Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ADDITIVES TO SUPPRESS SILICA SCALE BUILD-UP
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 and/or surfaces may be subject to silica scale build-up.
[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
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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.
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[0007] Silica (silicon dioxide) appears naturally in a number of crystalline
and
amorphous forms, all of which are sparingly soluble in water; thus leading to
the formation of
undesirable deposits. Silicates can be salts derived from silica or the
silicic acids, especially
orthosilicates and metasilicates, which may combine to form polysilicates.
Silica solubility
depends on, but not exclusively, a number of factors such as pH, temperature,
and ionic
composition. Most silicates, except the alkali silicates, are sparingly
soluble in water. A
number of different forms of silica and silicate salt deposits are possible,
and formation of
deposits depends, among other factors, on the temperature and pH of the water.
SUMMARY
[0008] The present disclosure relates to treatments and compounds useful in
subterranean formations, and, at least in some embodiments, to treatments and
compounds
wherein particulates and/or surfaces may be subject to silica scale build-up.
[0009] One embodiment of the present invention provides a method. The
method comprises providing a silica scale control additive in a subterranean
formation. The
method further comprises providing a particulate pack in the subterranean
formation. The
method further comprises allowing the silica scale control additive to
suppress silica scale
build-up proximate the particulate pack.
[0010] Another embodiment of the invention provides another method. The
method comprises providing a fluid comprising a carrier fluid, a plurality of
particulates, and
a silica scale control additive. The method further comprises introducing the
fluid into a
subterranean formation. The method further comprises allowing at least some of
the
particulates to form a particulate pack in the subterranean formation. The
method further
comprises allowing the silica scale control additive to suppress silica scale
build-up
proximate the particulate pack.
[0011] Yet another embodiment of the invention provides a composition. The
composition comprises a plurality of particulates a silica scale control
additive, wherein the
silica scale control additive is capable of suppressing silica scale build-up
proximate the
particulate pack.
[0012] The features and advantages of the present invention will be apparent
to those skilled in the art.
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DESCRIPTION OF PREFERRED EMBODIMENTS
[0013] The present disclosure relates to treatments and compounds useful in
subterranean formations, and, at least in some embodiments, to treatments and
compounds
wherein particulates and/or surfaces may be subject to silica scale build-up.
[0014] 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.
[0015] 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.
[0016] 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."
[0017] 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.
[0018] 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
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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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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
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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.
[0026] 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.
[0027] As used herein, the term "silica scale control additive" may be any
product capable of suppressing silica scale build-up by increasing the
solubility of silica in
solution, inhibiting silica polymer chain propagation, and/or decreasing the
size or quantity of
any silica scale created in a solution.
[0028] The term "gel," as used herein and its derivatives refer to a
viscoelastic
or semi-solid, jelly-like state assumed by some colloidal dispersions.
[0029] 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.
[0030] There are many advantages of the present invention, only some of
which are mentioned here. One advantage of the methods disclosed herein may be
the
suppression of silica scale build-up within a particulate pack in a
subterranean formation,
including in the rock itself, fractures within the rock, and/or a well bore
penetrating the
subterranean formation. Without limiting the invention to a particular theory
or mechanism,
it is nonetheless currently believed that, when placed within a formation, a
particulate pack
may experience silica scale build-up due to silicon dissolution from either
the particulates or
the formation. The silicon may dissolve in fluids, such as formation fluids or
treatment
fluids. The dissolved silicon may then precipitate in various forms to create
silica scale
within, upstream, or downstream of the particulate pack. Such silica scale may
have a
tendency to form or collect in the interstitial spaces of the particulate
pack, which may reduce
the permeability of the pack over time. As such, the suppression or inhibition
of silicon
dissolution and silica scale build-up may be able to reduce the permeability
loss in the
particulate pack, thereby increasing the ultimate productivity of the well.
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[0031] Protecting particulates from such damage may be achieved in several
ways. In an embodiment, a silica scale control additive may be utilized to
treat a particulate
pack. The silica scale control additive may suppress silica scale build-up by
increasing the
solubility of silicon within the particulate pack while simultaneously
preventing large build-
ups of silica scale. Various silica scale control additives may be used to
limit the silica scale
formation, as discussed in more detail below.
[0032] 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.
[0033] 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
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, gravel,
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
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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.
[0034] 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.
[0035] 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
particulates. For example, the particulates may be coated and/or used as
discussed in
"Prevention of Water Intrusion Into Particulates" by Nguyen et al., U.S.
Patent Serial Number
8,307,897, "Geochemical Control of Fracturing Fluids" by Reyes et al., U.S.
Patent
Publication No. 2012-0172263, and/or "Ceramic Coated Particulates" by Reyes et
al., US
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.
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[0036] In an embodiment, a silica scale control additive may be used with a
particulate pack (e.g., a proppant or gravel pack) to suppress silica scale
build-up by
mitigating, inhibiting, or suppressing the formation and build-up of silica
(also known as
silica scale). Formation of silica scale may occur on the particulates, on the
formation
fracture face, or in a solution within a particulate pack. Silica scale
control additives may
increase the amount of soluble silica within a solution. Without intending to
be limited by
theory, it is believed that the silica scale control additives inhibit the
polymerization and
build-up of silicic acid and colloidal silica by disrupting chain propagation.
In an
embodiment, a silica scale control additive may be any compound which controls
the
formation of scale to some degree and does not negatively react with the
particulates, the
formation, a treatment fluid, a formation fluid, or any other aspect of the
subterranean
environment. In an embodiment, suitable silica scale control additives may
include
polyaminoamide dendrimers and polyethyleneimine, which may be combined with
carboxymethylinulin and polyacrylates. In an alternative embodiment,
polyallylamines,
copolymers of polyacrylamides, and polyallyldiamethylammonium chloride may
also be used
as silica scale control additives. Examples of suitable silica scale control
additives include
AcumerTM 5000, commercially available from Rohm and Hass of Philadelphia, PA;
and
Cla-Sta XP and Cla-Sta FS available from Halliburton Energy Services, Inc.
of Duncan,
OK.
[0037] In some embodiments, a silica scale control additive may be added to a
treatment fluid (e.g., a fracturing fluid, a carrier fluid, a stimulation
fluid, etc.) in an amount
sufficient to suppress silica scale build-up by inhibiting the formation of
silica scale. The
treatment fluid may be aqueous, non-aqueous, or a combination of fluid types.
Generally, the
treatment fluid may comprise a carrier fluid, particulates, such as proppant,
and one or more
additives, such as silica scale control additives. In some embodiments, the
amount of silica
scale control additive may be any amount necessary to control silica and
silicate deposition in
the system being treated. In an embodiment, the amount may be any amount
sufficient to
obtain a retained permeability in a proppant pack of at least about 40%, the
measurement of
which is described in more detail below. In an embodiment, the amount of
silica scale
control additive may range from about 1 to about 1000 parts per million (ppm)
by weight of
the carrier fluid. In an alternative embodiment, the amount may range from
about 1 to about
100 ppm by weight of the carrier fluid. The pH of the carrier fluid may also
have an impact
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on the effectiveness of the silica scale control additive. In some embodiment,
the pH of the
carrier fluid may be maintained at between about 4.0 and about 8Ø In an
embodiment, the
pH of the carrier fluid may be maintained between about 6.5 and about 7.5.
[0038] Silica scale control additives may be added to a well bore before,
after,
or during the placement of a particulate pack. In an embodiment, the silica
scale control
additive may be added to a fracturing fluid and carried with the fracturing
fluid during
formation of the fractures. In this embodiment, the silica scale control
additive may be in the
fracturing fluid in the formation during the placement and setting of a
particulate pack.
Alternatively, the silica scale control additive may be mixed with a carrier
fluid used to carry
and set the particulate pack in the formation. In still another embodiment, a
silica scale
control additive may be utilized after a particulate pack has been placed in
the well bore. In
such embodiments, a carrier fluid may be used to carry the silica scale
control additive into
the well bore and through the particulate pack. By way of example, a
particulate pack may
be contacted by a silica scale control additive. This technique also may be
used as a
subsequent treatment method to periodically treat the particulate pack over
time, among other
purposes, in order to maintain permeability in the particulate pack.
[0039] One embodiment of the present invention provides a method. The
method comprises providing a silica scale control additive in a subterranean
formation. The
method further comprises providing a particulate pack in the subterranean
formation. The
method further comprises allowing the silica scale control additive to
suppress silica scale
build-up proximate the particulate pack. 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.
[0040] Another embodiment of the invention provides another method. The
method comprises providing a fluid comprising a carrier fluid, a plurality of
particulates, and
a silica scale control additive. The method further comprises introducing the
fluid into a
subterranean formation. The method further comprises allowing at least some of
the
particulates to form a particulate pack in the subterranean formation. The
method further
comprises allowing the silica scale control additive to suppress silica scale
build-up
proximate the particulate pack. In some embodiments, this method may be useful
in the
recovery of fluids from the subterranean formation. The fluids being recovered
may be a
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fluid previously introduced into the subterranean formation, an aqueous
reservoir and/or
formation fluid, a hydrocarbon fluid, or a combination thereof.
[0041] Yet another embodiment of the invention provides a composition. The
composition comprises a plurality of particulates a silica scale control
additive, wherein the
silica scale control additive is capable of suppressing silica scale build-up
proximate the
particulate pack. In some embodiments, this method may be useful in
preparation of
particulates for subterranean treatments and/or usage of particulates in
subterranean
treatments.
[0042] 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
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.
[0043] 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 crashed
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
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screened to remove fines and an approximately 8/35 mesh fraction may be used
in the
formation packs.
[0044] 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.
[0045] 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
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.
[0046] 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
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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).
[0047] 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.
[0048] 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-grain 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
= 2.8F
cr
rc d2
where d is the diameter of each particle and F is the load at failure.
[0049] 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-
1<cr2<cr3< . . <
where N represents the total number of samples. A probability of failure may
be calculated
from the equation:
Pf.
./V
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14
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 IV). A linear
plot may be
obtained by plotting
in ln 1 vs ln(cr)
1¨P
f
A Weibull distribution may be found by linear fitting and generating an
equation:
r
1
ln _______ (
= m ¨
1 ¨P a
f 0
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
cro and m values
increase. 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 may be calculated from
the equation:
6.0 exposed
0-0 retained un exposed
where, co exposed is the characteristic strength of the particles after
exposure to the simulated
formation fluid, and co 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.
[0050] In an embodiment, a single set of test conditions may be utilized for
comparison of different sets of 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
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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.
[0051] 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
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 0 exp osed
CY 0 retained
-0 unexposed
where, (Yo exposed is the characteristic strength of the particles after
exposure to the simulated
formation fluid, and Go unexposed is the characteristic strength of the
particles prior to exposure.
[0052] 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
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16
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.
[0053] 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
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 õõexposed )
where, Permeability, exposed 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.
[0054] 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,
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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%.
[0055] 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 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. If there is any
conflict in the usages of
