WO2014060686A1

WO2014060686A1 - Drilling fluid containing graphene

Info

Publication number: WO2014060686A1
Application number: PCT/FR2013/052421
Authority: WO
Inventors: Julien Beausoleil; Serge Bordere; Patrick Delprat; Patrice Gaillard; Alexander Korzhenko
Original assignee: Arkema France
Priority date: 2012-10-19
Filing date: 2013-10-10
Publication date: 2014-04-24
Also published as: FR2997090B1; FR2997090A1

Abstract

The invention relates to a drilling fluid having an organic or aqueous base, intended for drilling in underground formations, containing graphene and at least one weighting agent and, optionally, a surfactant and/or a thickening agent other than graphene. The invention also relates to a method for producing said fluid from a masterbatch based on graphene and oil, as well as to the use thereof for drilling in underground rock formations.

Description

Drilling fluid containing graphene

OBJECT OF THE INVENTION

The present invention relates to a water-based or organic-based drilling fluid for drilling in subterranean formations containing graphene and at least one weighting agent and optionally a surfactant and / or a thickening agent other than graphene. It also relates to a process for preparing this fluid, from a masterbatch based on graphene and oil, and the use of this fluid for drilling in underground rock formations.

BACKGROUND OF THE INVENTION

Drilling fluids, also known as drilling muds, are complex fluids used for drilling oil wells. They are injected, usually continuously, via the drill string into the borehole. Their multiple functions include, for example, the transport of rock cuttings to the surface, the maintenance in the borehole of sufficient hydrostatic pressure to prevent the collapse of the crossed rock formation, or the lubrication and cooling of the rock formation. drill head. There are two main families of drilling muds: oil-based sludge (usually inverse emulsions of brine in oil phase) and water-based sludge.

Maintaining a hydrostatic pressure sufficient to compensate for the lateral pressure of the rock formation traversed by the wellbore requires the gradual increase in the density of the drilling fluid as drilling progresses to the deep zones. This increase in density is obtained by addition of agents weighting agents), that is to say finely ground solid materials, of high density and insoluble in the drilling fluid. The greater the depth of the wellbore, the greater the quantity and / or density of the weighting agent used, and the more the system for keeping the agent weighing in the drilling fluid in suspension must be effective.

Indeed, the decantation of the weighting agent, for example during the temporary stop of the injection of sludge, can have disastrous consequences such as a plugging of the well or a local decrease in the hydrostatic pressure of the column. of fluid resulting in the collapse of the well.

Maintaining suspension of the weighting agent is typically provided by thickening or viscosifying agents, conventionally chosen from clays, organophilic or not, and organic polymers soluble in the drilling fluid. However, beyond a certain depth of drilling, when the suspension of the weighting agent suspension system must be particularly effective, the organic polymers undergo degradation due to the high temperatures that prevail at these depths and become partially or totally ineffective.

The problem of thermal degradation of organic polymers can not be solved by replacing them with clays. Indeed, clays conventionally used as thickening agents (bentonite, montmorillonite, attapulgite, organophilic clays) resist, certainly, at significantly higher temperatures than organic polymers, but for deep drilling the amount of clay necessary to maintain in suspension large amounts of very dense weighting agent is considerable. Drilling muds then have a grade in excessively high solids which poses problems of sludge maintenance due to excessive viscosity.

Thus, the systems currently used, whether based on polymers or clays, unfortunately do not allow to maintain suspension of the weighting agent beyond a temperature of about 250 ° C.

To overcome this problem, the Applicant has proposed to use carbon nanotubes to keep the weighting agents in suspension in the drilling muds.

Although they have good viscosifying properties over a wide temperature range, carbon nanotubes are expensive to manufacture and are not always available in sufficient quantities for application in the drilling of subterranean formations.

There is therefore still a need for other suspending agents which have the same advantageous properties as carbon nanotubes.

However, it has been found by the Applicant that graphene, used in relatively small amounts, is an excellent thickening agent which both has excellent heat stability and makes it possible to keep in suspension large quantities of very light-weighting agent. dense, such as barite or calcite, even under conditions of high temperature and high pressure, without giving the drilling fluid excessive viscosity.

The interest of the drilling fluids of the present invention containing graphene resides in particular in their particular viscoelastic behavior characterized by a high yield value or yield stress. associated with a relatively moderate viscosity. The yield point, determined according to the Herschel-Bulkley model (Hemphill T., Campos W., and Pilehvari A.: "Yield-power Law Model More Accurately Predicts Mud Rheology", Oil & Gas Journal 91, No. 34 August 23, 1993), pages 45 - 50), is the shear stress, below which the behavior of the fluid is substantially that of a solid (infinite viscosity) and beyond which the fluid has a thixotropic behavior.

The value of the flow threshold, in the model of

Herschel-Bulkley, provides information on the ability of the fluid to hold particles of a dense solid in suspension in a viscoplastic fluid. The higher this threshold, the more the fluid opposes the sedimentation of the particles in suspension. Graphene gives drilling fluids, aqueous or oily, a flow threshold significantly higher than organic polymers present in equivalent amounts.

Moreover, it is thermally stable at temperatures up to 325 ° C, or even beyond.

Finally, particularly when it is obtained by chemical vapor deposition (or CVD), graphene can be produced in large quantities under economically favorable conditions.

The use of graphene at very low levels, preferably less than 3% by weight, does not exhibit the excessive viscosity problems described above for thickening clays, which allows for easier pumping and better flow of fluids. containing them.

Graphene thus advantageously replaces, in part or in full, the thickeners of organic polymer type, clays, fatty acids or carbon nanotubes, used in drilling fluids, especially under conditions of high pressure and high temperature.

SUMMARY OF THE INVENTION

The present invention therefore relates to a drilling fluid in underground rock formations, comprising

(a) an aqueous and / or organic liquid base,

(b) at least one weighting agent, in particulate form, having a density of at least 2 g / cm ³ , preferably at least 4 g / cm ³ , suspended in said liquid base, and

(c) graphene.

It also relates to a drilling method in underground rock formations using such drilling fluids, wherein the graphene content of the drilling fluid is optionally increased as the depth of drilling, the drilling temperature and / or the drilling pressure.

The subject of the invention is also a process for manufacturing this drilling fluid, comprising the dilution of a masterbatch free of organic polymer, comprising graphene and at least one oil, in an aqueous and / or organic liquid base comprising at least one weighting agent in particulate form and optionally at least one surfactant and / or at least one thickening agent other than graphene.

It also relates to a masterbatch in the form of granules, suitable for the implementation of this method, comprising graphene and at least one oil, said masterbatch being free of organic polymer.

It also relates to a process for preparing this masterbatch, comprising the steps of: (a) introducing and kneading graphene and said at least one oil, in a compounding device, to obtain a composite,

(b) extruding and then cooling said composite to obtain a masterbatch in solid form,

(c) shaping said masterbatch to obtain granules.

DETAILED DESCRIPTION

The liquid base used in the drilling fluids of the present invention can in principle be any base conventionally used in drilling fluids. It may be for example a particularly advantageous aqueous base for economic and ecological reasons. These aqueous bases contain in a known manner water-soluble salts intended mainly to increase the density of the base. Preferred salts include halides and formates of sodium, potassium, calcium, zinc, cesium, and combinations thereof. Particularly preferred salts are calcium chloride, calcium bromide, potassium formate, cesium / potassium formate and combinations thereof. These aqueous bases may also contain small fractions of organic solvents that are miscible with water and / or immiscible with water. These aqueous bases may optionally be in the form of oil-in-water emulsions.

In some cases, however, it may be advantageous, even necessary, to limit the water content of the drilling fluids, for example when the well passes through rock formations containing a large fraction of water-soluble or water-dispersible components that may be washed away. the fluid. The liquid base is then either an oil or a water-in-oil emulsion containing preferably at most 50% by weight, in particular at most 20% by weight of water.

When the aqueous base is such a water-in-oil emulsion, also called inverse emulsion, or the aqueous base is an oil-in-water emulsion, the drilling fluid further contains at least one surfactant capable of stabilizing the oil-in-water emulsion. emulsion.

Surfactants capable of stabilizing an inverse emulsion generally have a hydro-lipophilic balance (HLB) of less than 7. The amount of surfactant sufficient to stabilize the water-in-oil emulsion depends, of course, on the respective proportions of the aqueous and oily but is generally between 1% and 5% by weight. The surfactant (s) are preferably chosen from nonionic and anionic surfactants. US2006-0046937 discloses surfactants suitable for use in the formulation of drilling muds of the present invention. On the other hand, surfactants capable of stabilizing an oil-in-water emulsion generally have a hydro-lipophilic balance (HLB) greater than 7.

The oil used in the drilling fluids of the present invention, i.e. the oil constituting the liquid base or the oil forming the continuous phase of the water-in-oil emulsion or discontinuous phase an oil-in-water emulsion, is defined as a medium, liquid at room temperature (25 ° C) and atmospheric pressure, immiscible with water (formation of 2 phases visible to the naked eye at ambient temperature and atmospheric pressure) . This liquid medium has in particular a solubility in water, measured according to the method OECD TG 105, less than or equal to 1 mg / l. This liquid medium may be more or less viscous; in particular, it has a dynamic viscosity at ambient temperature between 0.1cp and 500cp and preferably between 0.3 and 300cp.

According to the invention, it is possible to use one or more oils which are generally miscible with one another. These oils can be polar or, better, apolar.

It is preferred to use a mineral oil, a fluorinated oil, a diesel oil or a synthetic oil, more preferably a mineral oil. Advantageously, it may be a paraffin oil such as those sold by Shell under the brand Sarapar ^® or one marketed by Total under the trade name ^® EDC 99-DW or EDC ^® 95-11; this oil has a viscosity of 3.5 cps. Alternatively, a refined paraffinic oil having a content of polycyclic aromatic compounds of less than 3% by weight may be used.

(determined by DMSO extraction according to IP 346) and a glass transition temperature below -45 ° C, for example -58 ° C ± 3 ° C (as determined according to ASTM E 1356). Refined oils of this type include:

- MES produced by solvent extraction of petroleum heavy distillates or by treatment of these distillates with hydrogen in the presence of a catalyst (hydrotreatment),

- TDAE, which are aromatic extracts treated with treated distillates.

Examples of such oils are especially marketed by Shell under the trade name Catenex ^® SNR by Exxon Mobil under the trade name Flexon 683 TOTAL under the trade name Plaxolene MS or H & R under the name European Vivatec 500. The oils may comprise from 40 to 97% by weight, preferably from 45 to 95% by weight and, more preferably, from 70 to 95% by weight, based on the weight of the masterbatch.

It is possible to use, as weighing agent in principle, any particulate solid having a density greater than that of the liquid base, preferably with a density of at least 2 g / cm ³ and, for drilling at great depth. preferably a density greater than 3 g / cm ³ or even 4 g / cm ³ . These weighting agents are known and are chosen for example from barite (BaSO ₄ ), calcite (CaCO ₃ ), dolomite (CaCO ₃ .MgCO ₃ ), hematite (Fe ₂ O ₃ ), magnetite (Fe ₃ 0 ₄ ), ilmenite (FeTiO ₃ ) and siderite (FeC0 ₃ ). The weighting agent used in a particularly preferred manner is barite.

The amount of weighting agent depends essentially on the density that it is desired to impart to the drilling fluid. This density, and therefore the amount of weighting agent used, generally increases gradually with the depth of the wellbore. The drilling fluids of the present invention are preferably for deep drilling and therefore have a relatively high density, preferably an overall density of at least 1.5, preferably greater than 2.5. The upper limit of the weighting agent content is essentially determined by the viscosity problems caused by too high a solids content. In general, the weighting agent is used in the drilling fluids of the present invention in a concentration of between 10 and 70% by weight, based on the total weight of the drilling fluid. The percentage of weighting agent is very variable depending on the desired density. To maintain the weighting agent in suspension, the drilling fluid according to the invention also contains graphene. In this description, the term "graphene" is used to designate a plane graph sheet, isolated and individualized, but also, by extension, an assembly comprising between one and a few tens of sheets and having a flat structure or more or less wavy. This definition thus includes FLG (Few Layer Graphene or slightly stacked graphene), NGP (Nanosized Graphene Plates or graphene plates of nanometric dimension),

CNS (Carbon NanoSheets or nano-graphene sheets), GNRs (Graphene NanoRibbons or nano-graphene ribbons). On the other hand, it excludes carbon nanotubes and nanofibers, which consist respectively of the winding of one or more sheets of graphene in a coaxial manner and of the turbostratic stacking of these sheets. It is furthermore preferred that the graphene used according to the invention is not subjected to an additional step of chemical oxidation or functionalization.

The graphene used according to the invention is advantageously obtained by chemical vapor deposition or CVD. It is then typically in the form of particles having a thickness of less than 50 nm, preferably less than 15 nm, more preferably less than 5 nm, and less than one micron side dimensions, preferably less than 10 to 1000 nm, preferably 50 to 600 nm, and more preferably 100 to 400 nm. Each of these particles generally contains from 1 to 50 sheets, preferably from 1 to 20 sheets, more preferably from 1 to 10 sheets, or even from 1 to 5 sheets, which are capable of being disconnected from each other in the form of independent leaflets, for example during an ultrasound treatment. The process for the manufacture of graphene by CVD generally comprises the decomposition of a gaseous source of carbon, in particular a hydrocarbon, such as ethylene, methane or acetylene, under a flow of inert gas such as argon or nitrogen, the dilution ratio of the hydrocarbon in the inert gas being for example about 1: 5. This decomposition is carried out at a temperature of 900 to 1000 ° C., preferably from 960 to 1000 ° C., generally at atmospheric pressure, over a catalyst in the form of a powder. The can in particular be a metal catalyst supported or not on an inert substrate. It may be for example cobalt optionally mixed with iron and supported on magnesia, in a molar ratio of cobalt to magnesia generally less than 10%. The catalyst is usually prepared by impregnating the support with alcoholic or glycol solutions of cobalt salts and optionally iron, followed by evaporation of the solvent and a calcination step.

Another CVD method for obtaining graphene according to this invention comprises the following steps:

a) the introduction into a synthesis reactor, and optionally the fluidized bed in said reactor, of an active catalyst for the synthesis of graphene, comprising a mixed oxide of formula AFe ₂ O ₄ where A is at least one element mixed valence metal having at least two valencies, one of which is equal to +2, in particular chosen from cobalt, copper or nickel, the catalyst being of spinel structure,

b) heating said catalyst in the reactor at a temperature between 500 and 1500 ° C, preferably between 500 and 800 ° C, or even between 610 and 800 ° C, c) contacting a gaseous carbon source with the catalyst of step b), optionally in a fluidized bed, and catalytic decomposition thereof at a temperature of 500 to 800 ° C, preferably of 610 to 800 ° C , the gas source being selected from alcohols C ₁ -C ₁ 2 and hydrocarbons C ₁ -C ₁ 2, such as alkanes or alkenes, preferably ethylene, which may be mixed with a flow of a reducing agent such as hydrogen and optionally an inert gas,

d) the recovery of graphene produced in c) at the outlet of the reactor.

The amount of graphene used in the drilling fluids of the present invention depends, inter alia, on the amount and density of the weighting agent used, the drilling depth, the nature of the liquid base, and the absence or presence of other thickening agents in the drilling fluid.

This amount is preferably between 0.1 and 3% by weight, based on the total weight of the drilling fluid.

In a particular embodiment of the present invention, graphene is the only thickening agent, i.e. the drilling fluid is essentially free of other known thickeners such as organic polymers, fatty acids, clays or thickening systems based on surfactants and electrolytes and carbon nanotubes. The concentration of graphene in the drilling fluid is then relatively high, preferably between 1 and 3% by weight, and in particular between 1.5 and 3% by weight, relative to the total weight of the drilling fluid.

Graphene is also useful for enhancing the effect of conventional thickening systems, for example thickening systems based on polymers or carbon nanotubes (or CNTs). In another embodiment of the present invention, the drilling fluids of the present invention thus further contain one or more organic polymers soluble in the aqueous phase and / or in the oily phase of the liquid base and / or CNTs. The concentration of graphene is then preferably between 0.1 and 1% by weight, relative to the total weight of the drilling fluid.

The CNTs possibly used in this embodiment are, in particular, multi-wall nanotubes comprising, for example, from 5 to 15 sheets and preferably having a mean diameter of between 10 and 30 nm, or even between 10 and 15 nm, an average length of 0.1 to 10 μιη and a specific surface area of between 200 and 250 m ² / g. These nanotubes can also be prepared by CVD. In the present invention, crude (non-functionalized but optionally purified and / or milled) NTCs will preferably be used for oil-based or inverse-emulsion drilling fluids. For water-based drilling fluids, use will preferably be made of nanotubes functionalized with ionic organic groups. Such crude carbon nanotubes are especially commercially available from Arkema under the trade name Graphistrength® ^® C100.

These organic thickening polymers are chosen from those conventionally used in drilling fluids, and examples that may be mentioned include guar gum, hydroxypropylguar, carboxymethylguar, hydroxypropylcellulose, hydroxyethylcellulose and xanthan. starch, polyacrylates, poly (diallyldimethylammonium chloride). To manufacture the drilling fluid according to the invention, it is preferred that graphene be introduced in a form easy to handle for the manufacturers of drilling muds, which avoids its dispersion in the environment and therefore does not require the use of systems. complex hoods, filters, depressed premises, and other systems limiting its dispersion. To do this, the Applicant has developed a masterbatch in solid form, free of organic polymer, said masterbatch comprising (and preferably consisting of) graphene and at least one oil as described above, which also makes the subject of this invention. This masterbatch further ensures easy dispersion of graphene into the liquid base of the drilling fluid. The amount of graphene in the masterbatch is generally 5 to 30% by weight, preferably 10 to 20% by weight based on the weight of the masterbatch.

A preferred method of manufacturing the drilling fluid according to the invention thus comprises the dilution of a masterbatch free of organic polymer, comprising (and preferably consisting of) graphene and at least one oil, in an aqueous liquid base and or organic comprising at least one weighting agent in particulate form and optionally at least one surfactant and / or at least one thickening agent other than graphene.

The masterbatch used in this process may comprise any oil chosen from:

vegetable oils with a high content (for example at least 50% by weight) of triglycerides consisting of esters of fatty acids and of glycerol, the fatty acids of which may have various chain lengths, the latter possibly being linear or branched, saturated or unsaturated; these oils include wheat germ, corn, sunflower, flax, shea, castor oil, sweet almonds, macadamia, apricot, soya, cotton, alfalfa, poppy, pumpkin, sesame, squash, avocado, hazelnut, grape seed or blackcurrant, evening primrose, millet, barley, quinoa, olive, rye, safflower, bancoulier, passionflower, muscat rose; or the triglycerides of caprylic / capric acids;

synthetic oils of formula R5COOR6 in which R5 represents an aryl group or the residue of a higher linear or branched fatty acid containing from 7 to 30 carbon atoms and R6 represents a hydrocarbon chain, branched or otherwise, optionally hydroxylated, containing from 3 to 30 carbon atoms, such as for example PurCellin® (cetostearyl alcohol octanoate) oil, isononyl isononanoate, C12-C15 alcohol benzoate, isostearyl benzoate, isopropyl myristate, octanoates, decanoates or ricinoleates of alcohols or polyalcohols;

synthetic ethers such as petroleum ether;

linear or branched, saturated or unsaturated C6 to C26 fatty alcohols such as oleic alcohol or octyl dodecanol;

optionally, silicone oils such as polydimethylsiloxanes, liquid at room temperature; polydimethylsiloxanes comprising alkyl or alkoxy groups, pendent and / or at the end of the silicone chain, groups having from 2 to 24 carbon atoms; phenyl silicones such as phenyl trimethicones, phenyl dimethicones, phenyl trimethylsiloxy diphenylsiloxanes, diphenyl dimethicones and diphenyl methyldiphenyl trisiloxanes;

oils of mineral origin, such as linear or branched hydrocarbons, such as paraffin oils and its derivatives, optionally refined, petroleum jelly, polydecenes, hydrogenated polyisobutene such as Parleam®, squalane;

cyclic hydrocarbons such as

(alkyl) cycloalkanes and (alkyl) cycloalkenes in which the alkyl chain is linear or branched, saturated or unsaturated, having from 1 to

Carbon atoms, such as cyclohexane, dioctylcyclohexane, 2,4-dimethyl-3-cyclohexene and dipentene;

aromatic hydrocarbons such as benzene, toluene, p-cymene, naphthalene, anthracene;

fluorinated oils such as perfluoroalkanes in C8 to

C24;

fluorosilicone oils;

and their mixtures.

The oil contained in the masterbatch may be the same as, or different from, the formulation of the drilling fluid to which it is added.

The masterbatch according to the invention may alternatively comprise more viscous oils, often called greases.

Examples of fats include:

industrial greases, such as those with complex calcium sulphonate, available in particular in the CERAN range or under the reference AXA GRl from the company

TOTAL;

specialty fats, such as semisynthetic fats, bentone-based greases, optionally containing fluorinated compounds, lithium / calcium soap fats and greases containing copper, in particular those available from the company TOTAL under the trade names MARSON SY 00 and SY 2, SPECIS CU, CALORIS 23 and MS23, STATERMIC XHT and NR, TIFORA PG, BIOMULTIS SEP 2, MULTIS COMPLEX HV2; and

- their mixtures.

This masterbatch can be prepared using a compounding device.

Compounding devices are well known to those skilled in the art. They are conventionally used in the plastics industry for the melt blending of thermoplastic polymers and additives to produce composites. These devices generally comprise feed means, in particular at least one hopper for pulverulent materials (here, graphene) and / or at least one injection pump for liquid materials (here, the oil); high shear mixing means, for example a co-rotating or counter-rotating twin-screw extruder (for example a DSM micro-extruder) or a co-kneader, usually comprising a worm disposed in a sheath (tube ) heated; an outlet head which gives shape to the outgoing material; and cooling means, in air or with the aid of a water circuit, of the material. This is generally in the form of rod outgoing continuous device and can be cut or granulated after cooling. Other forms can however be obtained by fitting a die of the desired shape on the output head.

Examples of co-kneaders that can be used according to the invention are the BUSS MDK 46 co-kneaders and those of the BUSS MKS or MX series sold by the company BUSS AG, all of which consist of a screw shaft provided with fins. , disposed in a heating sleeve possibly consisting of several parts and whose inner wall is provided with kneading teeth adapted to cooperate with the fins for produce shearing of the kneaded material. The shaft is rotated and provided with oscillation movement in the axial direction by a motor. These co-kneaders may be equipped with a granule manufacturing system, adapted for example to their outlet orifice, which may consist of an extrusion screw.

The co-kneaders that can be used according to the invention preferably have an L / D screw ratio ranging from 7 to 22, for example from 10 to 20.

The compounding step is generally carried out at a close temperature (for example ± 5 ° C.) of the ambient temperature (25 ° C.).

As indicated above, the masterbatch according to the invention, obtained for example according to the method described above, can be diluted in an aqueous and / or organic liquid base comprising at least one weighting agent in particulate form and optionally at least one surfactant and / or at least one thickening agent other than graphene, for producing the drilling fluid according to the invention. According to one embodiment of the invention, the masterbatch is incorporated directly into the final formulation of the drilling fluid. It is preferred, however, that the weighting agent be added to the liquid base after introduction of the masterbatch therein.

In the latter case, it is furthermore preferred according to the invention that the masterbatch and the liquid base are subjected to a mechanical treatment, preferably before mixing with the weighting agent. This treatment may be of any kind, provided that it makes it possible to obtain a homogeneous dispersion of graphene in the liquid base. This treatment advantageously comprises an ultrasonic treatment or a shear of the dispersion mixture with using a rotor-stator system or using a blade mixer.

Such a rotor-stator system generally comprises a rotor controlled by a motor and provided with fluid guide systems perpendicular to the axis of the rotor, such as blades or blades arranged substantially radially or a flat disc provided with peripheral teeth, said rotor being optionally provided with a ring gear, and a stator arranged concentrically with respect to the rotor, and at a short distance outside thereof, said stator being equipped on at least a portion of its circumference; openings, for example in a grid or defining between them one or more rows of teeth, which are adapted to the passage of fluid sucked into the rotor and ejected by the guide systems to said openings. One or more of the aforementioned teeth may be provided with sharp edges. The fluid is thus subjected to high shear, both in the gap between the rotor and the stator and through the openings in the stator.

An example of a rotor-stator system is in particular marketed by SILVERSON under the trade name Silverson L4RT. Another type of rotor-stator system is marketed by the company IKA-WERKE under the trade name Ultra-Turrax. Other rotor-stator systems still consist of colloid mills, deflocculating turbines and high-shear mixers of the rotor-stator type, such as the apparatus marketed by the company IKA-WERKE or the company ADMIX.

It is preferred according to the invention that the speed of the rotor is set to at least 1000 rpm and preferably at least 3000 rpm or even at least 5,000 rpm, for example. example for 5 to 15 minutes. In addition, it is preferred that the width of the gap between the rotor and the stator is less than 1 mm and preferably less than 200 μm, more preferably less than 100 μm and better still less than 50 μm. less than 40 ym. Furthermore, the rotor-stator system used according to the invention advantageously confers a shear of 1,000 to 10 ⁹ s ^-1 .

Due to the excellent heat resistance of graphene used in the drilling fluids of the present invention, the latter is particularly suitable for deep drilling, i.e. under high temperature and high pressure conditions.

In a preferred embodiment of the drilling method of the present invention, the drilling temperature is therefore greater than or equal to 200 ° C, in particular greater than 250 ° C.

High-temperature and high-pressure drilling is, however, only a preferred embodiment of the process of the invention and the drilling fluids of the present invention, due to their high flow threshold associated with a relatively low viscosity, also prove very useful even at low or medium depth.

It is thus possible to use the drilling fluids of the present invention throughout the duration of the drilling by gradually increasing the graphene content as the drilling depth, the drilling temperature and / or or drilling pressure. Such a method is distinguished by a great simplicity due to the possibility of continuous recycling of drilling fluid that can be reused after removal of cuttings and addition of additional amounts of weighting agent and graphene. In a particular embodiment of the drilling method of the present invention, the drilling fluid preferably does not contain any thickening agent other than graphene and possibly CNTs.

In another embodiment, the drilling method of the present invention comprises the progressive replacement of one or more thickening agents present in the fluid, chosen for example from clays (bentonite, montmorillonite, attapulgite, organophilic clays) or polymers. graphene, and possibly

NTC, as the drilling depth, drilling temperature, and / or drilling pressure increases. It may indeed be interesting, mainly for reasons of production cost of the drilling fluids, to use at the start of drilling known and inexpensive thickeners such as organic polymers and / or thickening clays, and introducing graphene, and possibly CNTs, only from a certain depth when the thermal degradation of the organic polymers or the excessive content of solids provided by the clays begins to pose the problems described in the introduction.

In all cases, graphene can be introduced into the drilling fluid in the form of a masterbatch as described above but not necessarily containing a weighting agent.

The invention will be better understood in the light of the following example, given for purposes of illustration only and which is not intended to limit the scope of the invention as defined by the appended claims.

EXAMPLE a) Graphene manufacture by CVD

Graphene was made according to the method described below. 1- Preparation of a CoFe _Σ 0 ₄ catalyst for the synthesis of graphene

In a 250 ml beaker, 37.5 ml of an aqueous solution of citric acid at a concentration of 0.4 M was prepared, to which 1.1 g of cobalt nitrate (Co (NO ₃₎ ₂ ), 6H ₂ O) and 3.1 g of iron nitrate (Fe (NO ₃ ) ₃ ), 9H ₂ O).

The pH of the resulting solution was adjusted to a value of 6 by adding, dropwise and stirring, ammonia (NH ₄ OH). The molar ratio between iron nitrate and cobalt nitrate in the aqueous solution was substantially of the order of 2. This aqueous solution was placed in a Pyrex crystallizer at a temperature of 80 ° C. for a period of substantially order of 12 hours, so as to form a substantially dehydrated homogeneous gel.

The homogeneous gel thus obtained was heated to a temperature of about 200 ° C, so as to decompose the citric acid. The expansion of the homogeneous gel was then observed to foam which was allowed to develop for about 30 minutes until stabilization. This foam was then crushed gently to form a powder which was heated at a temperature of 400 ° C

4 hours to atmospheric air. A crystalline powder of cobalt ferrite was thus obtained.

This powder had a single oxide phase having a spinel type structure with a crystalline domain size of between 14 nm and 20 nm (determined by X-ray diffraction) and a specific surface area of 7 m ² / g. 2- Graphene synthesis

Graphene synthesis was performed in a horizontal quartz reactor. 20 mg of the catalyst powder obtained above was placed in an alumina crucible which was placed in the center of a horizontal quartz tubular reactor with an inside diameter of about 18 mm. The catalyst powder was heated under a gaseous flow of hydrogen (¾ 53 cm ³ / min) and argon (Ar 160 cm ³ / min) to a temperature of 650 ° C. temperature gradient of 630 ° C / h. When the temperature reached 650 ° C, ethylene (C ₂ H ₄ , 32 cm ³ / min) was introduced into the gas mixture and the gas flow and the temperature were maintained for one hour. After 1 h, the heating and gaseous flows of ethylene and hydrogen were stopped. The powder obtained was cooled to a temperature of 300 ° C. under argon. The amount of product recovered at the end of the reaction was 220 mg. b) Preparation of a masterbatch

A graphene obtained as described above is introduced into the zone 1 feed well of a BUSS MDK 46 (L / D = 11) co-kneader. A quantity by weight of mineral oil (EDC 99 DW of TOTAL) identical to that of graphene is introduced into the injection pump of the first zone of the apparatus, before the first restriction ring. The mixing is carried out at room temperature. At the outlet of the co-kneader, solid rods are obtained which are cut, without the use of a water jet, to obtain a masterbatch in the form of solid granules containing 15% by weight of graphene and 85% by weight of oil. . (c) Manufacture of a drilling fluid The masterbatch prepared as described above is impregnated with the same mineral oil as that used for its preparation, at a proportion of 1 part by weight of masterbatch to 2 parts by weight of oil, for at least 8 hours. The suspension is then rediluted in the same oil to reach a graphene content of 1% by weight. This suspension is then subjected to mechanical treatment in a rotor-stator system (Silverson L4RT Silverson ^®) for 10 minutes to obtain a stable graphene dispersion, that is to say having no apparent sedimentation after 24 hours. A weighting agent such as barite is then introduced into this dispersion to obtain a drilling fluid.

Claims

1. Drilling fluid in underground rock formations, including

(a) an aqueous and / or organic liquid base,

(c) graphene.

2. Drilling fluid according to claim 1, characterized in that the liquid base is an oily continuous phase base such as an oil or a water-in-oil emulsion containing at most 50% by weight, preferably at most 20% by weight of water.

3. Drilling fluid according to claim 1, characterized in that the liquid base is an aqueous continuous phase base, in particular an oil-in-water emulsion.

4. Drilling fluid according to any one of claims 1 to 3, characterized in that it contains from 0.1 to 3% by weight of graphene.

5. Drilling fluid according to any one of claims 1 to 4, characterized in that the graphene is obtained by a chemical vapor deposition process.

6. Drilling fluid according to claim 5, characterized in that the graphene is in the form of particles having a thickness of less than 50 nm, preferably less than 15 nm, more preferably less than 5 nm, and lateral dimensions from 10 nm to less than 1000 nm, preferably from 50 to 600 nm, and more preferably from 100 to 400 nm and in that each of the graphene particles contains from 1 to 50 sheets, preferably from 1 to 50 20 leaflets, more preferably from 1 to 10 leaflets, or even from 1 to 5 leaflets.

7. Drilling fluid according to any one of claims 1 to 6, characterized in that the oily phase contains a mineral oil, a fluorinated oil, a diesel oil or a synthetic oil, preferably a mineral oil.

8. Drilling fluid according to any one of claims 1 to 7, characterized in that the weighting agent is selected from baryta (BaSC ^) calcite

(CaCO ₃ ), dolomite (CaCO ₃ .MgCO ₃ ), hematite (Fe ₂ O ₃ ), magnetite (Fe ₃ O ₄ ), ilmenite (FeTiO ₃ ) and siderite (FeCO ₃ ), and mixtures thereof, preferably barite.

9. Drilling fluid according to any one of claims 1 to 7, characterized in that it further contains at least one thickening agent other than graphene, selected from organic polymers soluble in the aqueous phase and / or in the oily phase of the liquid base and / or carbon nanotubes.

10. Drilling fluid according to any one of claims 1 to 8, characterized in that it is free of organic polymers soluble in the aqueous phase and / or in the oily phase of the liquid base.

11. A method of manufacturing the drilling fluid according to any one of claims 1 to 10, characterized in that it comprises the dilution of a masterbatch free of organic polymer, comprising graphene and at least one oil, in an aqueous and / or organic liquid base comprising at least one weighting agent in particulate form and optionally at least one surfactant and / or at least one thickening agent other than graphene.

12. Masterbatch in the form of granules, suitable for carrying out the process according to Claim 11, comprising graphene and at least one oil, said masterbatch being free of organic polymer.

13. Masterbatch according to claim 12, characterized in that it contains from 5 to 30% by weight, preferably from 10 to 20% by weight, of graphene, relative to the weight of the masterbatch.

14. Process for the preparation of the masterbatch according to one of claims 12 and 13, comprising the steps of:

(a) introducing and kneading graphene and said at least one oil, in a compounding device, to obtain a composite,

(c) shaping said masterbatch to obtain granules.

15. A method of drilling in underground rock formations using a drilling fluid according to any one of claims 1 to 10.