Patent Description:
During drilling operations, whether for oil wells or in construction, a drilling fluid circulates between the earth's surface and the bottom of the borehole. The drilling fluid is usually injected inside the drill rod. It then passes through the drill bit before returning to the earth's surface through a ring. A gap between the drill rod and a tube surrounding the drill rod prevents rock and soil debris from rising, and the drilling fluid can then be recovered, treated, and reused. Drilling fluid has several critical roles in drilling operations, including lubrication and cooling of the drill bit, or removal of generated rock chips.

To enable the drilling fluid to perform these roles, a weighting agent (insoluble particles such as baryte or hematite) or a rheology modifier may be added to the fluid. This rheology modifier makes it possible to ensure the suspension of the weighting agent and for the waste material to be removed by making the drilling fluid more viscous. By allowing the suspension of the weighting agent, the density of the fluid is increased, which prevents the well from collapsing onto itself or the drilling fluid from seeping into the walls of the well. These two phenomena are due to a pressure difference between the drilling fluid and the earth. The rheological modifier helps compensate for this pressure difference. Choosing the rheology modifier is therefore very important, especially since it is subject to many constraints. These stresses may be mechanical with a risk of degradation due to shearing during the passage of the drilling fluid through the rod and into the drill bit. They may also be physicochemical due to high temperatures, extreme pH, or the presence of free radicals, especially in deep drilling operations. Furthermore, they may be due to ionic interactions when the injection fluid is highly charged with salts.

Polyacrylamides have long been used as rheology modifiers in several fields. The rheological modification properties of these polymers are highly dependent on their molecular weight. <CIT> teaches a drilling fluid comprising an amphoteric terpolymer comprising less than 75mol% of sulfonic acid monomer.

In general, in the case of polyacrylamides, having anionic charges of carboxylate type, multivalent salts will interact with the ionic groups of the polymer causing a contraction of the chains, even a precipitation of the polymer, thus reducing the thickening effect of the latter. When drilling at high temperature and/or pH, acrylamide may hydrolyze rapidly, causing an acceleration of the phenomenon described above and thus participating in the reduction of viscosity. Finally, the combination of reducing species and oxygen may lead to the formation of free radicals that will degrade the molecular weight of the rheology modifying polymer and thus reduce its ability to generate viscosity.

Associative monomers that are known to be temperature- and salt-resistant may be incorporated into the rheology modifying polymer. Associative monomers generally have a chemical function that allows them to react and be integrated into a polymer and a long chain with a rather hydrophobic character generally having between <NUM> and <NUM> carbon atoms. The hydrophobic chains will, depending on the physicochemical conditions of the drilling fluid, interact and form a reversible physical network. This network allows to improve the viscosity while keeping good resistance to the various constraints seen above.

<CIT> and <CIT> describe the use of associative amphoteric polymers as thickeners in the drilling field.

Although these polymers have better resistance to temperature and salts than conventional polymers, the risk of degradation and lack of stability remains significant, especially at temperatures above <NUM> and/or at salinities above <NUM>/L.

<CIT> therefore proposes an alternative by using an associative amphoteric polymer in combination with a surfactant as a thickener for a fracturing fluid. The surfactant is usually added during the preparation of the fracturing fluid.

<CIT> and <CIT> describe a fracturing fluid containing a polymer that may include a small amount of sulfonic acid monomer.

<CIT> describes a fracturing fluid comprising a polymer acrylamide (<NUM>-<NUM> parts by weight), acrylic acid (<NUM>-<NUM> parts by weight), ATBS (<NUM>-<NUM> parts by weight; ATBS = <NUM>-acrylamido-<NUM>-methylpropane sulfonic acid), rigid monomer (<NUM>-<NUM> parts by weight) and hydrophobic monomer (<NUM>-<NUM> parts by weight).

<CIT> describes a fracturing fluid comprising a polymer of sodium acrylate (<NUM>-<NUM> wt%), acrylamide (<NUM>-<NUM> wt%), carboxylic acid monomer (<NUM>-<NUM> wt%), anionic functional monomer (<NUM>-<NUM> wt%), cationic functional monomer (<NUM>-<NUM> wt%).

Many studies exist on the synergistic effect between associative amphoteric polymers and surfactants, such as the document, "<NPL>. Surfactants increase the lifetime of hydrophobic interactions between polymer chains, thus improving the viscosity of the solution in which they are found. Surfactants may be added during the preparation of polymers, especially by emulsion polymerization, or during the preparation of drilling fluids.

Despite all the progress that has been made in the field of rheology modifiers for drilling, there are still unmet needs in this area today. As drilling is done at greater and greater depths, in increasingly extreme conditions, whether in terms of temperature, pH, presence of free radicals or salinity (large quantity of salts), there is still a need for rheology modifiers that can be effective regardless of the underground conditions.

Surprisingly, the applicant discovered that the conditions preparation of the rheology modifier and its monomeric composition improve its performance and resistance to extreme conditions (high temperature, pH, free radicals, high salinity).

The preparation of the polymers of the invention is part of a general principle of improving the performance of products and more particularly of improving the rheology modifying power. The improved performance of the polymers according to the invention makes it possible to reduce the amount of product needed for the application, which therefore implies a reduction in the release of greenhouse gases such as CO<NUM> associated with the manufacture and use of synthetic polymers.

This invention relates to a water-soluble associative amphoteric polymer of at least one monomer derived from a sulfonic acid and/or one of its salts and at least one associative cationic monomer of formula (I):
<CHM>.

This invention also relates to a method for preparing said water-soluble associative amphoteric polymer.

This invention also relates to the use of said water-soluble associative amphoteric polymer as a rheology modifier and/or suspending agent.

This invention also relates to a fluid, advantageously a drilling fluid, comprising said water-soluble associative amphoteric polymer.

Finally, this invention also relates to the use of a subterranean drilling or treatment fluid comprising said water-soluble associative amphoteric polymer for subterranean uses, particularly in the fields of drilling, construction, and geothermal energy.

According to this invention, the term "polymer" refers to a copolymer of at least two different ionic monomers of different ionicity. It is thus a copolymer of (i) at least one anionic monomer, (ii) at least one cationic monomer, (iii) optionally at least one non-ionic monomer and, (iv) optionally at least one zwitterionic monomer.

By water-soluble polymer, we mean a polymer which gives an aqueous solution without insoluble particles when dissolved under agitation for <NUM> hours at <NUM> and with a concentration of <NUM>. l-<NUM> in deionized water.

By underground use, we mean all uses that take place under the surface of the earth. For example, and without limitation, a subsurface use may be for drilling an oil well, an enhanced oil recovery process by sweeping a subsurface formation with a polymer solution, a hydraulic fracturing operation, oil well water permeability modification operations such as conformance operations, or for building or tunneling construction.

The invention is based on a specific combination of monomers and the absence of surfactants during their polymerization.

Preferably, the monomer derived from a sulfonic acid and/or one of its salts has a single ethylenic unsaturation (double bond between two carbon atoms).

The monomer derived from a sulfonic acid is advantageously selected from the group consisting of vinyl sulfonic acids, preferably from <NUM>-acrylamido-<NUM>-methylpropane sulfonic acid (ATBS), <NUM>-methacrylamido-<NUM>-methylpropane sulfonic acid, styrene sulfonic acid, allyl ether sulfonic acid derivatives or <NUM>-allyloxy-<NUM>-hydroxypropane sulfonic acid. Preferably, the monomer derived from a sulfonic acid is <NUM>-acrylamido-<NUM>-methylpropane sulfonic acid. In one particular embodiment of the invention, the monomer derived from a sulfonic acid may be salified.

By salified, we mean that the acid function of the sulfonic acid group is replaced by a salt neutralizing the negative charge of the sulfonate function. In other words, the non-salified form corresponds to the acidic form of the monomer, for example -S(=O)<NUM>OH in the case of the sulfonic acid function, while the neutralized form of the monomer corresponds to the -S(=O)<NUM>-O-A+ form, A+ corresponding to a salt. The neutralization of the sulfonic acid function may be partial or total.

The salified form corresponds advantageously to the salts of alkali metals (Li, Na, K. ), alkaline earth metals (Ca, Mg. ) or ammonium (for example, the ammonium ion or the tertiary ammonium). The preferred salts are sodium salts.

Salification may be done before, during or after polymerization.

In one particular embodiment of the invention, the sulfonic acid monomer comprises between <NUM>% and <NUM>% salified form, for example between <NUM>% and <NUM>% or between <NUM>% and <NUM>%.

In general, the terms "between X and Y" and "from X to Y" include the terminals X and Y. In one particular embodiment of the invention, the monomer derived from a sulfonic acid is <NUM>-acrylamido-<NUM>-methylpropane sulfonic acid in its hydrated form. The hydrated form of <NUM>-acrylamido-<NUM>-methylpropane sulfonic acid is one particular form of <NUM>-acrylamido-<NUM>-methylpropane sulfonic acid obtainable by controlled crystallization of <NUM>-acrylamido-<NUM>-methylpropane sulfonic acid monomer. <CIT> describes how to obtain the hydrated form of <NUM>-acrylamido-<NUM>-methylpropane sulfonic acid.

Generally, the amount of monomer derived from a sulfonic acid in the water-soluble associative amphoteric polymer is between <NUM> mol% and <NUM> mol%. It is generally at least <NUM> mol%, preferably at least <NUM> mol%, more preferably at least <NUM> mol%, more preferably at least <NUM> mol%, even more preferably at least <NUM> mol%. It may therefore be between <NUM> and <NUM> mol%.

The selection of the associative monomer is also crucial to the invention. Thus, the associative monomer is a cationic monomer of formula (I) above.

As already indicated, the R<NUM> group of formula (I) is an alkyl, arylene-alkyl or aryl-alkyl chain having from <NUM> to <NUM> carbon atoms, preferably between <NUM> and <NUM> carbon atoms, and even more preferably between <NUM> and <NUM> carbon atoms.

In general, the number of carbon atoms in a group of at least <NUM> carbon atoms is a number average. For example, a monomer of formula (I) in which the R<NUM> group is C16 corresponds to a mixture of monomers of formula (I), with, on average in number, R<NUM> being C16.

In one particular embodiment of the invention, the cationic associative monomer is selected from derivatives of formula (I), wherein R<NUM> is an alkyl, arylene-alkyl or aryl-alkyl chain having <NUM> to <NUM> carbon atoms.

In one particular embodiment of the invention, the cationic associative monomer is selected from derivatives of formula (I), wherein R<NUM> is an alkyl, arylene-alkyl or aryl-alkyl chain having <NUM> carbon atoms.

In one preferred embodiment of the invention, the R<NUM> group of formula (I) is a linear or branched alkyl chain, more preferably a linear alkyl chain.

Typically, the amount of associative cationic monomers is between <NUM> mol% and <NUM> mol%. It is generally lower than <NUM> mol%, preferably lower than <NUM> mol%, more preferably lower than <NUM> mol%, even more preferably lower than <NUM> mol%.

The applicant has found that improved performance is achieved with the water-soluble associative amphoteric polymer of the invention due to the selection of the component monomers combined with the absence of surfactants (oil-in-water or water-in-oil) during the polymerization of selected monomers.

According to IUPAC, a surfactant is a substance that decreases the surface tension of the medium in which it is present, and/or the interfacial tension with other phases, and thus is absorbed at the liquid/vapor interface and/or other interfaces.

The water-soluble associative amphoteric polymer of the invention may be obtained according to all the polymerization techniques well known to the person skilled in the art, provided that the polymerization is carried out in the absence of surfactant.

This may include any of the following techniques: solution polymerization; gel polymerization; solvent precipitation polymerization; reactive extrusion polymerization; brine precipitation polymerization.

Thus, the water-soluble associative amphoteric polymer is not obtained by emulsion, direct or reverse polymerization, as these techniques involve the presence of an oil-in-water or water-in-oil surfactant.

The polymerization is usually a free radical polymerization. In the term free radical polymerization, we include free radical polymerization using UV, azo, redox, or thermal initiators as well as controlled radical polymerization (CRP) or matrix polymerization techniques.

The polymerization initiators advantageously used may be any compounds that dissociate into radicals under the polymerization conditions, for example: organic peroxides, hydroperoxides, hydrogen peroxide, persulfates, azo compounds, and redox catalysts. The use of water-soluble initiators is preferred. In some cases, it is advantageous to use mixtures of several polymerization initiators, for example, mixtures of redox catalysts and azo compounds.

In one particular embodiment of the invention, the method for preparing the water-soluble associative amphoteric polymer may comprise a polymer drying step such as spray drying, spray drying and granulation, drum drying, electromagnetic radiation drying (microwave, high frequency) or even fluidized bed drying.

In one particular embodiment of the invention, the polymer is obtained by gel polymerization. The gel polymerization is advantageously followed by drying and grinding to obtain polymer particles of the desired medium size and optionally by sieving to obtain polymer particles with the correct particle size.

In one particular embodiment of the invention, the polymer is obtained by precipitation polymerization.

The solvents that may be used for precipitation polymerization are advantageously polar solvents, preferably water, an alcohol or a ketone, more preferably selected from the group comprising: water, methanol, ethanol, <NUM>-propanol, <NUM>-propanol, <NUM>-methyl-<NUM>-propanol, <NUM>-butanol, <NUM>-butanol, dimethylketone, diethylketone, pentan-<NUM>-one, butanone, tetrahydropyran, tetrahydrofuran, <NUM>-methyltetrahydrofuran, <NUM>,<NUM>-dioxane, <NUM>,<NUM>-dioxane, ammonium sulfate brine. The polar solvent mixture is preferably a protic (proton donors) solvent mixture.

The water-soluble associative amphoteric polymer of the invention may also comprise at least one other anionic monomer and/or at least one other cationic monomer and/or at least one nonionic monomer and/or at least one zwitterionic monomer. Preferably, these monomers have a single ethylenic unsaturation (double bond between two carbon atoms). The other anionic monomer(s) that may be used in the context of the invention may be selected from a broad group. These monomers may have a vinyl function, in particular acrylic, maleic, fumaric, malonic, itaconic, or allylic. They may also contain a carboxylate, phosphonate, phosphate, sulfate, or other anionically charged group. The anionic monomer may be in acid form or in the form of an alkaline earth metal salt, alkali metal salt or ammonium salt. Examples of suitable monomers include acrylic acid; methacrylic acid; itaconic acid; crotonic acid; maleic acid; fumaric acid; strong acid monomers having for example a phosphonic acid function, such as vinyl phosphonic acid, allyl phosphonic acid; and water-soluble salts of these monomers such as their alkali metal, alkaline earth metal, or ammonium salts.

Preferably, the water-soluble associative amphoteric polymer of the invention comprises not more than <NUM> mol% of anionic monomers not derived from sulfonic acid, preferably not more than <NUM> mol%, more preferably not more than <NUM> mol%, more preferably not more than <NUM> mol%, more preferably not more than <NUM> mol%, still more preferably not more than <NUM> mol%.

In one preferred embodiment of the invention, the water-soluble associative amphoteric polymer of the invention does not comprise any other anionic monomers than the sulfonic acid derivative and/or one of its salts.

The cationic monomer(s) that may be used in the context of the invention may be of the vinyl type, in particular of the acrylamide, acrylic, allylic or maleic type possessing an ammonium (advantageously quaternary ammonium) function. We may specifically mention without limitation, quaternized or salified dimethyl aminoethyl acrylate (ADAME); quaternized or salified dimethyl aminoethyl methacrylate (MADAME); dimethyl diallyl ammonium chloride (DADMAC); acrylamido propyl trimethyl ammonium chloride (APTAC); and methacrylamido propyl trimethyl ammonium chloride (MAPTAC).

Preferably, the water-soluble associative amphoteric polymer of the invention comprises not more than <NUM> mol% of other cationic monomers than the associative cationic monomer of formula (I) preferably not more than <NUM> mol%, more preferably not more than <NUM> mol%, more preferably not more than <NUM> mol%, more preferably not more than <NUM> mol%, even more preferably not more than <NUM> mol%.

In one preferred embodiment of the invention, the water-soluble associative amphoteric polymer of the invention does not comprise any cationic monomers other than the cationic associative monomer of formula (I) previously described.

The non-ionic monomer(s) suitable for use in the invention may be selected from the group consisting of water-soluble vinyl monomers, and particularly acrylamide; N-isopropylacrylamide; N,N-dimethylacrylamide; N-vinylformamide; acryloyl morpholine; N,N-diethyl acrylamide; N-tert-butyl acrylamide; N-tert-octylacrylamide; N-vinylpyrrolidone; N-vinyl caprolactam; N-vinyl imidazole, hydroxyethyl methacrylamide, hydroxypropyl acrylate, isoprenol and diacetone acrylamide.

Generally, the water-soluble associative amphoteric polymer of the invention comprises not more than <NUM> mol% of non-ionic monomers, preferably not more than <NUM> mol%, more preferably not more than <NUM> mol%, more preferably not more than <NUM> mol%, more preferably not more than <NUM> mol%, still more preferably not more than <NUM> mol%.

In one preferred embodiment of the invention, the water-soluble associative amphoteric polymer of the invention does not comprise a non-ionic monomer.

The water-soluble associative amphoteric polymer of the invention may also contain zwitterionic monomer(s) and/or associative monomers different from the associative cationic monomers of formula (I) previously described.

The quantities of the various monomer(s) will be adjusted by the person skilled in the art so as not to exceed <NUM> mol% when preparing the water-soluble polymers according to the invention.

In one preferred embodiment of the invention, the water-soluble associative amphoteric polymer of the invention is a terpolymer, i.e., a polymer consisting of <NUM> types of monomers, advantageously a polymer consisting of <NUM> distinct monomers.

In one preferred embodiment of the invention, the water-soluble associative amphoteric polymer of the invention is a polymer consisting of two types of monomers, i.e., a polymer of at least one sulfonic acid and/or a salt thereof and at least one associative cationic monomer of formula (I).

In one preferred embodiment of the invention, the water-soluble associative amphoteric polymer of the invention consists of at least one non-ionic monomer (advantageously acrylamide), acrylamido-<NUM>-methyl-<NUM>-propanesulfonic acid and/or one of its salts and at least one associative monomer derived from the formula (I).

In one preferred embodiment of the invention, the water-soluble associative amphoteric polymer of the invention consists of acrylamido-<NUM>-methyl-<NUM>-propanesulfonic acid and/or one of its salts and at least one associative monomer derived from the formula (I).

In another preferred embodiment of the invention, the water-soluble associative amphoteric polymer of the invention is a polymer consisting of <NUM>-acrylamido-<NUM>-methylpropane sulfonic acid and/or one of its salts and at least one associative monomer derived from formula (I), wherein R<NUM> is an alkyl, arylene-alkyl or aryl-alkyl chain having <NUM> to <NUM> carbon atoms.

In one preferred embodiment of the invention, the water-soluble associative amphoteric polymer of the invention is a polymer consisting of <NUM>-acrylamido-<NUM>-methylpropane sulfonic acid and/or one of its salts and at least one associative monomer derived from formula (I), wherein R<NUM> is an alkyl, arylene-alkyl or aryl-alkyl chain having <NUM> to <NUM> carbon atoms, preferably <NUM> to <NUM> carbon atoms.

In one preferred embodiment of the invention, the water-soluble associative amphoteric polymer of the invention is a polymer consisting of <NUM>-acrylamido-<NUM>-methylpropane sulfonic acid and/or one of its salts and at least one associative monomer derived from formula (I), wherein R<NUM> is an alkyl, arylene-alkyl or aryl-alkyl chain having <NUM> to <NUM> carbon atoms. In one preferred embodiment of the invention, the water-soluble associative amphoteric polymer of the invention is a polymer consisting of <NUM>-acrylamido-<NUM>-methylpropane sulfonic acid and/or one of its salts and at least one associative monomer derived from formula (I), wherein R<NUM> is an alkyl, arylene-alkyl or aryl-alkyl chain having <NUM> carbons.

In one preferred embodiment of the invention, the water-soluble associative amphoteric polymer of the invention is a polymer consisting of <NUM>-acrylamido-<NUM>-methylpropane sulfonic acid and/or one of its salts and at least one associative monomer derived from formula (I), wherein R<NUM> is an alkyl, arylene-alkyl or aryl-alkyl chain having <NUM> carbons.

In one preferred embodiment of the invention, the water-soluble associative amphoteric polymer of the invention is a polymer consisting of <NUM>-acrylamido-<NUM>-methylpropane sulfonic acid and/or one of its salts and at least one associative monomer derived from formula (I), where R<NUM> is a linear or branched alkyl chain, more preferably a linear alkyl chain.

According to the invention, the water-soluble associative amphoteric polymer may have a linear, branched, crosslinked, star-shaped, or comb-shaped structure. These structures may be obtained, according to the general knowledge of one skilled in the art, for example by selection of the initiator, the transfer agent, the polymerization technique such as controlled radical polymerization known as RAFT (reversible addition-fragmentation chain transfer), NMP (Nitroxide Mediated Polymerization) or ATRP (Atom Transfer Radical Polymerization), the incorporation of structural monomers, or the concentration.

The water-soluble associative amphoteric polymer may also be structured by at least one branching agent, which may advantageously be selected from the group comprising polyethylenically unsaturated monomers (having at least two unsaturated functions), such as vinyl functions, in particular allyl, acrylic and epoxy functions. Examples include methylene bis acrylamide (MBA), triallylamine, tetraallylammonium chloride, or macroinitiators such as polyperoxides, polyazoids, and polytransfer agents such as polymeric scavengers.

Generally, for a structured polymer, the amount of branching agent is advantageously between <NUM> and <NUM>% by weight with respect to the total mass of monomers constituting the water-soluble associative amphoteric polymer. More preferably, it is between <NUM> and <NUM>% by weight. The amount of branching agent is determined in relation to the weight of the monomers, it is not included in the percentages (molar or mass) of the monomers. Thus, when the water-soluble associative amphoteric polymer consists of two or three types of monomers, it may be structured.

When the water-soluble associative amphoteric polymer according to the invention comprises a branching agent, the water-soluble associative amphoteric polymer remains water-soluble. Those skilled in the art will know how to adjust the amount of branching agent, and possibly the amount of transfer agent to achieve this result.

In one particular embodiment of the invention, the water-soluble associative amphoteric polymer of the invention does not comprise a branching agent.

Generally, the water-soluble associative amphoteric polymer according to the invention has a weight-average molecular weight advantageously between <NUM> and <NUM> million g/mol, preferably greater than <NUM> million g/mol, more preferably greater than <NUM> million g/mol, even more preferably greater than <NUM> million g/mol, even more preferably greater than <NUM> million g/mol, even more preferably greater than <NUM> million g/mol. The molecular weight is the weight-average molecular weight. The water-soluble associative amphoteric polymer may also have a molecular weight between <NUM>,<NUM> and <NUM>,<NUM>/mol.

The molecular weight may be determined by the intrinsic viscosity of the polymer. The intrinsic viscosity may be measured by methods known to those skilled in the art and may in particular be calculated from the values of reduced viscosity for different concentrations by a graphical method consisting of plotting the values of reduced viscosity (on the y-axis ) as a function of the concentrations (on the x-axis) and by extrapolating the curve to zero concentration. The intrinsic viscosity value is read on the y-axis or using the least squares method. The molecular weight may then be determined by the Mark-Houwink equation: <MAT>.

According to this invention, the water-soluble associative amphoteric polymer may be in liquid (for example, in the form of an aqueous solution; it may be used in the form of a concentrated solution, or a dilute solution), gel or solid form when used. Preferably, the water-soluble associative amphoteric polymer according to this invention is in solid form and may be used as such.

The formation of solid particles of the water-soluble associative amphoteric polymer is a step known to those skilled in the art, who will be able to adapt and select the necessary technique depending on the polymerization. Examples include, but are not limited to, spray drying, spray granulation, drum drying, electromagnetic radiation drying (microwave, high frequency) or fluidized bed drying.

The particle size of water-soluble associative amphoteric polymer may vary depending on the polymerization process. Those skilled in the art will know how to adapt the polymer particle size to the application and will know how to adapt the polymer preparation process to produce particles with the desired size.

Generally, the size of the solid particles of water-soluble associative amphoteric polymer is advantageously between <NUM> and <NUM>, more advantageously between <NUM> and <NUM>, preferably between <NUM> and <NUM>, even more preferably between <NUM> and <NUM>. It may in particular be between <NUM> and <NUM>, or between <NUM> and <NUM>, or between <NUM> and <NUM>, or between <NUM> and <NUM>.

By way of example and without limitation, when the particles of water-soluble associative amphoteric polymer are obtained by precipitation polymerization in a solvent or in a brine, the size of the particles is then generally between <NUM> and <NUM>, preferably between <NUM> and <NUM>, even more preferably between <NUM> and <NUM>.

When the water-soluble associative amphoteric polymer particles are obtained by gel polymerization, the particle size depends on the post-treatment by drying, grinding and sieving, the particle size is generally between <NUM> and <NUM>, preferably between <NUM> and <NUM>, even more preferably between <NUM> and <NUM>.

Water-soluble associative amphoteric polymer particles may have a regular and spherical shape, like beads, or non-regular.

The term "size of the particles" denotes the average size, in number, of the particles of water-soluble associative amphoteric polymer. It corresponds to the most significant dimension, for example the diameter for spherical particles. It is measured with a laser measuring device using conventional techniques which are part of the knowledge of those skilled in the art. A Mastersizer type device from the Malvern company, for example, the MS2000, may be used for this purpose. This type of apparatus makes it possible to measure, by laser diffraction, the granulometric distribution of particles in liquid medium or in solid form, preferably in a polyphasic suspension.

In one particular embodiment according to this invention, the water-soluble associative amphoteric polymer may be in the form of a multiphase suspension of solid particles in a brine or salt solution, or in the form of a multiphase suspension of solid particles in an anhydrous oil, or in the form of a multiphase suspension of solid particles in an oil mixed with a brine or a salt solution.

This invention also relates to a method of preparing a water-soluble associative amphoteric polymer from at least one monomer derived from a sulfonic acid and/or a salt thereof and at least one cationic associative monomer of formula (I), described above, and polymerized in the absence of surfactants.

This invention also relates to a subterranean drilling or treatment fluid, comprising said water-soluble associative amphoteric polymer.

Spacer fluid is any liquid used to physically separate one liquid from another. By way of example and without limitation, spacer fluids may be used when changing the type of slurry or to separate slurry from cement during cementing operations. In changing the type of sludge, an oil-based fluid must be separated from a water-based fluid. In this case, the spacer fluid may be a base oil. In separating sludge from cement during cementing operations, a chemically treated water-based spacer fluid typically separates drilling sludge from cement slurry.

The amount of water-soluble associative amphoteric polymer present in the subterranean drilling or treatment fluid depends on many parameters (temperature, salinity, depth. It is generally between <NUM>% and <NUM>% by weight, preferably between <NUM>% and <NUM>% by weight, based on the weight of the subterranean drilling or treatment fluid. Those skilled in the art will know how to adjust this quantity according to the drilling or underground treatment conditions and the desired viscosity.

By brine, we mean a solution comprising water and organic or inorganic salts. The salts may be used to provide sufficient density to the subterranean drilling or treatment fluid, for example, to compensate for pressure during drilling or to reduce interactions between the subterranean drilling or treatment fluid and hydratable clays found underground. Salts may be selected for compatibility between different fluids used in subterranean drilling or treatment operations. For example, the drilling (or subterranean drilling or treatment) fluid and the completion/cleaning fluid may require the same or different phases. Salts may be used to adjust the density of fluids as needed.

The subterranean drilling or treatment fluid according to the invention may additionally and without limitation include other additives and chemicals that are commonly used in the relevant applications, including drilling. These additives may include, for example, diluents, gelling agents, shale inhibitors, pH buffers.

Other materials may be added to the subterranean drilling or treatment fluid to improve the composition thereof. Such other materials may include, for example: additives to reduce or control low temperature rheology or to provide diluent, additives to improve viscosity, additives to control high temperature pressure.

The subterranean drilling or treatment fluid according to the invention may include one or more surfactants.

In one particular embodiment of the invention, the subterranean drilling or treatment fluid according to the invention does not comprise a surfactant.

The water-soluble associative amphoteric polymer according to the invention may be used as a rheology modifier or a suspending agent for underground drilling and processing operations. These underground drilling and processing operations include, but are not limited to, civil construction drilling operations, geothermal drilling operations, oil drilling operations such as drilling new wells, stimulation treatments such as fracturing operations, completion operations and the process of enhanced oil recovery by sweeping a subsurface formation with a polymer solution, or operations to modify the water permeability of a subsurface formation such as conformation operations.

The water-soluble associative amphoteric polymer according to the invention is well-suited and may be used under all existing temperature conditions. It may be used, for example, at temperatures between <NUM> and <NUM>, or between <NUM> and <NUM>, or between <NUM> and <NUM>. Preferably, the temperature is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>, and even more preferably between <NUM> and <NUM>.

The water-soluble associative amphoteric polymer according to the invention is well-suited and may be used at a pH between <NUM> and <NUM>. It can be used, for example, at a pH between <NUM> and <NUM>, or between <NUM> and <NUM>, or between <NUM> and <NUM>, or between <NUM> and <NUM>. The pH depends on the polymer's field of application and in particular on the nature of the subterranean drilling or treatment fluid.

Thus, when the subterranean drilling or treatment fluid is seawater, brine, fresh water, mud, or spacer fluid for oil and gas or geothermal applications, such as, but not limited to, geothermal drilling operations, petroleum drilling operations such as drilling new wells, stimulation treatments such as fracturing operations, completion operations, and the improved process of recovering oil by sweeping a subterranean formation with a polymer solution, or operations to modify the water permeability of a subterranean formation such as conformation operations, the pH of the subterranean drilling or treatment fluid is generally between <NUM> and <NUM>, preferably between <NUM> and <NUM>, and even more preferably between <NUM> and <NUM>.

When the subterranean drilling or treatment fluid is a cement for construction applications, such as, but not limited to, civil construction operations, geothermal construction operations, or construction of new oil and gas wells, the pH of the subterranean drilling or treatment fluid is generally between <NUM> and <NUM>, preferably between <NUM> and <NUM> and even more preferably between <NUM> and <NUM>.

The water-soluble associative amphoteric polymer according to the invention is well-suited and may be used under all salinity conditions of the subterranean drilling or treatment fluid. It can be used for example for fluids with a salinity between <NUM>/L of salts and saturation of the fluid, preferably between <NUM>,<NUM>/L and saturation of the fluid, even more preferably between <NUM>,<NUM>/L and saturation of the fluid. The salts in the fluid may include monovalent salts, divalent salts, trivalent salts, and mixtures thereof. The water-soluble associative amphoteric polymer according to the invention may be dissolved in a mixer before use. As an example, and in a non-limiting way, such a mixer may be selected among reactors with agitators, loop reactors, static mixers, microreactors, and piston reactors. This may include a PSU (Polymer Slicing Unit) that both grinds and disperses the polymer in powder form into the dissolution water.

The water-soluble associative amphoteric polymer according to the invention may be added at one time, sequentially, discontinuously, or continuously during the preparation of the subterranean drilling or treatment fluid. It may also be an in-line injection.

The invention and the advantages thereof will be better understood from the following examples given to illustrate the invention, and not in a restrictive manner.

A list of abbreviations used in the following examples is given below:.

Polymer <NUM> (invention) - Polymer <NUM> is prepared using a <NUM>-liter double-walled reactor equipped with a distillation column, a pH probe, a thermometer, a powerful stirrer, a nitrogen injection nozzle, and an ammonia gas inlet. <NUM> of pure tertiobutanol (<NUM>-methyl-<NUM>-propane) and <NUM> of water are initially introduced into the reactor. <NUM> of acidic ATBS are then added with stirring. The monomer is then completely neutralized using a stream of ammonia gas that is passed through the suspension until the pH reaches <NUM>, at which point the introduction of ammonia is stopped. <NUM> of C16 (at a weight concentration of <NUM>% in water) and <NUM> of TAAC are then added. The solution is then degassed with nitrogen for one hour while the temperature is raised to <NUM>. When the temperature is stabilized at <NUM>, <NUM> of dibenzoyl peroxide is added to the solution to initiate the reaction and precipitate the formed polymer. Once the temperature has stopped rising, the solvent is vacuum evaporated to directly obtain a dry powder with a very small particle size of about <NUM>.

Polymer <NUM> (invention) - In a <NUM> beaker, <NUM> of ATBS-Na (at a concentration of <NUM>% by weight in water) and <NUM> of C16 are dissolved to obtain a content of about <NUM>% active ingredient. The solution is then stirred, cooled, and neutralized by adding caustic soda. The solution is then placed in a Dewar flask and degassed with a nitrogen stream to remove oxygen. The polymerization is initiated by a red/ox couple. The resulting gel is left in the Dewar's flask for <NUM> hours. The gel is then crushed and left to dry overnight in a furnace. A white powder is obtained and is ground again.

Polymer <NUM> (comparative example) - Traditionally, polymer <NUM> is prepared by reverse emulsion (water in oil, in the presence of surfactants) as described in <CIT>, with the composition described in Table <NUM> below.

Polymer <NUM> (comparative example) - The same process as that used for polymer <NUM> is applied, except that ATBS-Na is replaced by acrylic acid (at a concentration of <NUM>% by weight in water) which is neutralized with soda until the pH reaches <NUM>.

Polymer <NUM> (comparative example) - The same process as that used for polymer <NUM> is applied, in which C16 is replaced by stearyl acrylate.

Polymer <NUM> (invention) - The same process as that used for polymer <NUM> is applied, except that <NUM> of ATBS is used with <NUM> of AMD (<NUM>% by weight in water), <NUM> of C16 in <NUM> of pure tertiary butanol (<NUM>-methyl-<NUM>-propane) and <NUM> of water.

Polymer <NUM>' (comparative example) - The same process as that used for polymer <NUM> is applied, except that only <NUM> of ATBS is used with <NUM> of AMD (<NUM>% by weight in water), <NUM> of C16 in <NUM> of pure tertiary butanol (<NUM>-methyl-<NUM>-propane) and <NUM> of water.

Polymer <NUM> (comparative example) - The same process as that used for polymer <NUM> is applied, except that only <NUM> of ATBS is used with <NUM> of AMD (<NUM>% by weight in water), <NUM> of C16 in <NUM> of pure tertiary butanol (<NUM>-methyl-<NUM>-propane) and <NUM> of water.

Polymer <NUM>' (invention) - The same process as that used for polymer <NUM> is applied, except that <NUM> of ATBS is used with <NUM> of AMD (<NUM>% by weight in water), <NUM> of C16 in <NUM> of pure tertiary butanol (<NUM>-methyl-<NUM>-propane) and <NUM> of water.

Polymer <NUM> (invention) - The same process as that used for polymer2 is applied, in which C16 is replaced by C12.

Polymer <NUM> (invention) - The same process as that used for polymer2 is applied, in which C16 is replaced by C22.

All the polymers prepared are summarized in Table <NUM>.

A variety of drilling fluids are prepared comprising polymers <NUM> to <NUM>. The drilling fluid F1 comprises polymer <NUM>, the drilling fluid F2 comprises polymer <NUM> and so on.

Drilling fluids are prepared by mixing calcium chloride CaCl<NUM>, defoamer, buffer solution (NaOH in water) and water with a Hamilton Beach mixer for <NUM> minutes. CaCOs is then added and mixed for <NUM> minutes. Finally, the polymer is slowly added and mixed with the drilling fluid for <NUM> minutes.

Different drilling fluids were prepared (Table <NUM>).

The rheological properties of polymers <NUM> through <NUM> were evaluated in drilling fluids F1 through F9 (see Tables <NUM> through <NUM>).

Samples of fluids F1 to F9 are stability tested at <NUM> for <NUM> in a roller furnace (Table <NUM>). They are then aged in a standard furnace at <NUM> for another <NUM> days in static position (Table <NUM>). These two tests simulate the real stresses that polymers will face over time in underground formations.

Rheological tests are performed with a Grace M <NUM> rheometer. Constant shear stresses (direct viscometer reading) at multiple rotation rates, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> rpm (rotation per minute), are recorded and shown in Tables <NUM> and <NUM>.

During the rheological tests, the samples are subjected to the following protocol:.

This protocol is reproduced <NUM> times on the same sample to measure the viscosity at the shear considered. Specifically, when x = <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> rpm, the viscosity is the average of the up-ramp (<NUM> to <NUM> rpm) and the down-ramp (<NUM> to <NUM> rpm) values, at identical rpm, measured <NUM> times. At <NUM> rpm, the viscosity is the average of the <NUM> measurements.

The measured viscosity is expressed in lb. /<NUM> ft<NUM> (<NUM> lb. /<NUM> ft<NUM> = <NUM>/m<NUM> = <NUM> Pa).

Sedimentation is the visual observation of the tendency of the drilling fluid to flocculate. Ideally, no flocculation should be observed, which corresponds to a loss of the polymer's rheological properties present in the drilling fluid.

It may be seen from these tables that the polymers of the invention (F1, F2, F6, F7', F8 and F9) offer better performance under aging conditions. The effect of the rheology modifier and of the suspensive effect is also better for the polymers of the invention with no or very little sedimentation.

Claim 1:
Water-soluble associative amphoteric polymer of at least one monomer derived from a sulfonic acid and/or a salt thereof and at least one associative cationic monomer of formula (I):
<CHM>
With:
R<NUM>, R<NUM> being, independently of each other, a hydrogen, CH<NUM>, or C<NUM>H<NUM>;
R<NUM>: an alkyl, arylene-alkyl or aryl-alkyl chain having from <NUM> to <NUM> carbons;
X-: counterion of negative charge;
the polymer being obtained by polymerization of the monomers in the absence of surfactants;
the amount of monomer derived from a sulfonic acid and/or a salt thereof being at least <NUM> mol%, relative to the number of moles of polymerized monomers.