Method for injecting an aqueous polymer solution into an underground formation

Abstract

The present invention relates to a method for injecting an aqueous solution of a 2- acrylamido-2-methylpropane sulfonic acid homopolymer P and / or its salts having an average molecular weight greater than 1 million daltons, said method comprising the following successive steps: - in a location A: * preparation in a mobile unit U1 of 2-acrylamido-2-methylpropane sulfonic acid in hydrated crystalline form (AMPS. MH), * collection of an AMPS. OS 2-acrylamido-2 -methylpropane sulfonic acid aqueous solution SI, coming from the draining of the preparation of the AMPS. MH in the mobile unit U1, - in a location A': * preparation in a mobile unit U3 of a homopolymer P by gel polymerization of an AMPS. MH aqueous solution S3, * dissolution in a mobile unit U4 of the homopolymer P in a saline solution SSI to obtain a homopolymer P solution SM, * transfer of the solution SM from the location A' to a location B, - in the location B: * dilution in a mobile unit U5 of the solution SM by a saline solution SS2 to obtain a solution SF, * injection of the solution SF in the underground formation for the assisted extraction of hydrocarbons or hydraulic fracturing.

Description

[0001] METHOD FOR INJECTING AN AQUEOUS POLYMER SOLUTION INTO AN UNDERGROUND

[0002] FORMATION

[0003] Field of the invention

[0004] The invention relates to a method for injecting a 2-acrylomido-2-methylpropane sulfonic acid aqueous solution into an underground formation for the assisted extraction of hydrocarbons (oil and / or gas) or hydraulic fracturing.

[0005] More specifically, the method relates to the field of preparing polymer solution on fields in modular units for its direct injection into the underground formation.

[0006] Prior art

[0007] Documents WO 2018 / 172682 and WO 2018 / 172684 of the Applicant highlight the interest of injecting 2-acrylamido-2-methylpropane sulfonic (AMPS) acid (co)polymer saline solutions in hydrated form into underground formations for the assisted recovery of hydrocarbons (oil and / or gas) or hydraulic fracturing.

[0008] CN 113 528 113 relates to a fracturing fluid comprising proppants and a polymer of hydrated crystalline ATBS. WO 2018 / 172676 relates to hydrocarbon recovery involving a polymer of hydrated crystalline ATBS. CN 112 430 198 relates to ATBS polymers and use thereof in hydrocarbon recovery.

[0009] For oil or gas assisted recovery techniques, these polymers have improved properties in terms of filterability and chemical and thermal stability.

[0010] For hydraulic fracturing, 2-acrylamido-2-methylpropane sulfonic acid-based synthetic polymers in hydrated form make it possible to have a very high friction reduction effect, while guaranteeing an improved viscosifying effect in a saline solution (brine). In addition, the good solubility of the polymer in the fracturing fluid, combined with its sulfonic anionic character, makes it possible to avoid its adsorption on the rock, which induces a recovery of conductivity and therefore an increase in the hydrocarbon production yield (oil and / or gas).

[0011] However, the synthesis of the 2-acryl ami do-2 -methylpropane sulfonic acid-based polymers in hydrated form is done on manufacturing sites, which are far from the injection wells leading to these underground formations, and due to this, involves expensive logistics which consume a lot of energy to send the polymers at the hydrocarbon development fields.

[0012] The physical form of the polymer which makes it possible to have the greatest mass concentration in active material to supply the fields for the EOR or for the hydraulic fracturing is powder. However, this physical form involves specific dissolution units (PSU: Polymer Slicing Unit, maturation tanks, see document WO 2008 / 071808), which are expensive and consume a lot of energy.

[0013] Moreover, the powder comes from a gel polymerization method, which involves an operation of drying the polymer gel to transform it into powder (patent US 5633329). 1 to 5 volumes of water must typically be evaporated for 1 volume of powder, which involves increasing water and energy consumption, and therefore increasing the carbon footprint of the product.

[0014] Summary of the invention

[0015] The Applicant has thus developed a method for preparing 2-acrylamido-2-methylpropane sulfonic acid homopolymer solutions and / or its salts based on modular units in order to be able to carry out all the preparation steps on fields in the proximity of the underground formations to be developed.

[0016] This method includes (1) the preparation of 2-acrylamido-2 -methylpropane sulfonic acid in hydrated form in a first location, (2) the synthesis of the polymer and the preparation of a concentrated polymer solution in a second location and finally (3) the dilution of this solution for injection into the underground formation in the third location.

[0017] This method makes it possible to manufacture, in a continuous flow, the required quantity of injection solution. In addition, it makes it possible to considerably decrease the logistics costs (transport, dissolution of the polymer) with a low water and carbon footprint (no drying) and it can be transposed over any fields and under any field conditions (saltiness, hardness, temperature, etc.) without needing installations classified as high-risk (chemical).

[0018] The only monomer to be sent and to be possibly stored on the first location is 2-acrylamido- 2-methylpropane sulfonic acid (AMPS). This monomer, contrary to monomers such as acrylonitrile, acrylamide or acrylic acid, has the advantage of being in solid form and therefore of not having a risk of leakage or of spreading. In addition, it is not toxic (CMR) and remains stable in the solid state according to the temperature (not temperature-sensitive). Finally, another advantage of AMPS, compared with acrylamide, is that it can be polymerized at a higher concentration and without needing prior cooling, as less exothermal, which generates energy gains and makes the claimed method transposable anywhere, including in dry zones or with a seasonal water stress.

[0019] As an illustration, 1 volume of acrylamide and / or acrylic acid requires to be polymerized in the presence of at least 3 volumes of water and with a prior cooling to 0°C while the AMPS only requires 1 to 2 volumes of water with a start of polymerization in solution at the ambient temperature.

[0020] Presentation of the invention

[0021] More specifically, the invention relates to a method for injecting a 2-acrylamido-2- methylpropane sulfonic acid homopolymer P aqueous solution and / or its salts, the homopolymer P having an average molecular weight by weight greater than 1 million daltons, the homopolymer P aqueous solution being injected into an underground formation for enhanced recovery of hydrocarbons (oil and / or gas) or hydraulic fracturing, said method comprising the following successive steps:

[0022] - in a location A:

[0023] * preparation in a mobile unit U1 of 2-acrylamido-2-methylpropane sulfonic acid in hydrated crystalline form (AMPS.MH) having an X ray powder diffraction diagram comprising peaks at 10.58°, 11.2°, 12.65°, 13.66°, 16.28°, 18.45°, 20°, 20.4°, 22.5°, 25.5°, 25.88°, 26.47°, 28.52°, 30.28°, 30.8°, 34.09°, 38.19°, 40.69°, 41.82°, 43.74°, 46.04°degrees 2-theta(+ / - 0.1°),

[0024] * collection of a 2-acrylamido-2-methylpropane sulfonic acid aqueous solution SI AMPS.OS, coming from the draining of the AMPS.MH preparation in the mobile unit Ul,

[0025] - in a location A’ :

[0026] * preparation in a mobile unit U3 of a homopolymer P by gel polymerization of an AMPS.MH aqueous solution S3 to afford a homopolymer P,

[0027] * granulating the gel of homopolymer P in a granulation unit to obtain pieces of gel of homopolymer P

[0028] * dissolution in a mobile unit U4 of the pieces of gel of homopolymer P in a saline solution SSI containing at least Ig / L of alkaline and / or alkaline earth salts in water to obtain a homopolymer P solution SM,

[0029] * transfer of the solution SM from the location A’ to a location B, - at the location B:

[0030] * dilution in a mobile unit U5 of at least a factor 4 and as a maximum a factor 60 of the solution SM by a saline solution SS2 containing at least Ig / L of alkaline and / or alkaline earth salts in water to obtain an aqueous solution SF containing less than 0.6% by weight of homopolymer P,

[0031] * Injection of the solution SF into the underground formation.

[0032] The hydrated crystalline form AMPS.MH corresponds to hydrated AMPS crystals.

[0033] The ranges of values include the lower and upper limits. Thus, the ranges of values "between 0.1 and 1.0" and "from 0.1 to 1" include the values 0.1 and 1.0.

[0034] According to the present invention, the average molecular weight by weight of the homopolymer P is determined by measuring the intrinsic viscosity. The intrinsic viscosity can be measured by methods known to a person skilled in the art and can, in particular, be calculated from reduced viscosity values for different concentrations by a graphic method consisting of tracing the reduced viscosity values (on the y-axis) according to the concentrations (on the x-axis) and by extrapolating the curve at a zero concentration. The intrinsic viscosity value is read on the y-axis or by using the least-squares method. Then, the average molecular weight by weight can be determined by the famous Mark-Houwink equation:

[0035] [r|] = K M“

[0036] [q] represents the intrinsic viscosity of the polymer determined by the method for measuring the viscosity in solution,

[0037] K represents an empirical constant,

[0038] M represents the molecular weight of the polymer, a represents the Mark-Houwink coefficient, a and K depend on the particular polymer-solvent system. Tables known to a person skilled in the art give a and K values according to the polymer-solvent system.

[0039] The location A is advantageously a location comprising at least one mobile storage unit, at least one mobile mixture unit and at least one mobile filtration unit. Thus, the location A advantageously makes it possible to have clean water for the radical polymerization of the APMS.MH (for example, water coming from a method for treating industrial water and / or rainwater). Preparing the 2-acrylamido-2-methylpropane sulfonic acid in hydrated crystalline form (AMPS.MH) is done according to the method described in document WO 2018 / 172676.

[0040] The mobile unit U1 advantageously comprises at least one mixture subunit and at least one filtration subunit. These subunits are known to a person skilled in the art and can correspond to those described in document WO 2018 / 172676.

[0041] This mobile unit U1 is a relocatable modular unit which can be transported by lorry or by rail transport.

[0042] This mobile unit U1 contains a mobile storage subunit to collect the AMPS.OS solution SI. This solution SI comes from the draining of the AMPS.MH preparation and is therefore constituted of a mixture of the filtrates and of the solutions for washing the AMPS.MH crystals (AMPS hydrated crystalline form). The mobile storage subunit is preferably a tank.

[0043] Preferably, the AMPS.MH is prepared by purification of 2-acrylamido-2-methylpropane sulfonic acid in powder form previously stored in the location A in a mobile storage unit located in the proximity of the mobile unit U1 (and therefore distinct from the mobile storage subunit). This storage unit is replenished by lorry or rail transport from production sites of 2-acrylamido-2-methylpropane sulfonic acid which could be distant from the location by several tens or hundreds of kilometers. The mobile storage unit in the proximity of the mobile unit U1 can have any shape and orientation. It can be, for example, cylindrical or rectangular and oriented horizontally or vertically. The volume and the dimensions are only limited by the condition that the storage units can be moved.

[0044] Advantageously, the 2-acrylamido-2-methylpropane sulfonic acid in powder form stored in the mobile storage unit in the location A has been previously obtained on its production site by a reaction between acrylonitrile, fuming sulfonic acid and iso-butylene containing less than lOOOppm of butadiene and less than lOOppm of butene (document WO 201746546).

[0045] The X ray powder diffraction diagram for AMPS.MH is done conventionally by X ray crystallography, X ray radio crystallography or diffractometry. An example of a piece of equipment is a Rigaku-brand Miniflex II diffractometer equipped with a copper source.

[0046] Advantageously, the location A' is a location which makes it possible to install at least one mobile storage unit, at least one mobile polymerization unit and at least one mobile dilution unit. Thus, the location A' advantageously makes it possible to have clean water for the radical polymerization of APMS.MH (for example, water coming from a method for treating industrial water and / or rainwater), but also water of a lesser quality for preparing aqueous solutions (in particular, SSI or SS2).

[0047] The mobile unit U3 is advantageously composed of at least one polymerization subunit such as a reactor in inverted conic tubular shape (inverted cone). Thus, polymerization subunit makes it possible to discharge the polymer gel by application of an air pressure on the surface of the gel or in the form of a tipper which discharges the gel mass by making the reactor tip. Advantageously, this mobile unit U3 also contains storage subunits for additives necessary for gel polymerization (generally, one storage unit per additive). These additives are, for example, initiators (oxidizer / reducer, azos), polymerization regulators, enzyme (glucose oxidase). The polymerization additives and the gel polymerization conditions are known to a person skilled in the art. The features of each storage unit are adapted to the physicochemical properties and to the quantities of the different additives. The mobile unit U3 is a relocatable modular unit which can be transported by lorry or by rail transport.

[0048] Preferably, the polymerization of the AMPS.MH solution S3in the mobile unit U3 is done with an initial concentration of AMPS.MH in the solution S3 greater than 20% by weight, even more preferably greater than 30% by weight, and even more preferably, greater than 40% by weight. The initial concentration of AMPS.MH in the solution S3 is advantageously less than 70% by weight.

[0049] Advantageously, the initial polymerization temperature is the ambient temperature, namely between 15 and 30°C, and the final polymerization temperature of the AMPS.MH solution S3in the mobile unit U3 is greater than 80°C. A person skilled in the art will know how to adapt the polymerization conditions to reach this temperature.

[0050] Preferably, the gel polymerization of the AMPS.MH in the solution S3 within the mobile unit U3 is initiated in the presence of glucose oxidase. The radical polymerization requires the absence of any oxygen traces in the polymerization environment. The glucose oxidase is intended to deoxygenate the solution S3. The use of bubbling with inert gases such as nitrogen or argon is therefore generally useless in the presence of glucose oxidase. This reduces the need, all the more, of locally producing high energy-consuming inert gases and atmospheric releases, sources of pollution. The homopolymer P coming from the gel polymerization in the mobile unit U3 is dissolved in a mobile unit U4 in a saline solution SSI containing at least Ig / L of alkaline and / or alkaline earth salts in water to obtain a homopolymer P solution SM.

[0051] The mobile unit U4 is a relocatable modular unit which can be transported by lorry or by rail transport.

[0052] At the end of preparing the homopolymer P by gel polymerization of the AMPS.MH solution S3 in the mobile unit U3, the obtained gel of homopolymer P is granulated in a granulation subunit to obtain pieces of the gel of homopolymer P, which are directly dissolved in the solution SSI to obtain the solution SM in the mobile unit U4.

[0053] The size of pieces of the aqueous gel of homopolymer P obtained at the end of granulation is not specifically limited. In an embodiment of the invention, the granulated pieces of gel of aqueous polyacrylamide advantageously have a size such as at least two dimensions (length and diameter in the case of pieces in the form of cylindrical granules) are not greater than 1cm, preferably not greater than 0.5cm. Preferably, three dimensions (width, length and height in the case of parallelepiped-shaped pieces) of the pieces of gel of aqueous polyacrylamide should not be greater than 1cm, preferably not greater than 0.5cm. No lower limit is necessary for the pieces of the gel of aqueous polyacrylamide, as the smaller the pieces are, the more easily the polymer dissolves. Generally, the pieces of the gel of aqueous polyacrylamide can have a size such that the three dimensions are as low as 0.1cm. Often, the pieces of the gel of aqueous polyacrylamide tend to have three dimensions, each of between 0.1cm and 0.5cm.

[0054] In principle, any type of granulation means can be used to granulate the gel of water-soluble polymer into smaller pieces. Examples of suitable means include cutting devices, such as cutters or perforated plates, crushers, kneaders, static or dynamic mixers, or water jets. A person skilled in the art will choose the suitable means and its conditions of use to obtain pieces of gel of predetermined sizes and shapes.

[0055] Advantageously, the pieces of gel of homopolymer P obtained at the end of granulation are directly added into a dissolution tank of the mobile unit U4. In this case, the dissolution in the saline solution SSI is accelerated by means of a stirring blade. The pieces of gel can also be dissolved within a conduit equipped with, or not, static or dynamic mixers. The combination of a conduit and a dissolution tank is also possible. Advantageously, the pieces of gel of homopolymer P are not stored between granulation and dissolution.

[0056] Advantageously, between the mobile units U3 and U4, the homopolymer P in the form of gel is conveyed by a screw conveyor to be granulated in a granulation subunit.

[0057] Preferably, the saline solution SSI or SS2 contains between Ig / L and 350g / L of alkaline and / or alkaline earth salts in water, even more preferably between lOg / L and 300g / L.

[0058] Preferably, the saline solution SSI or SS2 is drawn directly within the location A. As an example, this solution SSI or SS2 can be seawater drawn within an offshore oil platform.

[0059] The saline solution SSI can optionally be prepared within the mobile unit U4 in a dissolution tank and / or in a conduit equipped with static and / or dynamic mixers by adding the required quantities of salts to the water. The solution SSI or SS2 preferably contains sodium (alkaline salt) and / or calcium (alkaline earth salt), for example a salt chosen from among calcium chloride, calcium bromide, sodium chloride, and their mixtures.

[0060] Advantageously, the mobile unit U4 comprises at least one dissolution subunit, for example a tank provided with a stirring blade and / or a conduit provided with mixers. Advantageously, it also comprises a tank for storing the saline solution SSI.

[0061] During the preparation of the solution SSI or SS2, various compounds known to a person skilled in the art can be added, like those cited in document SPE 152596. Thus, the solution SSI or SS2 can comprise, for example:

[0062] - clay anti-swelling agents, for example potassium chloride, or choline chloride, and / or

[0063] - Biocides to avoid the development of bacteria, in particular sulfate-reducing bacteria, which could form viscous masses reducing the passage surfaces Glutaraldehyde can be cited, for example, which is the most used, or also formaldehyde or isothiazolinones, and / or

[0064] - Oxygen reducers, for example ammonium bisulfite to avoid the destruction of other components by oxidation and the corrosion of injection tubes, and / or

[0065] - Anti-corrosion additives to protect the tubes against oxidation by residual oxygen quantities, N,N dimethylformamide being favored, and / or

[0066] - Lubricants, for example oil distillates, and / or

[0067] - Chelatants for iron, for example citric acid, EDTA (ethylenediaminetetraacetic acid), phosphonates, and / or - Anti-scale products, for example phosphate, phosphonates, polyacrylates or ethylene glycol.

[0068] For this mobile unit U4, no water treated for polymerization is necessary for preparing the solution SSI. This unit can use oil production water (conditioned for injection) or aquifer water.

[0069] The location Bis advantageously a location which makes it possible to install at least one mobile storage unit, at least one mobile dilution unit. The location B in particular makes it possible to inject a fluid into an underground formation to extract hydrocarbons (oil and / or gas).

[0070] The mobile unit U5 is advantageously a relocatable unit composed of at least one dilution subunit, for example a tank provided with a stirring blade and / or a conduit equipped with static and / or dynamic mixers. Optionally, the mobile unit U5 comprises a tank for storing the solution SM.

[0071] The mobile unit U5 is a relocatable modular unit which can be transported by lorry or by rail transport.

[0072] Within this mobile unit U5, the saline solution SM is diluted by at least a factor 4 and as a maximum a factor 60 by the saline solution SS2 to obtain a solution SF containing less than

[0073] O.6% by weight of homopolymer P. As an example, for a solution containing 60% by weight of homopolymer P, a dilution by a factor 4 corresponds to obtaining a solution containing 15% by weight of homopolymer P.

[0074] Preferably, the solution SF contains between 0.01% and 0.4% by weight of homopolymer

[0075] P, even more preferably between 0.02% and 0.3% by weight of homopolymer P.

[0076] Like for the mobile unit U4, the saline solution SS2 can be prepared within the mobile unit U5, for example in a dissolution tank by adding the required quantities of salts to the water or by directly drawing the solution SS2 within the location B.

[0077] After having optionally been stored in a storage tank, the solution SF is injected into the underground formation in order to extract hydrocarbons (oil and / or gas). The recovery of hydrocarbons is done, either by sweeping the underground formation (conventionally assisted extraction of hydrocarbons), or thanks to the natural pressure of the hydrocarbons after a hydraulic fracturing operation (non-conventionally).

[0078] Thus, the injection of the solution SF into the underground formation is followed by a step of recovering hydrocarbons by assisted extraction by sweeping the underground formation by means of the solution SF, or by a step of recovering hydrocarbons by hydraulic fracturing of the underground formation by means of the solution SF.

[0079] According to a preferred embodiment, the injection method of the invention is performed with the locations A and A' which overlap, or which are contiguous. In other words, in this configuration, the 2 locations become one.

[0080] Preferably, the injection method of the invention comprises the following steps:

[0081] - in the location A: polymerization (in solution, example of a method: document US 2013090425) in a unit U2 of the AMPS.OS solution SI collected in the mobile unit U1 to obtain an aqueous homopolymer P' solution S2,

[0082] - transfer through pipes of the solution S2 from the unit U2 of the location A to the mobile unit U3 of the location A',

[0083] - in the location A': preparation in a mobile unit U3, before the polymerization of AMPS.MH, of a composition CA' comprising the AMPS.MH solution S3 and at least some of the homopolymer P' solution S2, the mass ratio [P'] / [ AMPS.MH] being of between 0.05 and 0.20, with [P*] concentration by weight of homopolymer P' in the composition CA' and [AMPS.MH] concentration by weight of AMPS.MH in the composition CA'.

[0084] The transfer of the AMPS.OS solution SI from the storage subunit of the mobile unit U1 to the unit U2 is done preferably through a conduit (pipe).

[0085] The polymerization of the AMPS.OS solution SI in the unit U2 is a polymerization in solution known to a person skilled in the art to obtain a homopolymer P' of average molecular weight by weight advantageously of between 500 and 500000 daltons. Adding the homopolymer P' solution S2 into the solution S3 is done preferably before adding redox and / or thermal and / or glucose oxidase initiators.

[0086] The unit U2 is a relocatable modular unit which can be transported by lorry or by rail transport and which is composed of at least one polymerization subunit, for example a tank provided with a stirring blade. Preferably, between 1 and 100% of the AMPS.MH of the homopolymer P and / or of the AMPS.OS of the homopolymer P' is in the form of AMPS.S salts, said salts being alkaline or alkaline earth or ammonium salts (ammoniac salt: NH4+).

[0087] The alkaline salts are chosen from among lithium, potassium and sodium. The preferred alkaline salt is sodium. The alkaline earth salts are chosen from among calcium, magnesium. NH4+ammonium salt is also a preferred salt.

[0088] Advantageously, the AMPS.S salts of the homopolymer P and / or of the homopolymer P' are formed during the polymerization of the AMPS.MH in the solution S3 in the mobile unit U3 or during the preparation of the solution SM in the mobile unit U4 or during the preparation of the solution SF in the mobile unit U5. The AMPS.S salts of the homopolymer P’ can also be formed during the polymerization of the AMPS.OS in the solution S2 in the mobile unit U2. The formation of these salts is done by adding into the solution (S2, S3, SM or SF) the required quantity of basis of interest (examples of bases: NaOH or Na2COs for the formation of sodium salt, CaCOs for formation of calcium salt) or by ammoniac bubbling in the AMPS.MH or AMPS.OS solution to form NH4+ammonium salt.

[0089] According to the distances between the locations A' and B, the transfer of the solution SM from the location A' to the location B is done by pipes or by transport units.

[0090] For example, the distances between the locations A' and B can be between 10 and 3000km, or between 10 and 1500km, or between 20 and 500km, or also between 30 and 300km.

[0091] The pipes ensuring the transfer of the solution SM between the locations A' and B are preferably rigid and can include static mixers.

[0092] For the transport of the solution SM between the locations A' and B, a suitable transport unit is used. The transport unit can have a volume of Im3to 40m3, in particular of 5m3to 40m3, preferably of 10 to 30m3, for example of 20m3to 30m3or of 15 to 25m3. Examples of suitable transport units comprise ships comprising at least one opening or tank containers.

[0093] The transport of the solution SM between the locations A' and B can be done by any type of transport means suitable for transporting the transport unit, for example by lorries, carriages or ships. The term "transport unit" means one or more advantageously distinct transport units such as containers, for example ISO containers or intermediate loose containers, which are loaded on suitable transport means, for example trailers, container carriages or ships. The transport means can transport one single transport unit or a plurality of transport units. The term "transport unit" further includes the transport units in which the transport compartment is temporarily or permanently fixed to the transport means, like for example tankers or tank cars.

[0094] In an embodiment, the transport is done by lorries. The transport unit can also be fixed to a lorry. In an embodiment, the transport unit can be an ISO tank container.

[0095] In another embodiment, tanks fixed to a lorry can be used. In an embodiment, the reservoir comprises an outlet opening at the rear end of the lorry and, to facilitate the removal of the contents, the reservoir can be inclined. In another embodiment, the reservoir comprises an outlet opening on the lower side of the reservoir. Furthermore, the tank can comprise a cone on the lower side of the tank and the outlet opening is located at the lower end of the cone. Filling the transport unit with the solution SM can be done by pumping the solution SM into the transport unit.

[0096] The transport time, i.e. the transport time of the transport unit filled with homopolymer P solution SM, can be very different, according to the distance between the locations A' and B. It can vary by a few minutes to several days, for example from 1 hour to 28 days, in particular from 2 hours to 14 days, in particular from 5 hours to 7 days. In an embodiment of the invention, a homogenization step such as described below can be carried out during transport. In an embodiment, the transport unit, for example a lorry, can comprise a rotary drum making it possible to perform the homogenization. In other embodiments, the transport unit can comprise a circulation loop equipped with a pump and optionally mixture units, for example static mixers, such that the homopolymer P solution SM can be circulated during transport.

[0097] Advantageously the homopolymer P solution SM in the location A' is stored in a maturation and storage unit before being transferred to the location B. This maturation and storage unit is advantageously constituted of one or more tanks in series provided with stirring blades.

[0098] Figures Figure 1 represents a first embodiment of the present invention.

[0099] Figure 1 represents a second embodiment of the present invention according to which the AMPS.MH monomer is polymerized in the presence of homopolymer P'.

[0100] Description of the figures

[0101] The device of figure 1 comprises:

[0102] - a location A including:

[0103] * the preparation in a mobile unit U1 of AMPS.MH,

[0104] * the collection of the AMPS.SO aqueous solution SI, coming from the draining of the preparation of the AMPS.MH,

[0105] - a location A' including:

[0106] * the preparation in a mobile unit U3 of a homopolymer P by gel polymerization of an AMPS.MH aqueous solution S3,

[0107] * the dissolution in a mobile unit U4 of the homopolymer P in a saline solution SSI to obtain a homopolymer P solution SM,

[0108] * the transfer of the solution SM from the location A' to a location B,

[0109] - the location B including:

[0110] * the dilution in a mobile unit U5 of the solution SM by a saline solution SS2 to obtain a solution SF containing less than 0.6% by weight of homopolymer P,

[0111] * the injection of the solution SF into the underground formation.

[0112] The device of figure 2 comprises:

[0113] - a location A including:

[0114] * the preparation in a mobile unit U1 of AMPS.MH,

[0115] * the collection of the AMPS.OS aqueous solution SI, coming from the draining of the preparation of the AMPS.MH,

[0116] - a location A' including:

[0117] * the preparation in a mobile unit U3 of a homopolymer P by gel polymerization of an AMPS.MH aqueous solution S3,

[0118] * the preparation in a mobile unit U3, before the polymerization of AMPS.MH, of a composition CA' containing the AMPS.MH solution S3 and at least some of the homopolymer P' solution S2,

[0119] * the dissolution in a mobile unit U4 of the homopolymer P in a saline solution SSI to obtain a homopolymer P solution SM,

[0120] * the transfer of the solution SM from the location A' to a location B,

[0121] * the polymerization (in solution) in a unit U2 of the AMPS.OS solution SI to obtain a homopolymer P' aqueous solution S2, - the transfer of the solution S2 from the unit U2 of the location A to the mobile unit U3 of the location A',

[0122] - the location B including:

[0123] * the dilution in a mobile unit U5 of the solution SM by a saline solution SS2 to obtain a solution SF containing less than 0.6% by weight of homopolymer P, * the injection of the solution SF into the underground formation.

Claims

Claims1. Method for injecting an aqueous solution of a homopolymer P of 2-acrylamido-2- methylpropane sulfonic acid and / or its salts, the homopolymer P having an average molecular weight by weight greater than 1 million daltons, the aqueous solution of homopolymer P being injected into an underground formation for the enhanced recovery of hydrocarbons or hydraulic fracturing, said method comprising the following successive steps:- in a location A:* preparation in a mobile unit U1 of 2-acrylamido-2-methylpropane sulfonic acid in hydrated crystalline form (AMPS.MH) having an X ray powder diffraction diagram comprising peaks at 10.58°, 11.2°, 12.65°, 13.66°, 16.28°, 18.45°, 20°, 20.4°, 22.5°, 25.5°, 25.88°, 26.47°, 28.52°, 30.28°, 30.8°, 34.09°, 38.19°, 40.69°, 41.82°, 43.74°, 46.04° degrees 2-theta (+ / - 0.1°),* collection of an aqueous solution SI of 2-acrylamido-2-methylpropane sulfonic acid AMPS.OS, coming from the draining of the preparation of the AMPS.MH in mobile unit Ul,- in a location A':* preparation in a mobile unit U3 of a homopolymer P by gel polymerization of an AMPS.MH aqueous solution S3 to afford a homopolymer P,* granulating the gel of homopolymer P in a granulation unit to obtain pieces of gel of homopolymer P* dissolution in a mobile unit U4 of the pieces of gel of homopolymer P in a saline solution SSI containing at least Ig / L of alkaline and / or alkaline earth salts in water to obtain a homopolymer P solution SM,* transfer of the solution SM from the location A' to a location B,- in the location B:* dilution in a mobile unit U5 by at least a factor 4 and as a maximum a factor 60 of the solution SM by a saline solution SS2 containing at least 1 g / L of alkaline and / or alkaline earth salts in water to obtain a solution SF containing less than 0.6% by weight of homopolymer P,* injection of the solution SF into the underground formation.

2. Method according to claim 1, characterized in that the locations A and A' overlap or are contiguous.

3. Method according to claim 1 or 2, characterized in that it comprises the following steps:- in the location A: polymerization in a unit U2 of the AMPS.OS solution SI collected in the mobile unit U1 to obtain a homopolymer P' aqueous solution S2,- transfer by pipes of the solution S2 from the unit U2 of the location A to the mobile unit U3 of the location A',- at the location A': preparation in a mobile unit U3, before the polymerization of AMPS.MH, of a composition CA' containing the solution S3 of AMPS.MH and at least some of the solution S2 of the homopolymer P', the mass ratio [P'] / [ AMPS.MH] being of between 0.05 and 0.20, with [P*] concentration by weight of homopolymer P' in the composition CA' and [AMPS.MH] concentration by weight of AMPS.MH in the composition CA'.

4. Method according to one of the preceding claims, characterized in that between 1 and 100% of the AMPS.MH of the homopolymer P and / or of the AMPS.OS of the homopolymer P’ is in the form of AMPS.S salts, said salts being alkaline or alkaline earth or ammonium salts.

5. Method according to claim 4, characterized in that the AMPS.S salts of the homopolymer P and / or of the homopolymer P' are formed during the polymerization of the solution S3 in the mobile unit U3 or during the preparation of the solution SM in the mobile unit U4 or during the preparation of the solution SF in the mobile unit U5.

6. Method according to one of the preceding claims, characterized in that the transfer of the solution SM from the location A' to the location B takes place by pipes or by transport units.

7. Method according to one of the preceding claims, characterized in that the AMPS.MH is prepared by purification of 2-acrylamido-2-methylpropane sulfonic acid previously stored in the location A in a mobile storage unit.

8. Method according to one of the preceding claims, characterized in that the polymerization of the homopolymer P in the mobile unit U3 is initiated in the presence of glucose oxidase.

9. Method according to one of the preceding claims, characterized in that the solution SM at the location A' is stored in a maturation and storage unit before being transferred to the location B.

10. Method according to one of the preceding claims, characterized in that the polymerization of the solution S3 of AMPS.MH in the mobile unit U3 is carried out with an initial concentration of AMPS.MH in the solution S3 greater than 20% by weight.

11. Method according to one of the preceding claims, characterized in that the final temperature of the polymerization of the solution S3 of AMPS.MH in the mobile unit U3 is greater than 80°C.

12. Method according to one of the preceding claims, characterized in that the injection of the solution SF into the underground formation is followed by a step of enhanced recovery of hydrocarbons by sweeping the underground formation by means of the solution SF.

13. Method according to one of the preceding claims, characterized in that the injection of the solution SF in the underground formation is followed by a step of recovering hydrocarbons by hydraulic fracturing of the underground formation by means of the solutionSF14. Method according to one of claims 3 or 5, characterized in that the homopolymer P' has an average molecular weight by weight of between 500 and 500000 Daltons.

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