U.S. patent application number 10/745470 was filed with the patent office on 2004-09-02 for cement compositions with improved mechanical properties and methods of cementing in a subterranean formation.
This patent application is currently assigned to HALLIBURTON ENERGY SERVICES, INC.. Invention is credited to Ravi, Krishna M., Reddy, B. Raghava.
Application Number | 20040171499 10/745470 |
Document ID | / |
Family ID | 34710603 |
Filed Date | 2004-09-02 |
United States Patent
Application |
20040171499 |
Kind Code |
A1 |
Ravi, Krishna M. ; et
al. |
September 2, 2004 |
Cement compositions with improved mechanical properties and methods
of cementing in a subterranean formation
Abstract
The present invention relates to subterranean cementing
operations, and more particularly, to cement compositions
comprising elastic particles and having improved mechanical
properties, and methods of using such compositions in subterranean
cementing operations. An example of a method of the present
invention comprises the steps of: providing a cement composition
comprising a base fluid, a hydraulic cement, and a portion of
elastic particles; placing the cement composition in a well bore in
a subterranean formation; permitting a portion of the cement
composition to enter openings in a region of the subterranean
formation in fluid communication with the well bore; and permitting
the portion of the cement composition to seal the openings off from
the well bore. Another example of a method of the present invention
comprises the step of adding a portion of elastic particles to a
cement composition.
Inventors: |
Ravi, Krishna M.; (Kingwood,
TX) ; Reddy, B. Raghava; (Duncan, OK) |
Correspondence
Address: |
ATTN.: CRAIG W. RODDY
HALLIBURTON ENERGY SERVICES GROUP
2600 SOUTH SECOND STREET
DUNCAN
OK
73536
US
|
Assignee: |
HALLIBURTON ENERGY SERVICES,
INC.
DUNCAN
OK
|
Family ID: |
34710603 |
Appl. No.: |
10/745470 |
Filed: |
December 22, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10745470 |
Dec 22, 2003 |
|
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10350533 |
Jan 24, 2003 |
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Current U.S.
Class: |
507/200 |
Current CPC
Class: |
C04B 28/02 20130101;
C04B 20/04 20130101; Y02W 30/92 20150501; Y02W 30/94 20150501; C09K
8/473 20130101; C04B 2111/00146 20130101; C04B 16/04 20130101; C09K
8/46 20130101; C04B 2111/503 20130101; Y02W 30/91 20150501; C04B
2103/0052 20130101; C09K 8/42 20130101; C04B 20/0032 20130101; C04B
2103/0051 20130101; C04B 28/02 20130101; C04B 16/04 20130101; C04B
16/04 20130101; C04B 20/1051 20130101; C04B 16/04 20130101; C04B
20/1033 20130101; C04B 28/02 20130101; C04B 14/108 20130101; C04B
14/20 20130101; C04B 14/24 20130101; C04B 14/301 20130101; C04B
18/08 20130101; C04B 18/082 20130101; C04B 18/146 20130101; C04B
20/0048 20130101; C04B 2103/10 20130101; C04B 2103/20 20130101;
C04B 2103/40 20130101; C04B 2103/408 20130101; C04B 2103/46
20130101; C04B 2103/50 20130101; C04B 20/04 20130101; C04B 16/08
20130101; C04B 28/02 20130101; C04B 14/104 20130101; C04B 16/082
20130101; C04B 18/146 20130101; C04B 22/124 20130101; C04B 2103/20
20130101; C04B 2103/48 20130101; C04B 2103/50 20130101; C04B 28/02
20130101; C04B 14/104 20130101; C04B 18/146 20130101; C04B 22/124
20130101; C04B 24/2688 20130101; C04B 2103/20 20130101; C04B
2103/48 20130101; C04B 2103/50 20130101; C04B 28/02 20130101; C04B
14/104 20130101; C04B 18/146 20130101; C04B 22/124 20130101; C04B
24/2641 20130101; C04B 2103/20 20130101; C04B 2103/48 20130101;
C04B 2103/50 20130101; C04B 20/0032 20130101; C04B 14/104 20130101;
C04B 18/146 20130101; C04B 20/0032 20130101; C04B 22/124 20130101;
C04B 2103/20 20130101; C04B 2103/48 20130101; C04B 2103/50
20130101; C04B 28/02 20130101; C04B 14/104 20130101; C04B 16/08
20130101; C04B 18/146 20130101; C04B 22/124 20130101; C04B 2103/20
20130101; C04B 2103/48 20130101; C04B 2103/50 20130101 |
Class at
Publication: |
507/200 |
International
Class: |
E21B 043/00 |
Claims
What is claimed is:
1. A method of avoiding the loss of circulation of a cement
composition in a subterranean formation, comprising the steps of:
providing a cement composition comprising a hydraulic cement and a
portion of elastic particles; placing the cement composition in a
well bore in a subterranean formation; permitting a portion of the
cement composition to enter openings in a region of the
subterranean formation in fluid communication with the well bore;
and permitting the portion of the cement composition to seal the
openings off from the well bore.
2. The method of claim 1 wherein the hydraulic cement comprises
Portland cements, pozzolana cements, gypsum cements, high alumina
content cements, silica cements, or high alkalinity cements.
3. The method of claim 1 wherein the cement composition further
comprises a base fluid, and wherein the base fluid comprises water,
a nonaqueous fluid, or a mixture thereof.
4. The method of claim 3 wherein the nonaqueous fluid comprises an
organic liquid.
5. The method of claim 3 wherein the base fluid is present in the
cement composition in an amount sufficient to form a pumpable
slurry.
6. The method of claim 5 wherein the base fluid is present in the
cement composition in an amount in the range of from about 25% to
about 150% by weight of the cement.
7. The method of claim 1 wherein the elastic particles have a
specific gravity of at least about 0.05.
8. The method of claim 7 wherein the elastic particles have a
specific gravity in the range of from about 0.05 to about 0.99.
9. The method of claim 1 wherein the portion of elastic particles
comprises elastic particles comprising a copolymer of styrene and
divinylbenzene; a copolymer of styrene and acrylonitrile; or a
terpolymer of styrene, vinylidene chloride, and acrylonitrile.
10. The method of claim 1 wherein the elastic particles have a
compressibility factor in the range of from about
1.5.times.10.sup.-3 (1/psi) to about 1.5.times.10.sup.-9
(1/psi).
11. The method of claim 1 wherein a portion of the elastic
particles has a diameter of at least about 1 micrometer at a
temperature of about 25.degree. C. and at about atmospheric
pressure.
12. The method of claim 1 wherein the portion of elastic particles
is present in the cement composition in an amount in the range of
from about 1% to about 200% by weight of cement.
13. The method of claim 12 wherein the portion of elastic particles
is present in the cement composition in an amount in the range of
from about 5% to about 100% by weight of cement.
14. The method of claim 13 wherein the portion of elastic particles
is present in the cement composition in an amount in the range of
from about 5% to about 10% by weight of cement.
15. The method of claim 1 wherein a portion of the elastic
particles is substantially impermeable to a fluid present in the
cement composition or in the subterranean formation.
16. The method of claim 1 wherein the surface of a portion of the
elastic particles is coated with a substantially impermeable
material to render the elastic particles substantially impermeable
to a fluid present in the cement composition or in the subterranean
formation.
17. The method of claim 16 wherein the material is hydrophilic or
hydrophobic.
18. The method of claim 17 wherein the hydrophobic material
comprises silanes, silicone polymers, latexes, or a mixture
thereof.
19. The method of claim 17 wherein the hydrophilic material
comprises ethylene oxide, propylene oxide, acrylic acid,
2-acrylamido-2-methylpropa- nesulfonicacid, aminoalkoxysilanes, or
a mixture thereof.
20. The method of claim 1 wherein the elastic particles further
comprise an internal fluid.
21. The method of claim 20 wherein the internal fluid comprises
air, nitrogen, carbon dioxide, propane, isobutane, normal butane,
normal or branched pentane, ammonia, fluorinated hydrocarbons,
hydrochlorofluorocarbons, argon, helium, or a mixture thereof.
22. The method of claim 20 wherein a portion of the elastic
particles is capable of expanding up to about 40 times its original
volume.
23. The method of claim 1 wherein a portion of the elastic
particles can withstand a pressure of about 21,000 psi without
crushing.
24. The method of claim 1 wherein a portion of the elastic
particles can rebound upon release of pressure.
25. The method of claim 1 wherein the cement composition has a
density, and wherein the density of the cement composition may vary
with pressure.
26. The method of claim 1 wherein the cement composition comprising
the portion of elastic particles has a density sufficient to
prevent fluid influx from a region of the subterranean formation
adjacent to the well bore without fracturing a region of the
formation.
27. The method of claim 26 wherein the cement composition
comprising the portion of the elastic particles has a density in a
range of from about 6 pounds per gallon to about 22 pounds per
gallon.
28. The method of claim 1 wherein the cement composition further
comprises a surfactant, a dispersant, an accelerator, a retarder, a
salt, mica, fibers, a formation-conditioning agent, a fixed-density
weighting agent, vitrified shale, fumed silica, fly ash, a fluid
loss control additive, an expanding additive, a defoamer, a
viscosifier, a cenosphere, a glass sphere, a ceramic sphere, or a
mixture thereof.
29. The method of claim 20 further comprising the step of expanding
a portion of the elastic particles before introducing the elastic
particles to the cement composition.
30. The method of claim 1 wherein the step of permitting the
portion of the cement composition to seal the openings off from the
well bore comprises permitting the portion of elastic particles
within the portion of the cement composition to expand upon
entering the openings such that the openings are sealed off from
the well bore.
31. The method of claim 1 wherein the step of placing the cement
composition in a well bore in a subterranean formation involves
selectively placing the cement composition in a region of the well
bore that is in fluid communication with openings in a region of
the subterranean formation.
32. The method of claim 1 wherein the cement composition is placed
in a well bore in the subterranean formation; wherein the cement
composition has a density that may vary with pressure; wherein the
cement composition comprising the portion of elastic particles has
a density sufficient to prevent fluid influx from a region of the
subterranean formation adjacent to the well bore without fracturing
a region of the formation; wherein the portion of elastic particles
is present in the cement composition in an amount in the range of
from about 1% to about 200% by weight of cement; wherein the
portion of elastic particles comprises elastic particles comprising
a copolymer of styrene and divinylbenzene; a copolymer of styrene
and acrylonitrile; or a terpolymer of styrene, vinylidene chloride
and acrylonitrile; and wherein the elastic particles have a
compressibility factor in the range of from about
1.5.times.10.sup.-3 (1/psi) to about 1.5.times.10.sup.-9
(1/psi).
33. A method of improving the ability of a cement composition to
resist the loss of circulation, comprising the step of adding to
the cement composition a portion of elastic particles.
34. The method of claim 33 wherein the cement composition further
comprises a hydraulic cement, and wherein the hydraulic cement
comprises Portland cements, pozzolana cements, gypsum cements, high
alumina content cements, silica cements, or high alkalinity
cements.
35. The method of claim 33 wherein the cement composition further
comprises a base fluid, and wherein the base fluid comprises water,
a nonaqueous fluid, or a mixture thereof.
36. The method of claim 35 wherein the nonaqueous fluid comprises
an organic liquid.
37. The method of claim 35 wherein the base fluid is present in the
cement composition in an amount sufficient to form a pumpable
slurry.
38. The method of claim 37 wherein the base fluid is present in the
cement composition in an amount in the range of from about 25% to
about 150% by weight of the cement.
39. The method of claim 33 wherein the elastic particles have a
specific gravity of at least about 0.05.
40. The method of claim 39 wherein the elastic particles have a
specific gravity in the range of from about 0.05 to about 0.99.
41. The method of claim 33 wherein the portion of elastic particles
comprises elastic particles comprising a copolymer of styrene and
divinylbenzene; a copolymer of styrene and acrylonitrile; or a
terpolymer of styrene, vinylidene chloride, and acrylonitrile.
42. The method of claim 33 wherein the elastic particles have a
compressibility factor in the range of from about
1.5.times.10.sup.-3 (1/psi) to about 1.5.times.10.sup.-9
(1/psi).
43. The method of claim 33 wherein a portion of the elastic
particles has a diameter of at least about 1 micrometer at a
temperature of about 25.degree. C. and at about atmospheric
pressure.
44. The method of claim 33 wherein the portion of elastic particles
is present in the cement composition in an amount in the range of
from about 1% to about 200% by weight of cement.
45. The method of claim 44 wherein the portion of elastic particles
is present in the cement composition in an amount in the range of
from about 5% to about 100% by weight of cement.
46. The method of claim 45 wherein the portion of elastic particles
is present in the cement composition in an amount in the range of
from about 5% to about 10% by weight of cement.
47. The method of claim 33 wherein a portion of the elastic
particles is substantially impermeable to a fluid present in the
cement composition or in a subterranean formation.
48. The method of claim 33 wherein the surface of a portion of the
elastic particles is coated with a substantially impermeable
material to render the elastic particles substantially impermeable
to a fluid present in the cement composition or in a subterranean
formation.
49. The method of claim 48 wherein the material is hydrophilic or
hydrophobic.
50. The method of claim 49 wherein the hydrophobic material
comprises silanes, silicone polymers, latexes, or a mixture
thereof.
51. The method of claim 49 wherein the hydrophilic material
comprises ethylene oxide, propylene oxide, acrylic acid,
2-acrylamido-2-methylpropa- ne sulfonic acid, aminoalkoxysilanes,
or a mixture thereof.
52. The method of claim 33 wherein the elastic particles further
comprise an internal fluid.
53. The method of claim 52 wherein the internal fluid comprises
air, nitrogen, carbon dioxide, propane, isobutane, normal butane,
normal or branched pentane, ammonia, fluorinated hydrocarbons,
hydrochlorofluorocarbons, argon, helium, or a mixture thereof.
54. The method of claim 52 wherein a portion of the elastic
particles is capable of expanding up to about 40 times its original
volume.
55. The method of claim 33 wherein a portion of the elastic
particles can withstand a pressure of about 21,000 psi without
crushing.
56. The method of claim 33 wherein a portion of the elastic
particles can rebound upon release of pressure.
57. The method of claim 33 wherein the cement composition has a
density, and wherein the density of the cement composition may vary
with pressure.
58. The method of claim 33 wherein the cement composition
comprising the portion of elastic particles has a density
sufficient to prevent fluid influx from a region of a subterranean
formation adjacent to a well bore without fracturing a region of
the formation.
59. The method of claim 58 wherein the cement composition
comprising the portion of the elastic particles has a density in a
range of from about 6 pounds per gallon to about 22 pounds per
gallon.
60. The method of claim 33 wherein the cement composition further
comprises a surfactant, a dispersant, an accelerator, a retarder, a
salt, mica, fibers, a formation-conditioning agent, a fixed-density
weighting agent, vitrified shale, fumed silica, fly ash, a fluid
loss control additive, an expanding additive, a defoamer, a
viscosifier, a cenosphere, a glass sphere, a ceramic sphere, or a
mixture thereof.
61. The method of claim 52 further comprising the step of expanding
a portion of the elastic particles before introducing the elastic
particles to the cement composition.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 10/350,533 entitled, "Cement Compositions
Containing Elastic Particles and Methods of Cementing in
Subterranean Formations," filed Jan. 24, 2003, incorporated by
reference herein for all purposes, and from which priority is
claimed pursuant to 35 U.S.C. .sctn.120.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to subterranean cementing
operations, and more particularly, to cement compositions
comprising elastic particles and having improved mechanical
properties, 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
the annular space between the walls of a well bore and the exterior
surface of the pipe string disposed therein. The cement composition
is permitted to set in the annular space, thereby forming an
annular sheath of hardened substantially impermeable cement therein
that 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 also are 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 transversed by well bores are often
weak and extensively fractured. In some cases, the formation may be
unable to withstand the hydrostatic head pressure normally
associated with cement being pumped in the formation. In such
cases, the hydrostatic pressure may be sufficient to force cement
into the extensive fractures of the formation, which may result in
a significant loss of cement into the formation during cementing
operations. This problem of losing fluid into a subterranean
formation due to the hydrostatic pressure exerted by the fluid is
commonly referred to as "lost circulation." This loss of cement
composition is problematic because 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,
the loss of cement composition is of great concern. Resolution of
this concern may call for reducing the density of the cement, inter
alia, to reduce the hydrostatic pressure applied to the
formation.
[0005] A traditional means of reducing the density of the cement
composition has been to increase the cement composition's water
content, because, generally speaking, the higher the water content,
the less dense the cement composition. However, this method may be
problematic because the resultant cement composition often requires
extensive cure time and lacks the desired strength and mechanical
properties.
[0006] As an alternative means of reducing the density of cement
compositions, lightweight spherical or substantially spherical
particulates have been added to such compositions. Some lightweight
spherical or substantially spherical particulates include hollow
spheres, which are typically cenospheres, glass hollow spheres, or
ceramic hollow spheres. Cenospheres are hollow spheres primarily
made from silica (SiO.sub.2) and/or alumina (Al.sub.2O.sub.3), and
are filled with gas. These are a naturally occurring by-product of
the burning process of a coal-fired power plant. Conventional glass
hollow spheres and ceramic hollow spheres reduce the density of the
cement composition such that less water is required to form the
cement composition. As a result, the curing time of the cement
composition is reduced. However, conventional hollow spheres are by
nature brittle and fragile, and thus the cement containing the
spheres often cannot endure the repeated detrimental stresses that
the set cement may encounter in a subterranean well bore during the
life of a well. Often, the cement lacks sufficient elasticity to
elastically deform, resulting in cracking and breaking of the
cement when it is forced to deform under pressure. As a result,
failure rates of cement compositions containing microspheres is
particularly problematic.
[0007] Cement failure may also be caused by the phenomenon of
hydration volume reduction of the cement composition during the
curing process. Hydraulic cement compositions typically demonstrate
a decrease in volume as the cement composition develops compressive
strength and sets. This shrinkage may adversely impact the set
cement through the formation of cracks and other imperfections that
may occur in the set cement. For instance, any cracks may provide a
path for subterranean fluids to penetrate and weaken the cement
sheath, and ultimately attack the casing of the well bore,
potentially causing the casing to fail during the life of the well.
Premature casing failure can result in, inter alia, costly repairs,
lost production, and complete loss of the well under certain
circumstances.
[0008] In some cases, the problem of hydration volume reduction has
been addressed through the use of particulate expanding additives.
When added to the cement slurry, these expanding additives react
with the slurry to produce a gas. The volume of the slurry is
increased by the generation of this gas, which compensates for
hydration volume reduction. The use of expanding additives to
compensate for hydration volume reduction may necessitate testing
to optimize the cement composition. Furthermore, the particulate
nature of these expanding additives may necessitate the
incorporation of additional procedures. Thus, the existing methods
of resolving the dilemma of hydration volume reduction during the
curing process are challenging. Failure to properly resolve this
dilemma may lead to the increased probability of failure of the set
cement in the well bore, which may result in, inter alia, radial or
circumferential cracking of the set cement as well as a breakdown
of the bonds between the set cement and the pipe or between the
cement sheath and the surrounding subterranean formation. Such
failures can result in at least lost production, environmental
pollution, hazardous rig operations, and/or hazardous production
operations. A common undesirable result is the presence of pressure
at the well head in the form of trapped gas between casing
strings.
[0009] To successfully meet the subterranean challenges that a
cement composition may encounter, a cement composition should
develop high bond strength after setting, and also should have
sufficient mechanical properties including elasticity, flexibility,
compressibility, and ductility to resist loss of pipe or formation
bonding, cracking, and/or shattering as a result of all of the
stressful conditions that may plague the well, including impacts
and/or shocks generated by drilling and other well operations.
SUMMARY OF THE INVENTION
[0010] The present invention relates to subterranean cementing
operations, and more particularly, to cement compositions
comprising elastic particles and having improved mechanical
properties, and methods of using such compositions in subterranean
cementing operations.
[0011] An example of a method of the present invention is a method
of avoiding the loss of circulation of a cement composition in a
subterranean formation, comprising the steps of: providing a cement
composition comprising a base fluid, a hydraulic cement, and a
portion of elastic particles; placing the cement composition in a
well bore in a subterranean formation; permitting a portion of the
cement composition to enter openings in a region of the
subterranean formation in fluid communication with the well bore;
and permitting the portion of the cement composition to seal the
openings off from the well bore.
[0012] Another example of a method of the present invention is a
method of improving the ability of a cement composition to resist
the loss of circulation, comprising the step of adding to the
cement composition a portion of elastic particles.
[0013] The features and advantages of the present invention will be
readily apparent to those skilled in the art upon a reading of the
description of the preferred embodiments that follows.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0014] The present invention relates to subterranean cementing
operations, and more particularly, to cement compositions
comprising elastic particles and having improved mechanical
properties, and methods of using such compositions in subterranean
cementing operations. While the 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 multi-lateral subterranean
wells.
[0015] The cement compositions useful with the methods of the
present invention generally comprise a hydraulic cement, a portion
of elastic particles, and a base fluid. Other additives suitable
for use in conjunction with subterranean cementing operations also
may be added to these cement compositions if desired. In certain
embodiments, the cement compositions useful with the present
invention have a density in the range of from about 6 lb/gallon to
about 22 lb/gallon. In certain preferred embodiments, the density
is in the range of from about 8 lb/gallon to about 18
lb/gallon.
[0016] Any known cement may be utilized in the cement compositions
used with the present invention, including hydraulic cements
composed of 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, silica cements, and high
alkalinity cements.
[0017] The base fluid may be aqueous-based, nonaqueous-based, or a
mixture thereof. Where the base fluid is aqueous-based, it 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. Where the base
fluid is nonaqueous-based, the base fluid may comprise any number
of organic liquids. Examples of suitable organic liquids include,
but are not limited to, mineral oils, synthetic oils, esters, and
the like. Generally, any organic liquid in which a water solution
of salts can be emulsified is suitable for use as a base fluid in
the cement compositions used with the present invention. The base
fluid may be present in an amount sufficient to form a pumpable
slurry. More particularly, in certain embodiments the base fluid is
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 preferred embodiments, the base fluid is present in the
cement compositions in the range of from about 30% to about 75%
bwoc.
[0018] The cement compositions useful with the methods of the
present invention further comprise a portion of elastic particles.
As referred to herein, the term "elastic" will be understood to
mean the tendency for a particle to deform or compress under an
applied force, and then re-expand as the force is removed, without
substantial adverse effect to the structure of the particle. Any
elastic particle that is compatible with a cement (e.g., that is
relatively chemically stable over time upon incorporation into the
cement) and that is substantially impermeable to the fluids
typically encountered during cementing operations may be suitable
for use with the cement compositions used in the present invention.
In certain exemplary embodiments, the elastic particles have a
specific gravity in the range of at least about 0.05. In certain
preferred embodiments, the elastic particles have a specific
gravity in the range of from about 0.3 to about 0.99. Further, the
elastic particles will also have an isothermal compressibility
factor. As referred to herein, the term "isothermal compressibility
factor" will be understood to mean a particle's change in volume
with pressure per unit volume of the particle while temperature is
held constant. Any elastic particle having an isothermal
compressibility factor in the range of from about
1.5.times.10.sup.-3 (1/psi) to about 1.5.times.10.sup.-9 (1/psi)
may be suitable for use with the present invention. Generally, the
elastic particles are present in the cement compositions useful
with the present invention in an amount sufficient to provide a
cement composition having a desired density and desired mechanical
properties such as, inter alia, a desired Young's modulus and
tensile strength. More particularly, the elastic particles may be
present in the cement compositions in an amount in the range of
from about 1% to about 200% bwoc. In certain exemplary embodiments,
the elastic particles are present in the cement composition in an
amount in the range of from about 5% to about 100% bwoc. In certain
exemplary embodiments, the elastic particles are present in the
cement composition in an amount in the range of from about 5% to
about 10% bwoc.
[0019] In certain embodiments, the elastic particles will further
comprise an internal fluid. Where the elastic particles comprise an
internal fluid, the internal fluid may become incorporated within
the elastic particles, so that the elastic particle forms a
boundary around the fluid, by any suitable means. For example, the
internal fluid may be injected into the elastic particle. As
another example, the internal fluid may become incorporated within
the elastic particle as a natural consequence of the process of
manufacturing the elastic particle. One of ordinary skill in the
art with the benefit of this disclosure will recognize an
appropriate means by which the internal fluid may become
incorporated within the elastic particle. The incorporation of an
internal fluid within the elastic particles, inter alia, permits
adjustment of the density of the elastic particles by pre-expanding
them to a desired density. In certain embodiments, the elastic
particles comprising the internal fluid may be thermally
pre-expanded. In certain embodiments, the elastic particles may be
pre-expanded up to about 40 times their original volume before
being added to the cement composition. The internal fluid within
the elastic particles may comprise air, nitrogen, carbon dioxide,
butane, fluorinated hydrocarbons, hydrochlorofluorocarbons, or the
like. The preceding list is not intended to be an exhaustive list,
but rather is intended merely to provide an illustration of some
types of fluids that may be suitable for use as internal fluids in
accordance with the present invention. Other fluids may also be
suitable for use as internal fluids, and one of ordinary skill in
the art with the benefit of this disclosure will be able to
identify an appropriate internal fluid for a particular
application.
[0020] Generally, the elastic particles may be configured in any
shape. The elastic particles may generally be of any size
sufficient to permit the particle to behave elastically. In certain
exemplary embodiments, the elastic particles are spherical or
substantially spherical in shape. In certain exemplary embodiments,
the elastic particles have a substantially spherical shape and a
diameter of at least 1 micrometer when measured at about 25.degree.
C. and about atmospheric pressure. For example, in one exemplary
embodiment, the elastic particles have a substantially spherical
shape and a diameter of about 3,000 micrometers when measured at
about 25.degree. C. and about atmospheric pressure. In another
exemplary embodiment, the elastic particles have a substantially
spherical shape and a diameter in the range of from about 2 to
about 150 micrometers when, measured at about 25.degree. C. and
about atmospheric pressure. An example of a suitable elastic
particle comprises a polymer that, over the range of temperatures
and pressures encountered in the well bore, changes volume by
expansion and contraction, and consequently may impart desired
mechanical properties to the cement composition. Suitable polymers
may include those that possess sufficient rubbery and elastic
characteristics to allow the elastic particles to respond to
changes in volume of the fluid within the elastic particles at
temperatures and pressures commonly encountered in the well bore.
In certain exemplary embodiments of the present invention, the
elastic particles comprise a copolymer of styrene and
divinylbenzene. Another example of suitable elastic particles
comprises either a copolymer of styrene and acrylonitrile or a
terpolymer of styrene, acrylonitrile, and vinylidene chloride, and
a fluid, such as isobutane or the like. Such particles are
commercially available under the trade name "EXPANCEL" from Akzo
Nobel, Inc., of Duluth, Ga. Several grades of EXPANCEL elastic
particles with different polymer-softening temperatures, allowing
for expansion and contraction at different temperature ranges, are
available. Depending on the conditions of the subterranean well
bore in which the elastic particles may be placed, a particular
grade of EXPANCEL elastic particles may be suitable.
[0021] The substantial impermeability of the elastic particles to
the fluids typically encountered during cementing operations (e.g.,
to a fluid in the cement composition or in the subterranean
formation) may also be achieved by appropriately encapsulating or
coating a prefabricated elastic particle with appropriate
materials. For example, an elastic particle intended for use, inter
alia, in a nonaqueous-based cement composition, may be coated or
encapsulated with a hydrophilic material. An elastic particle
intended for use in an aqueous-based cement composition may be
coated or encapsulated with a hydrophobic material. Examples of
suitable hydrophobic materials include, inter alia, silanes,
silicone polymers, latexes, and the like. Examples of suitable
hydrophilic materials include, inter alia, ethylene oxide,
propylene oxide, acrylic acid, 2-acrylamido-2-methylpropane
sulfonic acid, aminoalkoxysilanes, and the like. The preceding
lists are not intended to be exhaustive lists, but rather are
intended merely to provide an illustration of some types of
materials that may be suitable for use in accordance with the
present invention. Other materials may also be suitable, and one of
ordinary skill in the art with the benefit of this disclosure will
be able to identify an appropriate material for a particular
application.
[0022] Optionally, certain exemplary embodiments of the elastic
particles may be expanded before mixing with the cement by heating
the elastic particles, thereby increasing the pressure of the fluid
therein. In determining whether or not to heat a particular elastic
particle, the benefit from expanding the elastic particle may be
weighed against the cost in terms of manpower and energy to achieve
such expansion. Further, while expansion by heating may be suitable
for certain embodiments of the elastic particles (e.g., the
EXPANCEL particles), other embodiments of the elastic particles may
be susceptible to thermal degradation from such heating. One of
ordinary skill in the art, with the benefit of this disclosure,
will be able to determine whether expansion by heating is
appropriate for a particular type of elastic particle. The
expansion of the elastic particles generally may be measured by a
corresponding reduction in the specific gravity of the expanded
elastic particle. In certain exemplary embodiments, the elastic
particles are capable of expanding up to about 40 times their
original volume, e.g., the volume at about 25.degree. C. and about
atmospheric pressure. The temperature to which the elastic
particles are heated depends on factors such as the chemical
composition of the particle. For example, the glass transition
temperature of the polymer used to make the particles could affect
the temperature to which the particles are heated. The temperature
to which the elastic particles are heated also depends on other
factors including, but not limited to, the desired density of the
cement composition. One of ordinary skill in the art, with the
benefit of this disclosure, will be able to determine the
appropriate temperature to which a particular type of elastic
particle may be safely heated for a particular application.
[0023] Among other benefits, the addition of the elastic particles
to a cement composition may reduce the density of the cement
composition. Among other benefits, the presence of the elastic
particles in the cement compositions used in the present invention
provides improved elasticity, resiliency, and ductility to the
ensuing hardened cement sheath, and protects it from experiencing
brittle failure during the life of the well. The elastic particle
contracts, to some extent, under pressure, and subsequently expands
when the pressure is removed. Certain exemplary embodiments of the
elastic particles of the present invention can withstand pressures
in excess of about 21,000 psi without crushing, and may rebound
upon release of the pressure to about their original dimensions.
Accordingly, the elastic particles provide a mechanism for the
cement compositions used in the present invention to absorb stress
imposed by the temperature and pressure conditions encountered in a
subterranean formation. Among other benefits, the elastic particles
also enable the cement composition to endure the reduction in
hydration volume ("shrinkage") and associated changes that may
occur while the cement sets in the subterranean formation.
[0024] Among other benefits, the elastic particles in the cement
compositions used in the present invention may reduce the problem
of loss of circulation of the cement composition into the fractures
of the subterranean formation, because they permit the density of
the cement compositions to vary. For example, the cement
composition may have a lower density at shallower depths, and
subsequently have a higher density at greater depths, due to
factors such as the compressibility of the elastic particles. This
may permit the cement compositions to have a sufficiently low
density at shallow depths to avoid lost circulation at such low
depths, yet also have a sufficiently high density at greater depths
to prevent fluid influx from the subterranean formation surrounding
the well bore. If the zones within the subterranean formation where
circulation may potentially be lost are at a shallow depth, then
the cement compositions may be able to prevent or minimize lost
circulation, because the cement composition will have a
sufficiently low density at such shallow depth to avoid fracturing
the subterranean formation. This lower density reduces the
hydrostatic pressure exerted by the column of cement composition at
such shallow depth that might otherwise cause the cement
composition to enter the fractures within the lost circulation
zone. Furthermore, where the cement compositions are actually lost
to any extent to a lost circulation zone, the presence of the
elastic particles in the cement compositions may minimize such loss
of the cement composition due to factors such as the expansion of
the elastic particles as they enter lower pressure zones within the
formation, so as to seal off such lower pressure zones from the
well bore, which will prevent further loss of circulation. Lower
pressures may exist within the lost circulation zones in the
formation for reasons including the fact that such zones may
provide a broad flow area, as well as because frictional losses may
occur as the cement composition travels through such zones within
the formation. One of ordinary skill in the art with the benefit of
this disclosure will recognize the amount and type of elastic
particles to include within the cement compositions in order to
optimize the expansion and sealing capability of the cement
compositions for a particular application.
[0025] Optionally, the cement compositions used in the present
invention may comprise fibers. Where fibers are included in the
cement compositions, the fibers are, in certain exemplary
embodiments, high tensile modulus carbon fibers that have a high
tensile strength. In certain preferred embodiments, the tensile
modulus of the fibers may exceed 180 GPa, and the tensile strength
of the fibers may exceed 3000 MPa. In certain exemplary
embodiments, the fibers may have a mean length of about 1 mm or
less. In certain embodiments, the mean length of the carbon fibers
is from about 50 to about 500 microns. In certain exemplary
embodiments, the fibers have a mean length in the range of from
about 100 to about 200 microns. In certain exemplary embodiments,
the fibers are milled carbon fibers. An example of suitable fibers
includes "AGM-94" carbon fibers commercially available from Asbury
Graphite Mills, Inc., of Asbury, N.J. AGM-94 fibers have a mean
length of about 150 microns and a diameter of about 7.2 microns.
Another example of suitable fibers includes the "AGM-99" carbon
fibers, also available from Asbury Graphite Mills, Inc., which have
a mean length of about 150 microns and a diameter of about 7.4
microns. One of ordinary skill in the art with the benefit of this
disclosure will recognize where fibers may be suitable for a
particular application, and in what amount they may appropriately
be included within the cement composition.
[0026] Optionally, the cement compositions useful with the present
invention may further comprise an expanding additive, for providing
a foamed cement. The expanding additive may be any component
suitable for performing the desired function of incorporating gas
into the cement composition. Further, foaming of the cement
composition can be accomplished by any suitable method. Where the
expanding additive is a gas, for instance, foaming of the cement
composition is achieved at the surface in one preferred embodiment,
and the foamed cement composition is then introduced into the
subterranean formation and permitted to set therein into a
resilient, ductile, and tough foamed cement mass. Where the cement
compositions are to be foamed, the cement composition is foamed in
one preferred embodiment by direct injection of the expanding
additive into the cement composition. For instance, where the
cement composition is foamed by the direct injection of gas into
the composition, the gas utilized can be air or any suitable inert
gas, such as nitrogen, or even a mixture of such gases. Preferably,
nitrogen is used. Where foaming is achieved by direct injection of
gas, the gas may be present in the composition in an amount
sufficient to foam the composition, generally in an amount in the
range of from about 0.01% to about 60% by volume of the
composition. In another preferred embodiment, the cement
composition is foamed by gas generated by a reaction between the
cement slurry and an expanding additive present in the cement
composition in particulate form. For example, the composition may
be foamed by hydrogen gas generated in situ as the product of a
reaction between the slurry and fine aluminum powder present in the
cement composition. Where an expanding additive in particulate form
is used, aluminum powder, gypsum blends, and deadburned magnesium
oxide are preferred. Preferred expanding additives comprising
aluminum powder are commercially available under the trade names
"GAS-CHEK.RTM." and "SUPER CBL" from Halliburton Energy Services of
Duncan, Okla.; a preferred expanding additive comprising a blend
containing gypsum is commercially available under the trade name
"MICROBOND" from Halliburton Energy Services of Duncan, Okla.; and
preferred expanding additives comprising deadburned magnesium oxide
are commercially available under the trade names "MICROBOND M" and
"MICROBOND HT" from Halliburton Energy Services, Inc., of Duncan,
Okla. Such preferred expanding additives are described in
commonly-owned U.S. Pat. Nos. 4,304,298; 4,340,427; 4,367,093;
4,450,010; and 4,565,578, the relevant disclosures of which are
hereby incorporated herein by reference.
[0027] Additional additives may be added to the cement compositions
used with the methods of the present invention as deemed
appropriate by one skilled in the art with the benefit of this
disclosure. Examples of such additives include, inter alia, fluid
loss control additives, salts, vitrified shale, fly ash, fumed
silica, bentonite, fixed-density weighting agents, set retarders,
and the like. An example of a preferred fixed-density weighting
agent is "HI-DENSE.RTM. No. 4," commercially available from
Halliburton Energy Services, Inc., of Duncan, Okla. An example of a
preferred fly ash is "POZMIX.RTM. A," commercially available from
Halliburton Energy Services, Inc., of Duncan, Okla. An example of a
preferred source of fumed silica is "SILICALITE," commercially
available from Halliburton Energy Services, Inc., of Duncan,
Okla.
[0028] Optionally, other nonflexible particles may be added, in
conjunction with the elastic particles, to the cement compositions
used in the present invention. Particularly suitable nonflexible
particles are cenospheres, which are commercially available from,
for example, Halliburton Energy Services, Inc., of Duncan, Okla.,
under the trade name "SPHERELITE"; other suitable nonflexible
particles are commercially available from PQ Corporation of Valley
Forge, Pa., under the trade name "EXTENDOSPHERES"; and from
Trelleborg Fillite, Inc., of Atlanta, Ga., under the trade name
"FILLITE". Alternatively, the nonflexible particles may be glass
particles or ceramic particles. In some cases, the nonflexible
particles are relatively inexpensive compared to the elastic
particles. This is particularly true in the case of cenospheres,
which are nonflexible particles that are formed as an industrial
waste by-product. However, the nonflexible particles may be more
likely to break when subjected to downhole temperature and pressure
changes. In determining the relative amounts of elastic particles
and nonflexible particles to add to the cement composition when
using them in combination, the cost savings produced by the use of
nonflexible particles may be considered in light of the mechanical
properties needed to withstand the stresses on the cement sheath
during the life of the well. One of ordinary skill in the art with
the benefit of this disclosure will recognize the appropriate
balance of elastic particles and nonflexible particles to provide
the best technical and economic solution for a given
application.
[0029] The cement compositions used with the methods of the present
invention may be prepared by dry blending the elastic particles
with the cement before the addition of water, or by mixing the
elastic particles with the water before the water is added to the
cement, or by mixing the elastic particles with the cement slurry
consecutively with or after the addition of the water. In certain
preferred embodiments, the elastic particles are dry-blended with
the cement before the addition of water. In other embodiments, the
elastic particles also may be pre-suspended in water and injected
into the cement mix fluid or into the cement composition as an
aqueous slurry, if desired. In embodiments where the elastic
particles are presuspended in water before injection into the
cement composition, a preferred elastic particle comprising a
styrene divinylbenzene copolymer may be surface-modified so that it
will remain suspended in water, despite the natural tendency of
such elastic particles to float. In other embodiments where elastic
particles are used that have not been so modified, surfactants may
be added to the cement compositions, if desired, to water-wet the
surface of the elastic particles so that the elastic particles--the
density of which is less than that of water--will remain suspended
in the aqueous phase. One of ordinary skill in the art with the
benefit of this disclosure will recognize when the use of a
surfactant is appropriate with the cement compositions.
[0030] An example of a cement composition suitable for use with the
methods of the present invention comprises Class G Portland cement,
49.4% water bwoc, 20% silica fume bwoc, 20% fly ash bwoc, and 52%
elastic particles bwoc. Another example of a cement composition
suitable for use with the methods of the present invention
comprises Class G Portland cement, 39.3% water bwoc, 24%
fixed-density weighting agent, and 4.5% elastic particles bwoc.
[0031] An example of a method of the present invention is a method
of avoiding the loss of circulation of a cement composition in a
subterranean formation, comprising the steps of: providing a cement
composition comprising a base fluid, a hydraulic cement, and a
portion of elastic particles; placing the cement composition in a
well bore in a subterranean formation; permitting a portion of the
cement composition to enter openings in a region of the
subterranean formation in fluid communication with the well bore;
and permitting the portion of the cement composition to seal the
openings off from the well bore. Additional steps include, but are
not limited to, selectively placing the cement composition in a
region of the well bore that is in fluid communication with
openings in a region of the subterranean formation.
[0032] Another example of a method of the present invention is a
method of improving the ability of a cement composition to resist
the loss of circulation, comprising the step of adding to the
cement composition a portion of elastic particles.
[0033] 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 the scope of the invention.
EXAMPLE 1
[0034] A test sample was made of an exemplary embodiment of a
cement composition useful in accordance with the present invention.
To prepare Sample Composition No. 1, Class G Portland cement was
mixed with 49.4% water bwoc, 20% silica fume bwoc, 20% fly ash
bwoc, and 52% elastic particles bwoc. The density of Sample
Composition No. 1 was measured at 9 lb/gallon.
EXAMPLE 2
[0035] Example 2 compares the physical properties of Sample
Composition No. 2, which is a cement composition prepared without
elastic particles, with the physical properties of Sample
Composition No. 3, which is a cement composition that comprises
elastic particles.
[0036] Sample Composition No. 2 comprises Class G Portland cement
mixed with 39.8% water bwoc, and 24% fixed density weighting agent
bwoc. The resultant density of Sample Composition No. 2 was 18
lb/gallon.
[0037] Sample Composition No. 3 is a cement composition of the
present invention comprising Class G Portland cement mixed with
39.3% water bwoc, 24% fixed density weighting agent bwoc, and 4.5%
elastic particles bwoc. The resultant density of Sample Composition
No. 3 was 16.2 lb/gallon. This demonstrates, inter alia, that the
addition of 4.5 weight percent elastic particles provides a
resultant 11.1% decrease in the density of a cement
composition.
EXAMPLE 3
[0038] The effect of the elastic particles on the cement
compositions used in the methods of the present invention may be
illustrated by considering a hypothetical cement composition of the
present invention comprising Class H cement, further comprising 50%
aqueous base fluid bwoc, 20% POZMIX.RTM. A bwoc, 20% SILICALITE
bwoc, and 50% elastic particles bwoc, the elastic particles having
a specific gravity of about 0.41 and an isothermal compressibility
factor of about 1.5.times.10.sup.-4 (1/psi). The density of such
hypothetical cement composition at sea level is 9.2 lb/gallon. The
following equations may be used to calculate the density of the
cement composition at different depths.
[0039] The change in volume of the elastic particle as the external
pressure changes may be determined from the relationship: 1 dv = (
v p ) dp Equation 1 or dv v = 1 v ( v p ) dp = Cdp Equation 2
[0040] In Equation 2, the value "C" is the compressibility of the
elastic particle. If the elastic particle is subjected to a change
in pressure of dp, then the new volume of the elastic particle is
given by:
v.sub.new=v.sub.old+dv Equation 3
[0041] and the new density is then calculated.
[0042] From the surface to a depth of 2,500 feet, the change in
pressure is 1,129 psi, which will cause the volume of the elastic
particles to change by 17%, using Equation 2. Using Equation 3, the
density at 2,500 feet is then calculated to be 10.2 lb/gallon. The
calculated density of the hypothetical cement composition at
increasing depths is shown in Table 1 below.
1 TABLE 1 Equivalent Cement Composition Density Depth (feet)
(lb/gallon) 0 9.2 2,500 10.2 5,000 11.4 7,500 13.1
[0043] 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 depicted, 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,
alternation, 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 equivalents in all respects.
* * * * *