OA16798A

OA16798A - Tracer fluids with a memory effect for the study of an oil deposit.

Info

Publication number: OA16798A
Application number: OA1201300533
Authority: OA
Inventors: Pascal Perriat; Nicolas Crowther; Matteo Martini; Olivier Tillement; Thomas Brichart; Nicolas Agenet
Original assignee: Total S.A
Priority date: 2011-06-22
Filing date: 2012-06-22
Publication date: 2016-01-04

Abstract

The field of the invention is that of the exploration and use of oil reservoirs. More precisely, this invention relates to the development of nanoparticles and tracer fluids containing them, intended to be injected into a well, and collected by reversal of fluid flow through the same well. The fluid tracers according to the invention have the advantage of producing a memory effect fluorescent signal, that is to say a signal modified as a function of the physicochemical conditions encountered in the medium through which the nanoparticles pass after injection into the geological underground area. The analysis of fluorescent signals in the fluids collected after diffusion makes it possible to deduce information on the characteristics of the oil reservoir.

Description

MEMORY EFFECT TRACER FLUIDS FOR THE STUDY OF AN OIL RESERVOIR

The field of this invention is that of exploration and exploitation of oil réservoirs. More precisely, this invention relates to the development of nanoparticles and tracer fluids containing them, intended to be injected into a well, and collected by reversai of the fluid flow through the same well.

The tracer fluids according to the invention hâve the advantage of producing a memory effect fluorescent signal, that is to say a signal modifîed as a function of the physicochemical conditions encountered in the medium through which the nanoparticles pass after injection into the geological underground area. The analysis of fluorescent signais in the fluids collected after diffusion makes it possible to deduce therefrom information on the characteristics of the oil réservoir.

TECHNOLOGICAL BACKGROUND

It is well known in the prior art to use of tracers in order to obtain information on an oil réservoir or more generally on a resource of an underground geological area, a réservoir of hydrocarbon, water, gas, oil or petroleum. Techniques using for example tracers with different partition coefficients hâve been described. The principle is founded in particular on chromatography. One of the tracers interacts more specifically with certain fluids contained in the rock, for example oil, and diffusion thereof will be slowed down in the presence of oil. By quantification of the diffusion time lag with respect to a tracer which interacts a little or not at ail with its environment (surreptitious tracer), the quantity of oil contained in the réservoir is deduced therefrom.

These methods of analysis can be conducted based on only one well (Single Well Tracer Test) or two wells, comprising an injection well and a production well.

With regard to the prior art relating to such tracers for injection waters (tracing fluid) enabling surveying of the oil réservoirs by diffusion between an injection well and a production well, reference may be made to the Patents US 4,231,426 B1 and US 4,299,709 B1 which disclose aqueous tracer fluids comprising from 0.01 to 10 % by weight of a nitrate sait associated with a bactericidal agent.

The patent US 3,623,842 describes a method of measurement an oil saturation in the vicinity of a well (Single Well Tracer Test) consisting of injecting a first partitioning tracer (water/oil) which releases a surreptitious tracer after a certain period of diffusion in the porous medium.

The site of Institute for Energy Teclmology (IFE) lias put online a PowerPoint présentation entitled SIP 2007 - 2009 New functional iracers based on nanotechnology and radiotracer generators Department for Réservoir and Exploration Technology (last modification dated 7 March 2011). In particular, this document suggests the use of surfacemodified nanoparticles as tracer for monitoring flows in oil réservoirs and oil wells and in studies of processes. Even more precisely, this présentation also describes functionalised tracers capable of emitting a signal modulated as a function of the physico-chemical conditions through which it passes.

In a quite different field, the French Patent Application FR 28 67 180 Al describes hybrid nanoparticles comprising, in the one hand, a core consisting of a rare eartli oxide, possibly doped with a rare earth or an actinide or a mixture of rare earths and actinide and, on the other hand, a coating around this core, the said coating consisting predominantly of polysiloxane functionalised by at least one biological ligand grafted by covalent bond. The core may be based on Gd2Û₃ doped with Tb³⁺ or by uranium and the coating of polysiloxane can be obtained by causing an aminopropyltriethoxysilane, a tetraethylsilicate and triethylamine to react.

These nanoparticles are used as probes for the détection, the tracking and the quantification of biological Systems.

Moreover, there are about ten families of appropriate molécules currently validated as tracer for injection waters in oil réservoirs. These families of molécules are for example fluorinated benzoic acids or naphthalenesulphonic acids.

It is also known that the fluorescent objects often hâve a fluorescence closely linked to the physico-chemical conditions encountered with a very wide possible variation of their émission spectra, their excitation spectra, their émission lifetime or their quantum yields.

For example, certain compounds exhibit an émission or an émission lifetime (fluorescence decay tîme) which is highly dépendent upon the température and are thus used in remote measurement of température (J. Lakowicz, Principles of fluorescence spectroscopy, Springer 2006, page 216).

Other compounds such as fluorescent and dérivatives thereof are themselves very sensitive to the pH conditions and may hâve an émission intensity which varies by several orders of magnitude between an acid and a base pH (N. Clonis, W.H. Sawyer, Spectral properties of the prototropic forms of fluorescein in aqueous solution, J. Fluorescence, 1996, 6,147).

These variations may be irréversible or réversible as a function of the compounds. If the use of fluorescent compounds as tracer is known, the use of the modification of irréversible fluorescence is generally considered as a drawback for the interprétation of tracing curves and the quantifications.

The détérioration of the fluorescence signal can nevertheless give of information on the medium encountered and could be then be used as a memory effect signal of the conditions encountered.

In the biological field several tests of modification of fluorescence linked to memory effects hâve been proposed: they are in relation to the encounter with a biomolecule or a spécifie cell. Mention may be made for example of the Patent Application US2010/0272651. This suggests the use of fluorescent tracers in relation to indicators for the détermination of particular pharmacokinetics or biodistributions within organisms.

Nevertheless, currently, the use of memory effect signais in the oil field has never been described nor even suggested.

In fact, the inventors had to develop novel tracers having a modified fluorescence détectable by resolved time (linked to the émission of lanthanide in particular), even in the presence a substantial background noise linked to the organic compounds présent in the different oils.

TECHNICAL PROBLEM AND OBJECTIVES TO BE ACHIEVED

In this context the object of the présent invention is to satisfy at least one of the following objectives:

- to propose a novel method of studying a solid medium, for example an oil réservoir, by diffusion of a liquid through said solid medium, which is simple to implement and economical;

- to remedy the drawbacks of tracers for injection waters of oil réservoirs according to the prior art;

- to provide nanoparticles liaving a memory effect fluorescence signal, that is to say a signal of which the émission and/or excitation spectrum is modified as a function of the physico-chemical conditions of the medium through which it passes;

- to provide a novel tracer fluid comprising these nanoparticles which can be used in particular in a process for studying a solid medium, for example an oil réservoir by diffusion of said liquid through said solid medium and recovery by the same well by reversai of the flow.

BRIEF DESCRIPTION OFTHE INVENTION

These objectives, amongst others, are achieved by the invention which relates in the first place to a method of studying a geological underground area, such as an oil réservoir, by diffusion of a liquid for injection into said underground area, characterized in that it comprises the following steps:

o an injection liquid is injected into the underground area to be studied, comprising nanoparticles:

of mean diameter between 20 and 200 nm;

capable of forming a stable colloïdal suspension in a saline medium.

of which at least a part consists of a core and, if applicable, a matrix coating the core;

and of which the core and/or, if applicable, the matrix comprise at least a or several fluorescent entities capable of producing at least one memory effect fluorescence signal, that is to say a fluorescence signal irreversibly modified as a function of the physico-chemical conditions encountered in the underground area;

o the injection liquid which has diffused is collected at different times following the injection period;

o and the memory effect fluorescent signal(s) emitted by the nanoparticles as a function of time, the analysis of the memory effect fluorescent signal(s) dctected making it possible to deduce thereffom information on the physicochemical conditions of the underground geological area studied, for example of the oil réservoir.

In a preferred embodiment of the method according to the invention, at least a part of the nanoparticles comprises • at least one organic fluorophore, and, • at least one organometallic fluorophore, the combination of two types of fluorophore being chosen in such a way that the nanoparticle produces at least one memory effect fluorescence signal.

The invention also relates to a tracer fluid which can be used in particular in the method according to the invention, and characterized in that it comprises nanoparticles:

• of mean diameter between 20 and 200 nm;

• capable of forming a stable colloïdal suspension in a saline medium.

• of which at least a part consists of a core and, if applicable, a matrix coating the core;

• and of which the core and/or, if applicable, the matrix comprises at least one organic fluorophore and at least one organometallic fluorophore, the combination of the two types of fluorophores being chosen in such a way that the nanoparticle produces at least one memory effect fluorescence signal, said signal being détectable by time-resolved fluorophore.

ln a spécifie embodiment, the nanoparticles are capable of emitting at least one memory effect fluorescence signal, and at least one fluorescence signal which is stable, that is to say which does not vary as a function of the physico-chemical conditions encountered or of which the variation is not irréversible.

DETAILED DESCRIPTION OF THE INVENTION

Method.pf.sftidyinga.geol.ogiçal underground.area

The underground area studied (e.g. rocks) may be of a varied geological nature. Preferably, this involves studying an underground réservoir of hydrocarbons, and more particularly an oil réservoir. In particular it involves measuring the proportion of oil and water on the edges of a well and also characterizing the physico-chemical properties such as the pH or the redox potential.

The nanoparticles:

The injection fluids used in the method according to the invention comprise nanoparticles with the following characteristics:

• they hâve a mean diameter between 20 and 200 nm;

• capable of forming a stable colloïdal suspension in a saline medium, • of which at least a part consists of a core and, if applicable, a matrix coating the core;

• the core and/or, if applicable, the matrix comprise at least one or several fluorescent entities capable of producing at least one memory effect fluorescence signal, that is to say a fluorescence signal irreversibly modified as a fonction of the physicochemical conditions encountered in the underground area.

These nanoparticles are détectable, that is to say that it is possible to identify their presence or absence in the medium above a certain concentration and that it is even possible to quantify the concentration thereof when they are présent in the medium.

These nanoparticles are capable of forming a stable colloïdal suspension in a saline medium which does not settle very much. For example, this suspension does not exhibit précipitation or agglomération over time, e.g. after 6 months at ambient température.

Accordîng to an advantageous embodiment of this method, the core of the nanoparticles contaîns at least one material chosen within the group comprising: semi-conductors, the noble metals (e.g. Au, Ag, Pt), fluorides, vanadates or rare earth oxides and mixtures and/or alloys thereof; preferably a lanthanide; alloys and mixtures thereof, and, even more preferably, a lanthanide chosen within the sub-group consisting of: Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm and Yb and mixtures and/or alloys thereof.

If applicable, the nanoparticles also contain a preferably transparent matrix chosen within the group of materials comprising: silicas, polysiloxanes, aluminas, zircons, aluminates, aluminophosphates, métal oxides (for example TiO₂, ZnO, CeO₂, Fe₂Oj, ...) and mixtures and/or alloys thereof, this matrix includîng within it and/or on its surface:

i. luminescent entities chosen within the group comprising: semiconductors, oxides, rare earth fluorides or vanadates, the organic fluorescent molécules (preferably tluorescein and/or rhodamine), the transition métal ions, the rare earth ions which are or are not bound to complexing molécules and/or molécules making it possible to improve the absorption and the mixtures and/or alloys thereof, ii. optionally other entities enabling a modification of the luminescence properties and chosen within the group comprising: particles of noble métal and mixtures and/or alloys thereof;

iii. and mixtures of these entities (i) and (ii).

The nanoparticles preferably hâve a matrix fonctionalised on the surface, that is to say which includes of radicals R grafted, preferably by covalence, preferably based on silane bonds Si-R on the surface and originating from:

i. hydrophilic compounds which may be charged, preferably hydrophilic organic compounds, molar masses below 5000 g/mol and more preferably below 450 g/rnol, preferably chosen from among the organic compounds including at least one of the following functions: alcohol, carboxylic acid, amine, amide, ester, ether oxide, sulphonate, phosphonate and phosphinate, and mixtures of these hydrophilic compounds which may be charged, ii. neutral hydrophilic compounds, preferably a polyalkylene glycol, more preferably a polyethylene glycol, Diethylene Triamine PentaAcetic acid (DTPA), dithiolated DTPA (DTDTPA) or a succinic acid, and mixtures of these neutral hydrophilic compounds, iii. one or more hydrophobie compounds, preferably polymers;

iv. or mixtures thereof.

If applicable, the matrix may comprise other materials, chosen from within the group consisting of silicas, aluminas, zircons, aluminates, aluminophosphates, métal oxides or also metals (example: Fe, Cu, Ni, Co...) passivated on the surface by a layer of the oxidised métal or another oxide and mixtures and alloys thereof.

In a particular embodiment, said nanoparticles comprise:

a core consisting of a noble métal or an alloy of noble metals, a matrix comprising (i) polysiloxanes, (ii) an organic fluorophore and (iii) an organometallic fluorophore, said fluorophores being bound covalently to the polysiloxanes, said matrix being functionalised on its surface in order to form silane bonds Si-R, wherein preferably at least 50%, preferably at least 75% of said radicals -R consist of neutral or charged hydrophilic compounds, preferably from amongst polyethers or polyols, or mixtures thereof.

Advantageously, the matrix of the nanoparticles includes radicals -R grafted at the rate of at least one radical R per 10 nm² of surface and preferably at least one per nm².

In order to monitor the interactions between, on the one hand, the solid medium to be studied, namely for example the geological underground area (e.g. rocks) containing the oil réservoir and, on the other hand, the nanoparticles, it is possible according to an advantageous arrangement of the invention to adjust the hydrophilic lipophilie balance and/or the zêta potential of the matrix of the nanoparticles as a function of the underground area to be studied.

In order to do this, for example, either the same surface charge is provided for the nanoparticles and the rocks of the solid medium, in order to create a repulsion and limit the interactions, or the respective charges are inodulated so that the nanoparticles and the rocks of the solid medium interact in a controlled and/or spécifie manner with respect to certain rocks.

The nanoparticles according to the invention hâve a mean diameter preferably between 20 nm and 100 nm, for example between 20 nm and 50 nm. In an advantageous embodiment the nanoparticles according to the invention hâve a polydispersity index of less than 0.3, preferably less than 0.2, for example less than 0.1.

The size distribution of the nanoparticles is for example measured with the aid of a commercial granulometer such as a Malvem Zetasizer Nano-S granulometer based on PCS (Photon Corrélation Spectroscopy). This distribution is characterized by a mean diameter and a polydispersity index.

Within the meaning of the invention, mean diameter is understood to mean the harmonie mean of the diameters of the particles. The polydispersity index makes reference to the width of the size distribution deriving from the analysis of the cumulants according to the standardISO 13321:1996.

An essential characteristic of the study method according to the invention résides in the use of nanoparticles capable of produce a memory effect signal.

The invention relates to a memory effect fluorescent signal, a signal of which the characteristics, for example the fluorescence intensity of the émission spectrum, the excitation spectrum, the émission lifetime or the quantum yields, are modifïed irreversibly as a function of certain physico-chemical conditions encountered in the underground area through which it passes. Thus, the nature and/or the intensity of the alteration of the fluorescent signal makes it possible to deduce therefrom certain physico-chemical conditions of the environment through which it passes.

The physico-chemical conditions studied include for example, the température of the underground, the pH, the hydrocarbon content or also the redox potential of the underground area through which it passes.

In an advantageous embodiment nanoparticles will be used which comprise at least one or several fluorescent entities makîng it possible to produce at least one memory effect fluorescence signal and one or more fluorescent entities producing a stable signal, that is to say, contrary to the memory effect, a signal which is not irreversibly modifïed as a function of the physico-chemical conditions encountered. As examples of fluorescent entities producing a stable signal, mention may be made of lanthanides or other entities of which the luminescence is not sensitive to the local environment because the f orbitals used are not very available to interact with the éléments présent in their sphere of coordination and therefore modify their luminescence properties.

In a preferred embodiment of the invention, at least a part of the nanoparticles comprises:

i. at least one organic fluorophore, and, ii. at least one organometallic fluorophore, the combination of two types of fluorophore being chosen in such a way that the nanoparticle produces at least one memory effect fluorescence signal.

It is known that the fluorescence signal of certain organic fluorophores is modified irreversibly as a function of the physico-chemical conditions encountered by the tracer carrying the fluorophores, and in particular as a function of the pH, the température and/or the redox potential.

As an exampie of an organic fluorophore capable of being used, in combination with an organometallic fluorophore, in order to obtain a memory effect fluorescent signal, mention may be made of fluorescein (for example fluorescein isothiocyanate FITC), rhodamîne (for example rhodamîne B isothiocyanate RBITC) or other fluorescent entities which hâve émission spectra in the same range as fluorescein or rhodamîne, for example the products with the brand names Alexa Fluor, Cy Dyes, Atto, FluoProbes.

The organometallic fluorophores of the nanoparticles are chosen from among rare earth vanadates or oxides, or mixtures thereof. In a spécifie embodiment they are chosen from among lanthanides, alloys thereof and mixtures thereof, bound to complexing molécules.

In a preferred embodiment the organometallic fluorophores are détectable by time-resolved fluorescence. Then lanthanides bound to complexing molécules are particularly preferred.

The metals of the lanthanide sériés comprise éléments with atomic numbers from 57 (lanthanum) to 71 (lutetium). For example, the lanthanides will be chosen from within the group consisting of: Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm and Yb and mixtures and/or alloys thereof, bound to complexing molécules, and preferably europium and terbium.

Complexing molécules or chelating agent are understood to mean any molécule capable of forming with a metallic agent a complex comprising at least two co-ordination bonds.

In a preferred embodiment, a complexing agent having a co-ordinance of at least 6, for example at least 8, and a dissociation constant of the complex pKd, greater than 10 and preferably greater than 15, with a lanthanide

Within the meaning of the invention, the dissociation constant pKd is understood to mean the measurement of the equilibrium between the ions complexed by the ligands and the free ligand dissociated in the solvent. Precisely, it is not so much the base 10 logarithm of the product of dissociation (-log(Kd)), defined as the equilibrium constant of the reaction which expresses the passage from the complexed state to the ionic state.

Such complexing agents are preferably polydentate chelating molécules chosen from amongst the families of molécules of the polyamine type, carboxylic polyacids and those having a high number of potential co-ordination sites preferably greater than 6, such as certain macrocycles.

In a more preferred embodiment, DOTA or 1,4,7,10-tetraazacyclododecane-1,4,7,10tetraacetic acid of the tollowing formula will be chosen:

HOOC—_χ / \ COOH

HOOC

COOH or one of the dérivatives thereof.

A cyclic agent is understood to be an organic molécule, having at least one aromatic ring or heterocyclic ring, preferably chosen from amongst benzene, pyridine or dérivatives thereof and capable of amplifying the fluorescent signal emitted by the organometallic fluorophore and/or the organic fluorophore, for example a complexing agent bound to lanthanide. These cyclic agents, which are of interest if they are characterized by a high absorbance, are used in particular to amplify the fluorescent signal emitted by the fluorophores (antenna effect by transfer of the excitation of the agent to the fluorophore).

The cyclic agent can be grafted covalently either directly to the polysiloxanes of the matrix or to the organometallic and/or organic fluorophore.

In a spécifie embodiment, the organometallic fluorophores consisting of a lanthanide with a complexing agent are grafted covalently to the polysiloxanes of the matrix of the nanoparticles via an amide function.

Organic fluorophore and organometallic fluorophore contained in the same nanoparticle are chosen in such a way as to produce a memory effect fluorescence signal, preferably détectable by time-resolved fluorescence.

In a more particularly preferred embodiment, the nanoparticles comprise at least one organic fluorophore chosen among fluorescein or one of the dérivatives thereof and at least one organometallic fluorophore, chosen among europium (Eu) or terbium (Tb), bound to a complexing agent.

In a more particularly preferred embodiment, the nanoparticles comprise at least one organic fluorophore chosen among rhodamine or one of the dérivatives thereof and at least one organometallic fluorophore, chosen among Eu or Tb, bound to a complexing agent.

In order to multiply the information on the environment studied, the injection liquid can comprise a mixture of nanoparticles, each type of nanoparticles being characterized by the émission of one or more spécifie fluorescence signais, and in that said signais emitted by each type of nanoparticles are détectable by multiplex détection means.

The multiplex détection makes it possible to analyses several fluorescence signais (characterized for example by different wavelengths) in parallel on the same sample. Use will also be made fluorescent entities with different émission and/or excitation wavelengths according to each type of nanoparticles.

Other signais emitted by the nanoparticles may also be detected in parallel, and for example signais détectable by analysis chemical, by ICP and/or by magnetic analysis (magnetic transition température, for example according to Curie or to Néel).

In order to further increase the level of information which can be collected, the injection liquid comprises at least two types of nanoparticles which are distinguished by their hydrophilic/lipophilic balance and/or their zêta potential, such that a part of the nanoparticles has a fluorescent signal delayed with respect to the other part of the nanoparticles because of their interaction with the underground area. Thus, for example, nanoparticles interacting with certain rocks of the underground area will hâve their memory effect signal more greatly modulated relative to the nanoparticles interacting a little or not at ail with these same rocks.

Nanoparticles which can be used in the method according to the invention and the préparation thereof are presented in the Examples below.

Methodology

In a preferred application of the method according to the invention, the injection liquid is injected and is collected in the same well (the injection well and the production well are identical) by inversion of the flow of the injected liquid.

According to a remarkable embodiment of the method according to the invention, before the analysis of the liquid which has diffused, said liquid is concentrated, preferably by filtration or dialysîs, and, even more preferably, by tangential filtration and preferably by use of a membrane with cut-off thresholds below 300 kDa (kilo Dalton).

The quantity of tracer in the liquid which has diffused can be measured, by détection by fluorescence and/or by analysis chemical and/or by ICP and/or by magnetic analysis (magnetic transition température, for example according to Curie or to Néel).

According to a variant for the measurement of the quantity of tracer in the liquid which has diffused, at least a détection is carried out by time-resolved fluorescence, that is to say activating the détection with a time lag (e.g. several microseconds) after an excitation puise on one or several fluorescent entities contained in the nanoparticle and capable of emitting a stable signal, that is to say which has not been modulated irreversibly as a function of the physico-chemical conditions encountered.

The memory effect fluorescent signal or signais are measured, preferably as a function of time after the injection, again preferably by time-resolved fluorescence. By comparison of the signal or signais obtained as a function of the time with respect to a stable signal it is possible to deduce therefrom the modification induced by the physico-chemical conditions encountered during the diffusion of the injection liquid in the vicinity of the well.

In a particular embodiment, the method of the invention makes it possible to obtain information on the température variations undergone by the tracer fluid in the underground area through which it passes. In another particular embodiment, the variations of pH in the traversed underground area are deduced therefrom. In another particular embodiment, the rate of exposurc to certain hydrocarbons is deduced therefrom.

Injection. liguid,(water)for, the. study. of.asolid rnediuni,. namely. e.g. an oi’[ réservoir

According to another of its objects, the invention relates to a liquid for injection (or a tracer fluid) in an oil réservoir which can be used in particular in the method defined above, characterized in that it comprises nanoparticles:

• of mean diameter between 20 and 200 nm;

• capable of forming a stable colloïdal suspension in a saline medium.

This liquid advantageously comprises water and nanoparticles (or a mixture of nanoparticles) as defined above.

ysepfthe.nanopgrticles

According to another of its objects, the invention relates to a novel use of the nanoparticles as defined above as tracers in injection waters of an oil réservoir, which are intended for the study of said réservoir by diffusion of these injection waters through said réservoir, for the purpose in particular of evaluating the volumes of oil in reserve in the reservoir.

According to another application, for example in methods of exploration or of prospecting including hydraulic fracturing, it is possible to map the température history of the nanoparticles after diffusion in the vicinity of an injection well then to deduce therefrom the presence of one or several of fracturing fines.

EXAMPLES.

Description of the drawings ♦ Figure 1 shows the émission spectra of the three solutions according to the préparation 1 brought to ambient température with an excitation wavelength of 330 nm (Figure 1 a), and 395 nm (Figure lb) measured with a time lag of 0.1 ms and an acquisition time of 5 ms.

♦ Figure 2 shows the émission spectra of the three solutions according to the préparation 3 brought to ambient température with an excitation wavelength of 285 nm (time lag 0.1 ms, acquisition time 5 ms).

♦ Figure 3 shows the émission spectra of the two solutions according to the préparation 2 brought to ambient température with an excitation wavelength of 330 nm (time lag 0,1 ms, acquisition time 5 ms).

♦ Figure 4 shows the émission spectra of the three solutions according to the préparation 4 brought to ambient température with an excitation wavelength of 285 nm (time lag 0.1 ms, acquisition time 5 ms).

♦ Figure 5 shows the excitation spectrum at a fixed émission for europium at 615 nm of the three solutions according to the préparation 1 at different pH values (time lag 0.1 ms, acquisition time 5 ms).

♦ Figure 6 shows the excitation spectrum at a fixed émission for europium at 615 nm of the two solutions of nanopartîcles according to the préparation 1 in DEG and a DEG/water mixture (time lag 0.1 ms, acquisition time 5 ms).

♦ Figure 7 shows the excitation spectra of the three solutions of colloids prepared according to the préparation 1 brought to ambient température with an émission wavelength of 615 nm (time lag 0.1 ms, acquisition time 5 ms).

Préparation 1. Colloïdal solution of nanopartîcles with a core of gold and a silica matrix encapsulating organic fluorophores derïved from fluorescein and europium complexes (DTPA)

200 mg of diethylenetriaminepentaacetic acid bisanhydride (DTPABA), 0.130 mL of APTES and 0.065 mL of triethylamine are introduced with 4 mL of DMSO (dimethyl sulfoxide) into a 10 mL bottle and stirred vigorously. After 24 hours, 200 mg of EuC1₃,6H2O are added and the mixture is stirred for 48 hours.

mg of F1TC (fluorescein isothiocyanate) are introduced with 0.5 mL of APTES ((3aminopropyljtriethoxysilane) into a 2.5 mL bottle and stirred vigorously. Homogenization is carried oui at ambient température for 30 minutes. 36 mL of Triton X-100 (surfactant), 36 mL of //-hexanol (co-surfactant), 150 mL of cyclohexane (oil) and 21 mL of aqueous solution containing 9 mL of HAuCLrSPhO at 16.7 mM, 9 mL of MES (sodium 2mercaptoethanesulphonate) at 32.8 mM and 3 mL of NaBH₄ at 412 mM are introduced into a 500 mL flask and stirred vigorously. After 5 minutes, 0.400 mL of solution containing fluorescein is added into the microemulsion with 1 mL of the solution containing the europium complex. Next, 0.200 mL of APTES and 1.5 mL of TEOS (tetraethyl orthosolicate) are also added to the microemulsion.

The polymerization reaction of the silica is completed by the addition of 0.800 mL of NH4OH after 10 minutes. The microemulsion is left and stirred for 24 hours at ambient température.

Next, 190 pL of silane gluconamide (N-(3-triethoxysilylpropyl)gluconamide at 50% in éthanol is added to the microemulsion and stirred at ambient température.

After 24 hours, 190 pL of silane gluconamide are again added to the solution and stirring is continued at ambient température.

After 24 hours, the microemulsion is destabilized in an ampoule for decanting by addition of a mixture of 250 mL of distilled water and 250 mL of isopropanol. The solution is left to decant for at least 15 minutes and the lower phase containing the particles is recovered.

The recovered colloïdal solution is then placed in a tangential filtration System VIVASP1N© at 300 kDa then centrifuged at 4000 r.p.m. until a purification rate greater than 500 is obtained.

The solution thus obtained is then filtered at 0.2 pm and diluted by 5 in DEG (diethyleneglycol). The solution obtained is composed of particles with a mean size 50.25 nm and a polydispersity index 0.091 with very good colloïdal stability in a salty aqueous medium (up to 100 g of salts).

Préparation 2. Colloïdal solution of nanoparticles with a corc of gold and a silica matrix encapsulating organic fluorophores derived from rhodamine B and europium complexes (DTPA).

The synthesis is similar to that described for the préparation 1 with the différence that the 20 mg of fluorescein isothiocyanate are replaced by 20 mg of rhodamine B isothiocyanate (RBITC). The rest of the synthesis is identical. The solution thus obtained is composed of particles with a mean size of 48 nm and a polydispersity index of 0,072.

Préparation 3. Colloïdal solution of nanoparticles with a corc of gold and a silica matrix encapsulating organic fluorophores derived from fluorescein and terbium complexes (DTPA).

The synthesis is similar to that described for the préparation 1 with the différence that the 200 mg of EuCl₃,6H₂O are replaced by 200 mg of TbCl₃,6H₂O. The rest of the synthesis is identical. The solution thus obtained is composed of particles with a mean size of 43 nm and a polydispersity index of 0.069.

Préparation 4. Colloïdal solution of nanoparticles with a core of gold and a silica matrix encapsulating organic fluorophores derived from rhodamine B and terbium complexes (DTPA).

The synthesis is similar to that described for the préparation 1 with the différence that the 20 mg of fluorescein isothiocyanate are replaced by 20 mg of rhodamine B isothiocyanate (RBITC) and that the 200 mg of EuCl₃,6H₂O are replaced by 200 mg of TbCl₃,6H₂O. The rest of the synthesis is identical. The solution thus obtained is composed of particles with a mean size of 46 nm and a polydispersity index of 0.073.

Results

Example 1: Détection of a memory effect fluorescent signal as a function of the température of the environment using nanoparticles according to the préparation 1

Three samples of 10 mL of colloïdal solutions of nanoparticles obtained according to the préparation 1 are heated to 80°C respectively for 0.1 and 72 hours. The fluorescence study is then carried out and indicates a marked variation in the émission spectra in particular those which are time-resolved. Figure 1 shows the émission spectra of the three solutions brought to ambient température with an excitation wavelength of 330 nm (Figure la) and 395 nm (Figure lb). The luminescence curves (Figure la) show a clear increase in the intensity of émission of the particles (peak at 615 nm, spécifie for europium) in relation to the heat treatment time at 80°C during the excitation is carried out at 330 nm, whilst at 395 nm no variation is observed (Figure lb). The ratio of the émission peaks between these different excitations can therefore serve as probes in order to measure the exposure time of the particles to the température of 80°C.

Example 2: Détection of a memory effect fluorescent signal as a function of the température of the environment using nanoparticles according to the préparation 3

Three samples of 10 mL of colloïdal solutions of nanoparticles obtained according to the préparation 3 are heated to 80^οΟ respectively for 0,1 and 72 hours. The fluorescence study is then carried out and indicates a marked variation in the émission spectra in particular those which are time-resolved. Figure 2 shows the émission spectra of the three solutions brought to ambient température with an excitation wavelength of 285 nm.

The luminescence curves (Figure la) show a clear increase in the intensity of émission of the particles (peak at 550 nm, spécifie for terbium) in relation to the heat treatment time at 80°C. The intensity of the émission peaks can therefore serve as probes in order to measure the exposure time of the particles to the température of 80°C, with an increase in the intensity as a function of the exposure time.

Example 3: Détection of a memory effect fluorescent signal as a function of the température of the environment using nanoparticles according to the préparation 2

Two samples of 10 mL of colloïdal solutions of nanoparticles obtained according to the préparation 2 are heated to 80°C respectively for 0.1 and 1 hours. The fluorescence study is then carried out and indicates a marked variation in the émission spectra, in particular those which are time-resolved. Figure 3 shows the émission spectra of the two solutions brought to ambient température with an excitation wavelength of 330 nm.

The luminescence curves show a clear decrease in the intensity of émission of the particles (peak at 550 nm, spécifie for terbium) in relation to the heat treatment time at 80°C. The intensity of the émission peaks can therefore serve as probes in order to measure the exposure time of the particles to the température of 80°C, with a decrease in the intensity as a function of the exposure time.

Example 4: Détection of a memory effcct fluorescent signal as a function of the température of the environment using nanoparticles according to the préparation 4

Three samples of 10 mL of colloïdal solutions of nanoparticles obtained according to the préparation 4 are heated to 80°C respectively for 0.1 and 72 hours. The fluorescence study is then carried out and indicates a marked variation in the émission spectra, in particular those which are time-resolved. Figure 4 shows the émission spectra of the three solutions brought to ambient température with an excitation wavelength of 285 nm.

Example 5: Détection of a memory effect fluorescent signal as a function of the pH of the environment using nanoparticles according to the préparation 1

Three samples of 1 mL of colloïdal solutions of nanoparticles are obtained according to the préparation 1 and dispersed in 10 mL of aqueous solution brought by a soda/hydrochloric acid mixture to a pH of 1.5 and 12 respectively. The fluorescence study is then carried out and indicates a marked variation in the émission spectra, in particular those which are time-resolved. Figure 5 shows the excitation spectrum at a fixed émission for europium at 615 nm of the three solutions at these different ambient pH values.

The luminescence curves show a clear increase in the excitation spectrum of the particles in relation to the increase in pH. The ratio of the émission (or excitation) peaks can therefore serve as probes in order to measure the pH exposure of the particles.

Example 6: Détection of a memory effect fluorescent signal as a function of the nature of the fluid of the environment using nanoparticles according to the préparation 1

To samples of 5 mL of colloïdal solutions of nanoparticles are obtained according to the préparation 1 and dispersed respectively in 5 mL of water and in 5 mL of DEG. The two solutions are then heated to 80°C for 3 days. The fluorescence study is then carried out and indicates a marked variation in the émission spectra, in particular those which are timeresolved. Figure 6 shows the excitation spectrum at a fixed émission for europium at 615 mn for the two solutions.

The luminescence curves show a clear détérioration of the excitation spectrum of the particles in relation to the increasing water content. The ratio of the émission (or excitation) peaks can therefore serve as probes in order to measure the rate of exposure of the particles to different water contents.

Example 7: Détection of a memory effect fluorescent signal as a function of the variations in température of the environment using nanoparticles according to the préparation 1

Three samples of 1 mL of colloïdal solutions of nanoparticles obtained according to the préparation 1 are mixed with 9 mL of water and heated for 1 hour to 60, 80 and 100°C. The fluorescence study is then carried out and indicates a marked variation in the excitation spectra, in particular those which are time-resolved. Figure 7 shows the excitation spectra of the three solutions brought to ambient température with an émission wavelength of 615 nm.

The luminescence curves show a clear variation in the excitation intensity of the component at 330 nm of the particles in relation to the treatment température. The intensity of the émission peaks can therefore serve as probes in order to measure the exposure of the particles, with a decrease in the intensity as a function of the exposure température.

Claims

1. Method of studying a geological underground area, such as an oil réservoir, by diffusion of an injection liquid into said underground area characterized in that it comprises the following steps:

• an injection liquid is injected into the underground area to be studied, comprising nanoparticles:

o of mean diameter between 20 and 200 nm;

o capable of forming a stable colloïdal suspension in a saline medium.

o of which at least a part consists of a core and, if applicable, a matrix coating the core;

o and of which the core and/or, if applicable, the matrix comprise at least one or several fluorescent entities capable of producing at least one memory effect fluorescence signal, that is to say a fluorescence signal irreversibly modified as a function of the physico-chemical conditions encountered in the underground area;

• the injection liquid which has diffused is collected at different times following the injection period;

• and the memory effect fluorescent signal(s) emitted by the nanoparticles as a function of time, the analysis of the memory effect fluorescent signal(s) detected making it possible to deduce therefrom information on the physicochemical conditions of the underground geological area studied, for example of the oil réservoir.

2. Method as claimed in Claim 1, characterized in that the injection liquid is collected by the injection well by inverting the flow of fluid after injection and diffusion.

3. Method as claimed in one of Claims 1 or 2, characterized in that at least a part of the nanoparticles comprises

i. at least one organic fluorophore, and, ii. at least one organometallic fluorophore, the combination of the two types of fluorophore being chosen in such a way that the nanoparticle produces at least one memory effect fluorescence signal.

4. Method as claimed in Claim 3, characterized ΐη that the organometallic fluorophore is chosen among the rare earth ions bound to a complexing agent, preferably among the lanthanides bound to a complexing agent.

5. Method as claimed in any one of Claims l to 4, characterized in that said injection liquid comprises a mixture of nanoparticles, each type of nanoparticles being characterized by the émission of one or more spécifie fluorescent signais, and in that said signais emitted by each type of nanoparticles are détectable by multiplex détection means.

6. Method as claimed in any one of Claims l to 5, characterized in that the memory effect fluorescent signal(s) are detected by time-resolved fluorescence.

7. Method as claimed in any one of Claims l to 6, characterized in that the matrix of the nanoparticles includes radicals R covalently grafted on the basis of silane bonds Si-R on the surface and originating from:

i. charged hydrophilic compounds, preferably hydrophilic organic compounds, molar masses below 5000 g/mol and more preferably below 450 g/mol, preferably chosen from among the organic compounds including at least one of the following functions: alcohol, carboxylic acid, amine, amide, ester, ether oxide, sulphonate, phosphonate and phosphinate, and mixtures of these charged hydrophilic compounds, ii. neutral hydrophilic compounds, preferably a polyalkylene glycol, more preferably a poiyethylene glycol, Diethylene Triamine PentaAcetic acid (DTPA), dithiolated DTPA (DTDTPA) or a succinic acid, and mixtures of these neutral hydrophilic compounds, iii. one or more hydrophobie compounds, iv. or mixtures thereof.

8. Method as claimed in any one of Claims l to 7, characterized in that the injection liquid comprises at least two types of nanoparticles which are distinguished by their hydrophilic/lipophilic balance and/or their zêta potential, such that a part of the nanoparticles has a fluorescent signal delayed with respect to the other part of the nanoparticles because of their interaction with the underground area.

9. Method as claimed in Claim 8, characterized in that at least a part of nanoparticles has a balance hydrophilic/lipophilic balance and/or the zêta potential adjusted in such a way that it does not interact with the medium of the underground area in which they diffuse and at least one other part of the nanoparticles has a hydrophilic/iipophilic balance and/or a zêta potential adjusted in such a way as to interact with spécifie rocks of the underground area.

10. Tracer fluid which can be used in particular in the method according to any one of Claims l to 9, characterized in that it comprises nanoparticles:

• of mean diameter between 20 and 200 nm;

• capable of forming a stable colloïdal suspension in a saline medium.

11. Tracer fluid as claimed in Claim 10, characterized in that said organometallic fluorophore is chosen among the rare earth ions bound to a complexing agent.

12. Tracer fluid as claimed in Claim 11, characterized in that the rare earth ions are chosen in group of lanthanides consisting of Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm and Yb and mixtures and/or alloys thereof.

13. Tracer fluid as claimed in any one of Claims 10 to 12, characterized in that at least a part of the nanoparticles comprise at least one organic fluorophore chosen among fluorescein and one of the dérivatives thereof and at least one organometallic fluorophore comprising a lanthanide chosen among europium or terbium, said lanthanide being bound to a complexing agent.

14. Tracer fluid as claimed in any one of Claims 10 to 12, characterized in that at least a part of the nanoparticles comprises at least one organic fluorophore chosen among rhodamîne or one of the dérivatives thereof and at least one organometallic fluorophore comprising a lanthanide chosen among europium or terbium, said lanthanide being bound to a complexing agent.

15. Tracer fluid as claimed in any one of Claims 10 à 14, characterized in that the complexing agent is chosen in the group consisting of DTPA, DOTA and dérivatives thereof.

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16. Use of a tracer fluid as claimed in any one of Claims 10 to 15 in the study of a hydrocarbon réservoir, for example an oil réservoir.

17. Use of a tracer fluid as claimed in any one of Claims 10 to 15 in a method of exploration or prospecting of a hydrocarbon réservoir comprising a step of hydraulic fracturing for mapping the fracture lines.