Note: Descriptions are shown in the official language in which they were submitted.
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MISSING AT THE OF PUBLICATION
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petroliferous formation), transportation of "cuttings" (pieces of formation
dislodged by the cutting action of the teeth on a drill bit) to the surface,
controlling form~.tion pressure to prevent blowouts, maintaining well
stability,
suspending solids in the well, minimizing fluid loss into and stabilizing the
formation through which the well is being drilled, fracturing the formation in
the vicinity of the well, displacing the fluid Wlthin the well with another
fluid,
cleaning the well, testing the well, implacing a packer fluid, abandoning the
well or preparing the well for abandonment, and otherwise treating the well or
the formation. Brines (such as CaBr2) commonly are used as well fluids
because of their wide density range and the fact that brines are typically
substantially free of suspended solids. Additionally, brines typically do not
damage certain types of downhole formations.
[0004] A variety of compounds typically are added to the brine-based well
fluids. For example, a brine-based well fluid also may include corrosion
inhibitors, lubricants, pH control additives, surfactants, solvents, and/or
weighting agents, among other additives. Some typical brine-based well fluid
viscosifying additives include xanthan gum and hydroxyethyl cellulose (HEC).
[0005] The natural and natural derivative polymers and oligomers listed above
have other uses in drilling applications as well. When drilling progresses to
the
level of penetrating a hydrocarbon bearing formation, special care may be
required to maintain the stability of the wellbore. Examples of formations in
which problems often arise are highly permeable and/or poorly consolidated
formations. In these types of formations, a technique lrnown as "under-
reaming" may be employed.
[0006] In this process, the wellbore is drilled to penetrate the hydrocarbon
bearing zone using conventional techniques. A casing generally is set ilZ the
wellbore to a point just above the hydrocarbon bearing zone. The hydrocarbon
zone then may be re-drilled, for example, using an expandable under-reamer
that increases the diameter of the wellbore. Under-reaming usually is
performed using special "clean" drilling fluids. Typical drilling fluids used
in
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under-reaming are expensive, aqueous, dense brines that are viscosified with a
gelling and/or cross-linlced polymer to aid in the removal of formation
cuttings.
The high permeability of the target formation, however, may allow large
quantities of the drilling fluid to be lost into the formation.
[0007] Once the drilling fluid is lost into the formation, it becomes
difficult to
remove. Calcium and zinc-bromide brines can form highly stable, acid
insoluble compounds when reacted with the formation or substances contained
therein. This reaction may reduce the permeability of the formation to any
subsequent out-flow of the targeted hydrocarbons. The most effective way to
prevent such damage to the formation is to limit fluid loss into the
formation.
[0008] Thus, providing effective fluid loss control is highly desirable to
prevent
damaging the formation in, for example, completion, drilling, drill-in,
displacement, hydraulic fracturing, work-over, packer fluid emplacement or
maintenance, well treating, or testing operations. Techniques that have been
developed to control fluid loss include the use of fluid loss "pills."
Significant
research has been directed to determining suitable materials for the fluid
loss
pills, as well as controlling and improving the properties of the fluid loss
pills.
Typically, fluid loss pills work by enhancing filter-cake buildup on the face
of
the formation to inhibit fluid flow into the formation from the well bore.
[0009] Because of the high temperature, high shear (caused by the pumping and
placement), high pressures, and low pH to which well fluids are exposed
("stress conditions"), the polymeric materials used to form fluid loss pills
and
to viscosity the well fluids tend to degrade rather quickly. In particular,
for
many of the cellulose and cellulose derivatives (such as HEC) used as
viscosifiers and fluid control loss agents, significant degradation occurs at
temperatures axound 200 °F and higher. HEC, for example, is considered
sufficiently stable to be used in an environment of no more than about 225
°F.
Likewise, because of the high temperature, high shear, high pressures, and low
pH to which well fluids are exposed, xanthan gum is considered sufficiently
3
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stable to be used in an environment of no more than about 290 to 300°F,
or
about 320 to 330°F in the presence of salts of formate / acetate
anions.
[0010] What is needed are natural and natural derivative polymer compositions
that can withstand the stress conditions for extended periods of time without
significant degradation. In particular, what is needed is a simple,
inexpensive
way to increase the thermal range for viscosifying agents used in downhole
applications. Preferably, this thermal extender would be applicable to various
viscosifying agents (unlike the salts of formate or acetate anions, which only
work for xanthan gum).
Summary of Invention
[OOlI] In one aspect, the present invention relates to a method for increasing
the thermal stability of viscosifying agents, and particularly polymers, used
in a
well fluid which comprises mixing a miscible tertiary amine compound into the
fluid.
[0012] In another aspect, the present invention relates to a method for
increasing the thermal stability of viscosifying agents, and particularly
polymers, in a well fluid which comprises mixing a miscible secondary amine
compound into the fluid.
[0013] In another aspect, the present invention relates to a thermally stable
viscosifying system for well fluids which comprises a polymer, a solvent, and
a
tertiary amine miscible in the solvent.
[0014] In another aspect, the present invention relates to a thermally stable
viscosifying system for well fluids, which comprises a polymer, a solvent, and
a secondary amine miscible in the solvent.
(0015] Other aspects and advantages of the invention will be apparent from the
following description and the appended claims.
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Detailed Description
[0016] The present invention discloses a novel composition for increasing tha
thermal durability of natural and natural derivative polymers used in downhole
applications. In general, the invention, in one embodiment, involves the
effect
of triethanol amine (TEA) on a conventional liquid viscosifier, such as
hydroxyethyl cellulose (HEC). HEC is a derivative of cellulose, where the
pendant hydroxyl moieties have been replaced with hydroxyethyl ether groups.
The presence of these long side chains prevent the individual polymer strands
from aligning and crystallizing, which allows HEC to be water soluble. The
general structure of a cellulose polymer is shown below.
H OH
KO
OH O H O ~ O- Eq. 1
H H
[0017] Triethanol amine (TEA) has the following structure:
HOH~CH2C.N.CH2CH20H E . ~
i q
CH2CH20H
[0018] In a first embodiment, the effects of high temperatures for long
periods
of time were measured on a TEA-containing composition. Specifically, 13.3
milliliters (mL) of TEA was added to a brine / HEC mixture. The brine / HEC
mixture was formed by the addition of 12.0 mL of an HEC suspension (41% by
weight active component of HEC in dipropylene glycol methyl ether) to the
brine solution. In this embodiment, the brine solution consisted of 0.965 lab
barrels (Lbbl) of a 13.8 pounds per gallon (ppg) CaBrz in water. All of the
use
of the word "barrel" in this specification relates to "lab barrels" - a lab
barrel is
equivalent to about 350 milliliters. (A lab barrel of water weighs about 350
grams; just as a regular barrel of water weighs the same number of pounds,
about 350. This is the formal origin of the term "lab barrel." Fortunately, a
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barrel of any fluid - regardless of density - happens to have the same volume
as that of a lab barrel of water). Additionally, while the particular
embodiments describe a particular order of addition for the chemical
components, such a description is not intended to limit the scope of the
invention in any fashion.
[0019] After mixing the components, initial Theological parameters were
measured. The Theological measurements were made using a Fann model 35
rotational viscometer (manufactured by Fame Instrument Co., of Houston,
Texas), using a B 1 bob on a "2 times" spring. Specifically, the apparent
viscosity was measured. Viscosity is the ratio of the shear stress to the
shear
rate and is an indication of flow resistance. For many fluids, apparent
viscosity
changes for different values of shear rate, and is measured in centiPoise
(cP).
Shear rate is measured in RPM or sec 1.
[0020] In this embodiment, the initial apparent viscosity of the brine / TEA /
HEC mixture was measured at six different shear rates: 600 rpm, 300 rpm, 200
rpm, 100 rpm, 6 rpm, and 3 rpm. Additionally, the initial pH of the bride /
TEA / HEC mixture was measured. The brine / TEA / HEC mixture was then
placed in an oven at 245 °F. After 20 hours, the brine / TEA / HEC
mixture
was removed from the oven and allowed to cool to room temperature. After
reaching room temperature, the apparent viscosity and pH of the mixture was
again measured. After takiilg the measurement, the mixture was returned to the
oven and left in the oven for 24 hours at 245 °F. Measurements of the
pH and
apparent viscosity were again taken after .the mixture was allowed to cool to
room temperature. The mixture was then returned to the oven for an additional
25 hours at 245 °F, after which the sample was allowed to cool axed
final
measurements were taken.
[0021] The results axe summarized below:
6
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Shear Rate
Initial 20 Hrs 44 Hrs 75 Hrs
(RPM)
600 631 (estimated)647 (estimated)648 (estimated)645 (estimated)
300 530 542 526 508
200 502 490 488 470
100 436 422 422 400
6 236 214 202 174
3 196 172 160 134
pH 7.57 7.3 7.44 7.33
TABLE 1: 13.3 ML TEA PRESENT (APPARENT VISCOSITY)
[0022] Table 1 shows that the apparent viscosity of the brine / TEA / HEC
mixture remained roughly constant during the entire 75 hour heat treatment.
Further, the pH of the mixture also remained roughly constant. Based on these
results, it is evident that the HEC polymer suffered no significant
degradation
during the entire 75 hour experiment when treated with TEA.
[0023] For comparison, an experiment was run under conditions similar to
those described above without the addition of TEA. In this experiment, 12.0
mL of an HEC suspension (41% by weight active component of HEC in
dipropylene glycol methyl ether) was poured slowly into an agitated brine
solution. As in the previous experiment, the brine solution consisted of 0.965
Lbbl of a 13.7 ppg CaBr2 in water.
[0024] Again, the initial apparent viscosity of the brine / HEC mixture was
measured at six different shear rates: 600 rpm, 300 rpm, 200 rpm, 100 rpm, 6
rpm, and 3 rpm. In addition, the initial pH was measured. As above, the brine
/ HEC mixture was placed in an oven at 245°F and measurements were
taken
after 20, 44, and 75 hours.
[0025] The results are summarized below:
7
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Shear Rate Initial 20 Hrs 44 Hrs 75 Hrs
(RP1V1)
600 596 662 (estimated)420 166
300 504 506 294 93
200 460 452 238 65
100 396 372 154 35
6 204 142 16 4
3 164 102 10 3
pH 5.9 6 4.68 5.43
TABLE 2: COMPARATIVE RUNS TEA ABSENT (APPARENT VISCOSITY)
[0026] As shown in Table 2, absent the TEA, viscosity reduction becomes
significant at the times / temperatures associated with this experiment. For
example, a dramatic loss in viscosity occurred within 44 hours into the
experiment. Also noticeable is the fact that the pH of the system was
significantly lower than that of the TEA-.containing system described above.
Thus, experimental evidence has determined that the TEA may provide a
buffering effect to maintain the pH of the system at a pH of approximately 7.
A discussion of why the buffering effect is believed to be significant is
provided below.
[0027] In a second embodiment, 49.4 mL of an HEC / TEA slurry was added to
0.859 Lbbl of a 14.18 ppg gallon CaBr2 in water. The HEC/TEA slurry was
formed by the addition of 91 pounds of TEA to 9 pounds of HEC powder. The
resulting slurry, therefore, comprises 9% by weight HEC.
[0028] As in the embodiment described with respect to Table 1, the initial
apparent viscosity of the HEC slurry was measured at six different shear
rates:
600 rpm, 300 rpm, 200 rpm, 100 rpm, 6 rpm, and 3 rpm. In addition, the pH
was measured. As above, the brine / HEC / TEA mixture was placed in an
oven at 245°F and measurements were taken after 20, 47.5, and 73.5
hours,
having allowed the solution to cool to room temperature before measuring.
8
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[0029] The results are summarized below.
Shear Rate Initial 20 Hrs 47.5 Hrs 73.5 Hrs
(RPM)
600 644 (estimated)604 (estimated)682 (estimated)659 (estimated)
300 560 512 578 520
200 520 464 522 464
100 464 404 440 384
6 270 210 228 160
3 232 174 186 120
pH 7.44 7.35 7 7.2
TABLE 3: RESULTS FROM HEC/TEA SLURRY (APPARENT VISCOSITY)
[0030] As in the first embodiment, it is apparent from examining the results
in
Table 3 that no significant viscosity degradation occurred. Polymer
degradation causes a loss in viscosity because, as the polymer decomposes (a
mechanism for this decomposition is proposed below), the high molecular
weight chains become substantially lower molecular weight chains. As more
low-molecular-weight chains are formed from the decomposition of the high
molecular weight chains, the entanglements among the polymer chains
decreases, which allows the polymer chains to flow more freely past one
another and thereby decreases fluid viscosity. It is clear from Table 3 that
even
if the TEA is added as part of a polymer slurry, there is no reduction in the
ability of TEA to increase the temperature stability of a polymer solution.
[0031] In a third embodiment, the effects of TEA in the presence of other
common additives was measured. Also, a suspension of HEC in synthetic oil
rather than an organic solution was used to determine whether TEA would have
a similar effect as in the other embodiments. Specifically, 12.5 mL of a
suspension of HEC (41% active component HEC by weight in a synthetic oil
solvent) was mixed into 0.916 Lbbl of a 13.9 ppg brine solution. In addition,
a
trace amount of an oxygen scavenger (sodium thiosulfate pentahydrate in this
9
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embodiment) was mixed as a dry reagent into the system. 13.3 mL of TEA
was then added to the HEC / brine system. In this embodiment, CaBrz was
used to create the brine solution.
[0032] As in the above embodiment, the initial apparent viscosity of the brine
/
HEC mixture was measured at six different shear rates: 600 rpm, 300 rpm, 200
rpm, 100 rpm, 6 rpm, and 3 rpm. In addition, the pH was measured. The brine
/ HEC / TEA mixture was placed in an oven at 245°F and measurements
were
taken after 21.5, 47, and 87 hours, allowing the mixture to cool to room
temperature prior to measuring pH and viscosity.
[0033] The results are tabulated below.
Shear Ratehiitial 21.5 Hrs 47 Hrs 87 Hrs
(RPM)
600 510 731 (estimated)623 (estimated)670 (estimated)
300 410 625 (estimated)510 520
200 366 570 468 468
100 306 490 400 396
6 154 264 192 160
3 130 220 152 118
pH 6.99 6.87 6.5 6.5
TABLE 4: HEC IN SYNTHETIC OIL SUSPENSION / OxYGEN SCAVENGER
PRESENT (APPARENT VISCOSITY)
[0034] It is apparent from Table 4 that changing the composition of the HEC
suspension in the manner described above has no apparent effect on the ability
of TEA to provide thermal stability to HEC polymers. In addition, it may be
noted that, in this embodiment, the mixture was subjected to heat treatment
for
87 hours. Even at this prolonged exposure, no major decomposition was noted.
It may be noted that the presence of the oxygen scavenger appeared to have no
effect on the mixture. Further, the pH of the system remained substantially
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constant, which is an indication that the TEA provides the same buffering
effect as with higher HEC concentrations.
[0035] As a comparison, 12.5 mL of a suspension of HEC (41% active
component in a synthetic oil solution) was added to 0.916 Lbbl of a 13.9 ppg
brine solution. To the HEC / brine mixture, 13.3 mL of TEA was added. As in
the above embodiment, the brine solution comprised CaBra in water.
[0036] As in the above embodiment, the initial apparent viscosity of the
mixture was measured at six different shear rates: 600 rpm, 300 rpm, 200 rpm,
100 rpm, 6 rpm, and 3 rpm. In addition, the initial pH was measured. As
above, the brine / HEC / TEA mixture was placed in an oven at 245°F and
measurements were taken after 21, 45, and 70 hours, allowing the mixture to
cool prior to measuring.
(0037] The results are tabulated below.
Shear RateInitial 21 Hrs 45 Hxs 70 Hrs
600 280 633 (estimated)624 (estimated)578_
300 214 526 494 510
200 186 496 444 420
100 146 426 368 344
6 56 224 156 132
3 44 182 118 96
pH 7.4 7.3 7 7
TABLE 5: HEC IN SYNTHETIC SUSPENSION/ NO OXYGEN SCAVENGER
PRESENT (APPARENT VISCOSITY)
[0038] The above results confirm that the addition of an oxygen scavenger to
the TEA / HEC / brine mixture has no significant effect on the ability of TEA
to provide thermal stability to the polymer system.
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[0039] In a fourth embodiment, the effect of TEA on polymer stability in mixed
brine systems was measured. In addition, the effect of TEA in the presence of
lower concentrations of HEC suspensions was measured. Specifically, 43.8
pounds of a suspension of HEC (9% by weight of HEC suspended in ethylene
glycol) was added to 0.796 Lbbl of 16.2 pounds per gallon ZnBr2 / CaBr2 in
water. The 16.2 pounds per gallon brine solution was formed by the dilution of
a 19.2 pounds per gallon ZnBrz / CaBrz mixture with water. In this
embodiment, the initial 19.2 pounds per gallon ZnBr2 / CaBr2 water mixture is
52.8% by weight ZnBr2, 22.8% CaBr2, with the balance water. To this, 19.9
pounds of TEA was added.
[0040] As in the above embodiments, the initial apparent viscosity of the
mixture was measured at six different shear rates: 600 rpm, 300 rpm, 200 rpm,
100 rpm, 6 rpm, and 3 rpm. In addition, the pH was measured. The brine /
HEC / TEA mixture was placed in an oven at 235°F and measurements
were
taken after 14, 35, and 52 hours, allowing the mixture to cool prior to
measuring.
[0041] The results are tabulated below.
Shear Initial 14 Hrs 35 Hrs 52 Hrs
Rate
(RPM)
600 660 (estimated)354 124 72
300 582 226 64 37
200 526 168 44 25
100 456 96 22 12
6 266 6 2 1
3 226 4 1 0
pH 3.8 4 4.1 4.3
TABLE 6: MIXED BRINE SOLUTION (APPARENT VISCOSITY)
[0042j As shown in Table 6, viscosity reduction becomes significant at the
times / temperatures associated with this experiment, despite the presence of
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TEA. For example, a dramatic loss in viscosity has occurred 14 hours into the
experiment. Also noticeable is that the pH of the system was significantly
lower than that of the TEA containing systems described above. The loss of
viscosity even in the presence of TEA was attributed to the low pH of this
system. The propensity of zinc bromide brines to cause low pH has previously
been noted, for example, in U.S. Patent No. 6,100,222, issued to Vollmer, et
al.
Basically, the inherent acidity of zinc bromide brines leads to the relatively
low
pH's measured in Table 6.
[0043] For comparison, an experiment was run under similar conditions as
above, but the relative concentration of ZnBra was decreased. Specifically,
36.2 pounds of a suspension of HEC (9% by weight of HEC suspended in
ethylene glycol) was added to 0.855 Lbbl of 16.2 pounds per gallon ZnBrz /
CaBr2 in water. The 16.2 pounds per gallon brine solution was formed by the
dilution of a 19.2 pounds per gallon ZnBr2 / CaBr2 mixture (having the same
composition as in the above embodiment) with 14.2 pounds per gallon CaBr2 in
water. To this, 12.8 pounds of TEA was added.
(0044] As in the above embodiments, the initial apparent viscosity of the
mixture was measured at six different shear rates: 600 rpm, 300 rpm, 200 rpm,
100 rpm, 6 rpm, and 3 rpm. In addition, the pH was measured. The brine /
HEC / TEA mixture was placed in an oven at 250°F and measurements
were
taken after 22.5, 39, 61, 78.5, and 93.5 hours, allowing the mixture to cool
prior
to measuring.
[0045] The results are tabulated below.
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Shear Initial 22.5 39 61 78 Hrs 93.5
Rate Hrs Hrs Hrs Hrs
(RPM)
600 568 606
(estimated)(estimated)S76 588 574 534
~
300 502 494 450 460 432 ~ 400
200 444 436 394 398 370 338
100 372 358 314 308 280 248
6 208 160 108 98 66 50
3 178 124 76 58 40 . 28
pH 5.2 5.3 5.9 5.8 5.9 5.8
TABLE 7: LOWER RELATIVE ZINC (APPARENT VISCOSITY)
[0046] As shown in Table 7, viscosity reduction becomes significant at the
times / temperatures associated with this experiment, despite the presence of
TEA. However, the viscosity reduction is not as great as the reduction seen in
Table 6. It also may be noted that the pH's in Table 7 are higher (less
acidic)
than those seen in Table 6. This experimental evidence further supports the
mechanism described below.
[0047] Like HEC, TEA is miscible in water, which prevents any undesirable
phase separation. While the foregoing embodiments reference a limited
number of compounds, it should be recognized that chemical compounds
having the same general characteristics also will function in an analogous
fashion. For example, it is expressly within the scope of the present
invention
that methyldiethanol amine (MDEA), dimethylethanol amine (DMEA),
diethanol amine (DEA), monoethanol amine (MEA), or other suitable tertiary,
secondary, and primary amines and ammonia could be substituted, in whole or
in part, for the triethanol amine described herein. In addition, it also is
expressly within the scope of the invention that other mixed TEA systems rnay
be used as additives, such as a TEA / glycol system or a TEA / alcohol system.
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Suitable alcohols would include methanol, ethanol, n-propanol and its isomers,
n-butanol and its isomers, n-pentanol and its isomers, n-hexanol and its
isomers, etc.
[0048] Similarly, other natural and natural derivative polymers may be
substituted for HEC, such as, for example, starch, derivatized starch, or
xanthan
gum. Furthermore, it should be noted that while the above examples discuss
the utility of amines in CaCl2 containing brine solutions, it will be clear to
one
of ordinary skill in the art that other brine solutions, such as ZnCl2, CaBr2,
and
ZnBr2, NaCI, KCI, NH4Cl, MgClz, seawater, NaBr, NaaS2O3, and combinations
thereof, may be used.
[0049] In addition, while specific amounts of the chemicals used are described
in the above embodiments, it is specifically within the contemplation of the
invention that amounts different than those described above may be used to
provide the desired thermal stability, depending on the particular
application.
For example, in one embodiment, a suitable system for increasing polymer
stability may comprise 0.1 % by weight to 50 % by weight HEC and 0.1% by
weight to 50 % by weight TEA. More preferably, in one embodiment the
system may comprise 0.1 % by weight to 5% by weight HEC and 0.2% by
weight to 20% TEA. Still more preferably, in one embodiment the system may
comprise 0.3% by weight to 1.5% by weight HEC and 0.5% by weight to 10%
by weight TEA.
[0050] Therefore, in some embodiments, it is expressly within the scope of the
invention that no water or brine will be present. In addition, no limitation
should be placed on the use of other systems such as a TEA / glycol / HEC
system or a TEA / glycol / HEC / brine system. Other systems expressly within
the scope of the present invention include TEA / alcohol additives.
[0051] One proposed mechanism for how the addition of TEA provides
additional thermal stability is based on the belief that TEA may act as a pH
buffer. Because HEC is derived from cellulose, many of the reactions that are
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associated with cellulose are relevant to the chemistry of HEC and other
related
biopolymers (such as starch). Specifically, acid catalyzed hydrolysis can
cause
degradation of cellulose. Acids (which are present in downhole formations
because of the release of acid gases such as H2S) attaclc the acetal linkages,
cleaving the 1-2 glycosidic bond, as labeled in Equation 1. The carbon atom
labeled 2 in Equation 1 may be considered an acetal. Generally speaking, an
acetal is simply a diether in which both ether oxygens are bound to the same
carbon. Acetals typically are much more stable toward alkali and, base-
catalyzed hydrolysis is much less likely to occur. Thus, by keeping the pH
above the base brine pH, or as near to 7 as possible, TEA may serve to prevent
an acid-catalyzed degradation of HEC.
[0052] In the above discussion involving an acid-catalyzed mechanisms for
polymer degradation, it should be noted explicitly that both Bronsted-Lowry
and Lewis definitions of acids are equally applicable. Thus in aqueous systems
where acids may be present and acting as such through the Bronsted-Lowry
definition of an acid, the role of the acid would be that of a "proton-donor"
while the complementary role of the TEA would be that of a "proton-acceptor".
Furthermore, in systems such as, for example, those containing the Lewis acid
zinc bromide, where the acid may be acting as such through the Lewis ,
definition of an acid, the role of the acid would be that of an "electron-
acceptor" while the complementary role of the TEA would be that of a
"electron-donor."
[0053] Another embodiment of this invention is the ability of the TEA to
improve the hydration time of HEC and the transition temperature at which
solutions of HEC in monovalent brines (such as KCl and NaCI) 'salt out,' or
separate into distinct phases (i.e., syneresis). Typically this phase
separation
manifests by the appearance of a phase of higher than original HEC
concentration, usually floating on top of a lower viscosity layer. In many
cases, the HEC will actually precipitate completely out of solution.
1b
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[0054] Two 10.0 lbm/gal NaCl brines, one treated with 0.043 vol% TEA and
the other untreated, were used to measure the effect of TEA on hydration time
and transition temperature. Both brines were viscosified with Union Carbide
HEC 10 at 4 lbm/bbl concentration. Both samples viscosified, however, the
TEA treated brine developed full viscosity in several minutes whereas the
untreated brine required over 1 hour of mixing to fully viscosify. Thus, the
addition of TEA significantly improved the hydration time.
[0055] Initial rheology measurements of the two fully viscosified brines were
taken using a Fann 35 rheometer at room temperature. The solutions were then
heat-aged in an oven at 180 °F for 22 hours, and then removed and
allowed to
cool to room temperature. Rheological measurements on both brines were then
taken on the Fann 35. As can be seen in Table 8 below, the TEA-treated
solution was homogeneous in appearance and rheological properties, whereas
the untreated solution formed separate phases in which HEC was concentrating
and salting out of solution, with the top phase considerably more viscous than
the lower phase, but neither phase quite so viscous as the homogeneous TEA-
treated solution. Clearly, some of the HEC salted-out and no longer
contributed fully to the viscosity of the un-TEA-treated fluid.
(0056] The results are tabulated below.
Initial After
Dial Heat
Aging
Reading TEA- UntreatedUntreatedTEA-TreatedTEA-Treated
(rpm) UntreatedTreatedB~om Top Bottom Top
Layer Layer Portion Portion
600 321 (est.)285 100 230 258 255
300 260 235 77 190 215 210
200 236 213 65 168 192 187
100 200 179 49 137 157 152
6 90 77 12 51 52 50
3 73 59 8 37 35 33
TABLE 8: EFFECT OF TEA ON HYDRATION TIME AND TRANSITION TEMPERATURE
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[0057] Table 8 shows that, after heat aging, there is substantially no
difference
in viscosity between the top and bottom portion of the HEC / brine / TEA
solution. However, after heat aging, Table 8 shows that distinct phases exist
in
the HEC / brine solution. Specifically, the bottom layer in the non-TEA
containing solution, has a substantially loss in viscosity, which may be
attributed to the aforementioned 'salt out' effect.
[0058] The present invention advantageously increases the effective
temperature range for natural polymer systems in an inexpensive, easy-to-
implement method. The addition of miscible amines into the polymer system
dramatically increases the temperature resistivity of the solution. Further,
the
present invention advantageously improves the hydration time and the
transition temperature of natural polymer systems in monovalent brines.
[0059] While the invention has been described with respect to a limited number
of embodiments, those skilled in the art, having benefit of this disclosure,
will
appreciate that other embodiments can be devised which do not depart from the
scope of the invention as disclosed herein. Accordingly, the scope of the
invention should be limited only by the attached claims.
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