Fluid composition for stimulation in the field of oil or gas production

Abstract

The present invention relates to filamentous polymer particles useful in oil, condensate or gas recovery from subterranean locations as hydraulic fracturing fluids, diverting fluids, fluids that make it possible to improve the distribution and the flow profiles of the fluids or products injected (referred to as conformance fluids) or permeability control fluids, sand control gravel pack placement fluids, acid fracturing fluids, and the like. These fluids are stimulation fluids injected in wells which serve also as producing wells for the hydrocarbons initially present in the subterranean formations.

Claims

1. A composition comprising water, dissolved salts, filamentous polymeric particles and solids particles other than the filamentous polymeric particles, wherein the filamentous polymeric particles are cylindrical fibers with a diameter ranging from 5 nm to 200 nm inclusive and a length ranging from 500 nm to 200 m and consist of block copolymers synthesized by controlled radical emulsion polymerization.

2. A composition according to claim 1, further comprising dissolved acids.

3. A composition according to claim 1, wherein the filamentous polymeric particles consist of block copolymers prepared by controlled radical emulsion polymerization performed using at least one hydrophobic monomer in the presence of water and a water-soluble macro-initiator derived from a nitroxide, or synthesized by radical polymerization with Reversible Addition Fragmentation Transfer (RAFT) performed using at least one hydrophobic monomer in the presence of water and a water-soluble macromolecular RAFT agent.

4. A composition according to claim 1, wherein the salts include monovalent and/or divalent and/or trivalent ions.

5. A composition according to claim 1 wherein the weight percentage of filamentous polymeric particles compared to the weight of the composition without the solid particles other than the filamentous polymeric particles is between 0.05% and 20% and the weight percentage of dissolved salts ranges from 0.1% to salt saturation concentration.

6. A composition according to claim 1, further comprising at least one additional component selected from the group consisting of oxygen scavengers, pH buffers, wetting agents, foamers, corrosion inhibitors, defoamers and antifoams, scale inhibitors, biocides, crosslinkers, gel breakers, non emulsifiers, fluid loss control additives, and injected gas bubbles.

7. A hydraulic fracturing fluid, diverting fluid, conformance fluid, permeability control fluid, sand control gravel pack placement fluid, or acid fracturing fluid containing the composition of claim 1.

8. A method comprising using the composition of claim 1 as a hydraulic fracturing fluid.

9. A method of preparing a fluid according to claim 7 comprising using an aqueous composition extracted through a well from a subterranean formation.

10. A process of fracturation of a subterranean formation comprising using a composition according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a plot of viscosity as a function of shear rate for a composition made according to Example 2 and;

(2) FIG. 2 is a plot of viscosity as a function of shear rate for a composition made according to Example 5.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THE INVENTION

(3) A first subject of the present invention is a composition comprising water, dissolved salts, filamentous polymeric particles and solid particles. The salts can be mineral salts such as the ones found in subterranean formation water like NaCl, KCl, MgCl.sub.2, CaCl.sub.2, SrCl.sub.2, BaCl.sub.2, or synthetic salts such as ammonium salts. The solid particles may be specific solid particles called proppants by those skilled in the art and are small inorganic particles, e.g. rock particles, for example sand, gravel, coated sand, bauxite, ores, tailings, or metal particles. The filamentous polymeric particle synthesis and structure are described in the applications WO 2012/085415 and WO 2012/085473 and are given here below.

(4) According to a preferred embodiment, in the composition of the present invention, the weight percentage of filamentous polymeric particles compared to the weight of the composition without the solids and proppants is between 0.05% and 20% and the weight percentage of dissolved salts ranges from 0.1% to salt saturation concentration.

(5) According to another embodiment, the present invention relates to a composition comprising water, dissolved salts, filamentous polymeric particles and dissolved acids, such as those described herein before. The dissolved salts can be mineral salts such as the ones found in subterranean formation water, e.g. mono-valent and/or di-valent and/or tri-valent ions, such as NaCl, KCl, MgCl.sub.2, CaCl.sub.2, SrCl.sub.2, BaCl.sub.2, or synthetic salts such as ammonium salts. The acids are chosen from among hydrochloric acid, hydrofluoric acid, formic acid, acetic acid. The filamentous polymeric particle synthesis and structure are described in applications WO2012/085415 and WO2012/085473 and are given here below.

(6) The filamentous particles have a length/diameter ratio of more than 100, said particles being composed of block copolymers synthesized by controlled radical emulsion polymerization performed from at least one hydrophobic monomer in the presence of a water-soluble macro-initiator.

(7) According to a first embodiment of the first two objects of the invention, said particles are synthesized from at least one hydrophobic monomer in the presence of a living macro-initiator derived from a nitroxide.

(8) Said filamentous particles are characteristically obtained in aqueous medium from synthesis of said block copolymers performed by heating the reaction mixture at a temperature of 60 C. to 120 C., with a percentage of the molar mass of the hydrophilic macro-initiator in the final block copolymer of between 10% and 50%, the degree of conversion of the hydrophobic monomer being at least 50%. The initial pH of the aqueous medium may vary between 5 and 10. This direct technique for preparing filamentous particles does not require the use of an organic co-solvent.

(9) A living macro-initiator is a polymer comprising at least one end suitable for re-engagement in a polymerization reaction by addition of monomers at appropriate temperature and appropriate pressure. Said macro-initiator is advantageously prepared by Controlled Radical Polymerization (CRP). A water-soluble macro-initiator is a polymer which is soluble in water and comprises at its end a reactive function capable of reinitiating a radical polymerization.

(10) This macro-initiator is principally composed of hydrophilic monomers, these being monomers having one or more functions capable of establishing hydrogen bonds or ion-dipole interaction with water. In the case of the polymerization of a hydrophobic monomer, an amphiphilic copolymer will be formed, with a hydrophilic block composed of the macro-initiator, while the hydrophobic block will be obtained from the polymerization of the hydrophobic monomer or monomers.

(11) According to one variant embodiment, said preformed water-soluble macro-initiator is added to the reaction medium comprising at least one hydrophobic monomer.

(12) According to another variant within the first embodiment, said water-soluble macro-initiator is synthesized in the aqueous reaction medium in a preliminary step, without isolation of the macro-initiator formed and without removal of any residual hydrophilic monomers. This second variant is a one-pot polymerization reaction.

(13) The hydrophobic monomers may be selected from the following monomers: vinylaromatic monomers such as styrene or substituted styrenes, alkyl, cycloalkyl, and aryl acrylates, such as methyl, ethyl, butyl, 2-ethylhexyl, or phenyl acrylates, alkyl, cycloalkyl, alkenyl, or aryl methacrylates such as methyl, butyl, lauryl, cyclohexyl, allyl, 2-ethylhexyl, or phenyl methacrylates, and vinylpyridine.

(14) According to a preferred embodiment said filamentous polymeric particles are obtained: in aqueous medium during the synthesis of said block copolymers, formed by heating the reaction medium at a temperature of 60 to 120 C., using a water-soluble macro-initiator, the percentage of the molar mass of the water-soluble macro-initiator in the final block copolymer being between 10% and 30%, and the degree of conversion of the hydrophobic monomer being at least 50%, the hydrophobic monomer being selected from vinylaromatic monomers, and optionally a crosslinking comonomer being used, the crosslinking monomer including divinylbenzenes, trivinylbenzenes, allyl (meth)acrylates, diallyl maleate, polyol (meth)acrylates, alkylene glycol di(meth)acrylates which have from 2 to 10 carbon atoms in the carbon chain, 1,4-butanediol di(meth)acrylates, 1,6-hexanediol di(meth)acrylates, and N, N-alkylenebisacrylamides.

(15) These hydrophobic monomers are added to the reaction medium which mainly comprises water.

(16) The percentage of the molar mass of the water-soluble macro-initiator in the final block copolymer is preferably between 10 and 30 wt %.

(17) Implementation of the method according to the invention produces filamentous polymeric particles in which the mass fraction of the hydrophilic moiety constituting the block copolymer is less than 25%.

(18) According to one embodiment, when the reaction medium is admixed with a crosslinking agent, crosslinked filamentous particles are obtained. Said crosslinking agent is a crosslinking comonomer other than the aforementioned hydrophobic monomers.

(19) A crosslinking comonomer is a monomer which, by virtue of its reactivity with the other monomers present in the polymerization medium, is capable of generating a covalent three-dimensional network. From a chemical view point, a crosslinking comonomer generally comprises at least two polymerizable ethylenic functions which, by reacting, are capable of producing bridges between a number of polymer chains.

(20) These crosslinking comonomers may be capable of reacting with the unsaturated hydrophobic monomers during the synthesis of said particles.

(21) The crosslinking comonomers include divinylbenzenes, trivinylbenzenes, allyl (meth)acrylates, diallyl maleate, polyol (meth)acrylates such as trimethylolpropane tri(meth)acrylates, alkylene glycol di(meth)acrylates which have from 2 to 10 carbon atoms in the carbon chain, such as ethylene glycol di(meth)acrylates, 1,4-butanediol di(meth)acrylates, 1,6-hexanediol di(meth)acrylates, and N,N-alkylene-bisacrylamides, such as N,N-methylene bisacrylamide. Preference will be given to using divinylbenzene or a dimethacrylate as crosslinking agent.

(22) The filamentous particles according to the invention characteristically have a percentage of the molar mass of the hydrophilic macro-initiator in the final block copolymer of between 10 wt % and 50 wt %. As observed by Transmission Electronic Microscopy (TEM), these particles may take the form of cylindrical fibers with a length/diameter ratio of more than 100; their diameter is constant over their whole length and is greater than or equal to 5 nm, while their length is greater than 500 nm, preferably greater than 1 m, advantageously greater than 5 m, and, more preferably still, is greater than or equal to 10 m. According to a preferred aspect, the filamentous polymeric particles are cylindrical fibers with a diameter ranging from 5 nm to 200 nm inclusive, a length ranging from 500 nm to 200 m, preferably greater than 1 m, advantageously greater than 5 m, and, better still greater than or equal to 10 m.

(23) The filamentous particles according to the invention maintain their form and structure in a dispersed medium, independently of their concentration in the medium and/or of changes in its pH or its salinity.

(24) According to a second embodiment, said filamentous particles are synthesized by radical polymerization by Reversible Addition Fragmentation Transfer (RAFT) in water in the presence of a macromolecular RAFT agent (or RAFT macroagent) which is hydrophilic.

(25) Other additives can be added like shear thinning hydrosoluble polymers such as for example polysaccharides, guar, guar derivatives containing hydropropyl, hydroxypropyl, hydroxybutyl, carboxymethyl functions, copolymers containing acrylamide monomers, partially hydrolyzed polyacrylamide, (co)polymers containing (meth)acrylic monomers, oxygen scavengers, pH buffers, wetting agents, foamers, corrosion inhibitors, defoamers or antifoams, scale inhibitors, biocides, crosslinkers, gel breakers, non-emulsifiers, fluid loss control additives, clay stabilizers. A gas can also be injected to produce gas bubbles inside the fracturing fluid such as nitrogen and/or carbon dioxide.

(26) A further subject of the invention is the use of the abovementioned compositions as stimulation fluids for oil, condensate and gas production, as hydraulic fracturing fluids, diverting fluids, conformance or permeability control fluids, sand control gravel pack placement fluid, acid fracturing fluids.

(27) Surprisingly it has been discovered that the abovementioned filamentous polymeric particles previously used as shear thinning additive give solutions with water which are shear thinning and have a limited viscosity decrease at a shear under or equal to 1 s.sup.1 when the salt content increases up to saturation concentration or even the viscosity of which increases depending on the salt used. The saturation concentration is defined as the concentration where the first crystals of solid salt appear. These viscosity variations are also of value for salt concentrations below saturation like for example 10 wt % to 40 wt %.

(28) The low sensitivity of the viscosity to variations of salinity at low shear rates (for example below 1 s.sup.1) for the solution containing the filamentous polymeric particles makes it possible to increase the salt content, such as for example NaCl, KCl, CaCl.sub.2, BaCl.sub.2, and ammonium salts in the hydraulic fracturing fluid while keeping a shear thinning behaviour. Furthermore, the density of the fluid is increased which increases the pressure in the subterranean formation at constant pumping power and hence the fracturing efficiency.

(29) Moreover, as the formation water may have different salinities at different locations of a same subterranean reservoir and as the formation water mixes with the hydraulic fracturing fluid thereby modifying its salinity and as the salinity has a lower impact on the new hydraulic fracturing fluid viscosity at low shear rates (for example below 1 s.sup.1) than for conventional fluids, then the viscosity of the new fracturing fluid has a lower reduction and hence the ability of the new hydraulic fracturing fluid to transport proppants inside the fractures is greater and the fractures are kept open wider or this reduces the amount of water and fracturing additives necessary to deliver the same output of hydrocarbons.

(30) This lower sensitivity or reversed sensitivity (in case of viscosity increase upon salt addition) also makes it possible to reuse the flow back water which is a mixture of hydraulic fracturing fluid and formation water for following fracturing operations, that is as a true recycling operation: 1for example starting from an amount of salt in the fracturing fluid close to the estimated formation water salt content, the viscosity of the flow back fluid will decrease essentially due to dilution of shear thinning additive. It is then necessary to add the lacking concentration of shear thinning additive. In the case of a hydraulic fracturing fluid of the prior art, as the viscosity decreases because of the increase of salt content and dilution by water, the relative lacking concentration is higher. 2for example starting from an amount of salt in the fracturing fluid lower than the estimated formation water salt content, and using a shear thinning additive having an inverse sensitivity to salt, the viscosity of the flow back fluid will decrease due to dilution of the shear thinning additive. But this effect will be limited due to the increase in salt content coming from the formation water.

(31) The reuse of the flow back water without separating contaminants such as salts is beneficial from several points of view: less energy is used and these contaminants stay at the fracturing site or below, thereby limiting the dissemination due to hauling. As such, another subject of the present invention is the use of an aqueous composition extracted through a well from a subterranean formation for the preparation of a composition of the present invention for the preparation of a hydraulic fluid for subterranean formation fracturation.

(32) In the case of diverting fluids, conformance or permeability control fluids, sand control gravel pack placement fluid, acid fracturing fluids, there is the same advantage in terms of efficiency for a shear thinning fluid (containing gravel in the case of sand control gravel pack placement fluid) the viscosity of which at low shear rate (0.1 s.sup.1 to 1 s.sup.1) decreases more slowly than the viscosity of existing fluids or even increases when its salt content increases up to 30 wt % with the salts typically found in formation water, at constant concentration of the shear thinning additive.

(33) Another subject of the invention relates to a hydraulic fracturing fluid, diverting fluid, conformance fluid, permeability control fluid, sand control gravel pack placement fluid, acid fracturing fluid containing a composition of the present invention as herein before described. The invention also relates to the use of a composition of the present invention as herein before described, as hydraulic fracturing fluid, as well as a process for subterranean formation fracturation using said composition according to the present invention.

(34) The invention is further illustrated by the following examples which do not aim at limiting the sought scope of protection.

Example 1: Preparation of Filamentous Polymeric Particles EG227 and ECLR5-13.06

(35) This example details the synthesis of a living copolymer poly(methacrylic acid-co-sodium styrene sulfonate) used as macro-initiator, controlling agent and stabilizer for synthesis of hairy particles as crosslinked fibrillar micelles of block copolymer poly(methacrylic acid-co-sodium styrene sulfonate)-b-poly(n-butyl methacrylate-co-styrene). This amphiphilic copolymer is synthesized in a one-pot reaction.

(36) Macro-initiator synthesis conditions can be changed (during polymerization, sodium styrene sulfonate concentration and pH) to adapt and change the macro-initiator composition.

(37) For that, a blend containing 6.569 g of methacrylic acid (0.84 mol.Math.L.sub.aq.sup.1 or 0.79 mol.Math.L.sup.1), 1.444 g of sodium styrene sulfonate (6.9710.sup.2 mol.Math.L.sub.aq.sup.1 or 6.5110.sup.2 mol.Math.L.sup.1 so f.sub.0,SS=0.076;

(38) $f_{0,\mathrm{SS}}=\frac{n_{\mathrm{SS}}}{\left(n_{\mathrm{SS}}+n_{\mathrm{MAA}}\right)}),$
0.3594 g of Na.sub.2CO.sub.3 (3.7510.sup.2 mol.Math.L.sub.aq.sup.1 or 3.5010.sup.2 mol.Math.L.sup.1) and 87.1 g of demineralised water is placed under N.sub.2 flux at room temperature during 15 min. In parallel, 0.3162 g (9.1810.sup.3 mol.Math.L.sub.aq.sup.1 or 8.5710.sup.3 mol.Math.L.sup.1) of alkoxyamine BlocBuilder MA (Arkema) is solubilised in 3.3442 g of 0.4 M sodium hydroxide solution (1.6 equivalent vs BlocBuilder MA methacrylic acid units) and bubbled with N.sub.2 during 15 min.

(39) ##STR00001##

(40) BlocBuilder-MA solution is introduced into a reactor at room temperature under 250 rpm stirring. Monomer solution is slowly introduced into the reactor. Reactor pressure is adjusted at 1.1 bar with N.sub.2 and still under stirring. Time t=0 is fixed when temperature is at 60 C. Temperature is at 65 C. after 15 min. During this reaction, in a Erlenmeyer flask, there are introduced 18.01 g of n-butyl methacrylate and 2.01 g of styrene (solid content=24%) and the mixture is placed under N.sub.2 flux at room temperature during 10 min.

(41) After 15 min of synthesis, that means, synthesis of poly(methacrylic acid-co-sodium styrene sulfonate)-SG1 macro-initiator, a second reactive system containing hydrophilic monomers is introduced under room pressure and 3 bar N.sub.2 pressure and 205 rpm stirring are applied. Temperature is fixed at 90 C. for the polymerization.

(42) After 54 min, 2.06 g of ethylene glycol dimethacrylate (f.sub.0,EGDmA=0.066 mol) (where

(43) $f_{0,\mathrm{EGDMA}}=\frac{n_{\mathrm{EGDMA}}}{\left(n_{\mathrm{EGDMA}}+n_{\mathrm{MABu}}+n_{\mathrm{Sty}}\right)})$
(solid content=25%) are introduced into the reactor for fiber crosslinking after their formation.

(44) Samplings are realised at regular times to determine polymerization kinetic by gravimetry.

(45) Table 1 presents characteristics of a latex sample prepared during the second step of nanoparticle synthesis.

(46) TABLE-US-00001 TABLE 1 Time (h) Conversion (%) pH 0.25 6.4 0.58 34.6 4.41 0.9 66.1 1.25 88.7 3.0 94.9 4.54

(47) Fiber diameters measured by Transmission electronic microscopy TEM (ImageJ software) is 45.3 nm. This microscope is JEOL 100 Cx II 100 keV with high resolution camera CDD Camera Keen View from SIS.

(48) Rheological tests: solutions of filamentous polymeric particles are prepared at 40 C. using tap water and different salts. First the salt is introduced in tap water and then the polymer solution resulting from the synthesis. The mixture is gently agitated at 40 C. for 60 min. Then the mixture is poured into a Couette device (air gap 2 mm) of a MCR301 Anton Paar rheometer and allowed to equilibrate at 20 C. Then the mixture is sheared starting at 10.sup.2 s.sup.1 and finishing at 10.sup.3 s.sup.1.

(49) In all the examples below, the dosage of polymer indicated is the dosage of the polymer without the water coming from the synthesis.

Example 2: Water Composition Containing 5 wt % Non-Crosslinked Filamentous Polymeric Particles

(50) Aqueous non-crosslinked filamentous polymeric particle solution EG216 synthesis follows the same procedure (see example 1) as crosslinked particles but without crosslinking agent.

(51) The composition is shear thinned as shown on FIG. 1.

Example 3: Water Composition Containing 5 wt % Non-Crosslinked Filamentous Polymeric Particles with KCl Compared with FIG. 8 of US2007213232

(52) Aqueous non-crosslinked filamentous polymeric particle solution EG216 synthesis follows the same procedure (see example 1) as crosslinked particles but without crosslinking agent.

(53) Rheological tests are run as described above. The results are presented in Table 2 below:

(54) TABLE-US-00002 TABLE 2 Comparative: viscosity at 1 s.sup.1 Viscosity at with EHAC/IPA 1 s.sup.1 with 4.5% in water EG216 at 5% at 40 C. KCl content at 20 C. (US2007213232) (wt %) (cPo) (cPo) No addition, 6690 <300 tap water 1% 5460 6000 4% 3750 22000 12% 2160

(55) The composition with 5 wt % EG216 is less sensitive to KCl than the 4.5 wt % EHAC/IPA mixture. In the case of 4.5 wt % EHAC/IPA the viscosity starts decreasing at a dosage above 3 wt % KCl.

Example 4: Water Compositions Containing 5 wt % Non-Crosslinked Filamentous Polymeric Particles without or with CaCl2 or with BaCl2

(56) Aqueous non-crosslinked filamentous polymeric particle solution ECL 13-04 is prepared in the same manner as EG 216 above.

(57) Rheological tests are run as described above. The results are presented in Table 3 below:

(58) TABLE-US-00003 TABLE 3 Composition Viscosity (Pa .Math. s) at 0.1 s.sup.1 5% EG227 in tap water 12 5% EG227 + 1% BaCl.sub.2 + tap water 20 5% EG227 + 12% BaCl.sub.2 + tap water 19 5% EG227 + 40% CaCl.sub.2 + tap water 13

(59) Surprisingly, ECL 13-04 makes it possible to keep constant or increase the viscosity at low shear rate with amounts up to 40% of salt, depending on the salt. This effect is not taught or even suggested by WO 2012/085415 and WO 2012/085473.

Example 5: Water Composition Containing 5 wt % Crosslinked Filamentous Polymeric Particles with 4% KCl and 15% Ethylene Diamine Tetracetic Acid (EDTA)

(60) EG227 can be considered as a covalent polymer because of the crosslinking, like guar and its derivatives. Surprisingly the viscosity of EG227 increases with the addition of a salt contrary to what is taught in US2009111716 about polyelectrolytes. The compositions are shear thinning, the low shear rate viscosity increases with 4% KCl and is independent of the presence of the scale inhibitor EDTA, as shown on FIG. 2

Example 6: Water Compositions Containing 0.3 wt % Crosslinked Filamentous Polymeric Particles from the Aqueous Composition ECLR5-13.06, or with KCl, Compared to US2009111716

(61) Rheological tests are run as described above. The results are presented in Table 4 below:

(62) TABLE-US-00004 TABLE 4 Viscosity (Pa .Math. s) Composition at 0.1 s.sup.1 0.3% ECLR5-13.06 in tap water 0.11 0.3% ECLR5-13.06 + 5% KCl + tap water 0.57 0.3% anionic guar in tap water (US2009111716, FIG. 8) 0.45 0.3% anionic guar + 5% KCl + tap water (US2009111716, 0.09 FIG. 8) 0.3% anionic guar + 2% BET-O-30 + 5% KCl + tap water 0.35 (US2009111716, FIG. 8)

(63) The anionic guar is useful with tap water for producing a hydraulic fracturing fluid that suspends solids. But once this fluid has come into contact with a salted subterranean formation water, it can lose its viscosity because of the salt increase (75% if the KCl concentration is 5 wt % in the water) and dilution with water and hence a part of its ability to transport proppants in areas with such a salt content. By contrast and surprisingly with ECLR5-13.06 the viscosity is multiplied by 5 with the addition of 5% KCl, so the risk of losing its ability to transport proppants is lower because it depends only on the dilution of the polymer by water. This solution is better than the addition of BET-O-30 because it avoids the handling of one more chemical and the viscosity is higher at a lower dosage.

Example 7: Water Composition Containing 5 wt % Crosslinked Filamentous Polymeric Particles from the Aqueous Composition ECLR5-13.06 and BaCl2 or CaCl2

(64) Rheological tests are run as described above. The results are presented in Table 5 below:

(65) TABLE-US-00005 TABLE 5 5% 5% ECLR5- 5% ECLR5- 5% ECLR5- Composition ECLR5- 13.06 + 1% 13.06 + 4% 13.06 + 5% ECLR5-13.06 + in tap water 13.06 CaCl.sub.2 CaCl.sub.2 12% CaCl.sub.2 40% CaCl.sub.2 Viscosity 66 160 100 181 100 (Pa .Math. s) at 0.1 s.sup.1 5% ECLR5- 5% ECLR5- 5% ECLR5- 13.06 + 1% 13.06 + 4% 5% ECLR5-13.06 + Composition 13.06 BaCl.sub.2 BaCl.sub.2 40% BaCl.sub.2 Viscosity 66 191 199 634 (Pa .Math. s) at 0.1 s.sup.1

(66) Surprisingly the viscosity with 5% ECLR5-13.06 and 40% of CaCl.sub.2 or BaCl.sub.2 is above that in tap water. It makes it possible to carry out hydraulic fracturing in areas with high salinities, that is above 5% of total dissolved solids, more preferentially above 10% of total dissolved solids. What's more, it facilitates the use of the flow back water which often has a high salinity and which is pumped back to the surface after a fracturing operation. Indeed its high salinity is not detrimental for use as a novel hydraulic fracturing fluid with the filamentous polymeric particles of the invention. Hence surface water is spared and replaced by formation water in the hydraulic fracturing fluid.

ABBREVIATIONS

(67) AA: acrylic acid CRP: controlled radical polymerization DMF: dimethylformamide DMSO: dimethyl sulfoxide EDGMA: ethylene glycol dimethacrylate MAA: methacrylic acid MABu: n-butyl methacrylate TEM: transmission electron microscopy P4VP: poly(4-vinylpyridine) PEGA: poly(ethylene glycol) methyl ether acrylate PNaA: poly(sodium acrylate) RAFT: polymerization by addition fragmentation (Reversible Addition Fragmentation chain Transfer) SG1: N-tert-butyl-N-[1-diethylphosphono(2,2-dimethylpropyl)] S or Sty: styrene SS: sodium styrenesulfonate n: number of moles rpm: revolutions per minute f.sub.0,sty: initial molar fraction of styrene in the mixture of monomers f.sub.0,SS: initial molar fraction of sodium sulfonate in the mixture of monomers f.sub.0,DVP: initial molar fraction of divinylbenzene in the mixture of monomers f.sub.0,EGDMA: initial molar fraction of ethylene glycol dimethacrylate in the mixture of monomers

(68) BlocBuilder-MA is (N-(2-methylpropyl)-N-(1-diethylphosphono-2,2-dimethylpropyl)-O-(2-carboxylprop-2-yl)hydroxylamine, available at Arkema.