Note: Descriptions are shown in the official language in which they were submitted.
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Process for mineral oil production using hydrophobically associating
copolymers
The present invention relates to a process for mineral oil production, in
which an aqueous
formulation comprising at least one water-soluble, hydrophobically associating
copolymer is
injected through at least one injection borehole into a mineral oil deposit,
and crude oil is
withdrawn from the deposit through at least one production borehole, wherein
the water-
soluble, hydrophobically associating copolymer comprises at least acrylamide
or derivatives
thereof, a monomer having anionic groups and a monomer which can bring about
the
association of the copolymer. The invention further relates to a water-
soluble,
hydrophobically associating copolymer which has only a low shear degradation
and has
particularly good suitability for execution of the process.
In natural mineral oil deposits, mineral oil is present in the cavities of
porous reservoir rocks
which are sealed toward the surface of the earth by impermeable top layers.
The cavities
may be very fine cavities, capillaries, pores or the like. Fine pore necks
may, for example,
have a diameter of only approx. 1 vm. As well as mineral oil, including
fractions of natural
gas, a deposit also comprises water with a greater or lesser salt content.
In mineral oil production, a distinction is drawn between primary, secondary
and tertiary
production.
In primary production, after commencement of drilling of the deposit, the
mineral oil flows of
its own accord through the borehole to the surface owing to the autogenous
pressure of the
deposit. The autogenous pressure can be caused, for example, by gases present
in the
deposit, such as methane, ethane or propane. The autogenous pressure of the
deposit,
however, generally declines relatively rapidly on extraction of mineral oil,
such that usually
only approx. 5 to 10% of the amount of mineral oil present in the deposit,
according to the
deposit type, can be produced by means of primary production. Thereafter, the
autogenous
pressure is no longer sufficient to produce mineral oil.
After primary production, secondary production is therefore typically used. In
secondary
production, in addition to the boreholes which serve for the production of the
mineral oil,
known as the production boreholes, further boreholes are drilled into the
mineral oil-bearing
formation. These are known as injection boreholes, through which water is
injected into the
deposit (known as "water flooding"), in order to maintain the pressure or to
increase it again.
As a result of the injection of the water, the mineral oil is gradually forced
through the cavities
in the formation, proceeding from the injection borehole, in the direction of
the production
borehole. However, this works only for as long as the cavities are completely
filled with oil
and the more viscous oil is pushed onward by the water. As soon as the mobile
water breaks
through cavities, it flows on the path of least resistance from this time
onward, i.e. through
the channel formed, and no longer pushes the oil onward. By means of primary
and
1
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secondary production, therefore, generally only approx. 30 to 35% of the
amount of mineral
oil present in the deposit can be produced.
After the measures of secondary mineral oil production, measures of tertiary
mineral oil
production (also known as "Enhanced Oil Recovery (EOR) ') are therefore also
used to
further enhance the oil yield. This includes processes in which particular
chemicals, such as
surfactants and/or polymers, are used as assistants for oil production. An
overview of tertiary
oil production using chemicals can be found, for example, in the article by D.
G. Kessel,
Journal of Petroleum Science and Engineering, 2 (1989) 81 - 101.
The techniques of tertiary mineral oil production include what is known as
"polymer flooding".
Polymer flooding involves injecting an aqueous solution of a thickening
polymer through the
injection boreholes into the mineral oil deposit, the viscosity of the aqueous
polymer solution
being matched to the viscosity of the mineral oil. As a result of the
injection of the polymer
solution, the mineral oil, as in the case of water flooding, is forced through
the cavities
mentioned in the formation, proceeding from the injection borehole, in the
direction of the
production borehole, and the mineral oil is produced through the production
borehole. By
virtue of the fact that the polymer formulation, however, has about the same
viscosity as the
mineral oil, the risk is reduced that the polymer formulation breaks through
to the production
borehole with no effect, and hence the mineral oil is mobilized much more
homogeneously
than in the case of use of mobile water. It is thus possible to mobilize
additional mineral oil in
the formation. Details of polymer flooding and of polymers suitable for this
purpose are
disclosed, for example, in "Petroleum, Enhanced Oil Recovery, Kirk-Othmer,
Encyclopedia of
Chemical Technology, online edition, John Wiley & Sons, 2010".
For polymer flooding, a multitude of different thickening polymers have been
proposed,
especially high molecular weight polyacrylamide, copolymers of acrylamide and
further
comonomers, for example vinylsulfonic acid or acrylic acid. Polyacrylamide may
especially
be partly hydrolyzed polyacrylamide, in which some of the acrylamide units
have been
hydrolyzed to acrylic acid. In addition, it is also possible to use naturally
occurring polymers,
for example xanthan or polyglycosylglucan, as described, for example, by US
6,392,596 B1
or CA 832 277.
Also known is the use of hydrophobically associating copolymers for polymer
flooding. These
are understood by the person skilled in the art to mean water-soluble polymers
which have
lateral or terminal hydrophobic groups, for example relatively long alkyl
chains. In aqueous
medium, such hydrophobic groups can associate with themselves or with other
substances
having hydrophobic groups. This forms an associative network by which the
medium is
thickened. Details of the use of hydrophobically associating copolymers for
tertiary mineral oil
production are described, for example, in the review article by Taylor, KC.
and Nasr-E/-Din,
H.A. in J. Petr. Sci. Eng. 1998, 19, 265-280.
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EP 705 854 Al, DE 100 37 629 Al and DE 10 2004 032 304 Al disclose water-
soluble,
hydrophobically associating copolymers and the use thereof, for example in the
construction
chemistry sector. The copolymers described comprise acidic monomers, for
example acrylic
acid, vinylsulfonic acid, acrylamidomethylpropanesulfonic acid, basic monomers
such as
acrylamide, dimethylacrylamide, or monomers comprising cationic groups, for
example
monomers having ammonium groups, and also monomers which can bring about the
hydrophobic association of the individual polymer chains.
Our prior application WO 2010/133527 A2 discloses hydrophobically associating
copolymers
which comprise at least hydrophilic, monoethylenically unsaturated monomers,
for example
acrylamide, and monoethylenically unsaturated, hydrophobically associating
monomers. The
hydrophobically associating monomers have a block structure and have - in this
sequence -
an ethylenically unsaturated group, optionally a linking group, a first
polyoxyalkylene block
which comprises at least 50 mol% of ethyleneoxy groups, and a second
polyoxyalkylene
group which consists of alkyleneoxy groups having at least 4 carbon atoms. The
application
discloses the use of such copolymers as thickeners, for example for polymer
flooding, for
construction chemical applications or for detergent formulations.
Our prior application WO 2011/015520 Al discloses a process for preparing
hydrophobically
associating copolymers by polymerizing water-soluble, monoethylenically
unsaturated
surface-active monomers and monoethylenically unsaturated hydrophilic monomers
in the
presence of surfactants, and the use of such copolymers for polymer flooding.
For polymer flooding, an aqueous, viscous polymer formulation is injected into
a borehole
sunk into the mineral oil formation. This borehole is also called "injection
borehole" and is
generally lined with cemented steel tubes which are perforated in the region
of the mineral oil
formation and thus allow the discharge of the polymer formulation from the
injection borehole
into the mineral oil formation.
Naturally, the aqueous polymer formulation on entry into the mineral oil
formation must at
first flow through the volume element immediately around the injection
borehole, and is
further distributed from there in the mineral oil formation. Accordingly, the
flow rate of the
aqueous polymer formulation on entry into the formation is at its greatest and
decreases with
increasing distance from the injection borehole. This is shown schematically
in Figure 1.
Since the mineral oil formation is a porous material and the formulation has
to flow through
the pores, very high shear forces are acting on the aqueous polymer
formulation on entry
into the formation.
In this case, the problem occurs with customary thickening polymers based on
acrylamide
that the polymers lose some of their viscosity-enhancing properties,
specifically as a result of
mechanical degradation of the polymer owing to high shear forces (see, for
example,
J.M Maerker, Shear Degradation of partially hydrolyzes polyacrylamide
solutions", SPE
Journal 15(4), 1975, pages 311 - 322 or R.S. Seright, "The effects of
mechanical
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degradation and viscoelastic behavior on injectivity of polyacrylamide
solutions", SPE Journal
23(3), 1983, pages 475- 485).
Various measures have been proposed to solve the problem, for example slower
injection of
the polymer solution, fracturing of the formation close to the injection
borehole, preliminary
shear of the polymer solution, or the use of a higher polymer concentration
than actually
needed to build up the desired viscosity (see, for example, D. Morel, M. Vert,
S. Jouenne,
E. Nahas, "Polymer injection in deep offshore field: The Dalia Angola case",
SPE Annual
Technical Conference and Exhibition, September 2008, Denver Colorado, USA,
paper
number: SPE 116674 However, all proposed solutions have the disadvantage that
they
impair the economic viability of polymer flooding, whether because the amounts
of the
polymer used have to be increased or because the reduced injection rate
decreases the
amount of mineral oil produced. Naturally, the problem of injection in mineral
oil formations
with a low porosity is higher than in the case of a formation of higher
porosity.
R. S. Seright, M Seheult and T. Talashek "Injectivity characteristics of EOR
polymers", SPE
Reservoir Evaluation & Enginnenng, 12 (5), 2009, pages 783 - 792 describe
studies of the
injection of aqueous solutions of xanthan and partly hydrolyzed polyacrylamide
into mineral
oil formations. They indicate that essentially three polymer properties are
crucial for the
injectivity of EOR polymers, namely gel fractions in the polymer, polymer
rheology in the
course of flow in the porous medium, and mechanical polymer degradation. Gel
fractions in
the EOR polymer can lead to blockage of the formation and thus make it more
difficult to
inject the EOR polymer. Blockages can also occur primarily on entry of the
aqueous polymer
formulation into the mineral oil formation. In order to facilitate the
injection of the EOR
polymers, polymer solutions with structurally viscous flow behavior are
preferred.
"Structurally viscous flow behavior" means, in a manner known in principle,
that the viscosity
of a solution decreases with increasing shear.
It was an object of the invention to provide an improved process for polymer
flooding,
especially for fine-pore mineral oil formations, in which the polymer can be
injected
particularly efficiently into the formation.
In a first aspect of the invention, a process for mineral oil production has
been found, in
which an aqueous formulation comprising at least one water-soluble,
hydrophobically
associating copolymer is injected through at least one injection borehole into
a mineral oil
deposit having an average porosity of 10 millidarcies to 4 darcies and a
formation
temperature of 30 C to 150 C, and crude oil is withdrawn from the deposit
through at least
one production borehole, and wherein
= the water-soluble, hydrophobically associating copolymer comprises
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(a) 0.1 to 15% by weight of at least one monoethylenically unsaturated,
hydrophobically associating monomer (a), and
(b) 85 to 99.9% by weight of at least two monoethylenically unsaturated,
5
hydrophilic monomers (b) different than (a), where the monomers (b)
comprise at least
(b1) at least one uncharged, monoethylenically unsaturated, hydrophilic
monomer (b1), selected from the group of (meth)acrylamide,
N-methyl(meth)acrylamide, N,N'-dimethyl(meth)acrylamide or
N-methylol(meth)acrylamide, and
(b2) at least one anionic, monoethylenically unsaturated, hydrophilic
monomer (b2) which at least one acidic group selected from the
group of ¨0001-1, ¨803H and ¨P03H2 and salts thereof,
where the proportions are each based on the total amount of all monomers in
the
copolymer,
= the
copolymer has a weight-average molecular weight Mw of 1*106 g/mol to
30*106 g/mol,
= the amount of the copolymer in the formulation is 0.02 to 2% by weight,
= the viscosity of the formulation is at least 5 mPas (measured at 25 C),
and
= the aqueous polymer formulation is injected into the formation with a
shear rate
of at least 30 000 s-1.
In a second aspect of the invention, water-soluble, hydrophobically
associating copolymers
having a weight-average molecular weight Mw of 1*106 g/mol to 30*106 g/mol
have been
found, comprising at least
(a) 0.1 to 15% by weight of at least one monoethylenically unsaturated,
hydrophobically associating monomer (a), and
(b) 85 to 99.9% by weight of at least one monoethylenically unsaturated,
hydrophilic
monomer (b) different than (a), where the monomers (b) comprise at least
(b1) at least one uncharged, monoethylenically unsaturated, hydrophilic
monomer (b1), selected from the group of (meth)acrylamide,
N-methyl(meth)acrylamide, N,N'-dimethyl(meth)acrylamide
Or
N-methylol(meth)acrylamide, and
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(b2) at least one anionic, monoethylenically unsaturated, hydrophilic monomer
(b2) which at least one acidic group selected from the group of ¨COOH,
-S03H and ¨P03H2 and salts thereof,
where the proportions are each based on the total amount of all monomers in
the copolymer,
wherein the shear degradation of the copolymer, measured by means of a
capillary shear
test to API RP 63, is not more than 10%.
Index of figures:
Fig. 1 Schematic diagram of the entrance of an injection liquid into
the mineral oil
formation.
Fig. 2 Schematic diagram of the apparatus for determining the shear
stability
according to API RP 63.
With regard to the invention, the following should be stated specifically:
Hydrophobically associating copolymers used
For the process according to the invention for mineral oil production, an
aqueous formulation
of at least one water-soluble, hydrophobically associating copolymer is used
and is injected
through an injection borehole into a mineral oil deposit.
The term "hydrophobically associating copolymer" is known in principle to
those skilled in the
art.
This comprises a water-soluble copolymer which, as well as hydrophilic
molecular
components which ensure sufficient water solubility, has lateral or terminal
hydrophobic
groups. In aqueous solution, the hydrophobic groups of the polymer can
associate with
themselves or with other substances having hydrophobic groups due to
intermolecular
forces. This gives rise to a polymeric network joined by intermolecular
forces, which thickens
the aqueous medium.
In the ideal case, the copolymers used in accordance with the invention should
be miscible
with water in any ratio. According to the invention, however, it is sufficient
when the
copolymers are water-soluble at least at the desired use concentration and at
the desired pH.
In general, the solubility of the copolymer in water at room temperature under
the use
conditions should be at least 25 WI.
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According to the invention, the water-soluble, hydrophobically associating
copolymer
comprises 0.1 to 15% by weight of at least one monoethylenically unsaturated,
hydrophobically associating monomer (a) and 85 to 99.9% by weight of at least
two
monoethylenically unsaturated, hydrophilic monomers (b) different than (a). In
addition, it is
optionally possible for further, ethylenically unsaturated, preferably
monoethylenically
unsaturated, monomers (c) different than the monomers (a) and (b) to be
present in an
amount of up to 14.9% by weight. The amounts mentioned are based in each case
on the
sum of all monomers in the copolymer. Preference is given to using exclusively
monoethylenically unsaturated monomers.
Monomers (a)
The water-soluble, hydrophobically associating copolymer used comprises at
least one
monoethylenically unsaturated monomer (a) which imparts hydrophobically
associating
properties to the copolymer and shall therefore be referred to hereinafter as
"hydrophobically
associating monomer".
The hydrophobically associating monomers (a) comprise, as well as the
ethylenically
unsaturated group, a hydrophobic group which, after the polymerization, is
responsible for
the hydrophobic association of the copolymer formed. They preferably further
comprise
hydrophilic molecular components which impart a certain water solubility to
the monomer. In
principle, it is possible to use any hydrophobically associating,
monoethylenically unsaturated
monomers (a), provided that the copolymer can be injected into the formation
at a shear rate
of at least 30 000 s-1. The person skilled in the art is aware of monomers
(a), and makes a
suitable selection.
Suitable monomers (a) have especially the general formula H2C=C(R1)-Y-Z where
R1 is H or
methyl, Z is a terminal hydrophobic group and Y is a linking hydrophilic
group. In a preferred
embodiment of the invention, the hydrophobic Z group comprises aliphatic
and/or aromatic,
straight-chain or branched C8-C32-hydrocarbyl radicals, preferably C12-C30-
hydrocarbyl
radicals. In a further preferred embodiment, the Z group is a group formed
from alkylene
oxide units having at least 3 carbon atoms, preferably at least 4 and more
preferably at least
5 carbon atoms. The Y group is preferably a group comprising alkylene oxide
units, for
example a group comprising 5 to 150 alkylene oxide units, which is joined in a
suitable
manner to the H2C=C(R1)- group, for example by means of a single bond or of a
suitable
linking group, using at least 50 mol%, preferably at least 90 mol%, of
ethylene oxide units.
Preferred monomers (a)
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At least one of the monoethylenically unsaturated water-soluble monomers (a)
is preferably
at least one selected from the group of
H2C=C(R1)-R2-0-(-CH2-CH(R3)-0-)k+CH2-CH(R4)-0-)I-R5 (I),
H2C=C(R1)-0-(-CH2-CH(R3)-0-)k-R6 (II),
H2C=C(R1)-(C=0)-0-(-CH2-CH(R3)-0-)k-R6 (III).
Monomers (a) of the formula (I)
In the monomers (a) of the formula (I), an ethylenic group H2C=C(R1)- is
bonded via a
divalent linking group ¨R2-0- to a polyoxyalkylene radical with block
structure
-(-CH2-CH(R3)-0-)k-(-CH2-CH(R4)-0-),-R5, where the two blocks -(-CH2-CH(R3)-0-
)k and
-(-CH2-CH(R4)-0-)1 are arranged in the sequence shown in formula (I). The
polyoxyalkylene
radical has either a terminal OH group (when R5=H) or a terminal ether group
¨0R5 (when R5
is a hydrocarbyl radical).
In the abovementioned formula, R1 is H or a methyl group.
R2 is a single bond or a divalent linking group selected from the group of
¨(CH2)- [R2a
group], -0-(Cr4-12)- [R2b group]- and ¨C(0)-0-(Cn-H2n..)- [R2c group]. In the
formulae
mentioned, n, n' and n" are each a natural number from 1 to 6. In other words,
the linking
group comprises straight-chain or branched aliphatic hydrocarbyl groups having
1 to 6
hydrocarbon atoms, which are joined to the ethylenic group H2C=C(R1)-
directly, via an ether
group ¨0- or via an ester group ¨C(0)-0-. The -(CH2)-, -(CH2)- and -(Cr,-1-
12n..)- groups are
preferably linear aliphatic hydrocarbyl groups.
The R2a group is preferably a group selected from ¨CH2-, -CH2-CH2- and ¨CH2-
CH2-CH2-,
more preferably a methylene group ¨CH2-.
The R2b group is preferably a group selected from -0-CH2-CH2-, -0-CH2-CH2-CH2-
and
-0-CH2-CH2-CH2-CH2-, more preferably ¨0-CH2-CH2-CH2-CH2-.
The R2c group is preferably a group selected from ¨C(0)-0-CH2-CH2-, -C(0)0-
CH(CH3)-
CH2_, -C(0)0-CH2-CH(CH3)-, -C(0)0-CH2-CH2-CH2-CH2- and -C(0)0-CH2-CH2-CH2-CH2-
CH2-CH2-, more preferably ¨C(0)-0-CH2-CH2- and -C(0)0-CH2-CH2-CH2-CH2-, and
most
preferably ¨C(0)-0-CH2-CH2-.
The R2 group is more preferably an R2a or R2b group, more preferably an R2b
group, i.e.
monomers based on vinyl ethers.
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In addition, R2 is more preferably a group selected from ¨CH2- and -0-CH2-CH2-
CH2-CH2-,
most preferably -0-CH2-CH2-CH2-CH2-.
The monomers (I) also have a polyoxyalkylene radical which consists of the
units
+CH2-CH(R3)-0-)k and -(-CH2-CH(R4)-0-)1 where the units are arranged in block
structure in
the sequence shown in formula (I). The transition between the two blocks may
be abrupt or
else continuous.
In the -(-CH2-CH(R3)-0-)k block, the R3 radicals are each independently H,
methyl or ethyl,
preferably H or methyl, with the proviso that at least 50 mol% of the R3
radicals are H.
Preferably at least 75 mol% of the R3 radicals are H, more preferably at least
90 mol%, and
they are most preferably exclusively H. The block mentioned is thus a
polyoxyethylene block
which may optionally also have certain proportions of propylene oxide and/or
butylene oxide
units, preferably a pure polyoxyethylene block.
The number of alkylene oxide units k is a number from 10 to 150, preferably 12
to 100, more
preferably 15 to 80, even more preferably 20 to 30 and, for example, approx.
22 to 25. It is
clear to the person skilled in the art in the field of the polyalkylene oxides
that the numbers
mentioned are averages of distributions.
In the second -(-CH2-CH(R4)-0-)1- block, the R4 radicals are each
independently hydrocarbyl
radicals of at least 2 carbon atoms, preferably at least 3, more preferably 3
to 10, most
preferably 3 to 8 carbon atoms and, for example, 3 to 4 carbon atoms. This may
be an
aliphatic and/or aromatic, linear or branched carbon radical. It is preferably
an aliphatic
radical.
Examples of suitable R4 radicals comprise ethyl, n-propyl, n-butyl, n-pentyl,
n-hexyl, n-heptyl,
n-octyl, n-nonyl or n-decyl, and phenyl. Examples of preferred radicals
comprise n-propyl,
n-butyl, n-pentyl, particular preference being given to an n-propyl radical.
The R4 radicals may also be ether groups of the general formula ¨CH2-0-R4
where R4' is an
aliphatic and/or aromatic, linear or branched hydrocarbyl radical having at
least 2 carbon
atoms, preferably at least 3 and more preferably 3 to 10 carbon atoms.
Examples of R3'
radicals comprise n-propyl, n-butyl, n-pentyl, n-hexyl, 2-ethylhexyl, n-
heptyl, n-octyl, n-nonyl
n-decyl or phenyl.
The -(-CH2-CH(R4)-0-)i- block is thus a block which consists of alkylene oxide
units having at
least 4 carbon atoms, preferably at least 5 carbon atoms, especially 5 to 10
carbon atoms,
and/or glycidyl ethers having an ether group of at least 2, preferably at
least 3, carbon atoms.
Preferred R3 radicals are the hydrocarbyl radicals mentioned; the units of the
second terminal
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block are more preferably alkylene oxide units comprising at least 5 carbon
atoms, such as
pentene oxide units or units of higher alkylene oxides.
The number of alkylene oxide units I is a number from 5 to 25, preferably 6 to
20, more
5 preferably 8 to 18, even more preferably 10 to 15 and, for example,
approx. 12.
The R5 radical is H or a preferably aliphatic hydrocarbyl radical having 1 to
30 carbon atoms,
preferably 1 to 10 and more preferably 1 to 5 carbon atoms. R5 is preferably
H, methyl or
ethyl, more preferably H or methyl and most preferably H.
In the monomers of the formula (I), a terminal monoethylenic group is joined
to a
polyoxyalkylene group with block structure, specifically firstly to a
hydrophilic block having
polyethylene oxide units, which is in turn joined to a second terminal
hydrophobic block
formed at least from butene oxide units, preferably at least pentene oxide
units, or units of
higher alkylene oxides, for example dodecene oxide. The second block has a
terminal ¨0R5-
group, especially an OH-group. The terminal -(-CH2-CH(R4)-0-)1 block with the
R4 radicals is
responsible for the hydrophobic association of the copolymers prepared using
the monomers
(a). Etherification of the OH end group is an option which may be selected by
the person
skilled in the art according to the desired properties of the copolymer. A
terminal hydrocarbyl
group is, however, not required for the hydrophobic association, and the
hydrophobic
association also works with a terminal OH group.
It is clear to the person skilled in the art in the field of polyalkylene
oxide block copolymers
that the transition between the two blocks, according to the method of
preparation, may be
abrupt or else continuous. In the case of a continuous transition, there is a
transition zone
between the two blocks, which comprises monomers of both blocks. When the
block
boundary is fixed at the middle of the transition zone, the first block +CH2-
CH(R3)-0-)k may
accordingly also have small amounts of -CH2-CH(R4)-0- units and the second
block
-(-CH2-CH(R4)-0-)1- small amounts of -CH2-CH(R3)-0- units, though these units
are not
distributed randomly over the block but arranged in the transition zone
mentioned.
Preparation of the monomers (a) of the formula (I)
The hydrophobically associating monomers (a) of the formula (I) can be
prepared by
methods known in principle to those skilled in the art.
To prepare the monomers (a), a preferred preparation process proceeds from
suitable
monoethylenically unsaturated alcohols (IV) which are subsequently alkoxylated
in a two-
stage process such that the block structure mentioned is obtained. This gives
monomers (a)
of the formula (I) where R5 = H. These can optionally be etherified in a
further process step.
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The type of ethylenically unsaturated alcohols (IV) to be used is guided here
especially by
the R2 group.
When R2 is a single bond, the starting materials are alcohols (IV) of the
general formula
H2C=C(R1)-0-(-CH2-CH(R7)-0-)d-H (IVa) where R, is as defined above, R7 is H
and/or CH3,
preferably H, and d is from 1 to 5, preferably 1 or 2. Examples of such
alcohols comprise
diethylene glycol vinyl ether H2C=CH-O-CH2-CH2-0-CH2-CH2-0H or dipropylene
glycol vinyl
ether H2C=CH-O-CH2-CH(CH3)-0-CH2-CH(CH3)-0H, preferably diethylene glycol
vinyl ether.
To prepare monomers (a) in which R2 is not a single bond, it is possible to
use alcohols of
the general formula H2C=C(R1)-R2-0H (IVb) or alcohols which already have
alkoxy groups
and are of the formula H2C=C(R1)-R2-0-(-CH2-CH(R7)-0-)d-H (IVc), where R7 and
d are each
as defined above, and R2 in each case is selected from the group of R2a, R2b
and R2b.
The preparation of the monomers with a linking R2a group preferably proceeds
from alcohols
of the formula H2C=C(R1)¨(CnH2n)-0H, especially H2C=CH¨(CnH2n)-0H, or alcohols
of the
formula H2C=C(R1)-0-(-CH2-CH(R7)-0-)d-H. Examples of preferred alcohols
comprise ally'
alcohol H2C=CH-CH2-0H or isoprenol H2C=C(CH3)-CH2-CH2-0H.
The preparation of the monomers with a linking R2b group proceeds from vinyl
ethers of the
formula H2C=C(R1)-0-(C1-12,,.)-0H, preferably H2C=CH-0-(Cn,H2,,.)-0H. It is
more preferably
possible to use co-hydroxybutyl vinyl ether H2C=CH¨O-CH2-CH2-CH2-CH2-0H.
The preparation of the monomers with a linking R2c group proceeds from
hydroxyalkyl
(meth)acrylates of the general formula H2C=C(R1)-C(0)-0-(Cn-H2n..)-OH,
preferably
H2C=C(R1)-C(0)-0-(Cn-1-12n..)-0H. Examples of preferred hydroxyalkyl
(meth)acrylates
comprise hydroxyethyl (meth)acrylate H2C=C(R1)-C(0)-0-CH2-CH2-0H and
hydroxybutyl
(meth)acrylate H2C=C(R1)-C(0)-0-CH2-CH2-CH2-CH2-0H.
The starting compounds mentioned are alkoxylated, specifically in a two-stage
process, first
with ethylene oxide, optionally in a mixture with propylene oxide and/or
butylene oxide, and
in a second step with alkylene oxides of the general formula (Xa) or (Xb)
0 0
/ (Xa) \ /0¨R4
(Xb)
4 CH2
where R4 in (Xa) and R4' in (Xb) are each as defined at the outset.
The performance of an alkoxylation including the preparation of the block
copolymers from
different alkylene oxides is known in principle to those skilled in the art.
It is likewise known to
those skilled in the art that the reaction conditions, especially the
selection of the catalyst,
CA 02818847 2013-05-23
PF 70977
12
can influence the molecular weight distribution of the alkoxylates and the
orientation of the
alkylene oxide units in a polyether chain.
The alkoxylates can be prepared, for example, by base-catalyzed alkoxylation.
For this
purpose, the alcohol used as the starting material can be admixed in a
pressure reactor with
alkali metal hydroxides, preferably potassium hydroxide, or with alkali metal
alkoxides, for
example sodium methoxide. By means of reduced pressure (e.g. <100 mbar) and/or
increasing the temperature (30 to 150 C), water still present in the mixture
can be removed.
Thereafter, the alcohol is present as the corresponding alkoxide. This is
followed by
inertization with inert gas (e.g. nitrogen) and, in a first step, stepwise
addition of ethylene
oxide, optionally in a mixture with propylene oxide and/or butylene oxide, at
temperatures of
60 to 180 C, preferably 130 to 150 C. The addition is typically effected
within 2 to 5 h, though
the invention should not be restricted thereto. After the addition has ended,
the reaction
mixture is appropriately allowed to continue to react, for example for 1/2 h
to 1 h. In a second
step, alkylene oxides of the general formula (Xb) are subsequently metered in
stepwise. The
reaction temperature in the second stage can be maintained or else altered. A
reaction
temperature lower by approx. 10 to 25 C than in the first stage has been found
to be useful.
The alkoxylation can also be undertaken by means of techniques which lead to
narrower
molecular weight distributions than the base-catalyzed synthesis. For this
purpose, the
catalysts used may, for example, be double hydroxide clays as described in
DE 43 25 237 Al. The alkoxylation can more preferably be effected using double
metal
cyanide catalysts (DMC catalysts). Suitable DMC catalysts are disclosed, for
example, in
DE 102 43 361 Al, especially paragraphs [0029] to [0041] and the literature
cited therein.
For example, it is possible to use catalysts of the Zn-Co type. To perform the
reaction, the
alcohol used as the starting material can be admixed with the catalyst, and
the mixture can
be dewatered as described above and reacted with the alkylene oxides as
described.
Typically, not more than 250 ppm of catalyst based on the mixture are used,
and the catalyst
can remain in the product due to this small amount.
The alkoxylation can additionally also be undertaken under acid catalysis. The
acids may be
Bronsted or Lewis acids. To perform the reaction, the alcohol used as the
starting material
can be admixed with the catalyst, and the mixture can be dewatered as
described above and
reacted with the alkylene oxides as described. At the end of the reaction, the
acidic catalyst
can be neutralized by addition of a base, for example KOH or NaOH, and
filtered off if
required.
It is clear to the person skilled in the art in the field of the polyalkylene
oxides that the
orientation of the hydrocarbyl radicals R4 and optionally R3 may depend on the
conditions of
the alkoxylation, for example on the catalyst selected for the alkoxylation.
The alkylene oxide
groups can thus be incorporated into the monomer either in the -(-CH2-CH(R4)-0-
) orientation
CA 02818847 2013-05-23
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13
or else in the inverse -(-CH(R4)¨CH2-0-)- orientation. The description in
formula (I) should
therefore not be considered to be restricted to a particular orientation of
the R3 or R4 groups.
When the terminal OH group of the monomers (a) of the formula (I) (i.e. R5 =
H) is to be
etherified, this can be accomplished with customary alkylating agents known in
principle to
those skilled in the art, for example alkyl sulfates. For etherification, it
is especially possible
to use dimethyl sulfate or diethyl sulfates.
The preferred preparation process described for the monomers (I) has the
advantage that
the formation of potentailly crosslinking by-products with two ethylenically
unsaturated
groups is substantially avoided. Accordingly, it is possible to obtain
copolymers with a
particularly low gel content.
Monomers (a) of the formulae (II) and (III)
In the monomers of the formulae (II) and (III), R1, R3 and k are each defined
as already
outlined.
R6 is an aliphatic and/or aromatic, straight-chain or branched hydrocarbyl
radical having 8 to
40 carbon atoms, preferably 12 to 32 carbon atoms. For example, it may
comprise n-alkyl
groups such as n-octyl, n-decyl or n-dodecyl groups, phenyl groups, and
especially
substituted phenyl groups. Substituents on the phenyl groups may be alkyl
groups, for
example Ci-C6-alkyl groups, preferably styryl groups. Particular preference is
given to a
tristyrylphenyl group.
The hydrophobically associating monomers of the formulae (II) and (III) and
the preparation
thereof are known in principle to those skilled in the art, for example from
EP 705 854 Al.
Amounts of monomers (a)
The amount of the monoethylenically unsaturated, hydrophobically associating
monomers (a)
is 0.1 to 15% by weight, based on the total amount of all monomers in the
copolymer,
especially 0.1 to 10% by weight, preferably 0.2 to 5% by weight and more
preferably 0.5 to
2% by weight.
In general, at least 50% by weight, preferably at least 80% by weight, of the
monomers (a)
are monomers (a) of the general formula (I), (II) and/or (III), and particular
preference is given
to using only monomers (a) of the general formula (I), (II) and/or (III).
Particular preference is
given to using only mononomers (a) of the general formula (I) to prepare the
inventive
copolymers, most preferably monomers (a) of the general formula (I) in which
R2 is an R2b
radical.
CA 02818847 2013-05-23
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14
Monomers (b)
Over and above the monomers (a), the hydrophobically associating copolymer
used in
accordance with the invention comprises at least two monoethylenically
unsaturated,
hydrophilic monomers (b) different than (a).
More preferably, the monoethylenically unsaturated hydrophilic monomers (b)
used are
miscible with water in any ratio, but it is sufficient for execution of the
invention that the
inventive, hydrophobically associating copolymer possesses the water
solubility mentioned at
the outset. In general, the solubility of the monomers (b) in water at room
temperature should
be at least 50 g/I, preferably at least 150 g/I and more preferably at least
250 g/I.
According to the invention, the copolymer comprises at least one uncharged,
monoethylenically unsaturated, hydrophilic monomer (b1) selected from the
group of
(meth)acrylamide, N-methyl(meth)acrylamide, N,N'-dimethyl(meth)acrylamide or N-
methylol-
(meth)acrylamide. Preference is given to (meth)acrylamide, especially
acrylamide. When
mixtures of different monomers (b1) are used, at least 50 mol% of the monomers
(b1) should
be (meth)acrylamide, especially acrylamide.
According to the invention, the copolymer used further comprises at least one
hydrophilic,
monoethylenically unsaturated anionic monomer (b2) which comprises at least
one acidic
group selected from the group of ¨COOH, ¨S03H and ¨P03H2 and salts thereof.
Preference
is given to monomers comprising COOH groups and/or ¨S03H groups, particular
preference
to monomers comprising ¨S03H groups. The monomers may of course also be the
salts of
the acidic monomers. Suitable counterions comprise especially alkali metal
ions such as Lit,
Na + or K+, and ammonium ions such as NH4 + or ammonium ions with organic
radicals.
Examples of monomers comprising COOH groups comprise acrylic acid, methacrylic
acid,
crotonic acid, itaconic acid, maleic acid or fumaric acid. Preference is given
to acrylic acid.
Examples of monomers comprising sulfo groups comprise vinylsulfonic acid,
allylsulfonic
acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-
methylpropanesulfonic
acid, 2-acrylamidobutanesulfonic acid, 3-acrylamido-3-methylbutanesulfonic
acid or
2-acrylamido-2,4,4-trimethylpentanesulfonic acid. Preference is given to
vinylsulfonic acid,
allylsulfonic acid or 2-acrylamido-2-methylpropanesulfonic acid, and
particular preference to
2-acrylamido-2-methylpropanesulfonic acid.
Examples of monomers comprising phospho groups comprise vinylphosphonic acid,
allylphosphonic acid, N-(meth)acrylamidoalkylphosphonic acids or
(meth)acryloyloxyalkyl-
phosphonic acids, preference being given to vinylphosphonic acid.
CA 02818847 2013-05-23
PF 70977
For the sake of completeness, it should be mentioned that the monomers (b1)
can be
hydrolyzed at least partly to (meth)acrylic acid under some circumstances in
the course of
preparation and use. The copolymers used in accordance with the invention may
accordingly
comprise (meth)acrylic acid units, even if no (meth)acrylic acid units at all
have been used for
5 the synthesis. The tendency to hydrolysis of the monomers (b1) decreases
with increasing
content of sulfo groups. Accordingly, the presence of sulfo groups in the
copolymer used in
accordance with the invention is advisable.
The copolymers used in accordance with the invention may additionally
optionally comprise
10 at least one monoethylenically unsaturated, cationic monomer (b3) having
ammonium ions.
Suitable cationic monomers (b3) comprise especially monomers having ammonium
groups,
especially ammonium derivatives of N-(w-aminoalkyl)(meth)acrylamides or (0-
aminoalkyl-
(meth)acrylic esters.
More particularly, monomers (b3) having ammonium groups may be compounds of
the
general formulae H2C=C(R8)-CO-NR9-R10_NR113*X- (Va) and/or H2C=C(R8)-COO-R10-
NR113+X- (Vb). In these formulae, R8 is H or methyl, R9 is H or a Ci-C4-alkyl
group, preferably
H or methyl, and R10 is a preferably linear C1-C4-alkylene group, for example
a 1,2-ethylene
group ¨CH2-CH2- or a 1,3-proplyene group ¨CH2-CH2-CH2- .
The R11 radicals are each independently Cl-C4-alkyl radicals, preferably
methyl, or a group of
the general formula ¨R12-S03H where R12 is a preferably linear Cl-C4-alkylene
group or a
phenyl group, with the proviso that generally not more than one of the R11
substituents is a
substituent having sulfo groups. More preferably, the three R11 substituents
are methyl
groups, i.e. the monomer has a ¨N(CH3)3+ group. X- in the above formula is a
monovalent
anion, for example Cl-. X- may of course also be a corresponding fraction of a
polyvalent
anion, though this is not preferred. Examples of preferred monomers (b3) of
the general
formula (Va) or (Vb) comprise salts of 3-
trimethylammoniopropyl(meth)acrylamides or
2-trimethylammonioethyl (meth)acrylates, for example the corresponding
chlorides such as
3-trimethylammoniopropylacrylamide chloride (DIMAPAQUAT) and 2-trimethyl-
ammoniomethyl methacrylate chloride (MADAME-QUAT).
The copolymers used in accordance with the invention may additionally also
comprise further
monoethylenically unsaturated hydrophilic monomers (b4) different than the
hydrophilic
monomers (bl), (b2) and (b3). Examples of such monomers comprise monomers
comprising
hydroxyl groups and/or ether groups, for example hydroxyethyl (meth)acrylate,
hydroxypropyl
(meth)acrylate, allyl alcohol, hydroxyvinyl ethyl ether, hydroxyvinyl propyl
ether, hydroxyvinyl
butyl ether, or compounds of the formula H2C=C(R1)-000-(-CH2-CH(R13)-0-)b-R14
(Via) or
H2C=C(R1)-0-(-CH2-CH(R13)-0-)b-R14 (Vlb), where R1 is as defined above and b
is a number
from 2 to 200, preferably 2 to 100. The R13 radicals are each independently H,
methyl or
ethyl, preferably H or methyl, with the proviso that at least 50 mol% of the
R13 radicals are H.
CA 02818847 2013-05-23
PF 70977
16
Preferably at least 75 mork of the R13 radicals are H, more preferably at
least 90 mol%, and
they are most preferably exclusively H. The R14 radical is H, methyl or ethyl,
preferably H or
methyl. Further examples of monomers (b4) comprise N-vinyl derivatives, for
example N-
vinylformamide, N-vinylacetamide, N-vinylpyrrolidone or N-vinylcaprolactam,
and vinyl
esters, for example vinyl formate or vinyl acetate. N-Vinyl derivatives can be
hydrolyzed after
polymerization to give vinylamine units, and vinyl esters to give vinyl
alcohol units.
The amount of all hydrophilic monomers (b) in the inventive copolymer is, in
accordance with
the invention, 85 to 99.9% by weight, based on the total amount of all
monomers in the
copolymer, preferably 90 to 99.8% by weight.
The amount of the uncharged, hydrophilic monomers (b1) here is generally 30 to
95% by
weight, preferably 30 to 85% by weight and more preferably 30 to 70% by
weight, based on
the total amount of all monomers used.
When the copolymer comprises only uncharged monomers (b1) and anionic monomers
(b2),
it has been found to be useful to use the uncharged monomers (b1) in an amount
of 30 to
95% by weight and the anionic monomers (b2) in an amount of 4.9 to 69.9% by
weight, each
amount being based on the total amount of all monomers used. In this
embodiment, the
monomers (b1) are preferably used in an amount of 30 to 80% by weight and the
anionic
monomers (b2) in an amount of 19.9 to 69.9% by weight, and the monomers (b1)
are more
preferably used in an amount of 40 to 70% by weight and the anionic monomers
(b2) in an
amount of 29.9 to 59.9% by weight
When the copolymer comprises uncharged monomers (b1), anionic monomers (b2)
and
cationic monomers (b3), it has been found to be useful to use the uncharged
monomers (b1)
in an amount of 30 to 95% by weight, and the anionic (b2) and cationic (b3)
monomers
together in an amount of 4.9 to 69.9% by weight, with the proviso that the
molar (b2)/(b3)
ratio is 0.7 to 1.3. The molar (b2)/(b3) ratio is preferably 0.8 to 1.2 and,
for example, 0.9 to
1.1. This measure makes it possible to obtain copolymers which are
particularly insensitive to
salt burden. In this embodiment, the monomers (b1) are used in an amount of 30
to 80% by
weight, and the anionic and cationic monomers (b2) + (b3) together in an
amount of 19.9 to
69.9% by weight, and the monomers (b1) are more preferably used in an amount
of 40 to
70% by weight and the anionic and cationic monomers (b2) + (b3) together in an
amount of
29.9 to 59.9% by weight, where the molar ratio already mentioned should be
observed in
each case.
Monomers (c)
In addition to the hydrophilic monomers (a) and (b), the inventive copolymers
may optionally
comprise ethylenically unsaturated monomers different than the monomers (a)
and (b),
CA 02818847 2013-05-23
PF 70977
17
preferably monoethylenically unsaturated monomers (c). Of course, it is also
possible to use
mixtures of a plurality of different monomers (c).
Such monomers can be used for fine control of the properties of the copolymer
used in
accordance with the invention. If present at all, the amount of such
optionally present
monomers (c) may be up to 14.9% by weight, preferably up to 9.9% by weight,
more
preferably up to 4.9% by weight, based in each case on the total amount of all
monomers.
Most preferably, no monomers (c) are present.
The monomers (c) may, for example, be monoethylenically unsaturated monomers
which
have more hydrophobic character than the hydrophilic monomers (b) and which
are
accordingly water-soluble only to a minor degree. In general, the solubility
of the monomers
(c) in water at room temperature is less than 50 WI, especially less than 30
g/I. Examples of
such monomers comprise N-alkyl- and N,N,'-dialkyl(meth)acrylamides, where the
number of
carbon atoms in the alkyl radicals together is at least 3, preferably at least
4. Examples of
such monomers comprise N-butyl(meth)acrylamide, N-cyclohexyl(meth)acrylamide
or
N-benzyl(meth)acrylamide.
Preparation of the hydrophobically associating copolymers
The copolymers used in accordance with the invention can be prepared by
methods known
in principle to those skilled in the art, by free-radical polymerization of
the monomers (a), (b)
and optionally (c), for example by solution or gel polymerization in the
aqueous phase.
For polymerization, the monomers (a), (b), optionally (c), initiators and
optionally further
assistants for polymerization are used in an aqueous medium.
In a preferred embodiment, the preparation is undertaken by means of gel
polymerization in
the aqueous phse. For gel polymerization, a mixture of the monomers (a), (b)
and optionally
(c), initiators and optionally further assistants with water or an aqueous
solvent mixture is first
provided. Suitable aqueous solvent mixtures comprise water and water-miscible
organic
solvents, where the proportion of water is generally at least 50% by weight,
preferably at
least 80% by weight and more preferably at least 90% by weight. Organic
solvents in this
context include especially water-miscible alcohols such as methanol, ethanol
or propanol.
Acidic monomers can be fully or partly neutralized before the polymerization.
The
concentration of all components except the solvents in the course of the
polymerization is
typically approx. 20 to 60% by weight, preferably approx. 30 to 50% by weight.
The
polymerization should especially be performed at a pH in the range from 5.0 to
7.5 and
preferably at a pH of 6Ø
CA 02818847 2013-05-23
PF 70977
18
Polymerization in the presence of a nonpolymerizable, interface-active
compound
In a preferred embodiment of the invention, the copolymers used are prepared
in the
presence of at least one nonpolymerizable, surface-active compound (T).
The nonpolymerizable, surface-active compound (T) is preferably at least one
nonionic
surfactant, but anionic and cationic surfactants are also suitable to the
extent that they do not
take part in the polymerization reaction. They may especially be surfactants,
preferably
nonionic surfactants, of the general formula R13-Y' where R13 is a hydrocarbyl
radical having
8 to 32, preferably 10 to 20 and more preferably 12 to 18 carbon atoms, and Y'
is a
hydrophilic group, preferably a nonionic hydrophilic group, especially a
polyalkoxy group.
The nonionic surfactant is preferably an ethoxylated long-chain aliphatic
alcohol which may
optionally comprise aromatic components.
Examples include: C12C14-fatty alcohol ethoxylates, C16C18-fatty alcohol
ethoxylates, C13-oxo
alcohol ethoxylates, Clo-oxo alcohol ethoxylates, C13C15-oxo alcohol
ethoxylates,
C10-Guerbet alcohol ethoxylates and alkylphenol ethoxylates. Useful compounds
have
especially been found to be those having 5 to 20 ethyleneoxy units, preferably
8 to 18
ethyleneoxy units. It is optionally also possible for small amounts of higher
alkyleneoxy units
to be present, especially propyleneoxy and/or butyleneoxy units, though the
amount in the
form of ethyleneoxy units should generally be at least 80 mol% based on all
alkyleneoxy
units.
Especially suitable are surfactants selected from the group of the ethoxylated
alkylphenols,
the ethoxylated, saturated iso-C13-alcohols and/or the ethoxylated C10-Guerbet
alcohols,
where in each case 5 to 20 ethyleneoxy units, preferably 8 to 18 ethyleneoxy
units, are
present in alkoxy radicals.
Surprisingly, the addition of nonpolymerizable, interface-active compounds (T)
during the
polymerization leads to a distinct improvement in performance properties of
the copolymer in
polymer flooding. More particularly, the thickening action is increased and
the gel content of
the copolymer is also reduced.
This effect can probably be explained as follows, without any intention that
the invention thus
be tied to this explanation: In the case of polymerization without presence of
a surfactant, the
hydrophobically associating comonomers (a) form micelles in the aqueous
reaction medium.
In the polymerization, this leads to blockwise incorporation of the
hydrophobically associating
regions into the polymer. If, in accordance with the invention, an additional
surface-active
compound is present in the preparation of the copolymers, mixed micelles form.
These mixed
micelles comprise polymerizable and nonpolymerizable components. As a result,
the
hydrophobically associating monomers are then incorporated in relatively short
blocks. At the
same time, the number of these relatively short blocks is greater per polymer
chain. Thus,
CA 02818847 2013-05-23
PF 70977
19
the structure of the copolymers prepared in the presence of a surfactant
differs from those
without the presence of a surfactant.
The nonpolymerizable, interface-active compounds (T) can generally be used in
an amount
of 0.1 to 5% by weight, based on the amount of all monomers used.
The weight ratio of the nonpolymerizable, interface-active compounds (T) used
to the
monomers (a) is generally 4:1 to 1:4, preferably 2:1 to 1:2, more preferably
1.5:1 to 1:1.5
and, for example, approx. 1:1.
Performance of the polymerization
For the polymerization, the components required are first mixed with one
another. The
sequence with which the components are mixed for polymerization is
unimportant; what is
important is merely that, in the preferred polymerization method, the
nonpolymerizable,
interface-active compound (T) is added to the aqueous polymerization medium
before the
initiation of the polymerization.
The mixture is subsequently polymerized thermally and/or photochemically,
preferably at
-5 C to 80 C. If polymerization is effected thermally, preference is given to
using
polymerization initiators which can initiate the polymerization even at
comparatively low
temperature, for example redox initiators. The thermal polymerization can be
undertaken
even at room temperature or by heating the mixture, preferably to temperatures
of not more
than 50 C. The photochemical polymerization is typically undertaken at
temperatures of -5 to
10 C. It is also possible to combine photochemical and thermal polymerization
with one
another, by adding both initiators for the thermal and photochemical
polymerization to the
mixture. In this case, the polymerization is first initiated photochemically
at low temperatures,
preferably -5 to +10 C. The heat of reaction released heats the mixture, which
additionally
initiates the thermal polymerization. By means of this combination, it is
possible to achieve a
conversion of more than 99%.
In a further preferred embodiment of the polymerization, it is also possible
to perform the
reaction with a mixture of a redox initiator system and a thermal initiator
which does not
decompose until relatively high temperatures. This may, for example, be a
water-soluble azo
initiator which decomposes within the temperature range from 40 C to 70 C. The
polymerization here is at first initiated at low temperatures of, for example,
0 to 10 C by the
redox initiator system. The heat of reaction released heats the mixture, and
this additionally
initiates the polymerization by virtue of the initiator which does not
decompose until relatively
high temperatures.
CA 02818847 2013-05-23
= PF 70977
The gel polymerization is generally effected without stirring. It can be
effected batchwise by
irradiating and/or heating the mixture in a suitable vessel at a layer
thickness of 2 to 20 cm.
The polymerization gives rise to a solid gel. The polymerization can also be
effected
continuously. For this purpose, a polymerization apparatus is used, which
possesses a
5 conveyor belt to accommodate the mixture to be polymerized. The conveyor
belt is equipped
with devices for heating and/or for irradiating with UV radiation. In this
method, the mixture is
poured onto one end of the belt by means of a suitable apparatus, the mixture
is polymerized
in the course of transport in belt direction, and the solid gel can be removed
at the other end
of the belt.
The gel obtained is preferably comminuted and dried after the polymerization.
The drying
should preferably be effected at temperatures below 100 C. To prevent
conglutination, it is
possible to use a suitable separating agent for this step. This gives the
hydrophobically
associating copolymer as granules or powder.
Further details of the performance of a gel polymerization are disclosed, for
example in
DE 10 2004 032 304 Al, paragraphs [0037] to [0041].
Since the polymer powder or granules obtained are generally used in the form
of an aqueous
solution in the course of application at the site of use, the polymer has to
be dissolved in
water on site. This may result in undesired lumps with the high molecular
weight polymers
described. In order to avoid this, it is possible to add an assistant which
accelerates or
improves the dissolution of the dried polymer in water to the inventive
polymers as early as in
the course of synthesis. This assistant may, for example, be urea.
Properties of the copolymers
The resulting copolymers preferably have a weight-average molecular weight M
of
1*106 g/mol to 30*106 g/mol, preferably 5*106 g/mol to 20*106 g/mol.
For the process, preference is given to using those copolymers which are
notable for
particularly low shear degradation.
The term "shear degradation" is defined as the percentage permanent alteration
in the
viscosity of a polymer solution after shearing of the polymer solution under
particular
conditions. "Permanent" means that the viscosity loss is maintained even after
the shear
stress ceases, and is not reversible as is the case with structurally viscous
(shear-diluting)
behavior when the shear stress ceases.
Shear degradation of high molecular weight solutions of polymers may arise
when the
mechanical stress on the polymer solutions due to shear is great enough to be
able to cause
CA 02818847 2013-05-23
PF 70977
21
breaking of polymer chains (see, for example, J.M. Maerker, Shear Degradation
of partially
hydrolyzes polyacrylamide solutions", SPE Journal 15(4), 1975, pages 311 - 322
or
R.S. Seright, "The effects of mechanical degradation and viscoelastic behavior
on injectivity
of polyacrylamide solutions", SPE Journal 23(3), 1983, pages 475- 485). As a
result of this,
the proportion of long polymer chains in the polymer solution is reduced, and
the viscosity of
the polymer solution accordingly decreases irreversibly.
The shear degradation of polymers can be measured by means of a capillary
shear test to
API RP 63. For the measurement, a solution of the polymer is pressed through a
narrow
capillary under pressure. In each case, the viscosity of the polymer solution
is determined
before and after the pressing through the capillary. The shear stress on the
polymer can be
adjusted via the pressure with which the solution is pressed through the
capillary, length and
diameter of the capillary, and viscosity of the polymer solution (i.e.
ultimately the
concentration of the polymer solution). The details of the performance of the
capillary shear
test to API RP 63 are given in the examples section for this invention, to
which explicit
reference is hereby made.
The shear degradation of the copolymers used for the process according to the
invention,
measured by means of a capillary shear test to API RP 63, under the conditions
specified in
the examples section is preferably less than 10%, more preferably less than
8%. Due to this
preferred property, the amount of the copolymer used can be kept lower than in
the case of
copolymers which have a higher shear degradation.
In a second aspect, the present invention therefore relates to a
hydrophobically associating
copolymer of the composition described at the outset, which further features
shear
degradation measured by means of a capillary shear test to API RP 63 under the
conditions
specified in the examples section of less than 10%, preferably less than 8%.
Preferred
compositions and the preparation of the inventive copolymers have likewise
already been
described.
Processes for mineral oil production
To execute the process according to the invention, at least one production
borehole and at
least one injection borehole are sunk into the mineral oil deposit. In
general, a deposit is
provided with several injection boreholes and with several production
boreholes. An aqueous
formulation of the copolymer described is injected into the mineral oil
deposit through the at
least one injection borehole, and mineral oil is withdrawn from the deposit
through at least
one production borehole. The term "mineral oil" in this context of course does
not only mean
single-phase oil, but the term also comprises the customary crude oil-water
emulsions. As a
result of the pressure generated by the formulation injected, known as the
"polymer flood",
the mineral oil flows in the direction of the production borehole and is
produced via the
production borehole.
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The porosity (more correctly known as "permeability") of a mineral oil
formation is reported by
the person skilled in the art in the unit "darcy" (abbreviated to "D" or "mD"
for "millidarcies")
and can be determined from the flow rate of a liquid phase in the mineral oil
formation as a
function of the pressure differential applied. The flow rate can be determined
in core flooding
tests with drill cores taken from the formation. Details on this subject can
be found, for
example, in K. Weggen, G. Pusch, H. Rischmuller in "Oil and Gas", pages 37 if,
Ulmann's
Encyclopedia of Industrial Chemistry, online edition, Wiley-VCH, Weinheim
2010. It is clear
to the person skilled in the art that the permeability in a mineral oil
deposit need not be
homogeneous, but generally has a certain distribution, and the reported
permeability of a
mineral oil deposit is accordingly an average permeability.
According to the invention, the deposit is one having an average permeability
of 10 mD to
4 D, preferably 100 mD to 2 D and more preferably 200 mD to 1 D.
The deposit temperature is 30 to 150 C, preferably 40 to 100 C and more
preferably 50 to
80 C.
To execute the process, an aqueous formulation which comprises, in addition to
water, at
least the hydrophobically associating copolymer described is used. It is of
course also
possible to use mixtures of different copolymers.
The formulation can be made up in fresh water, or else in water comprising
salts. For
example, it is possible to use sea water, or it is possible to use produced
formation water,
which is reused in this manner. In the case of offshore production platforms,
the formulation
is generaly made up in sea water. In the case of onshore production units, the
polymer can
advantageously first be dissolved in fresh water, and the resulting solution
can be diluted to
the desired use concentration with formation water. The formulation can
preferably be
prepared by initially charging the water, sprinkling in the copolymer as a
powder and mixing it
with the water.
In addition, the aqueous formulation may of course comprise further
components. Examples
of further components comprise biocides, stabilizers or inhibitors.
The concentration of the copolymer is fixed such that the aqueous formulation
has the
desired viscosity for the end use. The viscosity of the formulation should,
however, in any
case be at least 5 mPas (measured at 25 C and a shear rate of 7 s-1,
preferably at least
10 mPas.
According to the invention, the concentration of the polymer in the
formulation is 0.01 to 2%
by weight based on the sum of all components of the aqueous formulation. The
amount is
preferably 0.05 to 0.5% by weight, more preferably 0.04 to 0.2% by weight and,
for example,
approx. 0.1% by weight.
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The injection of the aqueous copolymer formulation can be undertaken by means
of
customary apparatus. The formulation can be injected into one or more
injection boreholes
by means of customary pumps. The injection boreholes are typically lined with
cemented
steel tubes, and the steel tubes including the cement layer are perforated at
the desired site.
The formulation exits through the perforation from the injection borehole into
the mineral oil
formation. The pressure applied by means of the pumps, in a manner known in
principle,
fixes the volume flow of the formulation and hence also the shear stress with
which the
aqueous formulation enters the formation. The shear stress on entry into the
formation can
be calculated by the person skilled in the art in a manner known in principle
on the basis of
the Hagen-Poiseuille law using the area flowed through on entry into the
formation, the mean
pore radius and the volume flow. The average porosity of the formation can be
determined in
a manner known in principle by measurements on drill cores. By its nature, the
greater the
volume flow of aqueous copolymer formulation injected into the formation, the
greater the
shear stress.
The volume flow in the course of injection and hence the shear rate can be
fixed by the
person skilled in the art according to the conditions in the formation.
According to the
invention, the shear rate on entry of the aqueous polymer formulation into the
formation is
generally at least 30 000 s-1, preferably at least 60 000 s-1 and more
preferably at least
90 000 s-1.
The person skilled in the art selects the copolymers for use in accordance
with the invention
according to the desired properties of the formulation to be injected. The
copolymers and
preferred copolymers have already been described at the outset. Particular
preference is
given to using, for the process according to the invention, copolymers which
have a shear
degradation of less than 10%, preferably less than 8%.
Copolymers particularly preferred for execution of the process comprise
monomers (a) of the
general formula H2C=CH-0-(CH2),,,-0-(-CH2-CH2-0-)k+CH2-CH(R4)-0-)I-H (la)
where n' is 2
to 6, preferably 2 to 4 and more preferably 4. R4 in the preferred variant is
a hydrocarbyl
radical having 3 to 10 carbon atoms, especially an n-propyl radical. In
addition, in formula
(la), k is a number from 20 to 30 and I is a number from 6 to 20, preferably 8
to 18. The
amount of the monomers (a) of the formula (la) is 0.2 to 5% by weight,
preferably 0.5 to 2%
by weight. As monomer (b1), the preferred copolymer comprises 40 to 60% by
weight of
acrylamide and, as monomer (b2), 35 to 55% by weight of a monomer (b2) having
sulfo
groups, preferably 2-acrylamido-2-methylpropanesulfonic acid or salts thereof.
Further copolymers preferred for execution of the process likewise comprise
0.2 to 5% by
weight, preferably 0.5 to 2% by weight, of monomers (a) of the general formula
(la) and 30 to
40% by weight of acrylamide. They additionally comprise 25 to 35% by weight of
at least one
monomer (b2) having sulfo groups, preferably 2-acrylamido-2-
methylpropanesulfonic acid or
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salts thereof, and 25 to 35% by weight of at least one cationic monomer having
ammonium
ions, preferably salts of 3-trimethylammoniopropyl(meth)acrylamides and 2-
trimethyl-
ammonioethyl (meth)acrylates.
The examples which follow are intended to illustrate the invention in detail:
Capillary shear test to API RP 63
Measurement principle
The shear stability or the shear degradation of polymers for tertiary mineral
oil production can
in principle be measured by means of a core flooding experiment. Owing to the
high
complexity of a core flooding experiment, the American Petroleum Institute
defined a
simplified standard test in which the polymer solution is sheared in a
capillary, and the
viscosity of the solution before and after the shear stress is compared. This
test is used in
the context of the present invention.
The shear degradation of the copolymers is determined by means of a capillary
shear test
according to method API RP 63, title "Recommended Practices for Evaluation of
Polymers
Used in Enhanced Oil Recovery Operation?, chapter 6.6 "Evaluation of shear
stability of
polymer solutions", published by the American Petroleum Institute on June 1,
1990.
Apparatus
The apparatus for measuring shear degradation consists of a steel cylinder
with pressurized
gas connection (nitrogen) to accommodate the polymer solution to be analyzed,
pressure
release valve, venting tap and an outlet valve to which capillaries of
different diameter can be
secured. The steel cylinder can be pressurized from a nitrogen bomb or a
pressurized gas
line.
The essential elements of the apparatus used are shown schematically in Figure
2. It
consists of a pressure vessel (2) with a capacity of approx. 1.5 I, which has
an outlet valve
(3), a gas inlet (1). Below the outlet valve (3) is mounted an exchangeable
capillary (4). A
receiver vessel (5) serves to receive the polymer solution forced through the
capillary. Unless
stated otherwise hereinafter, the capillary used for analysis has a length of
200 mm and an
internal diameter of 0.6 mm. The gas inlet valve can be screwed off to fill
the apparatus with
polymer solution.
Performance of the analysis
All analyses are undertaken at room temperature.
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First, the viscosity of the polymer solution to be analyzed is determined
according to the test
method below.
5 The outlet valve (3) of the apparatus used is closed, the apparatus at
ambient pressure is
filled with the polymer solution to be analyzed (approx. 800 ml) and the
apparatus is closed
again. The desired analysis pressure is established on the manometer of the
nitrogen supply,
and the desired analysis pressure is applied to the apparatus. For the
analysis, the outlet
valve (3) is opened. The polymer solution then flows through the capillary
into the collecting
10 vessel (5). Then an analysis vessel is held in the jet of the polymer
solution, and approx. 60
to 100 g of the solution are collected: after the collection has ended, the
analysis vessel is
pulled out again from the jet of the polymer solution. A stopwatch is used to
determine the
time for collection of the polymer solution, and the mass of the collected
polymer solution is
determined in each case. This operation is repeated several times, and the
corresponding
15 collection times and amounts are determined in each case.
The viscosity of all polymer solutions collected is determined again. The
shear degradation is
the percentage decrease in the viscosity of the polymer solution after
shearing compared to
the solution before shearing.
The shear stress is calculated by the following formula:
= 4Q I ide
7': apparent shear rate at the capillary wall (without newtonian
correction)
Q: flow of the polymer solution in ml/s (the density of the polymer
solution can be
considered to be 0 as a first approximation, such that the mass also
corresponds to
the volume).
R: internal diameter of the capillary
The percentage shear degradation is calculated from the measured viscosities
ribefore and
11after as follows: (ii before -11after) / Ti before
The shear degradation is measured at shear rates 22 in the range from 80 000 s-
1 to
100 000 s-1. Given the same concentration of the polymer solution in a test
series, the shear
rates can be set within the desired range by altering the pressure.
Determination of viscosity
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The viscosity measurements were carried out at room temperature with an LVDV-
UL
Brookfield viscometer at a shear rate of 7 s-1.
Monomers (a) used
Monomer M1
Hydroxybutyl vinyl ether alkoxylate with 22 EO units and 12 Pe0 units
H2C=CH-0-(CH2)4-0-(-CH2-CH2-0-)22-(-CH2-CH(C3H7)-0-)12-H
A 1 I stirred stainless steel autoclave is initially charged with 44.1 g of
hydroxybutyl vinyl
ether. Subsequently, 3.12 g of KOMe (32% in Me0H) are metered in and the
methanol is
drawn off at 80 C and approx. 30 mbar. This is followed by heating to 140 C,
purging of the
reactor with nitrogen and establishment of a nitrogen pressure of 1.0 bar.
Then 368 g of EO
are metered in within approx. 3 h. After continued reaction at 140 C for a
half hour, the
reactor is cooled to 125 C, and a total of 392 g of pentene oxide are metered
in over the
course of 3.5 h. The reaction continues overnight.
The product has an OH number of 31.9 mg KOH/g (theory: 26.5 mg KOH/g). The OH
number is determined by means of the ESA method.
Monomer M2
Commercially available monomer of the general formula
H2C=C(CH3)-000-(-CH2-CH2-0-)25-R (R = tristyrylphenyl) (Sipomer SEM 25, from
Rhodia).
Preparation of the copolymers
Example 1:
Preparation of a copolymer from 2% by weight of monomer Ml, 50% by weight of
acrylamide
and 48% by weight of 2-acrylamido-2-methylpropanesulfonic acid
A plastic bucket with magnetic stirrer, pH meter and thermometer is initially
charged with
121.2 g of a 50% aqueous solution of NaATBS (2-acrylamido-2-
methylpropanesulfonic acid,
sodium salt), and then 155 g of distilled water, 0.6 g of a defoamer (Surfynol
DF-58), 0.2 g
of a silicone defoamer (BaysiIon EN), 2.3 g of monomer Ml, 114.4 g of a 50%
aqueous
solution of acrylamide, 1.2 g of pentasodium diethylenetriaminepentaacetate
(complexing
agent, as a 5% aqueous solution) and 2.4 g of a nonionic surfactant
(nonylphenol,
alkoxylated with 10 units of ethylene oxide) are added successively.
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After adjusting the pH with a 20% or 2% sulfuric acid solution to a value of 6
and adding the
rest of the water, the monomer solution is adjusted to the start temperature
of 5 C. The total
amount of water is such that - after the polymerization - a solids
concentration of approx. 30
aid of a meat grinder. The gel granules obtained are dried in a fluidized bed
dryer at 55 C for
two hours. This gives white, hard granules which are converted to a
pulverulent state by
means of a centrifugal mill. This gives a copolymer with a weight-average
molecular weight
of approx. 1*106 g/mol to 30*106 g/mol.
Example 2:
Preparation of a copolymer from 5% by weight of monomer Ml, 50% by weight of
acrylamide
and 45% by weight of 2-acrylamido-2-methylpropanesulfonic acid
The procedure is as in Example 1, except that the amount of monomer M1 is
increased from
2% by weight to 5% by weight based on the sum of all monomers, and the amount
of
2-acrylamido-2-methylpropanesulfonic acid is reduced from 48% by weight to 45%
by weight.
The amount of the surfactant (proportions by mass) corresponds to that of
monomer Ml.
Example 3:
Preparation of a copolymer from 5% by weight of monomer M2, 50% by weight of
acrylamide
and 45% by weight of 2-acrylamido-2-methylpropanesulfonic acid
The procedure is as in Example 2, except that monomer M2 is used instead of
monomer Ml.
No surfactant is used.
Example 4:
Preparation of a copolymer from 2% by weight of monomer Ml, 36% by weight of
acrylamide
and 30% by weight of 2-acrylamido-2-methylpropanesulfonic acid and 32% by
weight of
3-trimethylammoniopropylacrylamide chloride (DIMAPAQUAT)
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The procedure is as in Example 1, except that the cationic monomer DIMAPAQUAT
(used as
a 60% aqueous solution) is additionally used in the amounts specified above.
The molar
(b2)/(b3) ratio is 0.94.
Example 5:
Preparation of a copolymer from 3% by weight of monomer M2, 35% by weight of
acrylamide
and 30% by weight of 2-acrylamido-2-methylpropanesulfonic acid and 32% by
weight of
3-trimethylammoniopropylacrylamide chloride (DIMAPAQUAT)
The procedure is as in Example 1, except that the monomer M2 and additionally
the cationic
monomer DIMAPAQUAT (used as a 60% aqueous solution) are used in the amounts
specified above.
Comparative polymer 1:
This is a commercially available copolymer for polymer flooding, formed from
approx. 50% by
weight of acrylamide and approx. 50% by weight of 2-acrylamido-2-
methylpropanesulfonic
acid with a weight-average molecular weight Mõ,, of approx. 8 to 13*106 g/mol.
Comparative polymer 2:
This is a commercially available copolymer for polymer flooding, formed from
approx. 72% by
weight of acrylamide and approx. 28% by weight of sodium acrylate units,
having a weight-
average molecular weight Mõ of approx. 20 000 000 g/mol.
Performance tests
Shear stability
Polymer solutions of each of the polymers according to Examples 1 to 5 and
Comparative
Polymers 1 and 2 were prepared in synthetic sea water (composition: 10 692 ppm
Nat,
420 ppm K , 1295 ppm Mg2+, 422 ppm Ca2+, 19 318 ppm Cl-, 145 ppm HCO3-, 2697
ppm
S042-). The concentration of each was such that the shear stress in the
capillary shear test
was of the same order of magnitude in each case.
First, the viscosity of the solutions was determined, then the capillary shear
test was carried
out, and the viscosity of the sheared solution obtained was measured once
again. This
involved carrying out a first viscosity measurement approx. 1/2 h after the
shear stress, and
also carrying out another test measurement after 2 days in order to check that
the viscosity
loss was truly irreversible. Some polymer solutions were sheared for a second
time for
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control purposes after the first shear. All measurements were carried out at
room
temperature.
In a first test series, measurements were carried out at a shear rate in the
range from
80 000 s-1 to 100 000 s-1. In a second test series, measurements were carried
out at a shear
rate of more than 100 000 s-1.
The test conditions and the results are compiled in Tables 1 and 2.
The examples and comparative examples show that the shear degradation of the
copolymers which comprise hydrophobically associating monomers (a) is
distinctly less than
with the comparative polymers without monomers (a).
Surprisingly, an increase in the viscosity in the course of shear was even
observed for some
copolymers. Without being tied to a particular theory, we suspect that this
effect could be
caused by a change in conformation. The polymer solutions which exhibited an
increase in
viscosity were sheared once again for test purposes thereafter. In the second
shear, they
exhibit a low shear degradation of distinctly less than 8%.
-ci
Polymer Monomers (a) Monomers (b) Polymer Pres- Shear
rate j, 11 71 Shear Comments -n
Type Amount concentration sure [s-1]
before after shear degradation
0
(% by [PPrri] [bar] shear
[mPas] co
-.I
--.1
wt.] [mPas]
No. 1 M1 2 (b1), (b2) 1400 4 82 654 21.9 21.8
0.4%
No. 2 M1 5 (b1), (b2) 1000 4 85 865 21.6 21.5
0.5% _
No. 3 M2 5 (b1), (b2) 3000 5 86 003 24 22.3
6.9%
No. 3 M2 5 (b1), (b2) _. 3000 6 99 220 24 21.6
9.9%
_
No. 4 M1 2 (b1), (b2), (b3) 4000 4 80
922 23.9 29.5 -23.2% Increase in the viscosity!
No. 4 M1 2 (b1), (b2), (b3) 4000 4 80
386 21 20.5 2.4% Second shear n
No. 5 M2 3 (b1), (b2), (b3) 3000 _ 5 88
549 19 . 22.7 -19.5% Increase in the viscosity!
0
iv
Cl 0 (b1), (b2) . 3000 8 89 990 24.8 ,
19.9 19.8% co
-
H
C2 I - 0 ' (b1), (b2) 2000 8 97 000 20 15.4
23.8% co
co
.1,.
-A
IV
Table 1: Compilation of the results of the shear test at a shear rate in the
range from 80 000 s1 to 100 000 s-1. 0
F-,
,.....)
(A
0 I
0
I
Polymer Monomers (a) Monomers (b) Polymer Pres- Shear
rate y., 71 11 Shear Comments iv
Type Amount concentration sure [s-1]
before after shear degradation u.)
[% by IPPrril [bar] shear
[mPas]
wt.] [mPas]
_
No. 3 M2 5 . (b1), (b2) 3000 _8 120 103 22.8 23.8
_3.9% Increase in the viscosity!
_
.No. 4 M1 2 (b1), (b2), (b3) 2500 8 130
421 23.9 40 -65.3% Increase in the viscosity
'
No. 4 M1 2 (b1), (b2), (b3) _ 2500 8 132
840 40 37.2 6.0% Second shear
_
No. 5 M2 3 (b1), (b2), (b3) _ 3000 6 , 100
770 19 21.3 - 12.1% Increase in the viscosity
No. 5 M2 3 (b1), (b2), (b3) _3000 8 127
388 23.9 21.8 8.7%
_
No. 5 M2 3 (b1), (b2), (b3) 3000 8 129
414 21.8 21.6 1.3% Second shear
Table 2: Compilation of the results of the shear test at a shear rate of more
than 100 000 s-1
