Note: Descriptions are shown in the official language in which they were submitted.
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AUTO-INVERTIBLE INVERSE POLY1VIER EMULSION
FIELD OF THE INVENTION
The present invention relates to the technical field of polymers as a water-in-
oil
emulsion, otherwise known as an inverse emulsion. More specifically, the
invention relates to an inverse polymer emulsion having the particular feature
of
auto-inverting without requiring the use of an inverting agent.
The invention also relates to the use of this inverse emulsion in various
fields such
as the oil and gas, water treatment, slurry treatment, paper manufacturing,
construction, mining, cosmetics, textiles, detergents, and agriculture
industries.
PRIOR STATE OF THE ART
Inverse polymer emulsions are widely used in various fields such as water
treatment, enhanced oil recovery and hydraulic fracturing.
The use of these inverse emulsions is based on dissolving the polymer in water
or
brine. To that end, the inverse emulsion inverts so as to release the polymer
contained in the aqueous phase of the inverse emulsion. After release, the
polymer
is in the water or brine to which the inverse emulsion was added. To date,
this
inverse emulsion inversion step involves the presence of inverting agents,
which
are generally hydrophilic surfactants with a high HLB, generally greater than
10.
The presence of hydrophilic surfactants in an inverse polymer emulsion may
affect the viscosity and/or stability parameters of the inverse emulsion. This
results in significant increases in the viscosity of the inverse emulsion
(which can
lead to caking) or by an acceleration of the phase separation (sedimentation
of the
polymer particles and occurrence of an oily phase on the surface).
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On the other hand, it is acknowledged that most hydrophilic surfactants are
ethoxylated products which may present environmental problems.
In addition, the hydrophilic surfactants must be selected specifically
according to
the composition of the medium in which the inverse emulsion is implemented
(water or brine), and according to the temperature of this medium, which
requires
a complex adjustment process for the hydrophilic surfactant to act as an
inverting
agent.
Thus, it would be advantageous to have an inverse emulsion which can invert
without using an inverting agent. Therefore, the problem which the present
invention proposes to solve is to provide an inverse emulsion which auto-
inverts
without requiring the use of an inverting agent such as an oil-in-water
surfactant.
DISCLOSURE OF THE INVENTION
The applicant surprisingly discovered that the introduction of macromonomer
with lower critical solution temperature (LCST) in the polymer during its
synthesis in inverse emulsion could give the inverse emulsion an auto-
inversion
property.
This auto-inversion property means that the polymer dissolves in water (or
brine)
without necessarily resorting to the use of an inverting agent such as an oil-
in-
water surfactant. In addition, this emulsion can rapidly invert even under
conditions of high temperature and/or high salinity, which is of great
interest,
particularly in the fields of oil and gas recovery.
More specifically, the present invention relates to an auto-invertible inverse
emulsion comprising:
- an oil,
- some water,
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- at least one water-in-oil surfactant,
- at least one polymer containing monomer units of at least one water-
soluble
monomer and at least one LCST macromonomer.
The inverse emulsion according to the invention is advantageously free of oil-
in-
water surfactant.
The present invention also relates to a polymeric aqueous solution obtained by
inversion of the inverse emulsion described above. The inversion is
advantageously carried out in the absence of an oil-in-water surfactant. It
also
relates to the use of the inverse emulsion described above to thicken an
aqueous
medium, or to flocculate suspended particles or reduce the level of frictional
resistance during transport of an aqueous medium.
Finally, the present invention also relates to the use of the inverse emulsion
described above for the recovery of oil and gas, or for the treatment of
water, or
for the treatment of slurry, or for the manufacture of paper, or in
construction, or
in the mining industry, or in the formulation of cosmetics, or in the
formulation of
detergents, or in the manufacture of textiles, or in agriculture.
Polymer
The polymer in the inverse emulsion is generally water-soluble or water-
swelling.
The term "water-soluble polymer" is understood to mean a polymer which gives
an aqueous solution when it is dissolved under stirring at 25 C and with a
concentration of 50 g.L-1 in water. The term "water-swelling polymer" is
understood to mean a polymer which swells and thickens an aqueous solution
(water) in which it is placed at 25 C.
The polymer is a polymer of at least one water-soluble monomer and at least
one
LCST macromonomer. In other words, the polymer is obtained from at least one
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water-soluble monomer and at least one LCST macromonomer. Therefore, it
contains monomer units derived from the monomer(s) and macromonomer(s)
mentioned. In other words, the polymer of the inverse emulsion according to
the
invention is a polymer of at least one water-soluble monomer bearing at least
one
unsaturated function (advantageously, a vinyl group R1R2C=CR3-, R1, R2 and
R3 being independently of one another a hydrogen atom or a hydrocarbon or a
non-hydrocarbon group which may comprise heteroatoms) which might be
polymerized to form a backbone, and of at least one LCST macromonomer. Thus,
the polymer comprises units derived from the water-soluble monomer and units
derived from the LCST macromonomer.
As defined by IUPAC, a macromonomer is a polymer or oligomer bearing a
terminal group that acts as a monomer, thus each polymer or oligomer
corresponds to a monomer unit in the final polymer chain.
According to an advantageous embodiment, the molar percentage of units
(monomer units) derived from LCST macromonomers in the polymer is between
10-5 and 5 mol% (>10-5 mol% and <5 mol%) relative to the total number of moles
of monomer units of water-soluble monomer(s) and LCST macromonomer(s),
preferably between 10-4 and 1 mol%. This percentage is preferably greater than
10' mol% (>10-3 mol%), even more preferably greater than 5.10-3 mol%. This
percentage is preferably less than 1 mol% relative to the total number of
moles of
monomer units of water-soluble monomer(s) and LCST macromonomer(s),
preferably less than 0.1 mol%, preferably less than 8.10' mol%, more
preferably
less than 6.10-2 mol%, even more preferably less than 5.10' mol%, even more
preferably less than 4.10-2 mol%.
In general, the amount of monomer units of a monomer (monomer or
macromonomer) corresponds to the amount of this monomer used in the
preparation of the polymer. This definition is applicable for the preparation
of the
water-soluble copolymer or the macromonomer and, therefore, of the oligomer
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(see below).
According to an embodiment of the invention, the polymer may be obtained by
polymerizing at least one water-soluble monomer bearing at least one
unsaturated
5 function and at least one LCST macromonomer. In other words, the water-
soluble
monomer(s) and the LCST macromonomers are polymerized at the same time in a
reactor. The polymer chain is formed gradually in the presence of water-
soluble
monomers and LCST macromonomers.
According to another embodiment, a water-soluble prepolymer, called a
backbone, is first obtained by polymerizing the water-soluble monomers, then,
in
a second step, the LCST oligomers are grafted onto said prepolymer. A person
skilled in the art is familiar with the techniques for grafting LCST
macromonomers onto a polymer. Mention may be made, for example, of patent
application WO 2014/047243 which discloses this technique.
According to a third embodiment, the polymer may be obtained by polymerizing
water-soluble monomers on a structured LCST macromonomer obtained by
controlled radical polymerization (RAFT) in the presence of LCST monomers and
at least one crosslinking agent. Therefore, the polymers thus obtained are in
a star-
shaped form with an LCST core. The crosslinking agent may, in particular, be
selected from the group comprising polyethylene unsaturated monomers (having
at least two C=C unsaturated functions), such as, for example, vinyl, allylic
and
acrylic functions and mention may be made, for example, of methylene bis
acrylamide (MBA).
The polymer may also be obtained by the same technique but without using a
crosslinking agent for obtaining the macromonomer by controlled radical
polymerization (RAFT).
Of course, methods other than these two methods for obtaining the polymer may
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be used without departing from the scope of the invention.
The water-soluble monomers which may be used are preferably selected from
nonionic monomers, anionic monomers, cationic monomers and zwitterionic
monomers. Preferably, they are selected from nonionic, anionic and cationic
monomers.
The water-soluble monomer may be a nonionic monomer which may, in
particular, be selected from the group comprising vinyl monomers soluble in
water, and particularly acrylamide; methacrylamide; N-vinylformamide; and N-
vinylpyrrolidone. Advantageously, at least one water-soluble monomer is
acrylamide.
At least one water-soluble monomer may also be an anionic monomer. The
anionic monomer(s) which may be used in the context of the invention may be
selected from a large group. These monomers may have at least one function
among the vinyl functions (for example, acrylic, maleic, fumaric, itaconic,
allylic)
or a malonic function, and they may contain at least one group from
carboxylate,
phosphonate, phosphate, sulfate, sulfonate groups, or another anionically
charged
group. The anionic monomer may be in acid form or else in the form of an
alkaline earth metal or an alkali metal or ammonium (in particular, quaternary
ammonium) salt. Examples of anionic monomers are acrylic acid; methacrylic
acid; itaconic acid; crotonic acid; maleic acid; fumaric acid; monomers of
strong
acid type exhibiting, for example, a function of sulfonic acid or phosphonic
acid
type, such as 2-acrylamido 2-methylpropanesulfonic acid, vinylsulfonic acid,
vinylphosphonic acid, allylsulfonic acid, allylphosphonic acid, styrene
sulfonic
acid; and the water-soluble salts of these monomers such as their alkali
metal,
alkaline earth metal, or ammonium (especially quaternary ammonium) salts.
At least one water-soluble monomer may optionally be a cationic monomer of
vinyl type (for example, acrylamide, acrylic, allylic or maleic) having at
least one
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ammonium function (for example, a quatemary ammonium). Mention may be
made, in particular and without limitation, of quatemized or salified
dimethylaminoethyl acrylate (ADAME); quatemized or salified
dimethylaminoethyl methacrylate (MADAME); dimethyldiallylammonium
chloride (DADMAC); acrylamido propyltrimethyl ammonium chloride (APTAC);
and methacrylamido propyltrimethyl ammonium chloride (MAPTAC).
Monomers of hydrophobic nature may also be used as a comonomer for the
preparation of the polymer, but at a concentration by weight based on the
total
monomer content of preferably less than 5%. They are preferably selected from
the group comprising esters of (meth)acrylic acid having an alkyl, arylalkyl
or
ethoxylated chain; (meth)acrylamide derivatives having an alkyl, arylalkyl or
dialkyl chain; cationic allylic derivatives; anionic or cationic hydrophobic
(meth)acryloyl derivatives; and derivatives of anionic or cationic monomers of
(meth)acrylamide carrying a hydrophobic chain. The alkyl chains are
advantageously C8-C16. Most preferred is bromoalkylated C8-C16
methacrylamide.
It is also possible to use a branching agent or a crosslinking agent. Such an
agent
is, for example, selected from methylene-bis-acrylamide (MBA), ethylene glycol
diacrylate, tetraallyl ammonium polyethylene glycol chloride, diacrylamide,
cyanomethyl acrylate, epoxies and mixtures thereof.
It is also possible to use a free radical chain transfer agent, also known as
a chain
stopper. The use of a chain transfer agent is particularly advantageous for
controlling the molecular weight of the polymer obtained. By way of example of
a
transfer agent, mention may be made of methanol, isopropanol, sodium
hypophosphite, 2-mercaptoethanol, sodium methallylsulphonate, and mixtures
thereof. A person skilled in the art will adjust in a known manner the amounts
of
branching agent, and optionally of transfer agent or branching agent.
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The polymer may be obtained by radical polymerization in inverse emulsion.
Polymerization techniques such as controlled radical polymerization known as
RAFT (Reversible-Addition Fragmentation chain Transfer), NMP (Nitroxide
Mediated Polymerization) or ATRP (Atom Transfer Radical Polymerization),
may be used to obtain the polymer.
According to the invention, the polymer has a molecular weight advantageously
of at least 0.5 million g/mol, preferably between 0.5 and 40 million g/mol,
more
preferably between 5 and 30 million g/mol. Molecular weight is referred to as
weight average molecular weight.
Molecular weight is determined by the intrinsic viscosity of the polymer. The
intrinsic viscosity may be measured by methods known to a person skilled in
the
art and may be calculated from the values of reduced viscosity for different
polymer concentrations by a graphic method consisting in recording the values
of
reduced viscosity (y-axis) on the concentration (x-axis) and extrapolating the
curve to zero concentration. The intrinsic viscosity value is recorded on the
y-axis
or using the least squares method. The molecular weight may then be determined
by the Mark-Houwink equation:
[i]=K M
represents the intrinsic viscosity of the polymer determined by the solution
viscosity measurement method,
K represents an empirical constant (K = 3.73.104),
M represents the molecular weight of the polymer,
a represents the Mark-Houwink coefficient (a = +0.66),
K and a depend on the particular polymer-solvent system.
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LCST macromonomer and its synthesis
According to the general knowledge of a person skilled in the art, the LCST
groups correspond to groups whose solubility in water for a determined
concentration is modified beyond a certain temperature and based on the
salinity.
These are groups exhibiting a transition temperature by heating that defines
their
lack of affinity with the solvent medium. Lack of solvent affinity results in
clouding or loss of transparency.
The minimum transition temperature is called "LCST" (Lower Critical Solution
Temperature). For each LCST group concentration, a transition temperature by
heating is observed. It is greater than the LCST which is the minimum point of
the
curve. Below this temperature, the polymer is soluble in water, above this
temperature, the polymer loses its solubility in water.
The LCST may be measured visually in the usual manner: the temperature is
determined when the cloud point appears, which is when the lack of affinity
with
the solvent occurs. The cloud point corresponds to the clouding or loss of
transparency of the solution.
The LCST may also be determined according to the type of phase transition, for
example by DSC (Differential Scanning Calorimetry), by a transmittance
measurement or by a viscosity measurement.
Preferably, the LCST is determined by determining the cloud point by
transmittance according to the following protocol.
The transition temperature is measured for an LCST compound for a solution
having a mass concentration of 1% by weight of said compound in deionized
water. The cloud point corresponds to the temperature at which the solution
has a
transmittance equal to 85% of light rays having a wavelength between 400 and
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800 nm.
In other words, the temperature at which the solution has 85% transmittance
corresponds to the minimum LCST transition temperature of the compound, in
5 this case, from the LCST macromonomer.
In general, a transparent composition hos a maximum light transmittance value,
regardless of the wavelength between 400 and 800 nm, through a 1-cm-thick
sample, of at least 85 %, preferably at least 90%. This is the reason why the
cloud
10 point corresponds to a transmittance of 85%.
In general, the LCST macromonomer is obtained by synthesis of an LCST
oligomer having a functional end, then by grafting an ethylenic group onto
this
functional end.
Mention may thus be made, by way of example, of the synthesis of the LCST
macromonomer from an LCST oligomer of controlled size and functionality,
carried out using a radical or ionic initiator having the desired chemical
function,
and/or by introducing a transfer agent substituted by the desired chemical
group
and/or by polycondensation.
The LCST monomers which may be used to produce the LCST oligomer, which is
used to obtain the LCST macromonomer, are preferably selected from N-
isopropylacrylamide; N,N-dimethylacrylamide; acryloyl morpholine; N,N-diethyl
acrylamide; N-tert-butyl acrylamide; N-vinyl caprolactam; and diacetone
acrylamide.
In the context of the invention, the LCST oligomer advantageously comprises
between 10 mol% and 100 mol% of monomer(s) comprising an LCST unit, more
advantageously between 40 mol% and 100 mol% and even more advantageously
between 50 mol% and 100 mol% relative to the total number of moles of
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monomers in the oligomer. According to a particular embodiment, the LCST
oligomer may, in particular, comprise 90 to 96 mol% of monomer(s) comprising
an LCST unit.
In addition to the LCST monomers, the water-soluble monomers which may be
used to make the LCST oligomer are preferably selected from nonionic
monomers, anionic monomers, cationic monomers and zwitterionic monomers.
Preferably, they are selected from nonionic monomers and anionic monomers.
In the context of the invention, the LCST oligomer advantageously comprises
between 0 mol% and 90 mol% of this (these) (nonionic and/or anionic and/or
cationic and/or zwitterionic) monomer(s), more advantageously between 0 mol%
and 60 mol% and even more advantageously between 0 mol% and 50 mol%
relative to the total number of moles of monomers in the oligomer. According
to a
particular embodiment, the LCST oligomer may, in particular, comprise 4 to 10
mol% of this (these) monomer(s). These monomers may be hydrophilic or
hydrophobic in nature.
Thus, the LCST oligomer, and therefore the LCST macromonomer, is obtained
from at least one LCST monomer and, optionally, at least one water-soluble
monomer. Therefore, it contains monomer units derived from the monomer(s) and
macromonomer(s) mentioned.
The water-soluble monomer may be a nonionic monomer which may, in
particular, be selected from the group comprising vinyl monomers soluble in
water, and particularly acrylamide. Thus, the LCST oligomer may comprise a
nonionic monomer advantageously selected from the group comprising
acrylamide; methacrylamide; N-vinylformamide; and N-vinylpyrrolidone.
The water-soluble monomer of the LCST oligomer may also be an anionic
monomer. The anionic monomer(s) of the LCST oligomer may be selected from a
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broad group. These monomers may have at least one function from vinyl
functions (such as, acrylic, maleic, fumaric, itaconic, allylic) or a malonic
function, and may contain at least one group from the carboxylate,
phosphonate,
phosphate, sulphate, sulphonate groups, or another anionically charged group.
The
anionic monomer of the LCST oligomer may be in acid form or in the form of an
alkaline earth metal or an alkali metal or ammonium sait (in particular,
quaternary). Examples of suitable monomers include acrylic acid; methacrylic
acid; itaconic acid; crotonic acid; maleic acid; fumaric acid; monomers of
strong
acid type exhibiting, for example, a function of sulfonic acid or phosphonic
acid
type, such as 2-acrylamido 2-methylpropanesulfonic acid, vinylsulfonic acid,
vinylphosphonic acid, allylsulfonic acid, allylphosphonic acid, styrene
sulfonic
acid; and the water-soluble salts of these monomers such as their alkali
metal,
alkaline earth metal or ammonium (in particular quaternary) salts.
Optionally, the LCST oligomer may include at least one cationic monomer.
The monomer of the LCST oligomer may optionally be a cationic monomer of
vinyl type (for example, acrylamide, acrylic, allylic or maleic) having a
quaternary ammonium function. Mention may be made, in particular and without
limitation, of quaternized or salified dimethylaminoethyl acrylate (ADAME);
quaternized or salified dimethylaminoethyl methacrylate (MADAME);
dimethyldiallylammonium chloride (DADMAC); acrylamido propyltrimethyl
ammonium chloride (APTAC); and methacrylamido propyltrimethyl ammonium
chloride (MAPTAC).
Hydrophobic monomers may also be used to prepare the LCST oligomer. They
may be selected, in particular, from vinyl type monomers (for example
acrylamide, acrylic, allylic or maleic) having a pendant hydrophobic function.
It
may, in particular, be the butyl methacrylate monomer.
According to a preferred embodiment, the LCST oligomer is a polymer of an
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LCST monomer (preferably N-isopropylacrylamide), of an anionic monomer
(preferably acrylic acid) and of a hydrophobic monomer (preferably butyl
methacrylate).
Thus, according to another preferred embodiment, the LCST oligomer is a
polymer of an LCST monomer (preferably N-isopropylacrylamide), of a cationic
monomer (preferably MADAME.MeC1) and of a hydrophobic monomer
(preferably butyl methacrylate).
As regards the synthesis of the LCST macromonomer, in a first step, mention
may
be made of telomerization, which is a method of synthesizing an LSCT oligomer
with low molar masses (called telomers).
According to the invention, the LCST macromonomer has a molecular weight
preferably between 500 g/mol and 200,000 g/mol, more preferably between 1,000
g/mol and 100,000 g/mol, even more preferably between 1,500 g/mol and 100,000
g/mol. Molecular weight is referred to as weight average molecular weight.
The telogen agents may be selected, inter alia, from thiols, alcohols,
disulfides,
phosphorus derivatives, boron derivatives and halogen derivatives. They may,
in
particular, make it possible to introduce specific functions at the end of the
telomer chains, for example silane, trialkoxysilane, amine, epoxy, hydroxyl,
phosphonate or acid functions.
Once these LCST oligomers have been formed, in a second step, a vinyl double
bond (R1R2C=CR3-, R1, R2 and R3 being, independently of one another, a
hydrogen atom or a hydrocarbon or a non-hydrocarbon group, which may
comprise heteroatoms) may be introduced at the end of the chain so that they
serve as LCST macromonomers which, in turn, may be polymerized.
According to another synthesis method, an LCST macromonomer may be
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obtained by controlled radical polymerization known as RAFT (Reversible-
Addition Fragmentation chain Transfer) of LCST monomers in the presence of at
least one crosslinking agent. Therefore, the macromonomer thus obtained is
structured and may be used as a core for obtaining water-soluble copolymers in
star-shaped form. The crosslinking agent may, in particular, be selected from
the
group comprising polyethylene unsaturated monomers (having at least two C=C
unsaturated functions), such as, for example, vinyl, allylic and acrylic
functions
and, for example, and mention may be made, for example, of methylene bis
acrylamide (MBA).
The LCST macromonomer may be obtained by the same technique but without
using a crosslinking agent.
There are numerous reactions that may be implemented for couplings on
monomers: alkylation, esteri fi cati on,
ami dati on, trans esterifi cati on or
trans ami dati on.
In a preferred embodiment, the preparation of the LCST macromonomer is carried
out by radical reaction between an LCST oligomer and a compound containing a
C=C double bond, the double bond still being present after said radical
reaction.
Advantageously, the LCST oligomer has the characteristic of having a nitrogen
or
oxygen atom at its end, such as, for example, an alcohol or amine function,
which
is functionalized using a compound containing a C=C double bond. This
compound containing a double bond is preferably selected from acryloyl
chloride,
acrylic acid, methacryloyl chloride, methacrylic acid, maleic anhydride,
methacrylic anhydride, unsaturated aliphatic isocyanates, allyl chloride,
allyl
bromide, glycidyl acrylate, glycidyl methacrylate.
According to a particular embodiment, the LCST macromonomer may be of
formula (I):
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CH
/ 3
H2C=C\ 1/ JO
C
\ 0,
HO--:
m
¨0
H
(I)
In which:
m is an integer advantageously between 2 and 40.
5
The LCST groups of the water-soluble polymer have a transition temperature by
heating advantageously between 0 and 180 C for a mass concentration in
deionized water of 1% by weight of said LCST groups, preferably between 0 and
100 C, even more preferably between 10 and 80 C.
Inverse polymer emulsion
An inverse emulsion, otherwise called a water-in-oil emulsion, is composed of
an
oily phase, generally a lipophilic solvent or an oit, which constitutes the
continuous phase in which water droplets comprising a polymer are in
suspension,
these water droplets forming a dispersed phase. An emulsifying surfactant
(called
water-in-oit surfactant) at the water/oit interface stabilizes the dispersed
phase
(water + polymer) in the continuous phase (lipophilic solvent or oit).
In inverse emulsions according to the prior art, an oit-in-water surfactant,
which is
an inverting agent, makes it possible to invert the emulsion and therefore to
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release the polymer when the emulsion is mixed with an aqueous fluid. For the
purposes of the invention, it is not necessary to add an inverting surfactant
(oil-in-
water surfactant) to the inverse emulsion, including during its use. In other
words,
and preferably, the inverse emulsion according to the invention does not
contain
an oil-in-water surfactant and, in general, it is not necessary to add an oil-
in-water
surfactant in the fluid in which the emulsion is implemented, whether before,
during or after the addition of the inverse emulsion in said fluid.
The inverse emulsion according to the invention may be prepared according to
any method known to a person skilled in the art. Generally, an aqueous
solution
comprising the monomer(s) and the water-in-oil surfactant(s) is emulsified in
an
oily phase. Then, the polymerization of the monomers is carried out,
advantageously by adding a free radical initiator.
Generally, the polymerization is carried out isothermally, adiabatically or at
controlled temperature. In other words, the temperature is kept constant,
usually
between 10 and 60 C (isothermal), or the temperature increases naturally
(adiabatic) and, in this case, the reaction usually starts at a temperature
below 10
C and the final temperature is generally above 50 C or, finally, the increase
in
temperature is controlled so as to have a temperature curve between the
isothermal curve and the adiabatic curve.
The inverse emulsion according to the invention is preferably prepared
according
to the process comprising the following steps:
a) preparing an aqueous phase comprising at least one water-soluble monomer
and at least one LCST macromonomer,
b) preparing an oily phase comprising at least one oil and at least one water-
in-
oil surfactant,
c) mixing the aqueous phase and the oily phase in order to form an inverse
emulsion,
d) once the inverse emulsion is formed, polymerizing the monomers in the
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aqueous phase using a radical polymerization initiator.
In the inverse emulsion, the weight ratio of the aqueous phase to the oily
phase is
preferably from 30:70 to 90:10, more preferably from 70:30 to 80:20.
At the end of the polymerization reaction, it is also possible to dilute or
concentrate the inverse emulsion obtained. Dilution is usually done by adding
water, preferably salted, in the inverse emulsion. In this case, the inverse
emulsion
may be diluted to obtain a polymer concentration of up to 10% by weight. It is
possible to concentrate the emulsion obtained, for example by distillation. In
this
case, the inverse emulsion may be concentrated and a polymer concentration of
up
to 60% by weight may be obtained.
As already discussed above, it is not necessary to add an inverting surfactant
(oil-
in-water surfactant) to the inverse emulsion during its preparation. In
addition, the
use of the inverse emulsion does not require an inverting surfactant.
However, it is possible to introduce an inverting surfactant. Indeed, as
mentioned
above, the object of the invention is to limit, and even eliminate, the use of
an
inverting surfactant to invert an inverse emulsion.
The oil of the inverse emulsion according to the invention advantageously
denotes
an oil or a solvent immiscible in water. The oil used to prepare the water-in-
oil
emulsion of the invention may be mineral oil, vegetable oil, synthetic oil, or
a
mixture of several of these oils. Examples of mineral oil are mineral oils
containing saturated hydrocarbons of the aliphatic, naphthenic, paraffinic,
isoparaffinic, cycloparaffinic or naphthyl type. Examples of synthetic oil are
hydrogenated polydecene or hydrogenated polyisobutene; an ester such as octyl
stearate or butyl oleate. ExxonMobil's Exxsol0 products are suitable oils.
The inverse emulsion preferably comprises from 12 to 50% by weight of oil or
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lipophilic solvent, more preferably from 15 to 30% by weight.
The water-in-oil emulsion of step a) above preferably comprises from 30 to 55%
by weight of water, more preferably from 35 to 48% by weight.
In the present invention, the term "inverse emulsion surfactant" or
"emulsifying
agent" or "water-in-oil surfactant" refers to an agent capable of emulsifying
water
in oil while an "inverting agent" or "oil-in-water surfactant" refers to an
agent
capable of emulsifying oil in water. More specifically, it is considered that
an
inverting agent is a surfactant having an HLB greater than or equal to 10, and
that
an emulsifying agent is a surfactant having an HLB less than 10.
The hydrophilic-lipophilic balance (HLB) of a chemical compound is a measure
of the degree of hydrophilicity or lipophilicity, determined by calculating
values
for different regions of the molecule, as described by Griffin in 1949
(Griffin WC,
Classification of Surface-Active Agents by HLB, Journal of the Society of
Cosmetic Chemists, 1949, 1, pages 311-326).
In the present invention, we have adopted Griffin's method based on
calculating a
value based on the chemical groups of the molecule. Griffin assigned a
dimensionless number between 0 and 20 to provide information on water and oil
solubility. Substances with an HLB value of 10 are distributed between the two
phases so that the hydrophilic group (molecular mass Mh) projects completely
into the water while the lipophilic group (usually a hydrophobic hydrocarbon
group) (molecular mass Mp) is in the non-aqueous phase.
The HLB value of a substance having a total molecular mass M, a hydrophilic
part of a molecular mass Mh and a lipophilic part of a molecular mass Mp is
given
by the following formula:
HLB =20 (Mh / M)
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The emulsifying agent (water-in-oil surfactant) may, in particular, be
selected
from surfactant polymers such as:
- polyesters having a weight average molecular weight of between 1000 and
3000 g/mol, for example the products of condensation between a
polyisobutenyl succinic acid or its anhydride and a polyethylene glycol,
- block polymers having an average molecular weight by weight
advantageously between 2500 and 3500 g/mol, for example those sold under
the names Hypermer0,
- sorbitan extracts such as sorbitan monooleate, sorbitan isostearate or
sorbitan
sesquioleate,
- sorbitan esters,
- diethoxylated oleoketyl alcohol
- tetraethoxylated lauryl acrylate,
- condensation products of higher fatty alcohols with ethylene oxide, such as
the
reaction product of oleyl alcohol with 2 ethylene oxide units;
- condensation products of alkylphenols and ethylene oxide, such as the
reaction product of nonylphenol with 4 units of ethylene oxide.
Products such as Witcamide0 511, betaine-based products and ethoxylated
amines may also be used as water-in-oil emulsifiers.
The inverse emulsion may contain several water-in-oil emulsifying agents. It
preferably contains between 0.8 and 20% by weight of water-in-oil emulsifier,
more preferably between 1 and 10% by weight.
The radical polymerization initiator may be selected from initiators
conventionally used in radical polymerization. These may be, for example,
hydrogen peroxides, azo compounds or redox systems.
The water-in-oil emulsion according to the invention preferably comprises from
8
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to 60% by weight of polymer, preferably from 12 to 40%.
The inverse emulsion may comprise from 1 to 40% by weight of salts, preferably
from 3 to 30% by weight, more preferably from 5 to 25% by weight of salts.
5
The salts present in the water-in-oil emulsion may be, for example, sodium
salts,
lithium salts, potassium salts, magnesium salts, aluminum salts, ammonium
salts,
phosphate salts, sulfate salts, chloride salts, fluoride salts, citrate salts,
acetate
salts, tartrate salts, hydrogen phosphate salts, water-soluble inorganic
salts, other
10 inorganic salts and their mixtures. These salts include sodium
chloride, sodium
sulfate, sodium bromide, ammonium chloride, lithium chloride, potassium
chloride, potassium bromide, magnesium sulfate, aluminum sulfate, and their
mixtures. Sodium chloride, ammonium chloride and ammonium sulfate are
preferred and their mixtures are even more preferred.
Property of the inverse emulsion
Thanks to the presence of LCST macromonomer units in the polymer, the inverse
emulsion is capable of auto-inverting when it is used in water or a brine,
although
said emulsion may advantageously contain no inverting surfactant. In the
absence
of LCST macromonomer units in the polymer, inversion of the inverse emulsion
requires the presence of an inverting surfactant such as an oil-in-water
surfactant.
Thus, this particular property makes it possible to solve the environmental
problems linked to the presence of an inverting surfactant. It also makes it
possible to simplify the formulation of such emulsions.
This last advantage is particularly interesting when the surfactants must be
selected specifically according to the composition of the medium in which the
inverse emulsion is implemented (water or brine), and according to the
temperature of that medium, which is the case in oil and gas recovery.
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21
Uses of the inverse emulsion
The present invention also relates to a polymeric aqueous solution obtained by
inversion of the inverse emulsion as described above in an aqueous medium,
preferably in the absence of an oil-in-water surfactant. In other words, it is
a
process for inverting an inverse emulsion consisting in bringing it into
contact
with an aqueous medium, preferably in the absence of an oil-in-water
surfactant.
The present invention also relates to the use of the inverse emulsion to
thicken an
aqueous medium, to flocculate suspended particles or to reduce the level of
frictional resistance during transport of an aqueous medium.
Finally, the present invention also relates to the use of the inverse emulsion
in the
oil and gas recovery, in water treatment, in slurry treatment, in paper
manufacturing, in construction, in the mining industry, in the formulation of
cosmetic products, in the formulation of detergents, in textile manufacturing,
or in
agriculture.
Usually, the inverse emulsion is implemented by adding most often water, or a
brine (such as sea water), in an aqueous medium. The polymer is released and
dissolved or swelled in the aqueous medium.
The inverse emulsion may be advantageously prepared with the device and
method of US 8,383,560, in which the inverse emulsion is dissolved
continuously
with an arrangement of multiple static mixers.
The inverse emulsion is used such that the polymer concentration in the medium
in which it is implemented is advantageously between 25 and 100,000 ppm by
weight, more preferably between 50 and 10,000 ppm. This amount of polymer
depends on the process in which the inverse emulsion is used.
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The inverse emulsion according to the invention is particularly useful in the
recovery of oit and gas. Indeed, oit and gas recovery companies use large
quantities of inverse polymer emulsion and seek to limit the environmental
impacts of their activities.
In addition, the inverse emulsions according to the invention can auto-invert
under
many conditions. More precisely, they auto-invert even under conditions
generally considered difficult, or even extreme, in particular when the
aqueous
medium in which they are used is very salty and/or when their temperature is
high. These advantages are highly sought after in the field of oit and gas
recovery.
The inverse emulsion according to the invention is capable of auto-inverting
in
sea water but also in very concentrated brines.
Likewise, the inverse emulsion according to the invention is capable of auto-
inverting even at high temperatures.
Oit and gas recovery processes are generally treatments of subterranean
formations in which a polymer is used to increase the viscosity of the aqueous
injection fluid and/or to reduce the level of frictional resistance that
occurs during
the injection of said fluid into a subterranean formation, or even to
punctually or
permanently plug a part of the subterranean formation.
These subterranean treatments include, but are not limited to, drilling
operations,
stimulation treatments such as fracturing operations, completion operations
and
the improved process of oit recovery by sweeping with a polymer solution.
The present invention also relates to a method for fracturing an underground
formation, which comprises:
aa) providing an inverse emulsion as described above;
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23
bb) inverting the inverse emulsion by adding it to an aqueous fluid in order
to
form an injection fluid;
cc) optionally, adding at least one propping agent in the injection
fluid;
dd) introducing the injection fluid into part of the subterranean
formation;
ee) fracturing the underground formation with the injection fluid.
The present invention also relates to a process for the improved recovery of
hydrocarbons (oil and/or gas) by sweeping in a subterranean formation, which
comprises:
aaa) providing an inverse emulsion as described above;
bbb) inverting the inverse emulsion by adding it to an aqueous fluid to form
an
injection fluid;
ccc) introducing the injection fluid into part of the subterranean formation;
ddd) sweeping part of the subterranean formation with the injection fluid;
eee) recovering a mixture of hydrocarbons and aqueous fluid.
The following characteristics apply to the previous two processes (fracturing
and
oil and/or gas recovery).
Advantageously, the inverse emulsion according to the invention does not
contain
an inverting surfactant and it is advantageously not necessary to add an
inverting
surfactant in the fluid in which the inverse emulsion is implemented, whether
before, during or after adding the inverse emulsion to said fluid. Thus,
advantageously, the use of the inverse emulsion according to the invention
does
not require the presence of an oil-in-water surfactant.
The aqueous fluid may be a brine containing monovalent and/or polyvalent salts
or combinations thereof. Examples of salts include, without limitation, sodium
salts, lithium salts, potassium salts, magnesium salts, aluminum salts,
ammonium
salts, phosphate salts, sulfate salts, chloride salts, fluorinated salts,
citrate salts,
acetate salts, tartrate salts, hydrogen phosphate salts, soluble inorganic
salts, other
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24
inorganic salts and mixtures thereof.
The brine may contain more than 30,000 ppm of salts, preferably more than
70,000 ppm, even more preferably more than 100,000 ppm. The brine may be
saturated with salts.
The temperature of the aqueous fluid in which the inverse emulsion according
to
the invention is inverted is advantageously between 25 C and 160 C,
preferably
greater than 40 C, more preferably greater than 60 C, even more preferably
greater than 80 C, and even more preferably greater than 90 C.
The concentration of water-soluble copolymer in the aqueous injection fluid is
advantageously between 50 and 50,000 ppm by weight, preferably between 100
and 30,000 ppm, more preferably between 500 and 10,000 ppm relative to the
weight of the injection fluid.
The injection fluid may also include other components such as an alkaline
agent, a
propping agent, corrosion inhibitors, acids, scale inhibitors, guars, guar
derivatives, crosslinkers such as zirconium, titanate or borate.
The water or brine used for the preparation of the injection fluid may be
produced
water. The term "produced water" refers to all salted or unsalted water,
brines, sea
water, aquifer water which come from a hydrocarbon reservoir. This produced
water may be treated prior to the preparation of the injection fluid, for
example as
described in patent application WO 2018/020175.
Advantageously, the injection fluid has, at the time of its injection, a
viscosity of
between 1 and 200 cps (centipoise) (viscosity measurements at 20 C with a
Brookfield viscometer equipped with a UL module and at a speed of 6 rpm).
The implementation of the inverse emulsion according to the invention is
carried
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out on site, just upstream of the injection, into the oit field, of the
injection fluid in
which it is implemented. In general, the inverse emulsion is added to a more
or
less salty brine depending on the oit fields. Other components, such as, for
example, biocides, anti-corrosion agents, or propping agents, are also
introduced
5 into this fluid to prepare the injection fluid. Most often, they are
added to a
circulation une of the aqueous solution or the brine.
The present invention will be disclosed in more detail with reference to the
following examples and figures. The following examples simply illustrate the
10 invention and are not intended to be limiting. Unless otherwise
indicated, all
percentages are by weight.
FIGURES
15 Figure 1 is a graph showing the change in the percentage of inversion of
the EM1
inverse emulsion over time, in different fluids at a temperature of 25 C.
Figure 2 is a graph showing the change in the percentage of inversion of the
EM1
inverse emulsion over time, in different fluids at a temperature of 80 C.
Figure 3 is a graph showing the change in the percentage of inversion of the
EM2
20 inverse emulsion over time, in different fluids at a temperature of 25
C.
Figure 4 is a graph showing the change in the percentage of inversion of the
EM2
inverse emulsion over time, in different fluids at a temperature of 80 C.
EXA1VIPLES OF EMBODIMENT OF THE INVENTION
1/ Synthesis of telomers (or LCST oligomers)
To prepare a Telomere called Ti, the following process is carried out.
In a dual jacketed reactor:
- A hydroalcoholic solution (410g) and the N-isopropylacrylamide (NIPAM,
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26
113g, or 1 mol), butyl methacrylate (7.9g, or 0.055 mol) and acrylic acid
(4.44g, or 0.055 mol) monomers are loaded.
- The mixture is stirred.
- The pH of the mixture is adjusted to between 4.0 and 5.0 using a 40% by
weight NaOH solution in water.
- The mixture obtained is heated to 50 C.
- The mixture is de-oxygenated with nitrogen bubbling for 40 minutes.
- Aminoethanethiol HC1 (2.5g) is added.
- 2,2'-azobis(2-methylpropionamidine)dihydrochloride (0.22g) is added to
initiate telomerization.
- After stabilization of the temperature, the mixture is stirred for 2
hours and
then cooled to 25 C.
A concentrated viscous solution containing 23% by weight of a telomer with a
degree of polymerization of 50 monomer units (DPn 50) is obtained. The LCST of
this Ti telomere was estimated at 38 C according to the process described
above.
To prepare a Telomere called T2, the following process is carried out.
In a dual jacketed reactor:
- The N-isopropylacrylamide (NIPAM, 113g, or 1 mol), butyl methacrylate
(4.44g, or 0.031 mol) and chloromethyl dimethylamino-ethyl methacrylate
(MADAME.MeCl, 2.16g, or 0.01 mol) monomers are loaded in 445g of a
hydroalcoholic solution.
- The mixture is stirred.
- The pH of the mixture is adjusted to between 4.0 and 5.0 using a 40% by
weight NaOH solution in water.
- The mixture obtained is heated to 50 C.
- The mixture is de-oxygenated with nitrogen bubbling for 40 minutes.
- Aminoethanethiol HC1 (2.35g) is added.
- 2,2'-azobis(2-methylpropionamidine)dihydrochloride (0.22g) is added to
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27
initiate the polymerization.
- After stabilization of the temperature, the mixture is stirred for 2
hours and
then cooled to 25 C.
A concentrated viscous solution containing 21% by weight of a telomer with a
degree of polymerization of 50 monomer units (DPn 50) is obtained. The LCST of
this T2 telomere was estimated at 32 C according to the process described
above.
LCST Hydrophilic Hydrophobic LCST
Telomere monomer (A), monomer (B), monomer (C), telomere
mol% mol% mol% ( C)
Acrylic acid, Butyl
Ti NIPAM, 90 38
5 methacrylate, 5
MADAME.MeCl, Butyl
T2 NIPAM 96 32
1 methacrylate, 3
Table 1: List and monomeric compositions of T1 and T2 telomeres.
2/ Synthesis of macromonomers
The following process is carried out to prepare a macromonomer called Ml.
In a dual jacketed reactor:
- 400 g of Telomere Ti solution (5581 g/mol) at 23% by weight are loaded in
water.
- The solution is stirred.
- The pH of the solution is adjusted to 7.5 using a 40% by weight NaOH
solution in water.
- The solution is cooled to 5 C.
- Using a burette, 3.0g of acryloyl chloride are added dropwise.
- The pH is continuously adjusted between 7 and 9 using a 40% by weight
NaOH solution in water.
- The temperature is maintained at 5 C throughout the reaction.
- After the end of the reaction, the solution is stirred for 2 hours while
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continuously checking the pH.
A concentrated viscous solution containing 21.5% by weight of LCST
macromonomer M1 (5711 g/mol) is obtained.
The macromonomer M2 is prepared using the same process, with the telomer T2
(5740 g/mol). A concentrated viscous solution containing 21.5% by weight of
LCST macromonomer M2 (5869 g/mol) is obtained.
3/ Synthesis of polymers in inverse emulsion
The following process is carried out to prepare an inverse emulsion called
EM1.
In order to prepare the aqueous solution of monomers, 146g (74.997 mol%) of
acrylamide, 157g (25 mol%) of ATBS (2-acrylamido 2-methylpropane sulfonic
acid), 0.5g (0.003 mol%) of LCST macromonomer M1 and 370g of water are
loaded into a beaker. The pH of the monomer solution is adjusted between 5 and
6
using NaOH.
The following additives are added:
- 0.37g of Versenex 80 (complexing agent),
- 1.29g of TBHP (terbutylhydroperoxide) (oxidant).
295g of Exxsol D100 and 30g of Span 80 are mixed before being transferred into
a reactor together with the aqueous phase. Emulsification of the two-phase
mixture is carried out using a mixer, this mixture is deoxygenated using an
inert
gas and then cooled to a temperature of 15 C.
The synthesis starts with the addition of a solution of MBS (sodium
metabisulphite, 1g/1) at a flow rate of lml/min. The temperature of the medium
increases until it reaches a value of 40 C, which is maintained for 2 hours.
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The reaction medium is allowed to cool. An inverse emulsion with a polymer
concentration of 30% by weight is thus obtained.
An EM2 inverse emulsion is prepared according to the same process, with the
LCST macromonomer M2. An EM2 inverse emulsion with a polymer
concentration of 30% by weight is obtained.
As a counterexample, the EM3 inverse emulsion is prepared according to the
same process, but without using an LCST macromonomer. In other words, the
0.003 mol% of LCST macromonomer is replaced by 0.003 mol% of acrylamide.
4/ Test
The test consists of studying the inversion of inverse emulsions over time, in
different brines and at different temperatures. The inversion is characterized
by a
release of the polymer chains into the aqueous medium and thus by an increase
in
its viscosity.
Materials and method
The speed of inversion is studied using Thermo instruments iQ Rheometer.
During the inversion test, the stress is recorded as a function of time. It
increases
in proportion to the viscosity released.
The EM1, EM2 and EM3 inverse emulsions are tested, without any inverting
agent being added to them.
Four different fluids were used: tap water, and three brines of different
concentrations: 15,000 TDS (Total Dissolved Solids) (1.5% by weight of NaCl),
33,000 TDS (3% by weight of NaCl and 0.3% by weight of CaCl2), and 100,000
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TDS (10% by weight of NaC1). The TDS corresponds to the quantity in ppm of
organic and inorganic substances contained in a brine. In other words, 15,000
TDS equals 15,000 mg of sait per liter of fluid.
5 The tests were carried out at 2 different temperatures: 25 C and 80 C.
To this end, 1.2g of inverse emulsion are injected into 34m1 of brine under
rotation of the elliptical module (U1) at 800 rpm. The emulsions are tested
such
that the polymer concentration is 10,000 ppm (by weight) in the four fluids.
10 Another test is carried out with the same emulsions but at a
concentration of 100
ppm (by weight), only in brine (33,000 TDS).
5/ Results
15 The test results are recorded in the graphs of Figures 1 to 4. In these
figures, the
curves for the EM3 inverse emulsion are identical, regardless of the nature of
the
fluid and the temperature. Therefore, only one curve appears for the EM3
emulsion, that implemented in a brine of 33,000 TDS.
20 As shown in Figures 1 and 2, the EM1 inverse emulsion according to the
invention, in which the polymers comprise M1 macromonomer units, rapidly
inverts in a very wide range of brine compositions ranging from tap water to a
10% sait brine (100,000 TDS), both at low temperature (25 C) and at high
temperature (80 C). The EM1 emulsion also inverts very well at 100 ppm in
25 brine at 33,000 TDS.
Conversely, the EM3 inverse emulsion, which does not include an LCST
macromonomeric unit, does not invert at ail regardless of the fluid and the
temperature.
The same results are obtained with the EM2 inverse emulsion as shown in
Figures
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31
3 and 4. The EM2 emulsion inverts under ail brine and temperature conditions,
while the EM3 emulsion does not invert. The EM2 emulsion also inverts very
well at 100 ppm in brine at 33,000 TDS.
Consequently, the auto-inverting behavior of the EM1 and EM2 emulsions
according to the invention is clearly observed, while these emulsions do not
contain an inverting agent.
These auto-inverting properties are highly sought after by users of inverse
emulsions because they avoid ail of the potential problems associated with the
use
of an inverting agent.
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