EA043013B1 - METHOD FOR HYDRAULIC FRACTURING OF UNDERGROUND FORMATION AND METHOD FOR SUSPENDING AND TRANSPORTING PROPPANT - Google Patents

Description

There are many areas in which it is crucial to keep particles in suspension in suspension (for example, pigment particles in compositions such as paints or varnishes). In particular, in the field of oil production, many stages are carried out by pumping fluids under pressure into subterranean formations, and it is often necessary to keep the particles suspended in suspension to prevent them from settling, despite the extreme temperature and pressure conditions that typically exist in a subterranean formation.

In order to inhibit the phenomenon of separation by settling, additives can be introduced which make it possible to keep the particles in suspension in suspension. A number of such additives have been described, including, in particular, crosslinked or non-crosslinked polymers, polysaccharides and their derivatives, such as xanthan gum, cellulose ethers, or alternatively, borate or zirconate crosslinked guar and its derivatives. However, it turned out that these suspending agents decompose at temperatures above 150°C. This limitation makes such additives unsuitable for higher temperature applications (typically above 150°C, often in the range of 150 to 200°C, and even in excess of 200°C). In addition, when these agents are used in the vicinity of oil-bearing formations, namely, in particular in fluids such as drilling fluid, completion fluid, fracturing fluid, acidizing fluid, or buffer fluids , such agents have the disadvantage of decomposing to form insoluble residues that cannot be properly removed.

Brief description of the invention

In one embodiment, a method for hydraulically fracturing a subterranean formation includes the step of pumping an aqueous fracturing fluid into at least a portion of the subterranean formation at a pressure sufficient to fracture the formation, said fracturing fluid comprising an aqueous proppant slurry composition comprising water. and a polymer containing at least one hydrophobic monomer selected from:

n-hexyl(meth)acrylate, n-octyl(meth)acrylate, octyl(meth)acrylamide, lauryl(meth)acrylate, lauryl(meth)acrylamide, myristyl(meth)acrylate, myristyl(meth)acrylamide, pentadecyl(meth) acrylate, pentadecyl(meth)acrylamide, cetyl(meth)acrylate, cetyl(meth)acrylamide, oleyl(meth)acrylate, oleyl(meth)acrylamide, erucyl(meth)acrylate, erucyl(meth)acrylamide and combinations of these compounds; and at least one hydrophilic monomer selected from:

acrylate, salts of acrylic acid, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, salts of 2-acrylamido-2-methylpropanesulfonic acid, and combinations of these compounds, said polymer being a sequential copolymer containing blocks of hydrophobic monomers of essentially the same size, and at the same time, before adding to the specified aqueous composition, the specified polymer is in the form of a powder containing particles ranging in size from 5 μm to 400 μm, while the specified fluid contains at least a portion of the solid particles prior to injection and / or it is brought into contact with at least part of the solid particles in the subterranean formation after injection, and wherein said copolymer is associated with at least a part of the solid particles, providing an action both as a dispersing and stabilizing agent for the dispersion of these particles and as an agent for controlling fluid loss.

In another embodiment, the method of suspending and transporting proppant includes mixing an aqueous fluid and proppant and transporting the resulting combination using at least one pump, and said fluid contains a polymer in an amount in the range from 0.001 wt.% to 10 wt.% relative to the total weight combination, and the specified polymer contains:

at least one hydrophobic monomer selected from the group consisting of n-hexyl(meth)acrylate, n-octyl(meth)acrylate, octyl(meth)acrylamide, lauryl(meth)acrylate, lauryl(meth)acrylamide, myristyl(meth )acrylate, myristyl(meth)acrylamide, pentadecyl(meth)acrylate, pentadecyl(meth)acrylamide, cetyl(meth)acrylate, cetyl(meth)acrylamide, oleyl(meth)acrylate, oleyl(meth)acrylamide, erucyl(meth) acrylate, erucyl(meth)acrylamide and combinations thereof; and at least one hydrophilic monomer selected from the group consisting of acrylate, acrylic acid salts, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid salts, and combinations thereof, said polymer being a sequential copolymer containing blocks of hydrophobic monomers of essentially the same size.

Detailed description of the invention

The present inventors have discovered polymeric particle dispersion systems which, surprisingly, can be used in smaller amounts compared to conventional carrier systems and which still provide improved particle dispersion capabilities. In one of

- 1 043013 embodiments, an aqueous composition containing water and a polymer according to the present invention provides a particle suspension time in suspension of at least 1 hour. In another embodiment, the particle suspension time in suspension is at least 2 hours. In another embodiment, the particles remain in suspension in suspension for at least 4 hours. In another embodiment, the particles remain in suspension in suspension for more than 24 hours. In one embodiment, the aqueous composition maintains the particles in suspension in suspension. at a temperature of from about 68°F (20°C) to about 350°F (177°C) (or any temperature in the specified range).

In one embodiment, the polymer systems are applied to subterranean formations. In the present description, the reference to a subterranean formation is understood in the broadest sense and includes rock containing hydrocarbons, in particular oil, and various layers of rocks that are crossed to access said oil-bearing rock and to ensure the extraction of hydrocarbons. As used herein, rock is used to refer to any type of constituent material of a solid subterranean formation, whether or not said constituent material is rock in the narrow sense of the term. Thus, in particular, the expression oil-bearing rock is used as a synonym for an oil-bearing formation and refers to any underground formation containing hydrocarbons, in particular oil, regardless of the nature of the material containing these hydrocarbons (for example, rock or sand).

Among the fluids injected under pressure into subterranean formations, various well completion and workover fluids, in particular drilling fluids, whether used to reach an oil-bearing rock or to drill the formation itself (break-in), or fracturing fluids, or alternatively, well completion fluids, control fluids or reconstruction fluids, or annulus fluids, or packer fluids, or buffer fluids, or acidizing fluids, or also cementation fluids.

In one embodiment, the polymer contains at least one hydrophobic monomer selected from n-hexyl(meth)acrylate, n-octyl(meth)acrylate, octyl(meth)acrylamide, lauryl(meth)acrylate, lauryl(meth)acrylamide , myristyl(meth)acrylate, myristyl(meth)acrylamide, pentadecyl(meth)acrylate, pentadecyl(meth)acrylamide, cetyl(meth)acrylate, cetyl(meth)acrylamide, oleyl(meth)acrylate, oleyl(meth)acrylamide, erucyl(meth)acrylate, erucyl(meth)acrylamide and combinations of these compounds; and at least one hydrophilic monomer selected from acrylate, acrylic acid salts, acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid salts, and combinations of these compounds. In one embodiment, the hydrophilic monomers include acrylamide and 2-acrylamido-2-methylpropanesulfonic acid. In one embodiment, the polymer contains hydrophilic monomers in a total amount of from about 50 wt.% to about 99.9 wt.% relative to the polymer. In another embodiment, the polymer contains hydrophilic monomers in a total amount of from about 80 wt.% to about 99.9 wt.% relative to the polymer. In another embodiment, the polymer contains hydrophobic monomers in a total amount of from about 0.01 wt.% to about 50 wt.% relative to the polymer. In another embodiment, the polymer contains hydrophobic monomers in a total amount of from about 0.01 wt.% to about 20 wt.% relative to the polymer.

In one embodiment, the polymer chain end position includes a thiocarbonylthio functional group.

In one embodiment, the polymer is in the form of a powder with a particle size of about 5 microns to about 400 microns. In another embodiment, the particle size ranges from about 50 microns to about 200 microns. In another embodiment, the polymer is in the form of a slurry containing a solvent or hydrocarbon phase and a suspending agent, wherein the particle size of the polymer powder in the slurry varies from about 5 microns to about 400 microns.

In another embodiment, the polymer powder contains polymer particles with a particle size of from about 5 microns to about 400 microns and a molecular weight of from about 10,000 g/mol to about 20,000,000 g/mol, and the polymer contains acrylamide monomers and 2-acrylamido-2-methylpropane sulfonic acid and at least one hydrophobic monomer selected from n-hexyl(meth)acrylate, n-octyl(meth)acrylate, octyl(meth)acrylamide, lauryl(meth)acrylate, lauryl(meth)acrylamide, myristyl(meth)acrylate , myristyl(meth)acrylamide, pentadecyl(meth)acrylate, pentadecyl(meth)acrylamide yes, cetyl(meth)acrylate, cetyl(meth)acrylamide, oleyl(meth)acrylate, oleyl(meth)acrylamide, erucyl(meth)acrylate, erucyl(meth)acrylamide and combinations of these compounds. In one embodiment, the hydrophobic monomer is selected from lauryl(meth)acrylate, lauryl(meth)acrylamide, and combinations of these compounds.

In one embodiment, the implementation of the polymers according to the present invention is obtained by polymerization in micelles. The polymer system includes successive copolymers (P) containing at least one chain (C) of the type obtained by polymerization in micelles, to maintain solid particles (p) in suspension in suspension in a fluid (F) in which the specified

- 2 043013 chain (C) is soluble.

In particular, according to a specific aspect, the object of the present invention is the use of the above sequential copolymers as a suspending agent in a fluid (F) injected under pressure into a subterranean formation, said fluid (F) containing at least a portion of solid particles (p) and/or comes into contact with at least a portion of the solid particles (p) in the subterranean formation after injection. As used herein, the term fluid soluble chain (F) is understood to mean a chain (C) that typically has a solubility in fluid (F) at 20°C of 0.5% (5000 ppm) or more, preferably equal to 1% or more.

The polymerization in micelles schematically consists in carrying out the polymerization of hydrophilic monomers in a hydrophilic medium containing micelles containing hydrophobic monomers. Examples of polymerization in micelles have been described, in particular, in US patent No. 4432881 or also in Polymer, Vol. 36, no. 16, pp. 3197-3211 (1996), and for additional details, you can refer to these documents.

The chain (C) of the polymers (P) used according to the present invention is a chain which is completely soluble in the fluid (F) and which is predominantly formed by a series of hydrophilic units interrupted at various points by a plurality of hydrophobic sequences (B) of substantially the same size. The polymer according to the present invention may consist of chain (C) or may also be a block copolymer in which chain (C) constitutes one of the blocks.

The hydrophobic sequences (B) are preferably polymeric sequences insoluble in the fluid (F), typically having a solubility in the fluid (F) at 20° C. of 0.1% (1000 ppm) or less.

Copolymers (P) containing the above chain (C) are suitable for keeping the solid particles (p) in suspension in suspension. They may be particles present in the subterranean formation and/or particles injected into the subterranean formation, usually together with copolymers (such as, for example, proppant particles).

Typically, according to the present invention, micelle polymerization is used, in which the following monomers are copolymerized (usually by a radical route) in an aqueous dispersion medium (usually water or a water/alcohol mixture):

hydrophilic monomers in a dissolved or dispersed state in the specified environment; and hydrophobic monomers inside micelles of a surfactant formed in said medium by introducing a surfactant into it at a concentration exceeding the critical micelle concentration (CMC).

Preferably, the content of hydrophobic monomers, corresponding to the ratio of the mass of hydrophobic monomers to the total mass of hydrophobic and hydrophilic monomers, is greater than or equal to 0.01%, preferably greater than 0.1%, in fact even greater than 0.2%, and less than or equal to 5 %. In general, the percentage of hydrophobic units in chain (C) is of the same order, usually greater than or equal to 0.05%, preferably greater than 0.1%, in fact even greater than 0.2%, and less than or equal to 5%.

In micellar polymerization, the hydrophobic monomers present in the micelles are said to be in the micellar solution. Said micellar solution is a microheterogeneous system which is generally isotropic, optically transparent and thermodynamically stable. It should be noted that a micellar solution of the type used for micelle polymerization should be distinguished from a microemulsion. In particular, unlike a microemulsion, a micellar solution is formed at any concentration above the critical micelle concentration of the surfactant used, provided that the hydrophobic monomer is at least to some extent soluble in the interior of the micelles. In addition, a micellar solution differs from an emulsion in the absence of a homogeneous internal phase: micelles contain a very small number of molecules (usually less than 1000, in general less than 500 and usually from 1 to 100, most often from 1 to 50, monomer molecules and at most a few hundred surfactant molecules, if any), and the micellar solution generally has physical properties similar to those of monomer-free surfactant micelles. In addition, in general, a micellar solution is transparent to visible light because the small size of micelles does not cause refractive phenomena, unlike emulsion droplets, which refract light, resulting in a cloudy or white appearance. The micelle polymerization technique results in characteristic sequential polymers, each containing several hydrophobic blocks of substantially the same size, which size can be controlled. In particular, for a given content of hydrophobic monomers in micelles, each hydrophobic block contains essentially the same specified number of p _n hydrophobic monomers, and the specified number of p _n can be calculated by the following formula (Macromolecular Chem. Physics, 202, 8, 1384- 1397, 2001):

n _H =N _agg χ[ _{M H} ]/([surfactant]ccm), where N _agg is the aggregation number of the surfactant, which reflects the number of surfactant molecules contained in each micelle;

[ _MH ] is the molar concentration of the hydrophobic monomer in the medium;

- 3 043013

[surfactant] is the molar concentration of surfactant in the medium; and ccm is the critical (molar) micelle concentration.

Thus, the micelle polymerization technique makes it possible to preferentially control the hydrophobic units introduced into the synthesized polymers, namely:

general control of the mole fraction of hydrophobic units in the polymer (by adjusting the ratio of the concentrations of the two monomers); and more specific control of the number of hydrophobic units contained in each hydrophobic block (by modifying the parameters affecting p _n defined above).

Chain (C), completely soluble in fluid (F), obtained by polymerization in micelles, contains:

a hydrophilic component composed of hydrophilic monomers that corresponds to a hydrophilic polymer backbone that would have a solubility typically greater than or equal to 1% (10,000 ppm) at 20°C when separately introduced into the fluid (F), a hydrophobic component consisting of hydrophobic sequences, each of which has a solubility, usually less than or equal to 0.1% (1000 ppm) at 20°C in fluid (F).

In many cases, chain (C) can be described as a hydrophilic chain having the above solubility (at least 1%) to which hydrophobic side groups are grafted. In particular, in this case, the chain (C) has a total solubility at 20°C in the fluid (F), which preferably remains greater than or equal to 0.1%, in fact even 0.5%.

According to a particular embodiment, chain (C) is of the type obtained by a method comprising a micelle radical polymerization step (e) in which the following compounds are brought into contact in an aqueous medium (M):

hydrophilic monomers dissolved or dispersed in said aqueous medium (M) (usually water or a mixture of water/alcohol);

hydrophobic monomers in the form of a micellar solution, namely a solution containing, in a dispersed state in the medium (M), micelles containing said hydrophobic monomers (it is possible, in particular, to achieve said dispersed state using at least one surfactant); and at least one radical polymerization initiator, said initiator typically being water-soluble or water-dispersible.

According to a preferred embodiment, chain (C) is of the type obtained by a process comprising a micelle radical polymerization step (E) in which the following compounds are brought into contact in an aqueous medium (M):

hydrophilic monomers dissolved or dispersed in said aqueous medium (M) (usually water or a mixture of water/alcohol);

hydrophobic monomers in the form of a micellar solution, namely a solution containing, in a dispersed state in the medium (M), micelles containing said hydrophobic monomers (it is possible, in particular, to achieve said dispersed state using at least one surfactant);

at least one radical polymerization initiator, said initiator usually being water-soluble or water-dispersible; and at least one radical polymerization controlling agent.

Step (E) is similar to step (e) above, but additionally a controlling agent is used. This step, known as controlled nature radical polymerization in micelles, is described in particular in WO 2013/060741. You can also apply all alternative forms described in the specified document.

As used herein, the term radical polymerization controlling agent is understood to mean a compound that is capable of extending the lifetime of growing polymer chains in a polymerization reaction and of making the polymerization live or controlled. Said controlling agent is typically a reversible chain transfer agent used in controlled radical polymerization under the designation RAFT or MADIX, which is typically used in a reversible chain transfer process by an addition-fragmentation mechanism such as those described, for example, in WO 96/30421, WO 98/01478, WO 99/35178, WO 98/58974, WO 00/75207, WO 01/42312, WO 99/35177, WO 99/31144, FR2 794 464 or WO 02/26836. In one embodiment, the radical polymerization control agent used in step (E) is a compound containing a thiocarbonylthio -S(C=S) group. Thus, for example, it may be a compound containing a xanthate group (bearing functional groups SC=S-O-), for example, xanthate. Other types of control agents may be considered (eg, the types used in CRP or ATRP).

According to a particular embodiment, the controlling agent used in step (E) may be a polymer chain obtained in a controlled radical polymerization and a carrier group capable of controlling the radical polymerization (living type polymer chain, said type itself is good famous). Thus, for example, the controlling agent may be a polymeric chain (preferably hydrophilic or water-dispersible) carrying a xanthate functional group at the end of the chain, or, more generally, containing a -SC=S- group, for example, obtained according to the MADIX technology . Alternatively, the controlling agent used in step (E) is a non-polymeric compound bearing a radical polymerization control group, in particular a thiocarbonylthio -S(C=S) group.

According to a specific alternative form, the radical polymerization control agent used in step (E) is a polymer, preferably an oligomer, having a water-soluble or water-dispersible nature and bearing a thiocarbonylthio group -S(C=S), e.g. xanthate -SC =SO-group. Said polymer capable of acting both as a polymerization control agent and as a monomer in step (E) is also referred to hereinafter as a prepolymer. Typically, said prepolymer is obtained by radical polymerization of hydrophilic monomers in the presence of a controlling agent bearing a thiocarbonylthio group-S(C=S), such as xanthate. Thus, for example, according to the preferred embodiment illustrated at the end of this description, the controlling agent used in step (E) may advantageously be a prepolymer containing a thiocarbonylthio group -S(C=S), such as xanthate -SC=SO- group obtained at the end of stage (E ⁰ ) controlled radical polymerization before stage (E). In this stage (E ⁰ ) it is usually possible to bring into contact hydrophilic monomers, substantially identical to the monomers used in stage (E); a radical polymerization initiator; and a controlling agent containing a thiocarbonylthio group -S(C=S), such as xanthate.

The use of the above step (E ⁰ ) before step (E) allows, schematically, to make a large number of control agents containing thiocarbonylthio functional groups (for example, xanthates, which are rather hydrophobic in nature) hydrophilic by converting them into prepolymers that are soluble or dispersible in medium (M) in step (E). Preferably, the prepolymer synthesized in step (E ⁰ ) has a short polymer chain, eg less than 50 monomer units, in fact even less than 25 monomer units, eg 2 to 15 monomer units. When step (E) is carried out, the polymers of the present invention contain structure-controlled chains (C), namely, all chains (C) contained in the polymer are substantially the same size and the same structure. The chains (C) contain, in particular, the blocks (B) in substantially the same number and ratio.

The particular polymers (P) used in the context of the present invention, due to the presence of hydrophobic sequences in the hydrophilic polymer chain, provide a particularly effective fluid control effect: without wishing to be bound by theory, hydrophobic units in the hydrophilic chain and/or various hydrophilic chains seem to tend to to associate with each other.

In one embodiment, the injected fluid (F) contains polymers (P) but does not contain solid particles (p) and encounters said particles (p) in a subterranean formation after it has been injected. Then the association between particles and polymers occurs in situ. Such a fluid can, for example, be pumped during drilling, and then the pieces of rock formed during drilling play the role of particles (p) in situ.

Alternatively, the injected fluid (F) contains, prior to injection, at least a portion, and generally all, of the particles (p) associated with the polymer (P), and it is understood that it may optionally occur with other particles (p) in the subterranean formation. In particular, two forms are considered in this context:

Form 1: polymers (P) and particles (p) are mixed during the preparation of the fluid (F), at the site of operation or upstream, usually by introducing particles (p), in dry form or, optionally, in dispersed form, in a composition containing polymers (P) in solution;

Form 2: Fluid (F) is produced, predominantly on site, from a composition (premix) obtained upstream (hereinafter referred to as blend) containing polymers (P) and at least a portion of the particles (p ), in general, in a dispersing liquid. To obtain a fluid (F) the specified mixture is mixed with other components of the fluid (F).

In some embodiments, the polymers (P) associated with the particles (p) can be used as a dispersing and stabilizing agent for the dispersion of the particles (p) while also acting as a fluid loss control agent. The reference to fluid loss control refers to slowing down the effect of fluid loss observed when a fluid is pumped under pressure into a subterranean formation: the fluid contained in the fluid tends to penetrate into the rock constituting the subterranean formation, which can damage the well and even violate its integrity. Since these pressurized fluids contain insoluble compounds (in very many cases, in particular for petroleum cement slurries or drilling or fracturing fluids), the effect of fluid loss at the same time increases the risk of loss of control over an increase in the concentration of insoluble compounds in the injected fluid, which can lead to an increase in viscosity, which affects the mobility of the fluid.

In particular, when the fluid (F) is a fracturing, cementing or drilling fluid, the presence of the copolymers (P) allows control of fluid loss by limiting, even completely inhibiting, the release of the fluid (F), typically water. or an aqueous composition, into a subterranean formation in which mining takes place.

Various advantages and embodiments of the present invention will be described in more detail below.

Fluid (F).

The term "fluid" within the scope of this specification should be understood as any homogeneous or non-homogeneous medium containing a liquid or viscous carrier, which optionally transports a liquid or gel-like dispersed phase and/or solid particles, said medium being generally pumpable by pumping devices. pressure applied in this application.

The term liquid or viscous fluid carrier (F) should be understood as the fluid itself or the solvent, if the fluid contains dissolved compounds and/or a continuous phase, if the fluid contains dispersed elements (drops of liquid or gel-like dispersed phase, solid particles, etc.).

In a very suitable embodiment, the fluid (F) is an aqueous fluid. The term aqueous in the present description should be understood as a fluid containing water as a liquid or viscous carrier, or as the sole constituent of a liquid or viscous carrier, or in combination with other water-soluble solvents.

In case solvents other than water are present in the liquid or viscous fluid carrier (F), water advantageously remains the predominant solvent in the liquid or viscous carrier, preferably present in a proportion of at least 50% by weight, and even at least 75% by weight based on the total weight of solvents in a liquid or viscous carrier.

In one embodiment, the fluid (F) is selected from fresh water, sea water, salt solutions, salt water, produced water, recycled water, industrial waste water, oil production waste water, and combinations of these options.

Particles (p).

Reference to particles as used herein is not limited to reference to individual particles. In a more general sense, it refers to solids that can be dispersed in a fluid, in the form of objects (individual particles, aggregates and the like), all of which are less than 5 mm, preferably less than 2 mm, for example, less than 1 mm.

Particles (p) according to the present invention may be selected from: calcium carbonate or cement, silica or sand, ceramics, clay, barite, hematite, carbon black and/or mixtures of these materials.

According to a particular embodiment of the present invention, the particles (p) are particles of sand or cement.

Polymers (P).

hydrophilic monomers. Chain (C) may typically contain monomers selected from:

ethylenically unsaturated carboxylic acids, sulfonic acids and phosphonic acids and/or their derivatives, such as acrylic acid (AA), methacrylic acid, ethacrylic acid, α-chloroacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid, fumaric acid, single ethylenically unsaturated dicarboxylic acid monoesters containing 1 to 3 and preferably 1 to 2 carbon atoms, e.g. , sulfoethyl methacrylate, sulfopicarilate, sulfropilmetacrilate, 1-aleloxy-2-hydroilpropilpil sulfile, 2-hydroxy3-acryloxipyl sulfonic acid, 2-hydroxy-3-methacryloxyphoneic acid, pyroil sulfic acids, 2-acrylamido-2-metallippanippanippanippanippanine. sulfonic acid, vinyl phosphonic acid, α-methylivinyl phosphonic acid and allylphosphonic acid;

esters containing α,β-ethylenic unsaturated bonds of mono- and dicarboxylic acids and C ₂ -C ₃ alkanediols, for example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxyethyl ethacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropylacrylate, 3-hydroxypropyl methacrylate and (meth)acrylates of polyalkylene glycols;

amides containing α,β-ethylenic unsaturated bonds of monocarboxylic acids and their N-alkyl and N,N-dialkyl derivatives, such as acrylamide, methacrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-isopropyl ( meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, morpho-6 043013 folinyl(meth)acrylamide and methylolacrylamide (acrylamide and N,N-dimethyl( meth)acrylamide);

N-vinyl lactams and their derivatives, for example N-vinylpyrrolidone or N-vinylpiperidone;

open-chain N-vinylamide compounds, e.g. -methylpropionamide and N-vinylbutyramide;

esters containing α,β-ethylenic unsaturated bonds of mono- and dicarboxylic acids and amino alcohols, for example, N,N-dimethylaminomethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl acrylate and N,N -dimethylaminopropyl(meth)acrylate;

amides containing α,β-ethylenic unsaturated bonds of mono- and dicarboxylic acids, and diamines containing at least one primary or secondary amino group, such as N-[2(dimethylamino)ethyl]acrylamide, N-[2-(dimethylamino) ethyl]methacrylamide, N-[3-(dimethylamino)propyl]acrylamide, N-[3-(dimethylamino)propyl]methacrylamide, N-[4-(dimethylamino)butyl]acrylamide and N-[4(dimethylamino)butyl]methacrylamide ;

N-diallylamines, N,N-diallyl-N-alkylamines, their acid addition salts and their alkyl quaternization products, preferably C1- _C3 alkyls;

N,N-diallyl-N-methylamine and N,N-diallyl-N,N-dimethylammonium compounds, eg chlorides and bromides;

nitrogen-containing heterocycles substituted with vinyl and allyl, eg N-vinylimidazole, N-vinyl-2-methylimidazole, heteroaromatic compounds substituted with vinyl and allyl, eg 2- and 4-vinylpyridine, 2- and 4-allylpyridine, and salts thereof;

sulfobetaines; and salts of the above monomers;

mixtures and combinations of two or more monomers and/or their salts as mentioned above.

According to a specific implementation variant, these monomers may, in particular, contain acrylic acid (AA).

In another embodiment, the hydrophilic chain (C) monomers comprise (and usually consist of) (meth)acrylamide monomers, or more generally, (meth)acrylamide monomers, including:

acrylamide monomers, namely acrylamide (Am), dimethylamrylamide (DMA), their sulfonate derivatives, in particular acrylamide methyl propane sulfonic acids (AMPS);

quaternary ammonium ARTAS and sulfopropyldimethylammoniopropylacrylamide;

methacrylamide monomers such as sulfopropyldimethylammoniopropylmethacrylamide (SPP) or sulfohydroxypropyldimethylammoniopropylmethacrylamide.

In a particular embodiment, the hydrophilic monomers of chain (C) are acrylamides. The acrylamide is preferably a non-copper stabilized acrylamide.

In a specific embodiment, the hydrophilic chain (C) monomers are selected from acrylamides, dimethylacrylamides (DMA), acrylamide methyl propane sulfonic acids (AMPS), acrylic acids (AA), their salts, and mixtures of these compounds.

In a specific embodiment, the hydrophilic monomers of chain (C) may typically contain polymerizable acrylamide-type functional groups and side chains consisting of ethylene oxide or propylene oxide chains, or be Nisopropylacrylamide or N-vinylcaprolactam based compounds.

hydrophobic monomers. Of particular note, as non-limiting examples of hydrophobic monomers constituting insoluble blocks that can be used according to the present invention are the following:

vinylaromatic monomers such as styrene, α-methylstyrene, p-chloromethylstyrene, vinyltoluene, 2-methylstyrene, 4-methylstyrene, 2-(n-butyl)styrene, 4-(n-decyl)styrene or tert-butylstyrene;

halogenated vinyl compounds such as vinyl or vinylidene halides, for example vinyl or vinylidene chlorides or fluorides, corresponding to the formula

RbRcC=CX1X ² where X ¹ = F or Cl,

X ² = H, F or Cl, each of R _b and Rc independently represents:

H, Cl, F; or an alkyl group, preferably chlorinated and/or fluorinated, more preferably perchlorinated or perfluorinated.

esters containing α,β-ethylenic unsaturated bonds of mono- and dicarboxylic acids and C ₂ -C ₃₀ alkanols, for example, methyl ethacrylate, ethyl (meth) acrylate, ethyl ethacrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n -butyl(meth)acrylate, sec-butyl(meth)acrylate, tert-butyl(meth)acrylate, tert-butyl ethacrylate, n-hexyl(meth)acrylate, n-heptyl(meth)acrylate, n-octyl(meth )acrylate, 1,1,3,3-tetramethyl butyl(meth)acrylate, ethylhexyl(meth)acrylate, n-nonyl(meth)acrylate, n-decyl(meth)acrylate n-undecyl(meth)acrylate, tridecyl(meth )acrylate, myristyl(meth)acrylate, pentadecyl(meth)acrylate, palmityl(meth)acrylate, heptadecyl(meth)acrylate, nonadecyl(meth)acrylate, arachidyl(meth)acrylate, behenyl(meth)acrylate, lignoceryl(meth)acrylate , cerotinyl(meth)acrylate, melissinyl(meth)acrylate, palmitoleyl(meth)acrylate, oleyl(meth)acrylate, linoleyl(meth)acrylate, linoleyl(meth)acrylate, stearyl(meth)acrylate, lauryl(meth)acrylate, cetyl (meth) acrylate, erucyl (meth) acrylate and mixtures of these compounds;

esters of vinyl or allyl alcohol and C1- _C30 monocarboxylic acids, for example vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl laurate, vinyl stearate, vinyl propionate, vinyl versatate and mixtures of these compounds;

ethylenically unsaturated nitrites, such as acrylonitrile, methacrylonitrile and mixtures of these compounds; esters containing α,β-ethylenic unsaturated bonds of mono- and dicarboxylic acids and C ₃ -C ₃₀ alkanediols, for example, 3-hydroxybutyl acrylate, 3-hydroxybutyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, 6-hydroxyhexyl acrylate, 6-hydroxy hexyl methacrylate, 3-hydroxy-2-ethylhexyl acrylate and 3-hydroxy-2-ethylhexyl methacrylate, and the like; primary amides containing α,β-ethylenic unsaturated bonds of mono- and dicarboxylic acids and their N-alkyl and Ν,N-dialkyl derivatives, such as N-propyl (meth) acrylamide, N- (n-butyl) (meth) acrylamide, N -(tert-butyl)(meth)acrylamide, N-butylphenylacrylamide, N-methyl-N-hexylacrylamide, N,Ndihexylacrylamide, hexyl(meth)acrylamide, N-(n-octyl)(meth)acrylamide, N-(1, 1,3,3-tetramethylbutyl) (meth)acrylamide, N-ethylhexyl(meth)acrylamide, N-(h-nonyl)(meth)acrylamide, N-(n-decyl)(meth)acrylamide, N-(n- undecyl)(meth)acrylamide, N-tridecyl(meth)acrylamide, N-myristyl(meth)acrylamide, N-pentadecyl(meth)acrylamide, N-palmityl(meth)acrylamide, N-heptadecyl(meth)acrylamide, N-nonadecyl (meth)acryl mid, N-arachidyl(meth)acrylamide, N-behenyl(meth)acrylamide, N-lignoceryl(meth)acrylamide, N-cerotinyl (meth)acrylamide, N-melissinyl(meth)acrylamide, N-palmitoleyl( meth)acrylamide, N-oleyl(meth)acryl mid, N-linoleyl(meth)acrylamide, N-linolenyl(meth)acrylamide, N-stearyl(meth)acrylamide and N-lauryl(meth)acrylamide;

N-vinyl lactams and their derivatives such as N-vinyl-5-ethyl-2-pyrrolidone, N-vinyl-6-methyl-2-piperidone, N-vinyl-6-ethyl-2-piperidone, N-vinyl-7-methyl -2-caprolactam and N-vinyl-7-ethyl-2-capro-lactam, and the like;

esters containing α,β-ethylenic unsaturated bonds of mono- and dicarboxylic acids and amino alcohols, for example N,N-dimethylaminocyclohexyl(meth)acrylate;

amides containing α,β-ethylenic unsaturated bonds of mono- and dicarboxylic acids and diamines containing at least one primary or secondary amino group, for example, N-[4(dimethylamino)butyl]acrylamide, N-[4-(dimethylamino)butyl] methacrylamide, N-[2-(dimethylamino)ethyl]acrylamide, N-[4-(dimethylamino)cyclohexyl]acrylamide, N-[4-(dimethylamino)cyclohexyl]methacrylamide and the like; and monoolefins (C2-C8) and non-aromatic hydrocarbons containing at least two conjugated double bonds, such as ethylene, propylene, isobutylene, isoprene, butadiene and the like.

In a preferred embodiment, the hydrophobic monomers used in the present invention may be selected from:

C 1 -C ₃₀ alkyl and preferably C ₄ -C ₂₂ alkyl α,β-unsaturated esters, in particular acrylates and methacrylates, such as methyl-, ethyl-, butyl-, 2-ethylhexyl-, isooctyl-, lauryl-, isodecyl, stearyl, octyl, myristyl, pentadecyl, cetyl, oleyl or erucyl acrylates and methacrylates (in particular lauryl methacrylate has been shown to be particularly preferred);

C 1 -C ₃₀ alkyl and preferably C ₄ -C ₂₂ alkyl α,β-unsaturated amides, in particular alkylacrylamides and alkylmethacrylamides, such as methyl-, ethyl-, butyl, 2-ethylhexyl, isooctyl-, lauryl-, isodecyl-, stearyl, octyl, myristyl, pentadecyl, cetyl, oleyl or erucyl acrylamide or methacrylamide (in particular lauryl methacrylamide has been shown to be particularly preferred);

esters of vinyl or allyl alcohol and saturated carboxylic acids, such as vinyl or allyl acetate, -propionate, -versatate or -stearate;

α,β-unsaturated nitriles containing from 3 to 12 carbon atoms, such as acrylonitrile or methacrylonitrile; α-olefins and conjugated dienes; vinylaromatic monomers such as styrene, α-methylstyrene, p-chloromethylstyrene, vinyltoluene, 2-methylstyrene, 4-methylstyrene, 2-(n-butyl)styrene, 4-(n-decyl)styrene or t-butylstyrene; mixtures and combinations of two or more of the above monomers.

According to a preferred embodiment, particularly when the fluid (F) is a fracturing fluid, hydrophobic monomers loosely bound to chain (C) can be used. This allows the polymers introduced into the subterranean formation to be removed if necessary (due to their amphiphilic nature, the polymers of the present invention are generally self-associating in nature and tend to form

- 8 043013 hard-to-remove gels; under the influence of, in particular, temperature and/or pH, hydrophobic monomers can be cleaved off if they are not too strongly bound to the polymer, which allows removal from the fluid). Hydrophobic monomers suitable for said embodiment are, in particular, the above esters.

It should be noted that when other monomers are used, removal from fluids is still possible using known techniques for introducing thinners (demulsifiers), such as oxidizing agents. The previous embodiment made it possible to dispense with the use of such thinners, which in particular results in cost savings. In one embodiment, the diluent is selected from peroxides, persulfates, peracids, bromates, chlorates, chlorites, and combinations of these compounds.

In a specific embodiment, the polymer may have a molecular weight of from about 10,000 g/mol to about 20,000,000 g/mol. In another embodiment, the molecular weight of the polymer ranges from about 100,000 g/mol to about 10,000,000 g/mol. In another embodiment, the molecular weight of the polymer ranges from about 500,000 g/mol to about 5,000,000 g/mol.

Radical polymerization agent.

The control agent used in step (E) or, if necessary, step (E ⁰ ) of the method according to the present invention is preferably a compound containing a thiocarbonylthio group -S(C=S). In a specific embodiment, the controlling agent may contain multiple thiocarbonylthio groups. It may optionally be a polymer chain containing the specified group.

Thus, said controlling agent may, for example, correspond to formula (A) below:

^Z (A) where Z is: hydrogen atom, chlorine atom, optionally substituted alkyl or optionally substituted aryl radical, optionally substituted heterocycle, optionally substituted alkylthio radical, optionally substituted arylthio radical, optionally substituted alkoxy radical, optionally substituted aryloxy radical, optionally substituted amine radical, optionally substituted hydrazine radical, optionally substituted alkoxycarbonyl radical, optionally substituted aryloxycarbonyl radical, optionally substituted acyloxy or carboxyl radical, optionally substituted aroyloxy radical, optionally substituted carbamoyl radical, cyano radical, dialkyl- or diarylphosphonato radical, dialkylphosphinato radical or diarylf osfinato, or polymer chain, and R1 is an optionally substituted alkyl, acyl, aryl, aralkyl, alkenyl or alkynyl group, saturated or unsaturated, aromatic, optionally substituted carbocycle or heterocycle, or a polymer chain which is preferably hydrophilic or water-dispersible if the agent used in step (E).

The R1 or Z groups, when substituted, may be substituted with optionally substituted phenyl groups, optionally substituted aromatic groups, saturated or unsaturated carbocycles, saturated or unsaturated heterocycles, or groups selected from the following: alkoxycarbonyl or aryloxycarbonyl (-COOR), carboxyl ( -COOH), acyloxy (-O ₂ CR), carbamoyl (-CONR ₂ ), cyano (-CN), alkylcarbonyl, alkylarylcarbonyl, arylcarbonyl, arylalkylcarbonyl, phthalimido, maleimido, succinimido, amidino, guanidino, hydroxyl (-OH), amino (-NR2), halogen, perfluoroalkyl C _n F _2n+1 , allyl, epoxy, alkoxy (-OR), S-alkyl, S-aryl, hydrophilic or ionic groups such as alkali metal and carboxylic acids, salts formed by alkali metals and sulfonic acids, polyalkylene oxide chains (PEO, PPO), cationic substituents (quaternary ammonium salts), while R represents an alkyl or aryl group, or a polymer chain.

For the controlling agents of formula (A) used in step (E), it is generally preferred that the R1 group is of a hydrophilic nature. Preferably, it is a water-soluble or water-dispersible polymer chain.

The R1 group may alternatively be amphiphilic, ie both hydrophilic and lipophilic in nature. Preferably, the R1 group is not hydrophobic.

With regard to the controlling agents of formula (A) used in step (E ⁰ ), R1 may generally be a substituted or unsubstituted, preferably substituted, alkyl group. The control agent of formula (A) used in step (E ⁰ ) may, however, contain other types of R _b groups, in particular a ring or a polymer chain.

Optionally substituted alkyl, acyl, aryl, aralkyl or alkynyl groups generally contain 1 to 20 carbon atoms, preferably 1 to 12, and more preferably 1 to 9 carbon atoms. They can be linear or branched. They can also be substituted

- 9 043013 oxygen atoms, in particular in the form of esters, sulfur atoms or nitrogen atoms.

Of particular note among the alkyl radicals are the methyl, ethyl, propyl, butyl, pentyl, isopropyl, tert-butyl, pentyl, hexyl, octyl, decyl or dodecyl radicals.

Alkyne groups are in general radicals containing from 2 to 10 carbon atoms; they contain at least one acetylenic unsaturation, such as an acetylenyl radical.

An acyl group is a radical generally containing from 1 to 20 carbon atoms with a carbonyl group.

Of particular note among the aryl radicals is the phenyl radical optionally substituted, in particular with a nitro or hydroxyl functional group.

Of particular note among the aralkyl radicals is the benzyl or phenethyl radical optionally substituted, in particular with a nitro or hydroxyl functional group.

If R1 or Z is a polymer chain, said polymer chain can be obtained by radical or ionic polymerization, or by polycondensation.

Preferably, it is possible to use as a controlling agent in step (E) and also in step (E ⁰ ), if necessary, compounds containing the functional group xanthate -S(C=S)O-, trithiocarbonate, dithiocarbamate or dithiocarbazate, for example containing functional group Oethylxanthate formula -S(C=S)OCH ₂ CH ₃ .

When carrying out step (E ⁰ ), it is particularly preferred to use a compound selected from xanthates, trithiocarbonates, dithiocarbamates and dithiocarbazates as the controlling agent in said step. Xanthates have been shown to be particularly preferred, in particular compounds containing the functional group O-ethylxanthate -S(C=S)OCH2CH3, such as O-ethyl-S-(1(methoxycarbonyl)ethyl)xanthate (CH3CH(CO2CH3) )S(C=S)OEt Another possible controlling agent in step (E ⁰ ) is dibenzyltrithiocarbonate of the formula PhCH2S(C=S)SCH ₂ Ph (wherein Ph=phenyl).

It has been proven that the living prepolymers obtained in step (E ⁰ ) through the use of the above controlling agents are particularly preferred for step (E).

Initiation and implementation of radical polymerization in stages (E) and (E ⁰ ). When used in step (E), the radical polymerization initiator is preferably water-soluble or water-dispersible. Under this preferred condition, any known radical polymerization initiator (source of free radicals) suitable for the conditions selected for said steps can be used in step (E) and step (E ⁰ ) of the process of the present invention.

Thus, the radical polymerization initiator used according to the present invention may be selected, for example, from those conventionally used in radical polymerization. This could be, for example, one of the following initiators:

hydroperoxides such as: t-butyl hydroperoxide, cumene hydroperoxide, t-butylperoxyacetate, t-butylperoxybenzoate, t-butylperoxyoctoate, t-butylperoxyneodecanoate, t-butylperoxyisobutyrate, lauroyl peroxide, t-amylperoxypivalate, t-butylperoxypivalate, dicumylperoxide, benzoylperoxide, potassium persulfate or ammonium persulfate, azo compounds such as: 2,2'-azobis(isobutyronitrile), 2,2'-azobis-(2-butanenitrile), 4,4'-azobis-(4-pentanoic acid), 1,1' -azobis(cyclohexanecarbonitrile), 2-(t-butylazo)2-cyanopropane, 2,2'-αzobis-[2-methyl-N-(1,1)bis-(hydroxomethyl)2-hydroxyethyl]propionamide, 2, 2'-azobis-(2-methyl-N-hydroxyethyl]propionamide, 2,2'-azobus-(N,N'dimethyleneisobutyramidine) dichloride, 2,2'-azobis-(2-amidinopropane) dichloride, 2,2' -azobis-(N,N'-dimethylenisobutyramide), 2,2'-azobis-(2-methyl-N-[1,1-bis-(hydroxymethyl)2-hydroxyethyl]propionamide), 2,2'-azobis -(2-methyl-N-[1,1-bis-(hydroxymethyl)ethyl]propionamide), 2,2'-azobis-[2-methyl-N-(2-hydroxyethyl)propionamide] or 2,2' -azobis-(isobutyramide) dihydrate;

redox systems containing combinations such as: mixtures of hydrogen peroxide, alkyl peroxides, peroxyesters, percarbonates and the like, and iron salts, divalent titanium salts, zinc formaldehyde sulfoxylate or sodium formaldehyde sulfoxylate, and reducing sugars, alkali metal persulfates, perborates or perchlorates or ammonium in combination with an alkali metal bisulfite such as sodium metabisulphite and reducing sugars, and alkali metal persulfates in combination with an arylphosphinic acid such as benzenephosphonic acid and the like and reducing sugars.

Generally, the amount of initiator used is preferably determined such that the amount of generated radicals is at least 50 mole % and preferably at least 20 mole % relative to the controlling or chain transfer agent.

In particular, it has generally proven to be particularly advantageous to use a redox-type radical initiator in step (E), which has the advantage, inter alia, that it does not require heating of the reaction medium (no thermal initiation) and, apart from In addition, the present inventors have found evidence that it is suitable for micelle polymerization in step (E).

Thus, the radical polymerization initiator used in step (E) may typically be a redox initiator, typically requiring no heat for thermal initiation. Typically, it is a mixture of at least one oxidizing agent and at least one reducing agent.

The oxidizing agent present in said redox system is preferably a water-soluble agent. Said oxidizing agent can be selected, for example, from peroxides such as: hydrogen peroxide, t-butyl hydroperoxide, cumene hydroperoxide, t-butylperoxyacetate, t-butylperoxybenzoate, t-butylperoxyoctoate, t-butylperoxy neodecanoate, t-butylperoxyisobutyrate, lauroyl peroxide, t- amyl peroxy pivalate, t-butyl peroxy pivalate, dicumyl peroxide, benzoyl peroxide, sodium persulfate, potassium persulfate, ammonium persulfate, or also potassium bromate.

The reducing agent present in said redox system is also preferably a water-soluble agent. The reducing agent may generally be selected from sodium formaldehyde sulfoxylate (particularly in the form of the dihydrate known as Rongalit or in the form of an anhydride), ascorbic acid, erythorbic acid, sulfites, bisulfites or metasulfites (in particular alkali metal sulfites, bisulfites or metasulfites). ), nitrilotrispropionamides and tertiary amines and ethanolamines (which are preferably water soluble).

Possible redox systems include combinations such as: mixtures of water-soluble persulfates with water-soluble tertiary amines, mixtures of water-soluble bromates (e.g. alkali metal bromates) with water-soluble sulfites (e.g. alkali metal sulfites), mixtures of hydrogen peroxide, alkyl peroxide, peroxyesters, percarbonates and the like and any iron salt, divalent titanium salt, zinc formaldehyde sulfoxylate or sodium formaldehyde sulfoxylate, and reducing sugars, alkali metal or ammonium persulfates, perborates or perchlorates in combination with an alkali metal bisulfite such as sodium metabisulfite and reducing sugars, and alkali persulfates metals in combination with an arylphosphinic acid such as benzenephosphonic acid and the like, and reducing sugars.

The preferred redox system contains (and preferably consists of) a combination of ammonium persulfate and sodium formaldehyde sulfoxylate.

In general, and in particular in the case of using a redox system of the ammonium persulfate/sodium formaldehyde sulfoxylate type, it has proven to be preferable that the reaction medium in step (E) does not contain copper. When copper is present, it is generally desirable to add a copper complexing agent, such as EDTA, in an amount capable of masking its presence.

Whatever the nature of the initiator used, the radical polymerization in step (E ⁰ ) can be carried out in any suitable physical form, for example in solution in water or in a solvent such as alcohol or THF, in emulsion in water (latex method) or in mass, if convenient, while controlling the temperature and/or pH to keep the substances liquid and/or soluble or insoluble.

After step (E) is carried out, with a specific use of a controlling agent, polymers bearing chain transfer functional groups (living) polymers are obtained. This lively character makes it possible, if desired, to use said polymers in a subsequent polymerization reaction, according to well known procedures. Alternatively, if desired, chain transfer groups can be deactivated or destroyed, for example by hydrolysis, ozonolysis, or reaction with amines, according to known means. Thus, in a specific embodiment, the process of the present invention may include, after step (E), step (E1) of hydrolysis, ozonolysis, or reaction with amines that are capable of deactivating and/or destroying all or part of the chain transfer groups contained in the polymer. obtained in step (E).

Surfactants. It may be useful, to obtain a micellar solution of hydrophobic monomers used in stage (E), the use of any suitable surfactant in a non-limiting manner; you can use, for example, surfactants selected from the following list:

Anionic surfactants may be selected from:

alkyl ester sulfonates, for example, the formula R-CH(SO ₃ M)CH2COOR', or alkyl ester sulfates, for example, the formula R-CH(OSO ₃ M)CH2COOR', where R represents C ₈ -C ₂₀ and preferably C ₁₀ -C _1b alkyl radical, R is C ₁ -C _b and preferably C ₁ -C ₃ alkyl radical, and M is an alkali metal cation, eg sodium cation, or ammonium cation. Of particular note are, in particular, methyl ester sulfonates in which the R radical is a C ₁₄ -C _1b radical;

alkylbenzenesulfonates, in particular C9- _C20 alkylbenzenesulfonates, primary or secondary alkylsulfonates, in particular C8-C22 alkylsulfonates, or alkylglycerol sulfonates _, alkylsulfonates, for example of the formula ROSO3M, where R is _C10 - _C24 and preferably _C12-20 alkyl or a hydroxyalkyl radical and M is a cation as defined above;

- 11 043013 alkyl (ether) sulfates, for example, the formula RO(OA) _n SO ₃ M, where R represents

C10-C24 and preferably _C12 - _C20 alkyl or hydroxyalkyl radical, OA is an ethoxylated and/or propoxylated group, M is a cation as defined above, and n generally ranges from 1 to 4, such as, for example, lauryl ether sulfate with n=2;

alkylamide sulfates, for example of the formula RCONHR'OSO ₃ M, where R is a C ₂ -C ₂₂ and preferably a C ₆ -C ₂₀ alkyl radical, R is a C ₂ -C ₃ alkyl radical, and M is a cation, the same as defined above, as well as their polyalkoxylated (ethoxylated and/or propoxylated) derivatives (alkylamide(ether) sulfates); salts of saturated or unsaturated fatty acids such as C ₈ -C ₂₄ and preferably C ₁₄ -C ₂₀ acids and an alkaline earth metal cation, N-acyl-N-alkyl taurates, alkyl isethionates, alkyl succinamates and alkyl sulfosuccinates, alkyl glutamates, monoesters or complex diesters of sulfosuccinates, N-acylsarcosinates or polyethoxycarboxylates; monoester and diester phosphates, for example, of the following formula:

(RO)x-P(=O)(OM)x, where R is an optional polyalkoxylated alkyl, alkylaryl, arylalkyl or aryl radical, x and x' are 1 or 2, provided that the sum of x and x' is 3, and M is an alkaline earth metal cation;

Nonionic surfactants may be selected from:

alkoxylated fatty alcohols such as laureth-2, laureth-4, laureth-7 or oleth-20, alkoxylated triglycerides, alkoxylated fatty acids, alkoxylated sorbitan esters, alkoxylated fatty amines, alkoxylated di-(1-phenylethyl)phenols, alkoxylated triglycerides -(1-phenylethyl)phenols, alkoxylated alkylphenols, condensates of ethylene oxide with a hydrophobic compound obtained by condensing propylene oxide with propylene glycol, such as Pluronic products manufactured by BASF, condensates of ethylene oxide with a compound obtained by condensing propylene oxide with ethylenediamine, such as BASF's Tetronic products of alkyl polyglycosides such as those described in US Pat. No. 4,565,647 or alkyl glucosides or fatty acid amides, such as C ₈ -C ₂₀ fatty acid amides, in particular fatty acid monoalkanolamides, such as MEA cocamide or MERA cocamide ;

Amphoteric surfactants (truly amphoteric compounds containing an ionic group and a potentially ionic group of opposite charge, or zwitterionic compounds containing two opposite charges at the same time) can be: betaines in general, in particular carboxybetaines, for example, lauryl betaine (Mirataine BB from Rhodia) or octylbetaine or cocobetaine (Mirataine BB-FLA from Rhodia);

amidoalkyl betaines such as cocamidopropyl betaine (CAPB) (Mirataine BDJ from Rhodia or Mirataine BET C-30 from Rhodia);

sulfobetaines or sultaines such as cocamidopropylhydroxysultaine (Mirataine CBS from Rhodia);

alkylamphoacetates and alkylamphodiacetates, such as, for example, those containing a cocoyl or lauryl chain (Miranol C2M Cone. NP, C32, L32 in particular from Rhodia);

alkylamphopropionates or alkylamphodipropionates (Miranol C2M SF);

alkylamphohydroxypropylsultaines (Miranol CS);

alkylamine oxides, for example lauramine oxide (INCI);

Cationic surfactants may be optionally polyethoxylated salts of primary, secondary or tertiary fatty amines, quaternary ammonium salts such as tetraalkylammonium, alkylamidoalkylammonium, trialkylbenzylammonium, trialkylhydroxyalkylammonium or alkylpyridinium chlorides or bromides, imidazoline derivatives or cationic amine oxides. An example of a cationic surfactant is cetrimonium chloride or bromide (INCI);

the surfactants used according to the present invention may be block copolymers containing at least one hydrophilic block and at least one hydrophobic block other than the hydrophilic block, which are preferably obtained according to a polymerization process in which:

(a ₀ ) at least one hydrophilic (respectively, hydrophobic) monomer, at least one source of free radicals and at least one controlling agent of radical polymerization type -S(C=S) are combined in an aqueous phase;

(a1) the polymer obtained at the end of step (a0) is brought into contact with at least one hydrophobic (respectively, hydrophilic) monomer other than the monomer used in step (a0) and at least one source of free radicals; a diblock copolymer is thus obtained.

Polymers of the triblock type, or containing more blocks, can optionally be obtained by carrying out, after step (a1), step (a ₂ ) in which the polymer obtained at the end of step (a ₁ ) is brought into contact with at least at least one monomer other than the monomer used in step (a1) and at least one source of free radicals; and more generally, by carrying out (n+1) steps such as steps (a ₁ ) and (a ₂ ) described above, where n is an integer, typically ranging from 1 to 3, where, in each step (an), when n>1, the polymer obtained at the end of step (a _n _1) is brought into contact with at least one monomer other than the monomer used in step (a _n _1) and at least one source of free radicals. It is possible to use, for example, according to the present invention, copolymers of the type described in WO03068827, WO03068848 and WO2005/021612. In one embodiment, one or more polymers of the present invention are present in the aqueous composition. In another embodiment, one or more polymers of the present invention are present in the aqueous composition in an amount ranging from about 0.001 wt% to about 10 wt%, based on the total weight of the aqueous composition.

In one embodiment, the rate of hydration of the polymer powder of the present invention is increased by low shear mixing (eg, less than 10,000 rpm). In one embodiment, the dry polymer is combined with mineral oil before being added to water. In another embodiment, the dry polymer is pre-treated or post-treated with a solvent (eg, mutual solvent) before being added to water. In another embodiment, a hydrating surfactant is included during polymer synthesis. In another embodiment, examples of hydrating surfactants include, but are not limited to, EO/PO copolymers, e.g., ANTAROX 31R1, ANTAROX LA EP 16, and ANTAROX BL 225. In another embodiment, examples of solvents include, but are not limited to, ethylene glycol, propylene glycol, monobutyl ether ethylene glycol (EGMBE), and green solvents such as RHODISOLV DIB.

The present invention also provides methods for using the polymers of the present invention and related compositions.

In one embodiment, a method for fracturing a subterranean formation includes the step of injecting an aqueous fracturing fluid into at least a portion of the subterranean formation at a pressure sufficient to fracture the formation, said fracturing fluid comprising a polymer of the present invention. In one embodiment, said polymer contains: at least one hydrophobic monomer selected from nhexyl(meth)acrylate, n-octyl(meth)acrylate, octyl(meth)acrylamide, lauryl(meth)acrylate, lauryl(meth)acrylamide, myristyl(meth)acrylate, myristyl(meth)acrylamide, pentadecyl(meth)acrylate, pentadecyl(meth)acrylamide, cetyl(meth)acrylate, cetyl(meth)acrylamide, oleyl(meth)acrylate, oleyl(meth)acrylamide, erucil (meth)acrylate, erucyl(meth)acrylamide and combinations of these compounds; and at least one hydrophilic monomer selected from acrylate, acrylic acid salts, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid salts, and combinations of these compounds.

In one embodiment, prior to injection of the aqueous fracturing fluid, the polymer is in the form of a powder with a particle size of from about 5 microns to about 400 microns. In one embodiment, the polymer is present in an amount ranging from about 0.001% by weight to about 10% by weight. relative to the total mass of the hydraulic fracturing fluid.

In one embodiment, the fracturing fluid suspends the particles at a temperature of from about 68°F (20°C) to about 350°F (177°C). In another embodiment, the fracturing fluid suspends the particles at a temperature of from about 250°F (121°C) to about 350°F. In another embodiment, the fracturing fluid suspends the particles at a temperature of from about 300°F (149°C) to about 350°F.

In one embodiment, the fracturing fluid further comprises a surfactant. In one embodiment, the surfactant is selected from, without limitation, tridecyl alcohol ethoxylate and EO/PO block copolymers (eg, ANTAROX 31R1, ANTAROX LA EP 16, ANTAROX BL 225). In one embodiment, the surfactant is present in an amount of from about 0.01 wt% to about 10 wt%, based on the weight of the polymer. In one embodiment, the fracturing fluid further comprises a proppant. In one embodiment, the proppant is used in an amount of from about 20 wt.% to about 60 wt.%, based on the total weight of the fracturing fluid.

In one embodiment, the fracturing fluid further comprises a clay stabilizer. In one embodiment, said clay stabilizer is selected from choline chloride, potassium chloride, ammonium chloride, sodium chloride, calcium chloride, and combinations of these compounds. In one embodiment, the clay stabilizer is present in an amount of from about 0.01 wt.%, to about 30 wt.%, based on the total weight of the fluid.

In one embodiment, the method further includes the step of pumping a breaker into at least a portion of the subterranean formation. In one embodiment, the fracturing fluid is selected from fresh water, sea water, salt solutions, salt water, produced water, recycled water, industrial waste water, oil production associated waste water, and combinations of these options.

In another embodiment, a fracturing fluid is provided comprising a polymer at a mass concentration of from about 0.1 parts per trillion (ppt) to about 200 ppm, based on the total volume of the composition, a plurality of proppant particles at a mass concentration of from approximately 0.1 lb/gal. (11.98 kg/m ³ ) to about 12 lb/gal. (1438 kg/m ³ ), relative to the total volume of the composition, and the diluent is present in a mass concentration of from 0 h/tr to about 20 h/tr relative to the total volume of the composition.

Also provided is a method for acidizing a formation through which a wellbore passes, comprising the steps of pumping into the wellbore, at a pressure below the hydraulic fracturing pressure, a treatment fluid containing a polymer of the present invention and an aqueous acid solution, and allowing the treatment fluid to perform acid treatment of the formation and/or self-deviate into the formation. As used herein, the term self-divert refers to a composition that thickens as the formation is stimulated and thus diverts any remaining acid into zones of less permeability in the formation.

In one embodiment, a method for acidizing a subterranean formation through which a wellbore passes includes the steps of:

(a) pumping into the wellbore, at a pressure below the hydraulic fracturing pressure of the subterranean formation, a treatment fluid having a first viscosity and containing an aqueous acid solution and a polymer containing: at least one hydrophobic monomer selected from nhexyl(meth)acrylate, n-octyl(meth)acrylate, octyl(meth)acrylamide, lauryl(meth)acrylate, lauryl(meth)acrylamide, myristyl(meth)acrylate, myristyl(meth)acrylamide, pentadecyl(meth)acrylate, pentadecyl(meth)acrylamide, cetyl(meth)acrylate, cetyl(meth)acrylamide, oleyl(meth)acrylate, oleyl(meth)acrylamide, erucyl(meth)acrylate, erucyl(meth)acrylamide and combinations of these compounds; and at least one hydrophilic monomer selected from acrylate, acrylic acid salts, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid salts, and combinations of these compounds;

(b) creating at least one cavity in the subterranean formation under the action of the treatment fluid; and (c) allowing the fluid to reach a second viscosity greater than the first viscosity. In one embodiment, the method further includes creating at least one cavity in the subterranean formation under the action of the treatment fluid after said fluid reaches a second viscosity.

In another embodiment, the method further comprises reducing the viscosity of the treatment fluid to a viscosity that is less than the second viscosity.

Optionally, the treatment fluid further comprises one or more additives. In one embodiment, the fluid contains one or more additives selected from corrosion inhibitors, iron control agents, clay stabilizers, calcium sulfate inhibitors, scale inhibitors, mutual solvents, non-emulsifiers, anti-sludge agents, and combinations of these additives. In one embodiment, the corrosion inhibitor is selected from alcohols (eg, acetylene); cationic compounds (eg quaternary ammonium salts, imidazolines and alkyl pyridines); and non-ionic compounds (for example, alcohol ethoxylates). Suitable aqueous acid solutions include acids compatible with the polymers of the present invention for use in the acidizing process. In one embodiment, the aqueous acid is selected from hydrochloric acid, hydrofluoric acid, formic acid, acetic acid, sulfamic acid, and combinations of these acids. In one embodiment, the treatment fluid contains acid in an amount of up to 30% by weight, based on the total weight of the fluid.

The compositions of the present invention can also be used to limit or prevent pump damage during surface transport of proppant. During surface transport, proppant (eg sand) can settle causing damage to the pump. Maintaining sand production is necessary to produce oil at cost-effective rates. If there is mechanical damage to the wellbore or pump due to sand, a reconstruction is required. The tubing is retrieved and the well is thoroughly de-sanded using a mechanical bailer, pump-to-surface machine, jet pump, foam treatment, or other techniques prior to re-installation. Oil production resumes after the pump is reinstalled.

In one embodiment, a method for suspending and transporting proppant at a surface (e.g., above ground level) includes the step of mixing an aqueous fluid and proppant and transporting the resulting combination with at least one pump, said fluid containing a polymer containing at least one hydrophobic monomer selected from n-hexyl(meth)acrylate, n-octyl(meth)acrylate, octyl(meth)acrylamide, lauryl(meth)acrylamide, lauryl(meth)acrylamide, myristyl(meth)acrylate, myristyl(meth )acrylamide, pentadecyl(meth)acry

- 14 043013 lata, pentadecyl (meth) acrylamide, cetyl (meth) acrylate, cetyl (meth) acrylamide, oleyl (meth) acrylate, oleyl (meth) acrylamide, erucyl (meth) acrylate, erucyl (meth) acrylamide and combinations of these compounds ;

and at least one hydrophilic monomer selected from acrylate, acrylic acid salts, acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid salts, and combinations of these compounds.

The compositions of the present invention may also be used in gravel filling methods. Some oil and gas wells end up in loose formations containing loose particles and sand. When fluids are produced from such wells, loose particles and sand can migrate into the produced fluids and can damage equipment such as electric submersible pumps (ESPs) and other systems. For this reason, the completion of such wells may require sand screens to control the sand. For hydrocarbon wells, especially horizontal wells, the completion includes a screen section with a perforated inner tube and a screen cap. The purpose of the filter is to block the flow of dispersed particles into the interior of the production tubing string.

The gravel backfilling operation is one way to reduce particulate matter before it reaches the sand screen. In a graveling operation, gravel (eg, sand) is filled into the annulus around the sand screen. Gravel is a material in the form of particles of a certain size, such as graded sand or proppant. When packed around the sand screen into the annulus, the gravel acts as a filter, keeping any particles and sand from the formation from entering the sand screen with the produced fluids. The backfilled gravel also provides the reservoir with a stabilizing force that can prevent annulus compression. In general, gravel packing is used to stabilize the formation and maintain well productivity. Gravel backfilling is used in combination with hydraulic fracturing, but at much lower pressures.

In one embodiment, the gravel filling method includes the step of transporting a fluid with at least one pump and underground gravel filling, said fluid comprising a polymer containing at least one hydrophobic monomer selected from n-hexyl(meth)acrylate, n-octyl(meth)acrylate, octyl(meth)acrylamide, lauryl(meth)acrylate, lauryl(meth)acrylamide, myristyl(meth)acrylate, myristyl(meth)acrylamide, pentadecyl(meth)acrylate, pentadecyl(meth)acrylamide, cetyl (meth) acrylate, cetyl (meth) acrylamide, oleyl (meth) acrylate, oleyl (meth) acrylamide, erucyl (meth) acrylate, erucyl (meth) acrylamide and combinations of these compounds; and at least one hydrophilic monomer selected from acrylate, acrylic acid salts, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid salts, and combinations of these compounds.

When discussing specific implementation options, the present description is illustrative only and is not restrictive.

Many variants of the present description will be clear to a person skilled in the art after reading the present description.

Unless otherwise indicated, all technical and scientific terms used in the present description have the same meanings that are usually understood by specialists in the field of technology to which the description relates.

In the description and in the claims, terms in the singular include an indication of the plural, unless the context clearly dictates otherwise.

In the present description, unless otherwise indicated, the term approximately or approximately means the acceptable error of a particular value, as determined by an average person skilled in the art, which depends, in particular, on how the specified value was measured or determined. In some embodiments, the term about or approximately means within 1, 2, 3, or 4 standard deviations. In some embodiments, the term about or approximately means within 50%, 20%, 15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5% or 0.05% of the given value or range.

It should also be understood that any specified numerical range must include all of its subranges. For example, the range 1 to 10 must include all subranges between and inclusive of the specified minimum value of 1 and the specified maximum value of 10; that is, having a minimum value equal to or greater than 1 and a maximum value equal to or less than 10. Since the numerical ranges described are continuous, they include every value between the minimum and maximum values. Unless otherwise noted, the various numerical ranges given in this specification are approximate. Hereinafter, the present invention will be described with reference to the following examples. The following examples are illustrative only and are not meant to be limiting.

Example 1 - Synthesis of an associative polymer (PPS) (polyacrylamide/AMPS/LMAM 2000000 g/mol).

29.3 g 30% SDS solution, 89.03 g distilled water, and 1.66 g lauryl methacrylamide monomer

- 15 043013 (LMAM) was placed in a 500 ml round bottom flask at room temperature (20°C). The mixture was stirred with a magnetic stir bar for 6 hours until a clear micellar solution was obtained. 32.9 g of the micellar solution thus obtained, 7.53 g of water, 40.7 g of acrylamide (aqueous solution of 50% by mass), 32 g of AMPS (aqueous solution of 51% by mass), 0.454 g of Rhodixan A 1 (solution in ethanol 1.0% by weight) and 6.00 g of ammonium persulfate (an aqueous solution of 0.67% by weight) were placed in a 250 ml round bottom flask at room temperature (20°C). The resulting mixture was degassed by purging with nitrogen for 20 min. 1.5 g of sodium formaldehyde sulfoxylate in the form of an aqueous solution of 0.13% by weight was added to the resulting medium at one time. The resulting mixture was degassed by purging with nitrogen for 15 min. Left for the polymerization reaction with stirring for 16 h at room temperature (20°C).

Example 2 Viscosity of Hydration.

The PPS polymer powder prepared in Example 1 was added to a 0.3% choline chloride solution, mixed in a Waring mixer at high shear (10,000 rpm) for 3 minutes, then centrifuged to remove trapped bubbles. Viscosity was measured using an Ofite 1100 instrument. Typically, the viscosity of 0.3% polymer was 200-1000 cps at room temperature (25° C.) and 100 s' ¹ .

Example 3 - Viscosity test for proppant slurry.

The PPS polymer powder prepared in Example 1 was added to a 0.3% choline chloride solution, mixed in a Waring mixer at high shear (10,000 rpm) for 3 minutes, then centrifuged to remove trapped bubbles. A rheological test was performed immediately after centrifugation using an OFITE 1100 viscometer at 400 psi (2758 kPa). Carried out a linear change in the shear rate of 100, 75, 50 and 25 s - ¹ after reaching the desired temperature. The temperature was raised in steps from 80°F (27°C) to 425°F (218°C). In general, polymer solutions with a viscosity greater than 50 centipoise are capable of suspending sand.

Example 4 Sand Suspension Tests.

The sand settling test was carried out in a solution of 0.3% polymer powder prepared in Example 1 (PPS) in fresh water. 400 g of fluid and 250 g of sand were well mixed and placed in an oven at 180°F (82°C). The sand remained well suspended after 3 hours and after 24 hours.

For comparison, 0.42% guar powder was dispersed in fresh water.

400 g of guar fluid and 250 g of sand were mixed and heated to 65°C.

Sand separation was measured after 1 hour, 3 hours and 24 hours. After 3 hours at 65° C., approximately 50% sand settled out of the guar solution compared to no observed separation in the 0.3% PPS polymer solution. After 24 hours at 65° C., almost all of the sand had settled out of the guar compared to no sand settling for the PPS polymer solution.

Example 5 Viscosity reduction using a thinner.

0.1% ammonium persulfate (APS) was added to the 0.3% PPS polymer solution obtained in Example 3, which was then mixed and centrifuged. Rheological testing was performed immediately after centrifugation using an OFITE 1100 viscometer at 400 psi at 250°F (121°C) and a shear rate of 100 s ^-1 . The viscosity decreased significantly to close to 0 centipoise.

The essence of the present invention has been described with reference to certain details of specific embodiments of the present invention. Such details are not intended to be construed as limiting the subject matter of the invention, except and to the extent that they are included in the appended claims.

Therefore, the exemplary embodiments described are well adapted to achieve the purposes and advantages both indicated and inherent in them. The specific embodiments described above are illustrative only, as the exemplary embodiments described may be modified and practiced differently, but in an equivalent manner that would be understood by one of ordinary skill in the art having read the present disclosure. In addition, the construction or design details shown herein are not intended to be limiting in any way other than those described in the claims below. Therefore, it is obvious that the above-described specific illustrative implementation options can be changed, combined or modified, and all of these options are considered to be within the scope and spirit of the described examples of implementation options. The described illustrative examples of implementations can be practiced in the absence of any element not specifically described in this application and/or an optional element described in this application. Although compositions and methods are described in terms of comprising, containing, or including various components or steps, compositions and methods may also consist essentially of or consist of various components, materials, and steps. In the present description, the term consisting essentially of should be considered as meaning including the listed components, substances or steps, and such additional components, substances or steps that do not significantly affect the basic or new properties of the composition or method. In some embodiments, a composition according to embodiments of the present invention, which consists essentially of these

- 16 043013 components or substances, does not include any additional components or substances that change the basic and new properties of the composition. In the event of any conflict in the use of a word or term in this specification and in one or more patents or other documents that may be incorporated into this specification by reference, definitions consistent with this specification should be adopted.

Claims (15)

1. A method for hydraulically fracturing a subterranean formation, comprising the step of injecting an aqueous fracturing fluid into at least a portion of the subterranean formation at a pressure sufficient to fracture the formation, said fracturing fluid comprising an aqueous proppant slurry composition comprising water and a polymer , containing: at least one hydrophobic monomer selected from the group consisting of nhexyl(meth)acrylate, n-octyl(meth)acrylate, octyl(meth)acrylamide, lauryl(meth)acrylate, lauryl(meth)acrylamide, myristyl(meth)acrylate , myristyl(meth)acrylamide, pentadecyl(meth)acrylate, pentadecyl(meth)acrylamide, cetyl(meth)acrylate, cetyl(meth)acrylamide, oleyl(meth)acrylate, oleyl(meth)acryl mide, erucyl(meth)acrylate, erucyl(meth)acrylamide and combinations thereof; and at least one hydrophilic monomer selected from the group consisting of acrylate, acrylic acid salts, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid salts, and combinations thereof, said polymer being a sequential copolymer containing blocks of hydrophobic monomers of essentially the same size, and at the same time, before being added to the specified aqueous composition, the specified polymer is in the form of a powder containing particles ranging in size from 5 μm to 400 μm, while the specified fluid contains at least a portion of the solid particles before injection and/or it is brought into contact with at least a portion of the solid particles in the subterranean formation after injection, wherein said copolymer is associated with at least a portion of the solid particles to act both as a dispersing and stabilizing agent for the dispersion of said particles and as a fluid loss control agent. 2. The method according to claim 1, characterized in that said polymer contains hydrophilic monomers in a total amount of from 50 wt.% to 99.9 wt.% relative to the weight of the polymer. 3. The method according to claim 1, characterized in that said polymer contains hydrophobic monomers in a total amount of from 0.01 wt.% to 50 wt.% relative to the weight of the polymer. 4. The method according to claim 1, characterized in that the terminal position of the polymer chain contains a functional group thiocarbonylthio. 5. The method according to claim 1, characterized in that the polymer has a molecular weight of from 10,000 g/mol to 20,000,000 g/mol. 6. The method of claim 1, wherein the aqueous fracturing fluid comprises a polymer in an amount in the range of 0.001 wt% to 10 wt% relative to the total weight of the aqueous fracturing fluid. 7. The method of claim 1, wherein the aqueous fracturing fluid further comprises a surfactant. 8. The method according to claim 7, characterized in that said surfactant is present in an amount in the range from 0.001 wt.% to 50 wt.% relative to the weight of the polymer. 9. The method of claim 1, wherein at least a portion of the solids contains a proppant. 10. The method according to claim 9, characterized in that the proppant is contained in an amount in the range from 20 wt.% to 60 wt.% relative to the total weight of the aqueous fracturing fluid. 11. The method of claim 9, wherein said aqueous fracturing fluid suspends the proppant at a temperature of 68°F (about 20°C) to 350°F (about 177°C). 12. The method of claim 1, further comprising injecting a breaker into at least a portion of the subterranean formation. 13. The method according to claim 12, characterized in that said diluent is selected from the group consisting of peroxides, persulfates, peracids, bromates, chlorates, chlorites, and combinations of these compounds. 14. The method of claim 1, wherein the aqueous fracturing fluid is selected from the group consisting of fresh water, sea water, salt solutions, brine, produced water, recycled water, industrial waste water, waste water associated with oil production, and combinations of these options. 15. A method for suspending and transporting proppant, including mixing an aqueous fluid and proppant and transporting the resulting combination using at least one - 17 043013 pump, and the specified fluid contains a polymer in an amount in the range from 0.001 wt.% to 10 wt.% relative to the total weight of the combination, and the specified polymer contains at least one hydrophobic monomer selected from the group consisting of n-hexyl (meth)acrylate, n-octyl(meth)acrylate, octyl(meth)acrylamide, lauryl(meth)acrylate, lauryl(meth)acrylamide, myristyl(meth)acrylate, myristyl(meth)acrylamide, pentadecyl(meth)acrylate, pentadecyl (meth)acrylamide, cetyl(meth)acrylate, cetyl(meth)acrylamide, oleyl(meth)acrylate, oleyl(meth)acrylamide, erucyl(meth)acrylate, erucyl(meth)acrylamide, and combinations thereof; and at least one hydrophilic monomer selected from the group consisting of acrylate, acrylic acid salts, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid salts, and combinations thereof, said polymer being a sequential copolymer containing blocks of hydrophobic monomers of essentially the same size.