WO2015135708A1

WO2015135708A1 - Method for co2-flooding using alk(en)yl polyethersulfonates

Info

Publication number: WO2015135708A1
Application number: PCT/EP2015/052711
Authority: WO
Inventors: Christian Bittner; Günter OETTER; Benjamin Wenzke; Sebastian Alexander WEISSE
Original assignee: Basf Se
Priority date: 2014-03-12
Filing date: 2015-02-10
Publication date: 2015-09-17
Also published as: AR100669A1

Abstract

The invention relates to a method for extracting crude oil by means of CO₂-flooding, in which a liquid or supercritical CO₂ and at least one alk(en)yl polyethersulfonate is injected through at least one injection bore into an oil reservoir and the crude oil is extracted from the oil reservoir by means of at least one production bore. The alk(en)yl polyethersulfonate is preferably dissolved in the CO₂-phase. The invention also relates to a method for extracting crude oil by means of CO₂-flooding in which mixtures of the alk(en)yl polyethersulfonates are used with alk(en)yl polyalkoxylates and/or alkyl phenol polyalkoxylates.

Description

C02 flooding process using alk (en) yl polyether sulfonates

The invention relates to a method for producing crude oil by means of C02 flooding, in which liquid or supercritical CO2 and at least one alk (en) ylpolyethersulfonate are injected through at least one injection well into an oil reservoir and the crude oil is removed from the deposit by at least one production well. The alk (en) yl polyether sulfonate is preferably dissolved in the CO 2 phase. The invention furthermore relates to a process for crude oil production by means of CO 2 flooding, in which mixtures of the alk (en) ylpolyethersulfonates with alk (en) ylpolyalkoxylates and / or alkylphenolpolyalkoxylates are used.

In natural oil deposits, petroleum is present in the cavities of porous reservoirs, which are closed to the earth's surface by impermeable cover layers. The cavities may be very fine cavities, capillaries, pores or the like. Fine pore necks, for example, have a diameter of only about 1 μηη. In addition to crude oil, including natural gas, a deposit usually contains more or less saline water. After tapping a petroleum deposit, oil may first flow to the surface by itself through the borehole due to the inherent pressure of the reservoir. The autogenous pressure can be caused by gases present in the deposit such as methane, ethane or propane. This type of promotion is usually referred to as primary oil production. Depending on the type of deposit, however, only 5 to 10% of the oil in the deposit can be pumped by means of primary production, after which the autogenous pressure is no longer sufficient for production. There are also deposits where the autogenous pressure from the beginning is not sufficient for primary production. In order to promote more oil from a deposit, measures of secondary and / or tertiary oil production are used.

In the case of secondary production, in addition to the wells that serve to extract the oil, the so-called production wells, further drillings are drilled into the oil-bearing formation. Through these so-called injection wells water is injected into the reservoir to maintain or increase the pressure. By injecting the water, the oil is slowly forced through the cavities into the formation, starting from the injection well, toward the production well. But this works only as long as the cavities are completely filled with oil and the viscous oil is pushed through the water in front of him. As soon as the thin liquid water passes through cavities breaks, it flows from this time on the path of the least resistance, ie through the channel formed, and no longer pushes the oil in front of him. By means of primary and secondary production, as a rule only about 30-35% of the quantity of crude oil in the deposit can be extracted.

An overview of tertiary oil production can be found, for example, in the "Journal of Petroleum Science of Engineering 19 (1998)", pages 265 to 280. Tertiary oil extraction includes heat processes in which hot water or superheated steam is injected into the reservoir, thereby increasing the viscosity of the oil Tertiary oil extraction also includes processes involving the use of suitable chemicals, such as surfactants or thickening polymers, as an aid to oil production, which can be used to influence the situation towards the end of the flood and thereby promote the capture of crude oil previously held in the rock formation. Furthermore, techniques are known to inject gases such as CO2, N2 or CH ₄ in the formation to increase the oil production.

In so-called C02 flooding, liquid or supercritical CO2 is injected through one or more injection wells into a petroleum formation, flows from there to production wells, and mobilizes existing oil in the formation. The production wells are extracted from mobilized petroleum. This technology is also known as "CO2 enhanced oil recovery (EOR)" or "CO2 improved oil recovery (IOR)" and has great economic importance: Currently, more than 5% of US crude oil production is produced by C02 floods (RM Enick, DK Olsen, "Mobility and Conformance Control for Carbon Dioxide Enhanced Oil Recovery (CO2-EOR) via Thickeners, Foams, Gels - A Detailed Literature Review of 40 Years of Research", page 910, SPE 154122, 18 ^th SPE Improved Oil Recovery Symposium , Tulsa, Oklahoma, USA, April 14-18, 2012, Society of Petroleum Engineers, 2012) Several mechanisms account for the increased production of oil by pumping liquid or supercritical CO2 into a deposit: CO2 is soluble in and lowers petroleum Viscosity It goes without saying that lower viscous oil can be pumped better than highly viscous oil, and the CO2 dissolved in the oil will continue to swell the oil and make it easier to form a related oil bank. Another delivery mechanism may be the dissolution of preferably light levels of crude oil into the C02 phase rather than a type of extraction. Another aspect is the low interfacial tension between crude oil and liquid or supercritical CO2, which helps to overcome capillary forces: an oil drop can more easily deform in a C02 phase and pass through narrow pore necks than it could in a water phase. When pumping CO2 into a reservoir, pressure and temperature determine its physical state. The critical point of CO2 is 30.98 ° C and 73.75 bar. Above these values, CO2 is supercritical, ie it is almost as dense as a liquid but still has a very low viscosity similar to that of a gas. The viscosity of supercritical CO2 is typically several orders of magnitude lower than that of the oil in the reservoir.

The low viscosity of supercritical CO2 is one of the key problems of C02 flooding, making mobility mobility of CO2 in the reservoir much more difficult. To achieve a good de-oiling effect, the CO2 should flow in a uniform front from the injection well towards the production wellbore, flowing through all (still) oil filled areas of the formation. However, this is rarely the case in practice. On the one hand, the porosity of an underground oil deposit is generally not homogeneous, and in addition to fine-pored areas, an underground petroleum formation may also have areas of high porosity, cracks or fractures. Furthermore, even with the same porosity, the flow resistance for CO2 still filled with oil areas of the formation is significantly greater than the flow resistance of already de-oiled areas. Thus, there is a risk that the injected CO2 does not flow through oil-filled areas of the formation at all, but flows largely ineffectively through regions of low flow resistance directly from the injection to the production well. This effect is also called "fingering" and is shown schematically in Figure 1. The "breakthrough" of CO2 to the production well reduces the efficiency of C02 flooding significantly, because a more or less large part of the injected CO2 flows through the formation largely without Effect. Either you need more CO2 now or the pumped CO2 has to be separated, cleaned and recompressed after it has been extracted from oil or formation water so that it can be re-injected.

On the other hand, the density of liquid or supercritical CO 2 is significantly lower than the density of crude oil and formation water. Due to the buoyancy, therefore, CO2 preferably collects in the upper layers of the formation or preferably flows through the upper layers. The de-oiling is thus preferably carried out in the upper layers of the formation, while deeper layers are not detected by the CO2.

Various approaches have been proposed in the art to achieve CO2 flow through oil reservoirs more uniformly, both horizontally and vertically. For example, it has been proposed to alternately inject water and CO2 into the petroleum formation. The so-called "Water Alternating Gas" process (described by DW Green and GP Willhite in "Enhanced Oil Recovery" SPE Textbook Series Vol. 6 of 1998) is an established process for CO2 flooding.

It has also been proposed to thicken the injected CO2 to adjust the viscosity of the CO2 to the viscosity of the petroleum. For example, US Pat. No. 4,852,651 proposes the addition of certain polysilicon. Huang et al., Macromolecules, 2000, Vol. 33 (15), pages 5437 to 5442, suggest the use of styrene-fluoroacrylate copolymers. However, the moderate solubility of many polymers in CO2 and the high addition of another solvent make the process seem not economical.

In another known technique suitable surfactants are used to form CC n-water emulsions or CC n-water foams in the deposit of CO 2 and formation water and / or injected water. In CC n-water emulsions, the CO2 is in a discontinuous phase, while water forms the continuous phase. Such emulsions have a significantly higher viscosity than supercritical or liquid CO2 and thus no longer follow only the paths of least flow resistance, but flow much more uniformly through the formation. Mobility control by formation of C02-in-water emulsions allows for increased exploitation of the deposit through macroscopic displacement (mobility control) and microscopic displacement (interfacial tension)

The requirements for surfactants for CO 2 flooding are clearly different from requirements for surfactants for other applications, for example detergent applications; however, they also differ, in particular, from the requirements for surfactants for surfactant flooding, i. an EOR technique that injects aqueous solutions of surfactants but no CO2 into the deposit.

The primary role of surfactants in surfactant flooding is to reduce the interfacial tension between water and petroleum. Thus, petroleum droplets trapped in the formation are mobilized.

The primary role of surfactants in C02 flooding to form C02-in-water emulsions, however, is to stabilize the C02-water interfaces to generate long-term stable CC n-water emulsions in the deposit. The hydrophobic radicals of the surfactants protrude into the liquid or supercritical CO 2 phase and must therefore have good interaction with the CO 2 in order to ensure good stabilization of the CO 2 -water interface. Furthermore, the formation of CC n-water emulsions at the usual reservoir temperatures (typically about 15 ° C to 130 ° C) and in the presence of highly saline water, especially in the presence of high levels of calcium and / or magnesium ions guaranteed be. If the highly viscous CC n-water emulsion collapses, the low-viscosity supercritical CO 2, as described above, preferably follows the paths of lowest flow resistance and / or accumulates in the upper regions of the formation.

In addition, suitable surfactants must also be sufficiently soluble and sufficiently stable in reservoir water and / or injected water. The water is acidic due to dissolved CO2 (pH values of approx. 3). Suitable surfactants must therefore be soluble in an acidic environment and have sufficient long-term stability against hydrolysis. For surfactant flooding popular surfactants such as alkyl sulfates or alkyl ether sulfates are therefore less suitable for CO 2 flooding, since they are less soluble on the one hand by protonation and the sulfate group can be split off hydrolytically under the conditions mentioned. Amide group-containing compounds also tend to hydrolyze under the conditions mentioned.

Finally, the adsorption tendency of the surfactants on the rock should be as low as possible in order to minimize the loss of surfactant.

The prior art has already proposed a large number of surfactants for various techniques of CO 2 flooding. US 3,342,256 describes the improvement of oil production with the aid of CO2 and a surfactant for mobility control. The surfactant may optionally be injected via the CO2 phase or via the water phase. Suitable surfactants include octylphenol ethoxylates, dioctylsulfosuccinate sodium salt, laurylsulfate sodium salt or isopropylnaphthalenesulfonate sodium salt.

US Pat. No. 4,113,011 1 describes a process for oil extraction with injection of CO2 and an aqueous surfactant solution. The surfactant disclosed is an alkyl ether sulfate of the RO-EO sulfate type, which is composed of an alcohol having 9 to 11 carbon atoms and 1 to 5 EO units. Reference is made to a higher salt tolerance compared to the use of alkyl sulfates. However, sulfates are not sufficiently stable in the long term to hydrolysis under the conditions of CO 2 flooding.

No. 4,380,266 describes a process for the extraction of crude oil by injection of a mixture of CO 2 and EO-PO block polymers or alkyl ethoxylates or alkylphenol ethoxylates or alkyl alkoxylates, the conditions being selected so that the CO 2 is liquid under the reservoir conditions. As an example, Polytergent ^® Called SL-62. This is a linear alcohol of 6 to 10 carbon atoms, which is propoxylated and ethoxylated.

US 4,637,466 describes the use of alkyl ether carboxylates of the type RO- (AO) x R'COOM for CO 2 flooding, wherein R is a linear or branched alkyl radical having 8 to 24 carbon atoms, AO ethylene oxide or propylene oxide, R 'is a methylene or ethylene radical and x is a number from 3 to 1 1 stands.

US 5,033,547 discloses a process for oil recovery by injecting a mixture of CO 2 and a surfactant into a petroleum formation, forming an emulsion of CO 2, water and the surfactant in the formation together with formation water. The surfactants are alkyl ethoxylates or alkylphenol ethoxylates which have a hydrophobic group having 7 to 15 carbon atoms and a degree of ethoxylation of 4 to 8.

DE 30 454 26 A1 discloses the improvement of oil production by the injection of gaseous CO2 and surfactant to form a foam. As surfactants, alkylphenol alkoxylates, sodium dodecylsulfonate, sodium polyglycol ether sulfonate and polypropylene oxide ethylene oxide polymers are proposed, inter alia.

US 5,046,560 discloses a method for oil production with injection of a gas selected from the group of hydrocarbons, inert gases, steam or carbon dioxide and an aqueous Alkylarylpolyalkoxysulfonat solution. The sulfonate group is located on the aryl radical.

DE 32 086 62 A1 discloses a process for oil extraction by injection of a formulation comprising water, CO2 and nonionic surfactants. As examples of surfactants, alcohol ethoxylates based on octylphenol, nonylphenol or C 12 -C 15 -alcohol are mentioned.

US Pat. No. 7,842,650 describes a process for producing crude oil, which comprises producing foams from liquids using a surfactant mixture from a foaming agent (a) selected from the group of sulfates, sulfonates, phosphates, carboxylates, sulfosuccinates, betaines, quaternary ammonium salts, amine oxides, amines - Nethoxylaten, amide ethoxylates, acid ethoxylates, alkyl glucosides, EO-PO block copolymers and long-chain fatty alcohol ethoxylates and a cosurfactant (b) of the general formula RO- (AO) _y -H or RO- (AO) _y -Z, where R is a hydrocarbon radical with 6 to 12 carbon atoms, (AO) _{y is} an alkyleneoxy block, y is a number from 5 to 25 and Z is an anionic group, eg sulfate, phosphate or carboxylate. As an example of a formulation with increased foaming, the mixture of Cocoamidopropyl betaine with Cio-Guerbet alcohol - called 14 EO. The process is preferably a process of tertiary mineral oil extraction.

WO 2010/044818 A1 describes a process for producing oil by C0 ₂ fl ows by injecting a nonionic surfactant having a CO 2 Philicity of 1.5 to 5.0 into the formation, wherein the surfactant is to form a stable foam with formation water but not an emulsion with crude oil. The nonionic surfactant preferably has the formula RO- (AO) x- (EO) _y -H, where AO is an alkoxy group having 3 to 10 carbon atoms and EO is ethoxy groups, where R, AO, x and y are the following groups: Combinations can be selected:

R AO x y branched alkyl, alkylaryl or cycloalkyl C3 1, 5 - 1 1 6 - 25th

Rest with 3 to 1 1 carbon atoms C ₄ to C10 1 - 2 6 - 25 linear alkyl residue with 3 to 6 carbon atoms C3 4 - 1 1 6 - 25

Particularly preferred is the use of surfactants selected from the group of C ₈ Hi7- (PO) ₅ - (EO) ₉ -H, C ₈ Hi ₇ - (PO) ₅ - (EO) i iH, C ₈ Hi7- (PO ) 9- (EO) ₉ -H,

C ₆ Hi3- (PO) ₅ - (EO) i iH, C ₆ Hi3- (PO) ₅ - (EO) i3-H, C Hi ₉ ₉ - (PO) ₄ - (EO) ₈ -H or mixtures thereof ,

US 4,502,538 discloses a process in which liquefied CO2, an aqueous medium and a surfactant are injected into an underground formation containing oil and water. The surfactant may be an alkylpolyalkoxysulfonate which has, as the hydrophobic part, an aliphatic and / or aromatic hydrocarbon radical having 6 to 25 carbon atoms.

JK Borchardt, DB Bright, MK Dickson and SL Willington "Surfactants for C0 ₂ Fo on Flooding", SPE 14394, 60 ^th Annual Technical Conference and Exhibition of the Society of Petroleum Engineers, Las Vegas, NV, November 22 to 25, 1985 disclose studies of various surfactants, including surfactants R- (OCH2CH2) _n S03Na as well as R- (OCH2CH2) ₂ nOCH2CH2CH S03Na with regard to their behavior during C0 ₂ - foam flooding, wherein R is C9 to Cn alkyl groups or C 12 to C Cis-alkyl radicals.

WO 201 1/005246 A1 describes surfactants for crude oil production, which can be injected with C0 ₂ and water into a deposit. The nonionic surfactants are glycerin derivatives wherein two of the alcohol groups of the glycerol are capped with a hydrocarbon group which may include from 4 to 18 carbon atoms. The third alcohol group can be ethoxylated, propoxylated or butoxylated and have a degree of alkoxylation of 9-40. WO 201 1/152856 A1 discloses a method for oil production with the aid of supercritical CO2 and a surfactant which is injected into a CO 2 stream and dissolved in the CO 2. The reservoir is made up of reservoir water, surfactant and CO2 to form an emulsion. For example, nonionic surfactants (eg, alkylphenol ethoxylates), cationic surfactants (such as ethoxylated talc fatty amine), anionic surfactants (eg, alkyl ether sulfates), or betaine surfactants are used.

WO 2012/170835 A1 claims a process in which a nonionic surfactant formulation having a pour point of from -3 to -54 ° C. is used, dissolved in CO 2 and injected into the formation to form emulsions with water. To lower the pour point, alcohols such as methanol, ethanol, glycol or glycol ethers are proposed.

WO 2013/043838 A1 describes an oil production process with liquid or supercritical surfactant and an alkoxylated amine which is based on a secondary alkyl radical having 4 to 30 carbon atoms.

WO 2013/048860 A1 describes a process for crude oil production which claims the use of CO 2 and an alkyl alkoxylate which is based on a branched alkyl radical having 3 to 9 carbon atoms and the alkoxylation by means of double metal cyanide catalysis

Tertiary oil production by means of C02 flooding is a large-scale process. Although the surfactants are only used as dilute solutions in water or CO2, the volumes injected per day are high and the injection is typically continued for months to several years. The surfactant requirement for an average oil field can be about 2000 to 3000 t / a. Even a slightly better surfactant can significantly increase the efficiency of C02 flooding. As described above, the CO 2 flooding is said to form a viscous C02-in-water emulsion. In the C02-in-water emulsion, water forms the continuous phase and thus acts as a buffer between discrete CO 2 phases. If the CO 2 -in-water emulsion loses water, eventually it will cause the discrete CO 2 phases to unite, i. the C02-in-water emulsion breaks down. A breakdown of the emulsion in the petroleum formation is highly undesirable because it is precisely the higher viscosity of the emulsion compared to a pure C02 phase is required to avoid the "fingering".

The requirements for surfactants depend on the reservoir temperatures, in particular on the salinity of the reservoir water and the reservoir temperature. While many surfactants are found at low salinities and / or low Temperatures still yield satisfactory results, they do not provide good results at high temperatures and / or high salinities.

The object of the invention was to provide an improved process for CO 2 flooding, in particular for oil reservoirs with high salinity and / or high reservoir temperature. Even under such demanding conditions, stable CC n-water emulsions should be formed.

Accordingly, a process for the extraction of crude oil by means of C02 flooding was found, in which liquid or supercritical CO2 and at least one anionic surfactant (I) or a surfactant mixture comprising at least one anionic surfactant (I) are injected through at least one injection well into a crude oil deposit and the Deposits by at least one production well crude oil, characterized in that the at least one surfactant (I) or the at least one surfactant (I) comprising surfactant mixture is dissolved in liquid or supercritical CO2 and injected and / or dissolved in an aqueous medium and injected If the deposit has a deposit temperature of 15 ° C to 140 ° C, the deposit water has a salinity of 20,000 ppm to 350,000 ppm, the density of CO2 under deposit conditions is 0.70 g / mL to 0.90 g / mL, and the at least one anionic surfactant is an alk (en) ylpolyalkoxysulfonate of general formula

R - (OCR ² R ³ CR ⁴ R ⁵ ) i- (OCH ₂ CHR ⁶ ) _m - (OCH ₂ CH ₂ ) n -O-R ⁷ -SO 3 -V _a M ^{a +} (I) wherein

R ^{1 is} a branched or linear, saturated or unsaturated aliphatic hydrocarbon radical having 8 to 22 carbon atoms,

R ² , R ³ , R ⁴ , R ^{5 are} each H or a linear or branched alkyl radical having 1 to 8

Carbon atoms are available, with the proviso that the sum of the

Carbon atoms of the radicals R ² + R ³ + R ⁴ + R ^{5 is} 2 to 8,

R ⁶ for methyl,

R ^{7 is} an alkylene radical having 2 to 4 carbon atoms, which may optionally be substituted by an OH group,

I for a number from 0 to 5

m for a number from 0 to 15

n for a number from 5 to 30, and

M ^{a +} for an a-valent cation, where a is 1, 2, or 3, wherein the radicals -OCR ² R ³ CR ⁴ R ⁵ -, -OCH ₂ CHR ⁶ - and -OCH ₂ CH ₂ - are arranged blockwise in the order given in formula (I), and wherein the sum of I + m + n for values from 5 to 35, with the proviso that n> (l + m). List of pictures:

Figure 1: Schematic representation of fingering in C02 flooding.

Figure 2: Schematic representation of the high pressure reactor with viewing windows used for the examples and comparative examples.

Figure 3: View through the viewing window of the high-pressure reactor before mixing: C02 phase and water phase (schematic representation).

Figure 4: View through the viewing window of the high-pressure reactor after mixing: C02 phase, CC n-water emulsion and water phase (schematic representation).

Specifically, the following is to be carried out for the invention: In the process according to the invention for crude oil production by means of CO 2 flooding, liquid or supercritical CO 2 and at least one anionic surfactant (I) are injected into a crude oil deposit. In addition to the at least one anionic surfactant (I), other surfactants and other components can be used. In a preferred embodiment of the invention, the anionic surfactants (I) are used in combination with nonionic surfactants (II) and / or different anionic surfactants (III).

Anionic surfactants (I) The anionic surfactants (I) are alk (en) yl ether sulfonates of the general formula

R - (OCR ² R ³ CR ⁴ R ⁵ ) i - (OCH ₂ CHR ⁶ ) _m - (OCH ₂ CH ₂ ) n -O-R ⁷ -SO 3 - V _a M ^{a +} (I).

R ¹ is a branched or linear, saturated or unsaturated aliphatic hydrocarbon radical having 8 to 22 carbon atoms, preferably 8 to 18 carbon atoms, particularly preferably 10 to 14 carbon atoms. Examples of such radicals R ¹ include linear alkyl radicals such as in particular n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tetradecyl, n-hexadecyl, n-octadecyl, n-eicosyl or n-docosyl residues. It may also be surfactants comprising mixtures of different radicals R ¹ . Particularly noteworthy here are mixtures which derive from the use of natural fatty alcohols as starting material for the surfactants (I). For example, it may be a mixture of n-dodecyl and n-tetradecyl. Further examples of radicals R ¹ include branched alkyl radicals such as 2-ethylhexyl, 2-propylheptyl, 2-butyloctyl, 2-pentylnonyl, 2-hexyldecyl radicals and radicals derived from oxo alcohols, such as i-tridecyl radicals.

In a preferred embodiment of the invention, R ¹ is a branched alkyl radical of the formula C 5 Hn-CH (C 3 H 7) -CH 2 -, where at least 70 mol% of the pentyl radicals C 5 H 11 - is an n-CsHu radical. The substituent in 2-position, the propyl radical C3H7- may be in an n-C3H ₇ group or an i-C3H ₇ act radical. It is preferably an n-C3H ₇ radical. The pentyl radicals which are not n-pentyl radicals are preferably branched 1-alkyl radicals, preferably a 2-methyl-1-butyl radical C2H ₅ CH (CH 3) CH 2 - and / or a 3-methyl-1 - butyl CH 3 CH (CH 3) CH ₂ CH 2. In one embodiment of the invention, 70 to 99 mol% of the C5H11- radicals are n-C5Hn radicals, and from 1 to 30 mol% of the C5H11 radicals are C ₂ H ₅ CH (CH ₃ ) CH ₂ radicals and / or CH ₃ CH (CH ₃ ) CH ₂ CH ₂ radicals.

In a further embodiment of the invention, R ¹ is a 2-propyl-n-heptyl radical

In the formula (I), furthermore, the radicals R ² , R ³ , R ⁴ and R ⁵ are each independently H or a linear or branched alkyl radical having 1 to 8 carbon atoms, for example methyl, ethyl or propyl radicals, with the proviso in that the sum of the carbon atoms of the radicals R ² + R ³ + R ⁴ + R ^{5 is} 2 to 8, preferably 2 or 3 and particularly preferably 2. In one embodiment of the invention, the sum of R ² + R ³ + R ⁴ + R ⁵ = 2 is, wherein at least 70 mol%, preferably at least 80 mol% and particularly preferably at least 95 mol% of units -OCR ² R ³ CR ⁴ R ⁵ - R ² , R ³ and R ^{4 are} H and R ^{5 is} ethyl. Preference is given to -OCR ² R ³ CR ⁴ R ⁵ - that is, a butoxy group, particularly preferably a butoxy group, which is derived essentially from 1, 2-butene oxide.

R ⁶ is methyl, -OCH 2 CHR ⁶ - is thus a propoxy group and -OCH 2 CH 2 - an ethoxy group. R ⁷ is an alkylene radical having 2 to 4 carbon atoms, which may optionally be substituted by an OH group. It is preferably a group selected from the group of 1, 2-ethylene groups -CH ₂ -CH ₂ -, 1, 2-propylene groups -CH ₂ -CH (CH ₃ ) - or -CH (CH ₃ ) -CH ₂ - , 1, 3-propylene groups

-CH ₂ -CH ₂ -CH ₂ - or a substituted 1, 3-propylene group -CH ₂ -CH (OH) -CH ₂ -.

Furthermore, I is a number from 0 to 5, preferably 0, m is a number from 0 to 15, preferably 0 to 9 and n is a number from 5 to 30, preferably 5 to 20 and the sum of I + m + n is from 5 to 35, preferably from 8 to 29.

The indices I, m and n are further chosen with the proviso that n> (l + m) and particularly preferably n> 2 (l + m). Thus, not less ethoxy groups than - if present - alkoxy groups and propoxy groups should be present together. It will be apparent to those skilled in the art of polyalkoxylates that some distribution of chain lengths is obtained upon alkoxylation, and that I, m, and n are averages over all molecules. Accordingly, I, n and m are not natural numbers but rational numbers. A distribution of chain lengths can be described in a manner known in principle by the so-called polydispersity D. D = M _w / M _n is the quotient of the weight average molecular weight and the number average molar mass. The polydispersity can be determined by means of the methods known to the person skilled in the art, for example by means of gel permeation chromatography. It is further clear to the person skilled in the art that the orientation of the propoxy and / or butoxy groups depends on the reaction conditions -OCR ² R ³ CR ⁴ R ⁵ - or -OCH 2 CHR ⁶ - or else -OCR ⁵ R ⁴ CR ³ R ² -b. -OCHR ⁶ CH ₂ - can be. The representation in formula (I) is not intended to indicate the orientation of the alkoxy units.

In the above formula (I), the radicals -OCR ² R ³ CR ⁴ R ⁵ -, -OCH 2 CHR ⁶ - and -OCH ² CH ² - are arranged blockwise in the order given in formula (I). It is known to the person skilled in the art that small residues of alkylene oxides can remain in the course of an alkoxylation. After addition of the next alkylene oxide, these can then be copolymerized into the second block so that small amounts of an alkylene oxide are in the "wrong" block. [. In] As a rule, at least 90% of the above radicals are arranged in the order given in formula (I), ie at least 90% of the radicals are also found in the "right" block. In the case of the cation M ^{a +} , a is 1, 2 or 3, preferably 1 or 2. Particularly preferred is a = 1, ie it is a monovalent cation such as, for example, alkali metal ions, ammonium ions, where the ammonium ions may also have organic radicals. Examples of monovalent cations include Na ⁺ , K ⁺ , NH ₄ ⁺ , NMe ₄ ⁺ or NBu ₄ ⁺ .

Examples of preferred anionic surfactants (I) include

C ₅ Hii-CH (C ₃ H 7) -CH ₂ - (EO) i 4 -CH ₂ CH ₂ CH ₂ -SO 3 M,

C ₅ Hii-CH (C ₃ H 7) -CH 2 - (PO) ₅ - (EO) i ₅ -CH ₂ CH ₂ CH ₂ -SO 3 M,

C ₅ Hii-CH (C ₃ H 7) -CH 2 - (PO) 3- (EO) 8 -CH ₂ CH ₂ CH ₂ -SO 3 M,

C ₅ Hii-CH (C ₃ H 7) -CH 2 - (PO) 3- (EO) 9 -CH ₂ CH ₂ CH ₂ -SO 3 M,

C ₅ Hii-CH (C ₃ H 7) -CH 2 - (PO) ₅ - (EO) 9 -CH ₂ CH ₂ CH ₂ -SO 3 M,

C ₅ Hii-CH (C ₃ H 7) -CH ₂ - (EO) io-CH ₂ CH ₂ CH ₂ -SO 3 M,

iCi ₃ H27- (EO) io-CH 2 CH 2 CH 2 -SO ₃ M,

iCi3H27- (EO) i ₅ -CH 2 CH ₂ CH2-S03M,

iCi3H27- (EO) i8-CH 2 CH ₂ CH2-S03M,

iCi3H27- (EO) 25 -CH 2 CH ₂ CH2-S03M,

iCi3H27- (EO) 30 -CH 2 CH ₂ CH 2 SO 3 M,

iCi3H27- (EO) 37 -CH 2 CH ₂ CH2-S03M,

n (Ci2H25 Ci4H29) - (EO) 7-CH 2 CH ₂ CH2-S03M,

n (Ci2H25 Ci4H29) - (EO) i ₅ -CH 2 CH ₂ CH2-S03M or

n (Ci2H25 Ci4H29) - (EO) 28 -CH 2 CH ₂ CH2-S03M.

In the list, EO stands for an ethyleneoxy group, PO for a propyleneoxy group, 1C13H27- for a branched C 13 -alkyl radical and n (C 12 H 25 C ₄ H 29) - for a mixture of linear C 12 - and C 6 -alkyl radicals.

The preparation of the anionic surfactants (I) by means of a multi-step process.

In a first step, alk (en) ylpolyalkoxylate of the general formula (Ia) R - (OCR ² R ³ CR ⁴ R ⁵⁾ i (OCH ₂ CHR ⁶⁾ _m - (OCH ₂ CH ₂₎ n-OH (la)

by alkoxylation of branched or linear, saturated or unsaturated aliphatic alcohols R ¹ OH with -soofern existing alkylene oxides having 4 to 10 carbon atoms, preferably produced butylene oxide, propylene oxide and ethylene oxide, wherein the alkylene oxides are used in the order mentioned.

If butylene oxide is used, in principle all isomers, 1, 2-butene oxide, 2,3-butene oxide or isobutene oxide can be used. Preference is 1, 2-butene oxide. Advantageously, it is also possible to use technical mixtures which comprise 1, 2-butene oxide as the main constituent and, in addition, further butene oxide isomers. par- It is also possible to use mixtures which comprise at least 70 mol%, preferably at least 80 mol% and particularly preferably at least 95 mol% of 1,2-butene oxide. Suitable alcohols R ¹ OH are known to the person skilled in the art and are commercially available. For example, linear alcohols can be fatty alcohols or mixtures of different fatty alcohols. However, linear alcohols can also be prepared by oligomerization of ethylene and subsequent functionalization (eg Ziegler process). For the synthesis of surfactants with branched hydrocarbon radicals oxo alcohols or Guerbet alcohols can be used.

For the synthesis of preferred surfactants with C 5 Hn-CH (C 3 H 7) -CH 2 - radicals R ¹ , the alcohol C5HiiCH (C3H ₇ ) CI-l20l-l is used, wherein C5H11 and C3H7- have the abovementioned meaning, including the preferred meaning mentioned above to have.

Alcohols C5HnCH (C3H7) CH20H can be prepared by aldol condensation of valeraldehyde followed by hydrogenation. The preparation of valeraldehyde and the corresponding isomers is carried out by hydroformylation of butene, as described for example in US 4,287,370; Beilstein E IV 1, 32 68, Ullmanns Encyclopedia of Industrial Chemistry, 5th edition, volume A1, pages 323 and 328 f. The subsequent aldol condensation is described, for example, in US Pat. No. 5,434,313 and Römpp, Chemie Lexikon, 9th edition, keyword "aldol addition" on page 91. The hydrogenation of the aldol condensation product follows general hydrogenation conditions. Alcohols C5HnCH (C3H ₇₎ CH20H can also be prepared from 1 pentanol by the Guerbet reaction. For this purpose, technical 1-pentanols can be used, which usually contain certain amounts of methyl-1-butanols. In the Guerbet reaction, the 1-pentanols are reacted in the presence of KOH at elevated temperatures, see, eg, Marcel Guerbet, CR. Acad Sei Paris 128, 51 1, 1002 (1899), Rompp, Chemie Lexikon, 9th edition, Georg Thieme Verlag Stuttgart, and the literature mentioned there and Tetrahedron, Vol 23, pages 1723-1733.

In a preferred embodiment of the invention, the alcohol R ¹ OH used is C ₅ Hich (C ₃ H ₇ ) CH ² OH, where 70 to 99 mol% of the alcohol C ₅ Hn have the meaning n-CsHn and 1 to 30 percent by weight of the alcohol C5H11- the importance C2H ₅ CH (CH ₃₎ CH 2 and / or CH ₃ CH (CH 3) CH ₂ CH 2 has. Such alcohols are commercially available.

In a further embodiment of the invention, R ¹ OH is 2-propylheptanol-1 HsCCHzCHzCHzCHzCH vCsH ^ CHzOH. The execution of the abovementioned alkoxylation is known in principle to the person skilled in the art. It is also known to the person skilled in the art that the reaction conditions, in particular the choice of catalyst, can influence the molecular weight distribution of the alkoxylates.

Thus, the alcohols according to the general formula (Ia) can be prepared, for example, by base-catalyzed alkoxylation. In this case, the alcohol R ¹ OH can be mixed in a pressure reactor with alkali metal hydroxides, preferably potassium hydroxide, sodium hydroxide, alkaline earth metal hydroxides or with alkali metal alkoxides, such as, for example, sodium methylate. By reduced pressure (for example <100 mbar) and / or increasing the temperature (30 to 150 ° C), water or methanol still present in the mixture can be removed. The alcohol is then partly present as the corresponding alkoxide. The mixture is then inertized with inert gas (for example nitrogen) and the alkylene oxide (s) is added stepwise at temperatures of 90 to 180 ° C up to a maximum pressure of 10 bar. In one embodiment, the alkylene oxide is initially metered in at 120 ° C. In the course of the reaction, the temperature rises up to 170 ° C due to the released heat of reaction. The delay between injection of the various alkylene oxides can be shortened in one embodiment, so that the last injected alkylene oxide is not fully reacted and form by the newly injected alkylene oxide mixing blocks with small amounts of the previously added alkylene oxide. If present, butylene oxide can be added first at a temperature in the range of 125 to 145 ° C, then the propylene oxide at a temperature in the range of 125 to 145 ° C and then the ethylene oxide at a temperature in the range of 120 to 155 ° C. In the case of the absence of butyleneoxy units in the molecule, first propylene oxide and then ethylene oxide are metered in. At the end of the reaction, the catalyst can be neutralized, for example by addition of acid (for example acetic acid, citric acid or phosphoric acid) and filtered off if necessary. The alkoxylation of the alcohols R ¹ OH can of course be carried out by other methods, for example by acid-catalyzed alkoxylation. Furthermore, it is possible to use, for example, double hydroxide clays as described in DE 4325237 A1 or it is possible to use double metal cyanide catalysts (DMC catalysts). Suitable DMC catalysts are disclosed, for example, in DE 10243361 A1, in particular in sections [0029] to [0041] and in the literature cited therein. For example, Zn-Co type catalysts can be used. To carry out the reaction, the alcohol R ¹ OH is admixed with the catalyst, the mixture is dehydrated as described above and reacted with the alkylene oxides as described. It is usually not more than 1000 ppm catalyst used with respect to the mixture and the catalyst may remain in the product due to this small amount. The amount of catalyst can be in typically less than 1000 ppm, for example 250 ppm or 100 ppm or less.

The resulting alk (en) ylpolyalkoxylates (Ia) are sulfonated in one or more further reaction steps, the surfactants (I) being obtained.

The sulfonation can be carried out, for example, by substitution of the OH group of the alkoxylate for Cl using phosgene or thionyl chloride. The reaction can be carried out in the presence of a solvent such as chlorobenzene. HCl liberated as well as liberated CO2 or SO2 can advantageously be removed from the system by stripping with nitrogen so that ether cleavage is prevented. The alkylalkoxychlor compound is then reacted with an aqueous solution of sodium sulphite, the chloride being substituted by sulphite and the alkyl ether sulphonate being obtained. The substitution may be carried out in the presence of a phase mediator (eg Cr to Cs alcohols) at a temperature of 100-180 ° C and pressure. This gives a terminal group -CH 2 CH 2 -SO 3 M, ie R ¹⁰ is an ethylene group -CH 2 CH 2 -. An alternative to chlorination is the sulfation of the alkyl alkoxylates with SO3 in a falling film reactor and subsequent neutralization with NaOH. The alkyl ether sulfate formed can be converted into the alkyl ether sulfonate by nucleophilic substitution of the sulfate group by sodium sulfite analogously to the above description. The alkyl ether sulfonates (III) can alternatively be obtained by addition of vinyl sulfonic acid to the alkyl alkoxylate. Details of this are described for example in EP 31 1 961 A1. In this case, an alkyl ether sulfonate having a terminal group -CH2CH2-SO3M is obtained. Alkyl ether sulfonates having a terminal group -CH 2 -CH 2 -CH 2 -SO 3 M (ie R ¹⁰ = -CH 2 CH 2 CH 2 - can be obtained by reacting the alkyl alkoxylate with 1,3-propane sultone Alk (en) yl ether sulfonates having a terminal group -CH 2 -CH ( OH) -CH 2 -SO 3 M are accessible by the reaction of the corresponding alk (en) ylpolyalkoxylates with epichlorohydrin and subsequent nucleophilic substitution of the chloride group by sodium sulfite.

An important requirement for surfactants for CO 2 flooding is sufficient long-term stability under reservoir conditions. The flooding of an oil field with CO2 usually takes months, if not years, and accordingly, the surfactants must be stored at least a few months under reservoir conditions, i. a high temperature, high salinity and a strongly acidic pH (about pH 3 due to the CO2) remain stable. Alk (en) yl polyether sulfates hydrolyze under reservoir conditions due to the acidic pH. Although frequently described in particular in the patent literature, therefore, sulfates are not well suited to CO 2 flooding because they are not stable in the long term under acidic conditions. The described

Alk (en) ylpolyethersulfonates of the general formula (I) have, in comparison to corresponding The advantage of these alk (en) ylpolyether sulfates is that they do not hydrolyze in the acidic state and thus fulfill the requirement for adequate long-term stability.

Nonionic surfactants (II)

In addition to the anionic surfactants (I), it is also possible optionally to use nonionic surfactants (II) for the process according to the invention. The nonionic surfactants (II) is alk (en) ylkoxylate the general formula (II) R ⁸ - (OCR ² R ³ CR ⁴ R ⁵⁾ x (OCH ₂ CHR ⁶⁾ _y - (OCH ₂ CH 2) z-OH (II).

R ⁸ is a branched or linear, saturated or unsaturated aliphatic hydrocarbon radical having 8 to 22 carbon atoms, preferably 8 to 18 carbon atoms, particularly preferably 8 to 14 carbon atoms.

Examples of such radicals R ⁸ include linear alkyl radicals such as in particular n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tetradecyl, n-hexadecyl, n-octadecyl, n-eicosyl or n-docosyl residues. It may also be surfactants comprising mixtures of different radicals R ¹ . Particularly noteworthy here are mixtures which derive from the use of natural fatty alcohols as starting material for the surfactants (I). For example, it may be a mixture of n-dodecyl and n-tetradecyl. Further examples of radicals R ¹ include branched alkyl radicals such as 2-ethylhexyl, 2-propylheptyl, 2-butyloctyl, 2-pentylnonyl, 2-hexyldecyl radicals and radicals derived from oxo alcohols, such as i-tridecyl radicals.

In a preferred embodiment of the invention, R ⁸ is a branched alkyl radical of the formula C 5 Hn-CH (C 3 H 7) -CH 2 -, where at least 70 mol% of the pentyl radicals C 5 H 11 - is an n-CsHu radical. The substituent in 2-position, the propyl radical C3H7- may be in an n-C3H ₇ group or an i-C3H ₇ act radical. It is preferably an n-C3H ₇ radical. The pentyl radicals which are not n-pentyl radicals are preferably branched 1-alkyl radicals, preferably a 2-methyl-1-butyl radical C2H ₅ CH (CH 3) CH 2 - and / or a 3-methyl-1 - butyl CH 3 CH (CH 3) CH ₂ CH 2. In one embodiment of the invention, 70 to 99 mol% of the C5H11- radicals are n-C5Hn radicals, and from 1 to 30 mol% of the C5H11 radicals are C ₂ H ₅ CH (CH ₃ ) CH ₂ radicals and / or CH ₃ CH (CH ₃ ) CH ₂ CH ₂ radicals.

In a further embodiment of the invention, R ⁸ is a 2-propylheptyl radical HsCCHzCHzCHzCHzCH n-CsH ^ Ch -. In a further preferred embodiment, R ⁸ is a 2-ethylhexyl radical.

In a further preferred embodiment, R ⁸ is a linear, saturated hydrocarbon radical having 12 to 14 carbon atoms, in particular a mixture comprising n-dodecyl and n-tetradecyl radicals.

In formula (II), R ² , R ³ , R ⁴ , R ⁵ and R ^{6 have} the meanings given above and the preferred ranges given.

The subscript x stands for a number from 0 to 5, preferably 0, the index y for a number from 1 to 15, preferably 1 to 9, for example 2 to 8 and the index z for a number from 1 to 30, preferably 2 to 20, particularly preferably 5 to 18, for example 8 to 16, wherein the sum of x + y + z is 5 to 35, preferably 8 to 29, for example 10 to 25.

The indices x, y and z are furthermore selected with the proviso that z> (x + y), preferably z> (x + y) and particularly preferably z> 2 (x + y). Thus, not less ethoxy groups than, if present, alkoxy groups and propoxy groups should be present together.

The values x, y and z are of course average values. Please refer to the illustration for surfactant (I). It is further clear to the person skilled in the art that the orientation of the propoxy and / or butoxy groups depends on the reaction conditions -OCR ² R ³ CR ⁴ R ⁵ - or -OCH ₂ CHR ⁶ - or -OCR ⁵ R ⁴ CR ³ R ² - respectively. -OCHR ⁶ CH ₂ - can be. The representation in formula (II) is not intended to indicate the orientation of the alkoxy units.

In the above formula (II), the radicals -OCR ² R ³ CR ⁴ R ⁵ -, -OCH ₂ CHR ⁶ - and -OCH ₂ CH ₂ - are arranged blockwise in the order given in formula (I). However, it is known to the person skilled in the art that small amounts of alkylene oxides can remain in the course of an alkoxylation. After addition of the next alkylene oxide, these can then be copolymerized into the second block so that small amounts of an alkylene oxide are in the "wrong" block. [. In] As a rule, at least 90% of the above radicals are arranged in the order given in formula (I), ie at least 90% of the radicals are also found in the "right" block. The preparation of the surfactants (II) is carried out by alkoxylation of branched aliphatic alcohols R ⁸ OH with -soof existing alkylene oxides having 4 to 10 carbon atoms, preferably butylene oxide, propylene oxide and ethylene oxide, wherein the alkylene oxides are used in the order mentioned. Details of the preparation have already been described in detail in connection with the preparation of the alk (en) ylpolyalkoxylates of the general formula (Ia). This presentation is expressly referred to.

In a preferred embodiment of the invention, R ^{8 has} the same meaning as R ¹ , including the preferred ranges of R ¹ and for the indices x, y, and z holds x = I, y = m and z = n, where n, l and m can take the values defined above, including the preferred ranges.

In a further preferred embodiment of the invention, the alcohol R ⁸ OH is an alcohol R ¹ OH. This is first alkoxylated in the manner described and then sulfonated as described above, but only partially, ie he remains not yet sulfonated terminal OH groups. In this procedure, a mixture of a surfactant (I) and a surfactant (II) is obtained wherein R ⁹ = R ¹ , 1 = x, m = y and n = z.

Nonionic surfactants (I II)

In addition to the anionic surfactants (I), it is also possible optionally to use nonionic surfactants (II) for the process according to the invention. The nonionic surfactants (II I) are alkylphenol polyakoxylates of the general formula (II I)

R ⁹ -C ⁶ H ₄ -O- (OCR ² R ³ CR ⁴ R ⁵ ) u- (OCH ₂ CHR ⁶ ) v- (OCH ₂ CH ₂ ) w -OH (III).

In the formula (III), R ^{9 is} a linear or branched alkyl radical having 8 to 12 carbon atoms.

The group -ΟβΗ ₄ - represents a phenylene group, preferably a 1, 4-phenylene group.

In the formula (III), R ² , R ³ , R ⁴ , R ⁵ and R ^{6 have} the abovementioned meaning and the preferred ranges given.

The subscript u stands for a number from 0 to 5, preferably 0, the index v for a number from 0 to 15, preferably 0 and the index w for a number from 5 to 30, preferably 6 to 20, particularly preferably 8 to 18 where the sum of u + v + w is 5 to 35, preferably 6 to 29, for example 8 to 20. The subscripts u, v and w are further selected with the proviso that u a (v + w), preferably u> (v + w), and particularly preferably u ä 2 (v + w). Thus, not less ethoxy groups should be present than alkoxy groups and propoxy groups if they are present. The values u, v and w are of course average values. Please refer to the illustration for surfactant (I).

The radicals -OCR ² R ³ CR ⁴ R ⁵ -, -OCH ₂ CHR ⁶ - and -OCH ₂ CH ₂ - are arranged blockwise in the order given in formula (III). Other cosurfactants

In addition to the nonionic surfactants according to the general formula (I) and optionally the surfactants (II) and / or (III), it is optionally possible to use further surfactants. Examples of additional cosurfactants include anionic surfactants such as paraffin sulfonates, olefin sulfonates (alpha-olefin sulfonates or internal olefinsulfonates), nonionic surfactants such as alkyl ethoxylates other than the surfactants (II) or polyalkoxylates composed of propylene oxide and ethylene oxide or surfactants which are permanently cationic (with alkyl or alkoxy) Hydroxyalkyl-quaternized alkylamines such as Ν, Ν, Ν-trimethyl-dodecylammonium chloride) or cationic under the conditions of the reservoir (eg alkylamine alkoxylates which are cationic at pH 3).

Formulation (F) of the surfactants

For the process according to the invention, the surfactants (I), optionally further surfactants, especially the surfactants (II) and (III) and optionally further components can be used as such, for example, the surfactants and / or other components mentioned directly in liquid or supercritical C0 _{2 are} solved.

In a preferred embodiment of the invention, however, the abovementioned components are used in the form of a suitable aqueous formulation (F). This aqueous formulation (F) can be metered into liquid or supercritical CO2 and injected or the aqueous formulation can be injected as such or after further dilution into the formation. The stated formulation (F) may in particular be an aqueous concentrate which can be produced on site or else in a chemical production plant remote therefrom. The total concentration of all surfactants in such an aqueous concentrate is chosen by the skilled person depending on the desired properties. It may be 20 to 90 wt .-% with respect to all components of the concentrate. The concentrate may be liquid or liquid prior to injection supercritical CO2 and / or other aqueous solvents are diluted to the desired use concentration as will be described below.

In addition to water, the formulations (F) may optionally also comprise water-miscible or at least water-dispersible organic solvents. Such additives serve in particular to stabilize the Tensidlosung during storage or transport to the oil field. However, the amount of such additional solvents should as a rule not exceed 50% by weight, preferably 20% by weight. Examples of water-miscible solvents include in particular alcohols such as methanol, ethanol and propanol, butanol, sec-butanol, methoxypropanol, pentanol, ethylene glycol, diethylene glycol, propylene glycol, methylpropylene glycol, dipropylene glycol, methyldipropylene glycol, butyl ethylene glycol, butyldiethylene glycol or butyltriethylene glycol. In a particularly advantageous embodiment of the invention, only water is used for formulation.

In addition to the surfactants, the aqueous formulations (F), in particular the aqueous concentrates, may also comprise further components, for example scale inhibitors, biocides, radical scavengers, stabilizers, tracers or pour-point depressants. Particularly suitable pour point depressants are the abovementioned alcohols.

Process for oil production by means of CQ2 floods

For the method according to the invention for CO 2 flooding, at least one injection well and at least one production well removed therefrom are drilled into a crude oil deposit. As a rule, a deposit is provided with multiple injection wells and multiple production wells.

The crude oil deposits to which the method according to the invention is applied may, in principle, be any deposits, for example formations comprising carbonate rocks or formations comprising sandstone. The oil reservoirs include oil and saline reservoir water, with petroleum, reservoir water and possibly natural gas stored in pores, crevices or interstices of the formation.

The storage temperature is usually at least 10 ° C, in particular 15 ° C to 140 ° C, preferably 31 ° C to 120 ° C, more preferably 40 ° C to 120 ° C, most preferably 50 ° C to 100 ° C and for example 60 ° C to 90 ° C. It will be clear to those skilled in the art that the reservoir temperature may have some distribution about an average, with large deviations generally less caused by natural circumstances, but especially by human intervention, eg by prolonged flooding or prolonged steam flooding.

The total salinity of the reservoir water can be up to 350,000 ppm, for example 20,000 ppm to 350,000 ppm. The method may preferably be applied to deposits having a total salinity of 30,000 ppm to 250,000 ppm, preferably 35,000 ppm to 200,000 ppm, more preferably 35,000 ppm to 180,000 ppm, for example 120,000 ppm to 170,000 ppm. The salts in the deposit may be in particular alkali metal salts and alkaline earth metal salts. Examples of typical cations include Na ⁺ , K ⁺ , Mg ²⁺ or Ca ²⁺ and examples of typical anions include chloride, bromide, bicarbonate, sulfate or borate. As a rule, at least one or more alkali metal ions, in particular at least Na ^{+, are present} in the reservoir water. In addition, alkaline earth metal ions may also be present, the weight ratio of alkali metal ions / alkaline earth metal ions generally being> 5, preferably> 8. Suitable anions are usually at least one or more of halide ions, in particular at least Cl ^"available. In general, the amount of Ch is at least about 50 wt.%, Preferably at least 80 wt.% Relative to the total of all anions.

Liquid or supercritical CO2 and at least one anionic surfactant (I) or a surfactant mixture comprising at least one anionic surfactant (I) are injected into the petroleum formation through the at least one injection well and petroleum is taken from the deposit through at least one production well, the at least one Surfactant (I) or at least one surfactant (I) comprising dissolved in liquid or supercritical CO2 and is injected and / or dissolved in an aqueous medium and injected.

Of course, the term "petroleum" in this context does not only mean phase-pure oil, but also includes the usual crude oil-water emulsions, and also injects injected CO2 into the production well, depending on the stage of the process.

When pumping CO2 into a reservoir, pressure and temperature determine the physical state of CO2. The phase diagram of CO2 is known to the person skilled in the art. CO2 can be liquefied in the temperature range of -56.6 ° C to 30.98 ° C using a pressure of at least 5.2 bar. At less than 5.2 bar, depending on the temperature, only solid or gaseous CO2 exists. The critical point of CO2 is 30.98 ° C and 73.75 bar. At pressures and temperatures above these values, CO2 is supercritical, ie the phase boundary liquid-gaseous disappears. and the CO2 is almost as dense as a liquid but still has a very low viscosity similar to that of a gas.

To generate liquid or supercritical CO2, gaseous CO2 can be compressed on-site, for example from CO2 produced, or CO2 can already be delivered in a compressed state. The minimum pressure required for injection results from the reservoir temperature and is selected such that the injected CO2 is in a liquid or supercritical state at the respective reservoir temperature. It has proven useful to adjust the CO 2 flooding the density of CO2 under reservoir conditions to 0.65 g / ml to 0.95 g / ml, preferably 0.70 g / ml to 0.90 g / ml. The density of CO2 as a function of pressure and temperature can be found in relevant tables.

Injecting the at least one nonionic surfactant (I) or the surfactant mixture comprising at least one nonionic surfactant (I) can be carried out by various techniques.

In a first embodiment (A) of the process according to the invention, the surfactants or surfactant mixtures used as well as optionally further components are dissolved in liquid or supercritical CO 2 and the CO 2 solution is injected into the subterranean crude oil deposit. Such processes are also referred to as surfactant-in-gas (SinG) processes.

In the embodiment (A), the surfactant (I) or the surfactant (I) comprising surfactant mixture can be mixed as such with the CO2, dissolved and injected, or it can be a suitable formulation of the surfactants used. In particular, the formulations (F) described above, in particular as concentrates having a surfactant content of from 20 to 90% by weight with respect to the sum of all components, can be used and metered into a stream of liquid or supercritical CO 2 and mixed with the stream.

The amount of the surfactants or of the formulation (F) or of the concentrate is such that the amount of all surfactants together 0.02 to 2 wt.%, Preferably 0.02 to 0.5 wt .-% with respect to the sum of all components the solution of surfactants in liquid or supercritical CO2.

After entering the formation, the CO2 flows in the direction of the production well or the production wells, mobilizing oil according to the mechanisms described above. If the liquid or supercritical CO2 with the dissolved surfactants hits deposit water after being injected into the formation, CO2 in-water emulsions, which are stabilized by the one or more surfactants (I) or surfactants (I) comprising mixtures and optionally other surfactants.

Since no phase boundary between gaseous and liquid phase is present in supercritical CO2, such CC n-water emulsions are occasionally referred to in the literature as CC n-water foams, and the term C02-in-water dispersions can also in the literature can be found. In the following, however, the term CC n-water emulsion is to be used uniformly. The C02-in-water emulsions have a significantly higher viscosity than the CO2 itself, and thus the difference between the viscosity of the CC n-water emulsion and the petroleum is lower, usually much less than the difference between the viscosity of liquid or supercritical CO2 and petroleum. C02-in-water emulsions also flow towards production wells or production wells. Liquid or supercritical CO2, which is incorporated in the emulsion, can also mobilize the oil in the same way as already mentioned when it encounters oil. Advantageously, the surfactants (I) and optionally further surfactants also lower the interfacial tension between oil and CO2 and thus also facilitate the miscibility of these two phases.

The injected liquid or supercritical CO2 naturally flows first into the higher permeable zones. As soon as more viscous C02-in-water emulsions form on the water, flow through the permeable zones becomes much more difficult, so that pumped-up CO2 can find its way through low-permeability zones and mobilize previously unreachable oil. This increases the oil production rate. If the capillary pressure in the very low-permeable zones becomes too high, the CO2-water aggregate may collapse. However, this is not a disadvantage since the very low-permeability zones would have been barely accessible to the CO2 if flooded alone with CO2 or in the water-alternating gas process.

In a second embodiment (B) of the method according to the invention, water or saline water, such as, for example, seawater or produced deposit water, is first injected into the deposit through the injection well.

Subsequently, analogously to embodiment (A), a solution of the surfactants or surfactant mixtures used and optionally further components is injected in liquid or supercritical CO2. The amount of surfactants or formulation (F) or of the concentrate is such that the amount of all surfactants together 0.02 to 2 wt .-%, preferably 0.02 to 0.5% by weight with respect to the sum of all components of the solution of surfactants in liquid or supercritical CO2.

The sequence of these two process steps can be repeated once or several times. At the contact points of the water phase and the CO 2 phase, CO2-in-water emulsions are formed. Such processes are also referred to as water-aging surfactant-in-gas (WAGS) processes.

In a third embodiment (C) of the process according to the invention, an aqueous formulation of the surfactants (I) or surfactants (I) comprising surfactant mixtures is injected into the formation and separately liquid or supercritical CO2.

For injecting, in particular, the above-described concentrates of formulation (F) may be mixed with water or saline water and injected into the formation.

The amount of surfactants is calculated so that the concentration of all surfactants together is 0.02 to 2 wt .-%, preferably 0.02 to 0.5 wt .-% with respect to the sum of all components of the injected aqueous solution.

Thereafter, liquid or supercritical CO2 is injected into the deposit. The sequence of these two process steps can be repeated once or several times. At the contact points of the water phase and the CO 2 phase, CC n-water emulsions form. Such processes are also referred to as Surfactant in Water Alternating Gas (SAG) processes.

To further improve the mobility control in embodiments (B) and (C), the water phase may be thickened with a water-soluble, thickening polymer such as polyacrylamide, partially hydrolyzed polyacrylamide, acrylamide-containing copolymers, acrylamide and sulfonate group-containing copolymers or biopolymers such as xanthan ,

It is preferred to inject the surfactants (I) as well as optionally further surfactants and components dissolved in liquid CO2 or supercritical CO2 (embodiments (A) and (B)). These variants have the advantage that the surfactant (I) and optionally further surfactants and components are present when the liquid or supercritical CO2 hits formation water after injection into the formation so that the rapid formation of CC n-water emulsions is possible becomes.

If the surfactant according to embodiment (C) injected separately from the CO2 by means of an aqueous solution, then water and CO2 due to their different egg in the formation also take (partially) different flow paths. There is thus the danger that part of the surfactant remains unused.

The person skilled in the art is familiar with details of the technical implementation of "C02 flooding", "Water Alternating Gas" flooding and the SinG, WAGS and SAG process and applies a corresponding technique depending on the nature of the deposit.

Of course, further embodiments of the method according to the invention are possible. For example, the described CC n-water emulsions can be formed before injection from liquid or supercritical CO2, tensides (I) and optionally further surfactants, and the CC n-water emulsions injected.

The main effect of the surfactants (I) used according to the invention lies in the stabilization of the CO 2 -water interface and thus in long-term stable CC n-water emulsions. The surfactants (I) stabilize the CC n-water emulsions better than surfactants according to the prior art. The CC n-water emulsions remain stable much longer than is the case with known surfactants. Selection of surfactants

Depending on the nature of the deposit, the person skilled in the art selects at least one surfactant (I) for carrying out the process according to the invention. Optionally, the surfactants (I) may be used in admixture with other surfactants (I), at least one surfactant (II) and / or at least one surfactant (III). Optionally, other surfactants and other components can be used.

The type of surfactant (I) to be used and possibly other surfactants depends on the conditions of the reservoir, in particular on the temperature of the reservoir and the salinity of the reservoir water. The skilled person will make an appropriate choice depending on the reservoir conditions.

As a rule, the cloud point of the surfactant or of the surfactant mixture used should be at least 1 ° C., preferably at least 3 ° C., above the reservoir temperature under reservoir conditions. If the deposit has a distribution of store temperatures, this means the highest store temperature in the area through which the liquid or supercritical CO2 or the C02-in-water emulsion flows.

The cloud point of a nonionic surfactant is the temperature at which the solution becomes cloudy. The reason for this is that the surfactant increases with increasing temperature. hydrated and thus insoluble. This separates the solution into a cloudy surfactant and a clear, low-surfactant phase. This phase behavior is found not only with nonionic surfactants, but also with surfactants which have a nonionic, hydrophilic moiety, for example a polyalkoxy group and an anionic group. Cloud points are also measurable with the anionic surfactants (III) of this invention.

The cloud point is measured by slowly heating a clear aqueous solution of the surfactant in water. The cloud point of a surfactant depends on the concentration of the surfactant and the salt content of the aqueous solution. A specific measurement instruction for the cloud point is contained in the example part of this application.

The term "under reservoir conditions" as defined above means that the cloud point of the surfactant (I) or surfactant (I) surfactant mixture in reservoir water at the concentration intended for injection, ie the concentration of surfactant in the aqueous medium to be injected or the concentration in the liquid or supercritical CO2 to be injected.

The cloud point of the surfactants of the formula employed in this invention (I) R ¹ - (OCR ² R ³ CR ⁴ R ⁵⁾ i (OCH ₂ CHR ⁶⁾ _m - (OCH ₂ CH 2) n-0-R ⁷ V _a -S03- M ^{a +} can be well adapted to the conditions in the deposit by the nature of the alkoxylation scheme.

The greater the number I of alkoxy groups -OCR ² R ³ CR ⁴ R ⁵ - and the number m of propoxy groups -OCH ² CHR ⁶ - the lower the cloud point and the higher the number n of ethoxy groups, the higher the cloud point. Analogous statements apply to cosurfactants (II) and (III).

In one embodiment of the process according to the invention, a surfactant of the general formula (I) is used in which I = 0, m = 0 and n = 10 to 18 and the radicals R ¹ to R ^{6 have} the meaning defined above. Such surfactants are particularly suitable for deposits with a temperature of 40 ° C to 120 ° C, especially 50 ° C to 100 ° C and for example 60 ° C to 90 ° C and a salinity of the reservoir water of 35000 ppm to 180000 ppm, in particular 120,000 ppm to 170000 ppm

In a further embodiment of the process according to the invention, a mixture of at least one anionic surfactant (I) and at least one nonionic surfactant (II) which is different therefrom is used.

Combinations of anionic surfactants of the formula (I) with the nonionic surfactants (II) are particularly economical. The anionic surfactants (I) have excellent en technical characteristics. They are still very useful especially at higher salinities and / or higher reservoir temperatures and have good long-term stability under reservoir conditions. However, the preparation of alk (en) ylpolyalkoxysulfonaten (surfactants (I)) is expensive. To prepare them, it is necessary first of all to prepare alk (en) ylpolyalkoxylates (surfactants (II)) which then have to be converted into alk (en) ylpolyalkoxysulphonates in a one- or two-stage process. Details of this have already been described above. The surfactants (II) are therefore necessarily more expensive than the surfactants (I). A mixture of the surfactants (I) with the surfactants (II) thus reduces the cost.

In a particularly preferred embodiment of the invention, a mixture of the surfactants (I) and (II) can be used, wherein R ^{8 is} equal to R ¹ and I = x, m = y and n = z. Such a mixture can be prepared by only partially surfactants (II) sulfonated to surfactants (I).

The weight ratio of surfactants of formula (I) to (II) in the mixture is chosen by the skilled person depending on the requirements. As a rule, the weight ratio (I) / (II) is 19: 1 to 1:19, preferably 4: 1 to 1: 9, more preferably 2: 1 to 1: 9 and for example 1: 1 to 1: 4. Preferred total amounts have already been mentioned.

The mixture of the surfactants (I) and (II) is still very soluble in water even at high salinity and also the solubility in CO2 is good.

Surprisingly, it has furthermore been found that a mixture of surfactants (I) with surfactants (III) has synergistic effects with regard to emulsifying ability. The mixture of (I) and (II) binds more saline water in the CC n-water emulsion than would have been expected on the basis of the measurements for the surfactants (I) alone and (II) alone. The adsorption of the mixture is low on sandstone.

In a further embodiment of the process according to the invention, a mixture of at least one anionic surfactant (I) and at least one surfactant (III) is used.

The weight ratio of surfactants of the formula (I) to (III) in the mixture is chosen by the person skilled in the art according to the requirements. As a rule, the weight ratio (I) / (II) is 19: 1 to 1:19, preferably 4: 1 to 1: 9, more preferably 2: 1 to 1: 9 and for example 1: 1 to 1: 4. Preferred total amounts for the amount of all surfactants have already been mentioned. The mixture of the surfactants (I) and (III) is still very soluble in water even at high salinity and also the solubility in CO2 is good.

The adsorption of the mixture is low on both carbonate rock and sandstone.

The following examples are intended to explain the invention in more detail: Part I: Synthesis of the surfactants used

1-1: Synthesis of Alk (en) ylpolyalkoxylates (Surfactants II)

For the synthesis, the following alcohols were used as starting materials.

General rule:

In a 21 autoclave, the alcohol (1, 0 eq) to be alkoxylated is optionally mixed with an aqueous KOH solution containing 50% by weight of KOH. The amount of KOH is 0.2% by weight of the product to be produced. With stirring, the mixture is dehydrated at 100-120 ° C and 20 mbar for 2 h. Then it is rinsed three times with N2, a pre-pressure of about 1.3 bar N2 is set and the temperature is increased to 130.degree. The alkylene oxides are then metered in succession in the respectively desired amount, so that the temperature remains between 135 to 145 ° C. Subsequently, the mixture is stirred for 1 h at 135 to 145 ° C, rinsed with N2, cooled to 80 ° C and the reactor emptied. The basic crude product is neutralized with acetic acid. Alternatively, the neutralization can be carried out with commercially available Mg silicates, which are then filtered off. The bright product is characterized by means of a 1 H-NMR spectrum in CDCl 3, a gel permeation chromatography and an OH number determination, and the yield is determined.

In accordance with the general procedure, various nonionic surfactants were synthesized for the performance tests. The formula of the synthesized products are given in the following tables. 1-2: Synthesis of Alk (en) ylalkoxysulfonates (Surfactants I)

1 . Step:

In a first stage of the synthesis, an alk (en) ylpolyalkoxylate was first synthesized according to the above general procedure.

2nd stage:

In a second stage of the synthesis, the alk (en) ylpolyalkoxylate obtained in the 1st stage is sulfonated according to the following procedure:

The alkyl alkoxylate (1, 0 eq) to be sulfonated is mixed with KOH flakes (1.1 eq) in a 500 ml flat-section glass reactor with three-stage bar stirrer and flow breakers and stirred at 60 ° C. under N 2. Now within 1 h propane sulphone (1, 0 eq) was added at 60 ° C and stirred for a further 3 h at 60 ° C. Unreacted propane sultone is destroyed by boiling with water. The basic crude product is neutralized at 60 ° C with the aid of hydrochloric acid. Ethanol may be added to the reaction mixture to lower the viscosity of the mixture.

Alternatively, it can be converted into the free sulfonic acid with an excess of HCl (1 .5 eq) and phase separated at 60-80 ° C. by addition of water and a volatile hydrophobic alcohol such as pentanol. The organic phase is then freed from the solvent and converted by means of base MOH (1 eq) into the corresponding sulfonate. The bright product is characterized by means of a 1 H-NMR spectrum in CDCl ₃ and MeOD, a ¹ H-TAI-NMR, an Epton titration and an OH number determination and the yield is determined.

In accordance with the general procedure, various nonionic surfactants were synthesized for the performance tests. The formula of the synthesized products are given in the following tables.

I-3 surfactants (III)

The surfactants used (III), 4-octylphenol-10 EO, 4-octylphenol -16 EO are commercially available.

Part II: Application Testing

11-1: Measurement of the cloud point in water In a first series of experiments, the cloud point of the surfactants or mixtures of different surfactants was determined. General measuring instruction:

50 ml of the respective aqueous surfactant solution are heated in a test tube over a Bunsen burner. The solution is stirred with a spatula. The temperature of the solution is determined by means of a thermometer submerged in the solution. After the haze has appeared, the bunsen burner is removed so that the solution can slowly cool and continue to stir until the solution is clear again. The cloud point is the change from cloudy to clear and is usually in a temperature range of 1 ° C.

Carrying out the measurements

The measurements were carried out with aqueous surfactant solutions both in fresh water and in salt water of various salt concentrations. The salt water used was aqueous solutions containing NaCl and CaC in a ratio of 9 to 1 (by weight). The salinity ranges from 0 to 250,000 ppm TDS (total dissolved salt).

The respective salinity, the type and amount of the surfactants used in each case and measured cloud points are summarized in Tables 1 a to 1 c.

The object of the invention was to provide an improved process for CO 2 flooding for oil refineries, in which the most stable CC n-water emulsions are formed. Table 1 shows the influence of the structure of the surfactants (I) used according to the invention and the salinity on the measured cloud points.

Table 1: Influence of structure and salinity on cloud points in water (PO = propoxy, EO = ethoxy)

Table 1 shows that the alkyl polyalkoxy sulfonate 2-PH-I 4-EO-C3H6-SO3K has a very high cloud point of greater than 95 ° C at higher concentrations. It is thus also suitable for C02 floods in formations with a particularly high reservoir temperature. It is noteworthy that this also occurs at a salinity of 160000 ppm. Even at a salinity of 200,000 ppm, the cloud point is still 77 ° C.

II-2 Solubility in supercritical CO2 The solubility of the surfactants in supercritical CO2 was then investigated. The apparatus used was a 280 ml high-pressure reactor with two viewing windows in the lower region of the reactor. The construction of the apparatus is shown schematically in Figure 2. The reactor comprises a CO 2 inlet (1), a manometer (2), a CO 2 pressure relief valve (325 bar) and two opposing viewing windows (4) mounted in the lower reactor area. The reactor can be stirred via a stirrer.

For solubility determination different pressures and temperatures were set. First, surfactant was added with stirring with CO2 and at a certain temperature, the pressure changed. If turbidity sets in - compared to the surfactant-free CO 2 phase under the same conditions - the conditions were noted.

Next, conditions were chosen which can often be found at a corresponding reservoir depth (lithostatic and hydrostatic pressure as well as reservoir temperature as a function of depth). The density of CO2 was approx. 0.78 to 0.82 g / ml under the selected conditions (175 bar at 40 ° C or 300 bar at 65 ° C). Surfactant concentrations of 0.1 and 0.5% by weight with respect to the CO 2 phase were investigated.

The results are summarized in Table 2. The evaluation of solubility was as follows:

Rating Description very good no residue on sight glass or cloudiness of the solution good low residue on sight glass or turbidity of the solution, for example small, discrete streaks moderately visible residues on sight glass or turbidity of the solution; large streaks Ex. Surfactant surfactant pressure Tempe solubility

Concentration

tration [%] [° C]

1 1 2-PH-I 4-EO-C 3 H 6 -SO 3 K 0.1 175 40 very good

12 2-PH - 3 PO - 9 EO 0.1 175 40 very good

13 2-PH - 5 PO - 15 EO 0.1 175 40 very good

14 2-PH - 5 PO - 15 EO 0.5 175 40 good

15 2-PH - 5 PO - 15 EO 0.1 300 65 very good

16 2-EH - 5 -PO - 9 EO 0.1 175 40 good

17 2-EH - 5 -PO - 9 EO 0.5 175 40 moderate

18 4-Octylphenol - 10 EO 0.1 175 40 very good

19 4-Octylphenol - 16 EO 0.1 175 40 very good

Table 2: Solubility in supercritical CO2

11-3 emulsifying ability

Furthermore, the ability of various surfactants and surfactant blends to stabilize C02-in-water emulsions was tested.

The above reactor was used. Surfactant was prepared at the concentrations shown in the tables below and made up to 40 ml with saline water. The saline water was a solution of NaCl and CaC in water (weight ratio NaCl: CaC = 9: 1). It has been tested at different total salinity levels. These are given in the following tables.

The high pressure apparatus was filled with the aqueous solution exactly to the middle of the viewing window. The reactor was then charged to 280 ml with supercritical CO2. The water phase and the C02 phase are clear and the viewing window shows clearly the phase boundary between CO2 and water. This is shown schematically in Figure 3a. Then the mixture is stirred.

Through the viewing window, the formation of C02-in-water emulsions can now be observed. The C02-in-water emulsions formed are not as clear as the CO2 phase and the water phase, but cloudy to opaque. Depending on the degree of conversion of the water phase into the C02-in-water emulsion, only the C02-in-water emulsion can be seen through the viewing window or all 3 phases, viz Water, CC n-water emulsion and CO2. This is shown schematically in Figure 4.

The proportion of water bound in the CC n-water emulsion can be determined by determining the level of the water in the viewing window compared to the level of the water do in the viewing window before mixing (center of the viewing window) according to the relation [% ] = 100 ^* (do-di) / do. The proportion of the visible part of the CO2 in the window, which is bound in the emulsion can be determined in an analogous manner.

After switching off the stirrer, it can be observed how quickly the C02-in-water emulsion decays again by observing the fill levels as a function of time through the viewing window. Table 3 shows the test parameters as well as the proportions of water and CO2 that can be seen in the viewing window 1 hour after the stirrer has been switched off.

Table 2: C02-in-water emulsions at different salinities. The proportions of bound water and bound CO 2 were determined as described above by means of the ratio [%] = 100 ^* (do-di) / do.

Comments on the experiments carried out:

In the CC n-water emulsion, water forms the continuous phase and thus acts as a buffer between discrete CO 2 phases. When the CC n-water emulsion loses water, it eventually causes the discrete CO 2 phases to unite, i. the CC n-water emulsion breaks down. Deterioration of the emulsion in the petroleum formation is highly undesirable because the emulsion has a significantly higher viscosity than the supercritical CO2 (see above) and this higher viscosity is needed to avoid "fingering." It is therefore advantageous if the CC n Water emulsion in a given amount of CO2 binds the largest possible amount of water in the emulsion to keep the emulsion stable for as long as possible.The more water is bound, the more water can lose the emulsion without the emulsion decomposes, and accordingly, it takes longer for the emulsion to disintegrate.

Comparative experiments V1 to V6 show the importance of the cloud point for the formation of the C02-in-water emulsions. If the cloud point of the surfactant in water at the respective salinity is below the measurement temperature, then no CC n-water emulsions are formed.

The surfactant (I) 2-PH-14 EO-C ₃ H6-S0 ₃ K has more excellent cloud points of> 95 ° C (tests 20 and 21), even at high salinity of 160,000 ppm. Furthermore, it binds at 50 ° C and a salinity of 160,000 ppm 60% water in the CC n-water emulsion. At 65 ° C even 85% water are bound. It is therefore ideal for CO2 floods.

As already shown above, the preparation of alkylpolyalkoxysulphonates is complicated and accordingly expensive. It is therefore interesting to blend the surfactants with other surfactants for less demanding conditions. Experiments 22 and 23 show that even mixtures with the surfactants (II) and surfactants (III) in a mixing ratio of 1: 1 still bind 60 to 65% water.

Claims

claims

Process for the production of crude oil by means of C02 flooding, in which liquid or supercritical CO2 and at least one anionic surfactant (I) or a surfactant mixture comprising at least one anionic surfactant (I) are injected through at least one injection well into a crude oil deposit and the deposit through at least one production well crude oil takes, characterized in that

the at least one anionic surfactant (I) or the surfactant mixture comprising at least one anionic surfactant (I) is dissolved in liquid or supercritical CO2 and injected and / or dissolved in an aqueous medium and injected, the deposit has a storage temperature of 15 ° C to 140 ° C, the deposit water has a salinity from 20,000 ppm to 350000 ppm, the density of the CO2 under deposit conditions is from 0.70 g / ml to 0.90 g / ml, and wherein the at least one anionic Surfactant to an alk (en) ylpolyalkoxysulfonat the general formula

Carbon atoms, with the proviso that the sum of the carbon atoms of the radicals R ² + R ³ + R ⁴ + R ^{5 is} 2 to 8,

R ⁶ for methyl,

I for a number from 0 to 5

m for a number from 0 to 15

n stands for a number from 5 to 30, and

M ^{a +} for an a-valent cation, where a is 1, 2, or 3, where the radicals -OCR ² R ^{3 are} CR ⁴ R ⁵ -, -OCH ₂ CHR ⁶ - and -OCH ₂ CH ₂ - block-like in the formula ( I), and where the sum of I + m + n is from 5 to 35, provided that n> (l + m).

A method according to claim 1, characterized in that the cloud point of the surfactant (I) or the surfactant used at least one surfactant mixture (I) is at least 1 ° C above the reservoir temperature, the cloud point in reservoir water and at the concentration of the surfactant in to inject determining aqueous medium or the concentration in the liquid or supercritical CO2 to be injected.

3. The method according to claim 2, characterized in that the cloud point of the surfactant used (I) or the at least one surfactant (I) used

Surfactant mixture is at least 3 ° C above the reservoir temperature.

4. The method according to any one of claims 1 to 3, characterized in that the deposit water has a salinity of 30,000 ppm to 250,000 ppm.

5. The method according to any one of claims 1 to 3, characterized in that the deposit water has a salinity of 35,000 ppm to 200,000 ppm.

6. The method according to any one of claims 1 to 5, characterized in that the storage tem- perature is 31 ° C to 120 ° C.

7. The method according to any one of claims 1 to 5, characterized in that the deposit temperature is 35 ° C to 100 ° C. 8. The method according to any one of claims 1 to 7, characterized in that R ^{1 is} a branched alkyl radical of the formula C5Hn-CH (C3H7) -CH2-, and wherein it is at least 70 mol% of the radicals C5H11- to an n -CsHu residue.

9. The method according to claim 8, characterized in that it is at

70 to 99 mol% of the C5H11 residues around n-CsHu residues, and in

• 1 to 30 mol% of the radicals C ₅ Hn- to C2H ₅ CH (CI-l3) Cl-l2 radicals and / or CH ₃ CH (CH ₃ ) CH ₂ CH ₂ radicals.

10. The method according to claim 7 or 8, characterized in that is at the radicals C3H7- to n-C3H ₇ radicals.

1 1. Process according to Claim 1, characterized in that R ¹ is a 2-propyl-n-heptyl radical

is. 12. The method according to any one of claims 1 to 1 1, characterized in that it is a surfactant mixture comprising at least an anionic surfactant (I) and a nonionic surfactant (II) of the general formula

R ^{8 is} - (OCR ² R ³ CR ⁴ R ⁵ ) x- (OCH ₂ CHR ⁶ ) _y - (OCH ₂ CH ₂ ) z -OH (II) where R ^{8 is} a branched or linear, saturated or unsaturated aliphatic hydrocarbon radical having 8 to 22 carbon atoms, and

R ² , R ³ , R ⁴ , R ⁵ and R ^{6 have} the abovementioned meaning,

x for a number from 0 to 5,

y for a number from 1 to 15,

z is a number from 1 to 30, the radicals -OCR ² R ³ CR ⁴ R ⁵ -, -OCH ₂ CHR ⁶ - and -OCH ₂ CH ₂ - being at least 90% block-like in the formula (II) Order are arranged, and wherein the

Sum of x + y + z stands for values from 5 to 35, with the proviso that z> (x + y).

13. The method according to claim 12, characterized in that R ^{8 is} equal to R ¹ . 14. The method according to claim 12, characterized in that R ^{8 is} equal to R ¹ and I = x, m = y and n = z.

15. The method according to any one of claims 12 to 14, characterized in that the weight ratio of surfactant (I) / surfactant (II) in the surfactant mixture is 19: 1 to 1: 19.

16. The method according to any one of claims 12 to 14, characterized in that the weight ratio of surfactant (I) / surfactant (II) in the surfactant mixture is 4: 1 to 1: 9.

Method according to one of claims 1 to 1 1, characterized in that it is a surfactant mixture comprising at least one anionic surfactant (I) and a nonionic surfactant (III) of the general formula

R ⁹ -C ⁶ H ₄ -O- (OCR ² R ³ CR ⁴ R ⁵ ) u- (OCH ₂ CHR ⁶ ) v- (OCH ₂ CH ₂ ) w -OH (III), wherein

R ^{8 is} a branched or linear alkyl radical having 8 to 12 carbon atoms, and

R ² , R ³ , R ⁴ , R ⁵ and R ^{6 have} the abovementioned meaning,

u for a number from 0 to 5,

v for a number from 0 to 15,

w is a number from 5 to 30, wherein the radicals -OCR ² R ³ CR ⁴ R ⁵ -, -OCH ₂ CHR ⁶ - and -OCH ₂ CH ₂ - are arranged blockwise in the order indicated in formula (III), and wherein the sum of u + v + w stands for values from 5 to 35, with the proviso that w> (u + v).

18. The method according to claim 17, characterized in that the weight ratio of surfactant (I) / surfactant (III) in the surfactant mixture is 19: 1 to 1: 19.

19. The method according to claim 17, characterized in that the weight ratio of surfactant (I) / surfactant (III) in the surfactant mixture is 4: 1 to 1: 9.

20. The method according to any one of claims 1 to 19, characterized in that the surfactant used or the surfactant mixture is injected as a solution in water in the deposit, wherein the concentration of all surfactants together 0.02 to 2 wt .-% with respect to the solution is.

21. A method according to claim 20, characterized in that the concentration of all surfactants together 0.02 to 0.5 wt .-% with respect to the solution. 22. The method according to any one of claims 1 to 19, characterized in that the surfactant used or the surfactant mixture is injected as a solution in liquid or supercritical CO2 in the deposit, the concentration of all surfactants together 0.02 to 2 wt .-% regarding the solution of liquid or supercritical CO2. 23. The method according to claim 22, characterized in that the concentration of all surfactants together 0.02 to 0.5 wt .-% with respect to the solution of liquid or supercritical CO2.