Auto-invertible inverse polymer emulsion
The invention relates to an inverse polymer emulsion having the particular feature of auto-inverting without any need for the use of an inverting agent and containing a polymer of at least one water-soluble monomer and at least one LCST macromonomer. The invention also relates to the use of the inverse emulsion in the fields of the oil and gas industry, water treatment, slurry treatment, paper manufacturing, construction, mining, cosmetics, textiles, detergents or agriculture.
1. An auto-invertible inverse emulsion comprising:
oil;
water;
at least one water-in-oil surfactant; and
at least one polymer having a molecular weight of between 5 and 30 million g/mol and containing monomer units of at least acrylamide, 2-acrylamido 2-methylpropane sulfonic acid (ATBS), and 10 −5 to 5 mol % of a lower critical solution temperature (LCST) macromonomer, said LCST macromonomer having a molecular weight of between 500 and 200,000 g/mol and having units from:
at least one anionic monomer selected from acrylic acid and ATBS; and
at least one LCST monomer selected from diethylacrylamide, N-isopropylacrylamide, dimethylacrylamide, and ter-butylacrylamide.
2. The inverse emulsion according to claim 1 , wherein the inverse emulsion is free of oil-in-water surfactant.
3. A method for preparing an inverse emulsion according to claim 1 , said method 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, and
d) once the inverse emulsion is formed, polymerizing the monomers in the aqueous phase using a radical polymerization initiator.
4. A polymeric aqueous solution obtained by inversion of the inverse emulsion according to claim 1 in an aqueous medium in the absence of an oil-in-water surfactant.
5. Use of the inverse emulsion according to claim 1 for thickening an aqueous medium, for flocculating suspended particles or for reducing the level of frictional resistance during transport of an aqueous medium.
6. A method for fracturing an underground formation, which comprises:
aa) providing an inverse emulsion according to claim 1 ;
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; and
ee) fracturing the underground formation with the injection fluid.
7. A method for the improved recovery of hydrocarbons by sweeping in an underground formation, which comprises:
aaa) providing an inverse emulsion according to claim 1 ;
bbb) inverting the inverse emulsion by adding it to an aqueous fluid in order 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; and
eee) recovering a mixture of hydrocarbons, gas and aqueous fluid.
8. The inverse emulsion according to claim 1 , wherein the LCST macromonomer has a weight average molecular weight between 1,000 and 100,000 g/mol.