Note: Descriptions are shown in the official language in which they were submitted.
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MODIFIED CELLULOSIC POLYMER FOR IMPROVED WELL BORE
FLUIDS
[0001] The present invention relates to methods for treating
subterranean formations. More particularly, the present invention relates
to drilling, completion, or workover fluids that comprise nonionic cellulose
ether polymers and their use in subterranean applications.
BACKGROUND
[0002] Many subterranean treatments require viscosified fluids.
For instance, viscosified fluids are used in drilling fluids, completion
fluids,
workover fluids, as well as other treating fluids. The term "drilling fluid"
as used herein refers to any of a number of liquid and gaseous fluids and
mixtures of fluids and solids (as solid suspensions, mixtures and
emulsions of liquids, gases and solids) used in operations to drill
boreholes into the earth. The term drilling fluid includes "drill-in fluids."
The term "completion fluid" as used herein refers to a fluid with a low
solids content that may be used to "complete" an oil or gas well, for
example, to facilitate final operations prior to initiation of production,
such
as setting screens production liners, packers, downhole valves or shooting
perforations into the producing zone. In some embodiments, a
completion fluid may be used to control a well should downhole hardware
fail, without damaging the producing formation or completion
components. The term "workover fluid" as used herein refers to well-
control fluids, for example a brine, that is used during workover
operations.
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[0003] Polymeric viscosifying agents, such as cellulose
derivatives, guar gums, biopolymers, polysaccharides, synthetic
polymers, and the like, have previously been added to treatment fluids to
obtain a desired viscosity. Viscoelastic surfactants have also been added
to treatment fluids to increase the viscosity thereof. Maintaining sufficient
viscosity in these treatment fluids may be important for a number of
reasons. For example, maintaining sufficient viscosity is important in
drilling operations, for example, to provide hydrostatic pressure to
prevent formation fluids from entering into the well bore, keep the drill bit
cool and clean during drilling, carry out drill cuttings, and suspend the
drill cuttings while drilling is paused and when the drilling assembly is
brought in and out of the hole. Also, maintaining sufficient viscosity may
be important to control and/or reduce fluid loss into the formation.
Moreover, a treatment fluid of a sufficient viscosity may be used to divert
the flow of fluids present within a subterranean formation (egg., formation
fluids, other treatment fluids) to other portions of the formation, for
example, by "plugging" an open space within the formation. At the same
time, while maintaining sufficient viscosity of the treatment fluid often is
desirable, it also may be desirable to maintain the viscosity of the
treatment fluid in such a way that the viscosity may be reduced at a
particular time, inter alia, for subsequent recovery of the fluid from the
formation.
[0004] Commonly used cellulose-based viscosifying agents are
generally not believed to be thermally stable and easily solubilized.
Biopolymers are frequently used instead of cellulose in treatment fluids
due to their favorable water solubility and thermal stability, however, use
of such biopolymers can be problematic because they leave residue
behind. After completing a treatment, remedial treatments may be
required to remove the residue so that the wells may be placed into
production. For example, a chemical breaker, such as an acid, oxidizer,
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or enzyme may be used to either dissolve the solids or reduce the
viscosity of the treatment fluids. In many instances, however, use of a
chemical breaker to remove the residue from inside the well bore and/or
the formation matrix may be ineffective due to the properties of such
biopolymers.
Furthermore, excessive use of chemical breakers to
degrade such polymers may be corrosive to downhole tools and may leak
off into the formation, carrying undissolved fines that may plug and/or
damage the formation or may produce undesirable reactions with the
formation.
SUMMARY
[0005] The present invention relates to methods for treating
subterranean formations. More particularly, the present invention relates
to drilling, completion, or workover fluids that comprise nonionic cellulose
ether polymers and their use in subterranean applications.
[0006] According to one aspect of the present invention there is
provided a method comprising: providing a drilling fluid, completion
fluid, or workover fluid comprising an aqueous base fluid and a nonionic
cellulose ether polymer having hydroxyethyl groups and being further
substituted with one or more hydrophobic substituents, wherein the cellulose
ether has at least one of the following properties (a), (b) or (c):
(a) a retained dynamic viscosity, %rlacv25, of at least 30
percent, wherein %nuns = [dynamic solution viscosity at 80 C / dynamic
solution viscosity at 25 C] x 100, the dynamic solution viscosity at 25 C and
80 C being measured as 1 % aqueous solution;
(b) a storage modulus of at least 15 Pascals at 25 C and a
retained storage modulus, %G 801n, of at least 12 percent, wherein %G80125 =
[storage modulus at 80 C / storage modulus at 25 C] x 100, the storage
modulus at 25 C and 80 C being measured as a 1 % aqueous solution;
(c) a critical association concentration of less than 15 ppm as
measured by light-scattering, and
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placing the drilling fluid, completion fluid, or workover fluid in a
subterranean formation.
[0007] Preferably,
the method comprises: providing a drilling
fluid comprising an aqueous base fluid and a nonionic cellulose ether
polymer having hydroxyethyl groups and being further substituted with one or
more hydrophobic substituents, wherein the cellulose ether has at least one of
the following properties (a), (b) or (c):
(a) a retained dynamic viscosity, Woriaons, of at least 30 percent, wherein
%n80125 = {dynamic solution viscosity at 80 C / dynamic solution viscosity
at 25 C] x 1001 the dynamic solution viscosity at 25 C and 80 C being
measured as 1 % aqueous solution;
(b) a storage modulus of at least 15 Pascals at 25 C and a
retained storage modulus, %G. 80/25r of at least 12 percent, wherein %G. 80/25
=
[storage modulus at 80 C / storage modulus at 25 C] X 100, the storage
modulus at 25 C and 80 C being measured as a 1 % aqueous solution;
[0008] (c) a
critical association concentration of less than 15 ppm
as measured by light-scattering; and drilling a well bore in a formation in
an operation comprising the drilling fluid.
[0009] Preferably, the method may comprise the step of placing
the drilling fluid, completion fluid, or workover fluid in the subterranean
formation is part of a subterranean operation selected from the group
consisting of an underbalanced drilling operation, an overbalanced drilling
operation, and a completion operation.
[0010] The subterranean formation may comprise a bottom hole
temperature of up to and including about 275 F (135 C). Preferably,
the subterranean formation comprises a bottom hole temperature of 200
F (93 C) or more and/or a pressure of at least 5,000 psi.
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[0011] The aqueous base fluid of the present invention may be
selected from the group consisting of fresh water, salt water, brine,
seawater, and any combinations thereof.
[0012] Preferably, the nonionic cellulose ether may be present in
the drilling fluid, completion fluid, or workover fluid in an amount in the
range of about 0.01% to about 15% by weight of the drilling fluid,
completion fluid, or workover fluid.
[0013] Preferably, the nonionic cellulose ether polymer has a
molecular weight in the range of from about 500,000 to 10,000,000.
Preferably, the nonionic cellulose ether polymer is crosslinked with a
metal ion.
[0014] The drilling fluid, completion fluid, or workover fluid of
the present invention may maintain thermal stability and gel strength at
temperatures up to about 350 F (177 C).
[0015] The nonionic cellulose ether polymer according of the
present invention may maintain the structure in a stress range exceeding
about 12 Pa.
[0016] Preferably, the nonionic cellulose ether polymer is
modified by the addition of a hydrocarbon group having from about 1 to
about 22 carbon atoms. The hydrocarbon group may be selected from the
group consisting of a linear alkyl, a branched alkyl, an alkenyl, an aryl, an
alkylaryl, an arylalkyl, a cycloalkyl, and a mixture thereof.
[0017] Preferably, the drilling fluid, completion fluid, or workover
fluid comprises additional additives selected from the group consisting of
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a defoamer, a surfactant, a crosslinking agent, a proppant particulate, a
gravel particulate, a pH-adjusting agent, a pH buffer, a breaker, a
delinker, a catalyst, and combinations thereof.
[0018] Preferably, the fluid provided is a drilling fluid and the
step of placing the drilling fluid may comprises the step of drilling a well
bore in a formation in an operation comprising the drilling fluid.
[0019] According to another aspect of the present invention,
there is provided a method comprising:
providing a drilling fluid comprising an aqueous base fluid and a
nonionic cellulose ether polymer having hydroxyethyl groups and being further
substituted with one or more hydrophobic substituents, wherein the cellulose
ether has at least one of the properties (a), (b) or (c):
(a) a retained dynamic viscosity, 130-./ n
80/25, of at least 30 percent,
wherein
%n80/25 --= [dynamic solution viscosity at 80 C / dynamic solution viscosity
at
25 C] x 100, the dynamic solution viscosity at 25 C and 80 C being measured
as 1 % aqueous solution;
(b) a storage modulus of at least 15 Pascals at 25 C and a retained
storage modulus, %G '80/25, of at least 12%, wherein %G sons = [storage
modulus at 80 C / storage modulus at 25 C] X 100, the storage modulus at
25 C and 80 C being measured as a 1 % aqueous solution;
(c) a critical association concentration of less than 15 ppm as
measured by light-scattering; and
drilling a well bore in a formation in an operation
comprising the drilling fluid.
(0020] Preferably,
the drilling fluid is placed in the subterranean
formation as part of a subterranean operation selected from the group
consisting of an underbalanced drilling operation, arid an overbalanced
drilling operation. The drilling fluid may comprise a hydrophobically
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modified hydroxyethylcellose in an amount in the range of about 0.01%
to about 15% by weight of the drilling fluid. Preferably, the drilling fluid
be able to maintain thermal stability and gel strength at temperatures up
to about 350 F (177 C).
[0021] 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 various aspects of the invention that follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] A more complete understanding of the present disclosure
and advantages thereof may be acquired by referring to the following
description taken in conjunction with the accompanying drawings,
wherein:
[0023] Figure 1 is a graphical representation of the rheological
performance of a fluid containing nonionic cellulose ether polymer in
various brines.
[0024] Figures 2A-B are graphical representations of the
rheological performance of a fluid containing nonionic cellulose ether
polymer versus various other viscosifying agents in 10 ppg of NaBr.
[0025] Figures 3A-B are graphical representations of the
rheological performance of a fluid containing nonionic cellulose ether
polymer versus various other viscosifying agents in 10 ppg of NaBr post
hot-roll at 220 F (104 C).
[0026] Figures 4A-B are graphical representations of the
rheological performance of a fluid containing nonionic cellulose ether
polymer versus various other viscosifying agents in 13.5 ppg of CaBr2.
[0027] Figures 5A-B are graphical representations of the
rheological performance of a fluid containing nonionic cellulose ether
polymer versus various other viscosifying agents in lOppg of CaBr2 post
hot-roll at 220 F (104 C).
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[0028] Figures 6A-B are graphical representations of the
rheological performance of a fluid containing nonionic cellulose ether
polymer versus various other viscosifying agents in 15.5 ppg Ca/ZnBr2.
[0029] Figures 7A-B show the temperature profiles for the
nonionic cellulose ether polymer versus various other viscosifying agents.
[0030] Figures 8A-B are graphical representations of the
rheological performance of a fluid containing nonionic cellulose ether
polymer and a defoamer.
[0031] Figure 9 depicts the dynamic rheological studies
performed to evaluate the storage (G') and loss (G") moduli of nonionic
cellulose ether polymer versus Xanthan and unmodified
hydroxyethylcelluiose.
[0032] Figure 10 depicts an evaluation of thermal stability via
temperature cycling to simulate drilling conditions for the nonionic
cellulose ether polymer.
[0033] Figure 11 is a graphical representation of the breakdown
of nonionic cellulose ether polymer in the presence of heat and acid.
[0034] While the present invention is susceptible to various
modifications and alternative forms, specific aspects thereof have been
shown by way of example in the figures and are herein described in
detail. It should be understood, however, that the description herein of
specific aspects is not intended to limit the invention to the particular
forms disclosed, but on the contrary, the intention is to cover all
modifications, equivalents, and alternatives falling within the spirit and
scope of the invention as defined by the appended claims.
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DETAILED DESCRIPTION
[0035] The present invention relates to methods for treating
subterranean formations. More particularlyõ the present invention
relates to drilling, completion, or workover fluids that comprise nonionic
cellulose ether polymers and their use in subterranean applications.
[0036] In the nonionic cellulose ether polymers used in the drilling,
completion, or workover fluids of the present invention may provide
better solubility of the polymer and have greater thermal stability as
compared to other fluids, while maintaining the removal capabilities of
traditional unmodified hydroxyethylcellulose in drilling, completion, or
workover operations. The drilling, completion, or workover fluids may
have greater gel strength during the operations, but require relatively
quick removal of the gels. The nonionic cellulose ether polymers of the
present invention may exhibit excellent suspension capabilities above
conventional unmodified hydroxyethylcellulose.
[0037] Another potential advantage of the methods of the
present invention is that they may allow use in subterranean formations
where complete removal of gels is needed by acid degradation. Another
potential advantage of the methods of the present invention is the
increased suspension of the nonionic cellulose ether polymer in a drilling,
completion, or workover fluid. The increased suspension of the nonionic
cellulose ether polymer in a drilling, completion, or workover fluid may
lead to better thermal stability that in turn, is believed to aid in clay
inhibition, especially in drilling, completion, and workover operations.
Drilling, completion, and workover fluids comprising a nonionic cellulose
ether polymer described herein may have increased viscosity efficiency
when compared to other commonly used polymeric viscosifying agents in
such operations.
[0038] The drilling, completion, and workover fluids of the
present invention may comprise an aqueous base fluid and a nonionic
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cellulose ether having hydroxyethyl groups and being further substituted with
one or more hydrophobic substituents, wherein the cellulose ether has at least
one of the following properties (a), (b) or (c): (a) a retained dynamic
viscosity,
%n80n5, of at least 30 percent, wherein Won80/25= [dynamic solution viscosity
at
80 C / dynamic solution viscosity at 25 C] x 100, the dynamic solution
viscosity at 25 C and 80 C being measured as I % aqueous solution; (b) a
storage modulus of at least 15 Pascals at 25 C and a retained storage modulus,
%G '80/25, of at least 12 percent, wherein %G 80/25 --'- [storage modulus at
80 C /
storage modulus at 25 C] x 100, the storage modulus at 25 C and 80 C being
measured as a 1 % aqueous solution; and (c) a critical association
concentration
of less than 15 ppm as measured by light-scattering.
[0039] The aqueous base fluid utilized in the drilling,
completion, and workover fluids according to the present invention may
be fresh water, salt water (e.g., water containing one or more salts
dissolved therein), brine (e.g., saturated salt water), seawater, and any
combinations thereof. The brines may contain substantially any suitable
salts, including, but not necessarily limited to, salts based on metals, such
as, calcium, magnesium, sodium, potassium, cesium, zinc, aluminum, and
lithium. Salts of calcium and zinc are preferred. The salts may contain
substantially any anions, with preferred anions being less expensive
anions including, but not necessarily limited to chlorides, bromides,
formates, acetates, and nitrates. The choice of brine may increase the
associative properties of the nonionic cellulose ether polymer in the
drilling, completion, or workover fluid. A person of ordinary skill in the
art, with the benefit of this disclosure, will recognize the type of brine and
ion concentration needed in a particular application of the present
invention depending on, among other factors, the other components of
the drilling, completion, and workover fluids, the desired associative
properties of such fluids, and the like. Generally, the aqueous base fluid
may be from any source, provided that it does not contain an excess of
compounds that may adversely affect other components in the drilling,
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completion, or workover fluid. Preferably, the aqueous base fluid may be
present in the drilling, completion, or workover fluids in an amount in the
range of about 20% to about 99% by weight of the drilling, completion,
or workover fluid. Preferably, the base fluid may be present in the
drilling, completion, or workover fluids in an amount in the range of about
20% to about 80% by weight of the drilling, completion, or workover
fluid.
[0040] The drilling, completion, or workover fluids generally
comprise a nonionic cellulose ether having hydroxyethyl groups and being
further substituted with one or more hydrophobic substituents, wherein the
cellulose ether has at least one of the properties (a), (b) or (c): (a) a
retained
dynamic viscosity, / n
r = mons, of
at least 30 percent, wherein Won80/25 = [dynamic
solution viscosity at 80 C / dynamic solution viscosity at 25 C] x 100, the
dynamic solution viscosity at 25 C and 80 C being measured as 1 % aqueous
solution; (b) a storage modulus of at least 15 Pascals at 25 C and a retained
storage modulus, %G.80/25, of at least 12 percent, wherein %G 80125 -=
[storage
modulus at 80 C / storage modulus at 25 C) x 100, the storage modulus at
25 C and 80 C being measured as a 1 % aqueous solution; (c) a critical
association concentration of less than 15 ppm as measured by light-scattering.
[0041] Suitable nonionic cellulose ethers are substituted with
one or more hydrophobic substituents, preferably with acyclic or cyclic,
saturated or unsaturated, branched or linear hydrocarbon groups, such as
an alkyl, alkylaryl or arylalkyl group having at least 8 carbon atoms,
generally from 8 to 32 carbon atoms, preferably from 10 to 30 carbon
atoms, more preferably from 12 to 24 carbon atoms, and most preferably
from 12 to 18 carbon atoms. As used herein the terms "arylalkyl group"
and 'Ialkylaryl group" mean groups containing both aromatic and aliphatic
structures. The most preferred aliphatic hydrophobic substituent is the
hexadecyl group, which is most preferably straight-chained. The
hydrophobic substituent is non-ionic.
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[0042] Suitable nonionic cellulose ethers preferably have a
weight average molecular weight of at least 1,000,000, more preferably
at least 1,300,000. Their weight average molecular weight is preferably
up to 2,500,000, more preferably up to 2,000,000.
[0043] Suitable nonionic cellulose ethers preferably have a
Brookfield viscosity of at least 5000 mPa-sec, more preferably at least
6000 mPa-sec, and even more preferably at least 9000 mPa-sec. The
nonionic cellulose ethers preferably have a Brookfield viscosity of up to
20,000 mPa-sec, more preferably up to 18,000 mPa-sec, and most
preferably up to 16,000 mPa-sec. The Brookfield viscosity is measured as
1% aqueous solution at 30 rpm, spindle #4 at 25.0 C on a Brookfield
viscometer. The Brookfield viscosity is dependent on the hydrophobe
substitution, but is also an indication of the molecular weight of the
nonionic cellulose ether.
[0044] Suitable nonionic cellulose ethers have at least one of the
properties further described below:
(a) a retained dynamic viscosity, %r180/25/ of at least 30
percent, wherein
%r180/25 = [dynamic solution viscosity at 80 C / dynamic solution viscosity
at 25 C] x 100, the dynamic solution viscosity at 25 C and 80 C being
measured as 1 % aqueous solution;
(b) a storage modulus of at least 15 Pascals at 25 C and a
retained storage modulus, %G = 80/25, of at least 12 percent, wherein %G 60/25
[storage modulus at 80 C / storage modulus at 25 C] x 100, the storage
modulus at 25 C and 80 C being measured as a 1 % aqueous solution; and
(c) a critical association concentration of less than 15 ppm as
measured by light-scattering.
[0045] , The nonionic cellulose ether may comprise two of the
properties (a), (b) and (c) in combination. Alternatively, the nonionic
cellulose ether has all three properties (a), (b) and (c) in combination.
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[0046] A description of suitable nonionic cellulose ether polymers
is in U.S. Provisional Patent Application Serial No. 61/373,436, which is
hereby incorporated by reference.
[0047] The nonionic cellulose ether polymer should be added to
the aqueous base fluid in an amount sufficient to form the desired drilling
fluid, completion fluid, or workover fluid.
Preferably, the nonionic
cellulose ether polymer may be present in an amount of about 0.01% to
about 150/0 by weight of the drilling, completion, or workover fluid.
Preferably, the nonionic cellulose ether polymer may be present in an
amount of about 0.1% to about 10% by weight of the drilling, completion,
or workover fluid. A person of ordinary skill in the art, with the benefit of
this disclosure, will recognize the amount of polymer or polymers to
include in a particular application of the present invention depending on,
among other factors, the other components of the drilling, completion, or
workover fluids, the desired viscosity of the drilling, completion, or
workover fluids, and the like.
[0048] Although not wishing to be limited by any particular
theory, the nonionic cellulose ether polymers may have increased thermal
stability when in the presence of brine versus water. The increase in
thermal stability may be attributed to the minimization of the hydrolytic
attack due to decreased free water in the drilling, completion, or workover
fluid. It is believed that the increase in thermal stability in aqueous base
fluid may be due to changing the contact of the aqueous media with the
backbone of the polymer chains, facilitating the protection of the acetal
linkage (e.g., 1,4-glycocidic linkage) of the backbone. The acetal linkage
is thought to be generally unprotected in unmodified
hydroxyethylcellulose polymers.
[0049] Nonionic cellulose ether polymer may be used to increase
the viscosity of drilling fluid, completion fluid, or workover fluid. The
nonionic cellulose ether polymer may increase the viscosity of such fluids,
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for example, by associative interactions between hydrophobic groups of
the nonionic cellulose ether polymer to form intermolecular micellar
bonds, which result in a three-dimensional network. The nonionic
cellulose ether polymers may result in a three.-dimensional network able
to maintain structure over a broader stress range, especially as compared
to other biopolymers that have not been similarly modified. The nonionic
cellulose ether polymer may maintain structure in a stress range
exceeding about 12 Pa.
[0050] Additional additives may be added to the drilling,
completion, or workover fluids as deemed appropriate for a particular
application by one skilled in the art, with the benefit of this disclosure.
Examples of such additives include, but are not limited to, weighting
agents, biocides, corrosion inhibitors, gel stabilizers, surfactants, scale
inhibitors, antifoaming agents, foaming agents, fluid loss control
additives, shale swelling inhibitors, radioactive tracers, defoamers,
surfactants, crosslinking agents, particulates, pH-adjusting agents, pH
buffers, salts, breakers, delinkers, weighting agents, corrosion inhibitors,
combinations thereof, and the like, and numerous other additives
suitable for use in subterranean operations.
[0051.] Surfactants may be used to facilitate the formation of
micellar bonds in a drilling fluid, completion fluid, or workover fluid. It is
believed that the hydrophobic groups of the nonionic cellulose ether
polymer may become incorporated into surfactant micelles, which are
believed to act as crosslinkers for the polymer, creating structure and
strength. These surfactants may show Newtonian or viscoelastic behavior
when present in water by themselves in concentrations of less than 20%.
The surfactant may be a non-viscoelastic surfactant. Suitable surfactants
may be anionic, neutral, cationic or zwitterionic. Aqueous
liquids
containing the surfactants may respond to shear with a Newtonian or
viscoelastic behavior. Anionic surfactants with Newtonian rheological
CA 02807827 2013-02-13
behavior are preferred. Examples of suitable anionic surfactants include,
but are not limited to, sodium decylsulfate, sodium lauryl sulfate, alpha
olefin sulfonate, alkylether sulfates, alkyl phosphonates, alkane
sulfonates, fatty add salts, arylsulfonic acid salts, and combinations
thereof. Examples of suitable cationic surfactants, include, but are not
limited to, trimethylcocoammoni urn chloride, trimethyltallowammonium
chloride, dimethyldicocoammonium chloride, bis(2-hydroxyethyptallow
amine, bis(2-hydroxyethyl)erucylamine, bis(2-hydroxyethyl)coco-amine,
cetylpyridinium chloride, and combinations thereof. Where used, the
surfactant may be included in the drilling, completion, or workover fluid in
an amount of about 0.1% to about 20% by weight of the drilling,
completion, or workover fluid. One should note that if too much
surfactant is used that the formation of micelles in the fluid may
negatively impact the overall fluid.
[0052] The nonionic cellulose ether polymer may be crosslinked
by any suitable crosslinking agent or method. A crosslinking agent may
be utilized to crosslink the nonionic cellulose ether polymer to form the
crosslinked viscosifying agent. The drilling, completion, or workover fluids
of the present invention may be formed by contacting an aqueous base
fluid comprising nonionic cellulose ether polymers with a crosslinking
agent, and allowing a crosslinked viscosifying agent to form.
[0053] A variety of crosslinking agents are suitable for use in the
present invention. When used, the nonionic cellulose ether polymer will
be referred to herein as being "crosslinked with a metal ion." Examples of
suitable crosslinking agents include, but are not limited to, borate
releasing compounds and compounds that release transition metal ions
when dissolved in an aqueous liquid. Suitable
borate releasing
compounds include, but are not limited to, boric acid, disodium octaborate
tetrahydrate, sodium diborate, ulexite, and colemanite. An example of a
suitable borate releasing compound is commercially available under the
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trade name "HMPTm Link" crosslinker from Halliburton Energy Services,
Duncan, Oklahoma. Another example of a suitable borate releasing
compound is commercially available under the trade name CL38TM
delayed borate crosslinker from Halliburton Energy Services, Duncan,
Oklahoma. Suitable compounds that release transition metal ions,
include, but are not limited to, compounds capable of supplying zirconium
ions such as, for example, zirconium lactate, zirconium lactate
triethanolamine, zirconium carbonate, zirconium acetyiacetonate, and
zirconium diisopropylamine lactate; compounds capable of supplying
titanium ions such as, for example, titanium ammonium lactate, titanium
triethanolamine, titanium acetylacetonate; aluminum compounds such as,
for example, aluminum lactate or aluminum citrate; compounds capable
of supplying iron ions, such as, for example, ferric chloride; compounds
capable of supplying chromium ion such as, for example, chromium III
citrate; or compounds capable of supplying antimony ions. Generally, the
crosslinking agent, may be added to the aqueous base fluid comprising
nonionic cellulose ether polymer in an amount sufficient, inter alia, to
provide the desired degree of crosslinking. One of ordinary skill in the
art, with the benefit of this disclosure, should be able to determine the
appropriate amount and type of crosslinking agent to include for a
particular application.
[0054] The drilling, completion, or workover fluids optionally may
comprise a pH buffer. The pH buffer may be included in the drilling,
completion, or workover fluids to maintain pH in a desired range, inter
alia, to enhance the stability of the drilling, completion, or workover fluid.
Examples of suitable pH buffers include, but are not limited to, sodium
carbonate, potassium carbonate, sodium bicarbonate, potassium
bicarbonate, sodium or potassium diacetate, sodium or potassium
phosphate, sodium or potassium hydrogen phosphate, sodium or
potassium dihydrogen phosphate, sodium borate, sodium or ammonium
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diacetate, sulfamic acid, and the like. The pH buffer may be present in a
drilling, completion, or workover fluid in an amount sufficient to maintain
the pH of the drilling, completion, or workover fluid at a desired level.
One of ordinary skill in the art, with the benefit of this disclosure, will
recognize the appropriate pH buffer and amount of pH buffer to use for a
chosen application.
[0055] Optionally, the drilling, completion, or workover fluids
further may include pH-adjusting compounds for adjusting the pH of the
drilling, completion, or workover fluid, inter alia, to a desired pH for
crosslinking and/or enhance hydration of the nonionic cellulose ether
polymer. Suitable pH-adjusting compounds include any pH-adjusting
compound that does not adversely react with the other components of the
drilling, completion, or workover fluid. Examples of suitable pH-adjusting
compounds include, but are not limited to, sodium hydroxide, potassium
hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate,
fumaric acid, formic acid, acetic acid, acetic anhydride, hydrochloric acid,
hydrofluoric acid, hydroxyfluoboric acid, polyaspartic acid,
polysuccinimide, ammonium diacetate, sodium diacetate, and sulfamic
acid. The appropriate pH-adjusting compound and amount thereof may
depend upon the formation characteristics and conditions, and other
factors known to individuals skilled in the art with the benefit of this
disclosure. For example, where a borate-releasing compound is utilized
as the crosslinking agent, the pH of the drilling, completion, or workover
fluids should be adjusted to above about 8 to about 12 to facilitate the
crosslink of the nonionic cellulose ether polymer. Those skilled in the art,
with the benefit of this disclosure, will be able to adjust the pH range in
the viscosified aqueous fluids as desired.
[0056] In some applications, after the drilling, completion, or
workover fluid has performed its desired function, its viscosity may be
reduced. For example, in subterranean treatments and operations, once
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the viscosity is reduced, the drilling, completion, or workover fluid may be
flowed back to the surface, and the well may be returned to production.
The viscosity of the drilling, completion, or workover fluids may be
reduced by a variety of means. Breakers capable of reducing the
viscosity of the drilling, completion, or workover fluids at a desired time
may be included in the drilling, completion, or workover fluid to reduce
the viscosity thereof. Delinkers capable of lowering the pH of the drilling,
completion, or workover fluids at a desired time may be included in the
drilling, completion, or workover fluid to reduce the viscosity thereof.
Such delinkers may be especially useful when the nonionic cellulose ether
polymer has been crosslinked with a metal ion.
[0057] The drilling, completion, or workover fluids of the present
invention may further comprise a breaker. Any breaker that is able to
reduce the viscosity of the drilling, completion, or workover fluids when
desired is suitable for use in the methods of the present invention.
Preferably, delayed gel breakers that will react with the drilling,
completion, or workover fluids after desired delay periods may be used.
Suitable delayed gel breakers may be materials that are slowly soluble in
a drilling, completion, or workover fluid. Examples of suitable delayed
breakers include, but are not limited to, enzyme breakers, such as alpha
and beta amylases, amyloglucosidase, invertase, maltase, cellulase, and
hemicellulase; acids, such as maleic acid and oxalic acid; and oxidizing
agents, such as sodium chlorite, sodium bromate, sodium persulfate,
ammonium persulfate, magnesium peroxide, lactose, ammonium sulfate,
and triethanol amine. An example of a suitable delayed gel breaker is
commercially available under the trade name "VICON WI" breaker from
Halliburton Energy Services, Duncan, Oklahoma. , Preferably, these
delayed breakers can be encapsulated with slowly water-soluble or other
suitable encapsulating materials. Examples of water-soluble and other
similar encapsulating materials that may be suitable include, but are not
CA 02807827 2013-02-13
19
limited to, porous solid materials such as precipitated silica, elastomers,
polyvinylidene chloride (PVDC), nylon, waxes, polyurethanes, polyesters,
cross-linked partially hydrolyzed acrylics, other polymeric materials, and
the like. The appropriate breaker and amount thereof may depend upon
the formation characteristics and conditions, the pH of the drilling,
completion, or workover fluid, and other factors known to individuals
skilled in the art with the benefit of this disclosure. Preferably, the
breaker may be included in a drilling, completion, or workover fluid in an
amount in the range of from about 0.1 gallons to about 100 gallons per
1000 gallons of the aqueous base fluid. Such breakers may be especially
useful when the nonionic cellulose ether polymer has been crosslinked
with a metal ion.
[0058] When the nonionic cellulose ether polymer is crosslinked,
the drilling, completion, or workover fluids may comprise a delinker that
is capable of lowering the pH of the drilling, completion, or workover fluid
at a desired time causing the crosslinks of the viscosifying agent to
reverse. For example, when certain crosslinking agents, such as borate-
releasing compounds, are used, the crosslinks may be reversed (or
delinked) by lowering the pH of the drilling, completion, or workover fluid
to below about 8. The delinker may comprise encapsulated pH-adjusting
agents or acid-releasing degradable materials capable of reacting over
time in an aqueous environment to produce an acid. Suitable pH-
adjusting agents include, but are not limited to, fumaric acid, formic acid,
acetic acid, acetic anhydride, hydrochloric acid, hydrofluoric acid,
hydroxyfluoboric acid, polyaspartic acid, polysuccinimide, combinations
thereof, and the like. Preferably, the pH-adjusting agents may be
encapsulated using any suitable encapsulation technique. Exemplary
encapsulation methodology is described in U.S. Patent Nos. 5,373,901;
6,444,316; 6,527,051; and 6,554,071, the relevant disclosures of which
are incorporated herein by reference. Acid-releasing degradable materials
CA 02807827 2013-02-13
also may be included in the drilling, completion, or workover fluids to
decrease the pH of the drilling, completion, or workover fluid. Suitable
acid-releasing degradable materials that may be used in conjunction with
the present invention are those materials that are substantially water
insoluble such that they degrade over time, rather than instantaneously,
in an aqueous environment to produce an acid. Examples of suitable
acid-releasing degradable materials include orthoesters; poly(ortho
esters); lactides; poly(lactides); glycolides; poly(glycolides); substituted
lactides wherein the substituted group comprises hydrogen, alkyl, aryl,
alkylaryl, acetyl heteroatoms and mixtures thereof; substantially water
insoluble anhydrides; and poly(anhydrides). Depending on the timing
required for the reduction of viscosity, the acid-releasing degradable
material may provide a relatively fast break or a relatively slow break,
depending on, for example, the particular acid-releasing degradable
material chosen. Materials
suitable for use as an acid-releasing
degradable material may be considered degradable if the degradation is
due, inter alia, to chemical and/or radical processes, such as hydrolysis,
oxidation, or enzymatic decomposition. The inclusion of a particular
delinker and amount thereof may depend upon the formation
characteristics and conditions, the particular crosslinking agent, and other
factors known to individuals skilled in the art with the benefit of this
disclosure. The delinker of the present invention may be included in a
drilling, completion, or workover fluid in an amount in the range of from
about 0.01 pounds to about 100 pounds per 1000 gallons of the single
salt aqueous fluid.
[0059] The drilling, completion, or workover fluids optionally may
comprise a catalyst. The use of a catalyst is optional, but a catalyst may
be included in the drilling, completion, or workover fluids to activate the
breaker dependent, inter alia, upon the pH of the drilling, completion, or
workover fluid and formation conditions. Examples of suitable catalysts
CA 02807827 2013-02-13
21
include, but are not limited to, transition metal catalysts, such as copper
and cobalt acetate. An example of a suitable cobalt acetate catalyst is
available under the trade name "CAT-OS-1" catalyst from Halliburton
Energy Services, Duncan, Oklahoma. Preferably, the catalyst may be
included in a drilling, completion, or workover fluid in an amount in the
range of from about 0.01 pounds to about 50 pounds per 1000 gallons of
the single salt aqueous fluid.
[0060] The drilling, completion, or workover fluids may be
prepared by any suitable method. The drilling, completion, or workover
fluids of the present invention may be produced at the well site. As an
example, of such an on-site method, nonionic cellulose ether polymer
may be combined with an aqueous base fluid. Furthermore, additional
additives, as discussed above may be combined with the aqueous base
=
fluid as desired. To form a drilling, completion, or workover fluid, a
crosslinking agent, as discussed above, may be added to the aqueous
base fluid that comprises the nonionic cellulose ether polymer and other
suitable additives.
[0061] A drilling, completion, or workover fluid concentrate may
be prepared by combining an aqueous fluid (e.g., water) and a nonionic
cellulose ether polymer described herein. Generally, the water in the
drilling, completion, or workover fluid concentrate may be fresh water or
water containing a relatively small amount of a dissolved salt or salts.
The nonionic cellulose ether polymer may be present in the drilling,
completion, or workover fluid concentrate in an amount in the range of
from about 40 lbs to about 200 lbs per 1000 gallons of the aqueous fluid.
The nonionic cellulose ether polymer may be crosslinked with a metal ion.
Furthermore, additional additives, discussed above, that may be included
in the drilling, completion, or workover fluids may be added to the drilling,
completion, or workover fluid concentrate as desired. The drilling,
completion, or workover fluid concentrate may be prepared at an offsite
CA 02807827 2013-02-13
22
manufacturing location and may be stored prior to use. Such methods
may be preferred, for example, when these drilling, completion, or
workover fluid concentrates are to be used in offshore applications, e.g.,
because the equipment and storage volumes may be reduced. After
preparing the drilling, completion, or workover fluid concentrate, the
aqueous base fluid, described above, may be combined with the
concentrate. When the concentrate is mixed with the aqueous base fluid,
no hydration time may be required because the nonionic cellulose ether
polymer may already be substantially fully hydrated. Furthermore, the
additional additives, discussed above, may be combined with the aqueous
base fluid as desired. To form the drilling, completion, or workover fluid,
a crosslinking agent, as discussed above, may be added to the aqueous
base fluid that comprises the nonionic cellulose ether polymer and other
suitable additives.
[0062] The drilling, completion, or workover fluids of the present
invention that comprise nonionic cellulose ether polymer may be used in
any of a variety of suitable applications. By way of example, the drilling,
completion, or workover fluids may be used in subterranean operations,
including, but not limited to, underbalanced drilling, overbalanced drilling,
completion, and workover operations. Among other things, the drilling,
completion, or workover fluids may be used in subterranean operations as
drilling fluid additives, and the like.
[0063] An example method of the present invention generally
may comprise providing a drilling, completion, or workover fluid
comprising an aqueous base fluid and a nonionic cellulose ether polymer;
and introducing the drilling, completion, or workover fluid into the
subterranean formation having a bottom hole temperature of about 275 F
(135 C) or more or a pressure of 5000 psi or more.
[0064] The method further may comprise allowing the nonionic
cellulose ether polymer to maintain thermal stability and gel strength at
CA 02807827 2013-02-13
23
temperatures up to about 350 F (177 C). The length of time for which
thermal stability can be maintained will vary with temperature. For
example, at the higher temperatures the gel may degrade at a faster
rate.
[0065] The drilling, completion, or workover fluid may undergo
acid hydrolysis of the nonionic cellulose ether polymer. The ability to acid
hydrolyze such drilling, completion, or workover fluids may be
advantageous in numerous subterranean operations, such as to facilitate
a reduction in viscosity of a fluid or to degrade a filter cake.
[0066] The present invention provides methods that may include
a method comprising: providing a drilling fluid, completion fluid, or
workover fluid comprising an aqueous base fluid and a nonionic cellulose
ether polymer having hydroxyethyl groups and being further substituted with
one or more hydrophobic substituents, wherein the cellulose ether has at least
one of the properties (a), (b) or (c): (a) a retained dynamic viscosity, /
gont30/25,
of at least 30 percent, wherein 0/0n60/25 = [dynamic solution viscosity at 80
C /
dynamic solution viscosity at 25 C) x 100, the dynamic solution viscosity at
25 C and 80 C being measured as 1% aqueous solution; (b) a storage modulus
of at least 15 Pascals at 25 C and a retained storage modulus, %G 80/25, of at
least 12 percent, wherein %G80i25 = [storage modulus at 80 C / storage
modulus at 25 C] x 100, the storage modulus at 25 C and 80 C being measured
as a 1% aqueous solution; (c) a critical association concentration of less
than 15
ppm as measured by light-scattering, and placing the drilling fluid,
completion fluid, or workover fluid in a subterranean formation.
[0067] In the present invention, a drilling fluid that comprises a
nonionic cellulose ether polymer as described herein, may be circulated in
a well bore while drilling. In the present invention the method may
include forming a filter cake comprising the solid particle upon a surface.
Fluid loss to the formation through the filter cake may be reduced. As the
filter cake comprises the nonionic cellulose ether polymer, the filter cake
may be easily removed in accordance with the present invention, in that
CA 02807827 2013-02-13
24
the filter cake may be removed by acid degradation. Though the filter
cake formed by the drilling, completion, or workover fluids in accordance
with the present invention may be easily removed by using an acidic
solution, an operator nevertheless occasionally may elect to circulate a
separate clean-up solution or breaker through the well bore under certain
circumstances, to enhance the rate of degradation of the filter cake. By
way of example, removal of the filter cake may be enhanced by
contacting the filter cake with water.
[0068] An example of a method of the present invention
comprises: placing a drill-in fluid in a subterranean formation, the drill-in
fluid comprising an aqueous base fluid and a nonionic cellulose ether
polymer; and forming a filter cake comprising the nonionic cellulose ether
polymer upon the surface within the formation whereby fluid loss through
the filter cake is reduced.
[0069] The drilling, completion, or workover fluids of the present
invention may be placed into the well bore as a pill in drilling, completion,
or workover operations.
[0070] In the present invention, the drilling, completion, or
workover fluids may be placed into the subterranean formation as a
viscosified pill during an underbalanced drilling operation. An
underbalanced drilling operation may be referred to as a managed
pressure drilling operation by some skilled in the art. Influxes from the
formation may be experienced during an underbalanced drilling operation.
Nitrogen may be used to combat this. The drilling, completion, or
workover fluids may be recovered by pumping gas into the formation to
lift the pill out of the subterranean formation. The treatment fluid is then
replaced with drilling fluid.
[0071] Another example of a method of the present invention
comprises using the drilling, completion, or workover fluids prior to a
cementing operation, for example, as a completion fluid. An example of
CA 02807827 2013-02-13
such method may comprise a pre-treatment providing the drilling,
completion, or workover fluid comprising an aqueous base fluid and a
nonionic cellulose ether polymer; introducing these fluids into the
subterranean formation before placing a cement composition into the
formation.
[0072] The present invention preferably provides drilling,
completion, or workover fluids that comprise a nonionic cellulose ether
polymer that has been crosslinked with a metal ion. Such drilling,
completion, or workover fluids may be useful in a variety of subterranean
applications, including, drilling, completion, or workover.
[0073] To facilitate a better understanding of the present
invention, the following examples of certain aspects are given. In no way
should the following examples be read to limit, or define, the scope of the
invention. Representative examples are shown below.
EXAMPLES
[0074] The following series of tests were performed to determine
the effect of a hydrophobic modification on a fluid viscosified with a
nonionic cellulose ether polymer. The properties of the nonionic cellulose
ether polymer were compared to those of conventional viscosifying
agents, such as xanthan gum, scleroglucan gum, diutan gum, and
unmodified hydroxyethylcellulose. To prepare viscous fluids, samples
were prepared by mixing the aqueous base fluid with the polymers. The
aqueous media of choice (either brine or freshwater) was added and
placed on the paddle mixer at 550 rpms. The polymer samples were then
weighed (1 wt Wo, 7 g) was slowly added to prevent the formation of local
viscosifled agglomerates. The solutions were allowed to agitate for 90 min
for complete and homogeneous mixing.
[0075] Rheological studies of each fluid sample were performed
and evaluated by a series of tests on the Anton Paar Series 501 and Fann
50 rheometers. Experiments involving shear and temperature sweeps as
CA 02807827 2013-02-13
26
well as dynamic rheological studies enabled a thorough screening of the
nonionic cellulose ether polymer in comparison to various biopolymers.
The drilling, completion, or workover fluids comprising the various
polymers and their performance in freshwater and various monovalent
and divalent brines was described.
EXAMPLE 1
[0076] Brine testing was performed to determine the solubility of
the nonionic cellulose ether polymer. The following brines were tested:
10.0 ppg NaBr; 10.0 ppg NaCl; 10.0 ppg Ca02 brines were tested for
performance before and after hot roll for the various certain polymers
remain insoluble in these fluid.
[0077] The solubility of the nonionic cellulose ether polymeric
material was evaluated in the numerous aqueous media listed above.
Following the mixing procedure detailed earlier, the HMHEC samples
exhibited excellent solubility and viscosity response after 90 min.
However, the concentrated NaCI (10.0 ppg) proved to be the only brine in
which the HMHEC did not yield the desired properties. We can attribute
this to the minimization of free water within the saturated brine as well as
the possible "salting out" effects of the Na l" and Cr ions on the C16 alkyl
modifications located on the hydrophobically modified polymer rendering
it solubility or "dispersibility" limited as the polymer adopts a very
collapsed conformation. Also, in the case of the 13.5 ppg CaBr2 and 15.5
ppg Ca/znBr2, a concentrated HMHEC glycol mixture was employed to
deliver the polymer into these brines to decrease the hydration time. The
HMHEC did yield in these particular brines in the dry form, but it was
much slower and needed the application of heat to achieve the proper
enthalpy of mixing. After the mixing was complete, the samples were
allowed to age at 150 F (66 C) for 4 hours to ensure polymer relaxation
before the rheological tests were completed. The data for the shear rate
CA 02807827 2013-02-13
27
sweeps at 77 F (25 C) for each solution is provided below (with the
exception of 10.0 ppg NaC1).
[0078] Figure 1 depicts the rheological performance in various
brines at 1 wt % polymer. It can be seen that the nonionic cellulose
ether polymer provides excellent low shear viscosity response that thins
off at high shear rates (i.e., thixotropic flow properties). It should be
noted that the 15.5 ppg Ca/ZnBr2 sample was actually gelled to the
extent that it was not possible to achieve the correct reading due to the
Weissenberg effect within the Anton Paar geometry. However, the
indication of such elevated low shear viscosities was evidence of possible
increased suspension capabilities versus traditional unmodified
hydroxyethylcellulose.
[0079] A comparative analysis of other biopolymers was also
performed, by comparing the properties of each biopolymer in each brine
mentioned above by monitoring the capabilities of the nonionic cellulose
ether polymer as to its rheological behavior (i.e., flow and suspension
properties) and thermal stability.
[0080] Figures 2A-B depict the comparative study of the various
biopolymers in 10.0 ppg NaBr. All the chosen biopolymers were mixed as
described above and allowed to equilibrate at 150 F (66 C) for 4 h before
testing. The low shear viscosity of the nonionic cellulose ether polymer is
comparable to the other biopolymers (particularly Xanthan) that are
known to provide excellent suspension characteristics. When compared
to unmodified hydroxyethylcellulose, the hydrophobically modified
polymer exhibits low shear viscosity values that are an order of
magnitude higher (10X). The experimental nonionic cellulose ether
polymer does not thermally thin to the extent of unmodified
hydroxyethylcellulose and provides viscosity comparable to Xanthan at
190 F (88 C). It should be pointed out that the Diutan and Scleroglucan
CA 02807827 2013-02-13
28
gums do not thermally thin to any extent within the tested temperature
parameters as expected from their physicochemical properties.
[0081] At the completion of the first set of examinations, the
samples were allowed to static age at 220 F (104 C) for 16 h inside glass
jars placed located in stainless steel aging cells. The samples were then
cooled and allowed to mix at 500 rpm for 10 min. The same test
sequences were then repeated. Figures 3A-B show the nonionic cellulose
ether polymer exhibits excellent thermal stability in the NaBr solution and
negligible thermal degradation was observed. When compared to
Xanthan, the nonionic cellulose ether polymer shows improved
performance post static aging as then Xanthan demonstrates dramatic
thermal thinning and decreased gelation behavior.
[0082] Figures 4A-B depict the comparative study of the various
biopolymers in 13.5 ppg CaBr2. The employment of divalent brines
proved to be quite interesting. The solubility of the various biopolymers
in the 13.5 ppg CaBr2 was limited as the Scleroglucan yielded only
minimal viscosity response and Diutan would not disperse to any extent.
However, the nonionic cellulose ether polymer proved to be an excellent
choice as it performed with superb rheological properties and nominal
thermal thinning. The nonionic cellulose ether polymer maintained its
thixotropic nature as well as elevated low shear viscosity values. Once
again, these rheological characteristics are indicative of increased
suspension properties when compared to traditional unmodified
hydroxyethylcellulose and are a result of the hydrophobic associations due
to the hydrophobic modifications.
[0083] The CaBr2 samples were also static-aged at 220 F (104 C)
for 16 h, as seen in Figures 5A-B. The divalent brine managed to drive
the Scleroglucan gum out of solution as the polymeric mixture phase
separated due to decreased solubility parameters resulting in a collapsed
conformation of the polymer structures. By
contrast, the nonionic
CA 02807827 2013-02-13
29
cellulose ether polymer continued with exemplary performance after the
static aging whereas Xanthan began to fail at the elevated temperatures.
[0084] Figures 6A-B depict the comparative study of the various
biopolymers in 15.5 ppg Ca/ZnBr2. Nonionic cellulose ether polymer
provided an excellent viscosity response when blended with the 15.5 ppg
Ca/ZnBr2 salt solution. Such an increase in viscosity was observed that
while performing the rheological studies, the fluid exhibited the
Weissenberg effect thus rendering the sample difficult to measure with
the chosen geometry for the polymer solution studies. HEC also rendered
excellent viscosity profiles but, in the case of both polymers, most of the
response was manifested in the viscous component (Le., loss modulus).
This behavior is seen when the polymers are not displaying any
intermolecular associations other than simple chain entanglement thus
leading to the reduction of suspension capabilities and thixotropic
behavior. In the case of the Diutan and Xanthan, neither biopolymer was
able to provide sufficient yield needed for evaluation.
[0085] In addition to the brine examinations, we also monitored
the performance in the presence of freshwater as a means of observing
its thermal stability. In the case of the deionized solutions, only nonionic
cellulose ether polymer and hydroxyethylcellulose were compared.
Figures 7A-B show the ambient temperature profiles were as expected
with the nonionic cellulose ether polymer providing superb gelation
behavior as well as shear thinning properties. At 220 F (104 C), both the
unmodified hydroxyethylcellulose and nonionic cellulose ether polymer
showed drastic losses in viscosity after the 16 h static aging although the
nonionic cellulose ether polymer still had slightly better performance. At
250 F (121 C), the hydroxyethylcellulose lost all viscosity as the polymer
underwent extensive hydrolysis while the nonionic cellulose ether polymer
maintained a reasonable some viscosity. It was observed that the
thermal stability of the nonionic cellulose ether polymer was enhanced
CA 02807827 2013-02-13
when utilized within brine. Such behavior was indicative of increased
rates of hydrolysis with increased amounts of free water existing within
the freshwater system as compared to brines.
EXAMPLE 2
[00863 The effect of a defoamer (i.e., BARABRINE defoamer) was
measured to assess the contamination stability (effect of defoamer,
glycols, etc.) of the nonionic cellulose ether polymer in the drilling,
completion, or workover fluids. The breakdown of the hydrophobically
modified hydroxyethylcellulose in the drilling, completion, or workover
fluids via acid hydrolysis or oxidation was also measured. BARABRINE
Defoamer was the defoaming agent of choice for the examinations. The
components were placed in the aqueous media before the polymers were
added to monitor the effect of the defoamer on the polymers solubility as
well as the associative performance that provides the gelation behavior of
the nonionic cellulose ether polymer system. Figures 8A-B depict that the
addition of defoamer had negligible consequence on the solubility of the
nonionic cellulose ether polymer. The polymers showed excellent yield
and viscosity response with the BARABRINE defoamer included, but there
was a slight decrease when compared to the profile provided by the
control sample. However, the utilization of the defoamer was not a
detriment to the performance of the nonionic cellulose ether polymer.
EXAMPLE 3
00873 As seen in the previous sections, the nonionic cellulose
ether polymer seemed to provide gelation behavior that was similar to
that of Xanthan. The ability of the new biopolymer to provide suspension
characteristics would be a vast improvement over the capabilities of
conventional hydroxyethylcellulose. In order to investigate this type of
behavior, dynamic rheological studies were performed via the Anton Paar
rheometer to evaluate the storage (G') and loss (G") moduli of nonionic
CA 02807827 2013-02-13
31
cellulose ether polymer versus Xanthan and hydroxyethylcellulose.
Xanthan and hydroxyethylcellulose were excellent representatives as both
are known to display both ends of the spectrum as Xanthan has gelation
behavior and hydroxyethyicellulose does not.
[0088] The polymer samples were mixed in 10.0 ppg NaBr at 1
wt % polymer additive. Figure 9
depicts that unmodified
hydroxyethylcellulose exhibited a loss modulus (G") greater than the
storage modulus (G'). The rheological response had a significant viscous
component but minimal elastic component which was indicative of a
polymer network that does not yield favorable gel strengths and
suspension properties. Xanthan displayed the opposite behavior than that
of unmodified hydroxyethylcellulose. It had a dramatic elastic response
thus providing evidence of its ability to produce preferred suspension
characteristics up to 10 Pa.
[0089] Figure 9 further shows that nonionic cellulose ether
polymer demonstrated behavior that was similar to Xanthan in nature but
superior in terms of performance. The storage modulus was more than
double the loss modulus.
EXAMPLE 4
[0090] 1 wt % solution of nonionic cellulose ether polymer in
10.0 ppg NaBr was also studied on the FANN 50 viscometer to investigate
the polymer's thermal stability in a simulated drilling environment 42 ml
of the polymer solution was placed inside the test cell and cycled to 250
F (121 C) and held for 30 minutes after which it was cooled to 100 F
(38 C) and held for ten minutes at a constant shear rate of 100 rpms.
The cycle was repeated for 20 h. It can be seen in Figure 10 that the
nonionic cellulose ether polymer maintained its composition and did not
diminish in viscosity response during the tested duration of simulated
drilling. The thermal stability was markedly improved over what is
traditionally observed with unmodified hydroxyethylcellulose.
CA 02807827 2013-02-13
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EXAMPLE 5
[0091] Nonionic cellulose ether polymer was monitored to assay
its ability to break down in the presence of acid and heat. The same
solution utilized in the previous section (i.e., 1 wt % solution of nonionic
cellulose ether polymer in 10.0 ppg NaBr) was treated with 9 M Ha to
lower the pH to 3Ø The solution was then placed in the FANN 50
viscometer and heated to 175 F (79 C) at 100 rpms. As seen by Figure
11, in less than 1 h, the viscosity of the solution had dramatically
decreased as acid hydrolysis had chemically broken down the polymer.
[0094 Therefore, the present invention is well adapted to attain
the ends and advantages mentioned as well as those that are inherent
therein. The particular embodiments disclosed above are illustrative only,
as the present invention may be modified and practiced in different but
equivalent manners apparent to those skilled in the art having the benefit
of the teachings herein. Furthermore, no limitations are intended to the
details of construction or design herein shown, other than as described in
the claims below. It is therefore evident that the particular illustrative
embodiments disclosed above may be altered, combined, or modified and
all such variations are considered within the scope and spirit of the
present invention. While compositions and methods are described in
terms of "comprising," "containing," or "including" various components or
steps, the compositions and methods can also "consist essentially of" or
"consist of" the various components and steps. All numbers and ranges
disclosed above may vary by some amount. Whenever a numerical range
with a lower limit and an upper limit is disclosed, any number and any
included range falling within the range is specifically disclosed. In
particular, every range of values (of the form, "from about a to about b,"
or, equivalently, "from approximately a to b," or, equivalently, "from
approximately a-b") disclosed herein is to be understood to set forth
every number and range encompassed within the broader range of
CA 02807827 2013-02-13
33
values. Also, the terms in the claims have their plain, ordinary meaning
unless otherwise explicitly and clearly defined by the patentee. Moreover,
the indefinite articles 'a" or 'an," as used in the claims, are defined herein
to mean one or more than one of the element that it introduces. Also,
the terms in the claims have their plain, ordinary meaning unless
otherwise explicitly and clearly defined by the patentee. If there is any
conflict in the usages of a word or term in this specification and one or
more patent or other documents that may be incorporated herein by
reference, the definitions that are consistent with this specification should
be adopted.
