WO2015059209A1

WO2015059209A1 - Method and unit for treating an aqueous composition including at least one polymer

Info

Publication number: WO2015059209A1
Application number: PCT/EP2014/072686
Authority: WO
Inventors: Matthieu JACOB; Jean-Philippe KHALFI; Anne DEMANGEL
Original assignee: Total Sa
Priority date: 2013-10-23
Filing date: 2014-10-22
Publication date: 2015-04-30
Also published as: FR3012129A1; AP2016009209A0; FR3012129B1

Abstract

The present invention relates to a method for treating an aqueous composition including at least one polymer in the context of hydrocarbon production, and specifically in the context of Enhanced Oil Recovery (EOR). Said treatment method includes the following steps: a) placing the aqueous composition including the polymer in contact with at least one agent for breaking down the polymer such as to reduce the size of the polymer; b) filtering with at least one membrane filter the aqueous composition resulting from step a) such as to obtain a retentate and a permeate including the reduced-size polymer. The invention also relates to a treatment unit designed such as to implement said method. The invention further relates to a method for enhanced oil recovery and to a plant for enhanced oil recovery.

Description

PROCESS AND UNIT FOR TREATING AN AQUEOUS COMPOSITION

COMPRISING AT LEAST ONE POLYMER

The present invention relates to a method for treating an aqueous composition comprising at least one polymer in the context of the production of hydrocarbons, and more particularly in the context of enhanced oil recovery ("enhanced oil recovery" or "enhanced oil recovery"). EOR). The invention also relates to a processing unit designed for the implementation of this method. The invention also relates to a process for enhanced hydrocarbon recovery and an assisted hydrocarbon recovery facility.

In the field of oil production, it is known to use a hydrocarbon production process known as enhanced oil recovery in a tank, by injection of an aqueous fluid, usually water or brine. This fluid sweeps the underground formation to force the hydrocarbons out of the pores of the rock where they are absorbed. This fluid is called the flushing fluid.

The scanning fluid may comprise additives such as polymers and / or surfactants and / or alkaline compounds. These additives modify the physicochemical properties of the water or injected brine (in particular its viscosity and its surface tension). These additives improve the efficiency of the sweeping fluid and increase the recovery efficiency of hydrocarbons contained in the underground formation. A mixture of hydrocarbons, solid particles in suspension, water and its additives (called production effluent) is thus produced at the production wells.

This effiuent is in the form of an emulsion that must be processed to obtain hydrocarbons ready for export or refining. A first separation step then consists of separating the hydrocarbons from the water while respecting the specifications relating to the export of hydrocarbons. A second step is to treat the water coming out of the separators (called production water) so that it can either be reinjected into an underground formation or released into the environment to the required specifications.

The presence of water-soluble polymer and / or other additives in the production water as part of a strategy for enhanced hydrocarbon recovery has many disadvantages, such as:

- an increase in solid waste (also called sludge),

disruptions of the water treatment chain related to the increase of the viscosity on the one hand and the stability of the emulsions on the other hand. These two phenomena reduce the dispersed hydrocarbon removal performance of conventionally used treatment processes (decanters, floats, hydrocyclones), clogging of the filters in depth (sand filter, multimedia filter) and / or membrane filters by adsorption of the polymer on the surface of the media or the membrane and by blocking the pores of the membranes. The membrane filtration step is recommended when the injection specifications require the elimination of all particles whose diameter is greater than 5 μιη or less.

Above this limit, deep filtration technologies can be used.

When it is necessary to reinject it into an underground formation, the production water must comply with injection specifications. These specifications depend on tank characteristics and injection modes. A production water quality that does not meet these injection specifications induces a loss of injectivity, which must then be compensated by an increase in the injection pressure. However, too much injection pressure increases the risk of fracture of the rock. In certain cases, the production water must therefore be of very good quality if it is desired to reinject it into an underground formation, especially when this reinjection is carried out in a matrix regime and / or in a pseudo-fracturing regime. By matrix regime is meant the injection of a fluid into an underground formation at a pressure lower than the fracturing pressure of the subterranean formation, in particular less than the fracturing pressure of the roofing rocks which seal said reservoir oil. The pseudo-fracturing regime corresponds to the injection of a fluid into an underground formation, then generally unconsolidated, at a slightly higher pressure, locally around the injection well, at the fracturing pressure of the cover rocks. By unconsolidated medium, we mean an underground reservoir, generally sandy clay, whose cementation between grains is weak to nonexistent. By "injection specification" is meant an aqueous composition having a dispersed hydrocarbon content of less than or equal to 50 mg / L, a solids content in suspension of less than or equal to 20 mg / L, the particles having a diameter d100 less than or equal to 5 μιη. By diameter d100, it is meant that 100% of the suspended solid particles contained in the aqueous composition have a given diameter. A diameter d100 less than or equal to 5 μιη means that 100% of the solid particles in suspension contained in the aqueous composition have a diameter less than or equal to 5 μιη. Good quality water is understood to mean a production water that meets the injection specifications required for reinjection and, more particularly, has a dispersed hydrocarbon content of less than or equal to 2 mg / L, a suspended solids content of less than or equal to at 1 mg / L, these particles having a diameter dl 00 less than or equal to 0.1 μιη.

It is known from WO-A-2012/049618 in the name of the applicant a process for treating a production water or a water taken from the environment for use in a process for enhanced hydrocarbon recovery. This method implements in particular the following steps: a step of membrane filtration of a production water or a water taken from the environment,

a retentate treatment step, in which solids and / or dissolved hydrocarbons are removed from the retentate to provide a treated retentate;

a step of recycling the retentate treated at the inlet of at least one membrane filtration module, the membrane module comprising at least one membrane filter.

This process provides treated water of consistent quality that can be injected into an underground formation. Although it is effective for production water that does not contain a hydrosulfide polymer, the process described in application WO-A-2012/049618 is still subject to the risk of clogging membrane filters in the presence of a polymer, which in the best case cases will multiply the maintenance or replacement of these filters.

There is therefore a need to develop a water treatment process in the context of enhanced hydrocarbon recovery, this process making it possible in particular to reduce the risks of clogging of the membrane filters, and to reinject water of very good quality. in an underground formation and generate a minimum of solid waste.

It is also known from EP2450314A1 a production water treatment process resulting from a process for enhanced oil recovery using water-soluble polymers. The method comprises the following steps:

an injection into the production water of an oxidant in an amount such that the viscosity of said water is lowered to a value of less than 2 cps within less than 5 hours after the injection of the oxidant, then

- An injection of a reducing agent in an amount necessary to neutralize all of the oxidant then in excess to obtain a low viscosity water.

This process makes it possible to obtain a treated water whose viscosity is compatible with the technologies used in the secondary production water separation processes (flotation, hydrocyclone, multimedia filtration). However, the production water obtained at the end of the filtration steps of this process does not achieve the injection specifications as defined above. This process does not allow a reinjection of production water matrix and / or pseudo-fracturing in an underground tank inconsolidated.

Finally, it is known from WO-A-2012/004474 a method of assisted hydrocarbon recovery comprising the following steps:

the injection into a reservoir of a sweeping fluid comprising a polymer so as to displace the hydrocarbons towards at least one producing well,

- the collection by a producing well of a production effluent including hydrocarbons, the injection into the effluent of production of at least one oxidizing agent, the injection being effected in situ at the bottom of the production well, or at the head of production wells.

The oxidizing agent makes it possible to destabilize the emulsion between the aqueous phase of the production fluid and the extracted hydrocarbons. The steps of pumping and transporting the effluent are then improved. In this process, the production water is treated to be rid of its pollutants before being released into the environment.

A first objective of the present invention is to provide a process for treating a production water comprising a polymer, which allows it to be reinjected into an underground formation, in particular in a matrix regime, that is to say with the injection specifications defined above. . This objective is achieved by coupling a step comprising contacting an aqueous composition derived from production water with at least one degradation agent of a polymer and a membrane filtration step of this treated composition. by the degradation agent.

To this end, the invention relates first of all to a method for treating an aqueous composition comprising at least one polymer, the process comprising the following steps:

a) contacting the aqueous composition comprising the polymer with at least one polymer degrading agent to reduce the size of the polymer, b) filtering with at least one membrane filter the aqueous composition obtained in step a) to obtain a retentate and a permeate comprising the reduced-size polymer.

In preferred embodiments, the method of treating an aqueous composition comprises one or more of the following characteristics:

the aqueous composition is a pretreated hydrocarbon production water fraction comprising, in addition to the polymer, suspended solid particles and dispersed hydrocarbons,

the permeate furthermore comprises dispersed hydrocarbons whose content is less than 50 mg / l and suspended solid particles whose content is less than 20 mg / l and whose particle diameter d100 is less than 5 μιη, preferably whose diameter d100 is between 0.01 and 5μιη,

the membrane of the membrane filter is chosen from the group formed by inorganic membranes, in particular ceramics, organic membranes and hybrid membranes,

the pore diameter of the membrane filter is at least 10 nm and at most 2000 nm, preferably 40 to 500 nm,

the polymer degradation agent is a chemical agent, a physical agent or a combination of these two types of agents such as, for example, an electro-oxidation treatment or a photo-catalytic treatment, the polymer degradation agent is a physical agent chosen from the group formed by ultrasonic waves and ultraviolet rays,

the degradation agent of the polymer is a chemical agent,

the chemical agent is an oxidizing agent chosen from the group formed by ammonium persulfate, sodium persulfate, potassium persulfate, sodium perborate, hydrogen peroxide, the mixture of hydrogen peroxide and a salt of a transition metal, ozone, sodium hypochlorite, sodium chlorite, chlorine dioxide, chlorine gas, air, oxygen, hydroxyl radicals and mixtures thereof.

the oxidizing agent is ozone or sodium hypochlorite, said agent being formed in situ by electrolysis of the air or by electrolysis of the sodium chloride, possibly present in the aqueous composition,

the oxidizing agent is the hydroxyl radicals obtained by a catalytic oxidation treatment of hydrogen peroxide, by an electro-oxidation treatment of oxygen, by a photochemical treatment of hydrogen peroxide, by a photochemical treatment ozone or by a photo catalytic oxidation treatment of hydrogen peroxide,

the process furthermore comprises a step c), subsequent to step a) or b) consisting of cl) injecting a reducing agent into the aqueous composition obtained at the end of step a) or into the permeate, when the degradation agent of the polymer is an oxidizing agent,

the method further comprises a step c2), subsequent to step b) of treating the retentate to obtain at least one aqueous phase,

the process further comprising a step c3) subsequent to step c2, consisting in recycling the aqueous phase obtained in step c2) into the permeate,

- The method further comprising a step c4) subsequent to step c2, of recycling the aqueous phase obtained in step c2) in the aqueous composition obtained at the end of step a).

A second object of the present invention is to provide a method of assisted hydrocarbon recovery which limits the formation of sludge, in particular the formation of sludge comprising a polymer, which allows a good functioning of the membrane filters used for the treatment of a water producing a polymer and allows a reinjection of the treated production water.

This objective is achieved by the implementation in a method of assisted oil recovery of a production water treatment step, this step comprising the coupling of at least one degradation agent of a polymer in a composition. aqueous solution from production water and a membrane filtration step of this composition treated with the degradation agent. The invention also proposes a method for the enhanced recovery of hydrocarbons contained in an underground formation, the process comprising at least the following steps:

i) injecting into the subterranean formation by at least one injector well at least one scanning fluid comprising at least one polymer, ii) recovering a production effluent from at least one producing well, iii) separating the production effluent into a phase hydrocarbons and an aqueous phase called hydrocarbon production water,

iv) pretreat the production water to obtain an aqueous composition comprising the polymer, and

v) implementing a method of treating said aqueous composition, this method being described above.

According to a preferred embodiment, the enhanced hydrocarbon recovery process further comprises the successive steps vi) and vii), subsequent to step v), consisting of:

vi) injecting at least one polymer into the permeate, and

vii) inject the permeate into the subterranean formation.

According to a preferred embodiment, step vi) comprises injecting at least one polymer and at least one surfactant and / or an alkaline compound into the permeate.

According to a preferred embodiment, the method further comprising a step c5) subsequent to step c2), of recycling the aqueous phase obtained in step c2) in the production water obtained at the end of the process. step iii).

The invention also proposes a treatment unit 500 of an aqueous composition for carrying out the method of treating an aqueous composition comprising at least one previously described polymer, the treatment unit 500 comprising at least:

a degradation unit 501 of the polymer to obtain a polymer of reduced size,

a membrane filtration module 503 comprising a retentate recovery zone and a permeate recovery zone,

a feed line 410 of the aqueous composition comprising the polymer connected to the inlet of the degradation unit 501,

a connection line 504 connecting the degradation unit 501 to the membrane filtration module 503,

a collection line 506 connected at the outlet of the permeate recovery zone of the membrane filtration module 503,

a collection line 508 connected at the outlet of the retentate recovery zone of the membrane filtration module 503. According to a preferred embodiment, the treatment unit 500 of an aqueous composition comprising at least one polymer comprises one or more of the following characteristics:

the degradation unit of the polymer 501 comprises at least one means of degradation of the polymer chosen from an ultrasound probe, a source generating ultraviolet rays (such as an ultraviolet lamp) and a setting device in contact with the aqueous composition with an oxidizing agent and a combination of these means for forming hydroxyl radicals,

a retentate processing unit 507 comprising solid / liquid / liquid separation means,

a neutralization unit 505,

a connection line 502 and a connection line 526 when the neutralization unit 505 is placed upstream of the membrane filtration module 503; the connection line 502 being connected at the output of the degradation unit 501 and connecting the degradation unit 501 to the neutralization unit 505, the connection line 526 being connected at the output of the neutralization unit 505 and connecting the neutralization unit 505 at the inlet of the membrane filtration module 503,

a connection line 528 and a collection line 530 when the neutralization unit 505 is placed downstream of the membrane filtration module 503; the connection line 528 is connected at the outlet of the permeate recovery zone of the membrane filtration module 503 and connects the membrane filtration module 503 to the inlet of the neutralization unit 505, the collection line 530 being connected in output of the neutralization unit 505, a recirculation line 510 fed by the collection line 508 and connected to the connection line 504 or 526,

collection lines 514, 516, 518 connected at the output of the processing unit of the retentate 507,

a recirculation line 524 fed by the collection line 16 and connected to the connection line 504 or 526,

a supply line 520 fed by the collection line 516 and connected to the collection line 506,

a collection line 522 fed by the collection line 516, optionally connected to the connection line 406,

a supply line 512 fed by the collection line 516 and connected to the collection line 530. The invention also proposes an installation 400 for the implementation of the hydrocarbon recovery process previously described, the facility 400 for enhanced hydrocarbon recovery comprising at least:

a hydrocarbon extraction unit 401,

a separation unit 403 comprising hydrocarbon / water separation means,

a production water pre-treatment unit 405 comprising solid / liquid / liquid separation means,

a treatment unit 500 of an aqueous composition as described above,

a connection line 402 connecting the hydrocarbon extraction unit 401 to the separation unit 403,

a connection line 406 connecting the separation unit 403 to the pretreatment unit 405,

a supply line 410 connecting the pretreatment unit 405 to the processing unit 500,

a collection line of the treated aqueous composition 414.

Other features and advantages of the invention will appear on reading the following description of an embodiment of the invention, given by way of example and with reference to the accompanying drawings.

FIG. 1 diagrammatically represents a flowchart of a method for the enhanced recovery of hydrocarbons contained in an underground formation,

FIG. 2 is a graph showing, as a function of time, the permeation flux of three aqueous compositions through a ceramic membrane of pore diameter announced by the supplier of 200 nm. The permeation flux, in ordinate, is expressed in L / hm ² bar at 20 ° C. The time on the abscissa is expressed in minutes (min). Curve No. 1 represents a composition comprising 600 mg / l of polymer and not comprising an active closure. Curve No. 2 represents an aqueous composition comprising no polymer and no active chlorine. Curve No. 3 represents an aqueous composition comprising 600 mg / l of polymer and 500 mg / l of active chlorine.

FIG. 3 is a graph showing, as a function of time, the permeation flux of three aqueous compositions through a ceramic membrane of pore diameter announced by the supplier of 40 nm. The permeation flux, in ordinate, is expressed in L / hm ² bar at 20 ° C. The time on the abscissa is expressed in minutes (min). Curve No. 4 represents an aqueous composition comprising 600 mg / l of polymer and 250 mg / l of active chlorine. Curve No. 5 represents an aqueous composition comprising 600 mg / l of polymer and 100 mg / l of active chlorine. Curve No. 6 represents an aqueous composition comprising 600 mg / L of polymer and 50 mg / L of active chlorine. Curve # 7 represents represent an aqueous composition comprising 600 mg / l of polymer and not comprising active chlorine. Curve No. 8 represents an aqueous composition comprising neither polymer nor active chlorine.

FIG. 4 schematically represents an assisted hydrocarbon recovery facility,

FIG. 5 diagrammatically represents an embodiment of a processing unit implemented in the assisted oil recovery plant of FIG. 4,

FIG. 6 diagrammatically represents another embodiment of a processing unit implemented in the assisted oil recovery plant of FIG. 4,

FIG. 7 schematically represents another embodiment of a processing unit implemented in the assisted oil recovery plant of FIG. 4,

FIG. 8 schematically represents a filtration circuit for the study of the filtration properties of a membrane.

In the remainder of the description, the elements that are identical or of identical function bear the same reference sign. For the sake of brevity of the present description, the elements common to the various examples are not described with regard to each of these examples. In other words, only the differences between the different examples are described in detail, the common elements being described with regard to a single example.

FIG. 1 represents a flowchart of a method for the enhanced recovery of hydrocarbons contained in an underground formation.

This method has a first step 110 of supplying a stream of water intended to be injected into a subterranean formation containing the hydrocarbons to be recovered.

The flow of water can in particular be taken from the environment. The term "environment" refers not only to the natural environment (for example, water may be taken from rivers or bodies of surface water, including rivers, lakes and the sea, or may be underground aquifer formation, usually salty) but also non-natural sources of water, such as industrial or domestic wastewater. In general, the water withdrawn comes from any water source, which can be processed cost-effectively to meet the injection specifications.

The method notably comprises a step 112 for treating the water to be injected.

This step depends on the nature and quality of the water taken as well as the nature of the reservoir and the method of injection. The treatment step 112 comprises in particular one or more steps chosen from a preliminary filtration, a deoxygenation, a chlorination, desulfation, biocide treatment, injection of anti-deposition or anti-corrosion compounds ...

Next, the method comprises a step 114 of adding at least one additive to the stream of water to obtain a flushing fluid. These additives are especially water-soluble and high molecular weight polymers. These polymers increase the viscosity of the sweeping fluid. They are called viscosifiers. These polymers are preferably non-biodegradable, of natural origin or of synthetic origin. Among the polymers used in the enhanced hydrocarbon recovery technique, there may be mentioned acrylamide-based polymers or copolymers, such as partially hydrolysed polyacrylamides known as HPAM, or xanthan gums. The scanning fluid may further comprise at least one ionic or nonionic surfactant in combination or not with at least one polymer and / or an alkaline compound.

The method comprises a step i) of injecting the flushing fluid into a subterranean formation. The injection of the sweeping fluid takes place via an injector well. The sweeping fluid makes it possible, by its viscosity, to push the hydrocarbons out of the pores of the rock of the underground formation. It transports the hydrocarbons to the production well (s).

Then, the process comprises a step ii) 118 of recovery of a production effluent. The production effluent is recovered by means of pumping and transport at at least one producing well. The production effluent is a mixture of hydrocarbons, polymer (s), water, solid particles, additives and possibly gas.

The process then comprises a step iii) 120 of separation of the production effluent to obtain at least one oily fraction comprising hydrocarbons and an aqueous phase called hydrocarbon production water. In the rest of the description, the expression "hydrocarbon production water" and "production water" are synonymous terms. Production water is water that is obtained after primary separation of the production effluent. This step 120 implements water / hydrocarbon separation means, such as decanters, separators.

The process then comprises a step iv) 122 of pre-treatment of the production water. The pretreatment step uses liquid / liquid / solid separation means such as gravity separators, hydrocyclones, and floats. At the end of this step, a production water is obtained having a dispersed hydrocarbon content of less than 500 mg / l, preferably less than 100 mg / l, preferably less than 30 mg / l. This aqueous composition obtained at the end of step iv) 122 of pretreatment can be viscous. The viscosity of this aqueous composition depends on the polymer concentration and its degradation rate (which vary in time following the breakthrough of the polymer). Then, the process comprises a step v) of treating the aqueous composition comprising at least one polymer.

In the process for treating the aqueous composition which comprises at least one polymer, a first step a) comprises contacting the aqueous composition comprising the polymer with at least one polymer degradation agent to reduce the size of the polymer.

Then, a second step b) 126 consists of filtering with at least one membrane filter the aqueous composition obtained in step a) 124 to obtain a retentate and a permeate comprising the reduced-size polymer. The membrane filtration step b) 126 makes it possible to obtain:

a filtered aqueous composition (permeate) which comprises at least one polymer of reduced size and which satisfies the injection specifications, and

a retentate which comprises the impurities retained by the membrane, such as at least the suspended solid particles and / or the dispersed hydrocarbons.

Step b) 126 thus makes it possible to remove the dispersed hydrocarbons and the solid particles in suspension from the aqueous composition resulting from step a) 124 while allowing the reduced-size polymer to pass through the pores of the membrane filter.

The hydrocarbon content, the suspended solids content and the size of the solid particles in suspension, the distribution of the particles having a given diameter are measured by analytical techniques well known to those skilled in the art.

Treatment of the polymer in step a) 124 improves the filtration efficiency of step b) 126 because the size of the high molecular weight polymer molecules in the stream feeding the membrane filter is reduced. Since the polymer is no longer retained by the membrane, the permeation flux is thus increased with less associated maintenance (washing mainly). By coupling step a) 124 and step b) 126, suspended solid particles and dispersed hydrocarbons are retained and the retentate is charged with oil and suspended solids.

There is therefore a particularly effective coupling, and even a synergy, between the action of the degradation agent of the polymer and the membrane filter.

The coupling of step a) 124 and step b) 126 thus makes it possible to obtain a permeate that satisfies the injection specifications. It may be recycled 134 as a flushing fluid 114 to which at least one additive is added. This fluid is then injected into an underground formation, in particular into an inconsolidated underground formation.

In addition, the treatment method of the invention is more cost effective than prior art treatment methods. Indeed, thanks to the coupling of step a) 124 and step b) 126, several cubic meters of production water are treated without the permeation flow being reduced (CAPEX decrease (capital expenditure or cost). investment) compared to a membrane filtration process retaining the polymer The tests carried out with the method of the invention have in particular shown productivity gains multiplied by a factor 3 to 6 compared to tests performed with the same membranes without partial degradation of the polymer. The treatment method according to the invention makes it possible to obtain permeation flux values close to those of a permeation flux that would be obtained on the same membrane but with an aqueous composition that does not comprise a viscosifying polymer.

The treatment method of the invention has the particular advantage of reducing the clogging speeds of the membranes and therefore of reducing the operating costs relating to the membrane filtration process (cleaning, treatment of retentates, stops, etc.).

The process of the invention makes it possible to obtain an aqueous composition having a content of dispersed hydrocarbons and a content of suspended solid particles and a diameter of 100 suspended solid particles less than or equal to the injection specifications defined above.

The process according to the invention makes it possible in particular to obtain an aqueous composition having a dispersed hydrocarbon content of less than or equal to 50 mg / L, a solids content in suspension of less than or equal to 20 mg / L, the particles having a diameter dlOO less than or equal to 5 μιη, preferably having a content of dispersed hydrocarbons of between 1 and 50 mg / L, a solids content in suspension of between 0.1 and 20 mg / L, these particles having a diameter of d100 being understood between 0.01 and 5 μιη.

More particularly, in step a) the aqueous composition is a pretreated production water fraction comprising in addition to the polymer, suspended solid particles and dispersed hydrocarbons.

By "aqueous composition comprising at least one polymer" is meant in the sense of the present invention, a production water having undergone primary separation and secondary separation. The aqueous composition comprising a polymer is therefore obtained after the hydrocarbon / water separation steps and after the decantation, flotation and hydrocylone and / or any other type of production water treatment steps failing to achieve a d100 specification in the range 0.01 to 5 μιη.

The polymers of the aqueous composition are additives used in the enhanced hydrocarbon recovery technique. As indicated above, these polymers can be of synthetic or natural origin. Among the polymers of synthetic origin, mention may be made of acrylamide-based polymers or copolymers, such as the partially hydrolysed polyacrylamides called HPAM, which are copolymers of acrylamide and of salt acrylate (sodium type), copolymers of acrylamide with sulfonated monomers such as AMPS (2-acrylamido-2-methylpropane sulfonate) or copolymers of acrylamide with PVP (polyvinyl pyrrolidone) type monomers, copolymers of acrylamide and acrylic. The polymers of natural origin may be chosen from the group consisting of guar gums, cellulose and cellulose derivatives such as carboxymethylcellulose, hydroxyethylcellulose, and carboxyethylcellulose, starch, xanthan gums, galactomannans or mixtures thereof. The polymers may be functionalized with sulphonate, carboxylate, amine, imine, ammonium, carboxamide, imide, hydroxyl or acetyl groups. The polymers can be used in combination with alkaline compounds (AP technique (Alkaline Polymer)) or in mixture or not with surfactants (technique known as SP (Surfactant Polymer) and techniques called ASP (Alkaline, Surfactant Polymer)). These polymers increase the viscosity of the aqueous composition in which they are added.

The polymers used are polymers of high molecular weight, that is to say polymers whose size is greater than 500 000 Da and preferably between 1000 000 and 25 000 000 Da.

The amount of polymer in the aqueous composition is generally between 1 and 2000 mg / l, preferably between 1 and 1300 mg / l, even more preferably between 1 and 700 mg / l, even more preferably between 1 and 150 mg / L.

The amount of suspended solid particles (TSS for Total Suspended Solid in English) in the aqueous composition before contacting with the degradation agent of the polymer is in particular between 0.1 and 200 mg / L. . The size of these particles is in particular between 0.01 and 100 μιη.

Before contacting with the polymer degradation agent, the aqueous composition has a viscosity of less than 20 cps, preferably between 2 and 5 cps, even more preferably between 1 and 2 cps.

For the purposes of the present invention, the term "polymer degrading agent" is intended to mean any chemical agent, physical agent or combination of these two types of agents, such as a catalytic oxidation treatment, oxidation or a photo-catalytic oxidation treatment. These agents cause a change in the structure of the polymer, this change being characterized in particular by a reduction in viscosity and a reduction in the size of the polymer. The size of the polymer in the aqueous composition obtained after step a) 124 depends on the chosen degradation agent, the dose of this agent and the contact time with the aqueous composition.

In one embodiment, the degradation agent of the polymer is a chemical agent, especially an oxidizing agent, chosen from the group formed by ammonium persulfate, sodium persulfate, potassium persulfate, sodium perborate, hydrogen peroxide, the mixture of hydrogen peroxide and a salt of a transition metal, ozone, sodium hypochlorite, sodium chlorite, chlorine dioxide, chlorine gas, air, oxygen, hydroxyl radicals and mixtures thereof. Preferably, the polymer degradation agent is selected from the group consisting of sodium hypochlorite, sodium chlorite, chlorine dioxide, chlorine gas. The use of an oxidizing agent as a degradation agent for the polymer advantageously makes it possible to obtain a better quality of permeate. Among the salts of a transition metal, mention may be made especially of those whose metal is selected from the group VIIIB and the group IB of the periodic classification, preferably iron and copper. The counterion is selected from the group consisting of sulfate anions and nitrate anions.

The hydroxyl radicals can be obtained by a catalytic oxidation treatment of hydrogen peroxide in the presence of a catalyst such as Fe ²⁺ ions (also called Fenton's reagent), Cu ²⁺ ions. This treatment consists in initiating decomposition reactions of hydrogen peroxide (H ₂ O ₂ ) by these catalysts in order to generate radical species (HO ^' for example) which are very reactive with respect to the polymer. Preferably, the polymer degradation agent is a combination of hydrogen peroxide and Fe ²⁺ ions or Cu ²⁺ ions.

The hydroxyl radicals can be obtained by an electro-oxidation treatment of oxygen. This treatment consists of producing in situ and electrolytically the reagents involved in the Fenton reaction. Hydrogen peroxide is produced by cathodic reduction of oxygen and ferrous or cuprous ions are produced in solution by anodic dissolution of an iron or copper electrode. Preferably, the polymer degradation agent is a combination of oxygen and an iron or copper electrode.

Hydroxyl radicals can be obtained by ultraviolet treatment of hydrogen peroxide or ozone. Preferably, the polymer degradation agent is a combination of an ultraviolet ray source and hydrogen peroxide or ozone.

The hydroxyl radicals can be obtained by a photo-catalytic oxidation treatment of hydrogen peroxide. This treatment is used to initiate decomposition reactions of hydrogen peroxide in the presence of a catalyst such as Fe ²⁺ ions or Cu ²⁺ ions and in the presence of ultraviolet rays. Preferably, the polymer degradation agent is a combination of a source generating ultraviolet rays, hydrogen peroxide, and Fe ²⁺ ions or Cu ²⁺ ions.

Advantageously, the injected oxidizing agent participates in the declogging of the membrane by limiting the development of organic films or other organic deposits independent of the presence of polymer.

The polymer degradation agent and the conditions for bringing the agent into contact with the aqueous solution polymer are chosen so that the degradation of the polymer is partial. The contacting of the oxidizing agent can be controlled via a redox probe when a chemical degradant is used.

In one embodiment of the invention, the mass ratio between the oxidizing agent and the polymer ranges from 1: 10 to 2: 1.

In one embodiment of the invention, the oxidizing agent is sodium ozone or hypochlorite, said agent being formed in situ by electrolysis of the air or by electrolysis of the sodium chloride, possibly present in the composition. aqueous. The formation of the oxidizing agent in situ advantageously makes it possible to reduce the problems supply, storage of the degradation agent at the production site, to overcome the stability problems of the oxidizing agent due to improper storage before use. The amount of sodium hypochlorite brought into contact with the aqueous composition is in particular between 0.01 and 2 g / g of polymer, preferably between 0.01 and 1 g / g of polymer.

By "partial degradation" is meant in the sense of the present invention a reduction in the size of the polymer to make it penetrate inside the pores of the selected membrane without totally degrading it. It has been experimentally verified that the only decrease in viscosity is not sufficient for the proper functioning of a membrane filtration unit. The viscosity parameter is therefore not adequate in this case but rather the size distribution of the polymer molecule.

The initial size (size T1) corresponds to the size of the polymer before contacting the aqueous composition with the degradation agent. This size may be smaller than that injected into the mother solution because of its degradation in the reservoir and in the process upstream of the degradation unit. At the end of the implementation of step a) 124, a mixture of polymers of reduced size (size T2) is obtained. The polymers of reduced size are not exclusively in monomeric form. The reduced size polymers have the same sequence of monomer units as the initial size polymer; however, they have chains of reduced and partially oxidized lengths. Step a) 124 of the treatment process therefore does not lead to complete degradation of the polymer but only to a reduction in the length of the polymer chains. The measurement of the size of the polymer (in practice the weight-average or number-average molecular weight size distribution) before or after the contact with the degradation agent is carried out by the techniques known to those skilled in the art. such as gel permeation chromatography or size exclusion chromatography. In the remainder of the present invention, the terms "polymer mixture of reduced size" and "polymer of reduced size" are equivalent.

The degradation agent of the polymer and the conditions for bringing the agent into contact with the polymer in aqueous solution are chosen so as to obtain a reduced-size polymer capable of diffusing through a membrane whose pore diameter is between 10 and 2000 nm, preferably between 40 and 500 nm.

The aqueous composition obtained at the end of step a) 124 comprises from 1 to 2000 mg / l of at least one polymer of reduced size, preferably 1 to 1300 mg / l, even more preferably between 1 and 700 mg / L and even more preferably between 1 and 150 mg / L.

The viscosity of the aqueous composition comprising the reduced-size polymer obtained after the implementation of step a) 124 of the process is between the viscosity of the water at the operating temperature and 1.5 cps, of preferably less than 1.2 cps, more preferably less than 1.0 cps. More particularly, the membrane filtration step b) 126 is a micro-filtration, ultrafiltration, nanofiltration step, or a combination of two or more of these techniques.

The pore diameter of the membrane filter is at least 10 nm and at most 2000 nm, preferably 40 to 500 nm. The pore diameter of the membrane filter is chosen to provide a permeate meeting the injection specifications necessary for reinjection into an underground formation.

The membrane filter, especially ultrafiltration or nanofiltration, is a membrane selected from the group consisting of inorganic membranes, organic membranes and hybrid membranes.

The organic membranes consist of polymeric or copolymeric materials such as cellulose acetate, cellulose nitrate, polysulfone, polyether sulfone, polyvinylidene fluoride, polyamide, PVDF (polyvinylidene fluoride) and acrylonitrile.

Advantageously, the inorganic membranes are made of ceramic materials such as SiC silicon carbide, Al ₂ O ₃ alumina, zeolite, zirconia, TiO ₂ titanium oxide, ZrO ₂ zirconia oxide and the like. SiO ₂ silica oxide, magnesium oxide MgO or mixed oxides silica and alumina or zirconia. These membranes support in particular a content of dispersed hydrocarbons up to 1 or 3% by mass and a temperature above 100 ° C.

Advantageously, the SiC-based membrane filters are particularly preferred because of their high hydrophilicity and their resistance to abrasion: they make it possible to obtain a higher permeation flux and are easier to clean.

The membranes can be hybridized, that is to say partly made of organic materials and partly of inorganic materials. A hybrid membrane is in particular a membrane consisting of a polymer matrix with inclusion of inorganic particles, or a membrane whose support is ceramic and comprises a polymer active layer.

Many membrane configurations are used, such as, for example, spiral, plate or tube membranes. Preferably, when the membrane is a ceramic membrane, a tubular configuration is used.

Filtration is frontal or tangential.

The choice of the type of membrane, its configuration and the type of filtration depends on the volume of the treated fluxes, the compactness, the quality of the aqueous composition obtained at the end of step a) 124.

The treatment method further comprises a step c1) 128, subsequent to step a) 124 or step b) 126 of injecting a reducing agent into the permeate. Indeed, it may prove useful when an oxidizing agent is used during the treatment process to post-treat the permeate in order to stop the degradation reactions of the size of the permeate. polymer. The reducing agent makes it possible to neutralize the action of the oxidizing agent. The reducing agents are chosen in particular from compounds such as sulphites, bisulphites, metabisulphites (and especially metabisulphite, alkali metal or alkaline earth dithionites). The reducing agent is injected at a rate of 0.05 to 2 g / g of oxidizing agent remaining in solution after reaction advantageously 0.1 to 0.5 g / g. The mass of injected reductant can be controlled via a REDOX probe with instructions to remain in a reducing medium.

The treatment method further comprises a step c2) 130, subsequent to step b) 126 of treating the retentate. This step preferably implements a centrifugation means (such as a centrifuge or a cyclone). It makes it possible to obtain three phases: a solid phase, an oily phase and an aqueous phase. The solid phase is discharged as waste. The oily phase is discharged to a hydrocarbon processing unit.

The treatment method further comprises a step c3) subsequent to step c2) 130, of recycling the aqueous phase obtained in step c2) into the permeate. This variant is particularly implemented when the aqueous phase quality of the treated retentate meets the injection specifications.

In another variant, the process comprises a step c4) subsequent to step c2) of recycling the aqueous phase obtained in step c2) into the aqueous composition obtained at the end of step a) 124. This variant is particularly implemented when the aqueous phase quality of the treated retentate does not meet the injection specifications.

In another variant, the process comprises a step c5) subsequent to step c2) of recycling the aqueous phase obtained in step c2) in the production water obtained at the end of step iii). This variant is particularly implemented when the aqueous phase quality of the treated retentate does not meet the injection specifications.

The steps c3, c4 and c5 can be indifferently implemented successively or simultaneously.

By virtue of the coupling of steps a) 124 and b) 126, the permeate obtained at the end of step b) 126 or obtained at the end of step c1) 128 is an aqueous composition comprising in particular from 1 to 50 mg / L of dispersed hydrocarbons, from 0.1 to 20 mg / L of suspended solid particles whose diameter d100 is less than 5 μιη and from 1 to 2000 ppm of reduced polymer. Preferably, the aqueous composition comprises from 1 to 5 mg / L of dispersed hydrocarbons, from 0.1 to 1 mg / L of suspended solid particles whose diameter d100 is less than 1 μιη and from 1 to 2000 ppm of polymers of reduced size.

The permeate obtained at the end of step b) 126 or obtained at the end of step c1) 128 may be used as a sweeping fluid for reinjection into an underground formation after a new addition of additive such as a polymer, a surfactant, an alkaline their mixture. It is therefore recycled 134 as a flushing fluid 114 in the hydrocarbon recovery process described above.

Thus, the enhanced hydrocarbon recovery process further comprises the successive steps vi) and vii), subsequent to step v), consisting of:

vi) injecting at least one polymer into the permeate, and

vii) inject the permeate into the subterranean formation.

A facility 400 for enhanced hydrocarbon recovery for carrying out the hydrocarbon recovery process described above is described with reference to FIG. 4.

The assisted oil recovery plant 400 comprises a hydrocarbon extraction unit 401.

The hydrocarbon extraction unit 401 comprises an injector well drilled in the subterranean formation and at least one producing well. The injector well serves to inject the sweeping fluid. The flushing fluid moves the hydrocarbons to the producing well. The producing well comprises means of natural extraction, and possibly pumping of the production effluent to the surface. A connection line 402 makes it possible to convey the production effluent from the hydrocarbon extraction unit 401 to the separation unit 403.

The separation unit 403 comprises separation means, called primary, hydrocarbons / water. The separation unit makes it possible to separate the production effluent into at least one oily fraction comprising hydrocarbons and an aqueous fraction comprising at least one polymer, called production water. A collection line 404 is connected at the outlet of the separation unit 403. The collection line 404 makes it possible to evacuate the oily fraction containing the hydrocarbons to a hydrocarbon treatment unit or to a hydrocarbon export unit. , not shown in FIG. 4. A connection line 406 is connected at the output of the separation unit 403. The connection line 406 makes it possible to convey the production water from the separation unit 403 to the unit pretreatment 405.

The pretreatment unit 405 comprises in particular one or more separation means, said to be secondary. These separation systems may be for example hydrocyclones, gravity separators, floaters, etc. They are solid / liquid (hydrocarbon) / liquid (water) separators. The pretreatment unit serves to deoil and separate the solid particles from the production water to obtain an aqueous composition comprising a polymer. Collection lines 408, 416 are connected at the output of the pretreatment unit 405. The collection line 408 makes it possible to evacuate the solid particles. The collection line 416 makes it possible to evacuate the hydrocarbons. A feed line 410 is connected to the output of the pretreatment unit 405. It enables the aqueous composition comprising the polymer to be conveyed from the pretreatment unit 405 to the processing unit 500. The treatment unit 500 makes it possible to separate the dispersed hydrocarbons and the solid particles in suspension contained in the aqueous composition. Collection lines 412, 418 are connected at the output of the processing unit 500. The collection line 412 makes it possible to eliminate the solid particles in suspension. The collection line 418 makes it possible to eliminate the dispersed hydrocarbons. A collection line 414 is connected at the output of the processing unit 500. The collection line 414 makes it possible to recover the aqueous composition treated.

An embodiment of the processing unit 500 is now described with reference to FIG. 5.

The processing unit 500 comprises a degradation unit 501 of the polymer. The feed line 410 feeds the degradation unit 501 with the aqueous composition comprising the polymer.

The degradation unit 501 of the polymer comprises a means of degradation of the polymer chosen from the group formed by an ultrasonic unit, a source generating ultraviolet rays such as an ultraviolet lamp, a unit of electro-oxidation, means for injecting an oxidizing agent and a combination of these means for forming hydroxyl radicals. The hydroxyl radicals may be generated in particular from a source generating ultraviolet rays combined with a means for injecting an oxidizing agent such as hydrogen peroxide or ozone. They can also be generated from a source generating ultraviolet rays combined means for injecting an oxidizing agent in the presence or absence of an electro-oxidation unit. A connection line 504 is connected at the output of the polymer degradation unit 501 and connects the degradation unit 501 to the membrane filtration module 503. The connection line 504 feeds the membrane filtration module 503 with an aqueous composition comprising at least one polymer of reduced size.

The membrane filtration module 503 consists of a membrane filter or a plurality of membrane filters in series or in parallel. In the latter case, we speak of membrane filter trains. A collection line 508 connected at the outlet of the retentate recovery zone of the filtration module 503 makes it possible to recover the retentate which notably comprises solid particles in suspension and dispersed hydrocarbons. A collection line 506 connected at the outlet of the permeate recovery zone of the membrane filtration module 503 makes it possible to recover the permeate. The permeate is a treated aqueous composition which comprises at least one reduced-size polymer. The quality of its water meets the specifications of injection. In other words, the permeate collection line 506 feeds the treated production water collection line 414 as described above in connection with FIG. 4.

According to an embodiment illustrated in FIG. 6, the processing unit 500 comprises a neutralization unit 505 upstream of the membrane filtration module 503. A connection line 502 is connected at the output of the polymer degradation unit 501. and connects the degradation unit 501 to the neutralization unit 505. This connection line 502 supplies the neutralization unit 505 with an aqueous composition comprising at least one reduced-size polymer. A connection line 526 is connected to the output of the neutralization unit 505. This line 526 connects the neutralization unit 505 to the membrane filtration module 503. The neutralization unit 505 comprises means for injecting an agent reducing agent which neutralizes the action of the degradation agent injected into the degradation unit 501. The collection line 526 makes it possible to feed the membrane filtration module 503 with the neutralized aqueous composition comprising the reduced-size polymer.

According to an embodiment illustrated in FIG. 7, the processing unit 500 comprises a neutralization unit 505 downstream of the membrane filtration module 503. A connection line 528 is connected at the output of the membrane filtration module 503 and connects the module membrane 503 to the neutralization unit 505. This line 528 feeds the neutralization unit 505 with the permeate comprising the reduced-size polymer. A collection line 530 is connected at the outlet of the neutralization unit 505 to recover the neutralized permeate comprising the reduced-size polymer. In other words, the permeate collection line 530 feeds the treated production water collection line 414 as described above in connection with FIG. 4.

The processing unit 500 may further comprise at least one recirculation line 510 of the retentate. The recirculation line 510 is itself fed by the collection line 508 and is connected to the connection line 504 or 526. The feed line 510 allows direct recycling of the recovered retentate at the outlet of the filtration module 503 into the permeation flow supplied by the connection line 504 or 526 to the inlet of the membrane filtration module 503. Membrane filtration recirculation loops are well known to those skilled in the art. When a filtration module comprises a plurality of membrane filters connected in series, several recirculation loops can be arranged at the inlet of these filters.

The processing unit 500 further comprises a retentate processing unit 507. The retentate processing unit 507 comprises solid / liquid (hydrocarbon) / liquid (water) separation means such as centrifuges and hydrocyclones. The collection line 508 is connected to the output of the filtration module 503 and to the input of the retentate processing unit 507. The collection line 508 feeds the retentate filtration retentate treatment means. A collection line 514 is connected at the outlet of the retentate processing unit 507. This collection line 514 makes it possible to evacuate the hydrocarbons obtained after treatment of the retentate towards a hydrocarbon treatment unit or to an export unit. hydrocarbons. A collection line 518 is connected at the output of the retentate processing unit 507. This collection line 518 makes it possible to evacuate the solids obtained after the treatment of the retentate to a subsequent treatment of the solid waste. In other words, solid particles and hydrocarbons recovered via the collection lines 514 and 518 respectively feed lines 412 and 418 as described above in connection with FIG. 4. A collection line 516 is connected at the output of the retentate processing unit 507. The line 516 collection allows to evacuate the treated aqueous phase obtained after treatment of the retentate.

Alternatively, the collection line 516 may be connected to a recirculation line 524. The recirculation line 524 is itself fed by the collection line 516 and is connected to the connection line 504 or 526. The line supply 524 allows a recycling of the aqueous phase of the treated retentate in the permeate flow supplied by the connection line 504 or 526 to the inlet of the membrane filtration module 503. Such a variant is then particularly preferred when the quality of the aqueous phase of the treated retentate does not allow its release into the environment nor its reinjection as a sweeping fluid in a tank.

In another variant, the collection line 516 can be connected to a supply line 520. The supply line 520 is itself fed by the collection line 516. The supply line 520 allows a recycling of the aqueous phase of the retentate treated with the permeate collected by the line 506 or 528 at the outlet of the filtration means 503. The lines 520, 506 and 530 feed the treated production water collection line 414 as described above in relation to FIG. 4. Such a variant is then particularly preferred when the quality of the aqueous phase of the treated retentate makes it possible to reinject as a sweeping fluid into a reservoir.

In another variant, the collection line 516 can be connected to a collection line 522. This line 522 makes it possible to evacuate the aqueous phase of the treated retentate for release into the environment. Such a variant is then particularly preferred when the quality of the aqueous phase of the treated retentate corresponds to the discharge specifications in the environment.

In another variant, the collection line 522 can also feed the connection line 406. This variant is not shown in FIGS. 4 and 5. Such a variant is then particularly preferred when the quality of the aqueous phase of the retentate treated does not allow its release into the environment or recycling at the entrance of the membrane filtration module.

In a variant of this embodiment with reference to FIG. 7, the collection line 516 can be connected to a feed line 512. The supply line 512 is itself fed by the collection line 516 and is connected to the collection line 530. The feed line 512 allows a recycling of the aqueous phase of the treated retentate in the permeate downstream of the neutralization unit 505. The lines 516 and 530 feed the water collection line Processed production 414 as described above in connection with FIG. 4. Such an embodiment is then particularly preferred when the quality of the aqueous phase of the treated retentate corresponds to the injection specifications in a subterranean formation. The set of characteristics and preferences presented for the process for treating an aqueous composition comprising at least one polymer applies to the treatment unit 500 of an aqueous composition comprising at least one polymer.

Example

Several aqueous compositions are prepared whose formulations are presented in Table I below.

Compositions No. 1, No. 2, No. 7 and No. 8 are comparative examples.

Compositions No. 3, No. 4, No. 5 and No. 6 are examples according to the invention.

Table I

The polymer used is a polyacrylamide polymer FLOPAM3630S supplied by SNF FLOEGER.

Active chlorine is obtained by dissolving in the aqueous compositions an appropriate amount of bleach so as to obtain active chlorine concentrations ranging from 50 mg / L to 500 mg / L.

The hydrocarbon solution is identical for the compositions No. 1 to No. 8. The hydrocarbons come from a field of interest for the practice of improved oil recovery techniques.

The solid particles in suspension consist of a 50% by weight mixture of zeolite of average diameter equal to 2 μιη and of 50% by mass of silica of average diameter equal to 15 μιη. Compositions No. 2 and No. 8 are obtained by mixing with saline water, hydrocarbons and particles.

Composition No. 1 is obtained from Composition No. 2 to which the high molecular weight viscosifying polymer is added.

Composition No. 3 is obtained from composition No. 2 which has been brought into contact with a polymer degradation agent (here, 500 mg / l of active chlorine).

Composition No. 7 is obtained from Composition No. 8 to which the high molecular weight viscosifying polymer is added.

Compositions No. 4-5-6 are obtained from Composition No. 7 which has been contacted with a polymer-degrading agent at the active chlorine concentrations shown in the table above.

These compositions are tested in a filtration system comprising a filtration unit for filtering from 0 to 50 L / h of effluent.

The filtration system is shown schematically in FIG. 8. It comprises a feed tank 803 containing the compositions to be tested, a pump 805, a membrane 807, a receiving tank 812 for collecting the permeate and a backwash system 808. The feed pan 803 and the receiving vessel 812 are respectively placed on agitators 801 and 813. The membrane 807 is fed with the test composition via lines 802 and 804. The permeate is recovered via lines 806 and 809. In a first step, the line 806 feeds the backwashing system 808 and, in a second step, the receiving tank 812. The retentate is recovered via the line 815 and is either recycled at the inlet of the membrane via the line 817, is directed to the feed tray via line 816. The backwash system 808 is fed by line 806. In filtration mode, the valve 819 is closed and the valve 818 open. The permeate fills the backwash system 808 and then flows into the permeate receiving tank 812 where the permeate flow is measured using a scale and recorded using a computer 814. Every 10 minutes, the valve system reverses, that is to say that the valve 819 opens and the valve 818 closes, for 2 seconds, for injecting air 810 into the backwashing system 808 and therefore to push its liquid content towards the membrane 807 and thus achieve a backwash. The system is then reverted to production mode as described above. The tests were carried out at constant transmembrane pressure of 0.5 bar and at a temperature of 40 ° C. The evolution of the permeability is reported in standardized unit at 20 ° C (to be compared with other tests that would have been done at other temperatures). Two types of membranes were tested under the same experimental conditions.

Membrane performance was monitored in terms of flux drop over time and permeate and retentate quality (viscosity analyzes, total organic carbon, total nitrogen, hydrocarbon concentration). o Membrane flow analysis over time:

The compositions No. 1, No. 2 and No. 3 were tested on a ceramic multi-channel membrane (silicon carbide) of the CERAMEM supplier. The pore diameter announced by the supplier is 200 nm. The filtration results of this membrane are shown in FIG. 2. Without treatment with a polymer degradation agent, the permeability of the membrane is 3 times lower when the aqueous composition comprises a viscosifying polymer (curve No. 1). When the aqueous composition comprises a viscosifying polymer and is treated with a polymer degradation agent (curve No. 3), it is observed that the permeability of the membrane returns to the same value as the experiment carried out with an aqueous composition not including polymer (curve No. 2).

Compositions No. 4, No. 5, No. 6, No. 7 and No. 8 were tested on a multi-channel ceramic (silicon carbide) membrane of the LIQTECH supplier. The pore diameter announced by the supplier is 40 nm. It is noted that the greater the concentration of degradation agent of the polymer (here active chlorine) is large, the greater the permeability of the membrane is important and up to a plateau corresponding to the performance of the membrane in the presence of an aqueous composition not including polymer (curve No. 8). o Analysis of the quality of the retentate and permeate:

The quality of the treated water was analyzed by extracting the hydrocarbons with trichlorethylene, removing the polar compounds on florisil and then analyzing the sample by infrared (old OSPAR method). The particle size is analyzed by microscopy and then image analysis.

The analyzes carried out on the permeate obtained after filtration of the compositions No. 3, No. 4, No. 5 and No. 6 on the LIQTECH and CERAMEM membranes were below the detection limits of the laboratory equipment. The permeates of these compositions have a dispersed hydrocarbon content of less than 5 mg / L, a suspended particle content of less than 1 mg / L, the diameter of which is less than 1 μιη.

The above tests demonstrate that the coupling between a partial degradation step of a viscosifying polymer of an aqueous composition and a membrane filtration step makes it possible to obtain an aqueous composition (permeate) the quality of which is compatible for reinjection into matrix mode in an underground formation.

Without the implementation of the first step (step a) 124) of the treatment process, the polymer is retained by the membrane and a large amount of solid waste (also called sludge) is generated.

The coupling of the two steps (step a) 124 and step b) 126) makes it possible to work on the same flow as that implemented in a membrane filtration unit in which the aqueous composition comprising no polymer is filtered. Coupling these two steps also generates less solid waste. As the quality of the permeate has satisfied the fixed injection specifications, the reduced-size polymer is thus reinjected into an underground formation. It is no longer treated as solid waste.

Claims

A method of treating an aqueous composition comprising at least one polymer, the process comprising the steps of:

The treatment method according to claim 1, wherein the permeate obtained in step b) further comprises dispersed hydrocarbons having a content of less than 50 mg / L and suspended solid particles having a content of less than 20 mg / L, these particles having a diameter d100 less than or equal to 5 μιη.

The treatment method according to claim 1 or 2, wherein the aqueous composition is a pretreated hydrocarbon production water fraction comprising, in addition to the polymer, suspended solid particles and dispersed hydrocarbons.

Treatment process according to one of claims 1 to 3, wherein the membrane of the membrane filter is selected from the group formed by inorganic membranes, including ceramics, organic membranes and hybrid membranes.

The treatment method according to one of claims 1 to 4, wherein the pore diameter of the membrane filter is at least 10 nm and at most 2000 nm, preferably 40 to 500 nm.

Treatment process according to one of Claims 1 to 5, in which the polymer degradation agent is a chemical agent, a physical agent or a combination of these two types of agents, for example an electron treatment. oxidation or a photo-catalytic treatment.

The method of treatment of claim 6, wherein the polymer degradation agent is a physical agent selected from the group consisting of ultrasonic waves and ultraviolet rays.

The treatment method according to claim 6, wherein the polymer degradation agent is a chemical agent, more particularly an oxidizing agent selected from the group consisting of ammonium persulfate, sodium persulfate, potassium persulfate. , sodium perborate, hydrogen peroxide, hydrogen peroxide and transition metal salt mixture, ozone, sodium hypochlorite, sodium chlorite, chlorine dioxide , chlorine gas, air, oxygen, hydroxyl radicals and mixtures thereof. 9. The treatment method according to claim 8, wherein the oxidizing agent is ozone or sodium hypochlorite, said agent being formed in situ by electrolysis of the air or by electrolysis of sodium chloride.

10. The treatment method according to claim 8, wherein the oxidizing agent is the hydroxyl radicals obtained by a catalytic oxidation treatment of hydrogen peroxide, by an electrooxidation treatment of oxygen, by a treatment. photochemical hydrogen peroxide, photochemical ozone treatment or photo-catalytic oxidation treatment of hydrogen peroxide. 11. The method of treatment according to any one of claims 8 to 10, further comprising a step c), subsequent to step a) or step b) consisting of:

cl) injecting a reducing agent into the aqueous composition obtained in step a) or into the permeate. The treatment method according to any one of claims 1 to 11, further comprising a step c2), subsequent to step b) consisting of:

c2) treating the retentate to obtain at least one aqueous phase.

13. The treatment method as claimed in claim 12, comprising a step c3) subsequent to step c2):

c3) recycling the aqueous phase obtained in step c2) into the permeate.

The method of claim 12 or 13 further comprising a step c4) subsequent to step c2, comprising:

c4) recycling the aqueous phase obtained in step c2) in the aqueous composition obtained at the end of step a).

15. Process for the enhanced recovery of hydrocarbons contained in an underground formation, the process comprising at least the following successive steps: i) injecting into the subterranean formation by at least one injector well at least one scanning fluid comprising at least one polymer, ii) recovering a production effluent by at least one producing well,

iii) separating the production effluent into a hydrocarbon phase and an aqueous phase called hydrocarbon production water,

v) implementing the method according to any one of claims 1 to 14 with said aqueous composition obtained in step iv).

16. The method of assisted hydrocarbon recovery according to claim 15, wherein the method further comprises the successive steps vi) and vii), subsequent to step v):

vi) injecting at least one polymer into the permeate, and

vii) inject the permeate into the subterranean formation.

17. Treatment unit (500) of an aqueous composition comprising at least one polymer, said treatment unit (500) comprising at least:

a degradation unit (501) of the polymer to obtain a polymer of reduced size,

a membrane filtration module (503) comprising a recovery zone of a retentate and a permeate recovery zone, a feed line (410) of the aqueous composition comprising the polymer connected to the inlet of the degradation unit (501),

a connection line (504) connecting the degradation unit (501) to the membrane filtration module (503),

a collection line (506) connected at the outlet of the permeate recovery zone of the membrane filtration module (503), a collection line (508) connected at the outlet of the retentate recovery zone of the membrane filtration module (503). ).

18. Treatment unit (500) of an aqueous composition according to claim 17, wherein the polymer degradation unit (501) comprises at least one means of degradation of the polymer chosen from an ultrasound probe, a source generating ultraviolet rays, a device for contacting the aqueous composition with an oxidizing agent, and a combination of these means for forming hydroxyl radicals.

19. A treatment unit (500) of an aqueous composition according to claim 17 or 18, said treatment unit (500) comprising at least, in addition:

a neutralization unit (505),

a connection line (502) connected at the output of the degradation unit (501) and connects the degradation unit (501) to the neutralization unit (505), and

a connection line (526) connected at the output of the neutralization unit (505) and connects the neutralization unit (505) to the inlet of the membrane filtration module (503).

20. Treatment unit (500) of an aqueous composition according to claim 17 or 18, said treatment unit (500) comprising at least:

a neutralization unit (505),

a connection line (528) connected at the outlet of the permeate recovery zone of the membrane filtration module 503 and connecting the membrane filtration module (503) to the inlet of the neutralization unit (505), and

a collection line (530) being connected at the output of the neutralization unit (505).

21. Installation (400) for enhanced hydrocarbon recovery comprising at least:

a hydrocarbon extraction unit (401),

a separation unit (403) comprising hydrocarbon / water separation means,

a production water pre-treatment unit (405) comprising solid / liquid / liquid separation means, a treatment unit (500) of an aqueous composition according to any one of claims 17 to 20,

a connection line (402) connecting the hydrocarbon extraction unit (401) to the separation unit (403),

a connection line (406) connecting the separation unit (403) to the pre-treatment unit (405),

a feed line (410) connecting the pretreatment unit (405) to the processing unit (500),

a collection line of the treated aqueous composition (414).