevent diagensis.
[0018] As used herein, the term "diagenic protective materials" refers to one
or more diagenic products that may be selectively promoted in order to form a
diffusion
barrier.
[0019] As used herein, the term "filler" or "filler material" means a
particulate
material that is capable of fitting within a pore, void, crevice, crack, or
channel at or near the
surface of a particulate or on surfaces within the porous matrix of the
individual particulates.
[0020] As used herein, the term "relatively low molecular weight" refers to a
molecular weight that would encompass monomers and short-chain polymers having
physical
dimensions from a few angstroms to several hundred nanometers.
[0021] As used herein, a "monolayer" refers to a coating of a material
approximately one unit thick. For chemicals, this may mean a coating as thin
as one
molecule, and for particulate compositions, it may mean a coating one
particulate grain deep.
[0022] As used herein, the terms "pores," "voids," "crevices," "cracks," and
"channels" refer to features at or near the surface of a particulate. Any
given particulate may
have one or more pores, voids, crevices, cracks, or channels, or may be free
of such features.
One or more such features may be generally referred to as "surface features."
The use of the
terms in conjunction is in no way intended to indicate that all three must be
present
simultaneously, or at all, in order for the teachings of the present
disclosure to apply.
[0023] As used herein, the terms "particle," "particulate," "proppant
particulate," and "gravel" are all used to refer to either a single particle
or a plurality of
particles which may be used for supporting a fracture in an underground
formation, for
forming a proppant pack, or for use in forming a gravel pack. Such particles
may be disposed
in a subterranean formation, including in spaces in the rock itself, fractures
within the rock,
and/or a well bore penetrating the subterranean formation.
[0024] As used herein, the term "pack" or "particulate pack" refers to a
collection of particulates within an enclosed volume, wherein the particulates
may be
juxtaposed and/or in contact with one another, and wherein pore spaces may be
disposed
between the particulates. Examples of "packs" may include "proppant packs,"
which may
refer to a collection of proppant particulates within a fracture, and/or
"gravel packs," which
CA 02738978 2012-11-26
6
may refer to a grouping of particulates that are packed sufficiently close
together so as to
prevent the passage of certain materials through the pack.
[0025] The term "on-the-fly" is used herein to indicate that one flowing
stream comprising particulates is introduced into another flowing stream
comprising a
hydrophobic coating agent so that the streams are combined and mixed to flow
as a single
stream. In some instances, the streams may be combined to flow as a single
stream as part
of an on-going treatment at the job site. Such mixing can also be described as
"real-time"
mixing.
[0026] If there is any conflict in the usages of a word or term in this
specification and one or more patent or other documents, the definitions that
are consistent
with this specification should be adopted for the purposes of understanding
this invention.
[0027] There are many advantages of the present invention, only some of
which are mentioned here. One advantage of the present invention may be the
reduction
or prevention of mechanical strength degradation of particulates due to
aqueous fluid
interaction with a particulate, e.g. through infiltration of aqueous fluid
into the particulate
and/or diagenesis. In some embodiments, the methods disclosed herein pertain
to
providing a diffusion barrier on a particulate such that the surface features
(i.e., pores,
voids, crevices, cracks, or channels at or near the particulate's surface) may
be filled or
coated with a material that impedes and/or prevents aqueous fluid interaction
with the
particulate. By avoiding the aqueous fluid interaction, the mechanical
strength
degredation of the particulates may be reduced or prevented. Each particulate
may contain
a number of such surface features that may act as conduits for aqueous fluid
intrusion into
the particle itself. Such surface features may contribute to diagenesis
reactions by
providing a route for aqueous fluid intrusion into the interior of the
particle resulting in
particulate degradation. By limiting the particulate interactions with an
aqueous fluid, the
particulates may retain a greater percentage of strength relative to initial
placement
downhole. Treatments of subterranean formations, including of the rock itself,
fractures
within the rock, and/or a well bore penetrating the subterranean formation,
with such
particulates then may result in greater particulate pack permeability over
time than with
untreated particulate.
[0028] Another advantage of the present invention may be the ability to
quickly and easily coat particulates using a pre-treated filler material that
acts as a carrier
for ____________________________________________________________________
CA 02738978 2011-03-25
WO 2010/041031 PCT/GB2009/002422
7
or initiates a diffusion barrier. Such filler material may be pre-coated with
a material such as
a hydrophobic coating or a reactant that may allow a diffusion barrier to grow
on the
particulate once the particulates are placed downhole. Alternatively, the
filler material may
include a coating material which is encased in a dissolvable or degradable
outer shell. Once
placed downhole, the outer shell may dissolve or degrade, allowing a diffusion
barrier to
grow on the particulate. These methods may prevent aqueous fluid infiltration
and/or
diagenesis of the particulate. These methods may also allow the particulates
to be easily
coated with a pretreated filler material at or near the point of placement in
the formation.
[0029] A further advantage of the present invention may be the ability to at
least partially coat the particulate with a very thin diffusion barrier that
may impede aqueous
fluid interactions. For example, in an embodiment in which a diffusion barrier
is pre-coated
onto a filler material, a monolayer of the filler material may be created when
the particulate is
exposed to the filler material. In another embodiment, a very thin layer of
the filler material
may be coated on the particulate through the use of relatively low molecular
weight materials
with one or more of the coating techniques disclosed herein.
[0030] Protecting particulates from damaging interactions with aqueous fluids
may be achieved in several ways. In accordance with embodiments of the present
invention,
these generally may include treating a particulate with a diffusion barrier
which acts to
impede the particulate interaction with aqueous fluids during and/or after
placement in the
formation. The diffusion barrier may comprise one of several types of
materials, including
hydrophobic materials, diagenic protective materials, and various polymeric
compositions.
Some embodiments of the present invention may utilize filler material to fill
the pores, voids,
crevices, cracks, or channels that may be present in a particulate surface.
Alternatively, a
filler material may be used to generate and/or place the diffusion barrier.
For example, a
hydrophobic material may be used to coat a filler material, and the filler
material may then
generate a diffusion barrier (e.g., comprising a diageneous product) on the
particulates. The
filler material may fill the pores, voids, crevices, cracks, or channels on
the particulate
surface, resulting in a surface that may be more hydrophobic than the original
particulate
surface. Each of these materials and methods will be described in more detail
below.
[0031] The particulates that may be used in embodiments of the present
invention include any proppant or gravel particulates that may be used in a
subterranean
application. Suitable particulates may include sand, sintered bauxite, silica
alumina, glass
=
CA 02738978 2011-03-25
WO 2010/041031 PCT/GB2009/002422
8
beads, etc. Other suitable particulates include, but are not limited to, sand,
bauxite, garnets,
fumed silica, ceramic materials, glass materials, polymer materials,
polytetrafluoroethylene
materials, nut shell pieces, seed shell pieces, fruit pit pieces, wood,
composite particulates,
proppant particulates, degradable particulates, coated particulates, gavel,
and combinations
thereof. Suitable composite materials may comprise a binder and a particulate
material
wherein suitable particulate materials may include silica, alumina, garnets,
fumed carbon,
carbon black, graphite, mica, titanium dioxide, meta-silicate, calcium
silicate, kaolin, talc,
zirconia, boron, fly ash, hollow glass microspheres, solid glass, and
combinations thereof In
certain embodiments, the particles may comprise common sand. In some
embodiments, a
derivative of one or more of the particulate materials may also be used.
Derivatives may
include materials such as compounds, composite materials, and aggregated
materials of
various compositions. In some embodiments of the present invention, some or
all of the
particulates may be comprised of a diagenesis source material. In this
embodiment, the
particulates may comprise oxides or hydroxides of zirconium, magnesium,
aluminum,
titanium, calcium, strontium, barium, radium, zinc, cadmium, boron, gallium,
iron, or any
other element suitable for forming a diagenic product. Suitable particulates
may take any
shape including, but not limited to, the physical shape of platelets,
shavings, flakes, ribbons,
rods, strips, spheres, spheroids, ellipsoids, toroids, pellets, or tablets.
Although a variety of
particulate sizes may be useful in the present invention, in certain
embodiments, particulate
sizes may range from about 200 mesh to about 8 mesh.
[0032] Embodiments of particulates of the present invention may contain
pores, voids, crevices, cracks, or channels at or near the surface. For
example, SEM
micrographs at high magnification may show that the surfaces of particles,
such as
particulates made from bauxite, may be laden with pores, voids, crevices,
cracks, and
channels. Without being limited by theory, it is believed that these pores,
voids, crevices,
cracks, or channels at or near the particulate surface may provide a direct
path to allow a
detrimental interaction between aqueous fluids and the particles that may lead
to degradation
of the particles under formation pressure and temperature.
[0033] In some embodiments, the particulates may be treated or coated with
one or more suitable substances. Generally, the particulates may be treated or
coated with
any substance which is suitable for traditional particulate treatments. In
certain
embodiments, the particulates may be coated so as to impede the intrusion of
water into the
CA 02738978 2012-11-26
9
particulates. For example, the particulates may be coated and/or used as
discussed in
"Geochemical Control of Fracturing Fluids" by Reyes et al., U.S. Patent Serial
Number
8,307,897, "Additives to Suppress Silica Scale Build-up" by Reyes et al., U.S.
Patent
Publication No. 2012/0172263, and/or "Ceramic Coated Particulates" by Reyes
etal., U.S.
Patent No. 8,119,576, each filed on the same day herewith. In an embodiment, a
portion
of the particulates may be coated so as to limit their diagenic reactivity
while others may
remain uncoated so as to provide a reaction site for the diagenesis source
material.
[0034] The particle compositions used in some of the embodiments of the
present invention may comprise at least one particulate and a diffusion
barrier, which may
comprise a hydrophobic, or water repellant, material. Diffusion barriers may
be initiated
by and/or formed from a variety of materials. For example, certain materials
may initiate
diffusion barriers in some embodiments of the present invention. Suitable
materials may
be any chemical agent capable of forming a hydrophobic coating on the surface
of
particulates. In certain embodiments, particles comprising a diffusion barrier
may have a
retained strength greater than or equal to about 30%, as discussed in more
detail below. In
some embodiments, such diffusion barriers may enhance the recovery of a
reservoir,
formation, and/or treatment fluid. In certain embodiments, a surfactant may be
included in
the coating material so as to improve the coating process. Suitable coating
materials may
include oligomeric materials, monomeric materials, oil-wetting compounds, and
combinations thereof to provide at least a monomolecular film, which may make
the
mineral surfaces water-repellent or hydrophobic.
[0035] In one embodiment, a diffusion barrier may comprise the reaction
products of a compound having a reactive silyl group. The diffusion barrier
may be
formed by forming a silicon oxide layer or hybrid organo-silicon oxide anchor
layer from
a humidified reaction product of silicon tetrachloride or
trichloromethysilane, followed by
the vapor-deposition of a chloroalkylsilane. In another embodiment, the
diffusion barrier
may comprise a trimethylsilyl functional group. For example, if a fumed silica
filler
particle is used, the surface hydroxyl groups may be replaced with
trimethylsilyl
functional groups to form a hydrophobic filler particle. The diffusion barrier
may also
comprise silicones or siloxanes. In an embodiment, the diffusion barrier may
comprise an
organosilicon compound, which may include, for example, an organosiloxane, an
organosilane, a fluoro-
CA 02738978 2011-03-25
WO 2010/041031 PCT/GB2009/002422
organosiloxane, and a fluoro-organosilane. The diffusion barrier may also
comprise a
polysiloxane or an organo-modified polysiloxane, which may include a di-
betaine
polysiloxane or a di-quaternary polysiloxane.
[0036] In another embodiment, a diffusion barrier may comprise polymers of
a fluoroalkyl-group containing silane compound, and the polymers may include
at least
dimers and trimers of the silane compound. This diffusion barrier may be made
by preparing
a solution, the solution being produced by subjecting a fluoroalkyl-group
contained silane
compound to a hydrolysis and a condensation polymerization to produce at least
dimers and
trimers of the silane compound, coating the solution onto the surface of the
particulate or
filler material, and heating the material to cause the fluoroalkyl group in
the solution to be
bonded to the surface of the particulate solids so as to form a hydrophobic
film on the
material. In another embodiment, the diffusion barrier may comprise a fluoro-
organosiloxane
or a fluoro-organosilane compound, which may include, for example, 2-(n-
perfluoro-octy1)-
ethyltriethoxysilane and perfluoro-octyldimethyl chlorosilane.
[0037] In yet another embodiment, a diffusion barrier may comprise a
polyamide. In still another embodiment, the diffusion barrier may comprise a
silyl-modified
polyamide.
[0038] In an embodiment, a diffusion barrier may comprise
polytetrafluoroethylene, plant oils, hydrocarbons, copolymerized
polyvinylidene chloride, or
any other substance capable of hindering or preventing aqueous fluid
penetration,
permeation, or wetting of a particulate.
[0039] The filler material may comprise materials with particles of
micrometer-size, sub-micrometer-size, nano-size, or a combination thereof The
filler
material may be reinforcing or non-reinforcing. Filler materials may include,
for example,
fumed silica, fused silica, garnet powder, clay, mica, alumina, finely divided
quartz powder,
amorphous silicas, meta-silicates, calcium silicates, calcine, kaoline, talc,
zirconia, fly ash,
boron, carbon black, fumed carbon, graphite, diamond, silicone carbide,
aluminum hydrates,
metal nitrides (such as boron nitride, and aluminum nitrides), metal oxides
(such as
aluminum oxide, zinc oxide, titanium dioxide or iron oxide), and any
combination thereof In
another embodiment, the filler material may comprise metal particles, such as
aluminum,
zirconium, titanium, or derivatives thereof In one embodiment, the average
diameter of the
filler material particles may be less than about 20 micrometers. In one
embodiment, the
CA 02738978 2011-03-25
WO 2010/041031 PC T/GB2009/002422
11
average filler material particle diameter may range from about 0.05
micrometers to about 10
micrometers, or from about 0.1 micrometers to about 10 micrometers. In another
embodiment, the particles of filler material may have a size range of from
about 0.1
micrometer to about 0.5 micrometers, or from about 0.2 micrometers to about
0.5
micrometers.
[0040] In accordance with embodiments of the present invention, the filler
material particle size may be chosen, among other purposes, to achieve a
coating of a
particulate including the pore spaces on the particulate surface. The choice
of a filler material
particle size may be based upon a consideration of the surface characteristics
of the
particulate, which may be based on the choice of particulate material, crystal
structure, and/or
other characteristics. In an embodiment, the filler material particle size may
be such that the
maximum filler material particle size may be at least equal to, and, in some
embodiments,
less than, the expected diameter of a pore, void, crevice, crack, or channel
at or near the
surface of the particulate. Consideration of any additional coating thickness
that the coating
material may add to the filler material also may be a consideration in
choosing a filler
material having certain particle sizes and shapes.
[0041] In some embodiments of the present invention, some or all of the filler
material may be comprised of a material useful for promoting a diagenesis
reaction, such as a
diagenesis source material. For example, the filler material may comprise
oxides or
hydroxides of zirconium, magnesium, aluminum, titanium, calcium, strontium,
barium,
radium, zinc, cadmium, boron, gallium, iron, or any other element suitable for
forming a
diagenic product.
[0042] In an embodiment, the filler material may comprise certain metallic
compositions that may have the ability to fill the pores, voids, crevices,
cracks, or channels of
the particulates, which, among other things, may limit the interaction between
the particulates
and aqueous fluids. The metallic compositions may have physiochemical
properties that may
render the dissolution in aqueous fluids negligible under certain conditions.
The metallic
compositions may be chemically resistant. For example, certain metallic
compositions may
be capable of forming diagenic protective materials when placed in contact
with reservoir,
formation, and/or treatment fluids downhole. In an embodiment, the metallic
compositions
may include, but are not limited to, metal alkoxides, organometallic compounds
(such as
metal esters) of aluminum, zirconium, titanium, antimony, silicon, tin, boron,
chromium,
CA 02738978 2011-03-25
WO 2010/041031 PCT/GB2009/002422
12
iron, and rare earth element compounds. In another embodiment, the metallic
compounds
may include metal cationic cross linking agents selected from boron (such as
boric acid,
borax, metal borates including tetraborates, tetrafluoroborates, boron ore),
aluminum,
zirconium, titanium, and antimony. In some embodiments of the present
invention, some or
all of the metallic compositions may be comprised of a material useful for
promoting a
diagenesis reaction. In this embodiment, the proppant particulates may
comprise oxides or
hydroxides of zirconium, magnesium, aluminum, titanium, calcium, strontium,
barium,
radium, zinc, cadmium, boron, gallium, iron, or any other element suitable for
forming a
diagenic product.
[0043] In an alternative embodiment, polymeric materials that include the
metallic elements also may be used to coat the particulates. For example,
silicon polymers
(such as polymethylsilsesquioxane, polydimethylsiloxanes, and polysiloxazane)
or any other
metallic polymer capable of being delivered in polymeric form may be used. In
some
embodiments, suitable monomeric compositions may be used to coat the
particulates and then
polymerized using an appropriate activator.
[0044] One of ordinary skill in the art, with the benefit of this disclosure,
will
be able to determine which metallic compound or polymeric composition should
be included
for a particular application based on, for example, formation chemistry,
particulate
composition, and the potential growth of diagenic protective materials.
Without limiting the
invention to a particular theory or mechanism of action, it is currently
believed that the
introduction of the metallic or polymeric compositions may be used to promote
a protective
layer of diagenic product around the particulate once the coated particulate
is placed within
the formation. In an embodiment, the coating may be a diagenesis source
material and may
be used to create a diagenic product in a subterranean formation. For example,
a silicon-
based compound may be used to promote the growth of silicates when placed in
contact with
an aqueous fluid at formation conditions. For a properly placed silicon
compound within the
pores, voids, crevices, cracksor channels of a particulate, the silicate
growth may fill the
pores, voids, crevices, cracks, or channels, thereby limiting the interaction
between the
aqueous fluid and the interior of the particulate. In an embodiment, the
diagenic product may
also grow between individual proppant particulates to act as a binder.
[0045] In an embodiment, the diffusion barrier may be applied to the
particulates using any coating technique known in the art. In an embodiment,
one or more of
CA 02738978 2011-03-25
WO 2010/041031 PCT/GB2009/002422
13
a variety of techniques may be used, including chemically coating the
particulate by means of
spraying, dipping or soaking the particulate in a liquid solution of the
hydrophobic material;
application of a sheet of film such as copolymerized polyvinylidene chloride
to essentially
"shrink-wrap" the particulate and encapsulate it in a chemically desirable
coating; fusing
material to the particulate by placing heated particulates into a fusible
powder, such as a glass
fit or enamel, which may bond to the particulate; electroplating using
electrostatic
techniques known to those of ordinary skill in the art to transfer a diffusion
barrier, including
a less chemically reactive metallic layer, to the particulate; plasma
spraying; sputtering;
fluidizing the particulate in a fluidized bed; and powder coating. The
particulates also may
be coated with a solid coating, such as glass fit, high alumina clays, or
bauxites, metals, or
other hydrophobic powders. Such diffusion barriers could be applied by
spraying, tumbling,
or other means known in the art for applying powder coatings.
[0046] In another embodiment of the present invention, a method of initiating
a fluid barrier may comprise coating a filler particle with a protective
coating, such as a
hydrophobic material, and then mixing the coated filler particle with a
particulate to form a
diffusion barrier. For example, a fumed silica nano-particle may be treated
such that surface
hydroxyl groups are replaced with trimethylsilyl functional groups to form a
protective
coating on the filler material. In this example, the particulates may exhibit
hydrophobic
properties when mixed with the coated filler material. For another example,
the filler
material may be a metallic compound capable of promoting the formation of
diagenic
products when placed in the formation. In this example, the particulates may
be coated with
filler material, and a diffusion barrier may be formed upon placement in the
formation. In an
embodiment, the filler material may be a dry, free-flowing material suitable
for mixing with a
particulate. The treated filler material may be mixed with the particulates in
an amount
sufficient to impart a diffusion barrier to the particulates. This may be an
amount sufficient
to partially coat the particulates but not provide 100% coverage of each
particle. In an
embodiment, the treated filler material may be mixed with the particulates in
an amount
ranging from about 0.025% to 50% by weight of particulates, or from about
0.25% to 50% by
weight of particulates. In an alternative embodiment, the treated filler
material may be mixed
with the particulates in an amount ranging from about 0.25% to 5% by weight of
particulates.
[0047] In an embodiment in which the filler material is first treated with a
protective coating, the treated filler material may be mixed with the
particulates during the
CA 02738978 2011-03-25
WO 2010/041031 PCT/GB2009/002422
14
manufacturing and processing of the particulates, or it may be mixed on-the-
fly at or near the
time of being placed in a formation, as discussed in more detail below. One
skilled in the art,
with the benefit of this disclosure, may be able to determine when the
particulates should be
coated with a treated filler material.
[0048] In some embodiments, a diffusion barrier may also be placed on a
particulate using a solvent to carry coating material into the pores, voids,
crevices, cracks, or
channels of the particles. In such embodiments, an appropriate solvent for a
protective
compound may be utilized to dissolve an amount of the coating material. The
particulates
may then be sprayed, dipped, or soaked in the resulting liquid solution of the
solvent and
coating material. One skilled in the art should be aware of appropriate
solvents and
solubilities of the various coatings materials described herein. A drying step
then may be
utilized to remove the solvent and leave a diffusion barrier behind. Such
drying step may
occur at a pressure sufficient to ensure that the drying temperature is below
the
decomposition temperature of the coating material. In some embodiments, the
drying step
may take place under vacuum pressure.
[0049] In yet another embodiment, a carrier fluid, a solvent, a sol (e.g., a
colloidal suspension of solid particles in a liquid), a gel (e.g., a soft,
resilient, solid or
semisolid material which consists of at least two components, one of which is
a liquid), a
microemulsion, a slurry, or any combination thereof, may be used to deliver a
filler material
and a coating material to the particulates, thereby forming a diffusion
barrier. In such
embodiments, a filler material or a treated filler material may be mixed with
a fluid capable
of supporting the filler material. In such embodiments, the fluid may comprise
a coating
material that coats the particulates and filler material during mixing. The
resulting mixture
then may be mixed with particulates for a sufficient time to allow the filler
materials and/or
treated filler materials to coat the particulates, and/or enter the pores,
voids, crevices, cracks,
or channels of the particulates. The particulates then may be allowed to dry,
undergo a rinse
step to remove the carrier fluid, solvent, sol, gel, microemulsion, and/or
slurry, or be placed
directly into the formation, depending on the application.
[0050] In still other embodiments, any of the above methods may be utilized
to coat a polymeric or monomeric composition on the particulates, either alone
or in
combination with a filler material, thereby forming a diffusion barrier. In
these
embodiments, an activator may be required in order to bond the composition to
the
CA 02738978 2011-03-25
WO 2010/041031 PCT/GB2009/002422
particulate surface, in the pores, voids, crevices, cracks, or channels, or
both. Any method of
initiating polymerization known to one skilled in the art may be used to
perform this function,
and the selection of a suitable method may depend on, among other things, the
type of
polymeric or monomeric composition used. For example, exposure to an
ultraviolet light
source or chemical initiators prior to placement into the formation may be
used to initiate a
polymerization reaction capable of forming polymers within the particulates.
[0051] In practicing certain embodiments of the present invention, the process
of coating the plurality of particulates may be performed at any stage of the
particulate
preparation and/or use. This coating may be accomplished in treatments
performed prior to
transporting the particulates to a job site, or in a treatment performed "on-
the-fly." One such
on-the-fly mixing method may involve continuously conveying the particulates
and the
hydrophobic coating agent (e.g., a treated filler material) to a mixing
vessel, for example,
using a sand screw. Once inside the mixing vessel, the particulates may be
contacted with the
coating material and continuously removed from the mixing vessel. In that
situation, the sand
screw may be used both to aid in mixing the particulates with the hydrophobic
coating agent
and to remove the hydrophobic coating agent from the mixing tank. Batch or
partial batch
mixing may also be used to accomplish such coating at a well site prior to
introducing the
particulates into a subterranean formation, in accordance with embodiments of
the present
invention.
[0052] Certain methods of the present invention may result in a very thin
diffusion barrier, comprising a protective material, a diagenic product, a
treated filler
material, or any combination thereof on a particulate. The use of relatively
low molecular
weight compounds in the coating methods may result in diffusion barriers as
thin as a
monolayer. In another embodiment, filler materials may act to produce a
diffusion barrier on
a particulate less than about 10 micrometers thick. In an alternative
embodiment, the
diffusion barrier may be less than about 1 micrometer thick, or alternatively
less than about
0.5 micrometers thick. Such thin coatings may effectively allow the coating of
the pores,
voids, crevices, cracks, or channels of the particulates. This may help to
limit the particulate
degradation due to interactions with aqueous fluids while preventing any
detrimental
interactions between the particulates due to agglomeration of the particulate
pack.
[0053] One embodiment of the present invention provides a method. The
method comprises providing a plurality of particulates, wherein at least a
first portion of the
CA 02738978 2011-03-25
WO 2010/041031 PCT/GB2009/002422
16
particulates comprise a diffusion barrier. The method further comprises
introducing the
plurality of particulates into a subterranean formation. The method further
comprises
allowing an aqueous fluid to flow through the plurality of particulates. The
method further
comprises allowing the diffusion barrier to impede aqueous fluid interactions
between the
aqueous fluid and the plurality of particulates. In some embodiments, this
method may be
useful in the recovery of fluids from the subterranean formation. The fluids
being recovered
may be a fluid previously introduced into the subterranean formation, an
aqueous reservoir
and/or formation fluid, a hydrocarbon fluid, or a combination thereof
[0054] Another embodiment of the invention provides another method. The
method comprises providing a plurality of particulates. The method further
comprises
providing a diffusion barrier initiator. The method further comprises
introducing the plurality
of particulates into a subterranean formation. The method further comprises
introducing the
diffusion barrier initiator into the subterranean formation. The method
further comprises
allowing an aqueous fluid to flow through the plurality of particulates. The
method further
comprises allowing the diffusion barrier initiator to form a diffusion barrier
for at least a
portion of the plurality of particulates. The method further comprises
allowing the diffusion
barrier to impede aqueous fluid interactions between the aqueous fluid and the
plurality of
particulates. In some embodiments, this method may be useful in the recovery
of fluids from
the subterranean formation. The fluids being recovered may be a fluid
previously introduced
into the subterranean formation, an aqueous reservoir and/or formation fluid,
a hydrocarbon
fluid, or a combination thereof
[0055] Yet another embodiment of the invention provides yet another method.
The method comprises providing a plurality of particulates. The method further
comprises
providing a coating material. The method further comprises allowing the
coating material to
form a diffusion barrier for at least a first portion of the plurality of
particulates. In some
embodiments, this method may be useful in preparation of particulates for
subterranean
treatments and/or usage of particulates in subterranean treatments.
[0056] In order to quantify the mechanical strength of the particulates and
permeability of the particulate pack, both before and after exposure to
formation conditions
and fluids, several test procedures may be utilized to determine various
particulate properties.
The first test method studies temperature-promoted diagenesis of a particulate
pack by
exposing a particulate pack to a flowing solution of simulated formation fluid
at an
CA 02738978 2011-03-25
WO 2010/041031 PCT/GB2009/002422
17
approximate formation temperature. The second procedure studies
stress/temperature-
promoted diagenic growth through exposure of a particulate pack to a static
flow
environment under simulated formation pressures and temperatures. The
mechanical strength
of individual particulates may be measured before and after the test
procedures to determine
the percentage of particulate strength lost due to exposure to formation
temperature or
pressure. Alternatively, the permeability of the particulate pack may be
measured before and
after the temperature-promoted diagenesis test in order to determine a
retained permeability
value for the particulate pack. As would be understood by one of ordinary
skill in the art
with the benefit of this disclosure, expected subterranean formation
conditions (e.g.,
temperature, pressure, formation fluid composition) for a selected
subterranean formation
will determine the appropriate formation conditions for test procedures.
[0057] In the temperature-promoted diagenesis test procedure, deionized
water may first be heated to a test temperature of between about 200 degrees
Fahrenheit ( F)
and about 600 F by passing it through a heat exchanger coil. Simulated
formation fluid may
be formed by passing the deionized water through multiple packs of crushed
formation
material arranged in series. The number of formation packs required for the
test may vary
such that the simulated formation fluid leaving the last pack may be in
equilibrium with the
crushed formation material. Through experimentation, the typical number of
formation packs
may generally be between about 1 and about 10. Crushed formation material may
be
screened to remove fines and an approximately 8/35 mesh fraction may be used
in the
formation packs.
[0058] In an embodiment, once a simulated formation fluid in equilibrium
with the crushed formation material is obtained, the simulated formation fluid
may be
directed to a column containing a particulate pack. The temperature in the
particulate pack
may be maintained at an approximate formation temperature between about 200 F
and about
600 F, which approximately corresponds to the temperature of the deionized
water first
entering the system. A flow rate of simulated formation fluid may be
maintained at
approximately 1 milliliter per minute during the test.
[0059] The flow test may be maintained for between about 10 to about 200
days, and in an embodiment, for at least about 20 days. After this time, the
particulate pack
may be disassembled in order to test the mechanical properties of individual
particles, as
discussed in more detail below. For example, surface and compositional
analysis may be
CA 02738978 2011-03-25
WO 2010/041031 PCT/GB2009/002422
18
made after disassembly to determine what types of materials are being formed
under the
simulated formation conditions. A permeability test may also be performed at
this time. In
this test, the permeability of the particulate packs may be measured at room
temperature prior
disassembly of the particulate pack. The measured permeability of the pack may
then be
compared with an initial permeability measurement made of the pack at room
temperature
before the pack is placed in the testing apparatus. Comparing the initial
permeability
measurement with the permeability measurement obtained after the pack is
subjected to the
test conditions may allow for a retained permeability to be calculated.
[0060] The stress/temperature-promoted diagenesis test method may involve
the testing of the particulate pack under static flow conditions at
approximate formation
pressures and temperatures. In this method, a pack of particulates may be
loaded in a test cell
and filled with a salt solution. The test cell may be loaded from between
about 0.5 pounds
per square foot (1b/ft2) of particulates to about 3.0 lb/ft2 of particluates.
In an embodiment, an
approximately 2% KC1 solution may be used as the fluid medium. Formation
wafers, either
manufactured from formation core material or from rock outcrop material, may
be placed
above and below the particulate pack in the test column. The system may then
be shut in and
placed under simulated formation pressure and heated to approximate formation
temperatures. In an embodiment of this method, the temperature may be
maintained at
between about 100 F and about 550 F. In another embodiment, the temperature
may be
maintained at between about 100 F and about 350 F. The pressure may be
maintained at
between about 2,000 psi and about 10,000 psi. In another embodiment, the
pressure may be
maintained at between about 5,000 psi and about 8,000 psi. In an embodiment,
the test may
be conducted for between about 1 to about 50 weeks, and in another embodiment,
the test
may be conducted for at least about 4 weeks (about 28 days).
[0061] Upon completion of the stress/temperature-promoted diagenesis test,
the test cell may be disassembled and the particulate pack removed for
testing. As with the
flow test method, additional tests may also be performed at this time. For
example, surface
and compositional analysis may be made after disassembly to determine what
types of
materials are being formed under the simulated formation conditions.
Alternatively, the
resulting interstitial fluid may be analyzed to determine the relative
solubility of the
particulates under formation conditions.
CA 02738978 2011-03-25
WO 2010/041031 PCT/GB2009/002422
19
[0062] Changes in the mechanical properties of the particulates obtained from
either the stress/temperature-promoted diagenesis test or the temperature-
promoted
diagenesis test may be determined using a single-gain crush-strength analysis.
The analysis
may utilize a Weibull statistical analysis procedure based on a plurality of
particulate crush
samples. The crush test may be based on a uni-axial compressive point loading
of a particle.
Under a compressive loading in the uni-axial direction, a spherical particle
may be under
tension in directions perpendicular to the loading with a tensile stress, a,
calculated by
o- = 2.8F
71" d 2
where d is the diameter of each particle and F is the load at failure.
[0063] A Weibull analysis may include a statistically significant number of
crush samples, which may range from about 10 to about 50 individual crush
samples, or from
about 20 to about 40 individual crush samples. In an embodiment, a sample size
of between
about 25 and about 30 individual crush samples of particulates may be used in
the analysis.
All of the strength data points may then be sorted from low to high as o-i<o-
2<(73< = = = < crAh
where N represents the total number of samples. A probability of failure may
be calculated
from the equation:
p _______________________________________
N )
where, as before, Nis the total number of samples, for example about 30
samples, and # is the
index number for the sorted strength values (e.g., 1 through N). A linear plot
may be
obtained by plotting
1
ln ln vs ln(o-)
1¨ P
f 1)
A Weibull distribution may be found by linear fitting and generating an
equation:
(
1
n ____ = m ln(¨a
l
Pf j
where m is the Weibull modulus and co is the characteristic strength. The
strength will tend
to increase along with the reliability of the strength calculation when the ao
and m values
increase. The characteristic strength changes in the particulates may then be
determined. By
CA 02738978 2011-03-25
WO 2010/041031 PCT/GB2009/002422
comparing the characteristic strength of the particulates prior to exposure to
the simulated
formation fluid with the characteristic strength of the particulates after
exposure to the
simulated formation fluid, a retained strength value may be calculated from
the equation:
(
CFO exp osed
a 0 retained
\..0 unexposed
where, ci-0 exposed is the characteristic strength of the particles after
exposure to the simulated
formation fluid, and a-0 unexposed is the characteristic strength of the
particles prior to exposure.
Similarly, a retained permeability may be calculated by dividing the
permeability measured at
the end of the temperature-promoted diagenesis test with the permeability
measured at the
beginning.
[0064] In an embodiment, a single set of test conditions may be utilized for
comparison of different sets of particles comprising diffusion barriers and/or
filler materials.
The retained strength value is defined to be measured by the
stress/temperature-promoted
diagenesis test. In this method, a pack of particulates is loaded in a test
column and filled
with a salt solution comprising an approximately 2% KC1 solution. The test
cell is loaded
with about 2 lb/ft2 of particulates. Formation wafers are placed above and
below the
particulates in the test cell. The system is then shut in and placed under a
pressure that is
approximately equal to the pressure expected in the formation in which the
particulates are
expected to be placed. The temperature may be maintained at a temperature that
is
approximately equal to the formation temperature where the particulates are
expected to be
placed. For example, the system may be placed under simulated formation
pressure of about
9000 psi and temperature of about 250 F. These conditions are then maintained
for about 28
days.
[0065] Upon completion of the stress/temperature-promoted diagenesis test,
the test cell is disassembled and the particulate matrix removed for testing.
Changes in the
mechanical properties of the particulates are obtained using particulates
tested using the
stress/temperature-promoted diagenesis test. The analysis utilizes a Weibull
statistical
analysis procedure based on a plurality of particulate crush samples, as
discussed above. A
single analysis includes a statistically significant number of samples, which
may be between
about 20 and about 40 samples, e.g., approximately 30 crushed samples of
individual
particles. However, in some instances, the sample size may vary such that the
actual number
CA 02738978 2011-03-25
WO 2010/041031 PCT/GB2009/002422
21
of samples is smaller or larger in order to obtain a statistically significant
number of samples.
The characteristic strength changes in the particulates may then be
determined. By
comparing the characteristic strength of the particulates prior to exposure to
the simulated
formation fluid with the characteristic strength of the particulates after
exposure to the
simulated formation fluid, a retained strength value is calculated from the
equation:
(
cr exposed
o-0 retained =
unexposed j
where, GO exposed is the characteristic strength of the particles after
exposure to the simulated
formation fluid, and cro unexposed is the characteristic strength of the
particles prior to exposure.
[0066] Similarly, the retained permeability value of the particulate pack is
defined to be measured by the temperature-promoted diagenesis test. In the
temperature-
promoted diagenesis test procedure, an initial permeability measurement is
made of a
particulate pack while the particulate pack is at room temperature. Deionized
water is then
heated to a test temperature of approximately 500 F by passing it through a
heat exchanger
coil. Lower test temperatures may also be used depending on the specific
particulate material
and coating used. For example, one of ordinary skill in the art may determine
that a lower
test temperature is required in order to avoid thermal decomposition of the
particulates, the
diffusion barrier, or the filler material. Simulated formation fluid is formed
by passing the
deionized water through multiple packs of crushed formation material arranged
in series. The
number of formation packs required for the test may vary such that the
simulated formation
fluid leaving the last pack is in equilibrium with the crushed formation
material at the flow
rate used during the test of approximately 1 milliliter per minute. The
typical number of
formation packs is generally between about 2 and about 5. Crushed formation
material is
screened and an approximately 8/35 mesh fraction is used in the formation
packs. The
formation material is obtained by crushing a core withdrawn from a specific
well during
drilling or from dill cuttings obtained while a well is being drilled through
a zone of interest.
[0067] The simulated formation fluid is then directed to a column containing a
particulate pack. The temperature in the particulate pack is maintained at a
temperature of
about 500 F. A lower test temperature may be used depending on the specific
particulate
material and coating material used. For example, one of ordinary skill in the
art may
determine that a lower test temperature is required in order to avoid thermal
decomposition of
CA 02738978 2012-11-26
22
the particulates, the diffusion barrier, or the filler. A flow rate of
simulated formation
fluid is maintained at approximately 1 milliliter per minute during the test.
The flow test
is maintained for about 30 days. After this time, permeability of the
particulate pack is
measured prior to disassembly and after the particulate pack has been allowed
to cool to
room temperature, allowing for a retained permeability to be calculated from
the equation:
(
Permeability
"exposed
Permeability
" retained
Permeability
" unexposed )
where, Permeabili
Ayexposed is the permeability of the particles after exposure to the
simulated formation fluid, and Permeability unexposed is the permeability of
the particles
prior to exposure.
[0036] Particulates prepared and tested according to the methods of the
current invention using the characteristic conditions of the embodiment may
exhibit a
retained strength value of greater than about 20%. Alternatively, the
particulates may
exhibit a retained strength value of greater than about 60%. In still another
embodiment,
the particulates may exhibit a retained strength value of greater than about
80%. In yet
another embodiment, the particulates may exhibit a retained strength value of
greater than
about 90%. In an embodiment, the particulates used to form a pack may be
characterized
by a retained permeability value of at least about 40%. In another embodiment,
the
particulates may be characterized by a retained permeability of at least about
60%. In still
another embodiment, the particulates may be characterized by a retained
permeability of at
least about 80%. In some embodiments, the retained permeability may be at
least about
99%.
[0037] Therefore, the present invention is well adapted to attain the ends
and advantages mentioned as well as those that are inherent therein. The
particular
embodiments disclosed above are illustrative only, as the present invention
may be
modified and practiced in different but equivalent manners apparent to those
skilled in the
art having the benefit of the teachings herein. Furthermore, no limitations
are intended to
the details of construction or design herein shown, other than as described in
the claims
below. While compositions and methods are described in terms of "comprising,"
"containing," or "including" various components or steps, the compositions and
methods
can also "consist essentially of' or "consist of" the various components and
steps. All
numbers and ranges disclosed above may vary by some amount. Whenever a
numerical
range with a lower limit and an upper limit is disclosed, any number and any
included
CA 02738978 2012-11-26
23
range falling within the range is specifically disclosed. In particular, every
range of values
(of the form, "from about a to about b," or, equivalently, "from approximately
a to b," or,
equivalently, "from approximately a-b") disclosed herein is to be understood
to set forth
every number and range encompassed within the broader range of values. Also,
the terms
in the claims have their plain, ordinary meaning unless otherwise explicitly
and clearly
defined by the patentee. Moreover, the indefinite articles "a" or "an," as
used in the
claims, are defined herein to mean one or more than one of the element that it
introduces.
