FR3075806A1 - PROCESS FOR OPERATING A SUBTERRANEAN FORMATION BY INJECTING A FLUID COMPRISING AN ADDITIVE COMPRISING MAGNETIC NANOPARTICLES - Google Patents

Abstract

The present invention relates to a method for operating an underground formation, in which at least one fluid is injected. According to the invention, the fluid comprises at least one additive, the additive consisting of at least one adjuvant bonded to at least one magnetic nanoparticle. In this way, by applying a magnetic field, the additive can be separated from the effluent produced

Description

The present invention relates to the field of exploration and exploitation of an underground formation. The invention relates more particularly to the treatment of a fluid recovered from the underground formation. The invention relates in particular to the field of enhanced oil recovery (EOR from English Enhanced Oil Recovery) and the field of treatment of production water.

For the exploration and exploitation of an underground formation, it is common to inject a fluid into the underground formation in order to increase the efficiency of the processes. To optimize these processes, it is customary to include at least one adjuvant in the injected fluid. This adjuvant can take the form of organic molecules, such as polymers, copolymers and / or surfactants, etc. It can also take the form of inorganic molecules such as minerals (clays, barite, etc.), oxide particles (titanium oxides, iron oxides, etc.) etc. Although the method is improved, the addition of adjuvant (s) poses certain problems linked in particular to the pollution by the adjuvant of the underground formation, to the pollution by the adjuvant of the water contained in the underground formation, pollution of water and / or hydrocarbons produced by the admixture, etc. It is therefore necessary to monitor the behavior of the adjuvant in the underground formation.

For the enhanced recovery of hydrocarbons, it is interesting to know whether the adjuvant used, generally polymers, copolymers and surfactants, is found in the water produced, and if so, to eliminate this adjuvant from the water. produced, in order to carry out an adequate water treatment.

No current method allows a simple and rapid treatment of the effluent, in order to remove from the effluent the adjuvants injected.

To solve these problems, the present invention relates to a method of operating an underground formation, in which at least one fluid is injected. According to the invention, the fluid comprises at least one additive, the additive consisting of at least one adjuvant linked to at least one magnetic nanoparticle. In this way, by applying a magnetic field, the additive can be easily separated (without the need for complex equipment) and quickly (without the need for long separation steps) from the effluent produced.

The method according to the invention The invention relates to a method of operating an underground formation, in which at least one fluid is injected into said underground formation, said injected fluid comprising at least one additive. For this process, the following steps are carried out: a) at least one additive is synthesized by binding at least one magnetic nanoparticle to at least one adjuvant of said fluid; b) injecting said fluid comprising said additive into said underground formation; c) recovering at least one effluent from said underground formation; and d) removing said additive present in said effluent by the application of a magnetic field.

According to one embodiment of the invention, said adjuvant is an organic compound such as a polymer, a copolymer, or a surfactant.

Advantageously, said adjuvant is a partially hydrolyzed polyacrylamide HPAM or a terpolymer composed of acrylamide, acrylic aid and N-Vinylpyrrolidone or acrylamide-tert-butyl sulfonate (ATBS), a biopolymer such as xanthan or scleroglucan or a schizophyllan .

Alternatively, said adjuvant is an anti-deposition adjuvant, or an anticorrosion adjuvant or an anti-hydrate adjuvant.

According to an implementation of the invention, said recovered effluent is a production effluent from said underground formation comprising hydrocarbons, or a fluid taken from an aquifer of said underground formation, or a drilling fluid.

In one aspect, said magnetic nanoparticle is coated with silica or alumina.

According to one characteristic, said magnetic nanoparticle comprises a ferromagnetic core, in particular of iron, preferably of magnetite or maghemite.

According to one embodiment, said additive is synthesized by grafting said magnetic nanoparticle onto the adjuvants or by incorporating said magnetic nanoparticle directly into the structure of the adjuvants or by coating the adjuvants and the magnetic nanoparticles with another material.

According to one implementation, said magnetic nanoparticle is linked to said adjuvant by a bond of chemical nature, such as for example covalent bonds, or of ionic nature, or of physical nature such as for example electrostatic, or hydrophobic or Van der type associations. Waals.

Preferably, said additive comprising said magnetic nanoparticle present in said effluent is separated by means of at least one magnet located within or near a pipe or a reservoir or a tank in which the effluent is located. recovered.

According to one aspect, said step of separation of said additive comprising said magnetic nanoparticle comprises a preliminary step of separation of the aqueous and organic phases of said effluent.

According to one characteristic, the method comprises a final step of separation of the aqueous and organic phases of said effluent.

Advantageously, said magnetic nanoparticles and / or said labeled additive from the step of separating said additive comprising said magnetic nanoparticle is recycled.

Detailed description of the invention

The present invention relates to a method of operating an underground formation, in which at least one fluid is injected, the fluid comprising at least one additive. For the method according to the invention, the following steps are carried out: 1) Synthesis of the additive, and formulation of the fluid with the additive 2) Injection of the fluid 3) Recovery of an effluent from the underground formation 4) Magnetic separation additive and fluid

According to one embodiment, the method can include an optional step: 5) Recycling of the nanoparticles and / or of the additive

The injected fluid can be an aqueous fluid or an organic solvent. It can be a drilling fluid, water containing the synthesized additive, a fracturing fluid, an enhanced oil recovery fluid, etc. The fluid additive consists of at least one adjuvant linked to at least one magnetic nanoparticle. The adjuvant of the injected fluid can take the form of organic molecules, such as polymers, copolymers (for example a polyacrylamide).

Preferably, the adjuvant can be a synthetic polymer such as, for example, more or less hydrolyzed polyacrylamide: HPAM, a copolymer based on acrylamide and sulfonated monomer, or a terpolymer composed of acrylamide, acrylic acid and N -Vinylpyrrolidone or acrylamide-tert-butyl sulfonate (ATBS), or a natural polymer (biopolymer) such as xanthan, scleroglucane or schizophyllane. These polymers are commonly used in the field of enhanced oil recovery (called EOR for Enhanced Oil Recovery) for their viscosifying properties. In addition, these polymers are adapted to be magnetically separable from the fluid into which it has been introduced in a simple manner to be implemented by grafting one (or more) nano or microparticle (s) magnetic (s) ( such as iron oxide nanoparticles) on the polymer. By the term "magnetic materials" is meant materials which may exhibit permanent magnetization or which may exhibit magnetization when a magnetic field is applied to them.

The term “recovered effluent” is understood to mean in particular complex fluids comprising, alone or as a mixture, production water, hydrocarbons, drilling fluids, fracturing fluids, water from geological formations, etc. The term effluent designates a complex fluid comprising alone or in combination production water and hydrocarbons, which can be recovered by a producing well. 1) Summary of the additive

According to the invention, the synthesized additive is an adjuvant of the fluid (in particular a polymer) which has magnetic properties, and which, when it is present in the fluid, can be separated and isolated from it by using its properties. magnetic, in particular by means of a magnetic field. This step of the method according to the invention consists in binding at least one fluid adjuvant to at least one magnetic nanoparticle. It is recalled that the adjuvants are those used in the petroleum industry and can be of various chemical natures.

The magnetic properties of the additive are provided by one or more magnetic nanoparticles which are linked to the adjuvant. The bonds can be of chemical nature, such as for example covalent bonds, or ionic, or of physical nature such as for example electrostatic associations, or hydrophobic or of Van der Waals type.

Thus, the magnetic characteristics of nanoparticles allow their attraction by application of a magnetic field, regardless of the fluid in which they are found. Thanks to the bond between the adjuvant and the nanoparticle (s), the additive thus acquires magnetic properties. Thus if the additive is present in the recovered effluent, its magnetism allows simple and rapid separation of the additive present in the recovered effluent (and allow possible recycling of the additive).

Fluid adjuvant is any chemical compound that can be added to the fluid to improve its role in underground formation. The adjuvant can be an organic compound such as a polymer, a copolymer, or a surfactant, in particular for an application of an EOR process. Preferably, the adjuvant can be a partially hydrolyzed polyacrylamide HPAM or a terpolymer composed of acrylamide, acrylic acid and N-Vinylpyrrolidone or ATBS, a biopolymer such as xanthan or scleroglucan or a schizophyllan L ′ adjuvant can also be an anti-deposition adjuvant, or an anticorrosive adjuvant or an anti-hydrate adjuvant.

Nanoparticles are objects whose size is typically between 1 and 500 nanometers. Magnetic nanoparticles are made of magnetic material or contain magnetic material.

According to one example, the magnetic material is magnetite which is iron oxide of formula Fe304, which has good magnetic properties. Alternatively, the magnetic material is maghemite, which has good magnetic properties.

Magnetic nanoparticles can be synthesized in any manner known to those skilled in the art. They can be synthesized by different routes such as the coprecipitation of metal salts, in particular ferrous and ferric salts, the thermal decomposition of organometallic compounds such as, for example, iron acetylacetonates or iron carboxylates. They can also be synthesized from microemulsions or by hydrothermal syntheses.

These synthetic routes are widely described for example in the documents “magnetic nanoparticles: synthesis, protection, functionnalisation and applications, An-Hui Lu et al, Angew. Chem. int. Ed. 2007, 46, 1222-1244 ”or“ magnetic iron oxide nanoparticles: synthesis, stabilization, vectorization, physicochemical characterization and biological application, S. Laurent et al, Chem. Rev. 2008, 108, 2064-2110 ”.

For example, nanoparticles can be synthesized by coprecipitation of ferric and ferrous ions by addition of a base (method sometimes called Massart method), an example of such a method is described in the document "Bee, A .; Massart, R .; Neveu, S. Synthesis of very fine maghemite particles. J. Magn. Magn. Matr. 1995. 149 (1): 6-9 ”. Following the reaction, the nanoparticles can be purified and / or isolated by means of, for example, washing, centrifugation and filtration steps.

The nanoparticles obtained can be isolated or maintained in the form of a suspension in a liquid matrix.

Three nonlimiting examples of synthesis of iron-based magnetic nanoparticles are described below: Example 1: nanomagnetic particles MNPs-1: the iron salts FeSO4 and FeCl3 are mixed in a molar ratio of 1: 2 in 100 ml of water at a concentration of 0.13 M iron ions. Trisodium citrate is added to the mixture in a molar ratio of 1% relative to the total iron concentration. The mixture is vigorously stirred (280 rpm) for 30 minutes with a mechanical stirrer under an argon atmosphere. Then, 6 ml of ammonium hydroxide are rapidly injected into the mixture and the reaction is continued for 1 h at room temperature under an argon atmosphere. Example 2: nanomagnetic particles MNPs-2: This synthesis protocol is similar to the previous one, except for the total iron concentration which is 0.08 M and the addition of citrate which is done after 1 hour of synthesis. Then the medium is brought to the temperature of 80 to 90 ° C for 30 minutes. example 3: nanomagnetic particles MNPs-3: This synthesis protocol is similar to the previous one, except for iron sulphate which is replaced by the same molar quantity of ferrous chloride FeCI2. The salts of FeCI2 and FeCI3 are mixed at a concentration of 0.08 M in iron ions.

According to one embodiment of the invention, the magnetic nanoparticle can be coated with an inorganic layer, for example of silica and / or alumina.

According to one embodiment of the invention, the magnetic nanoparticle can be coated with an organic layer, for example of polymer.

This coating optionally makes it possible to protect the iron oxide from any undesirable reaction, to promote the dispersion of the nanoparticles and also to facilitate the functionalization of the nanoparticle, that is to say the grafting of one or more chemical functions which will allow or promote the bond between the nanoparticle and the adjuvant of the invention such as for example a polyacrylamide type polymer partially hydrolyzed HPAM.

This coating can be carried out by the Stober method described in particular in the document "Stober, W .; Fink, A .; Bohn, E. Controlled growth of monodisperse silica spheres in the micron size range. J. Colloid Interface Sci., 26 (1968), pp. 62-69 ".

According to a nonlimiting exemplary embodiment, the magnetic nanoparticle comprises an iron core, for example made of magnetite or maghemite, covered with a coating which is a layer of silica.

This type of nanoparticle is particularly suitable for grafting on partially hydrolyzed polyacrylamide type polymers (HPAM). This embodiment is particularly suitable for an enhanced recovery process of chemical EOR hydrocarbons, in which a formulation containing at least the "magnetic" HPAM polymers will be injected. Thus, when these additives come out with the effluent produced, they can be removed in a simple manner, by applying a magnetic field.

The connection between the nanoparticle (s) and the polymeric adjuvant (s) can be carried out either by chemical grafting or by physical interaction.

There are different possibilities to link magnetic nanoparticles with polymers. These different techniques are described in the literature and can be adapted to the process according to the invention. They are listed below in a non-exhaustive manner.

According to a first alternative embodiment, the grafting by chemical bonding can be carried out by means of a covalent bond. These bonds can be created by reactions of specific functions judiciously chosen and available on magnetic nanoparticles and / or on polymer additives.

According to a second alternative embodiment, the grafting can for example be carried out from a magnetic nanoparticle whose surface carries amine functions. These functions can react chemically with functions carried by a partially hydrolyzed polyacrylamide type polymer.

According to a third alternative embodiment, the grafting of a magnetic nanoparticle the surface of which carries amine functions on a polymer of partially hydrolyzed polyacrylamide type can be carried out by the direct amidation reaction of a carboxylic function in its acid form and the amine function carried by the nanoparticle. This reaction can also be carried out according to a well-known method which consists in reacting a carboxylic acid function with a carbodiimide such as 1-ethyl-3- (3-dimethylaminopropyl) carbodiimide hydrochloride followed by the reaction with sodium salt N-hydroxysulfosuccinimide and then the reaction with an amine function carried by the nanoparticle.

According to a fourth alternative embodiment, it is also possible to graft a magnetic nanoparticle whose surface carries amine functions on a polymer of polyacrylamide type from a polymer mainly of acrylamide type which is obtained by copolymerization in addition to acrylamide and optionally other monomers such as for example sodium acrylate or the acrylic acid of an acrylate or an alkyl methacrylate such as methyl acrylate or ethyl acrylate. The grafting of the nanoparticle is then carried out by an amidation reaction between the amine and ester functions introduced into the polymer.

These synthetic routes are illustrated by reaction schemes 1 and 2 below. On these NP representations illustrate the magnetic nanoparticles.

Reaction scheme 2

According to the syntheses described above, the magnetic nanoparticles are distributed along the chain of a polymer if each nanoparticle has only one bond with the polymer, but a nanoparticle can be linked to several polymer chains or several monomers of the same polymer chain. Similarly, each nanoparticle can be linked to several polymer chains, themselves linked to several nanoparticles thus forming an aggregate-type structure.

It is also possible, according to a well known prior art, to synthesize magnetic nanoparticles the surface of which carries thiol functions and in this case proceed to the polymerization of unsaturated monomers, such for example without being acrylamide, sodium acrylate or l acrylic acid, in the presence of a radical polymerization initiator, such as a peroxide or an azo compound. Thus, according to a well known principle, the thiol function carried by the nanoparticle written here R-SH is converted into radical R-S ° and this radical initiates the polymerization or the copolymerization of the monomer (s). This amounts to initiating a (co) polymerization of acrylamide-type monomers from a nanoparticle. By this route, magnetic nanoparticles are mainly obtained, in which each nanoparticle is linked to several polymer chains according to a so-called star structure.

This synthetic route is illustrated by reaction scheme 3 below. In this representation NP illustrate the magnetic nanoparticles.

Reaction diagram 3

This type of structure can also be obtained from magnetic nanoparticles the surface of which carries unsaturated polymerizable functions, for example vinyl. This consists in copolymerizing these nanoparticles with unsaturated monomers such as, for example, acrylamide, sodium acrylate or acrylic acid in the presence of a radical polymerization initiator such as a peroxide or an azo compound. The polymerizable unsaturated function carried by the nanoparticle participates in the polymerization or copolymerization of the monomer (s). This amounts to integrating one or more nanoparticles in the (co) polymerization of acrylamide type monomers. By this route, either magnetic nanoparticles are obtained, in which each nanoparticle is linked to several polymer chains according to a so-called star structure, or nanoparticles distributed along the chain of a polymer, or aggregate-type structures, in which each nanoparticle can be linked to several polymer chains or several monomers of the same polymer, themselves linked to several nanoparticles.

Alternatively, the connection between the magnetic nanoparticle (s) and the polymeric adjuvant (s) can be achieved by physical interaction, it can be a: - coupling by electrostatic attraction, or - hydrophobic attraction coupling between hydrophobic groups of the additive and hydrophobic groups introduced on the surface of the magnetic nanoparticles.

To bind the magnetic nanoparticles and the polymeric adjuvants, it is noted that the methods described above involve functionalizing the magnetic nanoparticles; the functionalization consists either of modifying the surface state of the magnetic nanoparticles or by coating the nanoparticle with a material having reactive functions, or by grafting chemical groups which will make it possible to establish a bond with the chemical groups of the additive to be bound , or to carry out the synthesis of the magnetic nanoparticle or its coating simultaneously with the incorporation of the chemical functions necessary for the connections with the polymer additive.

Functionalization methods have been well known since the late 1990s. The following articles describe these methods:

Bruchez Jr. M., Moronne M., Gin P., Weiss S., Alivisatos A.P., 1998, Semiconductor nanocrystals as fluorescent biological labels, Science. - Chan W.C.W., Nie S., 1998, Quantum dot bioconjugates for ultrasensitive nonisotopic detection, Science.

Functionalization can consist of grafting organic ligands on the surface of magnetic nanoparticles. The grafting of the ligands can be carried out on the metal oxide surface or if the magnetic nanoparticle is coated with an inorganic or organic layer, on the surface of the inorganic coating such as for example silica or on the surface of the coating organic. The coating may be a shell of a polymer or of a copolymer having the desired properties, for example, hydrophilicity for uses in aqueous media, or, on the contrary, hydrophobicity for uses in organic solvents . By way of example, the ligands can be amine, carboxyl, amide, thiol, etc. groups.

According to an exemplary embodiment, the functionalization of nanoparticles can be carried out by reaction of well-known grafting agents such as 3-aminopropyltriethoxysilane or 3-mercaptopropyltriethoxysilane which react with the hydroxyl functions, for example the silanol functions present on the surface of a silica coating. These grafting agents can also react directly with the surface of a nanoparticle made of iron oxide Fe304 by creating chemical bonds Fe-O-Si. This type of grafting is illustrated by the following reaction schemes 4 or 5.

Reaction scheme 4

Reaction scheme 5

According to one embodiment of the invention, the adjuvant and the magnetic nanoparticle can be coated in a coating in another material, for example silica and / or alumina. Following the synthesis, the formulation of the fluid to be injected is carried out with the additive. The type of fluid, the type of additives, and the amount of additives depend in particular on the function of the fluid and on the underground formation (constitution, porosity, etc.).

The injected fluid can be an aqueous fluid or an organic solvent. It can be a drilling fluid, water containing the synthesized additive, a fracturing fluid, an enhanced oil recovery fluid, etc.

The injected fluid can comprise a single additive. Alternatively, the injected fluid may comprise a plurality of adjuvants, for which a single adjuvant is made magnetic, for example the adjuvant which is the most polluting and which must be treated, or the adjuvant which is likely to be found in the fluid recovered first or the adjuvant most impacting the water / hydrocarbon (oil) separation of the surface effluent.

In addition, the injected fluid may include a plurality of additives. 2) Fluid injection

The fluid prepared with the additive is injected into the underground formation. The injection of a fluid into an underground formation can be carried out by any method known in the field of the petroleum industry. It can notably involve an injection of a fluid into an injector well by means of a pumping system. 3) Recovery of an effluent

This step consists in recovering an effluent, called recovered fluid, from the underground formation, which is used in the next separation step. The recovered fluid comprises complex fluids comprising alone or as a mixture at least one of the hydrocarbons produced by a producing well, or the water produced by a producing well, or the water taken from the underground formation, in particular the water taken from a aquifer of the underground formation, or a drilling fluid raised to the surface during the drilling operation, etc.

In addition, the effluent comprises at least part of the additive (s) synthesized in step 1) (rendered magnetic) of the injected fluid. 4) Magnetic separation

During this step, the additive (s) synthesized in step 1) (magnetic renderings) contained in the recovered effluent are separated. To do this, we use the magnetic property of magnetic nanoparticles: separation is achieved by applying a magnetic field. Thus, after this step the remaining effluent is devoid, quickly and simply, of the additive (s) injected into the underground formation.

According to one embodiment of the invention, the separation can be carried out using a magnet or a series of magnets. For example, the magnet or series of magnets can be placed near a pipe or a tank or tank in which the recovered effluent is located. Alternatively, the magnet or series of magnets can be located in a pipe or in a tank or vessel.

In accordance with an implementation of the invention, this separation step may include a prior step of separation of the aqueous (water) and organic (oil) phases from the effluent. The aqueous phase can be treated to be recycled (for example reinjected into the underground formation). The treatment of the aqueous phase then comprises the step of separating the additive (s) contained in the aqueous phase by magnetism.

In another embodiment of the invention, the magnetic separation step of the additive (s) can precede the water / oil separation step to facilitate the latter.

For the embodiment in which the additive is partially hydrolyzed polyacrylamide HPAM and in which the magnetic nanoparticles comprise an iron core (for example magnetite or maghemite) covered with a layer of silica, this step consists in separating the polymer HPAM marked by the magnetic nanoparticles of the recovered effluent. 5) Recycling of nanoparticles

It is recalled that this is an optional step in the process according to the invention. Recycling can correspond to: • the re-use of magnetic nanoparticles only and / or • the re-use of additives.

In accordance with an implementation of the invention, the magnetic nanoparticles can be recycled in order to use them again for the synthesis of additives. This step makes it possible to limit the cost of the method according to the invention, by limiting the quantity of magnetic nanoparticles used.

According to one aspect of the invention, for this step, the following steps can be implemented: - from the previous step, the additives comprising the magnetic nanoparticles are recovered; - The magnetic nanoparticles are separated from the adjuvants, for example by a pyrolysis method; - the magnetic nanoparticles are regenerated to make them suitable for their use; and - the magnetic nanoparticles are recycled in step 1) of synthesis of the additives.

According to a variant of this embodiment, this step may also include the regeneration and / or recycling of the additive. This limits the costs associated with the injected additive.

According to a second preferred variant, the additive comprising at least one magnetic nanoparticle (that is to say the adjuvant-mNP assembly) which has been magnetically separated can be directly reused in the formulation of the EOR fluid injected into the underground formation. This is direct recycling that requires the least amount of operations.

Process applications

The method of operating an underground formation according to the invention can be applied to all the processes for which a fluid, which comprises at least one additive, is injected into an underground formation, in particular for the exploration and operation of an underground formation. In particular, the operating method according to the invention can be used in an enhanced recovery process for EOR hydrocarbons, a method for treating the water produced, a drilling method, an oil production method and / or of bedrock gas, etc.

We briefly recall the different methods of exploring and exploiting an underground formation. However, the method according to the invention is not limited to the applications described.

Process for enhanced oil recovery (EOR)

At the start of the exploitation of an oil reservoir, the pressure prevailing in the deposit is sufficient to produce the hydrocarbons in place. However, over time, the pressure in the reservoir drops and is no longer sufficient to expel the oil from the reservoir rock. After this primary recovery, it becomes necessary to compensate for this drop in pressure by injecting either water or gas into the tank. This stage of production is called secondary recovery, but the recovery rate of hydrocarbons in place is limited to around 30%. The petroleum industry has developed improved oil recovery techniques (EOR). These techniques, called tertiary recovery, aim to modify the mobility and / or the saturation of the oil in place in the rock-reservoir. Among these improved recovery techniques, a distinction is made between E0R-C02 which consists of injecting C02 into the reservoir, and Chemical EOR which consists of injecting solutions of surfactants, microemulsions, or solutions aqueous synthetic polymers, such as polyacrylamide (for example HPAM), or biopolymers such as xanthan or any other biopolymer (the injection of these polymer solutions bears the English name of "polymer flooding"). One of the problems is the presence in the recovered effluent of injected additives. These latter notably impact the separation of the recovered effluent, the quality of the separated water and the quality of the separated oil, in addition to being a potential pollutant. The method according to the invention solves these problems. Water / oil separation

When we recover hydrocarbons, we also produce water, either that which was initially present in the underground formation, or that which was injected. The water and oil produced are mixed within the effluent. The recovered effluent can be polluted by the various additives injected. There are processes for separating oil and water. However, these separation processes can be made less efficient due to the additives present in the effluent. This is why, water treatment operations are planned to clean up the effluent produced. In this context, the method according to the invention provides a simple and rapid solution to allow separation of water and oil from a petroleum effluent.

Water treatment on fields with chemical EOR

When we recover hydrocarbons, we also produce water, either that which was initially present in the underground formation, or that which was injected. The recovered water can be polluted by the various additives injected. As a result, this water may be unsuitable for reuse or discharge into the environment, in a natural water reserve. This is why, water treatment operations are planned to clean up the produced water. These operations are complex and costly. The method according to the invention provides a simple and rapid solution to this problem.

Process for the production of oil and gas from source rocks

The production of these unconventional oils requires the fracturing of the bedrock. The most commonly used technique is hydraulic fracturing. Hydraulic fracturing consists in pumping under very high pressure a fluid containing different additives (solid particles called propants, polymers -polyacrylamide, ...-, clays, ...) so as to crack the rock. During poorly controlled hydraulic fracturing operations, it is possible that upwelling of the fluids used for fracturing may occur and cause pollution. The method according to the invention makes it possible to limit this phenomenon.

Well drilling method

For the drilling of a well, a fluid is injected which fulfills four functions which are: raising the rock cuttings, keeping the cuttings in suspension during circulation stops, maintaining the pore pressure in line with the training as well as cooling and lubrication of the drilling tool. The drilling fluid contains several additives to fulfill these four functions such as viscosifiers, lubricants, anti-foaming agents, filtrate reducers, etc. The dosage of each of the additives in the formulation of the drilling fluid is optimized so that this formulation has the desired properties. The additives can be either organic molecules, such as polymers, copolymers, associative polymers, surfactants, or inorganic particles (clays, barite, etc.). However, a variation in the concentration of additive (s) results in the fact that the drilling fluid no longer fulfills the functions mentioned above. On the drilling platform, a person is responsible for constantly checking that the properties of the drilling fluid comply with the initial specifications. For this purpose, it may be advantageous to have a method for recovering certain additives contained in the drilling fluid once brought to the surface, in particular for metering or re-use for a future formulation.

Flow assurance method

Such a process makes it possible to maintain the flow of hydrocarbons in the underground formation, by injection of a fluid comprising additives optimizing the flow, for example anti-deposit additives (in English anti-scale), anti-corrosion additives, and anti-hydrate additives. Examples of anti-deposit additives are polymers (polyacrylates, polycarboxylates, etc.). These additives can be found in the effluent. The method according to the invention makes it possible to limit this pollution.

Claims (13)

Claims 1) Method of operating an underground formation, in which at least one fluid is injected into said underground formation, said injected fluid comprising at least one additive, characterized in that the following steps are carried out: a) synthesizing at least one additive by binding at least one magnetic nanoparticle to at least one adjuvant of said fluid; b) injecting said fluid comprising said additive into said underground formation; c) recovering at least one effluent from said underground formation; and d) removing said additive present in said effluent by the application of a magnetic field. 2) The method of claim 1, wherein said adjuvant is an organic compound such as a polymer, a copolymer, or a surfactant. 3) Method according to claim 2, wherein said adjuvant is a partially hydrolyzed polyacrylamide HPAM or a terpolymer composed of acrylamide, acrylic acid and N-Vinylpyrrolidone or acrylamide-tert-butyl sulfonate (ATBS), a biopolymer such as a xanthan or scleroglucan or a schizophyllan. 4) Method according to claim 1, wherein said adjuvant is an anti-deposition adjuvant, or an anticorrosion adjuvant or an anti-hydrate adjuvant. 5) Method according to one of the preceding claims, wherein said recovered effluent is a production effluent from said underground formation comprising hydrocarbons, or a fluid taken from an aquifer of said underground formation, or a drilling fluid. 6) Method according to one of the preceding claims, wherein said magnetic nanoparticle is coated with silica or alumina. 7) Method according to one of the preceding claims, wherein said magnetic nanoparticle comprises a ferromagnetic core, in particular iron, preferably magnetite or maghemite. 8) Method according to one of the preceding claims, wherein said additive is synthesized by grafting said magnetic nanoparticle on said adjuvant or by incorporating said magnetic nanoparticle directly into the structure of said adjuvant or by coating said adjuvant and said magnetic nanoparticle another material. 9) Method according to one of the preceding claims, in which said magnetic nanoparticle is bonded to said adjuvant by a bond of chemical nature, such as for example covalent bonds, or of ionic nature, or of physical nature such as for example electrostatic associations, or hydrophobic or Van der Waals type. 10) Method according to one of the preceding claims, wherein separating said additive comprising said magnetic nanoparticle present in said effluent by means of at least one magnet located within or near a pipe or a tank or d '' a tank in which the recovered effluent is located. 11) Method according to one of the preceding claims, wherein said step of separating said additive comprising said magnetic nanoparticle comprises a prior step of separation of the aqueous and organic phases of said effluent. 12) Method according to one of claims 1 to 10, wherein the method comprises a final step of separation of the aqueous and organic phases of said effluent. 13) Method according to one of the preceding claims, wherein said magnetic nanoparticle and / or said additive from step d) of recycling of said additive comprising said magnetic nanoparticle is recycled.