U.S. patent application number 11/637496 was filed with the patent office on 2007-05-03 for cement compositions containing degradable materials and methods of cementing in subterranean formations.
Invention is credited to Trinidad JR. Munoz, Philip D. Nguyen, Anthony V. Palmer, B. Raghava Reddy, Frank Zamora.
Application Number | 20070100029 11/637496 |
Document ID | / |
Family ID | 34984957 |
Filed Date | 2007-05-03 |
United States Patent
Application |
20070100029 |
Kind Code |
A1 |
Reddy; B. Raghava ; et
al. |
May 3, 2007 |
Cement compositions containing degradable materials and methods of
cementing in subterranean formations
Abstract
The present invention provides cement compositions that include
degradable materials, and methods of using such compositions in
subterranean cementing operations. An example of a method of the
present invention includes: providing a cement composition that
includes a hydraulic cement, and a degradable material; placing the
cement composition in a subterranean formation; allowing the cement
composition to set therein; and allowing the degradable material to
degrade. Another example of a method of the present invention is a
method of enhancing the mechanical properties of a cement
composition including adding a degradable material to the cement
composition and allowing the degradable material to degrade.
Inventors: |
Reddy; B. Raghava; (Duncan,
OK) ; Zamora; Frank; (Duncan, OK) ; Nguyen;
Philip D.; (Duncan, OK) ; Munoz; Trinidad JR.;
(Duncan, OK) ; Palmer; Anthony V.; (Ardmore,
OK) |
Correspondence
Address: |
CRAIG W. RODDY;HALLIBURTON ENERGY SERVICES
P.O. BOX 1431
DUNCAN
OK
73536-0440
US
|
Family ID: |
34984957 |
Appl. No.: |
11/637496 |
Filed: |
December 12, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10802340 |
Mar 17, 2004 |
7172022 |
|
|
11637496 |
Dec 12, 2006 |
|
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Current U.S.
Class: |
524/5 |
Current CPC
Class: |
C09K 8/473 20130101;
C09K 8/487 20130101; E21B 33/13 20130101; C04B 38/02 20130101; C04B
2103/0067 20130101; C04B 28/02 20130101; C04B 28/02 20130101; C04B
24/06 20130101; C04B 24/24 20130101; C04B 24/26 20130101; C04B
24/2611 20130101; C04B 24/2676 20130101; C04B 38/02 20130101; C04B
38/103 20130101; C04B 28/02 20130101; C04B 24/06 20130101; C04B
24/26 20130101; C04B 24/2652 20130101; C04B 38/02 20130101; C04B
2103/40 20130101; C04B 2103/46 20130101; C04B 2111/503
20130101 |
Class at
Publication: |
524/005 |
International
Class: |
C04B 24/26 20060101
C04B024/26 |
Claims
1. A cement composition comprising a hydraulic cement, water
sufficient to form a pumpable slurry, and a degradable material,
wherein the degradable material is selected from the group
consisting of aliphatic polyesters, poly(lactides),
poly(glycolides), poly(.epsilon.-caprolactones),
poly(hydroxybutyrates), poly(anhydrides), aliphatic polycarbonate,
ortho esters, poly(orthoesters), poly(vinylacetates), polyamides,
proteins, polyaminoacids, nylons, poly(caprolactams), polylactic
acid, cellulose acetate, and combinations thereof.
2. The cement composition of claim 1 wherein the hydraulic cement
is selected from the group consisting of Portland cements,
pozzolanic cements, gypsum cements, high alumina content cements,
phosphate cements, silica cements, and high alkalinity cements.
3. The cement composition of claim 1 wherein the degradable
material comprises a material that degrades at a desired time after
contact with the cement composition.
4. The cement composition of claim 1 wherein the degradable
material comprises a material that prevents fluid loss into the
subterranean formation.
5. The cement composition of claim 1 wherein the degradable
material, upon degradation, forms at least one gas, salt or
combination thereof.
6. The cement composition of claim 1 wherein the cement composition
further comprises an additive selected from the group consisting of
fluid loss control additives, defoamers, dispersing agents, set
accelerators, salts, formation conditioning agents, weighting
agents, set retarders, ceramic beads, glass beads, elastomers, and
combinations thereof.
7. The cement composition of claim 1 wherein the degradable
material comprises particles in the form of a thin film, a flake, a
substantially spherical particle, a bead, a fiber, or a combination
thereof.
8. The cement composition of claim 1 wherein the degradable
material is present in the cement composition in an amount
sufficient to leave voids in the set cement that enhance the
mechanical properties of the set cement.
9. The cement composition of claim 1 wherein the degradable
material is present in the cement composition in an amount in the
range of from about 1% to about 25% by weight of cement.
10. The cement composition of claim 1 wherein the cement
composition further comprises a polymer emulsion, wherein the
polymer emulsion is present in the cement composition in an amount
in the range of from about 5% to about 100% by weight of an amount
of water in the cement composition.
11. The cement composition of claim 10 wherein the polymer emulsion
comprises a polar monomer selected from the group consisting of
vinylamine, vinyl acetate, acrylonitrile, and the acid, ester,
amide, and salt forms of acrylates, and at least one
elasticity-enhancing monomer selected from the group consisting of
ethylene, propylene, butadiene, 1,3-hexadiene, and isoprene.
12. The cement composition of claim 11 wherein the polar monomer is
present in the polymer emulsion in an amount in the range of from
about 1% to about 90% by weight of the polymer emulsion.
13. The cement composition of claim 11 wherein the at least one
elasticity-enhancing monomer is present in the polymer emulsion in
an amount in the range of from about 10% to about 99% by weight of
the polymer emulsion.
14. The cement composition of claim 11 wherein the polymer emulsion
further comprises a stiffness-enhancing monomer.
15. The cement composition of claim 14 wherein the
stiffness-enhancing monomer is selected from the group consisting
of styrene, t-butylstyrene, .alpha.-methylstyrene, and sulfonated
styrene, and is present in the polymer emulsion in an amount in the
range of from about 0.01% to about 70% by weight of the polymer
emulsion.
16. The cement composition of claim 10 wherein the polymer emulsion
is an aqueous styrene butadiene latex.
17. The cement composition of claim 10 wherein the cement
composition further comprises a surfactant, wherein the surfactant
is present in the cement composition in an amount in the range of
from about 10% to about 20% by weight of the polymer emulsion.
18. The cement composition of claim 1 wherein the cement
composition comprises a gas, wherein the gas is present in the
cement composition in an amount sufficient to provide a gas
concentration in the range of from about 0.5% to about 30% by
volume of the cement composition, measured when the cement
composition has been placed in a subterranean formation.
19. The cement composition of claim 1 wherein the cement
composition comprises a gas-generating additive selected from the
group consisting of an aluminum powder and azodicarbonamide,
wherein the gas generating additive is present in the cement
composition in an amount in the range of about 0.1% to about 5% by
weight of the cement.
20. The cement composition of claim 1 wherein the cement is a
Portland cement; wherein the degradable material is polylactic
acid, wherein the polylactic acid is present in the cement
composition in an amount in the range of about 1% to about 25% by
weight of the cement; and wherein the water is present in the
cement composition in an amount in the range of from about 25% to
about 150% by weight of the cement.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of U.S. patent application
Ser. No. 10/802,340, filed Mar. 17, 2004, entitled "Cement
Compositions Containing Degradable Materials And Methods Of
Cementing In Subterranean Formations," by B. Raghava Reddy, et al.,
which is incorporated by reference herein for all purposes, from
which priority is claimed pursuant to 35 U.S.C. .sctn. 120.
BACKGROUND
[0002] The present invention relates to methods and compositions
for use in subterranean cementing operations. More particularly,
the present invention relates to cement compositions comprising
degradable materials, and methods of using such compositions in
subterranean cementing operations.
[0003] Hydraulic cement compositions are commonly utilized in
subterranean operations, particularly subterranean well completion
and remedial operations. For example, hydraulic cement compositions
are used in primary cementing operations whereby pipe strings such
as casings and liners are cemented in well bores. In performing
primary cementing, hydraulic cement compositions are pumped into an
annular space between the walls of a well bore and the exterior
surface of a pipe string disposed therein. To ensure that the
annular space is completely filled, a cement slurry is pumped into
the annular space until the slurry circulates to the surface. The
cement composition is then permitted to set in the annular space,
thereby forming an annular sheath of hardened, substantially
impermeable cement. The hardened cement substantially supports and
positions the pipe string in the well bore and bonds the exterior
surfaces of the pipe string to the walls of the well bore.
Hydraulic cement compositions are also used in remedial cementing
operations, such as plugging highly permeable zones or fractures in
well bores, plugging cracks and holes in pipe strings, and the
like.
[0004] Subterranean formations traversed by well bores naturally
may be weak, extensively fractured, and highly permeable. In some
cases, if the fracture gradient of the formation is exceeded by the
hydrostatic head pressure normally associated with cement pumped
into the well bore, the formation will fracture. This may result in
the loss of cement into the extensive fractures of the formation.
This can be problematic because, inter alia, less cement
composition will remain in the annular space to form the protective
sheath that bonds the pipe string to the walls of the well bore.
Accordingly, loss of circulation of the cement slurry into the
formation is of great concern.
[0005] Conventional attempts to solve the problem of lost
circulation of cement slurries include adding polymeric flakes or
film strips that may bridge the cracks and fractures in the
formation and, thus, prevent the loss of the cement slurry.
Examples of such materials include cellophane flakes, polypropylene
flakes, or mica flakes, among others. However, the use of
polypropylene flakes may be undesirable because the polymer is not
biodegradable. Mineral flakes such as mica often have unsuitable
sizes that preclude their use.
[0006] Conventional attempts to solve the problem of inadvertently
fracturing the subterranean formation during cementing operations
have also involved, inter alia, the use of cementing slurries with
reduced densities. For example, cement slurry densities can be
desirably reduced by incorporating an expanding additive, such as
nitrogen, into the cement composition. Alternatively, lightweight
particulate additives, such as hollow glass or ceramic beads, may
be incorporated into the cement composition at the surface.
However, these methods may be problematic because, inter alia, they
can require elaborate and expensive equipment, which may not be
accessible for use in remote areas.
[0007] Certain conventional cement compositions also may become
brittle and/or inelastic at some point after setting into a cement
sheath. This may be problematic because, inter alia, an excessively
brittle or inelastic cement sheath may become unable to provide
desired zonal isolation, and may require costly remediative
operations. This may be particularly problematic in the case of
multilateral wells. If the cement sheath in the area of the
junction between a principal well bore and a lateral well bore in a
multilateral well is excessively brittle or inelastic, it may be
unable to withstand impacts that may occur, e.g., when tools used
in drilling and completing the well collide with casing in the
junction area as the tools are moved in and out of the well.
[0008] Well bores that comprise an expandable tubular present
another scenario where an excessively brittle or inelastic cement
sheath may be problematic. The expansion of an expandable tubular
inadvertently may crush at least a portion of the cement sheath
behind the tubular, thereby impairing the cement sheath's ability
to provide the desired zonal isolation.
SUMMARY OF THE INVENTION
[0009] The present invention relates to methods and compositions
for use in subterranean cementing operations. More particularly,
the present invention relates to cement compositions comprising
degradable materials, and methods of using such compositions in
subterranean cementing operations.
[0010] An example of a method of the present invention is a method
of cementing in a subterranean formation comprising: providing a
cement composition comprising a hydraulic cement and a degradable
material; placing the cement composition into a subterranean
formation; allowing the cement composition to set therein; and
allowing the degradable material to degrade.
[0011] Another example of a method of the present invention is a
method of enhancing the mechanical properties of a cement
composition comprising adding a degradable material to the cement
composition and allowing the degradable material to degrade.
[0012] An example of a composition of the present invention is a
cement composition comprising a hydraulic cement and a degradable
material.
[0013] Other and further features and advantages of the present
invention will be readily apparent to those skilled in the art upon
a reading of the description of preferred embodiments which
follows.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] The present invention relates to methods and compositions
for use in subterranean cementing operations. More particularly,
the present invention relates to cement compositions comprising
degradable materials, and methods of using such compositions in
subterranean cementing operations. While the compositions and
methods of the present invention are useful in a variety of
subterranean applications, they are particularly useful in well
completion and remedial operations, including primary cementing,
e.g., cementing casings and liners in well bores, including those
in multilateral subterranean wells.
[0015] The improved cement compositions of the present invention
generally comprise: a hydraulic cement; at least one degradable
material; and water sufficient to make the cement composition a
slurry. Other additives suitable for use in conjunction with
subterranean cementing operations also may be added to these
compositions if desired. When the cement compositions of the
present invention set, the resultant cement sheath may have
improved mechanical properties that enhance the cement sheath's
ability to sustain cyclic stresses due to temperature and pressure.
The cement composition also may have improved thixotropic
properties that may enhance its ability to handle loss of
circulation and gas migration during the time in which it sets. In
an exemplary embodiment of the present invention, degradation of
the degradable material may be accompanied by formation of a new
product, e.g., salts or gases, that may act as expanding additives
that will enhance the shrinkage compensation properties and/or
elasticity, of the resultant set cement.
[0016] Any cement may be utilized in the cement compositions of the
present invention, including, but not limited to, hydraulic cements
comprising calcium, aluminum, silicon, oxygen, and/or sulfur, which
set and harden by reaction with water. Examples of suitable
hydraulic cements are Portland cements, pozzolanic cements, gypsum
cements, high alumina content cements, phosphate cements, silica
cements, and high alkalinity cements. In certain exemplary
embodiments of the present invention, API Portland Cement Classes
A, G, and H are used.
[0017] The water used in the present invention may comprise fresh
water, salt water (e.g., water containing one or more salts
dissolved therein), brine (e.g., saturated salt water), or
seawater. Generally, the water can be from any source provided that
it does not contain an excess of compounds that may adversely
affect other components in the cement composition. The water may be
present in an amount sufficient to form a pumpable slurry. In
certain exemplary embodiments, the water may be present in the
cement compositions in an amount in the range of from about 25% to
about 150% by weight of cement ("bwoc"). In certain exemplary
embodiments, the water may be present in the cement compositions in
the range of from about 30% to about 75% bwoc.
[0018] The cement compositions of the present invention comprise a
degradable material. For example, the degradable material may be a
polymeric material capable of degrading into sorbable components
while in contact with the cement compositions of the present
invention. The degradable material may be present in the cement
compositions of the present invention in an amount sufficient to
result, upon partial or complete degradation of the degradable
material, in a resultant set cement having a desired density and
desired mechanical properties (e.g., a desired Young's modulus and
tensile strength). In certain exemplary embodiments of the present
invention, the degradable material degrades after the cement
composition has set in a subterranean formation. In certain other
exemplary embodiments, the degradable material may degrade before
or while the cement composition sets. In certain exemplary
embodiments, the degradable material may be present in the cement
compositions of the present invention in an amount in the range of
from about 1% to about 25% bwoc. In certain exemplary embodiments,
the degradable material may be present in the cement compositions
of the present invention in an amount in the range of from about 5%
to about 15% bwoc. In choosing the appropriate degradable material,
one should consider the degradation products that will result.
These degradation products should not adversely affect other
operations, or properties of the set cement sheath. The choice of
degradable material also can depend, at least in part, on the
conditions of the well, e.g., well bore temperature.
[0019] Nonlimiting examples of degradable materials that may be
used in conjunction with the present invention include, but are not
limited to, degradable polymers. Such degradable polymers may be
capable of undergoing an irreversible degradation downhole. In a
further exemplary embodiment, the products of the degradation may
be sorbable into the cement matrix. As referred to herein, the term
"irreversible" will be understood to mean that the degradable
material, once degraded downhole, should not reconstitute while
downhole, e.g., the degradable material should degrade in situ but
should not reconstitute in situ. The terms "degradation" or
"degradable" refer to both the two relatively extreme cases of
hydrolytic degradation that the degradable material may undergo,
e.g., bulk erosion and surface erosion, and any stage of
degradation in between these two. This degradation can be a result
of, inter alia, a chemical reaction. The rate at which the chemical
reaction takes place may depend on, inter alia, the chemicals
added, temperature and time. The degradability of a polymer depends
at least in part on its structure. For instance, the presence of
hydrolyzable and/or oxidizable linkages in the backbone often
yields a material that will degrade as described herein. The rates
at which such polymers degrade are dependent on factors such as,
but not limited to, the type of repetitive unit, composition,
sequence, length, molecular geometry, molecular weight, morphology
(e.g., crystallinity, size of spherulites, and orientation),
hydrophilicity, hydrophobicity, surface area, and additives. The
manner in which the polymer degrades also may be affected by the
environment to which the polymer is exposed, e.g., temperature,
presence of moisture, oxygen, microorganisms, enzymes, pH, and the
like.
[0020] Suitable examples of degradable polymers that may be used in
accordance with the present invention include, but are not limited
to, those described in the publication of Advances in Polymer
Science, Vol. 157 entitled "Degradable Aliphatic Polyesters,"
edited by A.-C. Albertsson, the relevant disclosure of which is
incorporated herein by reference. Examples of polyesters that may
be used in accordance with the present invention include
homopolymers, random, block, graft, and star- and hyper-branched
aliphatic polyesters.
[0021] Another class of suitable degradable polymers that may be
used in accordance with the present invention include polyamides
and polyimides. Such polymers may comprise hydrolyzable groups in
the polymer backbone that may hydrolyze under the basic conditions
that exist in cement slurries and in a set cement matrix. Such
polymers also may generate byproducts that may become sorbed into
the cement matrix. Calcium salts are a nonlimiting example of such
byproducts. Nonlimiting examples of suitable polyamides include
proteins, polyaminoacids, nylon, and poly(caprolactam). Another
class of polymers that may be suitable for use in the present
invention are those polymers that may contain hydrolyzable groups,
not in the polymer backbone, but as pendant groups. Hydrolysis of
the pendant groups may generate a water-soluble polymer and other
byproducts that may become sorbed into the cement composition. A
nonlimiting example of such a polymer includes polyvinylacetate,
which upon hydrolysis forms water-soluble polyvinylalcohol and
acetate salts.
[0022] A variety of processes may be used to prepare the degradable
polymers that are suitable for use in the cement compositions of
the present invention. Examples of such processes include, but are
not limited to, polycondensation reactions, ring-opening
polymerizations, free radical polymerizations, anionic
polymerizations, carbocationic polymerizations, coordinative
ring-opening polymerizations, and any other appropriate process.
Exemplary polymers that may be used in accordance with the present
invention include, but are not limited to, aliphatic polyesters;
poly(lactides); poly(glycolides); poly(.epsilon.-caprolactones);
poly(hydroxybutyrates); poly(anhydrides); aliphatic
poly(carbonates); ortho esters; poly(orthoesters); and
poly(vinylacetates). In an exemplary embodiment of the present
invention, the degradable material is poly(vinylacetate) in bead
form, commercially available from Aldrich Chemical Company. In
another exemplary embodiment of the present invention, the
degradable material is poly(lactic acid), commercially available
from Cargill Dow Polymers, LLC.
[0023] In certain exemplary embodiments, the rate of degradation of
the polymer is such that the unhydrolyzed polymer additive retains
its structure and shape until it may be suitable for an intended
application. For example, it may be desirable for the polymers of
the present invention to remain substantially insoluble (e.g.,
phase-separated) in the slurry until at least such time as the
slurry is placed in a subterranean application. Furthermore, the
rate of degradation of the degradable material may be varied
depending on factors such as the hydraulic cement, the degradable
material chosen, and the subterranean conditions of the
application.
[0024] Generally, the degradable materials may be present in the
cement composition in any shape, and may be of any size. In certain
exemplary embodiments, the degradable materials may be spherical,
substantially spherical, bead-shaped or fiber-shaped. In a further
exemplary embodiment of the present invention, voids in the shape
of the individual particles of the degradable material may form
within the cement sheath.
[0025] In other embodiments, the rate of degradation of the
degradable material may be such that a barrier may be formed by the
degradable material to prevent slurry loss into a permeable zone
(e.g., a zone comprising fractures). In a further exemplary
embodiment, the barrier may remain without substantially degrading
until the cement has set. In yet a further exemplary embodiment,
the degradable material used to form the barrier may be flakes or
film strips. Examples of such film-forming hydrolyzable polymers
include, but are not limited to, polylactic acid, polyvinylacetate,
and cellulose acetate. Such polymers also may have the additional
advantage of being biodegradable.
[0026] In one exemplary embodiment of the present invention, the
degradable material may enhance the properties of the cement
composition by degrading to form reactive gases, (e.g., carbon
dioxide, sulfur oxide, and the like), and/or by degrading to form
salts. In a further embodiment, the degradable material may degrade
to form gases that react with the cement composition to form an
insoluble salt. In still a further embodiment, the gases produced
may be inert, and may occupy the space formerly occupied by the
degradable material.
[0027] Optionally, the cement compositions of the present invention
may comprise a gas that is added at the surface (e.g., nitrogen) or
a gas-generating additive that may generate a gas in situ at a
desired time (e.g., aluminum powder or azodicarbonamide). When
included in a cement composition of the present invention, aluminum
powder may generate hydrogen gas in situ, and azodicarbonamide may
generate nitrogen gas in situ. Other gases and/or gas-generating
additives also may be suitable for inclusion in the cement
compositions of the present invention. The inclusion of the gas or
gas-generating additive in the cement compositions of the present
invention may allow a cement composition to have "tunable"
mechanical properties. For example, a cement composition of the
present invention may be formulated to have a desired initial
elasticity or flexibility through inclusion of a gas or
gas-generating additive, which elasticity or flexibility then may
change over time to a second desired value through degradation of
the degradable material. An example of a suitable gas-generating
additive is an aluminum powder that is commercially available from
Halliburton Energy Services, Inc., of Duncan, Oklahoma, under the
tradename "SUPER CBL." SUPER CBL is available as a dry powder or as
a liquid additive. Where included, a gas may be added at the
surface to the cement compositions of the present invention in an
amount sufficient to provide a gas concentration under downhole
conditions in the range of from about 0.5% to about 30% by volume
of the cement composition. Where included, a gas-generating
additive may be present in the cement compositions of the present
invention in an amount in the range of from about 0.1% to about 5%
bwoc. In certain exemplary embodiments where the gas-generating
additive is aluminum powder, the aluminum powder may be present in
the cement compositions of the present invention in an amount in
the range of from about 0.1% to about 1% bwoc. In certain exemplary
embodiments where the gas-generating additive is an
azodicarbonamide, the azodicarbonamide may be present in the cement
compositions of the present invention in an amount in the range of
from about 0.5% to about 5% bwoc. Where included, the gas or
gas-generating additive may be added to the cement compositions in
a variety of ways, including, but not limited to, dry blending it
with the hollow particles, or injecting it into the cement
composition as a liquid suspension while the cement composition is
being placed within the subterranean formation.
[0028] Optionally, the cement compositions of the present invention
may comprise a polymer emulsion comprising at least one polar
monomer and at least one elasticity-enhancing monomer. In certain
exemplary embodiments the polymer emulsion may further comprise a
stiffness-enhancing monomer. As used herein, the term "polymer
emulsion" will be understood to mean a water emulsion of a rubber
or plastic obtained by polymerization. Such a polymer emulsion is
commonly known as "latex," and the terms "polymer emulsion" and
"latex" are interchangeable herein. Generally, the polar monomer
may be selected from the group consisting of: vinylamine, vinyl
acetate, acrylonitrile, and the acid, ester, amide, and salt forms
of acrylates (e.g., acrylic acid). Generally, the
elasticity-enhancing monomer may be selected from the group
consisting of: ethylene, propylene, butadiene, 1,3-hexadiene, and
isoprene. In certain exemplary embodiments that include a stiffness
enhancing monomer, the stiffness enhancing monomer may be selected
from the group consisting of: styrene, t-butylstyrene,
.alpha.-methylstyrene, and sulfonated styrene. Generally, the polar
monomer may be present in the polymer emulsion in an amount in the
range of from about 1% to about 90% by weight of the polymer
emulsion. Generally, the elasticity-enhancing monomer may be
present in the polymer emulsion in an amount in the range of from
about 10% to about 99% by weight of the polymer emulsion. When the
polymer emulsion further comprises a stiffness-enhancing monomer,
the stiffness-enhancing monomer may be present in the polymer
emulsion in an amount in the range of from about 0.01% to about 70%
by weight. Varying the amounts of the constituents of a latex may
change the properties of the latex, so as to affect the type and
degree of properties of the cement compositions of the present
invention that optionally may include such latex. For example, when
a latex having a high concentration of an elasticity-enhancing
monomer (e.g., butadiene), is incorporated into a cement
composition of the present invention, the elasticity-enhancing
monomer may increase, inter alia, the elastomeric properties of the
cement composition. For example, a latex having a high
concentration of a stiffness-enhancing monomer (e.g., styrene), or
a polar monomer (e.g., acrylonitrile), may decrease, inter alia,
the elastomeric properties of the cement composition. Thus, one of
ordinary skill in the art, with the benefit of this disclosure,
will appreciate that the mechanical properties of a cement
composition may be adjusted by varying the constituents of a
polymer emulsion that may be incorporated in the cement
composition. In certain exemplary embodiments, a polymer emulsion
may be added to the cement compositions of the present invention by
mixing the polymer emulsion with water, which then may be mixed
with a hydraulic cement to form a cement composition. In certain
exemplary embodiments, a polymer emulsion may be added to the
cement compositions of the present invention by evaporating the
water from a latex prepared as a water emulsion, thereby forming a
dry polymer additive. The dry polymer additive then may be mixed
with a hydraulic cement, which then may be mixed with water to form
a cement composition. An example of a suitable polymer emulsion is
an aqueous styrene butadiene latex that is commercially available
from Halliburton Energy Services, Inc., of Duncan, Oklahoma, under
the tradename "LATEX 200OTM." Where present, the polymer emulsion
may be included within the cement composition in an amount in the
range of from about 5% to about 100% by weight of the water
therein. In certain exemplary embodiments, the cement composition
that comprises a polymer emulsion further may comprise a
surfactant, inter alia, to stabilize the polymer emulsion. In
certain exemplary embodiments, the surfactant may be a nonionic
ethoxylated nonylphenol. Examples of suitable surfactants are
commercially available from Halliburton Energy Services, Inc., of
Duncan, Oklahoma, under the tradenames "STABILIZER 434 B" and
"STABILIZER 434 C." Where included, the surfactant may be present
in the cement composition in an amount in the range of from about
10% to about 20% by weight of the polymer emulsion.
[0029] Additional additives optionally may be added to the cement
compositions of the present invention as deemed appropriate by one
skilled in the art with the benefit of this disclosure. Examples of
such additives include fluid loss control additives, defoamers,
dispersing agents, set accelerators, salts, formation conditioning
agents, weighting agents, set retarders, hollow glass or ceramic
beads, elastomers, fibers and the like. An example of a suitable
dispersing agent is commercially available from Halliburton Energy
Services, Inc., of Duncan, Okla. under the tradename "CFR-3." An
example of a suitable set retarder is a lignosulfonate that is
commercially available from Halliburton Energy Services, Inc., of
Duncan, Okla. under the tradename "HR.RTM.-5."
[0030] In certain exemplary embodiments, the cement compositions of
the present invention may be prepared by dry blending the
degradable materials with the cement before the addition of water,
or by mixing the degradable materials with water before it is added
to the cement, or by mixing the degradable materials with the
cement slurry consecutively with or after the addition of water. In
certain preferred embodiments, the degradable materials are dry
blended with the cement before the addition of water. In other
exemplary embodiments, the degradable materials may be
pre-suspended in water and injected into the cement composition, or
into the cement composition as an aqueous slurry, if desired.
[0031] An example of a method of the present invention comprises:
providing a cement composition that comprises a hydraulic cement,
and a degradable material; placing the cement composition in a
subterranean formation, allowing the cement composition to set
therein; and allowing the degradable material to degrade. In
certain exemplary embodiments of the present invention, the
subterranean formation may comprise a multilateral well. In certain
exemplary embodiments of the present invention, the subterranean
formation may comprise a well that comprises an expandable tubular.
Another example of a method of the present invention is a method of
enhancing the mechanical properties of a cement composition
comprising adding a degradable material to the cement composition,
and allowing the degradable material to degrade.
[0032] To facilitate a better understanding of the present
invention, the following examples of some of the preferred
embodiments are given. In no way should such examples be read to
limit, or to define, the scope of the invention.
EXAMPLE 1
[0033] Sample cement compositions were prepared in accordance with
API Recommended Practice 10B, Twenty-Second Edition, 1997.
[0034] Sample Composition No. 1 comprised Class A cement and about
37.85% water bwoc. Sample Composition No. 1 was cured for 1 day at
a temperature of 210.degree. F. and a pressure of 1000 psi.
[0035] Sample Composition No. 2 comprised Class A cement, about 8%
bwoc polylactic acid ("PLA") in bead form (about 0.75 mm in
diameter), and about 37.85% water bwoc. Sample Composition No. 2
was cured for 1 day at a temperature of 210.degree. F. and a
pressure of 1000 psi. The density of Sample Composition No. 2, upon
setting, was measured at 16.4 lb/gallon.
[0036] Sample Composition No. 3 comprised Class A cement, PLA at
about 8% bwoc and about 37.85% water bwoc. Sample Composition No. 3
was cured for 14 days at a temperature of 210.degree. F. and a
pressure of 1000 psi. The density of Sample Composition No. 3, upon
setting, was measured at 16.3 lb/gallon.
[0037] The sample cement compositions were cured in
2''.times.2''.times.2'' brass molds according to the API procedure
for measuring compressive strengths using Tinius Olsen (TO)
Instrument. The crushed samples were examined for the presence of
bubble structure. The results of the testing are set forth in the
table below. TABLE-US-00001 TABLE 1 Degradable Observed cement
material Compressive matrix Composition (% bwoc) strength (psi)
morphology Sample None 5290 solid Composition No. 1 Sample PLA 2220
Hollow bubbles Composition 8% bwoc No. 2 Sample PLA 4780 Hollow
bubbles Composition 8% bwoc No. 3
[0038] The above example demonstrates, inter alia, that the
inclusion in a cement composition of degradable material in bead
form contributes to the formation of voids upon degradation and
sorption of the degradable material.
EXAMPLE 2
[0039] The Young's Modulus of Sample Composition Nos. 1 and 2 was
determined after each Sample Composition had cured. The Young's
Modulus was measured by performing Load vs. Displacement
measurements on MTS Load Frame equipment under unconfining
conditions. The results are set forth in Table 2. TABLE-US-00002
TABLE 2 Degradable material Composition (% bwoc) Young's Modulus
(psi) Sample Composition None 2 .times. 10.sup.6 No. 1 Sample
Composition PLA 1.22 .times. 10.sup.6 No. 2 8% bwoc
[0040] The above example demonstrates, inter alia, that the cement
compositions of the present invention possess improved elasticity
and resiliency.
EXAMPLE 3
[0041] Sample cement compositions were prepared that comprised
Class A cement, about 0.375% bwoc CFR-3 dispersant, PLA at about
15% bwoc, and about 33.8% water bwoc. The sample cement
compositions were cured for 3 days at a temperature of 190.degree.
F. and a pressure of 1000 psi.
[0042] Sample Composition No. 4 did not comprise a retarder.
[0043] Sample Composition No. 5 comprised about 0.5% bwoc HR.RTM.-5
retarder.
[0044] Sample Composition No. 6 comprised about 1.0% bwoc of
HR.RTM.-5 retarder.
[0045] Thickening times at 190.degree. F. were measured according
to API procedure. The results of the testing are set forth in the
table below. TABLE-US-00003 TABLE 3 Retarder concentration
Thickening Time Sample Composition (% bwoc) (hrs:min) Sample
Composition No. 4 0 0:31 Sample Composition No. 5 0.5 1:00 Sample
Composition No. 6 1.0 1:18
[0046] The above example suggests, inter alia, that the
compositions of the present invention can be designed to set at a
desired time.
EXAMPLE 4
[0047] Two sample compositions were prepared that comprised Class A
cement, about 0.375% bwoc CFR-3 dispersing agent, about 15% PLA
bwoc and about 33.8% water bwoc. Both sample compositions were
cured at a temperature of 190.degree. F. and a pressure of 1000
psi.
[0048] Sample Composition No. 7 cured for three days.
[0049] Sample Composition No. 8 cured for five days.
[0050] The compressive strength of each sample composition was
measured according to the API procedure for measuring compressive
strengths using Tinius Olsen (TO) Instrument. The results are set
forth in the table below. TABLE-US-00004 TABLE 4 Compressive
Composition Cure time (days) strength (psi) Sample 3 2890
Composition No. 7 Sample 5 3080 Composition No. 8
[0051] The above example demonstrates, inter alia, that the cement
compositions of the present invention have suitable compressive
strengths for, inter alia, oil well cementing.
EXAMPLE 5
[0052] Three sample cement compositions were prepared comprising
Class A cement and about 37.85% water bwoc. The sample cement
compositions were cured at a temperature of 210.degree. F. and a
pressure of 1000 psi.
[0053] Sample Composition No. 9 was formulated to have a design
slurry density of 16.5 ppg. Sample Composition No. 9 comprised no
degradable material, and was cured for 1 day.
[0054] Sample Composition No. 10 was formulated to have a design
slurry density of 15.85 ppg. Sample Composition No. 10 comprised
about 8% bwoc polyvinyl acetate in the bead form, and was cured for
1 day.
[0055] Sample Composition No. 11 was formulated to have a design
slurry density of 15,85 ppg. Sample Composition No. 11 comprised
about 8% bwoc polyvinyl acetate in the bead form, and was cured for
6 days. TABLE-US-00005 TABLE 5 Design Degradable Slurry Cure
Compressive Cement Material Density Set Density Time strength
Matrix Composition (% bwoc) (ppg) (ppg) (days) (psi) Morphology
Sample None 16.5 Not 1 day 6230 Solid Composition Determined No. 9
Sample Polyvinyl 15.85 16.25 1 day 3960 Solid polymer Composition
acetate, 8% beads No. 10 bwoc Sample Polyvinyl 15.85 16.21 6 days
3770 Hollow bubbles Composition acetate, 8% and polymer No. 11 bwoc
beads
[0056] The above example demonstrates, inter alia, that the cement
compositions of the present invention may be designed to have
desired rates of degradation.
EXAMPLE 6
[0057] A 16.5 ppg slurry was prepared using Class H cement and
37.85% bwoc water. The slurry was divided into two portions of 300
ml each. A conventional lost-circulation material (FLOCELE flakes,
available from Halliburton Energy Services, Inc., of Duncan,
Oklahoma) was added to one portion in the amount of 0.2% bwoc. To
the other portion, flakes of polylactic acid film having a
thickness of 15-30 microns were added. Both portions were stirred
for four hours at room temperature, and visually inspected for
disappearance of the additive. In both cases, the flakes persisted
without undergoing degradation. The above example demonstrates,
inter alia, that degradable materials may be added to cement
compositions in order to prevent loss of the cement composition to
permeable zones in the formation, such as zones comprising
fractures.
[0058] Therefore, the present invention is well adapted to carry
out the objects and attain the ends and advantages mentioned as
well as those that are inherent therein. While the invention has
been described and is defined by reference to exemplary embodiments
of the invention, such a reference does not imply a limitation on
the invention, and no such limitation is to be inferred. The
invention is capable of considerable modification, alteration, and
equivalents in form and function, as will occur to those ordinarily
skilled in the pertinent arts and having the benefit of this
disclosure. The depicted and described embodiments of the invention
are exemplary only, and are not exhaustive of the scope of the
invention. Consequently, the invention is intended to be limited
only by the spirit and scope of the appended claims, giving full
cognizance to equivalence in all respects.
* * * * *