FR2547860A1 - Use of compounds of alkylamidobetaine type in assisted oil recovery, and microemulsions containing such compounds - Google Patents

Abstract

Use in assisted oil recovery of compounds of alkylamidobetaine type corresponding to the general formula: in which R<1> is a monovalent aliphatic hydrocarbon radical with 7 to 23 carbon atoms, R<2> and R<3> are saturated monovalent aliphatic hydrocarbon radicals with 1 to 4 carbon atoms, n is an integer from 2 to 4 and m an integer from 1 to 5. These compounds are employed to form aqueous solutions of varied concentrations as well as microemulsions, to be injected into oil deposits.

Description

The invention relates to the use in enhanced oil recovery of compounds of the alkylamido-betalnic type.

More particularly, compounds of this type are used as surfactants in the preparation of microemulsions or micellar solutions used in enhanced oil recovery.

The recovery of crude oil from the fields is generally carried out in several stages. Initially, the production results from the natural energy of the fluids which decompress.

This wall effect is reinforced by the presence of an underlying aquifer which delays the pressure drop in the deposit. At the end of this depletion phase, the quantity of oil recovered at the surface represents around 10% of the initial reserve. It is therefore necessary in a second step to employ techniques aimed at increasing recovery. The most frequently used method is to inject water into the deposit through wells drilled for this purpose. This operation, carried out until the water content in the mixture produced makes it uneconomical, makes it possible to extract additional oil representing about 20% of the volume of oil initially in place.

The reasons for the low efficiency of water injection have been known for a long time. There are many. First, at the level of surface scanning (macroscopic scanning), the greater mobility of water compared to that of oil creates a source of instabilities in fact, the injected water tends to take the paths of less resistance to move towards the production wells. As a result, only parts of the deposit are affected.

In addition, this defect in surface sweeping is accentuated by the natural heterogeneity of the sedimentary rocks and by the contrast in density of the fluids which tends to reduce drainage from the upper parts of the deposit.

In addition, in the areas of the deposit effectively swept by the water, the displacement of the oil is incomplete. In fact, the oil is stored in networks of pores, the dimensions of which are generally between 0.1 and 100 μm. The capillary forces exert a predominant effect there: after the expulsion of a part of the oil, the other part is trapped, generally in the form of small droplets, discontinuous phase resulting from the fact that most often the porous medium is preferably wettable with water. The available force, taking into account the low admissible pressure gradients, is then no longer sufficient for these globules to cross the capillary thresholds.

It is therefore essential, in order to increase the recovery rate, on the one hand to regularize the sweeping of the deposit, on the other hand to sufficiently reduce the capillary forces, in particular by lowering the interfacial tension between the oil and the injected fluid, to increase the efficiency of the microscopic displacement. This is the purpose of enhanced oil recovery.

Aside from the use of thermal methods, the sweeping efficiency of the water injection is generally improved by the reduction in water mobility obtained by the addition of water-soluble polymers. Several methods are proposed to increase the efficiency of microscopic displacement of the injected fluid: injection of solvents (hydrocarbon gases, carbon dioxide, alcohols, liquefied petroleum gas, etc.), injection of alkaline water and solutions of surfactants. -actives in various forms: aqueous solutions, microemulsions, etc. With regard to the use of surfactants, usually combined with that of water-soluble polymers to stabilize the displacement, it appeared that the recovery could reach 50% of the volume of the initial oil, and even, in favorable cases, 70%.

A technique, now classic, consists in injecting a solution of a surfactant whose characteristics are chosen according to the conditions imposed by the deposit, in particular the salinity of the bedding, the nature of the oil in place and of the rock - and temperature.

A solution of water-soluble polymers is then injected, followed by injection of water.

The surfactant compound is usually used at a concentration above its critical micellar concentration. The Mrcellaires solutions injected are either aqueous solutions containing variable amounts of surfactants and, optionally, other additives, such as cosurfactant, cosolvent, electrolytes, etc., or mixtures, in variable proportions, of water, electrolytes, hydrocarbons and, optionally, cosurfactant and / or cosolvent.

In the latter car, the presence of polar-apolar molecules, in sufficient concentration, leads to the formation of transparent mixtures, generally called microemulsions.

(dans laquelle R peut représenter un radical alkyle, un radical alkylcarboxagado, ou un radical naphténylcarboxamido,R' et R" peuvent -représenter des radicaux alkyles et n est généralement égal à 3) pour améliorer la récupération assistée du pétrole par abaissement de la tension interfaciale entre les hydrocarbures et les eaux fortement satinés de certains gisements. Or ces sulfo-bétalnes, dont la préparation est bien connue dans l'art antérieur (voir, par exemple, l'article de R.F. FISCWER, Industrial and Engineering Chemistry, vol.Very many types of surfactants have been proposed in the prior art for enhanced oil recovery. The most commonly used surfactants, for reasons of cost and availability, are of the sulfonate type, more precisely petroleum sulfonates; presented in the form of alkali metal or ammonium salts. The use of these surfactants is satisfactory as long as the salt content of the water does not exceed about 30 g / l (in sodium chloride equivalent), this value being given to situate the order of magnitude: in particular, the inter-facial tensions between the oil and the sulphonate solutions, obtained by the judicious choice of the characteristics of the product, are very low, of the order of 10 mN / m, and even less. But, when the salinity appreciably exceeds the value indicated above, it has been established that the interfacial properties of sulphonates deteriorate rapidly, especially as
In the particular field of enhanced oil recovery1, US Patents Nos. 3,939,911, 4,008,165, 4,193,452, 4,216,097 and 4,259,191, recommend the use of sulfo-betalnes, of general formula:

(in which R can represent an alkyl radical, an alkylcarboxagado radical, or a naphthenylcarboxamido radical, R 'and R "can -represent alkyl radicals and n is generally equal to 3) to improve the enhanced recovery of oil by lowering the voltage interfacial between the hydrocarbons and the highly satiny waters of certain deposits Now these sulfo-betalnes, the preparation of which is well known in the prior art (see, for example, the article by RF FISCWER, Industrial and Engineering Chemistry, vol.

dont on guaternise l'amine tertiaire. Cependant, on connaît bien à présent les propriétés carcinogéniques de la propane-sultone, dont la vente est actuellement interdite. C'est également par ce procédé de préparation que le brevet US 4.166.038 obtient des sultaines de sulfonium de formule générale

utilisables en récupération assistée du pétrole.56, nO 3, p. 44, March 1964) are obtained by adding the propane above mowing on various organic substrates of general formula:

from which the tertiary amine is guaternized. However, the carcinogenic properties of propane-sultone, the sale of which is currently prohibited, are well known. It is also by this preparation process that US Pat. No. 4,166,038 obtains sulfonium sultaines of general formula

usable in enhanced oil recovery.

Carboxy-betalnes have also been cited in various patents with the aim of improving oil recovery, either by using these surfactants at very low concentrations in the sweep water of the deposit so as to lower the interfacial tension ( US patent 4,216,097), or even by preparing microemulsions for injection into the deposits (Belgian patent 868,821). But, in these two cases, the content of divalent cations, calcium and magnesium in particular, is higher. In addition, the great sensitivity of the sulfonates to divalent cations, provogue, during the flow of the solution of surfactant in the reservoir. , phenomena of precipitation and / or transfer of the surfactant into an immobile phase, phenomena which are linked to the release of cations by the rock, tend to render the surfactant inoperative.

It has been proposed to substitute for petroleum sulfonates other types of anionic surfactants: for example, paraffin -sulfonates, olefin-sulfonates, alkylsulfates, alkylphosphates, alkanoates, N-acyl a-amino- alkanoates, carboxylates, sulphates and sulphonates of ethoxylated fatty alcohols and ethoxylated alkylphenols, etc., as well as nonionic surfactants: for example, ethoxylated fatty alcohols, ethoxylated alkylphenols, etc.

Despite everything, these petroleum sulphonate replacement surfactants undergo a significant loss of their interfacial efficiency when the salinity of the reservoir water is high. Nonionic surfactants are much less sensitive than anionic surfactants to the presence of divalent cations with regard to precipitation risks. On the other hand, their defect lies in that their properties in solution are very sensitive to slight variations in temperature. In addition, the distribution of this type of product (distribution linked to polydispersity between the various ligid phases is such that it leads to a reduction in its useful concentration in the solution.

The various drawbacks presented by the usual surfactants mentioned above have given rise to research focused on the use of other surfactant compounds, and more particularly on compounds of the zwitterionic type, products whose surfactant properties are little or not affected by the presence of polyvalent cations, and this over a wide pH range.

dans laquelle R2 et R3 sont généralement des groupes méthyles, et R un radical hydrocarboné aliphatique comprenant de préférence de 12 à 20 atomes de carbone. Ces amines tertiaires sont industriellement préparées par réaction de Leuckart sur les amines grasses primaires correspondantes provenant des acides gras naturels ; aussi leur prix de revient est-il assez élevé.the carboxy-betaines used derive from tertiary fatty amines of formula

in which R2 and R3 are generally methyl groups, and R an aliphatic hydrocarbon radical preferably comprising from 12 to 20 carbon atoms. These tertiary amines are industrially prepared by Leuckart reaction on the corresponding primary fatty amines originating from natural fatty acids; also their cost price is quite high.

It has now been discovered that products of the alkyl amibetin type can be advantageously used as surfactants in the formation of Ùii-cell systems (aqueous solutions, emulsions and microemulsions) for enhanced oil recovery. These products are more particularly suitable for. petroleum deposits containing water of high salinity, in particular with a high concentration of polyvalent ions, for example Ca and Mg, responsible for a large part of the loss of effectiveness of conventional surfactants. The compositions used in the invention also have the advantage of being effective from the point of view of lowering the interfacial tension over wide ranges of temperature and pH.

dans laquelle R1 est un radical hydrocarboné aliphatique monovalent, de préférence saturé, linéaire, comprenant de 7 à 23 atomes de carbone et, préférentiellement, de 11 à 17 atomes de carbone ; R et R , identiques ou différents, sont des radicaux hydrocarbonés aliphati ques monovalents saturés, comprenant de 1 à 4 atomes de carbone ; n est un nombre entier de 2 à 4 et m un nombre entier de 1 à 5.In general, the products considered in the invention, designated below by the term “alkylamido-betalne”, correspond to the formula:

in which R1 is a monovalent, preferably saturated, linear aliphatic hydrocarbon radical comprising from 7 to 23 carbon atoms and, preferably, from 11 to 17 carbon atoms; R and R, identical or different, are saturated monovalent aliphatic hydrocarbon radicals, comprising from 1 to 4 carbon atoms; n is an integer from 2 to 4 and m is an integer from 1 to 5.

où X est un atome d'halogène, de préférence un atome de chlore, R, R,
R3, n et m ont chacun la même signification que pour la formule (I) donnée plus haut.These alkylamido-betaines can be prepared by reacting a sodium salt of halogenocarboxylic acid with an alkylamido-amine (II) according to the following reaction scheme:

where X is a halogen atom, preferably a chlorine atom, R, R,
R3, n and m each have the same meaning as for formula (I) given above.

This quaternization reaction is carried out according to methods known per se.

ou R , R , R et n ont chacun la même signification que pour la formu- le (I), donnée précédemment et R4 est un atome d'hydrogène ou un radical alkyle de C1 à C6.Alkylamido-amines (II), for their part, are easily prepared by the action of fatty acids or light alkyl esters (for example of
C1 toC6) of fatty acids on compounds (III) comprising both a primary amine function and a tertiary amine function, according to the following reaction scheme:

or R, R, R and n each have the same meaning as for formula (I), given previously and R4 is a hydrogen atom or a C1 to C6 alkyl radical.

The reaction is carried out according to conventional methods and under conditions known per se.

As examples of alkylamido-betaines as defined above, there may be mentioned in particular those in which the number n is equal to 3, the number m equal to 1, the radicals R2 and R3 are each a methyl radical, and the radical R1 is a linear ållyl radical containing 11 carbon atoms (corresponding to lauzic acid), 15 carbon atoms (corresponding to palmitic acid) or 17 carbon atoms corresponding to stearic acid). mixtures of alkylamido-betaines which differ from one another by the nature of the radical R1, obtained in particular when one uses, pouz the preparation of the alkylamidoamine (II), a mixture of fatty acids or a mixture of esters of fatty acids obtained from the hydrolysis or transesterification of fatty substances (oils or fats) of vegetable or animal origin. In this regard, there may be mentioned as mixtures of fatty acids those which are derived from vegetable oils such as, for example, coconut, palm, soybean, colza, corn, sunflower, coconut, olive, and olive oils. peanut or cottonseed, and those derived from animal fats such as lard or tallow. These mixtures of fatty acids or alkyl fatty acid esters may have been saturated by hydrogenation.

According to the invention, the alkylamido-betaines as they have been defined above are used as surfactants in micellar systems of varied composition. They can be used as pure products or in the form of aqueous solutions formed beforehand, such solutions possibly having concentrations of about 10 to 40% by weight of active material, for example.

The surface-active products of the alkylamido-betaine type as they have been defined in the foregoing description can be used in the invention together with other products with surface-active properties which will be designated in the following by “co-surfactants”. or "cosolvents". They are mainly alcohols, in particular primary aliphatic monoalcohols of 1 to 12 carbon atoms. Among these, the following will be used advantageously: isobutanol, n-butanol-1, n-pentanol-1, n-hexanol-1, n-heptanol-1 or n-octanol-1, alone or as a co-surfactant, it is also possible to use amines, acids, ethers, polyols, as well as nonionic surfactants, such as ethoxylates of fatty alcohols, of fatty acids or of alkylphenols, or else anionic surfactants such as compounds bearing sulfate, sulfonate, carboxylate or phosphonate functions. These various cosurfactants can be used alone or as a mixture with one another.

The micellar systems considered in the invention can consist of aqueous solutions of concentrations of various surfactants, ranging for example from 0.1 to 15% by weight or more.

In one embodiment of the enhanced oil recovery process, it is possible to use micellar aqueous solutions of relatively low surfactant concentration, for example 0.1 to 5% by weight.

In another embodiment, more concentrated aqueous micellar solutions are used, for example containing from 5 to 15% by weight of surfactants, or more.

The micellar systems of the invention can also consist of microemulsions comprising - water, which, as indicated above, can contain mono and / or polyvalent cations, in particular Na, Ca, or Mg (the salt concentration total which may be for example 30 to 300 g / l); - at least one hydrocarbon liquid, which can be a pure hydrocarbon, containing for example 8 to 16 carbon atoms, a mixture of hydrocarbons, a petroleum fractionation cut or else a crude oil; - at least one alkylamido-betaine as described above; and - optionally at least one cosurfactant (or cosolvantJ as defined above.

The microemulsions can comprise various proportions of the various constituents, for example - from 10 to 90 t by weight of water - from 10 to 90% by weight of hydrocarbon liquid - from 0.1 to 15% by weight of surfactant ( alkylamido-betalne) - from 0 to 15% by weight of cosurfactant.
The water and the hydrocarbon-based liquid can be between them in weight ratios ranging, for example, from 20/80 to 95/5. Depending on the case, we may be dealing with a microemulsion of the “water in oil” or “oil in water” type.

The surfactant (alkylamido-betaine) and the cosurfactant can be between them in various ratios; advantageously, the weight ratio of the cosurfactant to the surfactant will be between 0 and 5.

The following examples illustrate the invention and should in no way limit its scope to the particular embodiments which they describe. Example 9 is given by way of comparison. In these examples, unless otherwise indicated, the temperature is 25 ° C.

avec R1 = n-undécyle ; elle sera désignée dans la suite par "lauryl ami do-bétalne". Examples 1 to 9 The alkylamido-betalne used in Examples 1 to 8 corresponds to the formula

with R1 = n-undecyl; it will be referred to below as “lauryl ami do-betalne”.

It is used in an aqueous solution containing 0% by weight of active material.

In Comparative Example 9, the corresponding alkyl-betaine (which may be denoted by lauryl-betaine) is used, also in the form of an aqueous solution containing 30% by weight of active material.

As a cosurfactant, n-hexanol-1 is also brought into play.

Water of various salinities is used, the respective concentrations of sodium chloride and calcium chloride of which are indicated in Table I below, as well as the sodium chloride / calcium chloride weight ratio and the total salinity.
TABLE I

<tb><SEP> Ex. <SEP> 1 <SEP> 2 <SEP> 3 <SEP><SEP> 4 <SEP> 5 <SEP> 6 <SEP> 7 <SEP> 8 <SEP> 9
<tb> Na <SEP> Cl <SEP> (g / l) <SEP> 58.5 <SEP> 81 <SEP> 81 <SEP> 81 <SEP> 162 <SEP> 234 <SEP> 270 <SEP> 100 <SEP> 100
<tb> Ca <SEP> C12 <SEP> tg / l) <SEP><SEP> 6.5 <SEP> 9 <SEP> 9 <SEP> 9 <SEP> 18 <SEP> 26 <SEP> 30 <SEP > 20 <SEP> 20
<tb> Na <SEP> Cl / Ca <SEP> Cl2 <SEP> 9/1 <SEP> 9/1 <SEP> 9/1 <SEP> 9 / <SEP> 9/1 <SEP> 9/1 <SEP> 9/1 <SEP> 5/1 <SEP> 5/1
<tb> Total <SEP> salinity <SEP> 65 <SEP> 90 <SEP> 90 <SEP> 90 <SEP> 180 <SEP> 260 <SEP> 300 <SEP> 120 <SEP> 120
<tb> (g / l) <SEP>
<tb>
In each of these examples, the hydrocarbon used is n-dodecane in a proportion corresponding to a weight ratio - water / oil of 1/1, except in Examples 2 and 4 where the water / oil ratio takes respectively the values 3 / 1 and 1/3.

For each mixture of n-dodecane and salt water, the amounts of surfactant (laurnamido-betaine and, in comparative example 9 lauryl-betalne) and of co-surfactant tn-hexanol-1) necessary to obtain the miscibility of water and n-dodecane in a single phase (microemulsion). The various proportions were calculated as% by weight of the total of the constituents and given in Table II below, where the value of the salinity was also recalled for each microemulsion.

TABLE II

<tb><SEP> Water <SEP> n-dodecane <SEP> surfactant <SEP> Alcohol
<tb><SEP> ** (n-hexanal-1)
<tb> Ex. <SEP> Salinity <SEP> Proportion <SEP> proportion <SEP> proportion <SEP> proportion <SEP>
<tb><SEP> (g / 1) <SEP> (% <SEP> weight) <SEP> (% <SEP> weight) <SEP> (% <SEP> weight) <SEP> (% <SEP> weight )
<tb> 1 <SEP> 65 <SEP> 41.5 <SEP> 41.5 <SEP> 8.0 <SEP> 9.0
<tb> 2 <SEP> 90 <SEP> 64.5 <SEP> 21.5 <SEP> 9.0 <SEP> 5.0
<tb> 3 <SEP> 90 <SEP> 41.0 <SEP> 41.0 <SEP> 9.0 <SEP> 9.0
<tb> 4 <SEP> 90 <SEP> 19.25 <SEP> 57.75 <SEP> 9.0 <SEP> 14.0
<tb> 5 <SEP> 180 <SEP> 41.5 <SEP> 41.5 <SEP> 6.9 <SEP> 10.1
<tb> 6 <SEP> 260 <SEP> 42.0 <SEP> 42.0 <SEP> 7.0 <SEP> 9.0
<tb> 7 <SEP> 300 <SEP> 41.1 <SEP> 41.1 <SEP> 8.8 <SEP> 9.0
<tb> 8 <SEP> 120 <SEP> 41.0 <SEP> 41.0 <SEP> 8.5 <SEP> 9.5
<tb> 9 <SEP> * <SEP> 120 <SEP> 35.5 <SEP> 35.5 <SEP> 14 <SEP> 15
<tb> * comparative example ** in aqueous solution containing 30% by weight of active material.

These results show that the amount of surfactant + cosurfactant required is relatively low and varies little as a function of the salinity of the water (for a water / hydrocarbon ratio of 1/1). Furthermore, similar amounts of surfactant are used for different water / hydrocarbon ratios: 3/1, 1/1 and 1/3 in Examples 2, 3 and 4. The comparison of Examples 8 and 9 finally shows the increased effectiveness of laurylamidobetaine compared to lauryl betaine.

où R1 = n-pentadécyle, désignée par la suite "palmi tylamido-bétane " ; elle est employée sous forme de solution aqueuse à 30 % en poids de matière active.Example 10
In this example, the alkylamidobetaine of formula

where R1 = n-pentadecyl, hereinafter referred to as "palmi tylamidobetane"; it is used in the form of an aqueous solution containing 30% by weight of active material.

The water involved has a total salinity of 90 g / l: 81 g / l of NaCl and 9 g / l of CaCl2 (NaCl / CaCl2 weight ratio = 9/1).

The hydrocarbon used is n-dodecane in a proportion corresponding to a weight ratio of water to the hydrocarbon of 1/1.

ou R = n-heptadécyle, désignée par la suite "stéarylamido-bétaine".The quantities of "palmitylamido-betaine" and of n-hexanol-1 (used as a cosurfactant) necessary to obtain the miscibility between salt water and the hydrocarbon by formation of a microemulsion j the corresponding weight proportions of the salts are determined. constituents are reduced to a total of 100%: - water (salinity 90 g / l): 41.55% - n-dodecane: 41.55% - palmitylamido-betaine: 10.9% (i.e. active ingredient) - n-hexanol-1: 6.0%
Example he
The surfactant used is an alkylamido-betaine of formula

or R = n-heptadecyl, hereinafter designated "stearylamido-betaine".

It is used in an aqueous solution containing 19% by weight of active material. We use water with salinities varying between 120 and 230 g / l in which the NaCl / CaCl2 weight ratio is 9/1.

The quantities of "stearylamido-betaine" and of n-hexanol-1 corresponding to the weight proportions indicated below are sufficient to obtain the formation of a single microemulsion phase) between salt water and n-dodecane - salt water: 37.5% - n-dodecane: 37.5% - stearylamido-betalne: 20% (i.e. 3.8% of active ingredient) - n-hexanol-1: 5%
Example 12
A microemulsion is prepared at 80 ° C., from a mixture of water having a salinity of 180 g / l (NaCl / CaC12 = 9/1 by weight and n-dodecane. salt water with n-dodecane is 3/1. The quantities of "laurylamido-betaine" and of n-octanol-1 necessary to obtain a microemulsion correspond to the following proportions by weight: - salt water: 64.05% - n -dodecane: 21.35% - "laurylamido-betalne": 9% (i.e. 2.7 S by weight of active material) - n-octanol-1: 5.6 t
Examples 13 and 14
To 60 g of 180 g / l salinity water (NaCl / CaCl 2 = 9/1 by weight), 10 g of “laurylamido-betalne” in aqueous solution at 30% by weight are added.

The solution obtained is stored for 10 days at 25 ° C. 60 g of n-dodecane are then added, then the amount of n-hexanol-1 necessary to obtain a single-phase system (microemulsion), ie 14.5 g.

The proportions expressed in% by weight of all the constituents are practically the same as in Example 5.

The same experiment is repeated, but the initial solution is brought to 90 ° C. for 10 days. The amount of n-hexanol-1 to be added in this case is 14.6 g.

The comparison of these results shows 1 shows the absence of degradation of laurylamido-betaine under the prolonged effect of heat.

Examples 15 and 16
Three-phase systems are prepared by mixing salt water with an equal weight of n-dodecane, as well as an alkylamido-betalne and an alcohol in proportions insufficient to cause the formation of a single phase (microemulsion).

The three phases are: an aqueous phase (lower phase), a microemulsion phase (intermediate phase) and a hydrocarbon phase (upper phase).

In Example 15, the salinity of the water is 90 g / l (NaCl / CaCl2 weight ratio = 9/1); the alkylamidobetaine is "laurylamidobetaine", the alcohol is n-hexanol-1, used in a weight ratio of 0.72.

In Example 16, the salinity of the water is 60 g / l (NaCl / CaCl2 weight ratio = 9/1; the alkylamido-betaine is "palmitylamido-betaine", the alcohol of n-pentanol- 1, used in a weight ratio of 2.35.

The interfacial tensions are measured at 25 ° C. using a rotating drip tensiometer. If we denote by y1 the interfacial tension between the microemulsion phase and the aqueous phase and by 1 (2 the interfacial tension between the microemulsion phase and the hydrocarbon phase, we find, expressed in mN / m, the following interfacial tension values example 15: &gamma; 1 = 9.10-3, &gamma; 2 = 3.10-3 example 16: &gamma; 1 = 6.10-3, &gamma; 2 = 15.10-3

Claims (10)

in which R1 is a monovalent aliphatic hydrocarbon radical of 7 to 23 carbon atoms, R2 and R3 are saturated monovalent hydrocarbon radicals of 1 to 4 carbon atoms, n is an integer of 2 to 4 and m an integer of 1 at 5.

CLAIMS 1.- Use in enhanced oil recovery of at least one alkylamido-betaine corresponding to the general formula 2.- Use according to claim 1, characterized in that said alkylamido-betaine is used in aqueous solution at 0.1 to 15% by weight. 3.- Use according to claim 1, characterized in that said alkylamido-betaine is used in a microemulsion further comprising water, at least one hydrocarbon liquid and -optionally at least one cosurfactant. 4.- Use according to claim 3, characterized in that said microemulsion comprises from 10 to 90% by weight of water from 10 to 90% by weight of hydrocarbon liquid from 0.1 to 15% by weight of alkylamido-betaine and from 0 to 15% by weight of cosurfactant. 5.- Use according to one of claims 3 and 4 characterized that said cosurfactant consists of at least one primary aliphatic monoalcohol of 1 to 12 carbon atoms. 6.- Use according to one of claims 3 to 5 characterized in that said water contains alkali cations etXou alkaline earth cations and in that its total salinity ranges from 30 to 300 g / l. 7.- Use according to claim 6, characterized in that the alkaline cation is Na and the alkaline earth cation is Ca ++ and / or Mg ++. 8.- Use according to one of claims 3 to 7, characterized in that the water and the liquidhudrocarbon are involved in a weight ratio of 20/80 to 95/5. 9.- Use according to one of claims 3 to 8, characterized in that the cosurfactant and 1 alkylamido-betaine are involved in a weight ratio of 0 to 5. 10. Microemulsion usable in enhanced oil recovery, characterized in that it is defined as in one of claims 3 to 9.