AU2011333834A1 - Method for oil recovery using hydrophobically associating polymers - Google Patents

Abstract

The invention relates to a method for oil recovery, according to which an aqueous formulation comprising at least one water-soluble, hydrophobically associating copolymer is forced through at least one injection well in an oil deposit and crude oil is extracted from the oil deposit through at least one production well, said deposit being at a temperature of between 35°C and 120°C, preferably between 40°C and 90°C. The water-soluble, hydrophobically associating copolymer comprises at least acryl amide or derivatives thereof, a monoethylenically unsaturated monomer having anionic groups and a monoethylencally unsaturated monomer that can cause the association of the copolymer.

Description

PF71248 1 Method for oil recovery using hydrophobicay associating polymers The present invention relates to a process for mineral oil production, in which an aqueous 5 formulation comprising at least one water-soluble, hydrophobically associating copolymer is injected through at least one injection borehole into a mineral oil: deposit having a deposit temperature of 35*C to 1204C, preferably 40*C to 90*C, and crude oil is withdrawn from the deposit through at least one production borehole, wherein the water-soluble, hydrophobicaily associating copolymer comprises at least acrylamide or derivatives thereof, a monamer 10 having anionic groups and a monomer which can bring about the hydrophobic association of the copolymer, In natural mineral oil deposits, mineral all is present in the cavities of porous reservoir rocks which are sealed toward the surface of the earth by impermeable top layers. The cavities 15 may be very fine cavities, capillaries, pores or the like. Fine pore necks may, for example, have a diameter of only approx.. [im. As well as mineral oi, including fractions of natural gas, a deposit also comprises water with a greater or lesser salt content In mineral oil production, a distinction is drawn between primary, secondary and tertiary 20 production. In primary production, after commencement of drilling of the deposit, the mineral oil flows of its own accord through the borehole to the surface owing to the autogenous pressure of the deposit. The autogenous pressure can be caused, for example, by gases present in the 25 deposit, such as methane, ethane or propane, The autogenous pressure of the deposit, however, generally declines relatively rapidly on extraction of mineral oil, such that usually only approx. 5 to 10% of the amount of mineral oil present in the deposit, according to the deposit type, can be produced by means of primary production. Thereafter, the autogenous pressure is no longer sufficient to produce mineral oiL 30 After primary production, secondary production is therefore typically used, In secondary production, in addition to the boreholes which serve for the production of the mineral oil, known as the production boreholes, further boreholes are drilled into the mineral oil-bearing formation, These are known as injection boreholes, through which water is injected into the 35 deposit (known as *water flooding'}, in order to maintain the pressure or to increase it again. As a result of the injection of the water, the mineral oil is gradually forced through the cavities .n the formation, proceeding from the injection borehole, in the direction of the production borehole, However, this works only for as long as the cavities are completely filled with oil and the more viscous oil is pushed onward by the water. As soon as the mobile water breaks 40 through cavities, it flows on the path of least resistance from this time onward, i.e. through the channel formed, and no longer pushes the oil onward. By means of primary and PF71248 2 secondary production, therefore, generally only approx. 30 to 35% of the amount of mineral oil present in the deposit can be produced. After the measures of secondary mineral oil production, measures of tertiary mineral oil 5 production (also known as "Enhanced Oil Recovery (EOR)") are therefore also used to further enhance the o yield. This includes processes in which suitable chemicals, such as surfactants and/or polymers, are used as assistants for oil production. An overview of tertiary oil production using chemicals can be found, for example, in the article by D. G. Kessel, Journal of Petroleum Science and Engineering, 2 (1989) 81- 101. 10 The techniques of tertiary mineral oil production include what is known as "polymer flooding". Polymer flooding involves injecting an aqueous solution of a thickening polymer through the injection boreholes into the mineral oil deposit, the viscosity of the aqueous polymer solution being matched to the viscosity of the mineral oil. As a result of the injection of the polymer 15 solution, the mineral oil, as in the case of water flooding, is forced through the cavities mentioned in the formation, proceeding from the injecton borehole, in the direction of the production borehole, and the mineral oil is produced through the production borehole, By virtue of the fact that the polymer formulation, however, has about the same viscosity as the mineral oil, the risk is reduced that the polymer formulation breaks through to the production 20 borehole with no effect, and hence the mineral oil is mobilized much more homogeneously than in the case of use of mobile water, It is thus possible to mobilize additional mineral oil in the formation. Details of polymer flooding and of polymers suitable for this purpose are disclosed, for example, in "Petroleun Enhanced Oil Recovery, Krk-Cthme, Encyclopedia of Chemical T6echnoogy, oi ne editont, John 'Wev & Sons, 201 0 25 For polymer flooding, a mulitude of different thickening polymers have been proposed, especally high molecular weight polyacryiamide, copolymers of acrylamide and further comonomers, for example vinylsulfonic acid or acrylic acid. Polyacrylarnide may especially be partly hydrolyzed poiyacrylamide, in which some of the acrylamide units have been 30 hydrolyzed to acrylic acid. In addition, it is also possible to use naturally occurring polymers, for example xanthan or polyglycosylglucan, as described, for example, by US 6,392,596 B1 or CA 832 277. Also known is the use of hydrophobically associating copolymers for polymer flooding. These 35 are understood by the person skilled in the art to mean water-soluble polymers which have lateral or terminal hydrophobic groups, for example relatively long alkyl chains, in aqueous medium, such hydrophobic groups can associate with themselves or with other substances having hydrophobic groups. This forms an associative network by which the medium is thickened. Details of the use of hydrophobically associating copolymers for tertiary mineral oil 40 production are described, for example, in the review article by Taylr; K C and Nasr-E-Din, HA. in J Petr Sci Eng. 1998, 19, 265-280.

PF71248 3 EP 705 854 Al, DE 100 37 629 Al and DE 10 2004 032 304 Al disclose water-soluble, hydrophobically associating copolymers and the use thereof, for example in the construction chemistry sector, The copolymers described comprise acidic monomers, for example acryliC acid, vinylsulfonic acid, acrylamidomethyipropanesulfonic acid, basic monomers such as 5 acrylarnide, dinethylacrylamide, or mronomers comprising cationic groups, for example monomers having ammonium groups, and also monomers which can bring about the hydrophobic association of the individual polymer chains. Our prior application WO 20101133527 A2 discloses hydrophobically associating copolymers 10 which comprise at least hydrophilic, monoethylenically unsaturated monomers, for example acrylamide, and monoethylenically unsaturated, hydrophobically associating monomers. The hydrophobically associating monomers have a block structure and have - in this sequence an ethylenically unsaturated group, optionally a linking group, a first polyoxyalkylene block which comprises at least 50 mcl% of ethyleneoxy groups, and a second polyoxyalkyene 15 group which consists of alkyleneoxy groups having at least 4 carbon atoms. The application discloses the use of such copolymers as thickeners, for example for polymer flooding, for construction chemical applications or for detergent formulations, Our prior application WO 20111015520 Al discloses a process for preparing hydrophobically 20 associating copolymers by polymerizing water-soluble, monoethylenically unsaturated surface-active monomers and monoethyienically unsaturated hydrophilic monomers in the presence of surfactants, and the use of such copolymers for polymer flooding. For polymer flooding, an aqueous polymer solution is injected through a borehole (called the 25 injection borehole) into a mineral oil deposit, and the viscosity of the polymer solution under formation conditions should correspond approximately to the viscosity of the mineral oil. Suitable polymers for polymer flooding must therefore also have the thickening action under the conditions of the mineral oil deposit, he. at temperatures above room temperature and in the presence of formation water with a high salt content. Formation waters may in the ex 30 treme case comprise up to 35% by weight of salts. The salts are, for example, alkali metal salts, but also alkaline earth metal salts. Formation temperatures may be up to 150*C, Studies on partly hydrolyzed polyacrylamide and copolymers of acrylamide and acryiamide methylpropanesulfonic acid show that the salt tolerance of the polymers can be enhanced by 35 the incorporation of suflo groups (see, for example, Masoud Rashidi, Anno Mardt Blokhus, Arrem Skauge, Journal of Appied Polyrner Science, Vol 117 (2010), pages 1551-1557). In the case of such polymers, however, the viscosity decreases with increasing temperature, Thus, to achieve a viscosity sufficient for polymer flooding, higher amounts of polymer have to be used, which impairs the economic viability of polymer flooding. 40 PF71248 4 It was an object of the invention to provide a process for polymer tiooding with which satisfactory results are achieved even at relatively high formation temperatures. Accordingly, a process for mineral oil production has been found, in which an aqueous 5 formulation comprising at least one water-soluble, hydrophobically associatng copolymer Is injected through at least one injection borehole into a mineral oli deposit, and crude oil is withdrawn from the deposit through at least one production borehole, and wherein e the water-soluble, hydrophobically associating copolymer composes 10 (a) 01 to 15% by weight of at least one manoethylenically unsaturated, hydrophobically associating monomer (a) of a selected from the group of

H

2

C=C(R'>R

2 O+CHrCH (RS)-O-)r(-CHtCH (RA)~O-)rRS (i)l 15 H2=(3-C=)OCrH( -- a(Ill), 20 where the *(-CH 2 CH(R)O-) and ±CH 2 -CH(R)O-)j units are arranged in block structure in the sequence shown in formula (1) and the radicals and indices are each defined as follows: k: a number from 10 to 150, 25 1, a number from 5 to 25,

R

1 : H or methyl, Ra a single bond or a divalent linking group selected from the group of -C>Ha)-t [R)., ~O(CeH 2 )- [R and -C(O)CO(CrcH 2 W)- [Rt], where n, n and n" are each natural numbers from I to 6, 30 R each independently H, methyl or ethyl, with the proviso that at least 50 moi% of the R 2 radicals are H, R: each independently a hydrocarbyl radical having at least 2 carbon atoms or an ether group of the general formula -CH2-)-R 4 where R 4 ' is a hydrocarbyl radical having at least 2 carbon atoms, 35 RN H or a hydrocarbyl radical having 1 to 30 carbon atoms, R6 an aliphatic and/or aromatic, straight-chain or branched hydrocarbyl radical having 8 to 40 carbon atoms, and also 40 PF71248 (b) 85 to 99.9% by weight of at least two monoethylenically Unsaturated, hydrophiic monomers (b) different than (a), where the monomers (b) comprise 5 (bi) at least one uncharged, monoethylenically unsaturated, hydropilic monomer (b1), selected from the group of (meth)acrylamide, N-methyi(meth)acrylamide, NN-dimethyi(meth)aorylamride or N-rnethyloi(meth)acrlamide, and 10 (b2) at least one anionic, rnonoethylenically unsaturated, hydrophilic monomer (b2) which at least one acidic group selected from the group of -COOH, -SOH and -PO 3

H

2 and salts thereof, where the proportions are each based on the total amount of all monomers in the 15 copolymer, * the copolymer has a weight-average molecular weight Mw of 1*10 g/mol to 30*10 g/mol, 20 0 the amount of the copolymer in the formulation is 0.02 to 2% by weight, and * the temperature of the mineral oli deposit is 35"C to 120*C In a preferred embodiment of the invention, the temperature of the mineral oil deposit is 40"C 25 to 90*C, in a further preferred embodiment, the aqueous formulation further comprises salits in an amount of 20 000 ppm to 350 000 ppm. 30 It has been found that, surprisingly, the viscosity of the aqueous polymer formulations used for the process at first does not decrease with rising temperature, but actually increases. The viscosity passes through a maximum and begins to decrease again only at higher tempera tures. This achieves a particularly good ratio of viscosity achieved to amount of substance used. 35 With regard to the invention, the following should be stated specifically: Hydrophobically associatn9copolymers used 40 For the process according to the invention for mineral oiW production, an aqueous formulation of at least one water-soluble, hydrophobically associating copolymer is used and is injected through an iniection borehole into a mineral oil deposit, PF71248 6 The term "hydrophobically associating copolymers" is known in principle to those skilled in the art, This comprises waterasoIuble copolymers which, as well as hydrophilic molecular 5 components, have hydrophobic groups In aqueous solution, the hydrophobic groups can associate with themselves or with other substances having hydrophobic groups due to intermolecular forces. This gives rise to a polymeric network joined by intermolecular forces, which thickens the aqueous medium. 10 In the ideal case, the copolymers used in accordance with the invention should be miscible with water in any ratio. According to the invention, however, It is sufficient when the copolymers are water-soluble at least at the desired use concentration and at the desired pH. In general, the solubility of the copolymer in water at room temperature under the use conditions should be at least 25 g&t 15 According to the invention, the water-soluble, hydrophobically associating copolymer comprises 0.1 to 15% by weight of at least one monoethylenically unsaturated, hydrophobically associating monomer (a) and 85 to 99.9% by weight of at least two monoethylenicaliy unsaturated, hydrophilic monomers (b) different than (a). In addition, it is 20 optionally possible for further, ethylenically unsaturated, preferably rnonoethylenicaliy unsaturated, monomers (c) different than the monomers (a) and (b) to be present in an amount of up to 14.9% by weight. The amounts mentioned are based in each case on the sum of all monomers in the copolymer. Preference is given to using exclusively monoethylenically unsaturated monomers. 25 Monomers (a) The water-soluble, hydrophobically associating copolymer used comprises at least one 30 monoethylenically unsaturated monomer (a) which imparts hydrophobically associating properties to the copolymer and shall therefore be referred to hereinafter as "hydrophobically assolating monomer According to the invention, the monomers (a) are selected from the group of 35 H (I), 40 PF71248 7 Monomers (a) of the formuLa (1) in the monomers (a) of the formula (1), an ethylenic group H2C=C(R 1 )- Is bonded via a divalent linking group -R 2 -0- to a polyoxyalkylene radical with block structure 5 +CHr-CH(R>)O)(CHrcH(Rt0)I-RQ where the two blocks -CHrCH(R3)-0) and (CHrCH(R 4 )04) are arranged in the sequence shown in formula (1). The polyoxyalkylene radical has either a terminal OH group (for R=H) or a terminal ether group -OR' (if R 5 is a hydrocarbyl radical), 10 in the abovementioned formula, R1 is H or a methyl group, R2 is a single bond or a divalent linking group selected from the group of -(CH)- [R 2 group], -O-(CH2)- [R" group]- and -C(0)--(CvH)-

{R

2 group]. In the formulae mentioned, n, n and n" are each a natural number from 1 to 6. In other words, the linking 15 group comprises straight-chain or branched aliphabc hydrocarbyl groups having I to 6 hydrocarbon atoms, which are joined to the ethylenic group HCC(R)- directly, via an ether group -0- or via an ester group -C(O)-0-. The -(C ),. CH2)- and -(C 1 -HW')- groups are preferably linear aliphatic hydrocarbyl groups. 20 The R2 group is preferably a group selected from -CH- -CHrCH- and -CHrCHr-CHr, more preferably a methylene group -CHr. The R2 group is preferably a group selected from -- CH-CHr, -0-CH-CH-CH- and -0&CH-CH 2 -CHrCHr, more preferably -O-CH-CHrCHrCHZ-. 25 The Rk group is preferably a group selected from -C(0)-0-CH 2 -CH-, -G(O)O-CH(CHz) CHt -C(O)O-CH-CH(CHj7), -C(0)0-CH -0H-CH 2 -CH- and -C(0)0-CH 2 -CHrCHr-CHr

CH

2 CH-, more preferably -C(0)-0-CH-CH 2 and -C(O)O-C-CHrCHrCH2-, and most preferably -C(O)-O-CH-CH.

30 The R group is more preferably an R or R 2 a group, more preferably an R4b group, In addition, R 2 is more preferably a group selected from -- CH 2 - and -0-CHrCHrCHrCHr, most preferably -O-CHrCHrOCH-, 35 The monomers (I) also have a polyoxyalkylene radical which consists of the units

+CH

2

-CH(R

3 )-)X and -(-CH 2 -CH(R4)-04 where the units are arranged in block structure in the sequence shown in formula (I). The transition between the two blocks may be abrupt or else continuous, 40 In the -CHr-CH(R 3 -O-), block, the Ra radicals are each independently H, methyl or ethyl, preferably H or methyl, with the proviso that at east 50 mol% of the R radicals are H, PF71248 a Poferably at least 75 moi% of the R radicals are H, more preferably at least 90 mol%, and they are most preferably exclusively H, The block mentioned is thus a polyoxyethylene block which may optionally also have certain proportions of propylene oxide and/or butylene oxide units, preferably a pure polyoxyethylene block. The number of alkyene oxide units k is a number from 10 to 150, preferably 12 to 100, more preferably 15 to 80, even more preferably 20 to 30 and, for example, approx. 22 to 25. It is clear to the person skilled in the art in the field of the polyaikylene oxides that the numbers mentioned are averages of distributions. 10 in the second (-HtCH(RTO- block, the R 4 radicals are each independently hydrocarbyl radials of at least 2 carbon atoms, preferably at least 3, more preferably 3 to 10 and most preferably 3 to 8 carbon atoms and for example 3 to 4 carbon atoms. This may be an aliphatic and/or aromatic, linear or branched carbon radical, it is preferably an aliphatic 15 radical Examples of suitable R4 radicals comprise ethy, n-propyi, n-butyl, n-pentyl, n-hexyi n-heptyl, n-octyl, n-nonyl or n-decyl, and phenyL Examples of preferred radicals comprise n-propyl, n-butyl, n-pentyl, particular preference being given to an n-propyi radical. 20 The P4 radicals may also be ether groups of the general formula -CHVXR' where RA is an aliphatic and/or aromatic, linear or branched hydrocarby radical having at least 2 carbon atoms, preferably at least 3 and more preferably 3 to 10 carbon atoms, Exampies of R.T radicals comprise n-propyl, nbutyl n-pentyl, r4hexy. 2-ethyihexyi, n-hepty, n-octyt r-nonry 25 n-decyl or phenyl. The (CH 2 -CH(RTO-)r block is thus a block which consists of alkylene oxide units having at least 4 carbon atoms, preferably at least 5 carbon atoms, especially 5 to 10 carbon atoms, and/or glycidyl ethers having an ether group of at least 2, preferably at least 3, carbon atoms. 30 Preferred Ra radicals are the hydrocarbyl radicals mentioned; the units of the second terminal block are more preferably alkylene oxide units comprising at least 5 carbon atoms, such as pentene oxide units or units of higher alkylene oxides. The number of alkylene oxide units I is a number from 5 to 25, preferably 6 to 20, more 35 preferably 8 to 18, even more preferably 10 to 15 and, for example, approx. 12. The R5 radical is H or a preferably aliphatic hydrocarbyi radicaI having I to 30 carbon atoms, preferably 1 to 10 and more preferably 1 to 5 carbon atoms. Ra is preferably H, methyl or ethyl, more preferably H or methyl and most preferably H. 40 in the monomers of the formula (1), a terminal monoethylenic group is joined to a poiyoxyalkyiena group with block structure, specifically firsty to a hydrophil:c block having PF71248 polyethylene oxide units, which is in turn joined to a second terminal hydrophobic block formed at least from butene oxide units, preferably at least penfene oxide units, or units of higher alkylene oxides, for example dodecene oxide. The second block has a terminal -OR group, especially an OH-group. The terminal %OHrCH(R 4 )-O-)i block with the R 4 radicals is 5 responsible for the hydrophobic association of the copolymers prepared using the monomers (a). Etherification of the OH end group is an option which may be selected by the person skilled in the art according to the desired properties of the copolymer. A terminal hydrocarbyl group is, however, not required for the hydrophobic association, and the hydrophobic association also works with a terminal OH group. 10 It is clear to the person skilled in the art in the field of polyalkylene oxide block copolyrners that the transition between the two blocks, according to the method of preparation, may be abrupt or else continuous. In the case of a continuous transition, there is a transition zone between the two blocks, which comprises monomers of both blocks. When the block 15 boundary is fixed at the middle of the transition zone, the first block +CHrCH(R 3 )O)kmay accordingly also have small amounts of -CHrCH(R 4 )O- units and the second block -{-CHrCH(R 4 )) small amounts of -CH 2 -CH(R)4 units, though these units are not distributed randomly over the block but arranged in the transition zone mentioned. 20 Proparatbn of the monomers (a) of the formula The hydrophobically associating monomers (a) of the fon-nula (1) can be prepared by methods known in principle to those skilled in the art. 25 To prepare the monomers (a), a preferred preparation process proceeds from suitable monoethylenically unsaturated alcohols (IV) which are subsequently alkoxylated in a two stage process such that the block structure mentioned is obtained. This gives monomers (a) of the formula (1) where R5 = H. These can optionally be etherified in a further process step. 30 The type of ethylenicalLy unsaturated alcohols (IV) to be used is guided here especially by the R group. When R2 is a single bond, the starting materials are alcohols (IV) of the general formula HgC=C(R1)-O-CH 2 CH(R)O-),H (Na) where R 1 is as defined above, Rr is H and/or CHs, 35 preferably H, and d is from I to 5, preferably 1 or 2. Examples of such alcohols comprise diethylene glycol vinyl ether HtC=CH=CXCH 2 -CHrO-CHv'CH-OH or dipropylene glycol vinyl ether H 2 C=CH-O-CHrCH(CH-O-CH2-CH(CHOH, preferably diethylene glycol vinyl ether To prepare monomers (a) in which R2 is not a single bond, it is possible to use alcohols of 40 the general formula H 2 C0C(R1)-RtOH (Mb) or alcohols which already have alkoxy groups and are of the formula H2C=C(R)-R 2 -O)(-CHrCH(Rr) ),H (Ic), where R and d are each as defined above, and R in each case is selected from the group of R- R, and R PF71248 10 The preparation of the monomers with a linking R 2 s group preferably proceeds from alcohols of the formula H 2 C=C(R1)-(CnH)-OH, especially H 2

C=CH-(CH

2 }-OH, or alcohols of the formula H2C4CR)OtCHrCH(R-O-)dH. Examples of preferred alcohols comprise allyl 5 alcohol H2C=CH-CH 2 -OH or isoprenot H2C=C(CHa)CHrCH2-OH. The preparation of the monomers with a linking R@ group proceeds from viny ethers of the formula H 2 C=C(R)O-(Crrkv)-OH, preferably H It is more preferably possible to use (ohydroxybutyl vinyl ether H 2

C=CH--CH

2 -CH-CH2-CHrOH. 10 The preparation of the monomers with a linking Rt group proceeds from hydroxyalkyl (meth)acrylates of the general formula H 2 C=C(R)C()O(CrrHn)-OH, preferably H- C Examples of preferred hydroxyalkyl (meth)acrylates comprise hydroxyethyl (meth)acrylate H 2 C=C(RG)-C(O)-O 2 -CH-OH and hydroxybuty 15 (meth)acrylate H 2 C=C(R)-(O-OHrCHrCHrCHrOH. The starting compounds mentioned are alkoxylated, specificay in a two-stage process, first with ethylene oxide, optionally in a mixture with propylene oxide and/or butylene oxide, and in a second step with alkylene oxides of the general formula (Xa) or (Xb) 20 0 0 4 7X)I (Xb) R CHO where R 4 in (Xa) and R 4 ' in (Xb) are each as defined at the outset. 25 The performance of an alkoxylation including the preparation of the block copolymers from different alkylene oxides is known in principle to those skilled in the art, It is likewise known to those skilled in the art that the reaction conditions, especially the selection of the catalyst, can influence the molecular weight distribution of the alkoxylates and the orientation of the alkylene oxide units in a polyether chain. 30 The alkoxylates can be prepared, for example, by base-cataiyzed alkoxylation. For this purpose, the alcohol used as the starting material can be admixed in a pressure reactor with alkali metal hydroxides, preferably potassium hydroxide, or with alkali metal alkoxides, for example sodium methoxide, By means of reduced pressure (e.g. <1CO mbar) and/or 35 increasing the temperature (30 to 150'C), water still present in the mixture can be removed. Thereafter, the alcohol is present as the corresponding alkoxide. This is followed by inertization with inert gas (e.g. nitrogen) and, a a first step, stepwise addition of ethylene oxide, optionally in a mixture with propylene oxide and/or butylene oxide, at temperatures of 60 to 180"C, preferably 130 to 150 C. The addition is typically effected within 2 to 5 h, though 40 the invention should not be restricted thereto. After the addition has ended, the reaction PF71248 11 mixture is appropriately allowed to continue to react, for example for % h to I h. In a second step, alkylene oxides of the general formula (Xb) are subsequently metered in stepwise. The reaction temperature in the second stage can be maintained or else altered. A reaction temperature lower by approx., 10 to 25*C than in the first stage has been found to be useful. The alkoxylation can also be undertaken by means of techniques which lead to narrower molecular weight distributions than the base-catalyzed synthesis. For this purpose, the catalysts used may, for example, be double hydroxide clays as described in DE 43 25 237 Al. The alkoxylation can more preferably be effected using double metal 10 cyanide catalysts (DMC catalysts). Suitable DMC catalysts are disclosed, for example, in DE 102 43 361 Al, especially paragraphs [0029) to [0041] and the literature cited therein. For example, it is possible to use catalysts of the Zn-Co type. To perform the reaction, the alcohol used as the starting material can be admixed with the catalyst, and the mixture can be dewatered as described above and reacted with the alkylene oxides as described. 15 Typically, not more than 250 ppm of catalyst based on the mixture are used, and the catalyst can remain in the product due to this small amount. The alkoxylation can additionally also be undertaken under acid catalysis The acids may be Bronsted or Lewis acids. To perform the reaction, the alcohol used as the starting material 20 can be admixed with the catalyst, and the mixture can be dewatered as described above and reacted with the alkylene oxides as described. At the end of the reaction, the acidic catalyst can be neutralized by addition of a base, for example KOH or NaOH, and filtered off if required 25 It is clear to the person skilled in the art in the field of the polyalkylene oxides that the orientation of the hydrocarbyl radicals R 4 and optionally R- may depend on the conditions of the alkoxylation, for example on the catalyst selected for the alkoxylation. The alkylene oxide groups can thus be incorporated into the monomer either in the -(H-CH(R 4 )-O-) orientation or else in the inverse -(~CH(R)-CHtO-0+ orientation. The description in formula (i) should 30 therefore not be considered to be restricted to a particular orientation of the R3 or R4 groups. When the terminal OH group of the monomers (a) of the formula (1) (i.e. R5 = H) is to be etherified, this can be accomplished with customary alkylating agents known in principle to those skilled in the art, for example alky sulfates, For etherification, it is especially possible 35 to use dimethyl sulfate or diethy sulfates. The preferred preparation process described for the monomers (1) has the advantage that the formation of potentially crosslinking by-products with two ethylenically unsaturated groups is substantially avoided. Accordingly, it is possible to obtain copolymers with a 40 particularly low gel content PF71248 12 Monomers (a) of the formulae (11) and (1I) in the monomers of the formulae (11) and (111), Ri, R3 and k are each defined as already outlined. 5 R is an aliphatic and/or aromatic, straight-chain or branched hydrocarbyl radical having B to 40 carbon atoms, preferably 12 to 32 carbon atoms. For example, it may comprise n-aikyl groups such as n-octyl, n-decyl or n-dodecy[ groups, phenyl groups, and especially substituted phenyl groups. Substituents on the phenyl groups may be alkyl groups, for 10 example CrQGalkyl groups, preferably styryl groups. Particular preference is given to a tristyrylphenyl group. The hydrophobically associating monomers of the formulae (Ui) and (111) and the preparation thereof are known in principle to those skilled in the art, for example from EP 705 854 Al. 15 Amounts of monomers (a) The amount of the monoethylenically unsaturated, hydrophobically associating rnonomers (a) is 0.1 to 15% by weight, based on the total amount of all monomers in the copolymer, 20 especially 0.1 to 10% by weight, preferably 0.2 to 5% by weight and more preferably 0.5 to 2% by weight. Particular preference is given to using monomers (a) of the general formula (1) to prepare the inventive copolymers, most preferably monomers (a) of the general formula (i) in which RW is 25 an R2 radical Monomers b) Over and above the monomers (a), the hydrophobically associating copolymer used in 30 accordance with the invention comprises at least two monoethylenically unsaturated, hydrophilic monomers (b) different than (a) More preferably, the hydrophilic monomers (b) used are miscible with water in any ratio but It is sufficient for execution of the invention that the inventive, hydrophobically associating 35 copolymer possesses the water solubility mentioned at the outset. In genera, the solubility of the monomers (b) in water at room temperature should be at least 50 g/i, preferably at least 150 g/l and more preferably at least 250 g/L According to the invention, the copolymer comprises at least one at least one uncharged, 40 monoethylenicasly unsaturated, hydrophilic monomer (bi) selected from the group of (meth)acrylarnide, N-methyl(meth)acrylamide, N,N'-dimethyl(meth)acrylamide or N-methylok (meth)acrylamide, Preference is given to (meth)acrylamide, especially acrylamide. When PF71248 13 mixtures of different monomers (h1) are used, at least 50 mot% of the monomers (b1) should be (meth)acrylamide, preferably acrylamide. According to the invention, the copolymer used further comprises at least one hydrophilic, 5 monoethylenically unsaturated anionic monomer (b2) which comprises at least one acidic group ,elected from the group of -COOH, -SO 3 H and -PO 3

H

2 and salts thereof. Preference is given to monomers comprising COH groups and/or -SO3H groups, particular preference to monomers comprising -SO,H groups, The monomers may of course also be the salts of the acidic monomers. Suitable counterions comprise especially alkali metal ions such as Lit, 10 Na+ or K+, and ammonium ions such as NFH or ammonium ions with organic radicals. Examples of monomers comprising COOH groups comprise acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid or fumaric acid. Preference is given to acrylic acid. 15 Examples of monomers comprising sulfo groups comprise vinyisulfonic acid, allylsulfonic acid, 2-acryamido~2-methypropanesulfonic acid, 2-rnethacryiamido-2-methylpropanesulfonic acid, 2-acrylamidobutaresulfonic acid, 3-acrylamido-3-methyibutanesulfonic acid or 2-acrylamido-2,4,4-trimethypentanesulfonic acid. Preference is given to vinylsulfonic acid, allyisuifonic acid or 2-acrylamido-2-methylpropanresulfonic acid, and particular preference to 20 or 2-acrylamndo-2-methylpropanesulfonic acid. Examples of monomers comprising phospho groups comprise vinylphosphonic acid, allyiphosphonic acid, N-(meth)acrylamidoaikylphosphonic acids or (rneth)acryloyloxyakyl phosphonic acids, preference being given to vinylphosphonic acid. 25 For the sake of completeness, it should be mentioned that the monomers (bl) can be hydrolyzed at least partly to (meth)acrylic acid under some circumstances in the course of preparation and use. The copolymers used in accordance with the invention may accordingly comprise (meth)acrylic acid units, even if no (meth)acrylic acid units at all have been used for 30 the synthesis. The tendency to hydrolysis of the monomers (bl) decreases with increasing content of sulfa groups. Accordingly, the presence of sulfo groups in the copolymer used in accordance with the invention is advisable. The copolymers used in accordance with the invention may additionally optionally comprise 35 at least one manoethylenically unsaturated, cationic monomer (b3) having ammonum ions. Suitable cationic monomers (b3) comprise especially monomers having ammronkrn groups, especially ammonium derivatives of N-(-aminoalkyi)(meth)acryiam.ides or waminoaiky (meth)acrylic esters. 40 More particularly, monomers (3) having ammonium groups may be compounds of the general formulae H 2

C=C(R)CO-NRR

1 NR*X (Va) and/or H 2

C=C(R)-COO-RIO-

PF71248 14 NRW+X- (Vb).. In these formulae, R 8 is H or methyl R is H or a CrC 4 si-alkyl group, preferably H or methyl, and RIG is a preferably linear CrC-alkylene group, for example a I 2-ethylene group -CHYCH - or a 1,3-propylene group -CH-rCH2-CHr-. 5 The R radicals are each independently C1-Crakyl radicals, preferably methyl, or a group of the general formula -RttSOsH where R.

2 is a preferably linear C 1 -Cralkylene group or a phneryl group, Wth the proviso that generally not more than Ole of the R1 substituents is a substituent having sulfo groups. More preferably, the three R: 1 substituents are methyl groups, i.e. the monomer has a -N(C1als+ group. X- in the above formula is a monovalent 10 anion, for example Cl. X- may of course also be a corresponding fraction of a polyvalent anion, though this is not preferred. Examples of preferred monomers (b3) of the general formula (Va) or (Vb) comprise salts of 3-trimethylammoniopropyl(meth)acrylamides or 24rimethylammonioethyl (meth)acrylates, for example the corresponding chlorides such as 3-trimethyiarnmoniopropylacrylamide choride (DIMAPAQUAT) and 2-trimethyl 15 ammoniornethyl methacrylate chloride (MADAM E-QUAT). The copolymers used in accordance with the invention may additionally also comprise further monoethylenically unsaturated hydrophilic monomers (b4) different than the hydrophilic monomers (b1), (b2) and (b3). Examples of such monomers comprise monomers comprising 20 hydroxyl groups and/or ether groups, for example hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, allyl alcohol, hydroxyvinyl ethyl ether, hydroxyvinyl propyl ether, hydroxyvinyl butyl ether, or compounds of the formula H2C=V(R1)-COO+CHrCH(RM)-a) or

H-CC(R

1 )-CHCH(R-)-Os),R! (Vlb), where R 1 is as defined above and b is a number from 2 to 200, preferably 2 to 100, The R- radicals are each independently H, methyl or 25 ethyl, preferably H or methyl, with the proviso That at least 50 mol% of the R'a radicals are H. Preferably at least 75 mol% of the R1 radicals are H, more preferably at least 90 mol%, and they are most preferably axcusively H. The R 1 4 radical is H, methyl or ethyl, preferably H or methyl. Further examples of monomers (b4) comprise N-vinyl derivatives, for example N vinylformarnide, N-vinylacetamide, N-vinylpyrrolldone or N-vinylcaprolactam, and vinyl 30 esters, for example vinyl ornate or vinyl acetate, N-Vinyl derivatives can be hydrolyzed after polymerization to give vinylamine units, and vinyl esters to give vinyl alcohol units. The amount of all hydrophilic monomers (b) in the inventive copolymer is, in accordance with the invention, 85 to 99.9% by weight, based on the total amount of all monomers in the 35 copolymer, preferably 90 to 99.8% by weight. The amount of the uncharged, hydrophilic monomers (b1) here is generally 30 to 95% by weight, preferably 30 to 85% by weight and more preferably 30 to 70% by weight, based on the total amount of all monomers used. 40 When the copolymer comprises only uncharged monomers (bi) and anionic monomers (b2), it has been found to be useful to use the uncharged monomers (b1) in an amount of 30 to PF71248 15 95% by weight and the anionic monomers (b2) in an amount of 4,9 to 69.9% by weight, each amount being based on the total amount of all monomers used. In this embodiment, the monomers (h1) are preferably used in an amount of 30 to 80% by weight and the anionic monomers (b2) in an amount of 19.9 to 69.9% by weight, and the monomers (bi) are more 5 preferably used in an amount of 40 to 70% by weight and the anionic monomers (b2) in an amount of 29.9 to 59.9% by weight When the copolymer comprises uncharged monomers (b1), anionic monomers (b2) and cationic monomers (b3), it has been found to be useful to use the uncharged monomers (b1) 10 in an amount of 30 to 95% by weight, and the anionic (b2) and cationic (b3) monomers together in an amount of 4.9 to 699% by weight, with the proviso that the molar (b2)/(b3) ratio is 0.7 to 13. The molar (b2);(b3) ratio is preferably 0.8 to 12 and, for example, 0.9 to 1 A This measure makes it possible to obtain copolymers which are particularly insensitive to salt burden. in this embodiment, the monomers (b1) are used in an amount of 30 to 80% by 16 weight, and the anionic and cationic monomers (b2) + (b3) together in an amount of 19.9 to 69.9% by weight, and the monomers (b1) are more preferably used in an amount of 40 to 70% by weight and the anionic and cationic monomers (b2) + (b3) together in an amount of 29.9 to 59.9% by weight, where the molar ratio already mentioned should be observed in each case. 20 Monomers (c) In addition to the hydrophilic monomers (a) and (b), the inventive copolyners may optionMly comprise ethylenically unsaturated monomers different than the monomers (a) and (b) 25 preferably monoethylenically unsaturated monomers (c). Of course, it is also possible to use mixtures of a plurality of different monomers (c). Such monomers can be used for fine control of the properties of the copolymer used in accordance with the invention. If present at all, the amount of such optionally present 30 monomers (c) may be up to 14.9% by weight, preferably up to 9.9% by weight, more preferably up to 4.9% by weight, based in each case on the total amount of all monomers, Most preferably, no monomers (c) are present. The monomers (c) may, for example, be monoethylenically unsaturated monomers which 35 have more hydrophobic character than the hydrophilic monomers (b) and wh ich are accordingly water-soluble on y to a minor degree. In general, the solublity of the monomers (c) in water at room temperature is less than 50 g1l, especially less than 30 g/l. Examples of such monomers comprise N-.alkyl- and NN-diaikyl(meth~acrylaides, where the number of carbon atorns in the alkyl radicals together together is at least 3, preferably at least 4, 40 Examples of such monomers comprise N-buty(meth)acrylamide,

N

cyclohexyi(m eth)acrylamide or N-benzyl(meth)acrylamide.

PF71248 16 Preparation of the hydrophobically associatingcopolymers The copolymers used in accordance with the invention can be prepared by methods known 5 in principle to those sled in the art, by free-radical polymerization of the monomers (a), (b) and optionally (c), for example by solution or gel polymerization in the aqueous phase. For polymerzation, the monomers (a), (b), optionally (c), initiators and optionally further assistants for polymerization are used in an aqueous medium 10 in a preferred embodiment, the preparabon is undertaken by means of gel polymerization in the aqueous phse. For gel polymerization, a mixture of the monomers (a), (b) and optionally (c), initiators and optionally further assistants with water or an aqueous solvent mixture is first provided. Suitable aqueous solvent mixtures comprise water and water-miscible organic 15 solvents, where the proportion of water is generally at least 50% by weight, preferably at least 80% by weight and more preferably at least 90% by weight. Organic solvents in this context include especialy water-miscible alcohois such as methanol, ethanol or propanol. Acidic monomers car be fully or partly neutralized before the polymerization. The concentration of all components except the solvents in the course of the polymerization is 20 typically approx. 20 to 60% by weight, preferably approx, 30 to 50% by weight The polymerization should especially be performed at a pH in the range from 5.0 to 7.5 and preferably at a pH of 6.0. 25 Polymerization in the presence of a nonpolymerizable, interface-active compound In a preferred embodiment of the invention, the copolymers used are prepared in the presence of at least one nonpolymerizabie, surface-active compound (T). 30 The nonpolymerizable, surface-active compound (T) is preferably at least one nonionic surfactant, but anionic and cationic surfactants are also suitable to the extent that they do not take part in the polymerization reaction. They may especially be surfactants, preferably nonionic surfactants, of the general formula Rs&Y' where R13 is a hydrocarbyl radical having 8 to 32, preferably 10 to 20 and more preferably 12 to 18 carbon atoms, and Y' is a 35 hydrophilic group, preferably a nonionic hydrophilic group, especially a polyalkoxy group, The nonionic surfactant is preferably an ethoxylated long-chain aliphatic alcoho which may optionally comprise aromatic components. Examples include: CuC4-fatty alcohol ethoxylates, Cieia-fatty alcohol ethoxylates, Ceoxo 40 alcohol ethoxylates, Cr-oxo alcohol ethoxylates, CciCxioxo alcohol ethoxylates, CwiGuerbet alcohol ethoxylates and aikyiphenol ethoxylates. Useful compounds have especially been found to be those having 5 to 20 ethyleneoxy units, preferably 8 to 18 PF71248 17 ethyleneoxy units. it is optionally also possible for small amounts of higher alkyleneoxy units to be present, especially propyleneoxy and/or butyleneoxy units, though the amount in the form of ethyleneoxy units should generally be at least 80 mol% based on all alkyleneoxy units. 5 Especially suitable are surfactants selected from the group of the ethoxylated alkylphenols, the ethoxylated, saturated iso-C13-alcohols and/or the ethoxylated Ci0-Guerbet aicohois, where in each case 5 to 20 ethyleneoxy units, preferably 8 to IS ethyleneoxy units, are present in alkoxy radicals. 10 Surprisingly, the addition of nonpolymerizable, interface-active compounds (T) during the polymerization leads to a distinct improvement in performance properties of the copolymer in polymer flooding. More particularly, the thickening action is increased and the gel content of the copolymer is also reduced. This effect can probably be explained as follows, without any 15 intention that the invention thus be tied to this explanation. In the case of polymerization without presence of a surfactant, the hydrophobically associating comonomers (a) form micelles in the aqueous reaction medium. In the polymerization, this leads to blockwise incorporation of the hydrophobically associating regions into the polymer, If, in accordance with the invention, an additional surface-active compound is present in the preparation of the 20 copolymers, mixed micelles form. These mixed micelles comprise polymerizable and nonpolymerizable components. As a result, the hydrophobically associating monomers are then incorporated in relatively short blocks. At the same time, the number of these relatively short blocks is greater per polymer chain. Thus, the structure of the copolymers prepared in the presence of a surfactant differs from those without the presence of a surfactant, 25 The nonpolymerizable, interface-active compounds (T) can generally be used in an amount of 0.1 to 5% by weight, based on the amount of all monomers used. The weight ratio of the nonpolymerizable, interface-active compounds (T) used to the 30 monomers (a) is generally 4:1 to 1:4, preferably 2:1 to 1:2, more preferably 1.5:1 to 1:15 and, for example, approx. 1: 1 Performance of the polymerization 35 For the polymerization, the components required are first mixed with one another, The sequence with which the components are mixed for polymerization is unimportant; what is important is merely that, in the preferred polymerization method, the nonpolymerizable, interface-active compound (T) is added to the aqueous polymerization medium before the initiation of the polymerization. 40 The mixture is subsequently polymerized thermally and/or photochemically, preferably at -5*C to 80*C. If polymerization is effected thermally, preference is given to using PF71248 16 polymerization initiators which can initiate the polymerization even at comparatively low temperature, for example redox initiators. The thermal polymerization can be undertaken even at room temperature or by heating the mixture, preferably to temperatures of not more than 50*C. The photochemical polymerization is typicaly undertaken at temperatures of -5 to 5 10C. It is also possible to combine photochem ical and thermal polymerization with one another, by adding both initiators for the thermal and photochemical polymerization to the mixture. In this case, the polymerization is first initiated photochemically at low temperatures, preferably -5 to +1 *C. The heat of reaction released heats the mixture, which additionally initiates the thermal polymerization, By means of this combination, it is possible to achieve a 10 conversion of more than 99%, in a further preferred embodiment of the polymerization, it is also possible to perform the reaction with a mixture of a redox initiator system and a thermal initiator which does not decompose until relatively high temperatures. This may, for example, be a water-soluble azo initiator which decomposes within the temperature range from 40"0 to 70*C. The 15 polymerization here is at first initiated at low temperatures of, for example, 0 to 10*C by the redox initiator system. The heat of reaction released heats the mixture, and this additionally initiates the polymerization by virtue of the initiator which does not decompose until relatively high temperatures. 20 The gel polymerization is generally effected without stirring. It can be effected batciwise by irradiating and/or heating the mixture in a suitable vessel at a layer thickness of 2 to 20 cn. The polymerization gives rise to a solid gel. The polymerization can also be effected continuously, For this purpose, a polymerization apparatus is used, for example, which possesses a conveyor belt to accommodate the mixture to be polymerized. The conveyor 25 belt is equipped with devices for heating and/or for irradiating with UV radiation. In this method, the mixture is poured onto one end of the belt by means of a suitable apparatus, the mixture is polymerized in the course of transport in belt direction, and the solid gel can be removed at the other end of the belt. 30 The gel obtained is preferably comminuted and dried after the polymerization. The drying should preferably be effected at temperatures below 100*C. To prevent conglutination, it is possible to use a suitable separating agent for this step. This gives the hydrophobically associating copolymer as granules or powder. 35 Further details of the performance of a gel polymerization are disclosed, for example in DE 10 2004 032 304 Al, paragraphs [0037] to [0041]. Since the polymer powder or granules obtained are generally used in the form of an aqueous solution in the course of application at the site of use, the polymer has to be dissolved in 40 water on site. This may result in undesired lumps with the high molecular weight polymers described. In order to avoid this, it is possible to add an assistant which accelerates or PF71248 19 improves the dissolution of the dried polymer in water to the inventive polymers as early as in the course of synthesis. This assistant may, for example, be urea. The resulting copolymers generally have a weight-average molecular weight M. of 5 1*101 gtmo to 30*1V g/moi, preferably 5*106 g/moi to 20*106 g/mo. Processes for mineral oil production To execute the process according to the invention, at least one production borehole and at 10 least one injection borehole are sunk into the mineral oil deposit in general, a deposit is provided with several injection boreholes and with several production boreholes, An aqueous form ulation of the copolymer descdbed is injected into the mineral oil deposit through the at least one injection borehole, and mineral oil is withdrawn from the deposit through at least one production borehole- The term m i nerall oir in this context of course does not only mean 15 single-phase oil, but the term also comprises the customary crude oil-water emulsions. As a result of the pressure generated by the formulation injected, known as the "polymer flood> the mineral oil flows in the direction of the production borehole and is produced via the production borehole. 20 The deposit temperature of the mineral oil deposit to which the process according to te in vention is applied is, in accordance with the invention, 35 to 120C, preferably 40*C to 90'C, more preferably 45"C to 75*C and, for example, 50*C to 70*C, it is clear to the person skilled in the art that a mineral oil deposit may also have a certain 25 temperature distribution. The deposit temperature mentioned relates to the region of the de posit between the injection and production boreholes which is covered by the polymer flood ing. Methods for determining the temperature distribution of a mineral oil deposit are known in principle to those skilled in the art. The temperature distribution is generally undertaken from temperature measurements at certain sites in the formation in combination with simula 30 tion calculaions, which take account, inter alia, of the amounts of heat introduced into the formation and the amounts of heat removed from the formation. The process according to the invention can be employed especially in the case of mineral oil deposits having an average permeabil ity of 10 mD to 4 0, preferably 100 mD to 2 0 and 35 more preferably 200 mD to 1 D. The permeability of a mineral oii formation is reported by the person skilled in the art in the unit 'darcy" (abbreviated to "D" or "mD* for "miilidaries") and can be determined from the flow rate of a liquid phase in the mineral oil formation as a function of the pressure differential applied. The flow rate can be determined in core flooding tests with drill cores taken from the formation. Details on this subject can be found, for r40 example, in K. Weggen, G. Pusch, H. Rischmiler in "O// and Gast pages 37 ff, U/mrann s EncyCtpeda Of inldustual Ohemisty online edaOn, viley-VCt W44inhetm 2040. It is dear to the person skilled in the art that the permeability in a mineral oil deposit need not be PF71248 20 homogeneous, but generally has a certain distribution, and the reported perneability of a mineral oil deposit is accordingly an average permeability. To execute the process, an aqueous fomulation which comprises, in addition to water, at 5 least the hydrophobically associating copolymer described is used. It is of course also possible to use mixtures of different hydrophobically associating copolymers. The formulation can be made up in fresh water, or else in water comprising salts. Of course, it can also comprise mxtures of different salts. For example, it is possible to use sea water to 10 make up the aqueous formulation, or It is possible to use produced formation water, which is reused in this manner, In the case of offshore production platforms, the formulation is generaly made up in sea water, in the case of onshore production units, the polymer can advantageously first be dissolved in fresh water, and the resulting solution: can be diluted to the desired use concentration with formation water. The formulation can preferably be 15 prepared by initially charging the water, sprinkling in the copolymer as a powder and mixing it with the water, The saits may especially be alkali metal salts and alkaline earth metal salts. Examples of typical cations comprise Nat K+, Mg* or Ca-t, and examples of typical anions comprise 20 chloride., bromide, hydrogencarbonate, sulfate or borate. When the formulation comprises salts, generally at least one or more than one alkali metal ion, especially at least NA, is present. In addition, it is also possible for alkalne earth metal ions to be present, where the weight ratio of alkali metal ions/alkaline earth metal ions is 25 generally > 2, preferably 3. The anions present are generally at least one or more than one halide ion, especially at least Clt In general, the amount of CP is at least 50% by weight, preferably at least 80% by weight, based on the sum of all anions. The total amount of all salts in the aqueous formulation is generally 20 000 ppm to 30 350 000 ppm (parts by weight), based on the sum of all components of the formulation. When sea water is used to make up the formulation, the salt content is generally 20 000 ppm to 50 000 ppm, and, when formation water is used, generally 100 000 ppm to 250 000 ppm. The amount of alkaline earth metal ions may preferably be 1000 to 53 000 ppm. 35 The aqueous formulation may of course comprise further components. Examples of further components comprise biocides, stabilzers or inhibitors. The concentration of the copolymer is fixed such that the aqueous formulation has the desired viscosity for the end use. The viscosity of the formulation should generally be at least 40 5 mPas (measured at 25*C and a shear rate of 7 s, preferably at least 10 mPas, PF71248 21 According to the invention, the concentration of the polymer in the formulation is 0.01 to 2% by weight based on the sum of al components of the aqueous formulation. The amount is preferably 0O5 to 0.5% by weight, more preferably 0.04 to 0.2% by weight and, to example, approx. 0.1% by weight, The injection of the aqueous copolymer formulation can be undertaken by means of customary apparatus. The formulation can be injected into one or more injection boreholes by means of customary pumps. The injection boreholes are typically lined with cemented steel tubes, and the steel tubes are perforated at the desired site. The formulation exits 10 through the perforation from the injection borehole into the mineral ol formation. The pressure applied by means of the pumps, in a manner known in principle, fixes the flow rate of the formulation and hence also the shear stress with which the aqueous fomiulation enters the formation. The shear stress on entry into the formation can be calculated by the; person skied in the art in a manner known in principle on the basis of the Hagen-Poiseulle law 15 using the area flowed through on entry into the formation, the mean pore radius and the volume flow. The average porosity of the formation can be determined in a manner known in principle by measurements on drill cores. By its nature, the greater the volume flow of aqueous copolymer formulation injected into the formation, the greater the shear stress. 20 The rate of irection can be fixed by the person skilled in the art according to the conditions in the formation. Preferably, the shear rate on entry of the aqueous polymer formulation into the formation is at least 30 000 s", preferably at least 60 000 sA and more preferably at least 90 000 sQ 25 Copolymers particularly preferred for execution of the process comprise monomers (a) of the general formula H2C=CH-{CH2)eO-CHrCHrO-),(-CHrCH(R4)},-H (la) where n' is 2 to 6, preferably 2 to 4 and more preferably 4, R in the preferred variant is a hydrocarbyl radical having 3 to 10 carbon atoms, especially an n-propyl radical. In addition, in formula (Ia), k is a number from 20 to 30 and I is a number from 6 to 20, preferably 8 to 18. The 30 amount of the monomers (a) of the formula (la) is 0.2 to 5% by weight, preferably 0.5 to 2% by weight As monomer (b1), the preferred copolymer comprises 40 to 60% by weight of acrylamide and, as monomer (b2), 35 to 55% by weight of a monomer (b2) having sulfo groups, preferably 2-acrylamido-2-methylpropanesuffonc acid or salts thereof. 35 Further copolymers preferred for execution of the process likewise comprise 0.2 to 5% by weight, preferably 0.5 to 2% by weight, of monomers (a) of the general formula (1a) and 30 to 40% by weight of acrylamide. They additionally comprise 25 to 35% by weight of at least one monomer (b2) having sulfo groups, preferably 2-acrytamido-2-methylpropaknesufonlc acid or salts thereof, and 25 to 35% by weight of at least one cationic monomer having ammonium 40 ions, preferably salts of 3-trimethylammoniopropyl(meth)crylaides and 2-4rimethyl amnmonkiethyl (meth)acryiates.

PF71248 22 The examples wNch follow are intended to lustrate the invention in detail: Monomers (a) used 5 Monomer MI Hydroxybutylvinyl ether alkoxyjate with 22 EQ units and 12 Pe unis H2C=CH-0-(CH 2 )4-(-CHrCHrO -)}2-CHrCH:(C 3

H

7 )O-)l rH 10 A I i stirred stainless steel autoclave is initially charged with 44.1 g of hydroxybuty vinyl ether. Subsequently, 3.12 g of KOMe (32% in MeOH) are metered in and the methanol is drawn off at 80*C and approx. 30 mbar. This is followed by heating to 140*C. purging of the reactor with nitrogen and establishment of a nitrogen pressure of 1,0 bar, Then 368 g of EO are metered in within approx 3 h. After continued reaction at 140C for a half hour, the 15 reactor is cooled to 125*C, and a total of 392 g of pentene oxide are metered in over the course of 3.5 h. The reaction continues ovemight, The product has an OH number of 31.9 mg KOHlg (theory: 26.5 mg KOHIg). The OH number is determined by means of the ESA method. 20 Preparation of the coplymers Polymer 1: Preparation ofacopolyer from 2%byweight of monomer by weightof acrylamide 25 and 48% by weight of 2-acrid~o2-methylpropanesulfonic acid A plastic bucket with magnetic stirrer, pH meter and thermometer is initially charged with 121.2 g of a 50% aqueous solution of NaATSS (2-acrylamido-2-methylproplnesUlfonic acid, sodium salt), and then 155 g of distilled water, 0.6 g of a defoamer (Surfynol t DF-58), 0.2 g 30 of a silicone defoarner (Baysilon* EN), 2.3 g of monomer Mi, 114A g of a 50% aqueous solution of acrylamide, 1.2 g of pentasodium diethylenetriaminepentaacetate completingg agent, as a 5% aqueous solution) and 2.4 g of a nonionic surfactant (nonylphenol, alkoxylated with 10 units of ethylene oxide) are added successively, 35 After adjusting the pH with a 20% or 2% sulfuric acid solution to a value of 6 and adding the rest of the water, the monomer solution is adjusted to the start temperature of -*C, The total amount of water is such that - after the polymerization - a solids concentration of approx. 30 to 36% by weight is attained. The solution is transferred to a thermos flask, a temperature sensor for the temperature recording is provided and the solution is purged with nitrogen for 40 30 minutes. The polymerization is then initiated by adding 1.6 ml of a 10% aqueous solution of a water-soluble cationic azo initiator 2,2'-azobis(2-amfiidinopopanle) dihydrochioride (Wako V-50) :0.12 ml of a 1% aqueous solution of ferbbuty hydroperoxide and 0.24 ml of a 1% PF71248 23 sodium sulfite solution. After the initiators have been added, the temperature rises to approx. 80'C within 15 to 30 mir. After 30 min, the reaction vessel is placed into a drying cabinet at approx. 8OC for approx. 2 h to complete the polymerizatin. The total duration of the polymerization is approx, 2 h to 2,5 it, 5 A gel block is obtained, which, after the polymerization has ended, is comminuted with the aid of a meal grinder. The gel granules obtained are dred in a fluldized bed dryer at 55*C for two hours. This gives white, hard granules which are converted to a pulverulent state by means of a centrifugal miL This gives a copolymer with a weight-average molecular weight 10 of approx. I *106 glmol to 30* I 0 g/moit Polymer 2: Preparation ofa copolymer from 5% by weight of monomer Mi, 50% by weight of acrylamida and 45% by weight of 2-acrylamid-2:-methylpropanesulfnic acid 15 The procedure is as in Example 1, except that the amount of monomer M1 is increased from 2% by weight to 5% by weight based on the sum of all monomers, and the amount of 2-acrylamido-2-mathylpropanesulfonic acid is reduced from 48% by weight to 45% by weight The amount of the surfactant (proportions by mass) corresponds to that of monomer M1, 20 Com prat vepolmer_1 This is a commercially available copolymer for polymer flooding, formed from approx. 50% by weight of acrylamide and approx, 50% by weight of 2-acryiamido-2-methylpropanesulfonic 25 acid with a weight-average molecular weight M, of approx. 8 to 13*10s g/rnoi. Comparative polymer 2.: This is a commercially available copolymer for polymer flooding, formed from approx, 72% by 30 weight of acrylamide and approx. 28% by weight of sodium acrylate units, having a weight average molecular weight M, of approx. 20 000 000 g/molt Comparative polymer 3: 35 A commercially available xanthan polymer was used for the tertiary mineral oil production. Performance tests Determination of viscosity 40 The viscosity measurements were carried out with a Brookfield LVDV-UL viscorneter at a shear rate of7 s.

PF71248 24 For the viscosity measurements, aqueous solutions of the polymers were used. To dissolve the polymers, the folowing aqueous media were used: 5 Tap water Total salinity 123 mg/I Sea water (syntheti Total salinity: approx. 35 000 mglI 10 Na' 10 692 mg/t K+ 420 mg/I. Mg 2 1295 mg/I, Ca: 422 mg/i, C1 19218 mg/i, HCD 145 mg/i, S042 2697 mg/I Ratio of alkali metal ions/aikaline earth meta[ ions: 6.2. Deposit water(synthetic): 15 Total salinity: 185 548 mg/i Na+ 52 079 mg/i, Mgz 4 2681 mg/i Ca- 15 383 mg/, Cl 115 105 mg/, borate 117 mg/, SW 183 mg/L. Ratio of alkali metal ions/alkaline earth metal ions: 2.9; deposit water with high Ca& content 20 The following tests were carried out: Test series 1: Solutions of polymers 1, 2 and C1, C2 and C3 were made up in a concentration of in each 25 case 1500 ppm in sea water. The viscosity of the solutions was measured at 20'C and at 50*C, Figure 1 shows the results obtained. The aqueous solutions of comparative polymers 2 and 3 have a higher viscosity at 20*C than the polymers 1 and 2 used in accordance with the invention. For all comparative polymers, 30 the viscosity at 60*C is, however, much lower than at 20"C. For polymers I and 2. in con trast, the viscosity at 60C is significantly higher than at 20*C. Test series 2: 35 Solutions of polymers I and C2 were made up In a concentration of in each case 1200 ppm in tap water, and the viscosity of each of the solutions was measured at 30C, 60*C, 90*C and 120'C. Figure 2 shows the results obtained. The solution of polymer I has, at 30"C, a viscosity approx. 4 x higher than the solution of 40 polymer C1. The viscosity of the latter solution decreases with increasing temperature. The viscosity of the aqueous solution of polymer 1 increases very significantly between 30*C and PF71 248 25 60*C, and decreases only when the temperature is increased further, Even at 120"C, the viscosity of the solution of polymer 1 is still greater than that of comparative polymer C1. Test series 3 to 5: 5 Solutions of polymer I were made up at different concentrations in tap water (test series 2), sea water (test series 3) and deposit water (test series 4), and the viscosity of each of the solutions was measured at 30*C, 60*C, 9C and 120*C. The results are shown in figures 2 to 5. The figures also comprise the information with regard to the concentrations used in 10 each case. In all tests, the viscosity of the solutions increases significantly from 30*C to 60"C and then decreases again. The viscosity maximum is in the range from approx, 50*C to 70"C. 15 Test series 6: Solutions of comparative polymer C1 were made up at different concentrations in tap water, and the viscosity of each of the solutions was measured at 30*C, 60C, 90'C and 120C, The results are shown in figure 6, The figure also comprises the information with regard to 20 the concertrations used in each case. For the comparative polymer, the viscosity levei is firstly lower than for inventive polymer I. In addition, the viscosity does not pass through a maximum, but decreases continuously with increasing temperature. 25 Core flooding tests The copolymer of example I and comparative polymer C1 were also used to carry out core flooding tests. 30 In each case, sandstone cores (composition 99% by weight of quartz) with an average porosity of approx. 2 darcies were used. The properties of the sandstone cores used are compiled in table 3 below.

PF71248 26 Core 1 Core 2 Copolymer used polymer 1 C1 Length &53 CM 8.56 C _m Cross-sectional area 7.02 ar 7.02 cm2 Gas permeability 1993 mD 2350 mD Water permeability 1734 m D 2077 mD Porosty 23.6% 24,6% ore142 cm 14.8 cm Table 3: Properties of the cores used For the core flooding tests, solutions of the polymers in deposit water of the composition 5 detailed above with a total salt content of 186 glI were prepared. The concentration of polymer I was 1200 ppm and that of comparative polymer C1 3000 ppm, For the tests, a customary apparatus for core flooding was used, in which the core is introduced into a pressure-resistant steel shell sealed at both ends, one end having an orifice 10 for injection of gases and aqueous solutions and the other end an outlet orifice. Gases or the aqueous formulations to be tested are injected with a particular pressure through the inlet orifice and low through the core under the influence of the pressure. The entire apparatus is stored in a bath for temperature control. The tests were carried out at 55"C. 15 By varying the injection rate (i.e. variation of the pressure applied), it is possible to calculate the apparent viscosity of the aqueous formulations according to equations I to 3: RF = (water)/ k(polymer solution) where X= k/p (equation 1) 20 RF resistance factor,, = mobility, k = permeability, gp= viscosity RR-F = (watery/ (water after the polymer solution has flowed through) RRF = residual resistance factor 25 3 = (RF/RRF)* pa Figure 7 shows the apparent viscosity of the two polymer solutions as a function of the finv rate in the core in r/day. 30 The apparent viscosties of the solutions determined by means of the core flooding test show that the viscosity efficiency of the polymer used in accordance with the invention at low flow rates is much better than that of comparative polymer 1, which does not have any hydrophobically associating monomers but apart from that is of similar structure to polymer 1, PF71248 27 Even at a concentration of 1200 ppm, a much higher viscosity is achieved than with comparative polymer I at a concentration of 3000 ppm, The core flooding tests also show that the solution of polymer I used in accordance with the 5 invention has highly shear-diluting (thixotropic) behavior, i.e. the viscosity of the polymer solution decreases very significantly with increasing flow rate. This is particularly advantageous for polymer flooding since - as already stated above - the flow rate is at its highest on entry into the formation and decreases again with increasing distance from the injection site. Advantageously, the viscosity of the solution decreases specifically at this 10 point, end thus enables easy injection into the formation. The solution of comparatve polymer 1, in contrast, exhibits shear-thickening (dilatant) behavior, i.e the viscosity increases with increasing flow rate.

Claims (19)

1. A process for mineral oil production, in which an aqueous formulation comprising at least 5 one water-solubie, hydrophobically associating copolymer is injected through at least one injection borehole into a mineral oil deposit, and crude oil is withdrawn from the deposit through at least one production borehole, wherein the water-soluble, hydrophobically associating copolymer comprises 10 (a) 01 to 15% by weight of at least one monoethylenically unsaturated, hydrophobically associating monomer (a) selected from the group of H 2 (=C(R})-O+CHrC H(R3)-0-)4(-GC H (R 4 )-O+R5 (I) '15 H 2 C=C (R 1 )-CHrC H(R3)-O-)rRe (1) 20 where the -(-CH 2 CH(R)-O-) and 0CH 2 -CH(R)-O-)0 units are arranged in block structure in the sequence shown in formula (i) and the radicals and indices are eaci defined as follows: k: a number from 10 to 150, 25 i: a number from 5 to 25, R 1 : H or methyl, Rt a single bond or a divalent linking group selected from the group of -(CnH 2 ln)- [R 2 a) -(CH,) ['IRa) and -C(Q)-O-(CNR- R, where n, n' and n" are each natural numbers from 1 to 6, 30 R 3 : each independently R, methyl or ethyl, with the proviso that at least 50 mnoi% of the R2 radicals are H, R 4 : each independently a hydrocarbyl radical having at least 2 carbon atoms or an other group of the general formula -CHrQ-Rt where R.' is a hydrocarbyl radical having at least 2 carbon atoms, 35 R5: H or a hydrocarbyl radical having I to 30 carbon atoms, R6: an aliphatic andlor aromatc, straight-chain or branched hydrocarbyl radical having 8 to 40 carbon atoms, and also 40 (b) 85 to 99,9% by weight of at least two monoethylenically unsaturated, hydrophilic monomers (b) different than (a), where the monomers (b) comprise 29 (bi) at least one uncharged, monoethylenically unsaturated, hydrophilic monomer (b1), selected from the group of (meth)acryiamide, N-methy(meth)acrylamide, N,N-imethyl(meth)acrylamide or 5 N-methylol(meth)acrylamide, and (b2) at least one anionic, monoethylenically unsaturated, hydrophilic monomer (b2) which at least one acidic group selected from the group of -COOH, -SOH and -POH2 and salts thereof, 10 where the proportions are each based on the total amount of all monomers in the copolymer, " the copolymer has a weight-average molecular weight Mw of 1*10 g/rol to 15 30*10 g/mol, * the amount of the copolymer in the formulation is 0,02 to 2% by wight, and a the temperature of the mineral oil deposit is 35C to I 20*C 20

2. The process according to claim 1, wherein the temperature of the mineral oil deposit is 40 to 90"C,

3, The process according to claim 1, wherein the temperature of the mineral oil deposit is 45 25 to 7 0 *C.

4, The process according to any of claIms I to 3, wherein the aqueous formulation further comprises salts in an amount of 20 000 ppm to 350 000 ppm. 30

5, The process according to claim 4, wherein the proportion of alkaline earth metal ions is 1000 to 53 000 ppm.

6. The process according to claims 1 to 3, wherein sea water is used to make up the aqueous formulation.. 35

7. The process according to claims I to 3, wherein produced deposit water is used to make Lp the aqueous formulation.

8. The process according to any of claims I to 7, wherein the average permeability of the 40 formation is 10 millidarcies to 4 darcies. 30

9. The process according to any of claims 1 to 7, wherein the average permeability of the formation is 100 millidarcies to 2 darcies,

10. The process according to any of claims 1 to 9, wherein polymer solution is injected into 5 the formation with a shear rate of at least 30 000 s

11. The process according to any of claims I to 10, wherein the amount of the copolymer in the formulation is 0.05 to 0.5% by weight. 10

12. The process according to any of claims I to 11, wherein the hydrophobically associating monomer (a) is at least one of the formula (I), and where * R 4 is a hydrocarbyl radical having 3 to 8 carbon atoms, k is a numberfrom 12 to 100, and 15 s R is H, methyl or ethyl.

13. The process according to claim 12, wherein * R4 is an n-propyl radical, 20 0 k is from 15 to 80, and & R& is H.

14, The process according to any of claims I to 13, wherein the uncharged monomers (b1) are used in an amount of 30 to 95% by weight and the anionic monomers (b2) in an 25 amount of 4.9 to 69.9% by weight, where the amounts are each based on the total amount of all monomers used.

15. The process according to any of claims 1 to 13, wherein the copolymer further comprises at least one cationic, rnonoethylenically unsaturated monomer (b3) comprising ammoniurn 30 ions.

16. The process according to claim 15, wherein the cationic monomer (b3) comprises salts of 3-irmethylammoni umpropyl(m eth)acrylamides and 2-trimethylammoniumethy (meth) acrylates., 35

17. The process according to claim 15 or 16, wherein the uncharged monomers (bI) are used in an amount of 30 to 95% by weight and the anionic monomers (b2) and cationic monomers (b3) together in an amount of 4.9 to 69.9% by weight, with the proviso that the molar (b2)/(b3) ratio is 0.7 to 1,3, and where the amounts are each based on the total 40 amount of al monomers used. 31

18, The process according to any of claims 1 to 17, wherein the amount of monomers (a) is 0,2 to 5% by weight.

19 The press according to any of claims 1 to 18, wherein the preparation of the 5 hydrophabically associating copolymer is undertaken in the presence of a nonpolymerizable, surface-active compound,