WO2015135777A2

WO2015135777A2 - Method for the production of oil and/or gas

Info

Publication number: WO2015135777A2
Application number: PCT/EP2015/054247
Authority: WO
Inventors: Vandana Kurkal-Siebert
Original assignee: Basf Se
Priority date: 2014-03-12
Filing date: 2015-03-02
Publication date: 2015-09-17
Also published as: WO2015135777A3

Abstract

Use of foams generated from an aqueous fluid, at least one gas and at least one surfactant in the production of oil and/or gas from subterranean formations. The surfactants are selected from the group of alkyl betains, alkyl N-oxides, amphoteric surfactants, anionically modified alkyl ethers, alkyl or alkenyl polyglucosides, modified alkyl or alkenyl polyglucosides and alkyl sulfates. The foams may be used for enhanced oil recovery.

Description

Method for the production of oil and/or gas

The present invention relates to the use of foams generated from an aqueous fluid, at least one gas and at least one surfactant in the production of oil and/or gas from subterranean formations. The surfactants are selected from the group of alkyi betains, alkyi N-oxides, amphoteric surfactants, anionically modified alkyi ethers, alkyi or alkenyl polyglucosides, modified alkyi or alkenyl polyglucosides and alkyi sulfates. The foams may be used for enhanced oil recovery.

Various methods for enhanced oil recovery are known in the art, such as waterflood, fireflood, micellar flood, miscible flood, and polymer flood. Besides such techniques it is also known to inject gases such as for example carbon dioxide, hydrocarbons, or nitrogen into subterranean formations in order to improve the oil production.

The continued use of gas injection to improve oil recovery and the prospects for its increased use throughout the world provides impetus to improve sweep efficiency of injected gas. Work is being carried out to improve understanding and the economics of mobility control agents.

There are no reservoirs that are completely homogeneous. The porous media in the reservoir are characterized by a size distribution of pores and pore throats, which leads to non-uniform displacement. According to Darcy's law, the mobility of a single phase in porous media is inversely proportional to its viscosity. Gases used in gas-flooding such carbon dioxide, hydrocarbons, or nitrogen are normally more than one order of magnitude less viscous and less dense than both water and crude oil, which results in gas channeling through the high permeability zones and gravity overriding. Thus, gas flooding normally has poor volumetric sweep efficiency, especially in an immiscible displacement, with the displacing phase being a lower viscosity.

A need for mobility control in gas flooding has led to the use of foam for sweep improvement and profile modification. Sweep efficiency is broadly defined as volume of formation swept/total volume.

Foam is a colloidal dispersion in which a gas is dispersed in a continuous liquid phase. Surfactants are added to the solution to stabilize foam by reducing interfacial tension. Many studies demonstrated that surfactant stabilized foam could drastically reduce the gas mobility in the porous media, consequently improving volumetric sweep efficiency and oil recovery.

There is considerable interest in the application of foams in enhanced oil recovery processes involving miscible or immiscible gas displacement (carbon dioxide, hydrocarbon gases). From a reservoir perspective foams can provide a means to counteract the displacing agent's naturally high mobility and low density and therefore can reduce fingering (channeling) and gravity over- ride. Foams can also be applied near-well to reduce gas coning.

Gases such as steam, carbon dioxide and hydrocarbon gases are injected into oil reservoirs to increase the recovery of oil. These gases are much less dense and less viscous than the oil they attempt to displace, so they tend to finger through or migrate to the top of the reservoir, leaving most of the oil behind. Foams can help these gases to sweep oil reservoirs more efficiently.

It is known in the art to use water-soluble polymers of high molecular weight such as partially hydrolyzed polyacrylamides for providing mobility control and thus improving sweep efficiency in surfactant and alkaline/surfactant processes for enhanced oil recovery. Foam offers the prospect of further improvement in sweep efficiency, especially in heterogeneous reservoirs, because foam mobility is lower (apparent viscosity is higher) in layers of high permeability than in those of low permeability. Apparent viscosity of the foam is approximately a factor of five larger in the sand pack with the higher permeability, confirming the ability of foam to provide a more uniform sweep than polymer. While additional surfactant is needed to generate the foam, its amount and cost is less than the decrease in the amount and cost of polymer because half or more of the injected fluid is gas in the foam case. Recovery of residual oil is excellent in both cases for the surfactant mixture used.

The use of foam to improve the sweep efficiency of the displacing fluid involves the utilization of two foam properties. The first is the high resistance to flow that is associated with foam. The second property is the high gas-liquid surface area. Thus, only relatively small amounts of an aqueous solution of a foaming agent need be used with relatively large amounts of gas or dense fluid. The gas disperses in the liquid, generating a large interfacial area and a large volume of foam, thereby increasing the resistance to flow. If this resistance to flow is in those regions of the reservoir where the resistance is least, then the displacing fluid is forced to flow through regions of higher resistance, sweeping larger portions of the reservoir and recovering larger quantities of oil. Thus, the use of foam improves sweep efficiency.

It is known in the art to use surfactants to stabilize foams which may be used in a wide range of techniques of oil and/or gas production.

A review article of Peter G.H. Bath, Journal of Petroleum Science and Engineering, 2 (1989) 103, 117 provides an overview about flooding oil reservoirs with hydrocarbons, carbon dioxide, and nitrogen.

US 2,866,507, US 3,185,634, US 3,318,379, and US 3,376,924 disclose processes for the recovery of oil from subterranean formations by injecting gases and surfactants into the formation thereby forming foams. A wide variety of surfactants is disclosed, such as water soluble, unsaturated quaternary amines having 8 to 20 carbon atoms in the longest chain, sodium lauryl sulfonate, sodium dioctylsulfosuccinate, sodium lignin sulfonates, ethoxylated alcohols, ethox- ylated fatty acids, and ethoxylated amines or amides, quaternary ammonium salts such as lauryl dimethyl benzyl ammonium chloride, Dicoco dimethylammonium chloride, alkyl aryl sul- fonates, fatty alcohol sulfates, sulfates and sulfonates esters and ethers, alkyl sulfonates, fatty acid alkanolamides sich as lauric diethanolamide, zwitterionic surfactants, such as cetylamino- acetic acid, sorbitan esters such as sorbitan monolaurate or sorbitanmonopalmitate. US 3,376,924 furthermore discloses surfactants of the general formula RNH_x-(A-COOM)_y, wherein R is an aliphatic Cs to C22 hydrocarbon group, A is a Ci to C6 divalent hydrocarbon radical, x and y are 1 or 2 each which the proviso that the sum of x and y is 2 and sulfated ethox- ylated n-decanol.

US 4,1 13,01 1 discloses a method for the recovery of oil by injecting CO2 and an aqueous solution of alkyl polyethylene oxide sulfates R-(EO)_x-S04M, wherein R is Cs or C9 alkyl, EO is ethylene oxide and x is 1 to 5. US 4,237,017 discloses to inject a mixture of CO2, steam and the surfactant quinoline-sulfonyl- (PO)x-(EO)y-S0₄M, wherein x is from 2 to 5, y is from 8 to 60 and x+y is > 55, US 4,637,466 discloses to inject alkyl polyalkoxycarboxylat.es of the formula RO-(AO)_xR'COOM, wherein R is linear or branched Cs to C24 alkyl moiety, AO is ethylene oxide and/or propylene oxide, x is 3 to 1 1 , and R' is methylene or ethylene. US 4,828,032 and US 5,046,560 disclose the use of sur- factants of the type RO-(PO)_x-(EO)_yH and RO-(PO)_x-(EO)yR'S0₃M, wherein R are sulfonated and and/or alkylated aryl moieties.

US 4,380,266 discloses a process for enhanced oil recovery by injecting CO2, a surfactant and water into an oil bearing formation using polyethylenoxide-polypropylene oxide block copoly- mers or ethyoxylated aliphatic and aromatic alcohols as surfactants.

US 4,703,797 discloses a process of CO2 using a surfactant mixture to create foams. The surfactant mixture comprises as one component surfactants selected from anionic surfactants such as akyl polyethoxysulfates, non-ionic surfactants such as linear alcohol ethoxylates or ampho- teric surfactants such as cocoamidopropyl betaine and as another component lignosulfonates.

US 5,033,547 discloses a process for recovering petroleum from an underground reservoir by injecting a mixture of CO2 and a surfactant into the formation for forming an emulsion in the reservoir of CO2, formation water and the surfactant. The surfactants suggested have the formula RO-(EO)_x-H, wherein R is C₇ to C15 alkyl or alkylaryl and x is 4 to 8.

US 7,842,650 B2 discloses a surfactant mixture for improved foaming in the extraction of petroleum or natural gas. The surfactant mixture comprises a at least one foamer selected from the group consisting of sulfates, sulfonates, phosphates, carboxylates, sulfosuccinates, betaines, quaternary ammonium salts, amine oxides, amine ethoxylates, amide ethoxylates, acid ethoxylates, alkyl glucosides, EO-PO block copolymers and long-chain fatty alcohol ethoxylates and furthermore at least one cosurfactant different therefrom. The cosurfactant has the structure RO-(AO)y-H or RO-(AO)_y-Z, wherein R is a C6- to C12 hydrocarbon group, preferably an aliphatic group, (AO)n is an alkylene oxide block having from 5 to 25 alkylene oxide groups, and Z is a terminal group, preferably a sulfate, phosphate or carboxylate group. R preferably is branched, for example R may be derived from a Guerbet-alcohol such as a 2-Propylheptanol group. Preferably, the surfactant has a block structure RO-(AO)_yi-(EO)_y2-Z, wherein (AO) is an alkylene oxide having at least 3 carbon atoms and EO is ethylene oxide. In one embodiment y1 may be from 0 to 2, and y2 may be from 8 to 25. The examples disclose a foaming mixture of cocami- dopropylbetaine and a Cio-Guerbet alcohol ^* 14 EO.

WO 2010/044818 A1 discloses a method for recovering oil from a reservoir that is penetrated by at least one injection well and at least one production well by injecting a surfactant dissolved in CO2 into the reservoir via the injection well. In the formation a stable foam of water, CO2 and the surfactant is formed. The surfactant may be any non-ionic, non-emulsifying surfactant having a CO2 philicity from 1 .5 to 5.0. Preferably, the surfactant has the formula RO-(AO)_x-(EO)_y-H, wherein AO is an alkylene oxide having 3 carbon atoms to 10 carbon atoms and EO is ethylene o

WO 201 1/152856 A1 discloses a method for oil recovery comprising the following steps: Providing a flow of supercritical CO2 to the oil containing reservoir, injecting a flow of a surfactant to the supercritical CO2 thereby forming a mixture of supercritical CO2 and the surfactant, forming an emulsion of the mixture in water within the oil containing reservoir, and reducing the flow of the surfactant. Suggested surfactants include non-ionic surfactants such as ethoxylated aliphatic alcohols, branched alkyl alkoxylates, linear or branched alkyl phenolalkoxylates, cationic surfactants, in particular quaternary ammonium salts such as cetyl trimethyl ammonium bromide or polyethoxylates tallow amine, anionic surfactants such as ethoxylated or propoxylated sulfates, or amphoteric surfactants such as betaines, amine oxides or imidazole-based carboxylates.

Although is known in the art to use surfactants for stabilizing foams there is still a need to improve such techniques. There are several requirements for surfactants suitable for stabilizing foams for enhanced oil recovery. The most important ones are foamability, i.e. the ability to cre- ate large amounts of foam and furthermore stability, i.e. the foam should be stable as long as possible. Furthermore, it is important that these requirements are still fulfilled under conditions prevailing in the oilfield such as high salinity, higher temperatures and pressure.

Although the surfactants mentioned in the state in the art have the ability to create foams the performance of many of them in oilfield applications, in particular with respect to their long term stability is only poor.

It is an object of the invention to provide improved foams which may be used in the production of oil and/or gas.

Correspondingly, a method of using foams has been found, wherein the foams are generated from an aqueous fluid, at least one gas and at least one surfactant in the production of oil and/or gas from subterranean formations penetrated by at least one injection well by providing an aqueous formulation comprising 0.05 % to 5 % by weight of at least one surfactant capable of stabilizing foams and generating a foam of the aqueous formulation comprising surfactants and the gases wherein

· the foam is generated at the surface and injected into the subterranean formation through at least one injection well, or

• the aqueous formulation and at least one gas injected successively, alternate or together into the subterranean formation through at least one injection well and foam is in-situ generated subsurface in the injection well and/or in the formation, and wherein at least one of the surfactants used is selected from the group of the surfactants (A) to (G) having the following structures:

(A) Alkyl betains of the general formula

R -N⁺(R2)₂-CH₂COO- (I), wherein,

• R¹ is an alkyl and/or alkenyl moiety having from 8 to 24 carbon atoms,

• R² independently are selected from Ci- to C₄ alkyl,

(B) Alkyl N-oxides of the general formula

R³-N⁺(R⁴)₂-0- (II),

wherein

• R³ is an alkyl and/or alkenyl moiety having from 8 to 24 carbon atoms,

• R⁴ independently are selected from Ci- to C₄ alkyl,

(C) Amphoteric surfactants having the general formula

R⁵-N(R⁶)(R⁷) (III)

wherein

• R⁵ is a group selected from the group of

> R^5a: alkyl and/or alkenyl groups having from 8 to 24 carbon atoms,

> R^5b: a group R⁸CO-, wherein R⁸ is an alkyl and/or alkenyl group having from 7 to 15 carbon atoms,

> R^5c: a group R⁸CO-NH-R⁹-, wherein R⁸ has the meaning as defined

above and R⁹ is an alkylene group having 1 to 4 carbon atoms,

• R⁶ and R⁷ are selected independently from the group of

> co-carboxyalkyl groups (R^6a, R^7a) of the general formula -(CH₂)n-COOM (IV), wherein M is H⁺ or a cation and n is a number from 1 to 10,

> co-hydroxyalkyl groups (R^6b, R^7b) of the general formula -(CH₂)_n-OH (V), wherein n is a number from 1 to 10 > groups (R^6c, R^7c) of the general formula -(CH₂CH2-R¹⁰)m-R¹¹-COOM (VI), wherein M is H⁺ or a cation, m is a number from 1 to 10, R¹⁰ is selected from -O- and -NH- and R¹¹ is an alkylene group having 1 to 4 carbon atoms,

(D) Anionically modified alkyl ethers of the general formula

R¹²0-(CH₂CH₂0)n-XM (VII),

wherein

• R¹² is a linear or branched C12- to C18 alkyl moiety,

• n is a rational number from 1 to 5,

• X- is an anionic group selected from the group of -S03^", -R¹³-S03^", or

-R ³-COO-,

• R¹³ is an alkylene group having from 1 to 10 carbon atoms, and

• M is H⁺ or a metal cation,

(E) Alkyl or alkenyl polyglucosides of the general formula

R¹⁵0[G]_P (VIII),

wherein

• R¹⁵ is an alkyl or alkenyl radical having from 8 to 22 carbon atoms,

• G is a sugar unit having 5 or 6 carbon atoms, and

• p is a number from 1 to 10,

(F) Modified alkyl or alkenyl polyglucosides of the general formula

R¹⁵-0-[(G)p](-R¹⁶-COOM)_q (IX)

wherein

• R¹⁵, G and p have the same meaning as mentioned above,

• R¹⁶ is a divalent linking group selected from the group of

> R^16a : divalent hydrocarbon groups comprising 1 to 6 carbon atoms,

> R^16b: divalent ester groups -C(0)-0-R¹⁷-, wherein R¹⁷ is a hydrocarbon group comprising 1 to 6 carbon atoms, and

• q is a number from 1 to 4,

• M is H⁺ or a metal cation, and

(G) Alkyl sulfates of the general formula

R¹⁸OS0₃M (X)

wherein

• R¹⁸ is a linear or branched Ci2to Cis alkyl moiety, and

• M is H⁺ or a metal cation. In particular, the foam may be used for enhanced oil recovery, fracturing, foam drilling, and conformance control.

List of figures:

Figure 1 Schematic representation of the apparatus for the determination of

foamability under pressure (filter test)

Figure 2 Static foam test: Surfactants with good foamability and good foam stability

Figure 3 Static foam test: Surfactants with good foamability and moderate foam

stability

Figures 4a, 4b Static foam test: Surfactants with good foamability and poor foam stability

Figure 5 Static foam test: Surfactants with poor foamability and poor foam stability

Figure 6 Filter test with N2 at 2 bar: Foam height as a function of injected N2

volume in SSW for various surfactants

Figure 7 Filter test with N2 at 2 bar: Stability of foams in SSW for various

surfactants

Figure 8 Filter test with N2 at 2 bar with surfactant S8, Foam height as a function of injected N2 volume at different salinities

Figure 9 Filter test with N2 at 2 bar with surfactant S8, Stability of foams in

formulation of different salinities

Figure 10 Filter test with N2 at 2 bar with surfactant S6, Foam height as a function of injected N2 volume at different salinities

Figure 1 1 Filter test with N2 at 2 bar with surfactant S6, Stability of foams in

formulation of different salinities With regard to the invention, the following should be stated specifically:

Foams The foams used according to the present invention are mixtures of a gas phase, an aqueous liquid phase and at least one surfactant. The fluid properties of foams are derived from a structure different from that found in gelled water.

The quality of the foam (f_g) may be defined as the volume of gas (q_g) divided by the total volume of the foam (q_g+w).

Foam quality, _g (%) = * 100%

Generally, the higher the quality of the foam the higher its viscosity. The high apparent viscosity of foam is due to the interfacial structure of the foam bubbles. In very low quality foams, for in- stance foams with a foam quality below 50 %, the spherical gas bubbles have freedom to move with little restriction from adjacent bubbles. In foams having a quality of above approximately 50 %, the bubbles touch each other and allow less freedom of movement within the total fluid. In high quality foams, for instance foams having a quality of above 75 %, the bubbles are crowded together and no longer have spherical shapes. Movement within the fluid is very restricted; hence, high apparent viscosity results.

Surfactants

For stabilizing the foams to be used in oil and/or gas production according to this invention, least one surfactant selected from the group of the surfactants (A), (B), (C), (D), (E), and (F) is used. Of course also combinations of two or more of the surfactants may be used. Furthermore, a surfactant mixture used for the method may optionally comprise further surfactants distinct from surfactants (A) to (F). Surfactants (A)

Surfactants of the group (A) are alkyl betains of the general formula

R -N⁺(R2)₂-CH₂COO- (I),

In formula (I) R¹ is an alkyl and/or alkenyl moiety having from 8 to 24, preferably from 8 to 16, and more preferably from 10 to 14 carbon atoms, and the two groups R² are independently se- lected from Ci- to C₄ alkyl. Preferably, the groups R² are methyl groups. Surfactants (A) and methods of manufacturing such surfactants are known to the skilled artisan.

In a preferred embodiment, R¹ is derived from coconut oil, i.e. surfactant (A) comprises a mixture of different compounds comprising linear Cs- to Ci6 alkyl and alkenyl groups wherein linear Ci2 alkyl groups and linear Ci₄ alkyl groups are the main components. Surfactants (B)

Surfactants of the group (B) are alkyl N-oxides having the general formula

R³-N⁺(R⁴)₂-0- (II),

In formula (II) R³ is an alkyl and/or alkenyl moiety having from 8 to 24, preferably from 8 to 16, and more preferably from 10 to 14 carbon atoms, and the two groups R⁴ are independently selected from Ci- to C₄ alkyl. Preferably, the groups R⁴ are methyl groups. Surfactants (B) and methods for manufacturing such surfactants are known to the skilled artisan. Preferably, R³ is a linear alkyl group, more preferably R³ is a linear C12 alkyl group. Surfactants (C)

Surfactants of group (C) are amphoteric surfactants having the general formula

R⁵-N(R⁶)(R⁷) (III) In formula (III) R⁵ is a group selected from the group of

R^5a: an alkyl and/or alkenyl group having from 8 to 24, preferably 8 to 16, more preferably from 10 to 14 carbon atoms

R^5b: a group R⁸CO-, wherein R⁸ is a preferably linear alkyl and/or alkenyl group having from 7 to 15, preferably from 9 to 13 carbon atoms, and

R^5c: a group R⁸CO-NH-R⁹-, wherein R⁸ has the meaning as defined above and R⁹ is an alkylene group having 1 to 4, preferably 2 carbon atoms, preferably a 1 ,2 ethylene group -CH2-CH2-.

R⁶ and R⁷ are selected independently from the group of

R^6a' R^7a : co-carboxyalkyl groups of the general formula -(Chb COOM (IV), wherein M is

H or a cation, preferably Na⁺ od K⁺, and n is a number from 1 to 10, preferably 1 to 4, and most preferably 2,

R^6b, R^7b: co-hydroxyalkyl groups of the general formula -(ChbJn-OH (V), n is a number

from 1 to 10, preferably 1 to 4, and most preferably 2,

R^6c, R^6c: groups of the general formula -(CH₂CH2-R¹⁰)m-R¹¹-COOM (VI), wherein M is

H+ or a cation, preferably Na⁺ od K⁺, m is a number from 1 to 10, preferably 1 to 4, most preferably 1 , R¹⁰ is selected from -O- and -NH- and R¹¹ is an alkylene group having 1 to 4, preferably 1 or 2 carbon atoms, more preferably a methylene group -CH2-. R⁶ is selected from R^6a, R^6b, and R^6c and R⁷ is selected from R^7a, R^7b, and R^7c with the proviso that at least one of the groups R⁶ and R⁷ comprises a -COOM group.

In one embodiment of the invention the surfactants (C) have the general formula

R^5a-N(R^6a)(R^7a), i.e. R^5a-N(-(CH₂)n-COOM)₂ (Ilia). In formula (Ilia) preferably n is 2, and R^11a is a preferably linear alkyl group having from 10 to 14 carbon atoms. An example for a surfactant (C) of formula (Ilia) comprises n-Ci2H₂5-N(-CH2CH₂-COOM)2. In another embodiment of the invention the surfactants (C) have the general formula R^5b-N(R^6b)(R^7c), i.e. R⁸CO-(-(CH₂)_n-OH)( -(CH₂CH₂-R¹⁰)m-R¹¹-COOM) (1Mb). In formula (1Mb) n preferably is 1 to 4, R¹⁰ is -NH-, R¹¹ is selected from -CH2- and -CH2CH2-, and m is 1 . An example for a surfactant (C) of formula (1Mb) comprises

R⁸CO-(-CH₂CH2-OH)(-CH2CH2-NH-CH₂-COOM).

In another embodiment of the invention the surfactants (C) have the general formula

R^5c-N(R^6a)(R^7c), i.e. R⁸CO-NH-R⁹-N(-(CH₂)_n-COOM) -(CH₂CH₂-R¹⁰)m-R¹¹-COOM) (lllc). In formula (III c) R⁹ preferably stands for -ChbChb-, n preferably is 1 to 4, R¹⁰ is -0-, R¹¹ is selected from -CH2- and -CH2CH2-, and m is 1. An example for a surfactant (C) of formula (lllc) comprises R⁸CO-NH-CH2CH2-N(-CH2-COOM)(-CH₂CH2-0-CH2-COOM).

Surfactants (D)

Surfactants of the group (D) are anionically modified alkyl ethers of the general formula

R¹²0-(CH₂CH₂0)_n -XM (VII).

In formula (VII) R¹² is a linear or branched C12- to C18 alkyl moiety, n is a rational number from 1 to 5, preferably 1.5 to 4.5, X is an anionic group selected from the group of -OSO3^", -R¹³-S03^" , or -R¹³-COO^" and M is H⁺ or a metal cation, preferably a metal cation selected from the group of alkali metal ions or earth alkali metal ions, preferably a cation selected from the group of Li⁺, Na⁺, or K⁺. R¹³ is an alkylene moiety having from 1 to 10 carbon atoms, preferably from 1 to 4 carbon atoms, which may optionally have functional groups as substituents. Examples comprise methylene groups -CH2-, 1 ,2-ethylene groups -CH2-CH2-, 1 ,2-propylene groups -CH2-CH(CH3)- or -CH(CH₃)-CH₂- or 1 ,3-propylene groups -CH₂-CH(R¹⁴)-CH₂-, where R¹⁴ is H or OH. The degree of ethoxylation is represented by n and for the skilled artisan it goes without saying that n is an average number and does not necessarily need to be an integer. In a preferred embodiment of the invention, n is selected according to the number of carbon atoms in R¹². If R¹² is a C12 - CM moiety n is preferably from 1 to 3, more preferably from 1.5 to 2.5, and if R¹² is a C15 - C18 moiety n is preferably from 3 to 5, more preferably from 3.5 to 4.5. Preferably the anionic group X is a sulfate group and R¹³ is a single bond, i.e. the surfactants (D) preferably have the following general formula R¹²0-(CH2CH₂0)nS03M (Vila). In formula (Vila), R¹² may preferably be a linear or branched C12- to C18 alkyl moiety, more preferably a C12 alkyl group and n may preferably be from 1 to 3, more preferably from 1.5 to 2.5. Surfactants A and methods for manufacturing such surfactants are known to the skilled artisan.

Surfactants (E)

Surfactants of the group (E) are alkyl or alkenyl poly glucosides of the general formula

R¹⁵0[G]_P (VIII)

In formula (II) R¹⁴ is an alkyl or alkenyl radical having from 8 to 22 carbon atoms, G is a sugar unit having 5 or 6 carbon atoms and p is a number from 1 to 10. The index p in general formula (III) indicates the average degree of oligomerisation (DP degree), i.e. it may also be a rational number. Preferably p may be 1 .1 to 3 more preferably 1 .2 to 1.4.. The alkyl or alkenyl radical R¹⁵ may be derived from primary alcohols comprising 8 to 22, preferably 8 to 16 carbon atoms. Typical examples are caprylic alcohol, capric alcohol, undecyl alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, palmitoleyl alcohol, stearyl alcohol, isostearyl alcohol, oleyl alcohol, elaidyl alcohol, petroselinyl alcohol, arachyl alcohol, gadoleyl alcohol, behenyl alcohol, erucyl alcohol and mixtures thereof. AlkyI poly glucosides based on Cs-Ci6 coconut oil alcohol or hy- drogenated Cs-Ci6 coconut oil having a DP of 1 to 3 are preferred. Surfactants B and methods for manufacturing such surfactants are known to the skilled artisan.

Surfactants (F)

Surfactants of the group (F) are alkyl or alkenyl poly glucosides modified with carboxylic groups of the general formula

R¹⁵-0-[(G)p](-R¹⁶-COOM)_q (IX)

In formula (IX) R¹⁵, G, M and p and its preferred ranges have the same meaning as mentioned above, and

R¹⁶ is a divalent linking group selected from the group of

R^16a : divalent hydrocarbon groups comprising 1 to 6 carbon atoms,

R^16b: divalent ester groups -C(0)-0-R¹⁷-, wherein R¹⁷ is a hydrocarbon group comprising

1 to 6 carbon atoms,

and q is a number from 1 to 4, preferably from 1 to 2. Surfactants (F) and methods for manufacturing such surfactants are basically known to the skilled artisan. The alkyl and/or alkenyl polyglycoside carboxylates may be obtained by reacting alkyl- and/or alkenyl polyglycosides or alkoxylated alkyl- and/or alkenyl polyglycosides with suitable reagents for introducing carboxylate groups. Examples of suitable reagents for introducing carboxylic acid groups comprise

(a) halogene substituted carboxylic acids, such as a-halogen carboxylic acids or co-halogen carboxylic acids, preferably chloroacetic acid or its sodium salt;

(b) alpha, beta-unsaturated carboxylic acids, preferably (meth)acrylic acid; or

(c) cyclic dicarboxylic acid anhydrides, preferably succinic acid anhydride, maleic acid an- hydride or phthalic acid anhydride,

as they are for example disclosed in WO 2002/090369 A2 and US 6,248,792 B1.

The nature of the linking group R¹⁶ depends on the nature of the reagent used for introducing the carboxcylic acid group. Alkyl and/or alkenyl polyglycoside carboxylates comprising groups - R^16a-COOX may be obtained by using halogene substituted carboxylic acids (a) comprising 2 to 7 carbon atoms. In case of using chloroacetic acid or its sodium salt R^16a is a methylene group - CH2-, in case of using co-chloro propionic acid or its salt, R^16a is a 1 ,2-ethylene group -CH2-CH2- , in case of using α-chloro propionic acid or its salt, R^16a is a -CH(CH3)- group. Groups R^5a may also be obtained by using alpha, beta-unsaturated carboxylic acids (b) as reagents. 1 ,2- ethylene groups -CH2-CH2- may be obtained by using acrylic acid or its salts, 1 ,2 propylene groups -CH2-CH(CH3)- may be obtained by using methacrylic acid or its salts. In a preferred embodiment of the invention, R^16a is a methylene group -CH2-. It goes without saying that also the carboxylation is a statistical process. Therefore, the number of carboxylic groups q does not necessarily need to be an integer but may be a rationale number.

Alkyl and/or alkenyl polyglycoside carboxylates comprising groups -R^16b-COOX may be obtained by using cyclic dicarboxylic acid anhydrides. In course of reacting with the OH-groups of the alkyl and/or alkenyl poly glycoside the anhydride cycle is opened. When succinic acid anhydride is used as reagent alkyl and/or alkenyl polyglycosides are formed which comprise -O- C(0)-CH₂-CH₂-COOX moieties, i.e. R^16b is a -0-C(0)-CH₂-CH₂- group and consequently R¹⁷ is an ethylene group -CH₂-CH₂-. In a preferred embodiment of the invention, R¹⁶ is selected from groups R^16a, and even more preferred R^16a is a methylene group -CH₂-.

In a preferred embodiment the surfactants (F) have the general formula

R¹⁵0-[(G)p](-CH₂-COOX)_q (IXa),

wherein R¹⁵ is an an alkyl and/or alkenyl moiety having from 8 to 16 carbon atoms, preferably from 10 to 14 carbon atoms, G is a glucose unit, p is a number from 1 to 2, and q is a number from 1 to 2.

Surfactants (G)

Surfactants of the group (G) are alkyl sulfates of the general formula

R¹⁸OS0₃M (X).

In formula (X) R¹² is a linear or branched Ci₂- to Cie alkyl moiety, preferably a C and Ci₂- to Cu moiety and M is H⁺ or a metal cation, preferably a metal cation selected from the group of alkali metal ions or earth alkali metal ions, preferably a cation selected from the group of Li⁺, Na⁺, or K⁺. Surfactant Formulation

For the use of foams according to the present invention a suitable aqueous formulation comprising at least one of the surfactants (A) to (F) is used. Of course a mixture of two or more surfactants (A) to (F) may be used and the formulation may comprise further surfactants different form the surfactants (A) to (F).

Examples of further surfactants comprise petroleum sulfonates and a-olefine sulfonates.

Besides water the aqueous formulation may also comprise organic solvents miscible with water. Examples of such solvents comprise alcohols such as ethanol, n-propanol, i-propanol, butylmo- noglycol, butyldiglycol, or butyltrigylycol. If organic solvents are present at all their amount should not exceed 25 % by weight with respect to all solvents present in the formulation, preferably it should not exceed 10 % by weight. In a preferred embodiment of the invention only water is used as solvent.

The water used may be saline water comprising dissolved salts. Examples of salts comprise halogenides, in particular chlorides, sulfates, borates of mono- or divalent cations such as Li⁺, The salinity of the water may be from 1 ,000 ppm to 230,000

The concentration of all surfactants together may be from 0.05 % to 5 % by weight with respect to the total of all constituents of the aqueous formulation, preferably from 0.1 % to 1 % by weight and very preferably from 0.1 % to 0.5 % by weight. The amount of surfactants (A) to (F) should be at least 50 % by weight with respect to the total amount of surfactants used, preferably at least 75% by weight, more preferably at least 90 % by weight. In one embodiment of the invention only surfactants selected from surfactants (A) to (F) are used.

Besides the surfactants, the aqueous formulation may additionally comprise further components. Examples of such further components comprise chelating agents or stabilizers.

In one embodiment of the invention, the surfactant formulation comprises at least one surfactant (A).

In one embodiment of the invention, the surfactant formulation comprises at least one surfactant

(B) . In one embodiment of the invention, the surfactant formulation comprises at least one surfactant

(C) .

(D) .

(E) .

In one embodiment of the invention, the surfactant formulation comprises at least one surfactant (F).

In one embodiment of the invention, the surfactant formulation comprises at least one surfactant (G). Use of foam for oil and/or gas production

According to the present invention a foam of the aqueous formulation comprising at least one surfactant, and at least one gas is generated and used in the production of oil and/or gas. The term "production" of oil and/or gas includes all techniques in order to stimulate, to maintain and/or to improve oil and/or gas production from subterranean formations. Foams may for instance be used in Enhanced Oil Recovery (EOR), acid diversion in matrix acid well stimulation, and environmental remediation. Improved Oil Recovery operations include for instance the use of foams as stimulant to increase gas production, to reduce water cut, to reduce the gas mobility or for gas shut off using foams. Enhanced Oil Recovery (EOR) includes technologies such as the use of foams as stimulant to increase gas production, the use of foams to reduce water cut, the use of foams to reduce gas mobility or gas shut-off using foam.

For the generation of foams according to the aqueous formulation the abovementioned aqueous surfactant formulation and at least one gas is used.

A gas shall be any compound which at is in the gaseous state at 295 K and 1 bar. Examples of suitable gases may be selected from the group of carbon dioxide, nitrogen, air, hydrocarbons such as methane, ethane, propane, or butane, hydrogen sulfide, flue or exhaust gas, or stream. Of course a mixture of two or more gases may be used. Preferably, the gas is at least one gas selected from the group of carbon dioxide, nitrogen, air, and methane, more preferably carbon dioxide and/or nitrogen. Most preferably, the gas is nitrogen.

The pressure of the gases for injection is selected by the skilled artisan according to his/her needs and is > 1 bar. It goes without saying that applying pressures > 1 bar to gases may cause the conversion of the gas to a liquid or a supercritical fluid. The term gas shall encompass also such fluids which are obtained

In one embodiment of the invention the foam is generated at the surface and injected into the subterranean formation through at least one injection well.

In another embodiment of the invention the aqueous formulation and the gas(es) are separately injected into the subterranean formation through at least one injection well and foam is in-situ generated subsurface in the injection well and/or in the formation. One embodiment of generating the foam in-situ within the reservoir comprises injecting the aqueous formulation simultaneously with the gas or ahead of injecting the gas. Gas may also be injected before and after injecting the aqueous fluid. Of course other techniques may be chosen, for instance an alternating injection of aqueous formulation and of gas.

In one embodiment of the invention, the foams generated according to this invention are used for Enhanced Oil Recovery (EOR). For EOR, at the subterranean formation is penetrated by at least one injection well and by at least on production well. Of course more than one injection well and more than one production well may be present.

In this embodiment a pre-formed foam or at least one gas, preferably carbon dioxide and/or nitrogen, more preferably nitrogen and the aqueous formulation as described above are injected into at least one injection well and crude oil is recovered through at least one production well. The term "crude oil" of course not only means pure oil but includes usual mixtures comprising oil and formation water. In one embodiment, the process of enhanced oil recovery may comprise the following steps:

Step 1 ) A gas or a mixture of gases is introduced into the formation at least one injection well and crude oil is produced through at least one production well. As the injection of the gas is con- tinued, the gas flows through the regions of least flow resistance, contacting the oil and displacing it. Thus, oil recovery is achieved within the shortest period.

Step 2) When the produced gas /oil ratio approaches levels that are too high for the process to be economical, an aqueous surfactant formulation comprising at least one surfactants selected from the group of surfactants (A) to (G) as described above is injected. This slug will again preferentially flow through those regions of the reservoir where resistance of flow is least, where most of the oil was recovered as in step 1.

Step 3) Injection of the gas is resumed. Initially, the gas will flow through those portions of the reservoir where resistance to flow is least, or regions of high permeability. There the gas will disperse throughout the aqueous formulation and generate foam. As more foam is generated, the resistance to flow increases in these regions of high permeability. Consequently, the gas is forced to flow through regions of lower permeability and displace additional quantities of oil. Step 4) Steps two and three may be repeated as frequently as deemed necessary, until the economics of the process become unfavorable.

In another embodiment of the invention, the foams generated according to this invention are used for fracturing.

A typical foam fracturing fluid may contain in addition one or more of the following additives selected from the group of gelling agents, breakers, flow back aid surfactants, foam stabilizer, proppant and other additives such as corrosion inhibitors, wettability changing agents, or bio- cides. Preferably, at least one proppant is used.

For foam fracturing a foam is injected into the formation through at least one wellbore at a pressures sufficient to cause fissures in the formation. The proppant is transported by the foam into the fissures thus created and keeps the fissure open after the pressure is released. Foams in the range of 65% to 80% quality are typically used in foam fracturing. So proppant is easily transported by the foam and then supported once the fracture has been created. As a result the proppant is more uniformly distributed within the fracture rather than simply allowed to settle to the bottom of the fracture. Foam has shown to have excellent fluid loss properties for low permeability formation.

Formation clays which are water sensitive can either expand to reduce permeability or migrate to block flow channels upon contact with water. Foam helps minimize water damage to the for- mation because of the overall low water content of the fluid. Additional clay protection can be achieved by the use of inorganic salts and polymeric clay stabilizers.

A major advantage of a foam fracturing fluid is its fluid recovery efficiency. When pressure is released at the wellhead, the low hydrostatic head in the wellbore presents lower resistance to production of the foam frac fluid than for a gelled water fluid. The compressible nature of foam also helps bring the liquid back due to expansion of the gas in its return to the wellbore. This gas expansion is most beneficial to wells with low formation pressure. The clean up of a foam fracturing treatment is usually accomplished within two days, whereas, a gelled water fracturing treatment may require several days.

In another embodiment of the invention, the foams generated according to this invention are used to increase gas production in gas-lift processes. In gas-lift processes water in the production wellbore is foamed thus diminishing the hydrostatic pressure of water in the wellbore which makes it easier for gas to flow from the formation to the surface.

In another embodiment of the invention, the foam is used for foam drilling.

In another embodiment of the invention, the foams generated according to this invention are used for conformance control.

In one embodiment of conformance control foams are used to reduce water cut. For this purpose foams are injected into a wellbore. Because their viscosity is significantly higher than that of water they preferably flow into the regions of the formation having a higher permeability and can at least partly plug such regions. When after such a treatment the injection of water is continued, water is forced to flow also into the regions having less permeability.

In another embodiment of conformance the foams are used to reduce gas mobility or for gas shut-off. Also for this purpose foams are injected into a wellbore. Because their viscosity is sig- nificantly higher than that of gas they preferably flow into the regions of the formation having a higher permeability and can at least partly plug such regions. When after such a treatment the injection of gas is continued, gas is forced to flow also into the regions having less permeability.

The invention is illustrated in detail by the examples which follow.

The following surfactants S1 to S14 were evaluated with respect to their performance for stabilizing foams for oilfield applications. Surfactants S1 to S8 are according to the invention:

No. Description type Formula

S1 Coco betaine (A) R-N⁺(CH₃)2-CH₂-COO-

S2 Lauramin oxide (B)

S3 Amphoteric coconut fatty (C) CH₂-CH₂-COONa acid amide R-CO-NH-CH₂-CH₂ ^{1 λ}

^CH₂-CH₂-OCH₂-COONa

S4 Na coco amphoacetate (C) CH₂-CH₂-OH

R-co—

^CH₂-CH₂-NH-CH₂-COONa

S5 Na-N-lauryl-β- (C)

iminodipropionate

S6 Sodium lauryl ether sulfate (D) Ci2H₂5-0-(EO)2-OS0₃Na

S7 Ce/14 alkyl poly glucoside (E)

S8 Ci2 alkyl poly glucoside, (F)

carboxylated

Surfactants S9 to S14 are for comparative purposes:

S9 Polyethyoxyalkylalkoxylate, based iCi3-(EO)i₂OH

on Ci3 oxo alcohol

S10 Alkyletherphosphate C₈/io-(EO)x-OP(0)(ONa)₂

S1 1 Cocoamidopropylbetaine C H₃

RCONH-CH₂-CH₂-CH₂— N- CH₂-COO^"

C H₃

S12 Coconut fatty acid monoethanol R-CO-NH-CH2CH2OH

amide

S13 Fatty acid diethanol amide R-CO-N-(CH₂CH₂OH)₂ S14 Fatty acid ester of saccharose

alkoyxlated with 20 EO units

S15 Alkylalkoxysulfate based on C12/14 Ci2/i4-(EO)i₂OS0₃Na

fatty alcohols

Fatty acids derived from coconut oil comprise dodecanoic acid (~ 45 to 53 % by wt.) and tetra- decanoic acid (~ 17 to 21 % by wt.) as main components. Further components comprise octanoic acid (~ 5 to 10 % by wt.), decanoic acid (~ 5 to 8) % by wt., hexadecanoic acid (~ 7 to 10 % by wt.) and oleic acid (~ 5 to 10 % by wt.).

Test 1 : Static foam test / Foamability with air

In the static foam test a mixer with a whisk was used to disperse air into the test solution at am- bient conditions.

Tests were performed in 1000 ml glass cylinders (height: 44 cm, diameter: 6 cm). 300 ml of an aqueous solution with the surfactant / surfactant mixtures were filled into the cylinder. The solution was stirred with a rod stirrer for 5 minutes at 2000 rpm, thereby creating foam of air, water and the surfactant(s). After stirring, the glass cylinder was sealed with a plastic film at the top. The foam height was examined directly after mixing and at different times after mixing.

The term "foamability" refers to the ability of the surfactant system to form foam, and is measured as maximum foam height after mixing. The term "stability" is understood as a parameter describing variation in foam height with time.

The following criteria have been used to rank the products based on foamability and stability:

Good foamability: foam height > 15 cm after mixing

Poor foamability: foam height < 15 cm after mixing

Good stability: foam height > 10 cm for more than 24 hours

Moderate stability: foam height < 10 cm after 24 hours

Poor stability: foam height < 5 cm after 5 hours For the tests synthetic seawater (SSW) having the following composition was used as solvent.

For all test, the total amount of surfactants was 1 wt. % with respect to all components of the aqueous formulation. All tests were performed at ambient temperatures (295 K). All surfactants S1 to S8 used according to the invention were tested and for comparative purposes also all comparative surfactants S9 to S14 were tested. The results are summarized in the Figures 2 to 5. The surfactants

51 (Coco betaine, class (A)),

52 (Lauramin oxide, class (B)),

53 (amphoteric coconut fatty acid amide, class (C),

56 (sodium lauryl ether sulfate, class (D)) and

S8 (Ci2 alkyl poly glucoside, carboxylated, class (F))

show both, a good foamability and a good foam stability, the best ones are surfactants S6 and S1 (see figure 2).

The surfactants

S4 (Na coco amphoacetate, class (C))

S5 (Na-N-lauryl-p-iminodipropionate , class (C)) and

57 (Ce/14 alkyl polyglucoside, class (E))

show a good foamability and a moderate foam stability. Surfactant S7 is the best of them and close to good stability (see figure 3).

The comparative surfactants S9, S10, S1 1 , and S15 show a good foamability, however only a poor foam stability (see figures 4a, 4b).

The comparative surfactants S12, S13, and S14 show a poor foamability as well as a poor foam stability (see figure 5).

Test 2: Foamability with N2 under pressure - Filter test

The filter method was used in order to investigate the effect of higher pressure (2 bar) and am- bient temperature on foamability and stability of the surfactant/surfactant formulations.

The apparatus used is schematically represented in Figure 1 . The apparatus permits not only to make measurements under pressure which represents a more realistic picture of using foams for the production of oil and/or gas but also permits to measure the amount of nitrogen neces- sary to obtain a certain amount of foam, i.e. a more quantitative measure of foamability.

A closed column with a porous filter located at the bottom were used to study surfactants to IM2- foam at 2 bar, 22°C . The filter element was obtained from Swagelok (length: 2.0 cm, diameter: 1 .2 cm, pore sizes: 7 μηη). The way the filter was placed in the column ensured that the gas had free supply of surfactant solution throughout generation. All experiments followed the same procedure:

(1 ) System pressure testing with IS -gas at 3.5 bar.

(2) Prior to generation - injection of test solution (150 ml) into the column filled with IS -gas at 2 bar.

(3) Foam generation at 2 bar - injection of IS -gas (5 ml/min) through the filter and into the test solution.

(4) Foamability was measured as gas volume needed to reach 10 cm foam height in the column.

(5) After foam generation the system was shut-in.

(6) Foam stability was measured as foam height versus time (24 hours).

(7) After each experiment the column was cleaned and a new filter (7 μηη) was replaced.

Repeatability of foamability using the filter method was within ± 20 ml of gas phase injected and foam stability within ± 0.5 cm. The surfactants were used at a concentration of 1 % wt. with respect to the aqueous formulation. For the tests synthetic seawater (SSW, composition see above) and severa NaCI-solutions having a concentration from 50000 ppm to 250000 ppm have been used.

All products tested have been evaluated based on their foamability and stability performances at 2 bar, 22°C. The term foamability refers to the ability of the surfactant system to produce foam at the experimental method and conditions given. Foamability in the filter method was measured as the IS -gas volume needed to be injected into the column in order to generate 10 cm foam height. Foam stability is understood as a parameter describing variation in foam height with time after the system was shut-in.

Following criteria have been used to rank the products based on their foamability and stability in the filter method:

Good foamability: < 400 ml of IS -gas injected to reach 10 cm foam height

Poor foamability: > 400 ml of IS -gas injected to reach 10 cm foam height

Good stability: foam height > 8 cm for more than 24 hours

Moderate stability: foam height > 5 cm after 24 hours

The results are represented in figures 6 to 1 1.

Figure 6 represents the foamability of surfactants S1 , S3, S6, and S8 in SSW and figure 7 represents the stability of the foams. All surfactants

S1 (Coco betaine, class (A)),

S3 (amphoteric coconut fatty acid amide, class (C),

S6 (sodium lauryl ether sulfate, class (D)) and

S8 (Ci2 alkyl poly glucoside, carboxylated, class (F))

show a good foamability, i.e. less than 400 ml of N2 is needed to obtain foam height of 10 cm (see figure 6).

Also the stability of the foams is good for all surfactants tested (see figure 7). The best one is surfactant S8 (C12 alkyl poly glucoside, carboxylated, class (F)) which shows no decrease in the foam height for a period of 25 hours.

Figure 8 represents the foamability of surfactant Figure 8 represents the foamability of surfactants S8 in SSW and several NaCI solution having a concentration from 50000 ppm to 250000 ppm and figure 8 represents the stability of the foams, and figure 9 represents the respective foam stability.

S8 in SSW and several NaCI solution having a concentration from 50000 ppm to 250000 ppm and figure 9 represents the respective foam stability.

Surfactant S8 was soluble in the NaCI solutions up to a concentration of 250000 ppm. At a NaCI concentration of 300000 ppm it was no longer possible to dissolve 1 % of surfactant S8.

The following table and also figure 7 shows that the foamability does not strongly depend on the salinity of the aqueous formulation. At all concentrations up to 250000 ppm a good foamability has been observed. Also the stability of the foam does not significantly depend on the salinity (see table and figure 9).

Figure 10 represents the foamability of surfactant S6 in SSW and NaCI solutions of 30000 ppm and of 60000 ppm and figure 1 1 represents the respective foam stability. Also with surfactant S6 no strong dependence of foamability and foam stability from the salinity is observed.

Claims

1 . Use of foams generated from an aqueous fluid, at least one gas and at least one surfactant in the production of oil and/or gas from subterranean formations penetrated by at least one injection well by providing an aqueous formulation comprising 0.05 % to 5 % by weight of at least one surfactant capable of stabilizing foams and generating a foam of the aqueous formulation comprising surfactants and the gases wherein

• the foam is generated at the surface and injected into the subterranean formation through at least one injection well, or

· the aqueous formulation and at least one gas injected successively, alternate or together into the subterranean formation through at least one injection well and foam is in-situ generated subsurface in the injection well and/or in the formation, wherein at least one of the surfactants used is selected from the group of the surfactants (A) to (G) having the following structures:

(A) Alkyl betains of the general formula

R -N⁺(R2)₂-CH₂COO- (I), wherein,

• R¹ is an alkyl and/or alkenyl moiety having from 8 to 24 carbon atoms,

• R² independently are selected from Ci- to C₄ alkyl,

(B) Alkyl N-oxides of the general formula

R³-N⁺(R⁴)₂-0- (II),

wherein

• R³ is an alkyl and/or alkenyl moiety having from 8 to 24 carbon atoms,

• R⁴ independently are selected from Ci- to C₄ alkyl,

(C) Amphoteric surfactants having the general formula

R⁵-N(R⁶)(R⁷) (III)

wherein

• R⁵ is a group selected from the group of

> R^5a: alkyl and/or alkenyl groups having from 8 to 24 carbon atoms,

> R^5c: a group R⁸CO-NH-R⁹-, wherein R⁸ has the meaning as defined

above and R⁹ is an alkylene group having 1 to 4 carbon atoms,

• R⁶ and R⁷ are selected independently from the group of

> co-hydroxyalkyl groups (R^6b, R^7b) of the general formula -(CH₂)n-OH (V), wherein n is a number from 1 to 10

> groups (R^6c, R^7c) of the general formula -(CH₂CH₂-R¹⁰)m-R¹¹-COOM (VI), wherein M is H⁺ or a cation, m is a number from 1 to 10, R¹⁰ is selected from -O- and -NH- and R¹¹ is an alkylene group having 1 to 4 carbon atoms,

(D) Anionically modified alkyl ethers of the general formula

R¹²0-(CH₂CH₂0)n-XM (VII),

wherein

• R¹² is a linear or branched Ci₂- to Cie alkyl moiety,

• n is a rational number from 1 to 5,

• X- is an anionic group selected from the group of -S03^", -R¹³-S03^", or

-R ³-COO-,

• R¹³ is an alkylene group having from 1 to 10 carbon atoms, and

• M is H⁺ or a metal cation,

(E) Alkyl or alkenyl polyglucosides of the general formula

R¹⁵0[G]_P (VIII),

wherein

• R¹⁵ is an alkyl or alkenyl radical having from 8 to 22 carbon atoms,

• G is a sugar unit having 5 or 6 carbon atoms, and

• p is a number from 1 to 10,

(F) Modified alkyl or alkenyl polyglucosides of the general formula

R¹⁵-0-[(G)p](-R¹⁶-COOM)_q (IX)

wherein

• R¹⁵, G and p have the same meaning as mentioned above,

• R¹⁶ is a divalent linking group selected from the group of

> R^16a : divalent hydrocarbon groups comprising 1 to 6 carbon atoms,

• q is a number from 1 to 4,

• M is H⁺ or a metal cation, and

Alkyl sulfates of the general formula

R¹⁸OS0₃M (X) wherein

• R¹⁸ is a linear or branched Ci2to Cie alkyl moiety, and

• M is H⁺ or a metal cation.

2. Use according to claim 1 , wherein the gas is selected from the group of carbon dioxide, nitrogen and methane.

3. Use according to claim 1 , wherein the gas is nitrogen.

4. Use according to any of claims 1 to 3, wherein the surfactants (C) have the general formula R^5a-N(-(CH₂)n-COOM)₂ (Ilia).

5. Use according to any of claims 1 to 3, wherein the surfactants (C) have the general formula R⁸CO-(-(CH₂)_n-OH)( -(CH₂CH₂-R¹⁰)m-R¹¹-COOM) (1Mb).

6. Use according to any of claims 1 to 3, wherein the surfactants (C) have the general formula R⁸CO-NH-R⁹-N(-(CH₂)_n-COOM) -(CH₂CH₂-R ⁰)_m-R -COOM) (lllc).

7. Use according to any of claims 1 to 3, wherein the surfactants (D) have the general formula R¹²0-(CH₂CH₂0)_nS0₃M (Vila), wherein R¹² is a linear or branched Ci₂ to Ci₈ alkyl moiety, and n is from 1 to 3.

8. Use according to any of claims 1 to 3, wherein the surfactants (F) have the general formula R¹⁵0-[(G)p](-CH₂-COOX)_q (IXa), wherein R¹⁵ is an alkyl and/or alkenyl moiety having from 8 to 16 carbon atoms, G is a glucose unit, p is a number from 1 to 2, and q is a number from

1 to 2.

9. Use according to any of claims 1 to 3, wherein the surfactants comprise at least one surfac- tant (F).

10. Use according to any of claims 1 to 9, wherein the foam is used for enhanced oil recovery.

1 1 . Use according to claim 10, wherein the process of enhanced oil recovery comprises at least the following steps:

(1 ) Injecting at least one gas into the formation through at least one injection well and recovering oil through at least one production well,

(2) Injecting the aqueous surfactant solution comprising at least one surfactant selected from surfactants (A) to (G),

(3) resuming the injection of at least one gas.

12. Use according to claim 1 1 , wherein after step (3) steps (2) and (3) are repeated at least once.

13. Use according to any of claims 1 to 9, wherein the foam is used for fracturing by injecting the foam through at least one well into the subterranean formation at a pressure sufficient to create fissures in the formation.

14. Use according to any of claims 1 to 9, wherein the foam is used for foam drilling.

15. Use according to any of claims 1 to 9, wherein the foam is used for conformance control.