WO2025209836A1 - Method for treating water produced during the production of hydrocarbons by in-situ steam injection into an underground formation - Google Patents

Abstract

The present invention relates to a method for treating an aqueous composition (E) derived from the production of hydrocarbons by in-situ steam injection into an underground formation, said method comprising at least the following steps: a) Prepare an aqueous solution (A1) containing between 0.1 and 2.0% by weight of at least one water-soluble amphoteric polymer (PA) of weight-average molecular weight of between 50 000 and 1 million daltons; b) Prepare an aqueous solution (A2) containing between 0.1 and 2.0% by weight of a water-soluble polymer (P) of weight-average molecular weight greater than or equal to 1 million daltons; c) Add into the aqueous composition (E), at least one mineral softening agent, the solution (A1) and the solution (A2) to obtain an aqueous composition (E3); d) Carry out a liquid solid separation of the aqueous composition (E3) to obtain an aqueous composition (CT).

Description

METHOD FOR TREATING WATER PRODUCED DURING THE PRODUCTION OF HYDROCARBONS BY IN-SITU STEAM INJECTION INTO AN UNDERGROUND FORMATION

FIELD OF THE INVENTION

The present invention relates to a method for treating wastewater coming from the production of hydrocarbons by in-situ steam injection into an underground formation. More specifically, the invention relates to the treatment of said wastewater by an amphoteric polymer.

PRIOR ART

Methods such as SAGD (Steam-Assisted Gravity Drainage) or CSS (Cyclic Steam Stimulation) involve the in-situ injection of steam into an underground formation for the production of hydrocarbons. Such methods can be applied for the exploitation of bituminous sand, heavy oils or conventional oils.

The step of softening wastewater produced during hydrocarbon exploitation by in-situ steam injection aims to reduce the hardness of the water, the silica concentration and the organic matter concentration potentially present in suspension. This water must be as soft and as clean as possible, in order to be able to be vaporized in view of a subsequent re-injection of steam in the formation of hydrocarbon to be exploited. The use of unsatisfactory quality water significantly accelerates the formation of organic and/or mineral deposits on the installations and the equipment, which multiplies the amount of shutdowns of the installation for maintenance and cleaning. This treatment step is generally carried by adding lime, sodium carbonate, magnesium oxide, coagulants and/or flocculants.

The softening of a water by this type of method is generally carried out between 50 and 80°C. This technique enables the precipitation of calcium, magnesium and silica, the solubility of which decreases when the temperature increases. However, the mineral particles thus formed remain in suspended colloidal form in the aqueous liquid phase and require the intervention of coagulants and/or of flocculants to precipitate more rapidly. Without using the latter, the removal of these fine colloidal particles is very difficult and slow, leading to a water with a high turbidity and a consequent residual hardness, even after treatment with the abovementioned inorganic compounds (lime, magnesium oxide and sodium carbonate).

There is therefore a real need for efficient coagulants and/or flocculants, capable of reducing rapidly and efficiently the turbidity and the hardness of production water resulting from the exploitation of hydrocarbons by steam injection.

The vast majority of colloidal impurities suspended in wastewater coming from hydrocarbon production by in-situ steam injection are negatively charged and remain suspended due to repulsive interaction forces which prevent them from agglomerating. Positive charge carrying polymers (coagulants) are thus necessary to neutralize these surface charges, thus facilitating the coalescence of these particles and accelerate their precipitation.

These coagulants can be of inorganic nature. We can for example cite aluminum chloride, aluminum polychloride, aluminum polyhydrochloride or ferric chloride.

Coagulants can also be of organic nature, the most commonly used being poly (diallyl dimethylammonium chloride), (poly(DADMAC)) or polyamines resulting from the reaction between epichlorohydrin and dimethylamine.

Using such coagulants is described, for example, in documents US 11034604 or US 11034597. These documents describe the use of polyamine and poly(DADMAC) mixtures as coagulant compositions for this application. A preferable system composed of a mixture comprising two-thirds of poly(DADMAC) and one-third of polyamine seems to be highlighted by the inventors, poly(DADMAC) preferably having a molecular weight of at least ten times that of polyamine.

Document US 10934189 also describes the use of two cationic polymers, the first being a DADMAC copolymer and acrylamide while the second is a polyamine. The use of a flocculant polymer after coagulation in order to further accelerate the precipitation of preformed flocs under the action of the coagulant(s) is described. Said flocculant can be either neutral, er anionic, er cationic.

DISCLOSURE OF THE INVENTION

The Applicant has discovered and developed a method for treating water coming from the hydrocarbon production by in-situ steam injection into an underground formation, said method comprising the addition of at least one amphoteric coagulant polymer. The turbidity and the content of colloidal particles of the water thus obtained is significantly improved compared to a method using a cationic coagulant polymer. In addition, the amount of coagulant used is significantly decreased, which makes it possible to decrease the cost and the carbon footprint of the treatment.

More specifically, the invention relates to the method for treating an aqueous composition (E) resulting from the production of hydrocarbons by in-situ steam injection into an underground formation, said method comprising at least the following steps: a) Preparing an aqueous solution Al containing between 0.1 and 2.0% by weight of at least one water-soluble amphoteric polymer PA of weight-average molecular weight of between 50000 and 1 million daltons; b) Preparing an aqueous solution A2 containing between 0.1 and 2.0% by weight of a water-soluble polymer P of weight-average molecular weight greater than or equal to 1 million daltons; c) Adding into the aqueous composition E at least one mineral softening agent, the solution Al and the solution A2 to obtain an aqueous composition E3; d) Carrying out a solid liquid separation of the aqueous composition E3 to obtain an aqueous composition CT.

In this method, the mineral softening agent is advantageously added before the solution Al and before the solution A2. The solution Al and the solution A2 can be added simultaneously or separately, the solution Al being advantageously added before the solution A2.

Thus, in this method, step c) may include the following addition sequence:

- Adding into the aqueous composition E, at least one mineral softening agent to obtain an aqueous composition El;

- Adding the solution Al into the aqueous composition El to obtain an aqueous composition E2;

- Adding the solution A2 into the aqueous composition E2 to obtain an aqueous composition E3.

Preferably, the method does not include the solid liquid separation step between the addition of additives (mineral softening agent, solution Al and solution A2) and the obtaining of the aqueous composition E3 (end of step c).

The invention also includes all possible combinations of the various embodiments disclosed, whether they are preferred embodiments or given as an example. Furthermore, when ranges of values are indicated, the limit values are included in these ranges. The disclosure also includes all of the combinations between the limit values of these ranges of values. For example, the value ranges of “1-20, preferably 5-15” imply the disclosure of the ranges “1-5”, “1-15”, “5-20” and “15- 20” and the values 1, 5, 15 and 20.

By "polymer", this means a homopolymer prepared from a monomer or a copolymer prepared from two different monomers. A terpolymer is prepared from three different monomers.

The polymer PA has a molecular weight of between 50,000 and 1 million daltons. The polymer P has a molecular weight greater than or equal to 1 million daltons, preferably between 1 and 40 million daltons, more preferably between 3 and 30 million daltons. Molecular weight is defined as weight-average molecular weight.

The molecular weight is determined by the intrinsic viscosity of the polymer. The intrinsic viscosity can be measured by methods known to a person skilled in the art and can be calculated from the reduced viscosity values for different polymer concentrations by a graphical method consisting in plotting the reduced viscosity values (y-axis) against the concentration (x-axis) and extrapolating the curve to zero concentration. The intrinsic viscosity value is plotted on the y-axis or using the least-squares method. The molecular weight can then be determined using the Mark-Houwink equation: [r|] = K M“

[q] represents the intrinsic viscosity of the polymer as determined by the solution viscosity measurement method.

K represents an empirical constant.

M represents the molecular weight of the polymer, a represents the Mark-Houwink coefficient.

K and a depend on the particular polymer-solvent system.

The term "water-soluble polymer", means a polymer which gives an aqueous solution without insoluble particles when it is dissolved under stirring at 25°C and with a concentration of 10g. L'¹ in deionized water.

The term “hydrophilic monomer” means a monomer that has an octanol/water partition coefficient, Kow, less than or equal to 1, in which the Kow partition coefficient is determined at 25°C in an octanol/water mixture with a volume ratio of 1/1, at a pH between 6 and 8.

[Math 1] The water-soluble amphoteric polymer PA is preferably composed of at least one anionic hydrophilic monomer, of at least one cationic hydrophilic monomer and optionally of at least one non-ionic hydrophilic monomer;

- the non-ionic hydrophilic monomer(s) being selected from the group comprising water-soluble vinyl monomers, such as acrylamide, methacrylamide, N- alkylacrylamides, N-alkylmethacrylamides, N,N-dialkyl acrylamides (for example, N,N-dimethylacrylamide or N,N-di ethyl acrylamide), N,N- dialkylmethacrylamides, acrylic acid alkoxyl esters, methacrylic acid alkoxyl esters, N-vinylpyrrolidone, N-methylol(meth)acrylamide, N-vinyl caprolactame, N-vinylformamide (NVF), N-vinyl acetamide, N-vinyl imidazole, N-vinyl succinimide, acryloyl morpholine (ACMO), glycidyl methacrylate, glyceryl methacrylate, acrylamide diacetone, methacrylic anyhydride, acrylonitrile, maleic anydride, itaconic anhydride, itaconamide, vinylpyridine, hydroxyalkyl (meth)acrylate, thioalkyl (meth)acrylate, isoprenol and its alcoxyl derivatives, hydroxyethyl(meth)acrylates and their alcoxyl derivatives, hydroxypropylacrylate and its alcoxyl derivatives, vinyl acetate, and their mixtures, the alkyl groups being C1-C3 hydrocarbon chains;

- the anionic hydrophilic monomer(s) being selected from among acrylic acid, methacrylic acid, dimethylacrylic, itaconic acid monomers, C1-C3, itaconic acid hemi-esters, acryloyl chloride, crotonic acid, maleic acid, fumaric acid, 3- acrylamido 3 -methylbutanoic acid, vinylsulfonic acid, vinylphosphonic acid, allylsulfonic acid, methallylsulfonic acid, 2-methylidenepropane-l,3-disulfonic acid, 2-sulfoethylmethacrylate, sulfopropylmethacrylate, sulfopropylacrylate, allylphosphonic acid, glycol ethylene methacrylate phosphate, sulfonic styrene acid, 2-acrylamido-2-methylpropane sulfonic acid (ATBS), 2-acrylamido-2- methylpropane disulfonic acid, 3-allyloxy-2-hydroxypropane sulfonic acid, diethylallylphosphonate, carboxyethyl acrylate; water-soluble salts of all of these monomers as their alkaline metal salts, alkaline earth metals, or ammonium; and their mixtures;

- the cationic hydrophilic monomer(s) being selected from among diallyldialkyl ammonium salts such as diallyldimethyl ammonium chloride (DADMAC); acidified or quatemized dialkyl-aminoalkyl(meth)acrylamide salts, such as for example, methacrylamido-propyl trimethyl ammonium chloride (MAPTAC), aery 1 amido-propyl trimethyl ammonium chloride (APTAC), acidified or quatemized dialkyl-aminoalkyl acrylate salts, such as quaternized or salified dimethylaminoethyl acrylate (ADAME), acidified or quaternized dialkyl aminoalkyl methacrylate salts, such as quatemized or salified dimethylaminoethyl methacrylate (MADAME), and their mixtures.

According to a particular embodiment, the polymer PA comes from partial or total hydrolysis of a copolymer containing at least N-vinylformamide (non-ionic hydrophilic monomer) and an anionic hydrophilic monomer. The hydrolysis of N- vinylformamide enables the formation of cationic monomers (amines) and the obtaining of an amphoteric polymer PA. Hydrolysis can be carried out on an NVF homopolymer.

The water-soluble salts of the anionic hydrophilic monomers are alkaline metal or alkaline earth or ammonium metal salts.

Optionally, the polymers PA contain at least one zwitterionic hydrophilic monomer. A zwitterionic monomer is an ionic monomer having a zero overall charge. Indeed, a zwitterionic monomer has a cationic charge number and an identical anionic charge number.

Advantageously, the zwitterionic hydrophilic monomer(s) that can be used in the scope of the invention are chosen, in particular, from among the derivatives of a vinyl-type pattern (advantageously, acrylamide, acrylic, allylic or maleic), this monomer having a quaternary amine or ammonium function and a carboxylic- type acid function (or carboxylate), sulfonic (or sulfonate) or phosphoric (or phosphate).

Preferably, this monomer includes a quaternary amine or ammonium function and a carboxylic-type acid function (or carboxylate), sulfonic (or sulfonate) or phosphoric (or phosphate). Examples include, but are not limited to, dimethylaminoethyl acrylate derivatives, such as 2 - ((2-9 (acryloyloxy) ethyl) dimethylammonio) ethane- 1 -sulfonate, 3 - ((2- (acryloyloxy) ethyl) dimethylammonio) propane- 1 -sulfonate, 4 - ((2- (acryloyloxy) ethyl) dimethylammonio) butane- 1 -sulfonate, [2- (acryloyloxy) ethyl] (dimethylammonio) acetate; dimethylaminoethyl methacrylate derivatives such as 2 - ((2- (methacryloyloxy) ethyl) dimethylammonio) ethane- 1 -sulfonate, 3 - ((2- (methacryloyloxy) ethyl) dimethylammonio) propane- 1 -sulfonate, 4 - ((2 - (methacryloyloxy) ethyl) dimethylammonio) butane- 1 -sulfonate, [2- (methacryloyloxy) ethyl] (dimethylammonio) acetate; dimethylamino propyl acrylamide derivatives such as 2 - ((3-acrylamidopropyl) dimethylammonio) ethane- 1- sulfonate, 3 - ((3-acrylamidopropyl) dimethylammonio) propane- 1 -sulfonate, 4 - ((3-acrylamidopropyl) dimethylammonio) butane- 1 -sulfonate, [3- (acryloyl) oxy) propyl] (dimethylammonio) acetate, dimethylamino propyl methylacrylamide, 2 - ((3- methacrylamidopropyl) dimethylammonio) ethane- 1 -sulfonate, 3 - (dimethylammonio) propane- 1 -sulfonate 4 - ((3 -methacrylamidopropyl) dimethylammonio) butane- 1 -sulfonate, propyl [3- (methacryloyloxy)] (dimethylammonio) acetate; and their mixtures.

The monomers of the water-soluble polymer P are advantageously selected from among the list of preferred monomers listed for PA.

Preferably, the water-soluble amphoteric polymer PA contains 5 to 95 mol% of anionic hydrophilic monomer, 5 to 95 mol% of cationic hydrophilic monomer, and 0 to 90 mol% of non-ionic hydrophilic monomer. More preferably, the water- soluble polymer PA contains 20 to 45 mol% of anionic hydrophilic monomer, 30 to 45 mol% of cationic monomer, and 10 to 50 mol% of non-ionic hydrophilic monomer.

Advantageously, the water-soluble polymer PA is a terpolymer of DADMAC, sodium acrylate and acrylamide. According to a preferred embodiment, the water-soluble polymer P is an amphoteric polymer composed of at least one anionic hydrophilic monomer, of at least one cationic hydrophilic monomer and optionally, of a non-ionic hydrophilic monomer. Even more preferably, the monomers are selected from the list of preferred monomers for the polymer PA.

Preferably, the water-soluble polymer P contains 20 to 60 mol% of cationic hydrophilic monomer, 10 to 40 mol% of anionic hydrophilic monomer, and 0 to 70 mol% of non-ionic hydrophilic monomer.

Advantageously, the water-soluble polymer P is a terpolymer of acrylamide, sodium acrylate and dimethylaminoethyl acrylate (ADAME) quatemized with methyl chloride.

The polymers used in the method of the invention (PA, P) can have a linear, branched, star-shaped or comb-shaped structure. This structure can be obtained, according to the general knowledge of the person skilled in the art, for example by selecting the initiator, the transfer agent, the polymerization technique such as Reversible Addition Fragmentation chain Transfer (RAFT) polymerization, Nitroxide Mediated Polymerization (NMP) or Atom Transfer Radical Polymerization (ATRP), the incorporation of structural monomers, or the

The polymers can also be structured by a branching agent. By structured polymer, this means a nonlinear polymer, which has side chains.

The branching agent is advantageously selected from among:

- structural agents, which can be selected from the group comprising unsaturated polyethylene monomers (having at least two unsaturated functions), for example, vinyl functions, in particular allyl or acrylic, and examples include, methylene bis acrylamide (MBA), triallyamine, or tetraallylammonium chloride or 1,2 dihydroxy ethylene bis-(N-acrylamide),

- monomers having at least two epoxy functions,

- monomers having at least one unsaturated function and one epoxy function, - macroinitiators such as polyperoxides, polyazoics and transfer polyagents, such as polymercaptan polymers, and polyols,

- functionalized polysaccharides,

- water-soluble metal complexes composed of:

* of a metal of a valence greater than 3 such as, by way of example and in a nonlimiting manner, aluminum, boron, zirconium, or also titanium, and

* of a ligand carrying a hydroxyl function.

The amount of branching agent in the polymers is advantageously less than 1000 ppm by weight compared to the total weight of the monomers of the polymer, preferably less than 100 ppm by weight, more preferably less than 10 ppm by weight.

In a particular embodiment, the polymers PA and P do not include a branching agent.

When the polymers PA and P include at least one branching agent, they remain water-soluble. The person skill in the art will know how to adjust the amount of branching agent, and possibly the amount of transfer agent needed to obtain this result.

During the preparation of solutions Al and A2, the water-soluble polymers PA and P can be in liquid form or in solid form, independently from one another. The polymers can be in the form of an aqueous solution, of an inverse emulsion (water- in-oil), of an aqueous suspension, of a powder or of a dispersion of the polymer in the oil. The polymer PA is preferably in the form of an aqueous solution. The polymer P is advantageously in the form of a powder or of an inverse emulsion.

Generally, the water-soluble polymers PA and P do not require to develop a particular polymerization method. Indeed, they can be obtained according to any polymerization techniques that are well-known to a person skilled in the art.

These may include polymerization solution; gel polymerization; precipitation polymerization; emulsion polymerization (aqueous or inverse); suspension polymerization; reactive extrusion polymerization; water-to-water polymerization; or micellar polymerization.

The polymerization is generally a free radical polymerization, preferably by inverse emulsion polymerization or by gel polymerization. By free radical polymerization, this includes free radical polymerization by means of UV, azoic, redox or thermal initiators, as well as CRP polymerization or more specifically, RAFT-type polymerization techniques.

The preparation of solutions Al and A2 for steps a) and b) of the method of the invention is done separately, preferably by adding polymers PA and P in water under stirring. If necessary, the person skilled in the art will know to choose the suitable stirring means to fully dissolve the polymer in the water.

For step c) of the method, said at least one mineral softening agent is advantageously selected from among calcium hydroxide, calcium oxide, sodium carbonate, potassium carbonate, magnesium hydroxide, magnesium oxide, and their mixtures.

The aqueous composition E preferably contains between 50 and 100 mg/L of silica or magnesium and/or calcium silicates. Preferably, the amount of softening agent added in the aqueous composition E makes it possible to reduce the concentration of silica to around 5 to 10 mg/L.

The addition of the mineral softening agent is advantageously carried out under stirring. The stirring can be maintained after the addition of the mineral softening agent has been completed.

Preferably, the added volume of solution Al is adjusted to obtain a final concentration of 0.001 to 0.01% by weight of polymer PA in the aqueous composition E3.

The addition of solution Al can be carried out 1 to 60 minutes after the addition of the mineral softening agent, for example 1 to 5 minutes. The addition of solution Al can be carried out after 1 to 60 minutes of decantation, for example 1 to 15 minutes, advantageously the decantation starting after the end of the addition of the mineral softening agent, eventually after a stirring step having followed the addition of the mineral softening agent.

Advantageously, in the aqueous composition E3, the polymer PA has a concentration of 0.001 to 0.01% by weight. More preferably, the final concentration of polymer PA in the aqueous composition E3 is between 0.001 and 0.008% by weight.

The addition of solution Al is advantageously carried out under stirring. The stirring can be maintained after the end of the addition of solution Al.

Advantageously, in the aqueous composition E3, the polymer P has a concentration of 0.0001 to 0.001% by weight.

The addition of solution A2 can be carried out 1 to 60 minutes after the end of the addition of solution Al, for example 1 to 5 minutes.

The addition of solution A2 can be carried out after 1 to 60 minutes of decantation, for example 1 to 15 minutes, advantageously the decantation starting after the end of the addition of solution Al, eventually after a stirring step having followed the addition of solution Al.

The addition of solution A2 is advantageously carried out under stirring. The stirring can be maintained after the end of the addition of solution A2.

Step d) is a liquid solid separation of the aqueous composition E3 to obtain an aqueous composition CT.

Advantageously, the liquid solid separation is carried out after a decantation step starting after the end of the addition of solution A2, eventually after a stirring step having followed the addition of solution A2.

The aqueous composition CT can then be recycled, for example in a method for producing hydrocarbons by in-situ steam injection into an underground formation. The recycling of the aqueous composition CT thus provides a climate change mitigation technology compared to conventional technologies thanks to the improvement of the treatment of the aqueous composition E.

Advantageously, step d) is carried out 1 to 60 minutes after the end of adding additives (mineral softening agent, solution Al and solution A2) to form the aqueous composition E3, more advantageously 5 to 30 minutes.

Step d) can be carried out after 1 to 60 minutes of decantation, more advantageously 5 to 30 minutes.

The liquid solid separation technique is part of the general knowledge of the person skilled in the art.

Thus, the method according to the invention can be carried out according to the following steps: a) Preparing the aqueous solution Al; b) Preparing the aqueous solution A2; c) Adding, advantageously under stirring, in the aqueous composition E, at least one mineral softening agent to obtain an aqueous composition El, advantageously, stirring the aqueous composition El for 1 to 60 minutes; optionally, letting the aqueous composition El decant, advantageously for 1 to 60 minutes;

- Adding (advantageously under stirring) the solution Al in the aqueous composition El to obtain an aqueous composition E2; advantageously, stirring the aqueous composition E2 for 1 to 60 minutes; optionally, letting the aqueous composition E2 decant, advantageously for 1 to 60 minutes;

- Adding the solution A2 (advantageously under stirring) in the aqueous composition E2 to obtain an aqueous composition E3; advantageously, stirring the aqueous composition E3 for 1 to 60 minutes; advantageously, letting the composition E3 decant, advantageously for 1 to 60 minutes; d) Carrying out a liquid solid separation of the aqueous composition E3 to obtain an aqueous composition CT.

The invention and the benefits derived from it will best emerge from the following examples given in order to illustrate the invention, in a non-limiting manner.

EXAMPLES

Example 1: Synthesis of an amphoteric polymer PAI (DADMAC/Sodium acrylate 90/10 mol%}

In a 2L glass reactor, 289.7g of DADMAC monomer, 14.58g of acrylic acid monomer and 530.1 of deionized water are introduced at 25°C. Then, 0.4g of EDTA and 0.9g of sodium persulfate are added. The pH of the reaction environment is adjusted to 4.5. The polymerization charge thus obtained is degassed for 20 minutes with nitrogen in order to eliminate a maximum amount of dissolved oxygen.

The temperature is then gradually increased to 110°C for 1 hour. During this temperature rise, a reducing agent and an oxidizing agent are added gradually in continuous casting in order to prime the polymerization reaction. The liquid obtained after 4 hours is then cooled. The polymer PAI obtained as a molecular weight of 500,000 daltons. An aqueous solution containing 28.2% by weight of polymer PAI is obtained.

Example 2 - Synthesis of a flocculant Pl (Acrylanude/ADAME-MC/Sodium acrylate 45/5/50 mol%}

In a 2 L glass beaker, 84.6 g of acrylamide monomer 9.4 g of acrylic acid monomer, 256.0 g of ADAME-MC monomer (dimethylaminoethyl acrylate quatemized with methyl chloride) and 180.4 g of deionized water are introduced at 25°C. We then add, 0.2 g of sodium hypophosphite and everything is homogenized under stirring for a few minutes. In a 2 L glass reactor, 205.5 g of Exxsol D120 aliphatic hydrocarbon oil, 88.1 g of heavy oil (CELTIS 903), 21.5 g of sorbitan mono-oleate, 5 g of Hypermer 2296 are introduced at 25°C, and everything is homogenized under stirring for a few minutes.

The aqueous phase consisting of water and monomers is then poured into the beaker containing the oily phase and everything is homogenized under stirring for a few minutes. The emulsion thus formed is maintained under mechanical stirring for 40 minutes, during which time everything is degassed with nitrogen in order to remove a maximum amount of dissolved oxygen.

A reducing agent and an oxidizing agent are then gradually added in continuous casting in order to prime the polymerization reaction, which leads to a gradual increase of the temperature up to 65°C for 35 minutes. The inverse emulsion thus obtained is then cooled to room temperature. The polymer Pl obtained has a molecular weight of 6,000,000 daltons. An inverse emulsion is obtained containing 34% by weight of polymer Pl.

Example 3 - Treatment of an aim eons composition E produced following an SAGD method

Tests have been carried out under laboratory conditions that differ from the conditions encountered on industrial sites. Laboratory conditions make it possible to validate the compositions that can then be used at the industrial level.

The polymers PAI and Pl are diluted separately in deionized water in order to obtain two distinct solutions Al and A2 (steps a) and b) of the method) containing respectively 0.4% by weight of polymer PAI and Pl. These solutions are mixed using a mechanical stirrer until obtaining homogeneous solutions.

Tests have been carried out on an aqueous composition E coming from an SAGD method, treated by a mineral softening agent (magnesium oxide, step c) of the method). The step of softening the aqueous composition E is carried out between 50 and 80°C. Thus, the calcium, magnesium and silica contained in the aqueous composition E precipitate at least partially (their solubility decreases when the temperature of the aqueous composition increases).

At the end of this softening step; the aqueous composition El obtained still contains suspended mineral particles in colloidal form. Without any other additional treatment, these fine colloidal particles sediment very slowly (several hours). The aqueous composition El therefore has a high turbidity and residual hardness (greater than 100 mg/L).

For the following additions (solutions Al and A2), the polymers PAI and Pl have been used, as well as a cationic polyamine PA2 (condensation product between epichlorohydrine, of molecular weight 250000 g/mol) of trade name Floquat FL 2250 (company SNF) and two polymers P2 and P3 in inverse emulsion form (P2: acrylamide cationic copolymer containing 10 mol% of dimethylaminoethyl acrylate (ADAME) quatemized with methyl chloride) (P3: acrylamide anionic copolymer containing 36 mol% of acrylic acid neutralized with sodium hydroxide) (P2 and P3 are respectively the products Flopam EM 140 CT and EM 630 (company SNF)). P2 has a weight-average molecular weight of 10 million daltons and P3, of 25 million daltons.

For each test, the solutions Al or A2 are added into a 250 mL graduated test tube containing 200 mL of aqueous composition El. The content of the test tube is homogenized by inversing the test tube 5 times and by ensuring to not spill the aqueous composition out of the test tube. At the end of this treatment, an aqueous composition E2 is obtained in the test tube. The polymer Pl or P2 or P3 is then added to the aqueous composition E2, then the test tube is again inversed 5 times, in order to homogenize everything. After 5 minutes, the turbidity of the aqueous composition obtained (E3) and the concentration of residual colloidal particles are measured. The values are reported in table 1. The polymer dosages are also reported in table 1 and are expressed in ppm, that is in mg/L of aqueous composition produced. These tests do not include any solid separation step between the addition of the mineral softening agent in the aqueous composition E and the obtaining of the aqueous composition E3.

For these tests, a maximum turbidity of 20 NTU (Nephelometric Turbidity Units) and a maximum concentration of residual colloidal particles of 20 mg/L are targeted. The turbidity is measured using a Hach TL 2300 turbidimeter. The concentration of colloidal particles in the aqueous composition after treatment is determined by vacuum filtration with a 0.45pm filter.

[Table 1]

Table 1 : Turbidity

It is observed that the necessary dosage of polymer PAI is clearly less than that of PA2 (whatever the polymer Pl, P2 or P3).

The combination PAI + P3 gives satisfactory results (turbidity and concentration in colloidal particles). Using the combination PAI + Pl (amphoteric) makes it possible to significantly reduce the dosage by coagulating while maintaining the turbidity and the concentration of residual colloidal particles well below the maximum targeted values.

Claims

1. Method for treating an aqueous composition (E) coming from the production of hydrocarbons by in-situ steam injection into an underground formation, said method comprising at least the following steps: a) Preparing an aqueous solution Al containing between 0.1 and 2.0% by weight of at least one water-soluble amphoteric polymer PA having a weight-average molecular weight of between 50 000 and 1 million daltons; b) Preparing an aqueous solution A2 containing between 0.1 and 2.0% by weight of a water-soluble polymer P having a weight-average molecular weight greater than or equal to 1 million daltons; c) Adding into the aqueous composition E, at least one mineral softening agent, the solution Al and the solution A2 to obtain an aqueous composition E3; d) Carrying out a liquid solid separation of the aqueous composition E3 to obtain an aqueous composition CT.

2. Method according to claim 1, characterized in that the water-soluble amphoteric polymer PA is a polymer of at least one anionic hydrophilic monomer, of at least one cationic hydrophilic monomer and optionally of at least one non-ionic hydrophilic monomer;

- the non-ionic hydrophilic monomer(s) being selected from the group including water-soluble vinyl monomers, such as acrylamide, methacrylamide, N- alkylacrylamides, N-alkylmethacrylamides, N,N-dialkyl acrylamides (for example, N,N-dimethylacrylamide or N,N-di ethyl acrylamide), N,N- dialkylmethacrylamides, acrylic acid alkoxyl esters, methacrylic acid alkoxyl esters, N-vinylpyrrolidone, N-methylol(meth)acrylamide, N-vinyl caprolactame, N-vinylformamide (NVF), N-vinyl acetamide, N-vinyl imidazole, N-vinyl succinimide, acryloyl morpholine (ACMO), glycidyl methacrylate, glyceryl methacrylate, acrylamide diacetone, methacrylic anyhydride, acrylonitrile, maleic anydride, itaconic anhydride, itaconamide, vinylpyridine, hydroxyalkyl (meth)acrylate, thioalkyl (meth)acrylate, isoprenol and its alcoxyl derivatives, hydroxyethyl(meth)acrylates and their alcoxyl derivatives, hydroxypropylacrylate and its alcoxyl derivatives, vinyl acetate, and their mixtures, the alkyl groups being C1-C3 hydrocarbon chains;

- anionic hydrophilic monomers being selected from among acrylic acid, methacrylic acid, dimethylacrylic, itaconic acid monomers, C1-C3, itaconic acid hemi-esters, acryloyl chloride, crotonic acid, maleic acid, fumaric acid, 3- acrylamido 3 -methylbutanoic acid, vinylsulfonic acid, vinylphosphonic acid, allylsulfonic acid, methallylsulfonic acid, 2-methylidenepropane-l,3-disulfonic acid, 2-sulfoethylmethacrylate, sulfopropylmethacrylate, sulfopropylacrylate, allylphosphonic acid, glycol ethylene methacrylate phosphate, sulfonic styrene acid, 2-acrylamido-2-methylpropane sulfonic acid (ATBS), 2-acrylamido-2- methylpropane disulfonic acid, 3-allyloxy-2-hydroxypropane sulfonic acid, diethylallylphosphonate, carboxyethyl acrylate; water-soluble salts of all of these monomers as their alkaline metal salts, alkaline earth metals, or ammonium; and their mixtures;

- cationic hydrophilic monomers being selected from among ammonium diallyldialkyl salts such as diallyldimethylammonium chloride (DADMAC); acidified or quatemized dialkyl-aminoalkyl(meth)acrylamide salts, such as for example, methacrylamido-propyl trimethyl ammonium chloride (MAPTAC), aery 1 amido-propyl trimethyl ammonium chloride (APTAC), acidified or quatemized dialkyl-aminoalkyl acrylate salts, such as quaternized or salified dimethylaminoethyl acrylate (ADAME), acidified or quaternized dialkyl aminoalkyl methacrylate salts, such as quatemized or salified dimethylaminoethyl methacrylate (MADAME), and their mixtures.

3. Method according to the preceding claims characterized in that the water- soluble polymer PA contains 5 to 95 mol% of anionic hydrophilic monomer, 5 to 95 mol% of cationic hydrophilic monomer and 0 to 90 mol% of neutral non-ionic hydrophilic monomer.

4. Method according to the preceding claims characterized in that the water- soluble polymer PA is a DADMAC, sodium acrylate and acrylamide terpolymer.

5. Method according to the preceding claims characterized in that the water- soluble polymer P is an amphoteric polymer of at least one anionic hydrophilic monomer, of at least one cationic hydrophilic monomer and optionally, of at least one non-ionic hydrophilic monomer.

6. Method according to the preceding claims, characterized in that the water- soluble polymer P has a weight-average molecular weight of between 3 and 30 million daltons.

7. Method according to the preceding claims characterized in that the water- soluble polymer P is a terpolymer of acrylamide, sodium acrylate and dimethylaminoethyl acrylate (ADAME) quaternized with methyl chloride.

8. Method according to the preceding claims characterized in that, in the aqueous composition E3, the polymer PA has a concentration of 0.001 to 0.01% by weight.

9. Method according to the preceding claims characterized in that the at least one mineral softening agent of step c) is selected from among calcium hydroxide, calcium oxide, sodium carbonate, potassium carbonate, magnesium hydroxide, magnesium oxide, and their mixtures.

10. Method according to the preceding claims characterized in that the addition of the solution Al of step c) is carried out 1 to 60 minutes after the addition of the mineral softening agent, more advantageously 1 to 5 minutes.

11. Method according to the preceding claims characterized in that step c) is advantageously carried out under stirring.

12. Method according to the preceding claims characterized in that the addition of the solution A2 of step c) is carried out 1 to 60 minutes after the addition of the solution Al, more advantageously 1 to 5 minutes.

13. Method according to the preceding claims characterized in that step d) is carried out, 1 to 60 minutes after the addition of the solution A2, more advantageously 5 to 30 minutes.

14. Method according to the preceding claims, characterized in that step c) comprises: - Adding, under stirring, in the aqueous composition E at least one mineral softening agent to obtain an aqueous composition El; stirring the aqueous composition El for 1 to 60 minutes; optionally, letting the aqueous composition El decant, advantageously for 1 to 60 minutes; - Adding, under stirring, the solution Al in the aqueous composition El to obtain an aqueous composition E2; stirring the aqueous composition E2 for 1 to 60 minutes; optionally, letting the aqueous composition E2 decant, advantageously for 1 to 60 minutes; - Adding, under stirring, the solution A2 in the aqueous composition E2 to obtain an aqueous composition E3; stirring the aqueous composition E3 for 1 to 60 minutes; letting the composition E3 decant, advantageously for 1 to 60 minutes.