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Polymer Chemistry and Applications MI
نویسنده : رضا سپهوند - ساعت ٢:٤٤ ‎ب.ظ روز ۱۳٩٤/٦/٢۱
 

A polymer is a large molecule comprised
of small, identical, repeating
units. The small, recurring units are
called monomers. Polymerization
occurs when the monomers are joined
together to form the large polymer
molecule. Polymers may have molecular
weights in the millions or they
may consist of only a few repeating
units. Polymers that have only a few
repeating units are called oligomers.
To express the written formula for a
polymer, the empirical formula of the
simple recurring unit is expressed to
the nth degree. For instance, the simplest
polymer is polyethylene ((C2H4)n).
Ethylene is the result of the polymerization
of the monomer ethylene
(CH2=CH2). During the polymerization
process, the double bond is lost and
the polymer polyethylene is formed.
n(CH2=CH2) ® (CH2 – CH2)n
ethylene polyethylene
The resulting polyethylene polymer
consists of a long chain of “n” repeating
units. The number of times that the
monomers are repeated is known as the
degree of polymerization. Polymers typically
have a degree of polymerization
greater than 1,000.
Polyethylene is an example of a
homopolymer. Homopolymers contain
only one monomer. Other examples of
homopolymers are polypropylene and
polystyrene. Copolymers are polymers
that are prepared from two or more
types of monomers. The monomers
can be present in various ratios and
in different positions in the chain.
Copolymerization offers a great deal
more flexibility in designing polymers.
STRUCTURE OF POLYMERS
Polymers’ structures are classified as
linear, branched or crosslinked.
Examples are given below.
Linear
Example:
CMC (Carboxymethylcellulose), PHPA
(Partially Hydrolyzed Polyacrylamide)
and HEC (Hydroxyethylcellulose).
Polymer Chemistry and Applications
Polymer Chemistry and Applications 6.1 Revision No: A-0 / Revision Date: 03·31·98
CHAPTER
6
Polymers have been used in drilling
fluids since the 1930s, when cornstarch
was introduced as a fluid-loss-control
additive. Since that time, polymers have
become more specialized and their
acceptance has increased accordingly.
Polymers are part of practically every
water-base system in use today. Indeed,
some systems are totally polymerdependent
and are termed broadly
as polymer systems.
A wide array of polymers is available
today. Some polymers — like starch,
for instance — originate from natural
sources. Other, more-specialized polymers
are modified natural polymers,
while still other more-sophisticated
polymers are derived from synthetics.
The unlimited potential of polymer
development makes polymers applicable
to virtually every drilling fluid function.
With polymer technology, it is possible
to analyze a situation on a molecular
level and design a polymer with the specific
properties to address the situation.
For this reason, polymers have an
unlimited future in drilling fluids.
A polymer
is a large
molecule
comprised
of small,
identical,
repeating
units.
Introduction
Polymer Chemistry and Applications
Polymer Chemistry and Applications
CHAPTER
6
Polymer Chemistry and Applications 6.2 Revision No: A-0 / Revision Date: 03·31·98
Branched
Example: Starch and xanthan gum.
Crosslinked
Example: Crosslinked xanthan gum
There is an infinite possibility of structural
variations. Some of the structural
possibilities that affect the performance
of polymers are listed below.
• Type of monomer or monomers.
• Molecular weight.
• Type and extent of subsequent
chemical modification on the
polymer.
• Number of branching or crosslinking
groups in the polymer chain.
CLASSIFICATION OF POLYMERS
Polymers in drilling fluids can be classified
in three ways. They can be classified
according to their chemistry, such as
anionic or nonionic; they can be classified
by their function, such as viscosifier
or filtration-control additive; or they can
be classified simply by their origin. For
this chapter, polymers are classified by
their origin. The polymers used in
drilling fluids come in three types:
• Naturally occurring.
• Modified naturally occurring.
• Synthetically derived.
NATURAL POLYMERS
Natural polymers are polymers produced
in nature, without Man’s intervention.
These materials are derived
from natural sources such as plants,
animals and bacteria fermentation.
The final product must go through
some processing — at least harvesting,
separating, grinding and drying
— before bagging. Natural polymers
have more complex structures than
synthetic polymers, and they typically
have higher molecular weights
as well. Natural polymers also are less
temperature-stable than synthetic
polymers and have a lower tolerance
to degradation by bacteria.
Natural polymers used in drilling fluids
are composed of polymerized sugar
molecules and belong to a class of
compounds called polysaccharides.
The monomers are the sugar units and
they contain carbon:hydrogen:oxygen
in the ratio of 6:12:6 (see Figure 1).
Polymerization of the sugar units
occurs through a condensation reaction
wherein water is removed from
the individual sugar units. The resulting
polysaccharide consists of the sugar
units linked together through common
oxygen atoms. Polysaccharides have a
C:H:O ratio of 6:10:5 or C6(OH2)5. The
backbone linkage of natural polymers
is more complicated than that of synthetic
polymers. The backbone consists
of carbohydrate ring structures and the
oxygen atoms that link the rings
together. Synthetic polymers have a
much simpler carbon-carbon linkage.
Figure 1: Glucose.
Starch is a natural polymer which
comes from a variety of plant and
grain sources, with corn and potato
starches being the most important
O
H
OH
H
HO
H
OH
OH
H
CH2OH
H
…polymers
used in
drilling
fluids come
in three
types…
Polymer Chemistry and Applications
Polymer Chemistry and Applications 6.3 Revision No: A-0 / Revision Date: 03·31·98
CHAPTER
6
source for drilling fluids. Starch consists
of two polysaccharides: amylose
and amylopectin. Amylose, a chain
of carbohydrate rings, makes up the
straight chain backbone of the starch
molecule. Amylopectin is a highly
branched chain of carbohydrate rings
that branches off from an amylose
backbone. The ratios of the amylose
and amylopectin fractions determine
the properties of the starch.
Starch in its raw form is not watersoluble;
it simply floats around as starch
particles. To make starch effective in
drilling fluids, it is necessary to rupture
the protective shell coating of amylopectin
to release the inner amylose.
The starch granules are heated until the
cells rupture, which allows the amylose
to disperse. This process is known as
pregelatination. Once dispersed, the
starch hydrates water. It is subsequently
dried and bagged as the final product. It
is non-ionic and soluble in saturated
saltwater as well as freshwater.
MY-LO-JELE is a cornstarch consisting
of an average of about 25% amylose and
75% amylopectin. POLY-SALE is a potato
starch which is slightly different from
cornstarch. Potato starch has a slightly
higher molecular weight than cornstarch
and also has a higher concentration
of amylose to amylopectin. For
these reasons, it functions somewhat
differently. POLY-SAL has greater tolerance
to hardness and a slightly higher temperature
stability than MY-LO-JEL. It also
produces slightly more viscosity.
The biggest drawback to the use of
starches is their tendency to ferment.
H
O
H
…O H
OH
OH
H
CH2OH
H
a
H
O
H
H
OH
OH
H
CH2OH
H
H
O
H
H
OH
OH
H
CH2OH
H
H H
H
OH
OH
H
CH2OH
H

O O O O
Figure 2: Amylose.
O
H•OH
O a O
…O O O
y
1
3
4
O
y
O…
CH2 O
x
O O
H•OH
x
a
a
6
O O O
O O O O
O O O
Figure 3: Amylopectin.
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Starch in
its raw
form is
not watersoluble…
Polymer Chemistry and Applications
CHAPTER
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Polymer Chemistry and Applications 6.4 Revision No: A-0 / Revision Date: 03·31·98
They are natural biodegrading materials
that must be preserved with a biocide
when used in drilling fluids. POLY-SAL
contains a biocide in the product. A second
limitation of starch is its low thermal
stability. Starch degrades rapidly
when exposed to prolonged temperatures
exceeding 225°F (102°C).
Some environments are more conducive
to bacterial degradation than
others. The worst environments center
around bioactive makeup water.
Stagnant pond water is the worst
source, although any water sourced
through rivers or streams should be
considered suspect. Higher temperatures,
neutral pH conditions and
fresher waters accelerate bacterial
growth. Bacterial problems in highsalt
systems and high-pH environments
are less likely; however, they
do occur after time.
Xanthan gum is classified as a natural
polymer although it is actually
obtained in its bacterially produced
form rather than in its natural form.
The bacteria Xanthomonas campestris
produces the gum during its normal
life cycle via a complex enzymatic
process. Xanthan is water-soluble,
slightly anionic and highly branched.
It has a molecular weight in the 2 to
3 million range, which is relatively
high for drilling fluids.
Xanthan is a five-ring, repeating
structure consisting of a two-ring
backbone and a three-ring side chain.
The backbone consists of glucose
residues identical in structure to cellulose.
Branching off the backbone are
three-ring side chains of additional
sugar residue. Attached to the side
chains are various functional groups
(carbonyl, carboxyl, hydroxyl and
others) which give xanthan its unique
viscosifying properties.
The long branching structure of the
polymer, coupled with the relatively
weak hydrogen bonding among the
side groups, imparts unique viscosifying
properties to xanthan. When a certain
concentration of the polymer is
reached, hydrogen bonding develops
among the polymer branches and the
result is a complex, tangled network of
weakly bound molecules. The electrostatic
interactions are weak, however, and
when shear is applied to the system, the
O
O
OH
CH2
OH
C
O
CH2
O
OH
COOOMÅ
OH
O
OH
CH2OCCH2
HO
CH2OH
OH
CH2OH
OH
O O
OH
O
O
O
O
O O
COOOMÅ
Figure 4: Structure of xanthan gum.
Xanthan
gum is
classified as
a natural
polymer…
MÅ º Na, K, 1⁄2/Ca
Polymer Chemistry and Applications
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CHAPTER
6
attractive forces holding the polymers
together are pulled apart. As the hydrogen
bonding breaks, the viscosity of the
fluid thins. When the shear is removed,
the polymer chains resume their intermolecular
hydrogen bonding and their
original viscosified state returns.
Xanthan polymer produces pseudoplastic
or shear-thinning fluids and gel
structures. As the shear is increased, viscosity
is progressively decreased. When
the shear is removed, the original viscosity
of the fluid is completely recovered.
Under high-shear-rate conditions
— in the drillstring, for instance — the
viscosity of the mud system decreases.
Under the very high shear rates experienced
in the drill bit nozzles, the fluid
thins dramatically until it behaves
almost like water. Under lower-shearrate
conditions — in the annulus, for
instance — hydrogen bonding forms
again and viscosity increases. Under
static conditions, xanthan fluids display
thixotropic characteristics providing
gels. Xanthan gum and a similar
biopolymer called welan gum are two
of only a few commercial polymers
that produce thixotropic properties
(gels) in water-base fluids.
The concentration of xanthan necessary
to develop thixotropic properties
depends on the makeup water. Only
0.5 lb/bbl may be sufficient for a highly
weighted freshwater system while it
may take 2 to 3 lb/bbl in a KCl or a
high-salinity NaCl system. In highsalinity
brines, xanthan polymer — like
other water-base polymers — does not
hydrate easily and, to some extent,
remains coiled. In freshwater, the
polymer expands and the polymer
branches come in contact, allowing
hydrogen bonding and the resulting
thixotropy to develop more easily.
Xanthan gum (such as DUO-VIST and
FLO-VIST) is added to drilling fluids for a
number of applications. Most often, it
is used as a clay substitute to impart
thixotropic properties. Xanthan gum is
used instead of loading a fluid with clay
solids to obtain viscosity and suspension.
This is beneficial in many ways,
most notably by maintaining optimum
suspension and carrying capacity in fluids
without increasing solids loading.
This property makes xanthan gum the
polymer of choice for increasing viscosity
in extended-reach and horizontal
wells, especially when the wells involve
low annular velocities.
Xanthan has several properties that
make it an ideal polymer for clay-free
“drill-in” and workover/completion
fluid applications. It viscosifies brines,
including seawater, NaCl, KCl, CaCl2,
NaBr and, to some extent, even CaBr2. It
is degradable with oxidizers (bleach) or
enzymes, and is acid-soluble for easy
clean-up. It develops gel strengths and
easily suspends acid-soluble materials
like CaCO3. FLO-VIS is a special, clarified
version of xanthan. The clarified version
has been processed to remove any bacterial
residue for clean fluid applications.
MODIFIED NATURAL POLYMERS
Modified natural polymers are very
common in drilling fluids. Cellulose
and starch are two natural polymers
that frequently are used to produce
modified natural polymers. The modified
versions can have substantially
different properties than the original,
natural polymers. For drilling fluids,
nonionic natural polymers — such as
cellulose and starch — are modified
to polyelectrolytes.
Polyelectrolytes. Many polymers are
not water-soluble and therefore are not
applicable to water-base drilling fluids
— unless they are modified. To obtain
water solubility, polymers are sometimes
modified to polyelectrolytes. This
modification involves an alteration of
the repeating unit of the polymer. A
polyelectrolyte is a polymer that dissolves
into water, forming polyions and
counter ions of the opposite charge. A
polyion has charges that repeat along
Modified
natural
polymers
are very
common
in drilling
fluids.
Polymer Chemistry and Applications
CHAPTER
6
Polymer Chemistry and Applications 6.6 Revision No: A-0 / Revision Date: 03·31·98
the polymer chain. The charges can be
positive, as in a cationic polymer, or
negative, as in an anionic polymer. A
few examples of cationic polymers exist,
but most often polymers in drilling
fluids are negatively charged.
The effectiveness of a polyelectrolyte
depends on the number of available
sites on the polymer which, in turn,
depends on the following factors:
• The concentration of the polymer.
• The concentration and distribution
of the ionizable groups.
• The salinity and hardness of the fluid.
• The pH of the fluid.
With an increasing number of ionized
sites on the polymer, it tends to extend
and uncoil. This is due to mutual charge
repulsion that elongates and stretches
the polymer into a configuration that
gives the maximum distance between
like charges. In spreading out, the polymer
exposes the maximum number of
charged sites. Spreading out allows the
polymer to attach to clay particles and
to viscosify the fluid phase.
CONCENTRATION EFFECTS
As discussed, polymers assume a
stretched or elongated configuration
when dissolved in the water phase of
a drilling fluid. This configuration is
not rod-like but twisted and curled
to obtain the maximum distance
between like charges on the polymer.
In dilute concentrations, the polymer
hydrates a thick envelope of water
(about 3 or 4 water molecules). There
is an electrostatic repulsion between
these envelopes, whose surfaces are
large when the fully extended shape
is assumed. This large surface area
contributes to the viscosity effects
of the polymer.
As the polymer concentration
increases, the envelopes of water surrounding
the polymers decrease. As
more polymer vies for less water, the
effect is an increase in viscosity. This
occurs when polymers become entangled
with one another by clinging to
a limited amount of water.
PH EFFECTS
Polymer solubility is affected by pH.
The pH often determines the extent of
the ionization of the functional groups
along the polymer chain. For instance,
the most common functional group
found in water-base polymers is the
carboxyl group. The ionized carboxyl
group is a distinguishing feature in
most anionic polymers including
CMCs, PHPAs and xanthan gums,
to name a few.
Figure 5: Ionized carboxyl group.
As seen in Figure 5, the ionized carboxyl
group has a double-bonded oxygen
and a single-bonded oxygen on the
terminal carbon. Ionization is accomplished
by reacting the carboxyl group
with an alkali material such as caustic
soda. By ionizing the previous insoluble
carboxyl group, solubility of the
polymer occurs (see Figure 6).
Figure 6: Polymer solubility.
The sodium carboxylate group draws
water to it through its anionic charged
site. When the polymer is added to
water, the sodium ion releases from the
polymer chain and leaves behind a negatively
charged site. The polymer is now
anionic and free to hydrate water. As the
polymer hydrates water, the envelope
C
O–
O
C
O
OH
Insoluble
C
O–
O
Soluble
NaOH
As the
polymer
hydrates
water…
viscosity
increases.
Polymer
solubility
is affected
by pH.
Polymer Chemistry and Applications
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CHAPTER
6
surrounding the polymer increases in
size, and viscosity increases.
The optimum solubility of the carboxyl
group occurs from 8.5 to 9.5 pH.
Enough caustic to reach 8.5 pH is necessary
to ionize and make the polymer
soluble. If greater amounts of caustic
soda are added, the viscosifying characteristics
are suppressed slightly. If a
pH reversal occurs — i.e., the solution
pH drops to acid conditions (less than
7) — then the carboxylate group
returns to its original carboxyl form
and the polymer loses its solubility.
SALINE EFFECTS
Salinity plays a very big role in determining
the effectiveness of a polymer.
Salt inhibits the unwinding, elongating
effect that occurs when a water-soluble
polymer is added to water. Rather than
uncoiling and expanding, the polymer
takes a comparatively smaller, balled
shape and its solubility is likewise
reduced. This results from the greater
competition for water. Salt limits the
availability of water in which a polymer
can hydrate and expand. As salinity
increases, polymers neither hydrate
as much water nor increase viscosity
as readily.
When salt is added to a freshwater
system in which polymers are fully
extended, the addition usually triggers
a viscosity hump. As salt hydrates
water and strips it from the polymers,
the system may be at least temporarily
destabilized, and an increase in viscosity
occurs. Polymers become entangled
with drill solids and other polymers
while shrinking back to their balled
state. Once the polymers assume their
balled state, viscosity is greatly reduced.
Typically, the effectiveness of polymers
in saline environments is reduced,
but this can be overcome with additional
treatment. For instance, PAC
(Polyanionic Cellulose) or xanthan
gum may require twice their normal
concentration, or even more, to perform
in a saline environment.
DIVALENT CATION EFFECTS
When divalent ions such as calcium
and magnesium are present in a drilling
fluid, their effect on the system
can be dramatic. Like the sodium ion,
which also hydrates water and limits
overall water availability, calcium and
magnesium ions hydrate even more
water than the sodium ion. This
makes polymer hydration in their
presence very inefficient.
Anionic polymers have an additional
problem with calcium in that
calcium reacts with the anionic group
on the polymer. In doing so, the polymer
becomes flocculated and can
be dropped from the system. For
this reason, soda ash is often recommended
to treat calcium from the system.
Polymers that are only slightly
anionic, such as xanthan gum, and
polymers that are nonionic, such as
starch, are not precipitated by calcium.
They are affected, however, by the
strong hydration characteristic of
calcium and their efficiencies are
diminished in its presence.
CELLULOSE DERIVATIVES
Cellulose is a natural polymer that is
insoluble in water. To become a useful
additive in drilling fluids, it is modified
to Carboxymethylcellulose (CMC).
CMC is an example of a polyelectrolyte.
Figures 7 and 8 show how the
repeating ring structure for cellulose is
modified by introducing the anionic
carboxymethyl group. Now the modified
polymer, through the anionic
group, has an affinity for water and
is water-soluble.
…calcium
and magnesium
ions
hydrate even
more water
than the
sodium ion.
Salt limits
the availability
of water
in which a
polymer can
hydrate and
expand.
Polymer Chemistry and Applications
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Polymer Chemistry and Applications 6.8 Revision No: A-0 / Revision Date: 03·31·98
Carboxymethylcellulose is formed
by the reaction of the sodium salt of
monochloroacetic acid (ClCH2COONa)
with cellulose. A substitution occurs
most often at the (-CH2OH) group to
form a soluble polyelectrolyte.
The properties of sodium carboxymethylcellulose
are dependent on
several factors:
• The Degree of Substitution (D.S.).
• The Degree of Polymerization (D.P.).
• The uniformity of the substitution.
• The purity of the final product.
The degree of polymerization refers
to the number of times the ring structure
is repeated. The ring structure is
the repeating structure that defines
the polymer. The higher the D.P., the
higher the molecular weight. Viscosity
increases as the D.P. for CMC increases.
High-viscosity CMC has a higher molecular
weight than low-viscosity CMC.
The degree of substitution refers to
the number of substitutions that occur
on a single repeating ring structure. In
the sodium carboxymethylcellulose
figure above, there is exactly one substitution
on each ring structure. That
means the D.S. is 1.
In the example above, the substitution
occurred only on the methyl
hydroxy (-CH2OH) group. Substitution
also could have occurred at either of
the two hydroxyl (-OH) groups, giving
a potential D.S. of 3. Water solubility is
achieved when the D.S. reaches 0.45.
The typical D.S. range for CMC is 0.7
to 0.8. High-viscosity CMC has the
same D.S. as medium- or low-viscosity
CMC. The only difference is their
respective D.P. Relatively higher substituted
CMC often is called Polyanionic
Cellulose (PAC). PAC has the same
chemical structure and the same D.P.
as CMC; only the D.S. for the two
polymers is different. The typical D.S.
range for PAC is 0.9 to 1.0.
The higher D.S. produces a polymer
that is more soluble than CMC. This
makes the performance of PAC generally
better than that of CMC. Both
materials perform about the same in
Figure 7: Cellulose.
H
O
HO
H
OH
H
H
H
OH
CH2OH
H
O
H
OH
H
H
CH2OH
H
OH
H
O
H
OH
H
H
H
OH
CH2OH
H
OH
H
H
CH2OH
H
n OH
O
O O
O
Figure 8: Sodium carboxymethylcellulose, D.S. = 1.0.
CH2OCH2COO–Na+
H
O
HO
H
OH
H
H
H
OH
CH2OCH2COO–Na+
H
O
H
OH
H
H
H
OH
H
O
H
OH
H
H
H
OH
H
OH
H
H
H
n OH
4 I
CH2OCH2COO–Na+
CH2OCH2COO–Na+
O
O
O
O
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The degree of
polymerization
refers to
the number
of times the
ring structure
is repeated.
Polymer Chemistry and Applications
Polymer Chemistry and Applications 6.9 Revision No: A-0 / Revision Date: 03·31·98
CHAPTER
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freshwater, but in saline and hard
waters, PAC outperforms CMC.
Sometimes CMC and PAC — with
identical D.P., D.S and purity — perform
differently. This is due to the
uniformity (or lack of uniformity) of
the substitution along the chain. A
good-quality CMC or PAC has uniform
substitution along the polymer.
A poorly performing CMC or PAC
may have substitution occurring at
only one end or in the middle of the
polymer. This results in a polymer
with limited solubility and, therefore,
poor performance.
POLYPACT is a high-quality polyanionic
cellulose. It provides fluid-loss control
in freshwater, seawater, NaCl and KCl
systems. It forms a thin, tough, pliable
filter cake which limits the loss of filtrate
to permeable formations. It also
produces excellent viscosity in both
saltwater and freshwater. POLYPAC is
recommended over CMC for use in
seawater, saltwater and waters with soluble
calcium levels above 400 mg/l. A
table with the technical specifications
and limitations of CMC and PAC is
found below.
Table 1: CMC and PAC.
HEC (Hydroxyethylcellulose) is
another type of modified cellulose
polymer. It is produced by soaking cellulose
in a caustic soda solution, then
reacting the alkali cellulose with ethylene
oxide. The result is a substitution
of hydroxyethyl groups on the hydroxymethyl
and hydroxyl sites. Even
though the polymer is non-ionic, the
hydroxyethyl groups have sufficient
affinity with water to make the polymer
water-soluble. In addition to the
D.S., the structure of the polymer is
affected also by the D.P. of the ethoxylated
side chains. The D.P. of the side
chains is called the Molar Substitution
(M.S.), or the average number of ethylene
oxide molecules that have reacted
with each cellulose unit. Once a hydroxyethyl
group is attached to each unit, it
can further react with additional groups
in an end-to-end formation. As long as
ethylene oxide is available, this reaction
can continue. The greater the M.S., the
greater the water solubility of the
polymer and, therefore, the greater
the tolerance to salt and hardness.
Typically, M.S. values range from
1.5 to 2.5 for HEC.
HEC is used primarily for viscosity
and fluid-loss-control in workover and
completion fluids. It is compatible with
most brines including seawater, KCl,
NaCl, CaCl2 and CaBr2. It is a very
clean polymer and is acid-soluble,
Product Mol. Wt D.P. D.S.
PAC LV 140-170 850-1,000 0.9-1.0
PAC HV 200-225 1,130-1,280 0.9-1.0
CMC LV 40-170 850-1,000 0.7-0.8
CMC HV 200-225 1,130-1,280 0.7-0.8
H
O
H
OH
H H
H
OH
H
O
H
OH
H
H
H
n
CH2OCH2CH2OCH2CH2OH OCH2CH2OH
CH2OCH2CH2OH
C
H
H
C
H
O
Ethylene oxide
Cellulose +
O
O
H
Figure 9: Hydroxyethylcellulose.
POLYPACT is a
high-quality
polyanionic
cellulose.
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Polymer Chemistry and Applications
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Polymer Chemistry and Applications 6.10 Revision No: A-0 / Revision Date: 03·31·98
which makes it ideally suited for gravelpacking
and other operations where the
completion fluid contacts the production
interval. Since HEC is non-ionic, it
does not react as strongly with charged
surfaces as do ionic polymers. This further
enhances its role as a completion
fluid additive.
HEC has a temperature limitation of
250°F (121°C). It is not affected greatly
by pH (above 10 pH, there may be a
minor loss of viscosity) and it is resistant
to bacteria. It is not a thixotropic polymer
(does not generate gel structures for
suspension) and, in fact, provides little if
any Low-Shear-Rate Viscosity (LSRV),
although it produces a great deal of
overall viscosity.
Starch derivatives. As stated earlier in
this chapter, starch is useful in many
applications without chemical modification.
But with chemical modification,
starch derivatives can be made to have
different properties. Starch can be modified
in such a way that it no longer is
susceptible to bacterial degradation. It
also can be made significantly more
temperature-stable with simple modifications.
A few examples of modified
starches are given below.
Carboxymethyl Starch (CMS).
Another example of a modified polymer
is carboxymethyl starch. Like CMC,
carboxymethyl starch undergoes a
carboxylate substitution at either the
hydroxymethyl group or at either of
the two hydroxyl groups on the ring
structure. Also like CMC, the substitution
occurs most readily at the
hydroxymethyl group.
THERMPACT UL, a carboxymethyl
starch, controls fluid loss with a
minimum increase in viscosity in
most water-base drilling fluids. It is
an alternative to PAC materials in
systems requiring tight filtration control
and low rheological properties.
THERMPAC UL performs more like a
CMC material than a starch. It has a
temperature stability similar to CMC
and PAC (up to 300°F (149°C)) and
does not require a bactericide.
THERMPAC UL is most effective when
applied in drilling fluids containing less
than 20,000 mg/l Cl– and 800 mg/l
Ca2+. It performs at any pH level and is
compatible with all water-base systems.
Hydroxypropyl starch. Another
example of modified starch is
Hydroxypropyl (HP) starch. It is produced
by reacting starch with propylene
oxide. The resulting modified starch is
nonionic and is water-soluble. The modification
actually adds to the water solubility
of the starch. As with CMS and
HEC, the substitution occurs at either
the hydroxymethyl group or at either
of the two available hydroxyl groups
on the ring structure. Also like CMC
and CMS, the substitution occurs most
readily at the hydroxymethyl group.
The result is a substitution of
propoxylated groups. The D.P. of the
propoxylated groups is known as the
H
O
OH
H
H
CH2OH
H
OH
H
H
H
OH
O
H
OH
H
H
H
n OH
CH2OCH2COO– CH2OH
…O
H
H
OH
a
H
O
OH
H
H
H
OH
CH2OCH2COO–
H H

O O O O
H
Figure 10: Carboxymethyl starch, D.S. = 1.0.
…HEC…does
not react as
strongly with
charged
surfaces
as do ionic
polymers.
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Polymer Chemistry and Applications
Polymer Chemistry and Applications 6.11 Revision No: A-0 / Revision Date: 03·31·98
CHAPTER
6
Molar Substitution (M.S.). The M.S. is
the average number of propylene oxide
molecules that have reacted with each
starch unit. Once a hydroxypropyl
group is attached to each unit, it can
react further with additional groups
in an end-to-end formation. The reaction
of propylene oxide with starch
has similarities to the reaction of cellulose
with ethylene oxide. In each
case, substitution occurs with a repeating
structure that must be defined by
its M.S.
Many types of HP starch are available.
The properties vary with the D.P.,
the D.S. and the degree of polymerization
of the substituted group (M.S.).
FLO-TROLE. An HP starch used primarily
for fluid-loss-control in FLO-PROT
systems. It works in conjunction with
calcium carbonate to form an easy-toremove,
acid-soluble filter cake. Like
starch, FLO-TROL is compatible with
most makeup brines including seawater,
NaCl, KCl, CaCl2, NaBr, CaBr2 and
formate brines. It does not require a
bactericide.
FLO-TROL has unique viscosifying
characteristics that make it suitable for
“drill-in” fluid applications. Unlike PAC
products, FLO-TROL contributes to LSRV.
It works synergistically with FLO-VIS to
increase Low-Shear-Rate Viscosity (LSRV).
Recommended FLO-TROL concentrations
are 2 to 4 lb/bbl for most applications,
although higher concentrations
are used to achieve lower filtration
rates. Temperature stability for FLO-TROL
is better than most starch materials. It
is thermally stable to 250°F (121°C) in
brine applications.
Mor-RexE. An enzyme-hydrolyzed
cornstarch which has been chemically
modified to a maltodextrin. The hydrolysis
of the starch results in a product
that is much lower in molecular weight
(less than 5,000) and imparts a slightly
anionic character to the polymer.
Mor-Rex has been used in limebase
drilling fluids almost exclusively.
This is due primarily to its tendency
to increase the calcium solubility in a
lime-base fluid environment. In such
an environment, the Mor-Rex polymer
is further hydrolyzed and Ca2+ attaches
to the free carboxylate groups formed
during hydrolysis. This results in an
increased concentration of soluble
calcium. In other words, a lime-base
system treated with Mor-Rex contains
more soluble calcium than the same
lime-base system without Mor-Rex.
It is thought that the additional Ca2+
provides additional inhibition benefits.
Functionally, Mor-Rex acts as a
deflocculant, which is consistent with
its size and anionic character. Typical
concentrations for Mor-Rex in a lime/
Mor-Rex system are 2 to 4 lb/bbl. Like
traditional starch, it is thermally stable
to about a 200°F (93°C) circulating
temperature and requires a bactericide.
SYNTHETIC POLYMERS
Synthetic polymers are chemically
synthesized, usually from petroleumderived
products. Unlike natural and
modified natural polymers, synthetic
CH2OH
H
O
OH
H
H
CH2OH
H
OH
H
H
H
OH
O
H
OH
H
H
H
n OH
CH2OCH2 – CH – O – CH2 – CH – OH CH2OCH2 – CH – OCH2 – CH – OH
…O
H
H
OH
a
H
O
OH
H
H
H
OH
H H

CH3 CH3 CH3 CH3
H
O O O O
Figure 11: Hydroxypropyl starch, D.S. = 0.5, M.S. = 2.0.
…FLO-TROL
contributes
to LSRV.
Polymer Chemistry and Applications
CHAPTER
6
Polymer Chemistry and Applications 6.12 Revision No: A-0 / Revision Date: 03·31·98
polymers are “built up” from relatively
smaller molecules. Synthetic polymers
afford an almost unlimited flexibility
in their design. They can be tailormade
to fit almost any application.
Their size and chemical composition
can be made to produce properties for
almost any function.
Frequently, synthetic polymers are
prepared from substituted ethylene. The
polymerization process occurs through
an addition reaction wherein the substituted
ethylene groups are added to the
end of the polymer chain. In the figure
below, the substituted group “A” can be
any functional group.
CH2 = CH
|A
Note the carbon-carbon backbone and
the unlimited substitution possibilities.
The carbon-carbon backbone is a more
stable linkage than the carbon-oxygen
linkage encountered earlier with starchand
cellulose-base polymers. The carboncarbon
linkage is resistant to bacteria
and has temperature stability in excess
of 700°F (371°C). The substitution
groups most likely will degrade before
the carbon-carbon linkage.
Polyacrylate. The polymerization of
acrylic acid and the subsequent neutralization
with sodium hydroxide yields
the polymer Sodium Polyacrylate (SPA).
SPA is an anionic polymer that can
function either as a deflocculant or a
fluid-loss control additive, depending on
the molecular weight of the polymer.
Figure 12: Sodium polyacrylate.
During the drilling of a well, the
interaction between the drilled solids
has a profound effect on the properties
of the mud. There is a natural tendency
for flocculation to occur (see
Figure 13). Flocculation results in an
overall increase in the rheological
properties of the drilling fluid.
Figure 13: Flocculation of drill solids.
SPA functions as a deflocculant at low
molecular weights (less than 10,000).
It is highly anionic and adsorbs on
the active solids in drilling fluids. The
adsorbed polymer neutralizes the positive
charges on aggregated particles,
which results in mutual repulsion and
deflocculation. This is best accomplished
with a small polymer. Shortchain
polymers create maximum
adsorption on the particle surfaces and
eliminate the flocculating effect that
occurs when one polymer adsorbs to
several particles (see Figure 14).
C
H
COO–Na+
CH
H
C
H
COO–Na+
CH
H
Synthetic
polymers
afford an
almost
unlimited
flexibility in
their design.
Polymer Chemistry and Applications
Polymer Chemistry and Applications 6.13 Revision No: A-0 / Revision Date: 03·31·98
CHAPTER
6
Many mud companies use lowmolecular-
weight sodium polyacrylate
as their primary deflocculant for lowsolids,
non-dispersed and other polymer
systems. It can be prepared as a
dry powder but usually is available in
liquid form.
SPA functions at much lower concentrations
than lignosulfonates. Typically,
concentrations of 0.25 to 1.0 lb/bbl are
sufficient to control rheological properties.
SPA does not depend on alkaline
pH and can tolerate temperatures to
500°F (260°C). It performs best in polymer
systems but is sometimes used as a
stand-alone product in spud mud and
in geothermal applications.
SPA is sensitive to high concentrations
of solids. Since it is a surface-active
material, it can get overwhelmed in a
high-solids environment. It works best
when the CEC of the mud is less than
20 lb/bbl bentonite equivalent and the
mud weight is less than 12 lb/gal.
TACKLET is also affected by soluble calcium,
although it is still effective in
seawater applications.
Copolymerization. So far, this chapter
has dealt only with homopolymers,
i.e., polymers prepared from identical
units (or monomers). It is possible to
start with more than one type of
monomer and undergo polymerization
and end up with a copolymer. A copolymer
contains two or more different
types of monomers.
Through copolymerization, polymers
can be made which have different properties
than any of the homopolymers
alone. Adding more monomers creates
a completely new dimension for design
possibilities. It is possible to use more
than a single monomer to impart specific
properties to the finished polymer
product. For instance, one monomer
can be used to extend temperature stability
and a second monomer can be
used to inhibit shale.
TACKLE is an example of a copolymer.
It is prepared from two monomers:
sodium acrylate (as in SPA) and a
monomer known in the industry as
AMPS (2-acrylamido-2-methyl propane
sulfonic acid). The AMPS monomer
provides a sulfonate group that imparts
greater temperature stability and tolerance
to solids, salinity and hardness
than the sodium acrylate group alone.

+


+
+
+
+
+



+
+

+ + +
– –
+ –
+ –

+

+
+


+
Figure 14: Diagram of SPA and clays.
nCH = CH2 + nCH = CH2
x
Monomer A
y
Monomer B
CH
x y
n
CH2 CH CH2
Figure 15: Copolymerization.
A copolymer
contains
two or more
different
types of
monomers.
TACKLE is an
example of a
copolymer.
SPA
Polymer Chemistry and Applications
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Polymer Chemistry and Applications 6.14 Revision No: A-0 / Revision Date: 03·31·98
AMPS is a fairly expensive monomer;
however, it can give high temperature
stability in the presence of contaminants,
which is more than PAC and
modified starch can give.
Figure 16: AMPS monomer.
TACKLE, due to the AMPS monomer,
has greater contamination resistance
and tolerance to solids than SPA
alone. Like SPA, it still is better suited
to polymer systems and low-solids,
non-dispersed applications. It also
has trouble controlling viscosity in a
high-solids environment. However,
it is more functional in seawater
than low-molecular-weight SPA.
SP-101T is a medium-molecular-weight
(±300,000) polyacrylate used primarily
for fluid-loss control. It is stable to very
high temperatures (>400°F (204.4°C))
and is often applied in geothermal
applications. Like TACKLE, it is not pHdependent
or subject to bacterial degradation,
but it is susceptible to soluble
calcium contamination. It is recommended
that soluble calcium be maintained
at a concentration of 300 mg/l
or less for optimum performance. It is
most effective in freshwater systems.
SP-101 is most often used in lowsolids,
non-dispersed systems and
other polymer systems like PHPA. In
addition to providing fluid-loss control,
SP-101 has a stabilizing effect on
drilled cuttings. SP-101 attaches to clay
particles and provides some encapsulation
of the drilled cuttings. Sometimes,
a viscosity hump is seen when SP-101 is
first added to a system. Once the polymer
is worked into the system at a sufficient
concentration to encapsulate the
solids, the system thins back and stabilizes.
Typically, this concentration
occurs at about 1 lb/bbl, but it can be
slightly more or less, depending on the
solids load. SP-101 is an effective deflocculant,
especially in high-temperature
applications and polymer applications.
While SP-101 does not provide the
immediate thinning effect that is seen
with TACKLE, it provides stabilization
of the rheological properties when the
concentration exceeds 1 lb/bbl. SP-101
is very effective at stabilizing the rheological
properties of many freshwater
systems including PHPA; geothermal;
and low-solids, non-dispersed systems.
Polyacrylamide/polyacrylate
copolymer. Partially Hydrolyzed Poly
Acrylamide (PHPA) is often used to identify
the copolymer polyacrylamide/polyacrylate.
The end product of a PHPA is
the same polymer that is formed by a
polyacrylamide/polyacrylate copolymerization.
Even though the product is frequently
referred to as PHPA, it actually is
made by the copolymerization of acrylamide
and sodium acrylate monomers.
For the sake of simplicity, the material
will be referred to as PHPA.
The properties of PHPA are affected
by the molecular weight and by the
ratio of the carboxyl groups to the
amide groups. Polyacrylamide by itself
is insoluble, so it must be copolymerized
with sodium acrylate to obtain
water solubility. Copolymerization with
sodium acrylate results in an anionic
polymer that is water-soluble. The ratio
CH2 CH
C = O
NH
C
CH2
SO3

CH3 CH3
2-Acrylamido-2-methyl propane sulfonic acid
TACKLE…is
more functional
in
seawater
than lowmolecularweight
SPA.
…SP-101
has a
stabilizing
effect on
drilled
cuttings.
Polymer Chemistry and Applications
Polymer Chemistry and Applications 6.15 Revision No: A-0 / Revision Date: 03·31·98
CHAPTER
6
of sodium polyacrylate to acrylamide
at the beginning of the process determines
the ratio of the two functional
groups on the final copolymer. The
two monomers that make up the
copolymer are shown below.
Figure 17: Sodium acrylate/acrylamide.
During copolymerization, the two
monomers are linked together in a
random fashion to form a linear, carboncarbon
backbone. The resulting copolymer
has carboxyl groups and amide
groups randomly distributed along its
backbone. The resulting copolymer is
shown in Figure 18.
Note that due to the carbon-carbon
linkage, the polymer has exceptional
thermal stability and is resistant to
bacteria. Also note that the polymer
is anionic, meaning it is affected by
hardness and cationic surfaces like
those found on clays.
POLY-PLUS.T The most commonly
used PHPA in drilling fluids is the highmolecular-
weight version which is
prepared with 65 to 70% acrylamide
and the remaining percentage acrylate.
Molecular weights range up to
20 million. POLY-PLUS is used as a shale
inhibitor and solids-encapsulating
polymer in freshwater, seawater, NaCl
and KCl systems. In addition to its
shale-inhibiting properties, it also provides
drilled cuttings encapsulation
and viscosity in freshwater systems.
The shale-inhibition feature of PHPA
occurs when the polymer attaches to
clays on the wellbore and blocks the
hydration and dispersion that normally
occurs. The anionic carboxyl
groups attach to the positive charges
on the edges of the clay particles.
Since the polymer has a high molecular
weight and is relatively long, it
combines with several sites along the
wellbore. This has the effect of coating
the wellbore and restricting water
from entering the clay.
The same effect is seen on the
drilled cuttings. The polymer helps
preserve the integrity of the cuttings,
which allows for much easier cuttings
removal at the surface.
PHPA also aids in shale stabilization
by thickening the water phase. PHPA
increases the viscosity of the drilling
fluid filtrate, which has the effect of
limiting the filtrate depth of invasion.
Although water may penetrate far into
a shale, a thick polymer filtrate faces
much greater resistance due to the rapid
buildup of capillary pressures. This has
the effect of reducing the amount of filtrate
water available for hydration. It
also limits the ability of a filtrate to
enter a small fissure or fracture plane
within a shale.
Shale studies have established that a
70:30 ratio of acrylamide units to acrylate
units is optimum for drilling fluids.
This often is referred to as 30%
hydrolysis. It has also been determined
CH = CH2
COO–Na+
Sodium acrylate
CH = CH2
C
Sodium acrylamide
O NH2
CH2
C
n
O NH2
C
O O–
C
O NH2
CH CH2 CH CH2 CH
Figure 18: PHPA.
PHPA also
aids in shale
stabilization
by thickening
the water
phase.
Polymer Chemistry and Applications
CHAPTER
6
Polymer Chemistry and Applications 6.16 Revision No: A-0 / Revision Date: 03·31·98
that higher-molecular-weight polymers
encapsulate shale better than
low-molecular-weight polymers.
As mentioned earlier, it is necessary
to copolymerize with sodium acrylate
to achieve water solubility; however,
a 100% polyacrylate does not provide
as much inhibition as the 70:30 ratio.
Even at similarly high molecular
weights, the 70:30 ratio provides
better shale inhibition.
It is thought that a high-molecularweight
polyacrylate has too much affinity
with the positive charges on clays.
Similar to lignosulfonates, as the polymer
remains in the system and attaches
to active clay edges both in the fluid system
and on the wellbore, strong attractive
forces may actually pull the clays
apart and cause them to disperse into
the system. The amide group helps by
providing some distance between the
strongly anionic carboxyl groups and
the cationic sites on the clay particles.
When the amide groups and the carboxyl
groups are distributed evenly
along the polymer chain, the bulkiness
of the amide group prevents the carboxyl
group from getting too close to
the clay charges and breaking the
clays apart.
The acrylamide group also has an
affinity with the clay surface, but it is
a relatively weak hydrogen bond compared
to the strong ionic interaction
between the carboxyl group and positively
charged edges on clay particles.
The acrylamide group is capable of
forming hydrogen bonds along the
clay surface. While not nearly as
strong as the ionic interaction taking
place alongside, it serves to hold the
polymer/clay interaction in place as
well as to provide distance between
the free charges.
In a salt environment, PHPA is still
very effective in a shale-stabilizing
capacity, although its concentration
must be increased to obtain a significant
effect on filtrate viscosity. As the
salinity of the water increases, the PHPA
does not hydrate free water as readily,
and the polymer remains somewhat
coiled. This leads to a decrease in the
viscosifying characteristic of the polymer.
The polymer is still anionic, however,
and is still adsorbed on the active
sites on the wellbore.
Applying PHPA to salt-base drilling
fluids simply means that more PHPA
polymer must be added to obtain the
same encapsulating and filtrate-thickening
effects. Since salt muds, particularly
KCl muds, impart a great deal of
shale stabilization on their own, a salt
PHPA mud offers exceptional shalestabilization
characteristics. The salt or
KCl provides excellent shale stabilization
and the PHPA provides a viscosified
filtrate that limits invasion depth.
One of the drawbacks to PHPA is its
sensitivity to soluble calcium. Like polyacrylate,
the anionic carboxyl site reacts
with calcium. This is particularly a problem
in freshwater systems, where calcium
can precipitate the PHPA polymer
as well as whatever solids the polymer is
adsorbed on. In some cases, PHPA functions
as a flocculant in the presence of
calcium, particularly when the solids
content of the drilling fluid is low.
When the solids content is low and calcium
is introduced, flocculation occurs
and the solids precipitate and settle out
of the mud. In high-solids systems, the
introduction of calcium flocculates the
system and very high viscosities result.
In a salt mud, the PHPA polymer
remains relatively coiled and is not as
susceptible to the flocculating effects
of soluble calcium. It is still affected
by Ca2+, at least to some extent. Since
the Ca2+ reacts directly on the polymer
with an anionic site, that anionic site
is no longer available for an active
wellbore site. In short, more polymer
must be used to overcome the effect
of calcium.
It is recommended to treat soluble
calcium to below 300 mg/l in PHPA
One of the
drawbacks
to PHPA is
its sensitivity
to soluble
calcium.
Polymer Chemistry and Applications
Polymer Chemistry and Applications 6.17 Revision No: A-0 / Revision Date: 03·31·98
CHAPTER
6
systems. This is easier to perform in
low-solids, low-density applications,
particularly when the solids are not that
hydratable. When the solids concentration
is relatively high, such as a mud
weight over 10 lb/gal and an MBT
above 20 lb/bbl bentonite equivalent,
then it is more difficult to treat calcium.
Removing calcium from the system
requires adding a carbonate source,
such as soda ash or bicarbonate of soda,
which may flocculate the system.
A similar analogy is made with magnesium
contamination. Magnesium
also is attracted to the anionic carboxyl
site. To treat magnesium, it is necessary
to increase the pH to the 10.0 to 10.5
level. Since the reaction that occurs at
that pH is reversible, the pH must be
maintained at that high level to prevent
the now-insoluble magnesium
from becoming soluble again. PHPA
systems are non-dispersed systems and
do not tolerate alkaline pH easily. Like
any non-dispersed system, the addition
of caustic soda has a flocculating effect
on PHPA systems. The hydroxide ion
(OH–) is very reactive and goes straight
to the unprotected clays in the system.
The result is the same that is seen when
caustic soda is added to spud mud,
which is flocculation.
Hydrolysis of the PHPA polymer
occurs at any pH, but it is insignificant
until a pH of 10 is reached, when
a more rapid hydrolysis begins. The
hydrolysis is nowhere complete at pH
10, but since hydrolysis results in the
release of ammonia gas (NH3), which
is very noticeable at low concentrations
at the rig site, it is something to
avoid. Hydrolysis is actually a fairly
slow process at pH 10, taking a very
long time for the reaction to proceed
through the coiled polymer. The process
can be accelerated by high temperatures.
At temperatures above 300°F
(149°C), hydrolysis occurs at a much
higher rate.
PHPA AS A BENTONITE EXTENDER,
SELECTIVE FLOCCULANT AND
TOTAL FLOCCULANT
Depending on its molecular weight
and ratio of acrylamide to acrylate
monomers, PHPA can serve several
functions in a water-base drilling fluid.
GELEX.T An example of PHPA used as
a bentonite extender. When the conditions
are right, very low concentrations
of PHPA can extend the viscosity of
bentonite. When the total solids of the
system are less than 4% by volume,
and the total bentonite concentration
is less than 20 lb/bbl, PHPA can attach
to the positive sites on a bentonite clay
particle. With the bentonite particle
attached to part of the polymer and
the remaining polymer free to hydrate
and/or attach to other clay particles,
the result is an increase in viscosity. In
effect, the PHPA polymer is hydrated
and uncoiled and in suspension with
colloidal bentonite particles.
For PHPA to extend the yield of bentonite
effectively, several conditions
other than bentonite and total solids
concentrations must be met. First, the
system must be a freshwater system and
relatively free of calcium (< 200 mg/l)
for the bentonite to hydrate properly.
Second, the amount of polymer must
be in the 0.05 to 0.1 lb/bbl concentration
range. Third, no dispersants — or
any other additive that adsorbs to the
bentonite — can be in the system.
The process of extending bentonite is
fragile and limited to low-solids, nondispersed
applications. The addition of
only a small amount of PHPA causes an
immediate increase in viscosity. As the
concentration of PHPA is increased, the
viscosity reaches a maximum value and
then, as additional polymer is added,
breaks back. The effective range of polymer
concentration is very narrow. Too
little polymer concentration, and the
system is little more than a gel slurry
with a low concentration of bentonite.
Removing
calcium from
the system
requires
adding a
carbonate
source…
Hydrolysis of
the PHPA
polymer…is
insignificant
until a pH
of 10 is
reached…
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Polymer Chemistry and Applications 6.18 Revision No: A-0 / Revision Date: 03·31·98
Overtreat with polymer, and the system
thins out too much.
The degree of bentonite extension
depends on the following factors:
• The MW and the ratio of acrlyamide
to acrylate.
• The size and hydration of the particle.
• The salinity and hardness of the
makeup water.
• The concentration of the PHPA
polymer.
FLOXIT.E PHPA also can be used as a
flocculant. Flocculation is the process by
which individual particles are connected
in loosely bound, large aggregates by a
flocculating polymer. The resulting mass
of linked particles increases to the point
at which the solids agglomeration falls
out of suspension. Settling is most
effective when the system is static.
The mechanism involved in flocculation
is very much like the mechanism
used for bentonite extension. PHPA is
also effective in both applications. It
should be noted that PHPA is not as
effective at flocculating systems that
contain bentonite. Since bentonite
breaks up into colloidal-size, hydrated
solids, bentonite does not settle. The
small hydrated particles do not have
enough density to settle.
The use of FLOXIT is limited to clearwater
drilling applications. Once solids
build in the water or the system is
weighted, the product is no longer useful.
Determining the optimum concentration
of FLOXIT must be determined by
pilot testing. The effectiveness of the
flocculation depends on the interaction
of the polymer with the solids, which
in turn depends on the following:
• Hydratability of the solids.
• The concentration of the solids.
• Salinity of the water.
• Hardness of the water.
• Chemical characteristics of the
polymer.
• Polymer concentration.
• Rheological properties of the system.
• Geometry and size of the settling pit.
• Retention time.
• Temperature.
It is recommended that FLOXIT be
mixed in dilution water at a concentration
of 1 to 2 lb/bbl before adding
it to the system. Again, pilot testing is
necessary to determine the optimum
concentration.
HIGH-TEMPERATURE
SYNTHETIC POLYMERS
Due to the thermally stable carboncarbon
linkage that makes up the
backbone of synthetic polymers, hightemperature
polymers are synthetically
derived. Several high-temperature polymers
are available for drilling fluids. A
number of them are prepared from the
AMPS (2-acrylamido-2-methyl propane
sulfonic acid) monomer. AMPS was
covered earlier in this chapter in conjunction
with TACKLE. AMPS is used in
the preparation of TACKLE to improve
tolerance to solids, salinity and hardness
at high temperatures.
AMPS is also used to improve the
high-temperature tolerance to contaminants
in fluid-loss-control additives.
Examples of copolymers and terpolymers
that incorporate the AMPS
monomer or other sulfonated monomers
are the Hoechst’s Hostadrill 2825,
Drilling Specialties’ Driscal-D and SKW’s
Polydrill. The manufacturers of these
materials claim that their respective
polymers withstand salt and hardness
at temperatures to 400°F (204°C).
Chemical structures for Hostadrill and
Polydrill are given in Figures 19 and 20.
An example of a high-temperature
polymer that functions to prevent hightemperature
gelation is a Sulfonated
Styrene Maleic Anhydride (SSMA)
copolymer. Generally, it is applied to
wells at high temperatures prior to logging
runs and at other times when the
drilling fluid is not circulated for an
extended period of time. It has the effect
PHPA also
can be used
as a
flocculant.
Polymer Chemistry and Applications
Polymer Chemistry and Applications 6.19 Revision No: A-0 / Revision Date: 03·31·98
CHAPTER
6
of maintaining stable gel strengths at
high temperatures. It is not a fluid-loss
control additive or a deflocculant (see
Figure 21).
Figure 21: SSMA.
The M-I POLYSTARE 450 system is based
on synthetic polymers. One product,
RHEOSTAR,E is used to control hightemperature
gelation, high-temperature
bentonite flocculation, and to provide
thinning or deflocculation. Due to the
complex nature of high-temperature,
water-base environments, RHEOSTAR is
actually a blend of three low-molecularweight
synthetic polymers. These
polymers are different from the
more traditional AMPS acrylate-base
polymers. RHEOSTAR is a dry powder that
is readily functional in seawater and
freshwater. It is stable to 450°F (232°C).
Typical concentrations vary from 6 to
12 lb/bbl.
DURASTAR.E DURASTAR provides hightemperature
filtration control in the
POLYSTAR 450 system. It is a crosslinked
copolymer prepared from acrylamide
monomer, a sulfonated monomer and
a crosslinking monomer. The degree of
crosslinking in the polymer structure
plays an important role in the polymer’s
solubility and fluid-loss control
characteristics. Too much crosslinking
results in a polymer that is rigid and
poorly hydrated, while too little
crosslinking results in a polymer that
has properties similar to PHPA, which
is long and linear with little tolerance
to contamination.
Due to its crosslinked structure,
DURASTAR is compact and globular in
structure. It retains a compact, spherical
shape compared to the expanded,
uncoiled forms of linear polymers (see
Figure 22) which uncoil into linearshaped
particles.
Figure 22: DURASTAR.
An advantage to its compact shape
is that DURASTAR is more protected
and, therefore, more thermally stable
and resistant to solids and hardness.
DURASTAR is stable to 450°F (232°C) in
both freshwater and seawater applications.
Typical concentrations range
from 5 to 10 lb/bbl. It is available as
a 30% active inverse emulsion.
CH2 CH
C =
NH
C
CH2
SO3Na
H3C CH
CH2 CH
N
C = O
CH3
CH3
CH2 CH
NH2
C = O
n
Figure 19: Hostadrill 2825.
CH2
SO3
–Na+
n
C CH2 C
SO3
–Na+
OH R’
OH
Figure 20: Polydrill.
CH
O = C
CH
O
CH2 CH
SO3Na
C = O
n
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The M-I
POLYSTARE 450
system is
based on
synthetic
polymers.