U.S. patent application number 13/622363 was filed with the patent office on 2013-01-17 for compositions and methods for mitigation of annular pressure buildup in subterranean wells.
This patent application is currently assigned to SCHLUMBERGER TECHNOLOGY CORPORATION. The applicant listed for this patent is Schlumberger Technology Corporation. Invention is credited to Laurent Delabroy, Emmanuel Therond, Robert Williams.
Application Number | 20130017980 13/622363 |
Document ID | / |
Family ID | 43402937 |
Filed Date | 2013-01-17 |
United States Patent
Application |
20130017980 |
Kind Code |
A1 |
Williams; Robert ; et
al. |
January 17, 2013 |
Compositions and Methods for Mitigation of Annular Pressure Buildup
in Subterranean Wells
Abstract
Compositions and methods that mitigate pressure buildup in the
annular space between two tubular bodies in subterranean wells. The
composition of the invention comprises an aqueous solution of
crosslinkable acrylamide-base polymer, a crosslinker and a gas.
Once foamed and placed in the annular space, the composition
provides a resilient, flexible, compressible and durable body that
is able to compensate for pressure increases in the annular space,
thereby protecting the integrity of the tubular bodies.
Inventors: |
Williams; Robert; (Houston,
TX) ; Therond; Emmanuel; (Paris, FR) ;
Delabroy; Laurent; (Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Schlumberger Technology Corporation; |
Sugar Land |
TX |
US |
|
|
Assignee: |
SCHLUMBERGER TECHNOLOGY
CORPORATION
Sugar Land
TX
|
Family ID: |
43402937 |
Appl. No.: |
13/622363 |
Filed: |
September 19, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12622562 |
Nov 20, 2009 |
|
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|
13622363 |
|
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Current U.S.
Class: |
507/202 |
Current CPC
Class: |
C04B 2103/0062 20130101;
C09K 8/44 20130101; C04B 26/04 20130101; C04B 14/28 20130101; C04B
26/04 20130101; C04B 14/18 20130101; C04B 14/022 20130101; C04B
14/06 20130101; C04B 24/04 20130101; C04B 14/047 20130101; C04B
14/08 20130101; C04B 38/02 20130101; C04B 14/368 20130101; C04B
14/10 20130101; C04B 40/0263 20130101; C04B 24/04 20130101; C04B
38/103 20130101; E21B 33/13 20130101; C04B 2103/0018 20130101 |
Class at
Publication: |
507/202 |
International
Class: |
C09K 8/00 20060101
C09K008/00 |
Claims
1. A composition for controlling pressure buildup within an annular
volume within a subterreanean wellbore, comprising at least one
water-soluble acrylamide polymer, a crosslinker, a gas and
water.
2. The composition of claim 1, wherein the polymer comprises one or
more members of the list comprising: polymethacrylamides,
polyacrylamides, acrylic acid-acrylamide copolymers, acrylic
acid-methacrylamide copolymers, acrylamide-sodium acrylate
copolymers, partially hydrolyzed polymethacylamides and partially
hydrolyzed polyacrylamides.
3. The composition of claim 1, wherein the polymer is
acrylamide-sodium acrylate copolymer.
4. The composition of claim 3, wherein the polymer molecular weight
is in the range from about 300,000 to 10,000,000.
5. The composition of claim 3, wherein the polymer is present in
the range between about 4% to about 7% by weight.
6. The composition of claim 1, wherein the gas comprises one or
more members of the list comprising: nitrogen, air and carbon
dioxide.
7. The composition of claim 1, wherein the gas is present at a
concentration between about 5% to 50% by volume.
8. The composition of claim 1, further comprising one or more
particulate additives chosen from the list comprising: amorphous or
crystalline silica, hematite, barite, ilmenite, manganese
tetraoxide, calcium carbonate, bentonite, attapulgite, smectite,
montmorillonite, kaolinite, illite, chlorite, zeolites,
diatomaceous earth, perlite, coal and gilsonite.
9. The composition of claim 1, wherein the crosslinker comprises at
least one water soluble chromium (III) compound.
10. The composition of claim 9, wherein the chromium (III) compound
is chromium (III) acetate.
11. The composition of claim 10, wherein the chromium (III) acetate
is present in an amount between about 0.3% to about 1.2% by
weight.
12. The composition of claim 9, further comprising one or more
carboxylate species, the carboxylate species chosen from the list
comprising: formate, acetate, proprionate, lactate, lower
substituted derivatives thereof, and mixtures thereof.
13. The composition of claim 12, wherein the carboxylate species is
sodium lactate.
14. The composition of claim 13, wherein the sodium lactate is
present in the range between about 0.25% to about 2.5% by
volume.
15. The composition of claim 1, wherein the crosslinker is one or
more members of the list consisting of: amine compounds and phenyl
compounds.
16. The composition of claim 15, wherein the amine compound is
hexamethylenetriamine.
17. The composition of claim 16, wherein the hexamethylenetriamine
is present in an amount between about 0.2% to about 0.5% by
weight.
18. The composition of claim 15, wherein the phenyl compound is
phenyl acetate.
19. The composition of claim 18, wherein the phenyl acetate is
present in an amount between about 0.2% to about 1.0% by
weight.
20. The composition of claim 15, further comprising one or more
members of the list consisting of: acetic acid, hydrochloric acid
and sodium bicarbonate.
Description
CROSS REFERENCED APPLICATION
[0001] This application is a continuation of the U.S. application
Ser. No. 12/622,562 incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] The statements in this section merely provide background
information related to the present disclosure and may not
constitute prior art.
[0003] This invention relates to compositions and methods for
treating subterranean formations, in particular, compositions and
methods to mitigate annular pressure buildup in subterranean
wells.
[0004] During the construction of a subterranean well, one or more
tubular bodies, such as casings or liners, are installed to support
the borehole and provide a conduit through which hydrocarbons or
other formation fluids may flow to the surface for recovery.
Usually, each pipe string extends to a greater depth than its
predecessor, and has a smaller diameter than its predecessor.
Primary cementing is usually performed after the installation of
each pipe string. This involves placing cement slurry in the
annular region between the exterior surface of the pipe string and
the borehole wall, and allowing it to harden. The set cement is
substantially impermeable, and bonds to the pipe and the borehole
wall. Thus, the set cement supports the pipe string and provides
hydraulic isolation. Hydraulic cements, usually Portland cement,
are typically used to cement the tubular bodies within the
wellbore. Remedial cementing operations may also be conducted,
involving plugging highly permeable zones or fractures in
wellbores, plugging cracks and holes in pipe strings, etc.
[0005] As mentioned above, multiple casing strings are usually
concentric; thus, there are annular spaces between them. Normally,
each annular volume between the casing strings is filled to some
extent with fluid that was present in the wellbore when the casing
was installed. The entire annulus between the casing strings is not
usually cemented; however, in many cases, set cement does seal the
bottom portion of each annulus.
[0006] Formation-fluid production from a well is initiated after
the strings of tubulars have been installed and primary cementing
operations have been completed. The formation fluids may include
crude oil, natural gas liquids, petroleum vapors, synthesis gas
(e.g., carbon monoxide), other gases (e.g., carbon dioxide), steam,
water or aqueous solutions. The temperatures of formation fluids
are usually higher than those further uphole. In such cases, as
formation fluids travel toward the production facility, they heat
the pipe strings and the surrounding wellbore. This will in turn
raise the temperature of fluids inside the annuli between the pipe
strings, and the fluids will tend to expand.
[0007] In many cases, such as wells on land, the fluid expansion
may be relieved at the surface. However, in offshore-well
situations in which the wellhead is submerged, both the top and
bottom of each annulus may be sealed. A typical scenario is shown
in a cross-sectional diagram (FIG. 1). A series of successive,
concentric casing strings 1 has been installed in a subterranean
wellbore. The cement sheath 2 covers the annular region between
each casing string and the formation 3. Only the casing string with
the widest diameter has been cemented to surface. The other strings
are not cemented to surface--only the regions between those casings
and the formation are covered by the cement sheath. This leaves
annular regions 4 that are not completely cemented; instead, they
are filled with other well-completion fluids such as drilling
fluid, spacer fluid, chemical wash and completion brine. Further
uphole, the annuli are sealed to prevent the fluids contained
therein from leaking into the environment.
[0008] Under these circumstances, there is no outlet for
annular-fluid expansion. When the formation fluids heat the fluid
trapped in the annulus between the casing strings, the resulting
expansion may pressurize the annulus to a level that would cause
severe wellbore damage, including damage to the cement sheath, the
casing, tubulars and other wellbore equipment. This process is
known in the art as annular pressure buildup (APB). The industry
has attempted to solve the APB problem in a variety of ways.
[0009] Foamed fluids have been used; however, operators have
encountered difficulties placing them near high-permeability
formations. In addition, the foam may not be stable over the long
term, leading to breakout of the gaseous phase and a reduction of
the fluid's ability to compensate for pressure fluctuations.
[0010] Another fluid system contains a polymerizable monomer, for
example methyl methacrylate (MMA). After placement in the annulus
between two casings, the MMA is made to crosslink when annular
temperature increases due to production of hot formation fluids.
The resulting polymer is significantly more dense than the monomer;
as a result, the fluid volume decreases, and the pressure inside
the sealed annulus also decreases. The amount of monomer is chosen
such that the pressure decrease in the annulus will be sufficient
to mitigate the APB. The fluid may comprise a gas-generating agent.
Liberation of gas inside the sealed annulus after fluid placement
provides a compressible gas pocket. The fluid may also comprise a
porous foam material such as polystyrene or polyurethane.
[0011] Syntactic foam is a wrapable or sprayable foam that is
impregnated with cenospheres or glass microspheres. The foam
typically covers the tubular body across the interval where APB is
anticipated. The hollow spheres are designed to rupture at a
predetermined pressure, creating more volume in the annulus.
However, this approach is problematic for two reasons. First, the
foam may break off during the tubular-body installation, creating
obstructions in the annulus that may impede proper fluid placement.
Second, the foam is not resilient--it works only once to reduce
annular volume.
[0012] Fluids that contain hollow glass microspheres have been
reported. The glass microspheres are available in several grades
with failure ratings between about 4,000 and 10,000 psi. Operators
choose grades that are most appropriate for the anticipated APB.
This approach can be problematic when the microsphere-containing
fluid is pumped around a casing shoe during a primary-cementing
operation. The bottomhole pressure may exceed the collapse pressure
of the glass spheres, and the resulting collapse of the spheres
destroys the utility of the fluid. Situations may also occur in
which an operator chooses a grade of microspheres that can survive
the bottomhole pressure, but the anticipated APB further up the
annulus is lower than the microsphere-failure rating. In such
situations, the microspheres will not rupture when needed to
control APB, potentially resulting in casing failure.
[0013] Several mechanical methods for controlling APB have been
developed, including burst disks and hollow centralizer elements.
Once ruptured, burst-disk assemblies may require well reentry for
replacement. Such operations involve considerable downtime which
can be very expensive in offshore environments. Hollow centralizer
elements are sealed by valves or rupture disks. When APB occurs,
the seals rupture and allow fluid influx into the hollow element to
relieve the pressure. These centralizers provide a limited amount
of volume mitigation, and the effects of fluid influx on the
structural integrity of the centralizer is unclear.
[0014] It is therefore desirable to develop a system for
controlling APB that overcomes the problems mentioned above.
SUMMARY OF THE INVENTION
[0015] The first aspect of the invention is a composition for
controlling annular pressure buildup between two tubular bodies
within a subterranean wellbore. The composition comprises an
aqueous solution of crosslinkable acrylamide-base polymer, a
crosslinker and a gas. Such gas-bearing fluids are known in the art
as being "foamed" or "energized." Nitrogen is the preferred gas;
however, other gases such as (but not limited to) air and carbon
dioxide are also envisioned. The preferred amount of gas in the
solution, or "quality," is between about 5% to about 50% by
volume.
[0016] A copolymer of acrylamide and sodium acrylate is the
preferred crosslinkable polymer and, henceforth, will be referred
to by the acronym ASAC.
[0017] One embodiment of the first aspect of the invention
comprises ASAC, a chromium (III) crosslinker, a gas and water. The
crosslinker is preferably a water-soluble chromium (III) compound,
most preferably chromium (III) acetate. The chromium (III) acetate
concentration may vary from about 0.2% to about 1.2% by weight,
preferably between about 0.3% to about 1.2% by weight.
[0018] Another embodiment of the first aspect of the invention
comprises ASAC, a gas, water and a crosslinker comprising amine and
phenyl compounds. The preferred amine compound is
hexamethylenetriamine, preferably present at concentrations ranging
from about 0.2% to 0.5% by weight. The preferred phenyl compound is
phenyl acetate, preferably present at concentrations ranging from
about 0.2% to 1.0% by weight. The fluid may further comprise an
activator to control the working time, and may also comprise a
high-temperature stabilizer. At fluid temperatures lower than about
52.degree. C., the preferred activator is hydrochloric acid,
preferably present in an amount up to about 0.5% by weight. At
fluid temperatures higher than about 52.degree. C., the preferred
activator is acetic acid, preferably present at a concentration up
to about 0.4% by weight. A stabilizer, preferably sodium
bicarbonate, may be necessary at fluid temperatures above about
60.degree. C.
[0019] Both of the above embodiments may also contain particulate
additives. These additives may be added for a number of reasons: to
adjust the fluid density, to increase the strength of the
crosslinked gel and as an extender to reduce fluid cost. The
particulate additives envisioned in the invention include (but are
not limited to) amorphous or crystalline silica, hematite, barite,
ilmenite, manganese tetraoxide, calcium carbonate, bentonite,
attapulgite, smectite, montmorillonite, kaolinite, illite,
chlorite, zeolites, diatomaceous earth, perlite, coal and
gilsonite.
[0020] The second aspect of the invention is a method for
controlling pressure buildup within an annular volume between two
tubular bodies in a subterranean wellbore. The method comprises the
following steps: (1) preparing a volume of a composition described
by the first aspect of the invention, the volume being sufficient
to fill at least a portion of the annular volume; (2) transporting
the composition to, and filling at least a portion of, the annular
volume; (3) sealing the annular volume; (4) allowing the polymer of
the composition to crosslink and form a gel; (5) heating the
annular volume, thereby increasing the pressure inside the annular
volume; and (6) allowing the composition described by the first
aspect of the invention to compress and compensate for the pressure
increase inside the annular volume.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] For a more complete understanding of the present invention,
and the advantages thereof, reference is now made to the following
descriptions taken in conjunction with the accompanying figures, in
which:
[0022] FIG. 1 is a diagram illustrating annular volumes between two
tubular bodies in a subterranean well, in which annular pressure
buildup may occur.
[0023] FIG. 2 is a plot showing the effect of sodium lactate on the
working time of a fluid containing a crosslinkable acrylamide-base
polymer.
[0024] FIG. 3 is a plot showing the effect of glacial acetic acid
on the working time of a fluid containing a crosslinkable
acrylamide-base polymer.
[0025] FIG. 4 is a plot showing the effect of 28% hydrochloric acid
on the working time of a fluid containing a crosslinkable
acrylamide-base polymer.
[0026] FIG. 5 is a diagram of the compression-cell device employed
during experiments described in Examples 1 and 2.
[0027] FIG. 6 is a plot associated with Example 1, showing the
volume response of a foamed crosslinked acrylamide-base polymer gel
to repeated pressurizations and depressurizations.
[0028] FIG. 7 is a plot associated with Example 2, comparing the
compressibility of a foamed crosslinked acrylamide-base polymer gel
to a foamed spacer fluid and a spacer fluid containing hollow glass
microspheres.
DETAILED DESCRIPTION
[0029] At the outset, it should be noted that in the development of
any such actual embodiment, numerous implementation--specific
decisions must be made to achieve the developer's specific goals,
such as compliance with system related and business related
constraints, which will vary from one implementation to another.
Moreover, it will be appreciated that such a development effort
might be complex and time consuming but would nevertheless be a
routine undertaking for those of ordinary skill in the art having
the benefit of this disclosure. In addition, the composition
used/disclosed herein can also comprise some components other than
those cited. In the summary of the invention and this detailed
description, each numerical value should be read once as modified
by the term "about" (unless already expressly so modified), and
then read again as not so modified unless otherwise indicated in
context. Also, in the summary of the invention and this detailed
description, it should be understood that a concentration range
listed or described as being useful, suitable, or the like, is
intended that any and every concentration within the range,
including the end points, is to be considered as having been
stated. For example, "a range of from 1 to 10" is to be read as
indicating each and every possible number along the continuum
between about 1 and about 10. Thus, even if specific data points
within the range, or even no data points within the range, are
explicitly identified or refer to only a few specific, it is to be
understood that inventors appreciate and understand that any and
all data points within the range are to be considered to have been
specified, and that inventors possessed knowledge of the entire
range and all points within the range.
[0030] The first aspect of the invention is a composition for
controlling annular pressure buildup between two tubular bodies
within a subterranean wellbore. The composition comprises an
aqueous solution of crosslinkable acrylamide-base polymer, a
crosslinker and a gas. Such gas-bearing fluids are known in the art
as being "foamed" or "energized." Nitrogen is the preferred gas;
however, other gases such as (but not limited to) air and carbon
dioxide are also envisioned. The preferred amount of gas in the
solution, or "quality," is between about 5% to about 50% by volume.
In this instance, quality is expressed in terms of the volume of
gas that would be present in the solution at atmospheric
pressure.
[0031] When the polymer crosslinks, the solution transforms into a
durable and flexible gel that encapsulates the gaseous phase. The
resulting composition is compressible, and is sufficiently strong
to maintain gas entrainment during multiple
pressurization/depressurization cycles. When present in a closed
annulus as described earlier, the gas-entrained gel will compress
in response to APB, relieving pressure that would otherwise be
exerted against the tubular bodies.
[0032] ASAC is the preferred crosslinkable polymer. The polymer
molecular weight is preferably between about 300,000 to 10,000,000,
and most preferably between about 300,000 to 1,000,000. The
preferred concentration range is between about 1% to 8% by weight,
and most preferably between about 4% and 7% by weight.
[0033] Those skilled in the art will appreciate that other
acrylamide-base polymers may be used. Examples include, but are not
limited to, polymethacrylamides, polyacrylamides, acrylic
acid-acrylamide copolymers, acrylic acid-methacrylamide copolymers,
partially hydrolyzed polymethacylamides and partially hydrolyzed
polyacrylamides.
[0034] One embodiment of the first aspect of the invention
comprises ASAC, a chromium (III) crosslinker, a gas and water. The
crosslinker is preferably a water soluble chromium (III) compound,
most preferably chromium (III) acetate. The chromium (III) acetate
concentration may vary from about 0.2% to about 1.2% by weight,
preferably between about 0.3% to about 1.2% by weight. As shown in
Table 1, the optimal ASAC/chromium (III) acetate ratio varies
according to the anticipated service temperature. This is necessary
to maximize gel stability.
TABLE-US-00001 TABLE 1 Optimal concentrations of ASAC and chromium
(III) acetate at various fluid temperatures. Fluid Temper- ASAC (MW
= 500K) Cr (III) Acetate ASAC/Cr (III) ature (.degree. C.) (wt %)
(wt %) Acetate Ratio <60 4 0.32 12.5/1 60-91 5 0.5 10/1 91-107 5
0.63 8/1 107-121 6-7 1.0-1.2 6/1
[0035] The pumping time may be adjusted by adding a delay agent
comprising one or more carboxylate species including (but not
limited to) formate, acetate, proprionate, lactate, lower
substituated derivatives thereof, and mixtures thereof. The
preferred delay agent is sodium lactate, preferably added at
concentrations ranging from about 0.2% to about 2.6% by weight. As
shown in FIG. 2, addition of sodium lactate can significantly
extend the working time of the solution when increasing
temperature.
[0036] Another embodiment of the first aspect of the invention
comprises ASAC, a gas, water and a crosslinker comprising amine and
phenyl compounds. The preferred amine compound is
hexamethylenetriamine, preferably present at concentrations ranging
from about 0.2% to 0.5% by weight. The preferred phenyl compound is
phenyl acetate, preferably present at concentrations ranging from
about 0.2% to 1.0% by weight. The fluid may further comprise an
activator to control the working time, and may also comprise a
high-temperature stabilizer. At fluid temperatures lower than about
52.degree. C., the preferred activator is hydrochloric acid,
preferably present in an amount up to about 0.5% by weight. At
fluid temperatures higher than about 52.degree. C., the preferred
activator is acetic acid, preferably present at a concentration up
to about 0.4% by weight. A stabilizer, preferably sodium
bicarbonate, may be necessary at fluid temperatures above about
60.degree. C. Optimal base-fluid compositions and performance data
are presented in Tables 2 and 3 and FIGS. 3 and 4.
TABLE-US-00002 TABLE 2 Optimal concentrations of ASAC,
hexamethylenetriamine, phenyl acetate, glacial acetic acid and
sodium bicarbonate at various fluid temperatures. Glacial Sodium
Fluid ASAC Hexamethy- Phenyl Acetic Bicar- Temperature (MW = 500K)
lenetriamine Acetate Acid bonate (.degree. C.) (wt %) (wt %) (wt %)
(wt %) (wt %) 52-60 4 0.2-0.3 0.2-0.6 0.2-0.5 0 60-93 5 0.2-0.4
0.2-0.8 0.1-0.4 0-1 93-107 5 0.2-0.4 0.2-0.8 0-0.4 0-1 107-121 6
0.3-0.5 0.3-1.0 0 2 >121 7 0.3-0.5 0.3-1.0 0 2
TABLE-US-00003 TABLE 3 Optimal concentrations of ASAC,
hexamethylenetriamine, phenyl acetate, and hydrochloric acid at
fluid temperatures lower than 52.degree. C. Fluid ASAC Hexamethy-
Phenyl Temperature (MW = 500K) lenetriamine Acetate Hydrochloric
(.degree. C.) (wt %) (wt %) (wt %) Acid (wt %) <52 4 0.2 0.2-0.4
0.1-0.5
[0037] Both of the above embodiments may also contain particulate
additives. These additives may be added for a number of reasons: to
adjust the fluid density to increase the strength of the
crosslinked gel and as an extender to reduce fluid cost. The
particulate additives envisioned in the invention include (but are
not limited to) amorphous or crystalline silica, hematite, barite,
ilmenite, manganese tetraoxide, calcium carbonate, bentonite,
attapulgite, smectite, montmorillonite, kaolinite, illite,
chlorite, zeolites, diatomaceous earth, perlite, coal and
gilsonite.
[0038] The second aspect of the invention is a method for
controlling pressure buildup within an annular volume between two
tubular bodies in a subterranean wellbore. The method comprises the
following steps: (1) preparing a volume of a composition described
by the first aspect of the invention, the volume being sufficient
to fill at least a portion of the annular volume; (2) transporting
the composition to, and filling at least a portion of, the annular
volume; (3) sealing the annular volume; (4) allowing the polymer of
the composition to crosslink and form a gel; (5) heating the
annular volume, thereby increasing the pressure inside the annular
volume; and (6) allowing the composition described by the first
aspect of the invention to compress and compensate for the pressure
increase inside the annular volume.
[0039] During Step 1, the base fluid of the composition may be
prepared in a typical batch mixer or a cementing skid. The
preferred acrylamide-base polymer in the composition is ASAC. The
polymer molecular weight is preferably between about 300,000 to
10,000,000, and most preferably between about 300,000 to 1,000,000.
The preferred concentration range is preferably between about 1% to
8% by weight, and most preferably between about 4% and 7% by
weight. It will be appreciated that other acrylamide-base polymers
may be used, including (but not limited to) polymethacrylamides,
polyacrylamides, acrylic acid-acrylamide copolymers, acrylic
acid-methacrylamide copolymers, partially hydrolyzed
polymethacylamides and partially hydrolyzed polyacrylamides.
[0040] One embodiment of a composition suitable for the method
comprises ASAC, a chromium (III) crosslinker, a gas and water. The
crosslinker is preferably a water soluble chromium (III) compound,
most preferably chromium (III) acetate. The chromium (III) acetate
concentration may vary from about 0.2% to about 1.2% by weight,
preferably between about 0.3% to about 1.2% by weight. The pumping
time may be adjusted by adding a delay agent comprising one or more
carboxylate species including (but not limited to) formate,
acetate, proprionate, lactate, lower substituated derivatives
thereof, and mixtures thereof. The preferred delay agent is sodium
lactate, preferably added at concentrations ranging from about 0.2%
to about 2.6% by weight.
[0041] Another embodiment of a composition suitable for the method
comprises ASAC, a gas, water and a crosslinker comprising amine and
phenyl compounds. The preferred amine compound is
hexamethylenetriamine, preferably present at concentrations ranging
from about 0.2% to 0.5% by weight. The preferred phenyl compound is
phenyl acetate, preferably present at concentrations ranging from
about 0.2% to 1.0% by weight. The fluid may further comprise an
activator to control the working time, and may also comprise a
high-temperature stabilizer. At fluid temperatures lower than about
52.degree. C., the preferred activator is hydrochloric acid,
preferably present in an amount up to about 0.5% by weight. At
fluid temperatures higher than about 52.degree. C., the preferred
activator is acetic acid, preferably present at a concentration up
to about 0.4% by weight. A stabilizer, preferably sodium
bicarbonate, may be necessary at fluid temperatures above about
60.degree. C.
[0042] At this time, particulate additives may also be included in
the composition. The particulate additives may include (but not be
limited to) amorphous or crystalline silica, hematite, barite,
ilmenite, manganese tetraoxide, calcium carbonate, bentonite,
attapulgite, smectite, montmorillonite, kaolinite, illite,
chlorite, zeolites, diatomaceous earth, perlite, coal and
gilsonite.
[0043] Using typical field equipment for preparing foamed cement
slurries, a gas is mixed with the base fluid of the composition to
achieve the desired quality. The preferred quality is between about
5% and 50%. A thorough description of foamed-cement design and
preparation may be found in the following publication: Rozieres, J.
and Griffin, T. J.: "Foamed Cement," in Nelson E. B. (ed.) Well
Cementing, Elsevier, Amsterdam (1990) 14-1-14-19.
[0044] During Step 2, the energized acrylamide-base fluid is
transported into the wellbore such that it fills at least a portion
of the annular volume. This may be accomplished by pumping the
fluid into the annulus during a primary-cementing operation. The
primary cementing operation may be performed by pumping the fluid
down the tubular and up the annulus, or by pumping the fluid
directly into the annulus from the top of the string.
Transportation of the energized acrylamide-base fluid may also be
accomplished by pumping the fluid during a remedial-cementing
operation. One example may be to perforate through one of the two
casing strings, and pump the fluid directly into the annular
region.
[0045] It will be understood by those skilled in the art that, as
shown in FIG. 1, the annular region 4 may not be completely filled
by the composition of the invention. Other fluids such as drilling
fluid, spacer fluid, chemical wash and completion fluid may share
this region.
[0046] During Step 3, the annular volume is sealed. This may
comprise closing valves, allowing a hydraulic cement slurry to set
and strengthen below the annular region 4, or both.
[0047] During Step 4, the polymer in the composition of the
invention is allowed to crosslink, thereby forming a gel that
encapsulates the gas of the composition. This process results in
the formation of a compressible body within the annular region
4.
[0048] During Step 5, the production of formation fluids commences.
The temperature of the formation fluids may be higher than that of
the fluids inside the annular region 4. In such cases, the fluids
in the annular region are heated. The resulting fluid expansion
increases the pressure in the annular region.
[0049] During Step 6, the composition of the invention compresses
in response to the pressure increase described in Step 5. This
compression compensates for the pressure increase, relieving
pressure that would otherwise be exerted against the tubular
bodies.
EXAMPLES
[0050] The following examples serve to further illustrate the
invention. Each example makes use of a device shown in FIG. 5. The
device comprises a hollow cylindrical cell 5, a piston 6 and a
loading rod 7. A test fluid 8 is placed inside the cell. A force 9
is exerted by the loading rod, causing the piston to compress the
test fluid. The operator measures the displacement of the piston
relative to force applied by the loading rod. Such measurements
provide information about how the test fluid responds to an applied
pressure.
[0051] This device was constructed by the inventors. The hollow
cylindrical cell is a standard Baroid-type fluid-loss cell. One end
the cell is sealed. The other end is sealed by a piston that
travels through the cell interior. The outer edge of the piston is
fitted with a rubber 0-ring to maintain a hydraulic seal. The
internal diameter of the cell is 5.9 cm (2.2 in), and the height
between the piston and the bottom of the cell is 8.1 cm (3.2 in). A
bar is fixed to the outer side of piston to act as the loading rod.
The apparatus is placed in a hydraulic press. The moving platen of
the hydraulic press applies force on the loading rod, which in turn
forces the piston into the cell interior.
[0052] During an experiment, sufficient test fluid is placed in the
cell to completely fill the space between the bottom of the cell
and the piston [200 cm.sup.3 (12.16 in.sup.3)]. The piston is
inserted into the cell, the loading bar is attached, and the
assembly is placed between the two platens in a hydraulic press.
The press applies force at a loading rate of 25.6 MPa/min (4000
lbf/min) While the moving plate of the hydraulic press applies
force on the loading rod, two measurements are taken continuously:
(1) the force required to move the piston into the cell; and (2)
the displacement of the piston into the cell. These data allow
calculation of the test-fluid volume reduction and the pressure
inside the cell.
Example 1
[0053] A fluid was prepared with the following composition.
TABLE-US-00004 Material Mass Quantity Deionized Water 661 g 661 mL
ALCOFLOOD 254S 39.8 g 39.8 g Chromium (III) Acetate (50 8.43 g 6.48
mL wt % solution) Sodium Lactate (60 wt % 6.31 g 4.74 mL solution)
Surfactant 1 12.0 g 11.9 mL Surfactant 2 12.7 g 11.9 mL Barite 1176
g 1176 g
[0054] ALCOFLOOD 254S is acrylamide sodium-acrylate polymer,
available from Ciba Specialty Chemicals. The molecular weight was
about 500,000, and the degree of hydrolysis was about 5%.
Surfactant 1 was a blend of the following components: 85% ammonium
fatty alcohol ether sulfate and 15% ethylene glycol monobutyl
ether. Surfactant 2 was an aqueous mixture of polyglycols,
oxyalkylates and methanol (CAS Number R597-1).
[0055] The base fluid was prepared as follows. The water, ALCOFLOOD
254S, chromium (III) acetate solution and sodium lactate solution
were mixed and blended in a paddle mixer for 30 minutes. Next, the
barite was added, and the mixture was stirred 30 additional minutes
in the paddle mixer. The density of the base fluid was 1920
kg/m.sup.3 (16.0 lbm/gal).
[0056] The mixture was transferred to a closed-cup foam blender,
and Surfactants 1 and 2 were added. Sufficient open volume was left
in the blender to achieve a foam quality of 27%. The cup was
sealed, and the mixture was sheared at 12,000 RPM to create a
stable foam.
[0057] The foam was then transferred to the test cell, and allowed
to cure for 24 hours in a 38.degree. C. (100.degree. F.) water
bath. The acrylamide-base polymer crosslinked during the curing
period, creating a foamed gel.
[0058] The piston and loading rod were fitted into the test cell,
and the assembly was installed in a hydraulic press. Force was
applied that was sufficient to reduce the volume inside the test
cell by 33%. As a result, the pressure inside the cell increased to
1.8 MPa (260 psi). Thirty cycles were performed, and the results
were essentially the same. FIG. 6 shows five of the cycles. This
demonstrates the resiliency of the foamed gel, and illustrates its
ability to mitigate several APB events without substantial
degradation.
Example 2
[0059] A foamed gel as described in Example 1 was prepared. Two
additional fluid systems were prepared for comparative purposes.
Both were made from the same base fluid--a 1680-kg/m.sup.3
(14.0-lbm/gal) MUDPUSH.TM. II spacer, available from Schlumberger.
The fluid composition is shown below.
TABLE-US-00005 Material Mass Quantity Deionized Water 637 g 637 mL
MUDPUSH II Spacer Mix 9.9 g 9.9 g Barite 779 g 779 g
[0060] A first MUDPUSH II spacer was foamed to a quality of 27%,
using a surfactant system described below.
TABLE-US-00006 Material Mass Quantity Surfactant 1 10.7 g 10.6 mL
Surfactant 2 11.3 g 10.6 mL Surfactant 3 44.4 g 42.3 mL
Surfactants 1 and 2 are described in Example 1. Surfactant 3 was a
blend of 80% di-secondary butyl phenol with 10 moles EO, 15% water
and 5% methanol.
[0061] A second MUDPUSH II spacer contained 30% hollow glass
microspheres by volume of solids, with a crush strength of 34.5 MPa
(5000 psi). The glass microspheres were available from 3M.
[0062] Each of the three fluids was tested in the compression cell
described above. The pressure buildup in the cell was monitored as
the fluid was compressed by the piston. The results are shown in
FIG. 7. The spacer fluid containing hollow glass microspheres was
able to withstand about 5 vol % compression before pressure buildup
commenced. The microspheres collapsed, and the fluid could no
longer compensate for further volume reduction. The foamed spacer
behaved as a compressible fluid up about 15% volume reduction,
after which the pressure increased rapidly. Finally, the foamed
acrylamide-base gel was able to compensate for about 25% volume
reduction, owing to the encapsulated gas and the compressibility of
the crosslinked gel.
[0063] Although various embodiments have been described with
respect to enabling disclosures, it is to be understood the
invention is not limited to the disclosed embodiments. Variations
and modifications that would occur to one of skill in the art upon
reading the specification are also within the scope of the
invention, which is defined in the appended claims.
* * * * *