Note: Descriptions are shown in the official language in which they were submitted.
llliS9S
This invention relates to water-swellable
polymer microgels and to methods for their use.
It has been known for some time to employ
water-soluble polymers such as polyacrylamide as thicken-
ing agents, e.g., as taught in EncYclopedia of Polymer
Science and Technology, Interscience Publishers, Vol. 1,
.
192 (1964), and as agents for restricting the flow of
liquids through subterranean formations, e.g., as taught
in U.~. Patent No. 3,039,529.
Normally such polymers which are generally
linear are advantageously prepared by a microdisperse
polymerization technique such as described in U.S. Patent
Nos. 3,284,393 and 2,982,749. Unfortunately, these
linear polymers exhibit virtually no gel strength, i.e.,
do not resist viscosity changes as a result Qf mechanical
_ working or milling. As a result, when such polymers are
subjected to the high shearing action that is common to
many applications wherein such polymers are used as
thickening agents or as agents for restricting the flow
of liquids through pore structures, they undergo substan- -
- tial degradation in molecular weight, thereby impairing
most of their desirable properties.
Attempts to improve the gel strength of such
polymers via cross-linking such polymers as shown in
2~ U.S. Patent No. 3,247,171 have not been very successful.
Accordingly, heretofore in order to obtain the desired
increase in viscosity or fluid mobility control with the
aforementioned polymers, it has been necessary to employ
rather low shearing, mixing or pumping apparatus in the
desired applications. Such low shearing apparatus are
1111S95
generally less economical and more time consuming to
employ.
In view of the aforementioned shear sensitivity
of the aforementioned water-soluble, linear polymers and
water-swellable, cross-linked polymers, it would be highly
desirable to provide a polymer capable of imparting sub-
stantial viscosity to an aqueous medium but which will
resist degradation when such aqueous medium is subjected
to the high shear common to many mixing and pumping apparatus.
The present invention is such a shear resistant,
viscosity-enhancing polymer which exists in the form of
discrete, spheroidal microgels of a water-swellable or
water-swollen, cross-linked polymer. The microgels have
partly or totally water-swollen diameters which are generally
within the range from about 0.5 to about 200 micrometers.
The microgels, when dispersed in water or other aqueous
media, exist in discrete, spheroidal, water-swollen par-
ticles which can be separated from the aqueous media by
filtration or similar technique.
These novel high molecular weight polymer
microgels, although highly water-swellable, are substan-
tially insensitive to mechanical shearing in aqueous
media. Consequently, such microgels can be used for a
variety of applications wherein high mechanical working,
milling or high shear pumping of an aqueous medium con-
taining the microgels is required. Unlike high molecular
weight polymers currently available which thicken aqueous
solutions but which also give solutions which are stringy,
the microgels of this invention are effective thickening
agents which, when dispersed in an aqueous medium, exhibit
,
pseudoplastic rheology and short solution characteristics.
By "short solution" characteristics is meant that an aqueous
medium containing the microgels does not produce threads
or strings of such aqueous medium when two surfaces wetted
with the medium are contacted and pulled apart.
Because of their uniform small particle size
and their ability to absorb substantial proportions of
water, the microgels are particularly suited for appli-
cations requiring thickening agents, applications requir-
ing rapid sorption of aqueous fluids, e.g., sanitary
articles such as diapers, belt pads and the like, and for
applications wherein the swelling or partial plugging
properties of the polymer are particularly important,
e.g., in the plugging of porous formations or structures.
Of particular interest are the applications
involving the use of such microgels in enhanced oil
recovery operations wherein a drive fluid is introduced
through a bore hole in the earth into a porous subterran-
ean formation penetrated by said bore hole, thereby
driving the oil from oil bearing structures toward a
producing well. In addition, fluid media containing the
microgels are usefully employed as the fluid in well
drilling operations, as packer fluids in well completion
operations and as mobility control fluids in other
enhanced oil recovery operations. It is further observed
that fluid media containing the microgels are very useful
in the treatment of subterranean structures containing
substantial amounts of salt water or brine which normally
hinder the application of conventional polymeric treating
agents.
.
17,132B-F -3-
-4- llliS95
The invention resides in a composition which
comprises discrete, spheroidal microgels of a water-
-swellable polymer consisting essentially of water-soluble
ethylenically unsaturated monomers wherein said microgels
in the dry state have diameters les than about 20 micro-
meters, said polymer being sufficiently cross-linked to
enable the microgels to remain as discrete spheroidal
particles having diameters in the range from about 0.5
to about 200 micrometers when said microgels are dispersed
in an aqueous fluid medium.
, The invention further resides in a viscous,
short aqueous composition comprising an aqueous medium
having dispersed.therein from 0.1 to 2 percent by weight
of microbeads'of a water-insoluble,'water-swellable polymer
of a water-soluble'vinyl monomer ox mixture of water-.'
-soluble vinyl monomers, cross-linked with a difunctional
cross-linking agent copolymerizable with said monomer or
monomers, said microbeads having diameters of from 0.2 to
4 microns in the dry state and having a gel capacity.of
at least about 10 grams per gram in aqueous 0.27 molar
sodium chloride solution, said polymer being cross-linked
with from 50 to 1000 parts by weight of cross-linking
agent per million parts of vinyl monomer or monomers
in the polymer.
The invention further resides in a method for
thickening an aqueous medium to obtain a composition having
the properties of a viscous short solution and being
resistant to viscosity degradation under conditons of high
. shear which comprises the step of thoroughly dispersing in
said medium from 0.1 to 2 percent by weight of microbeads
of a water-insoluble, water-swellable polymer of a water-
-soluble vinyl monomer or mixture of water-soluble vinyl
monomers, cross-linked with a difunctional cross-linking
17,321B-F -4_
-4a~
agent copolymerizable with said monomer of monomers,
said microbeads having diameters of from 0.2 to 4 microns
in the dry state and having a gel capacity of at least
about 10 grams per gram in aqueous 0.27 molar sodium
chloride solution, said cross-linking agent being present
in an amount from 50 to 1000 parts by weight of cross-
-linking agent per million parts of vinyl monomer or
monomers in the polymer.
Reference is hereby also made to copending
application Serial No. 291,282, filed November 21, 1977
claiming an invention by M. L. Zweigle et al for a
hydrocarbon recovery method for thickening an aqueous
medium to obtain a composition having the properties of
a viscous short solution and being resistant to viscosity
degradation under conditions of high shear which comprises
the step of thoroughly dispersing in said medium from about
O.l to about 2 percent by weight of microbeads of a
water-insoluble, water-swellable polymer of a water-
-soluble vinyl monomer or misture of water-soluble
vinyl monomers, cross-linked with a difunctional cross-
linking agent copolymerizable with said monomer or
monomers, said microbeads having diameters of from about
0.2 to about 4 microns and having a gel capacity of at
least about 10 grams per gram in aqueous 0.27 molar sodium
chloride solution, said cross-linking agent being present
in an amount from about 50 to 1000 parts by weight of
cross-linking agent per million parts of vinyl monomer
or monomers in the polymer.
The microgels of the present invention are gener-
ally characterized as discrete, well defined spheroids that
are water-swellable and/or water-swollen In their water-
swollen or at least partially water-swollen state, the
microgels comprise water and a cross-linked polymer of a
water-soluble, ethylenically unsaturated monomer.
In the dry state, the microgels exist as micro-
beads having diameters generally less than 20 micrometers,
17,321B-F -4a-
. .
ll~iS9S
preferably less than about 4 micrometers and most preferably
less than about 1 micrometer. In their partly or totally
water-swollen state, the particle sizes of the microgels E-
can range from about 0.5 to about 200 micrometers,
preferably from about 1 to about 10 micrometers. In
their partly water-swollen (preinversion) state, the -
microgels are water-swellable and contain at least 30
weight percent of cross-linked polymer and up to about 70 -
weight percent of water. In their totally water-swollen
(postinversion) state, the microgels contain up to about
99.9 weight percent of water and as little as about 0.1 -
weight percent of cross-linked polymer. The microgels,
when dispersed in a fluid aqueous medium such as water,
can be subjected to a substantial amount of high shear,
e.g., greater than 500 sec 1, without undergoing substan-
tial degradation, i.e., loss of particle size or capacity
to hold water ~often called gel capacity). Such high t
shear is ch æ acteristic of colloidal mixing employed in
preparing relatively high viscosity coating formulations
and the ~umping action existing in many enhanced oil
recovery operations.
Ethylenically unsaturated monomers suitable
for use in preparing the microgels are those which are
sufficiently water-soluble to form at least 5 weight
percent solutions when dissolved in water and which
readily undergo addition polymerization to form polymers
which are at least inherently water-dispersible and
preferably water-soluble. By "inherently water-dis-
persible", it is meant that the polymer when contacted with
an aqueous medium will disperse therein without the
X -
aid of surfactants to form a colloidal dispersion of
the polymer in the aqueous medium. Exemplary monomers
include the water-soluble ethylenically unsaturated
amides such as acrylamide, methacrylamide and fumaramide;
N-substituted ethylenically unsaturated amides such as
N-substituted-(N',N'-dialkylaminoalkyl)acrylamides, e.g.,
N-(dimethylaminomethyl)acrylamide and N-(diethylamino-
methyl)methacrylamide and quaternized derivatives thereof,
e.g., N-(trimethylammoniummethyl)acrylamide chloride;
ethylenically unsaturated carboxylic acids such as acrylic
acid, methacrylic acid, itaconic acid, fumaric acid and
the like; ethylenically unsaturated quaternary ammonium
compounds such as vinylbenzyltrimethylammonium chloride;
sulfoalkyl esters of carboxylic acids such as 2-sulfoethyl
methacrylate and the alkali metal and ammonium salts thereof;
aminoalkyl esters of unsaturated carboxylic acids such
as 2-aminoethyl methacrylate; vinylaryl sulfonates such
as vinylbenzene sulfonates including the alkali metal
and ammonium salts thereof and the like.
Of the foregoing water-soluble monomers,
acrylamide, methacrylamide and combinations thereof with
acrylic acid or methacrylic acid are preferred, with
acrylamide and combinations thereof with up to 70 weight
percent of acrylic acid being more preferred. Most
preferred are the copolymers of acrylamide with from
about 5 to about 40, especially from about 15 to about
30, weight percent of acrylic acid. The particle size
of the microgels of these most preferred copolymers is
more easily controlled than are the acid-free copolymers.
For example, the addition of polyvalent metal ions such
~i~
lll~$~S 1,
as calcium, magnesium and the like to aqueous compositions
containing the most preferred microgels reduces the -
particle sizes of microgels by a highly predictable
amount.
In the most preferred embodiments, it is -
desirable that the total monomer mixture contain a
relatively small proportion (i.e., an amount sufficient
to cross-link the polymer, thereby converting the polymer
to a non-linear polymeric microgel without appreciably
reducing water swellability characteristics of the
polymer) of a copolymerizable polyethylenic monomer.
Exemplary suitable comonomeric cross-linking agents
include divinylarylsulfonates such as divinylbenzene- ;
sulfonate, diethylenically unsaturated diesters including
,. .
alkylene glycol diacrylates and dimethacrylates such as
ethylene glycol diacrylate, ethylene glycol methacrylate
and propylene glycol diacrylate; ethylenically unsatur-
ated esters of ethylenically unsaturated carboxylic acids
such as allyl acrylate; diethylenically unsaturated
20 ethers s~ch as diallyl ethylene glycol ether, divinyl
ether, diallyl ether, divinyl ether of ethylene glycol,
divinyl ether of diethylene glycol, divinyl ether of
triethylene glycol; N,N'-alkylidene-bis(ethylenically
unsaturated amides) such as N,N'-methylene-bis(acrylamide),
N,N'-methylene-bis(methacrylamide), and other lower
alkylidene-bis(ethylenically unsaturated amides) wherein
the alkylidene group has from 1 to 4 carbons. When a
cross-linking comonomer is the means employed to provide
the necessary cross-linking, any amount of such cross-
-linking comonomer in the monomer mixture is suitable
~ '
17,i21B-F ~7~
lil~lS95
provided that it is sufficient to cross-link the polymer
to form a discrete, spheroidal, water-swellable microgel
as defined herein. Generally, the concentration of
cross-linking comonomer, particularly when the comonomex
is a methylene-bis(acrylamide), is in the range from
about 5 to about 5,000 weight parts of cross-linking
comonomer per million weight parts of total monomer.
Preferably, however, good results have been achieved when
the cross-linking agent i8 employed in concentrations
from about 5 to about 200, more preferably from about 10
to about 100 parts, by weight of cross-linking agent per
¦ million weight parts of total monomer.
The microgels are advantageously prepared by
¦ microdisperse solution polymerization technizues, e.g. J
¦ 15 the water-in-oil pol~erization method described in
U.S. Patent No. 3,284 J 393 issued November 8 J 1966 to The
¦ Dow Chemical Company. In the practice of this methodJ
a water-in-oil emulsifying agent is dissolved in the
¦ oil phase while a free radical initiatorJ when one is
i 20 used, is dissolved in the oil or monomer (aqueous)
phase, depending on whether an oil or water-soluble
initiator is used. The weight ratio of the aqueous
phase containing the monomer(s) to the oil phase may
vary from about 0.1:1 to about 4:1, preferably from about
25 ` 1:1 to about 3:1. An aqueous solution of monomer or
mixed monomers or a monomer per se is added to the oil
phase with agitation until the monomer phase is emulsi-
fied in the oil phase. Usually the agitation is sufficient
to provide disperse aqueous globules having diameters in
the range from about 0.5 to about 100 micrometersJ
A 17,32lB-F -8-
llliS95
preferably from about 1 to about 50 micrometers. In
cases where a cross-linking comonomer is employed, the
cross-linking comonomer is added along with the other
monomer(s) to the oil phase. The reaction is initiated
S by purging the reaction medium of inhibitory oxygen and
continued with agitation until conversion is substantially
complete. The product obtained has the general appearance
of a polymeric latex. When it is desirable to recover
the microgel in essentially dry form, the polymer microgel
is readily separated from the reaction medium by adding a
flocculating agent and filtering and then washing and
drying the microgel. Alternatively, and preferably, the
water-in-oil emulsion reaction product is suitably employed
as is.
A suitable, but less preferred, method for
preparing the microgels is a microsuspension method
wherein aqueous solutions of the monomers are suspended
in an oil phase and then subjected to conditions of free
radical suspension polymerization. In such method the
concentr~tion of monomer in the aqueous solution can be
varied over a wide range, for example, from about 5 to
about 80 weight percent of monomer in the aqueous solution,
preferably from about 20 to about 40 weight percent. The
choice of a particular monomer concentration depends
in large part upon the particular monomer being employed
as well as the polymerization temperature. The ratio
of the aqueous solution of monomer to the oil phase is
also widely variable, advantageously from about S to
about 75 weight parts of aqueous phase to correspondingly
from about 95 to about 25 weight parts of oil phase.
~ ' ' '
17,321B-F ~9~
1111595
The suspending agent suitably employed as a solid or
liquid substance having a low hydrophile-lipophile
balance, i.e., preponderantly hydrophobic. Exemplary
suitable suspending agents are described in U.S. Patent
S No. 2,982,749. A preferred suspending agent is an
organic polymer which, while predominantly hydrophobic,
has hydrophilic substituents such as amine, sulfone,
sulfonate, carboxy, and the like. The suspending agent
should be employed in an amount sufficient to assure
the desired particle size of the resultant microgel,
preferably from about 0.4 to about 1 weight percent,
based on the weight of the aqueous phase. Exemplary
preferred suspending agents include silani7ed silica,
ethyl cellulose and the like. In order to insure that
microgéls having the desired particle size are obtained,
it is often desirable to subject the water-in-oil sus-
pension to high rates of shear.
In either process, the oil phase can be any
inert hydrophobic liquid which (1) does not take part in
the polymerization reaction and (2) can be separated
readily from the polymeric product. Of such liquids the
hydrocarbons and chlorinated hydrocarbons such as toluene,
xylene, o-dichlorobenzene, ethyl benzene, liquid paraffins
having from 8 to 12 carbons, monochlorobenzene, propylene
dichloride, carbon tetrachloride, l,l,l-trichloroethane,
tetrachloroethylene, methylene chloride, etc., are
advantageously employed, with liquid paraffins, toluene,
xylene and the chlorinated hydrocarbons being preferred.
~11159S
Polymerization initiators suitably employed -
in either the suspension or emulsion polymerization tech- -
niques include peroxygen catalysts such as t-butylhydro-
peroxide, dimethanesulfonyl peroxide and redox systems
such as t-butyl hydroperoxide or alkali metal or ammonium
persulfates in combination with usual reducing agents
such as sulfide or bisulfide. Alternatively, any free
radical generating means can be suitably employed, for
example, those generated in situ by ultraviolet or X-rays
and the like. ~-
In addition to the employment of a cross-linking
monomer as a means for forming the desired polymer
microgel, other cross-linking techniques are also suitable.
For example, the polymer in dispersed particulate form
may be cross-linked subsequent to polymerization by treat-
ment with a chemical cross-linking agent for the polymer
such as bleach or similar alkali metal hypohalite or
aldehydes such as formaldehyde and dialdehyde, e.g.,
glyoxal, when the polymer is one bearing pendant amide
groups. '
In addition, it is sometimes desirable to
convert the polymer microgel to a product that has
substituted cationic character such as the N-amino-
methyl form (Mannich form) of polyacrylamide, or to a
polycation such as the quaternized derivative of the
Mannich derivative of polyacrylamide. For example, in
the preparation of polymer having cationic characteristics,
the polymer microgel may be reacted with formaldehyde and
an amine to produce the polymer in a manner as disclosed
in U.S. Patent No. 3,539,535. Alternatively, the cationic
~ '
~111595
Mannich polymer microgel can be made by polymerization of
cationic Mannich derivative of acrylamide and then homo-
polymerized or copolymerized with acrylamide or other
suitable comonomer. The polycation may be formed by
reacting the microgel of the Mannich derivative of
polyacrylamide with an alkyl halide and thereby quaternize
the amine nitrogen, for example, as described in the
procedure in U.S. Patent No. 3,897,333. Also it may be
desirable to hydrolyze some of the amide moieties of
acrylamide polymer microgels to acid form by treatment
with a hydrolyzing agent such as sodium hydroxide.
In using the cross-linked microgels as thickening
agents, it is generally desirable to assure that the micro-
gels are rapidly and thoroughly dispersed throughout the
aqueous medium in which thickening is desired. Thus,
for example, in employing the microgels to thicken a
styrene/butadiene copolymer latex for use in paper coating,
it has been found that direct introduction of the dry,
solid microgel into the latex may cause lumping or even
coagulation. In practice, it is therefore desirable
to disperse the microgels in a fluid medium as in the
case of a water-in-oil emulsion which is relatively inert
to the latex before introducing microgels into the latex.
For example, a water-in-oil emulsion of the microgels
can be thoroughly mixed with a finely divided mineral
pigment! such as calcium carbonate or titanium dioxide,
employed in such coating compositions and the resulting
mixture be rapidly dispersed in the latex. Alternatively,
the microbeads may be dispersed in a water-miscible liquid
in which the beads æ e not swelled appreciably and then
,
~ 7 '~
9~
rapidly dispersed in the aqueous medium to be thickened.
For example, the microgels prepared as in Example l herein-
after, can be moistened with methanol and dispersed in
tripropylene glycol to produce a slurry containing 30
weight percent of the microgels. Sufficient of this
slurry is then dispersed in the latex composition to
provide at least about 0.1 weight percent of the microgel
based on the total of available water remaining in the
latex composition, thereby producing a composition having
a viscosity of greater than 6,000 centipoises and suitable
for use as a carpet backing.
Generally, in the thickening applications, the
microgels are employed in amounts sufficient to give
viscosity suitable for the end use desired. Because such
viscosities vary with the different end uses and because
quantity of microgel needed to produce a particular
viscosity will vary with the gel capacity of a particular
microgel as well as a concentration of ions in the
aqueous medium to be thickened, specific numerical limits
of the a~ounts of microgel to be used in all systems
cannot be specified. However, in an aqueous composition
having very low ion concentration, microgels which have
normal gel capacities are usually employed in concentrations
from about 0.1 to about 2 weight parts, preferably from
about 0.1 to about l weight part, per hundred weight
parts of available water. For the purposes of this
invention, the term "available water" is defined as that
water which is not, in some way, bound to or coordinated
with the polymer or additives present in the system.
Thus, available water is water available for thic~ening
.. ~ _ . .
and provides fluid viscosity to the slurry. It should be
noted that the gel capacity of the water-swellable
microgels varies with the ionic strength of the aqueous
medium to be thickened. Thus, a given sample of beads
may sorb 5 to lO times as much deionized water as they
will when dispersed in a salt solution. In an aqueous
0.27 molar sodium chloride solution, the preferred
microgels have gel capacities of at least 10, preferably
at least 50, grams of solution per gram of polymer. In
such salt solutions the microgels often exhibit gel capa-
cities up to about 120 grams of solution per gram of polymer
whereas in distilled water, the same microgels may exhibit
gel capacities up to about 2,500-3,000 grams of water
per gram of polymer.
lS In the practice of employing the aforementioned
microgels in a process for controlling the permeability
of a porous structure such as, for example, plugging a
porous structure in a subterranean formation, it is
desirable to disperse the microgels in a fluid medium,
preferably water or a water-in-oil emulsion, such that
the resulting dispersion is reasonably stable. The con-
centration of the microgels in the fluid medium is suitably
any concentration that affects the desired control of
permeability of the treated formation. In this application,
it is desirable to minimize the viscosity of the fluid
medium containing the microgels and thereby-reduce the
amount of energy required to pump the fluid medium into
the porous structure. Accordingly, it is desirable to
dilute the microgel in the fluid medium as much as possible
prior to its introduction into the porous structure.
1111595
In preferred embodiments utilized for fluid mobility
control and enhanced oil recovery, it is desirable that
the concentration of the microgels in the fluid medium be
in the range from about 100 to about 50,000 parts per
million of dry polymer based on the total weight of the
fluid medium, more preferably from about 250 to about
10,000 parts per million, most preferably from 250 to
about 5,000 parts per million.
While the particle size of the microgels for
such permeability control applications is not particularly
critical, it is found that the microgels are most advan-
tageously employed in porous structures that are generally
free of large fractures or vugs that are more than 10
times the diameter of the swollen microgel and preferably
lS is free of vugs that are about 5 times or more in size
than the diameter of the swollen microgel. In most
preferred embodiments, it is desirable to employ microgels
having diameters that are from about one-third to about
the same size as the average pore size of the porous
formation. In selecting the microgel, it should be under-
stood that it is the particle size that the microgel will
possess in the pore subterranean structure to be treated
that is significant. Accordingly, the gel capacity of
the microgel as well as its sensitivity to ion concentration
which may exist in the pore structure, e.g., brines that
exist in many oil bearing subterranean formations, are
important.
The fluid medium used to carry the microgels
into the porous structure is suitably any fluid medium
which does not substantially inhibit the water-swelling
X
17,321B-F -lS-
111~595
characteristics of the microgels. Most commonly, the
fluid medium is an aqueous liquid which may contain a --
variety of other ingredients such as salts, surfactants,
bases such as caustic and other additaments commonly L
employed in controlling the permeability of pore structures. ~-
In light of their desirable utility for controlling
the mobility of liquids through pore structures, the micro-
gels of the present invention are very advantageously
employed in enhanced oil recovery operations wherein a
drive fluid is introduced through a bore hole in the earth
into a pore subterranean formation penetrated by said bore
hole, thereby driving oil from oil bearing structures
toward a producing well. In addition, fluid media con-
taining the microgels are also usefully employed as the
fluid in well drilling operation, as packer fluids in well
completion operations and as mobility control fluids in
other enhanced oil recovery operations. The microgels
of the present invention are particularly effective for
decreasing the mobility of the drive fluid, such as water
or other fluids, or decreasing the permeability of non-
-fractured porous formations prior to or during enhanced
oil recovery operations which involve the use of driving
fluids. The microgels are also useful for water shut-off
treatments in production wells in which the fluid medium
containing the microgels can be injected into the forma-
tion prior to or subsequent to the injection of another
fluid. Moreover, the microgels may be employed in oil
recovery operations wherein a dry fluid breaks through
into the production well excessive amounts. At such
time the microgels dispersed in the fluid medium are then
-~,~
17,321B-F -16-
1111595
pumped into the well through which the drive fluid is being -
supplied and into the pore formation until the desired
decrease in mobility of the drive fluid through such pore
formation is obtained.
The following examples are given to illustrate -
the invention and should not be used to limit its scope.
Unless otherwise indicated, all parts and percentages are
by weight.
Example 1 Cross-linked acrylamide-sodium
acrylate copolymer
168 Grams of acrylamide, 42 grams of acrylic
acid, 63 grams of Na2CO3, 0.21 gram of pentasodium
(carboxymethylimino)bis(ethylene-nitrilo)tetraacetic
acid (Versenex 80), 0.042 gram of methylene-bisacrylamide,
0.105 gram of sodium metabisulfite and 0.105 gram of
tertiary butyl hydroperoxide are dissolved in 1050 grams
of deionized water and sufficient sodium hydroxide added
thereto to bring ~he mixture to a pH of 9.5. The resulting
solution is mixed with an oil phase consisting of 31.5
grams of acrylic acid and 6.3 grams of a suspending agent
consisting of a chloromethylated polystyrene-dimethylamine
reaction product, wherein about 5-10 percent of the aromatic
rings are aminated, dissolved in 1575 milliliters of xylene.
The resulting mixture is sheared at high speed in a
Waring Blendor for two minutes, placed in an agitated
reactor and purged with nitrogen. The temperature of
the reaction vessel and contents is raised to 63C over
a period of one hour and thereafter held at about 52C
for an additional 2.5 hours to complete the polymerization
reaction. A portion of the resulting slurry is then
dewatered by azeotropic distillation and the resulting
17,321B-F -17-
111159S
suspension filtered to separate the copolymer in the
form of microgels. The latter are washed with acetone
and dried. The ability of the microgels to swell in
aqueous fluid is measured and it is found that the
copolymer held 82 grams of aqueous 0.27 molar sodium
chloride solution per gram of copolymer. To a further
55 gram portion of the above copolymer slurry are added
27.7 milliliters of dimethylamine and then 14.8 grams
of paraformaldehyde slurried in a little xylene. The
resulting mixture is heated to 40C for 1.5 hours, fil-
tered, and dried by acetone extraction to give cationic,
cross-linked polyacrylamide microgels, ranging in size
between 0.2 and 4 microns in diameter. The product
absorbs 50 grams of aqueous 0.27 M NaCl solution per
gram of product. The grams of aqueous fluid absorbed
and held by one gram of dry polymer beads (dried gels)
is herein referred to as the "gel capacity" of the polymer.
The product upon being uniformly dispersed in water,
quickly thickens the water to give a viscous, "shortn,
pseudoplastic dispersion.
In the above and succeeding recipes "Versenex 80"
is a trademark of The Dow Chemical Company for a chelating
agent in which the active chelant is pentasodium (carboxy-
methylimino)bis(ethylenenitrilo)tetraacetic acid. Also
the expression "ppm BOM" is hereafter employed to denote
parts per million based on monomers; that is, parts by
weight of the indicated ingredient per million parts by
weight of water-soluble, ethylenically unsaturated monomers
in the recipe. Hereinafter tertiary-butyl hydroperoxide
is abbreviated "t-BHP".
17.321B-F -18-
1~11595
Example 2 Cross-linked polyacrylamide microgel
Recipe:
Water Phase .--
.
Acrylamide 210 g .
Methylene bisacrylamide .042 g ..
Versenex 80 Chelant 1000 ppm BOM
NaOH to pH 11.5
Water 840 g
2 2 8 500 ppm BOM
t-BHP 500 ppm BOM
Oil Phase
Xylene 1575 ml
Aminated Chloromethylated
Polystyrene 6.3 g
Methanol 20 ml ' ,
The process is similar to that of the previous example.
lS The product is dewatered by azeotropic distillation,
separated by filtration, washed with acetone and dried.
It is found to have a gel capacity of 30 in aqueous
0.27 M NaCl solution.
Example ~ Cross-linked partially hydrolyzed
polyacrylamide microgel
Recipe:
Water Phase
Acrylamide 106 g
Methylene bisacrylamide .025 g
Water 463 g
2C 3 61.3 g
Versenex 80 Chelant 1000 ppm BOM
a2S28 500 ppm BO~
1~1595
Example 3 (continued)
t-BHP 500 ppm BOM
Oil Phase
Xylene 945 ml
Suspending Agent of Ex. 2 3.78 g
Acrylic Acid 20 g
The process is similar to that of the previous examples.
Ihe product exhibits similar properties and has a gel
capacity of 75 in aqueous 0.27 M NaCl solution.
Example 4 Emulsion method
When the emulsion route is used to make the
microgels, the ratio of monomer phase (liquid monomer
or aqueous solution of monomer) to oil phase, the emul-
sifying agents, the oil phase, the initiators, temperatures
and pressures are all generally found in U.S. Patent No.
3,284,393 or in U.S. Patent No. 3,826,771. The cross-
-linking agents described above in connection with the
suspension method can be similarly advantageously used
herein.
In this example, the water-in-oil emulsifying
agent is dissolved in the oil phase, while the free radical
initiator, when one is used, is dissolved in the oil or
monomer phase, depending upon whether an oil- or water-
-soluble initiator is used. An aqueous solution of
monomer or mixed monomers or a monomer per se is then
added to the oil phase along with the cross-linking
agent with agitation until the monomer phase is emulsified
in the oil phase. The reaction is initiated by purging
the reaction medium of inhibitory oxygen and continued
with agitation until conversion is substantially complete.
X
17 . ~2~R--F --20--
A water-in-oil dispersion of polymer microgels is thereby
obtained. The polymer is separated from the reaction medium
advantageously by adding a flocculating agent and filter-
ing, and is then washed and dried. Alternatively, the
dispersion can be used as such.
Recipe:
Ingredients Amount
Aqueous Phase
Acrylamide 525 g
Acrylic Acid 225 g
NaOH 120 g
Deionized water 695 g
Methylene bisacrylamide 0.150 g
Versenex 80 1000 ppm BOM
t-BHP 350 ppm BOM
Na2S25 700 ppm BOM
Oil Phase
Deodorized kerosene 1500 g
Distearyl dimethyl 75 g
ammonium chloride
~ (Arquad 2HT-100)
The water phase, less t-BHP and Na2S2O5, is mixed with
the oil phase and homogenized in a Manton-Gaulin homo-
genizer, placed in the reactor, and purged for 45 minutes
with nitrogen. t-BHP and Na2S2O5, both as 1.5 percent
aqueous solutions, are added portionwise, a third of
the total at a time, resulting in polymerization. The
product is azeotropically distilled at 40 mm pressure
from 40 to 110C to remove water and give a product
having particle size less than two microns. The micro-
bead polymeric product thickens water instantly on
being dispersed in water.
llllS~5
Example 5
A. Preparation of the Microgels
To an oil phase consisting of ingredients as
listed hereinafter is added an aqueous solution of monomers
as also described hereinafter with agitation until the
monomer phase is emulsified in the oil phase.
Ingredients Amount, grams
Aqueous Phase
Acrylamide 134.4
Acrylic acid 33.6
Sodium hydroxide 28.75
Deionized water 403.25
Methylene-bisacrylamide 0.0047 (28 ppm)
DETPA* 0.168 (1000 ppm)
t-butyl hydroperoxide 0.0420 (250 ppm)
Sodium bisulfite 0.0218 (130 ppm)
Oil ~hase
Deodorized kerosene 240.3
Isopropanolamide of oleic acid 16.8
*Pentasodium salt of diethylenetriamine-
pentaacetic acid
In forming the emulsion, the aforementioned
aqueous phase (less the t-butyl hydroperoxide and sodium
bisulfite) is mixed with the oil phase using controlled
high shear, i.e., 30 seconds in a Waring Blendor or
Eppenbach Homogenizer. The resulting emulsion is placed
in a reactor which is purged for 1 hour with N2. The
t-butyl hydroperoxide (20 percent aqueous solution
emulsified in oil at a weight ratio of ~3 oil to 5
water) is added to the reactor in a single shot. The
.. . ~
17,32`1B-F -22-
llllS95
sodium bisulfite (2 percent aqueous solution emulsified
in oil at a weight ratio of ~3 oil to 5 water) is added
portionwise to the reactor in 10 ppm increments until
polymerization of the monomers is completed. After
polymerization, the temperature is increased to 60C
for 2 hours. In a dispersion of the water-swellable
microgels in deionized water containing 30 percent polymer,
it is observed that the mean particle diameter of the
water-swollen microgels is about one micrometer.
B. Water Permeability Reduction Tests
The ability of the microgels to control perme-
ability of porous subterranean formations is determined
using a series of Berea sandstone cores according to
the following test procedure. In most of the core samples '
(2.54 cm length x 2.54 cm diameter), the pore volume is
from 2.8 to 3.2 ml and the pore size is from about 14 to
16 micrometers. The initial core permeability is determined
by pressuring an aqueous solution of NaCl (4%) through
the core in forward and reverse directions. The afore-
mentioned microgels are diluted to 0.02% solids by adding
deionized water and injected into the core sample at 10 psig.
The microgel injection is followed with a brine flow in
the forward and revexse direction to establish the
permeability reduction. The differential pressure during
the brine flow is then increased in 20 psi increments to
60 psi. After each incremental increase, 5~ ml of brine
is passed through the core sample and the flow rate is
determined. The pressure is then returned to the original
test pressure of 10 pqig and a final brine flow rate is
determined after the sample stabilizes (flow rate becomes
17,321B-F -23-
1~1159S
constant). Comparison of initial and final brine flow
rates establish the permeability reduction resulting from
the microgel treatment of the core sample. The results
~ for this sample (Sample No. 1) are recorded in Table I.
For the purposes of comparison, several
water-soluble (noncross-linked) acrylamide/acrylic
acid copolymers (Sample Nos. Cl-C5) are similarly
tested for water diverting capability. The results of
these tests are similarly reported in Table I.
Example 6
Following the general procedure for preparing
acrylamide/acrylic acid copolymer microgels as speci-
fied in Example 5, microgels are prepared using amounts
of methylenebis(acrylamide) ranging from 7 to 200 parts
per million instead of the 28 parts per million employed
in Example 5. Also runs are carried out using polyacryl-
amide microgels wherein the carboxyl moiety is varied
from 5 to 40 mole percent. The resulting microgels are
similarly tested for their water diverting capability by
the procedure set forth in Example 5 and the results
for the samples (Sample Nos. 2-7) are similarly recorded in
Table I.
~. . .
17,321B-F -24-
1~11595
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As evidenced by the data in Table I, the fluid
microgel compositions of the present invention exert a
generally greater control of the permeability of porous
.core samples (fluid mobility control) at lower viscosities
than do compositions containing linear polymer.
17 ~21B-F -27-
