CA1136839A - Oil displacement enhanced by lyothropic liquid crystals in highly saline media - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An improved process is disclosed for recovering oil from an oil-bearing formation by injecting into the formation a liquid containing an effective amount of a surfactant to displace oil, driving the liquid through the formation and recovering the dis-placed oil, the improvement comprising using as the liquid a lamellar lyotropic liquid crystal which exhibits decreasing viscosities at increasing shear rates and contains (a) 0.05 to 10 vol.% of surfactant of balanced hydrophilic-lipophilic character, (b) 0.1 to 20 vol.% of an oil, and (c) the balance brine containing from 5 to 30 wt.% of inorganic salts having sodium chloride as the major component and salts of divalent metals as minor components.

Description

1~3~ 9 . .

2 1. Field of the Invention

3 This invention relates to a method of recovering

4 oil from an oil-bearing formation using 2 liquid containing a surfactant. More particular~y, the liquid used to displace 6 oil is a liquid crystal which is especially useful for re-7 covering oil from high brine fields.
8 2 DescriPtion of the Prior Art 9 The use of microemulsions in secondary and tertiary oil recovery techniques is well-known. Liquid crystal compo-ll sitions, however, have not been studied to any extent with 12 respect to their potential for the chemically enhanced re-13 covery of crude oil.
14 ~n early work which suggests the use of a surfactant system which may possess a liquid crystalline character for 16 oil recove~y is U.S. Patent 3,391,736 (~bdo). This patent 7 describes a positive nonsimple fluid useful for recovering 18 oil which possesses a shear ~hickening response at low shear l9 rates and shear thinning response at high shear rates based on a carbo~ylate surfactant system. Both of these properties 21 were later claimed in Canadian Patent No. 921,690 to Murphy 22 who described a system exhibiting.birefringence and contsin-23 ing 59-94% water, 3-20% oil, 2-16% surfactant and 1-5% al-24 cohol.
U.S. Patent No. 3,954,627 (Dreher and Gogar~y) des-26 cribes a composition useful for stimulating oil wells and con-27 taining lamellar micelles exhibiting retro-viscous property.
28 These compositions contai~ from 4~15Z surfactant, 30-70Z

~13gi~339 1 hydrocarbon and 15 - 66~ water, and optionally 2 co-surfactant 2 and up to 5 wt.Z of an electrolyte. They are birefringent 3 Rnd are probably liquid crystalline in nature. Related 4 patents sre U.S. Patent Nos. 3,948,78~ and 3,928,215.
More recently, Dreher et al (J. Coll. and Interf. Sci.
6 ~ 379-387 (19763) studied a system composed of alkylbenzene 7 sulfonate, hydrocsrbon, water and co-surfac~ant as a model for 8 a tertiary o~l recovery fluid. The rheological properties 9 indicated that this system could exist as either a micro-emulsion or liqu~d crystal depending on the particul~r comp~-11 sition. Further studies o~ certain alkylaryl and petroleum 12 sulfonates indicate that liquid crystalline phases c~n be 13 formed and the formation of these phases are of ~nterest for 14- chemically enhanced oil recovery since they can affect, for example, interfacial tension, viscosity, and retention. For 16 reference, see articles in the Preprints, Div. Petr. Chem., 17 A.C.S., 23(2), 644 (1978) by Scriven et al snd ibid., 23(2), 18 68~ (1978) by Miller et al.
19 Finally, Shah et al in the J. Amer. Oil Chem. Soc., 55, 367 (1978) disclosed a surfactant system based on a mixture 21 of petroleum sulfonste and ethoxylated alkane sulfonate in 22 brine which was tolerant to salts including large amounts of 23 CaC12 and MgC12. At certain salt concentrations, it was re-24 ported that a stable birefringent phase formed.
In spite of the hypotheses of the above art~cles, 26 i~ is generally believed in the art that liquid crystals sre 27 not a practical fluid for oil displacement. The reason for 28 this is the high v~scosity associated with liquid crystals 29 For example, Reed and Healy ;n an article entitled, 'Some 1~3~3~

1 Physicochemical Aspectc of Microemulslon Flooding: A Review,"
2 which sppeared in the monograph Improved Oil Recovery by 3 Surfac~ant and Polymer Flooding, Shah and Schechter, Academic 4 Press~ N.Y., 1977, emphasized in part D, esPecially Page 402, that the excessive viscosity associated with lamellar struc-6 tures would prohibit application of these comPositions to 7 tertiary oil recovery. This pessimism is reflected in the ab-8 sence of published experiments wherein liquid crystals were 9 used to displace oil. In addition to viscosity considerations, high brine concentrations provide an additional negative 11 factor since it is generally believed that high salt concen-12 trations destabilize liquid.crystals.
13 It would be highly desirable to show that lyotropic 14 liquid crystals containing min~r amounts of surfactants and oil are stable in the presence of highly concentrsted brine 16 and provide an alternative and improved means to displac~
17 oil as compPred to microemulsions.
18 SUMMARY OF T~E INVEN~ION
l9 It has been discovered that lyotropic liquid crystals containing minor amounts of surfactants are stable 21 in the presence of higly concentrated brLne and that the 22 liquid crystals can be used to effectively`displace oil.
23 Accordingly, the present inventio~ relates to a process for 24 recovering oil from an oil-bearing formation by displacing oil with a primary displacement-fluid containin~ liquid 26 crystals. More particularly, ~he process comprises in-27 ~ecting into the formation a liquid containing an effective 28 amount of a surfactant to displace oil, said liquid comprising 29 a liquid crystal CDntaining from 0.05 to 10 vol.~ of sur-"` ~13~i~339 , l ~actant, 0.1 to 20 vol.Z of oil and brine containing up to 2 30 wt.%, based on water, of inorganic salts driving the 3 liquid through the formation and recovering the displaced 4 oil and brine containing up to 30 wt.~, based on water, of

5 inorganic salts, driving the liquid through the formation

6 and recovering the displaced oil.

7 ~n spite of the high viscosity and known tendency

8 to destabilize at high brine c~ncentrations, it has been found

9 that liquid crystals can be used for oil displacement at least

10 as effectively as microemulsions of comparable composition.

11 The formation of liquid crystals in high brine generally re-

12 quires somewhat higher molecular weight surfactants at slightly

13 hig~er concentrations than the formation of~icroemulsions.

14 On the other hand, liquid crystals possess higher integrity,

15 i.e., less miscibility, snd lead to an earlier banking of oil

16 ant greater recovery over comparable microemnlsions at high

17 brin~.

18 B~IEF DESCRIPTION OF T~E DRAWINGS

19 Figure 1 is a graph showing the comparison of oil

20 recovery by liquid crystal versus microemulsion.

21 ~igure 2 is a graph illustrating the effect ~n oil

22 recovery by liquid crystals based on different c~mbined sur-

23 factants.

24 Figure 3 is a graph demonstrating oil recovery by

25 liquid crystals containing different hydrocarbons as oils.

26 Figure 4 is a graph of oil recovery by a liquid

-27 cr~stal versus a microemulsion prepared from the same sur-

28 ~actant system.

113~i~39 ~igure 5 is a copy of photomicrographs of liquid crystalline phases.
DET~ILED DESCRIPTION OF THE INVENTION
Liquid crystals can be recognized by their anisotropic - character. For example, they exhibit birefringence with polar-izing microscopy. The present liquId crystals are more highly ; ordered than known micellar fluids and preferably have a lamellar structure as indicated by microscopy and proven by X-ray diffrac-tion studies.
The essential components of liquid crystals are minor amounts of surfactants and major amounts of brine. These f~ compositions preferably contain minor amounts of oil and mayalso contain optional additives such as co-solvents, co-suxfac-tants, hydrotropeq, chelating agents and polymers.
The present compGsitions contain from 0.05 to 10, preferably 0.1 to 7 and especially 0.2 to 3.8 vol.~ of surfac-tant: from 0 to 25, preferably 0.1 to 20 and particularly 0.5 to 10 vol.% of oil and the balance water containing up to 30 wt.%, based on water, of lnorganic salts. m e total inorganic salt concentration ls from 1 to 30, preferably 3 to 30 and especially 5 to 30 wt.%. Preferred brines have sodium chloride as the major component i.e. more than 50~ together with minor amounts of divalent metals such as Ca2+ and Mg2 .
The oil component of the li~uid crystal may be a crude oil or a distillate hydrocarbon oil product such aæ a pentane-hexane mixture, diesel fuel, gas oil, lubricating oil or al~yl benzenes. The non-sulfonated reæidual hydrocarbon oil of sulfonic acid components is preferably incorporated into the pre6ent compositions. In the caæe of technical petroleum , ~:

.'.:

~3~i~3~

1 sulfonates, this oil is often a major component of the sur-2 factant. Such surfactants may be employed for liquid cry.tal 3 prepsration ~Jithout added hydrocarbons.
4 Different hydrocarbons have a varying ability to stabilize liquid crystals Crude oil often is less preferred ~ than detergent range paraffins, e.g., those in diesel fuel 7 (such as n-decane) or gas oil from the viewpoint of liquld ~ crystal stability. If crude oil is used, it should preferably 9 have a similar composition ~o that of the oil iield ~here oil recovery is to be enhanced. It ~ay also contain added salts 11 such as sodium silicates, sodium phosphates and phDsphites.
12 The surfactants which are the active ingredients 13 in ~he liquid crystals can be anionic, cationic, nonionic, 14 amphoteric, combined anionic and cationic or mixtures thereof. Ethoxylated andlor propoxylated surfactants either 1~ alone or in combination with other surfac~ants are preferred.
17 Anionic surfactants are carboxylates, sulf~nates, 18 sulfates, phenolates and esters of phosphorus acids. Pre-19 ferred anionic surfactants are sulfonates, sulfates, phos-phates, phosphonates and phosphinates.
21 Surfactant carboxylates incLude C12 to C40 aliphatic 22 carboxylates and C16 ~o C40 alkylaryl carboxylates wherein 23 the a~kyl chain has at least 12 carbon atoms. The aliphatic 24 carboxylates can be open chain and isocyclic. Examples of open chain carboxylic acids are tall oil, palmitic, oleic, 26 hydroxystearic, linoleic, linolenic, undecylenic, lauric, 27 perfluorodecanoic acids. Among the isocyclic compounds, 28 naphthenic acids, rosin acids such as abietic acid and choLic 2~ acids are exemplary. Aroma~ic carboxylic acids include do-`

1~3~i~39 _ 7 -1 decylbenzoic àcid, octadecylsalicylic scid, hexadecylo~ybenzoi~
2 acid. Substituted carboxylic acids are exemplified by the N-3 acylsarcosinates derived ~rom fatty acids and ~-methyl glycine 4 sodium salt:
CnH2n+lCO,NCR2CH2CO2Na n ~ 12 - 30 7 Among the anionic sulfonates, C18 to C56 aLkylaryl 8 sulfonic acid salts are impor ant. ~igher alkyl derivatives 9 of benzene, toluene and ~ylene sulfonic-acids are preferred where the alkyl moiety is at least C12, preferably C12 to ll Cso, more preferably C14 to C36 and especially Cls to C30.
12 Among other aromatic sulfonates, alkyl derivatives of naph-13 thalene sulfonic acid, tetrahydronap~thalene sulfonic acid, 14 and.diphenyl ether sulfonic acid are preferred. The al~yl substituents of aromatic sulfonic acids can be substituted 16 by substituted alkyl group such as alkyloxy and alkylthio.
17 The aromztic group can be also polyethoxylated. Disulfonated 18 aromatics snd petroleum sulfon~tes are other classes of 19 ~nterest.
Sulfonate surfactants can be also aliphstic ~uch 21 ss alkane sulfonztes, which can be ~ -alko~ylated, hydroxy-alkane sulfo~ates and alkene sul~onates. These sulf~nates 23 are C~ to C60, preferably C16 to C40, ~n the aliphatic hy~ro-24 carbon groups. - Substituted aliphatic sulfona~es include sul~onate deri~8tives of ethoxylated alkyl phen~ls deri~ed 26 fro~ the corresponding ethoxy~ated suLfates. Another grDup 27 cf substituted sulfonates are represented ~y dialkyl sul~
28 ~osuccinates derived ~rom dialk.yl malea~es via the addition 2~ o~ sodium hydrogen sulfite. Further distinct cl sses of , ~ :
. .

: ` :

~3~39 1 su~s~itu~ed sul~onates ase those of N-acyl N-alXyl taurates 2 preferably derived from N-me~hyl or N-cyclohexyl tzurate snd 3 a fatty acid chlorid~ and su~foethyl estess of fatty acids 4 derived f~o~ sodium isothiorate and a fatty acid chloride, Cn~2~1lco~C~.2C~2SO3Na CnH2n+lco2c~2c~2s~3~a 7 n = J2 - 30~ R ~ CH3, ~ n ~l2 - 30 8 including 2nalcgous higher alkylated sulf~ethyl ester~
~ C2~ 2)~_1S~3Na lo ~ H2n~1 11 m - 1 - 30, n ~ 12-30--12 Surfactant sulfates include Cl~ to C40 aliphatic 13 sulfates. Alkyl sulfates such as lauryl and tall~w sulfate 14 represent the most common subgroup of this class derived from the corresponding alcohols. Unsaturated carboxylic acids 16 and their es~ers, such as fats and oils, can be also sulfa~ed 17 via sulfuric acid addition to their olef~nic gDOUpS and as 18 such, provide another type of sulfated surfactants.
19 Hydroxyethyl amides of C12 to C40 fatty acids can be also sulfated to yield members of the sulfated alkanol?~ide 21 class. More importantly, ethoxylated higher alcohols and alkyl-22 phenols are sulfated ;o yield very important classes of 23 ethoxylated sulfates. These ethoxylated inter~ediates can 24 be propoxylated before sulfation. The starting alcohols of a~ionic sulfate surfactants are preferably in the C12 to C36 26 range. The alkyl groups of the alkyl-phenols-cresols and 27 xylenols ran~e from C12 to C60, e.g., 113Çi~39 _ 9 _ 1 CmH~m+l(0CH2CH2~xOS03Na (~H2k+1) ~ 2 2~y 3 2 m = C12-C40~ x ~ 0-30, k - 12-60 3 Pareial C12-C40 esters of the ~rious phosphorus 4 acids particularly of orthophosphoric, polyphosphoric and phosphoric acids represent another brDad class of anionic 6 surfactants. Exemplary products of simple alcohols are di-7 ethylhexyl phosphste and polyphosphate. The phosphates 8 are preferably employed as ~ mixture of mono- and diesters, 9 e.g , ~ ~
I o CmE~2D~1 (OCH2CH2 )~OPO 3Na2 ¦[Cm~2~1 (QCE~2 CH2 ) ~ ~ 2P2Na 11 x - Q-30 ; m - 12-40 12 Such phosphate derivatives of dodecyl and octadecyl alcohols 13 and.their ethoxylated snd propoxylated derivatives are other 14 exemplary anionics of this type. Phosphate derivatives of ethoxylated alkyl phe~ols such as dodecylphenol and dinonyl-16 phenol are also included, e.g., 17 (GkH2k+l ~ 0cH2c~2)yopo3Na2 19 {(~ X2k+1 ~ oCH2C~2)yO3 2P2~a ~igher alkyl phenolates, such as octadecyl phenolate 21 and dodecyl naphtholate are also regarded as anionic eomponents.
22 Certain amphoteric compounds havihg a combi~ation 23 of weakly basic and strongly acidic groups can be also used 24 as anionic surfactant components. Exemplzry types of such 25 compounds are: -~L~3~i~39 -- 10 ~

C~H2rl+~ H2CH2S03- CnH2n+l 1 (CH3)CH2CH2S03 3 n - 12 - 30 4 Comicellization forming combined surfactants also occurs with amphoteric compounds in general, e.g., 6 CnH2n~l N(cH3)2cH2cH2cH2so3 ; n ~ 12 - 30 7 Suitable cationic components are surfactant bases 8 and their salts. In the present discussion, surfactant bases g will be usually co~sidered, although it is understood that they can be employed in the salt form. Quatern~ry salts, ll however, will be discussed as such since they are usually 12 unstable and not a~ailable as free b~ses. Am~n8 the cationic 13 surfactants, smmonium salts, phosphonium salts and quaternary 14 ammonium salt are preferred.
The most important class of cationic surfactants 16 are-higher aliphat~c amines. The carbon range of the ali-17 phatic groups is 12 to 40? preferably 13 to 30. The amines 18 can be primary, secondary and tertiary. The tertiary amines, 19 of course, may contain 1 to 3 higher alkyl groups. I~ the case of the higher mon~alkyl amines, the C16 to C30 aLkyl 21 range is most preferred.
2Z A preferred class of aliphatic amines has cpen chain 23 substituents such as straight chain saturated alkyl radicals.
24 Examples are lauryl and stParyl amine. They can also be branched alkyl groups, preferably ~ dimethyl alkyl 26 groups such as those in Primenes and ~ and ~ -substituted 27 alkyl groups wherein the~J-- and ~ -substitute is a C4 to 28 C12 straight chain alkyl group. Typical straight chain un-

29 saturated amines are the fatty amines, e.g., ~allow, oleyl and 1~3~ 39 1 soya amines. Aliphatic amines can also have isocyclic 2 structures such as the rosin amines, e.g., dehydroabietyl 3 amine and they can be benzylic such as octadecylbenzylamine.
A particularly preferred cationic amine is derived via the ethoxylation (and/or propoxylation) of cationic primary G and secondary amines such as octadecyl amine, rDsin amine, 7 ~ dimethyl octadecyl amine, dilauryl amine, alkyl ^~ pyridine, alkyl morpholine with from 2 to 30 moles of ~ ethylene oxide. Except for the ~ , ~ -disubstituted com-1~ po~nds, primary amines are ethoxylated involving both amine 11 hydrogen atoms to provide the types of cationic surfactants 1~ exemplified by the followi~g:

/ (C~2C~2o) 1-~ Cm~2m+1~ Cm~2D*lC(C~3)2N~(CR2C~20) lG m ~ i2 - 30~ y ~ 3 - 3 17 -' (C~2C~2o) ~
13 3 ~ Ç~2NJ~ . , g ~ y 2 - 30 19 ~ (CH2CR

- C~(c~3)2 ~1 Another preferred group of cationic amines is 22 represented by C12 to C40 diamines and tri~mines derived from 23 primary emines via cyanoethylation and reductive amination 2~ sequences. These types of compounds are derived from fatty ~5 a~ines. Examples of diamines derived from fàtty amines are tJ~ rl~
sold under the Treden~e Duomeens manufactured by Armak Co.
27 They also can be used in the form of their etho~ylated ~13~j~`39 1 derivatives, e.g., 2(C~2CH20) ~ x ~ y ~ z - 3 - 30 CnH2n ~ lN(CH2~3N\
_ I (C~2C~20) ~ n - 12 - 30 (~H2cx2~)zH
6 Among the fatty di~;nes and triamines ~re cycLic c~mpounds, 7 p~rticularly imid2zolines, derived by the reaction of fatty 8 ac~d salts with hydroxy.-ethyl ethylene diamine a~d diethylene 9 triEmine, respectively, ~.g., lo ~ 2 1 1 2 11 CnK2n+l-C ~ C~ 2n+1 ~ ~ C~2 13 C~zC~20~ CH2C~2~2 14 n - 12-- 30 These cationic imidazolines ca~ be also advantageously 16 etho~ylated. Amines can also possess polypropylene o~ide 17 ~locks as oleophilic units. A prefesred catio~ic com~onent l~aJe ~
18 of this ~ype is available under the Tr~dnn~of Poloxamlne 19 manufactured by BASF Wyandotte:

J ( 2 2)a~oC~C~23 1 Nc~2c~2N ~ 2C~O~ (C~ CX O) Hl 21 ~ C~3 bJ 2 ~ C~3 ~ - J 2 22 where the.molecular weight ranges from 300 ~o 2000 and the 23 weight ratio of ethylene oxide u~its in the oligomer rznges 24 from 10 to 80%;
Surfactant amides, especially ethoxylated fatty 26 amides m2y also serve as weakly basic cationic components, 27 e.g., 113~B39 ~ CH2CH20H
n 2n+1 1l \ Cn 2n+1 1l N (CH2CH20) XH

n = 12 - 30; x 3 1 to 25R = H, CH3 The second most important clas~ of cationic surfactants are higher aliphatic derivatives of quaternary ammonium salts.
The quaternary salts are usuaily derived from the corresponding cationic amines cited above. The agents for quaternarization include methyl chloride, dimethyl sulfate, diethyl sulfonate, alkyl tosylates, ethylene chlorohydrin and benzyl chloride, particularly methyl chloride.
The preferred quaternary compounds are fatty amine, fatty diamine, rosine amine derivatives, especially the quaternaries based on ethoxylated derivatives of these amines.
Ethoxylated alkyl pyridinium halides are another preferred type of cationic components.
Quaternary phosphorium salts having 1 to 4 ~12 tolC~0 aliphatic groups represent another important class of cationic surfactants. These phosphorium salts include compounds having structures analogous to the discussed ammonium salts. The -preferred quaternary phosphorium compounds also include phenyl substituted derlvatlves. References on the tetraalkyl phosphor-ium cation specie~ are U.S. Patents 3,929,849 and 3,998,754 (A. A. Oswald). In a manner sim~lar to the quaternary ammonium components, a pa~ticularly preferred class of phosphorium components possesses oxyethyl or oxypropyl units (x = 1-30).
Less common cationlc surfactantR include weakly ~ 13 -`` , ' 1 basic surfactant and surfactant precursors such as amine 2 oxides, ph~sp~ine oxides and suifoxides and the~r ethoxylated 3 and propoxylated derivatives, examples 5f ~ich are:
, 4 CmH2m+l~(C~3)2 Cm~2m+l~(CH2CH2c~20x~2 6 Cm~m~l~CH2CH2H m ~ 12 - 30 7 Amphoteric compounds having a combination of acidic 8 and basic groups can be also used. Exemplary types of such 9 compounds are the following:
10 Cn ~ n+l N~CX3)2-C ~ C02 C H2 ~ - ~ (CH3)3 11 ~~- CH2 12 n 2n+1 ~ ~ 2 13 / ~ n - 12 - 30 14 HOCH2C~2 CH2C~2 Nonionic surfactants ~re etho~ylated derivatives 16 of phenolst amines, carboxylic acids, alcohols, mercaptans and 17 polyhydroxy compounds. Ethoxylated C12 to C4~ alcohols and 18 alkylphenols are preferred. The ethoxylated phenols have 19 the formula:

(CnH2n~l)m ~ A - [0(CH2CH20)p~q~

21 where n is from 1 to 30; A is benzene, naphthalene or diphenyl ;
22 p is 2 to 30; q is 1 or 2 and m is from 1 to 5 with the 23 proviso that there is at least one C12 to C30 alkyl chain.
24 Com~ re~ ar;onic-cationic surfactants o, balanced hydrophilic-lipophilic character may be com~osed of the sur-26 factant ions of the above-defined anionic-cationic and 1136~339 1 ampho~eric surfactan~s. Their bal~nce is preferable assured 2 by an appropria~e degree of ethoxyl2tion. A preferred sur-3 factant system relates to anionic, ~nd cationic surfsctants 4 ~hich may be c~mbined to pr~duce balanced biamphi~hilic 5 anionic-cationic salt compositions. Ethoxylated alkyl am-6 morium sulfonates of the formula +,~ (cH2cH2o)xH
8 [CnH2n+lR S~3 ] [Cm~2m+11 ~ (CH C~ 0) H~
R' 11 where R is phenyl, tolyl or 2ylyl; R' ~ H or C~3; n is 12 to 12 40; m is 12 to 36 and x + y is from 2 to 30 are preferred.
13 The present liquid crystals are stabilized by higher 14 alkyl lipophilic moieties of the surfactants. In the case of olefin, alcohol and alkyl benzene derivatives, these lipophilic 16 moieties are at least C12 on the average. The op~imum alkyl 17 chain length, however, is generally higher for the surfactant 18 constituents of liquid crystals as compared to microemuls~o~s.
19 If one considers the hi~her alkyl moiety of sur-fac~ants generallyj lower ranges favor the formation of 21 microemulsions only, higher ranges liquid crystals only, 22 and both liquid crystals and microemulsions can be formu-23 lated from intermediate ranges.- The~~preci-se values are~ of 24 course, depe~dent on the surfactant system in question.
Balanced combined quaternary ammonium sulfonate surfact~nts 26 of the formula:
27 ~ ~(C~2CH20)~H
28 C H2 1 -~ r SD- 13 37 l\
29 H3C CH3 H3C (cH2cH2o)vH

x ~ y = ~-10;

113~83~

1 are an example wherein such a dependence was observed on the 2 higher alkyl substituent of the xylene sulfonate moiety. The 3 c'ombined am~oni~m i-nonyl xylene sulfonate formed only balanced 4 microe~ulsions when mixed with about one volume of n-decane per thirteen volumes Tar Springs Brine. The corresponding i-6 dodecyl derivative provided both microemulsions ~nd liquid 7 crystals. Finally, the i-octadecyl xylene sulfonate formed 8 only liquid crystsls. It is noted that if one relies on 9 unaided visual observations as is commonly done in the prior art, an oil-water based liquid crystal can easily be mistaken 11 for a "microemulsion-~t 12 The formstion and stability of liquid crystals are 13 dependent on structural parameters. Unlike mos~ micellar 14 systems, ~he present lyotropic liquid crystals are largely functions of the molecular packing of surfactants, and 16 therefore, minor structural changes will strongly influence 17 stability. For example, orth~-substituted alkyl benzene sul-18 fonates, such as a~kyl ~ylene sulfonates, are preferred. In 19 the case of anionic suLfonates, it is also preferred to have 20 branched rather than straight chain monoalkyl groups.
21¦ Other phenomena which influence liquid crystal 22 formation and stability include hydrGgen bonding and an 23 appropriate hydrophilic-lipophilic balance (HLB) of the sur-24 factant components. Systems in which hydrogen bonding is 25 possible, e.g., ethoxylsted ammonium segments terminated by 26 a hydroxy ~roup, possess a much higher tendency to form liquid 27 crystals over systems in which hydrogen bonding is not ~os-28 sible. Furthermore, liquid crystal compositions are stabilized ~9 by the balanced character for the surfactants and the pre-, ...

~3~1~39 1 ferred mea~s ror achieving this is surfactant ethoxylation.
2 Ethoxylated surfactants are also preferred from the 3 viewpoint of salt tolerance of the liquid crystal compositions.
4 An increasing number of ethoxy groups in a surfactant molecule S is known to increase both the hydrophilic character and the 6 salt tolerance of the surfactant. According to the present 7 invention, surfactant based lyotropic li~uid crystals are 8 increasingly stabilized in high brine containing media with 9 the increased ethoxylation of the surfactant. The brine 1~ s~ability of liquid crystals, however, does not increase 11 indefinitely with the increasing ethoxylation of the surfactant.
I2 An optimum of stability is reached then a sudden decrease is 13 observed. In general, the optLmum range of average ethoxyla-14 tion for any given composition is within 6, preerably within 1-~ 3, most preferably within 2 ethoxy units. The average 16 ethoxylation is below that of the corresponding microemul-17 sio~s.
18 Most primary technical e~hoxylated surfactant pro-19 ducts have a Poisson distribution of the number of ethoxy units due to the epoxide rin~ opening involved in their synthe-21 sis. These primary products of varying average ethoxylation 22 are often mixed to produce a desired average ethoxylation for 23 certain applications. Of course, such mixin~ of two ethoxylated 24 surfactants results in a wider molecular weight distribution of bimodal character. In some use areas, mixtures of sur-26 factants of widely different ethoxylationare desirable. How-27 ever~ for the synthesis of the present li~uid crys~als of 28 increased stability, a narrow molecular weight distribution lL~3~i~3~3 1 is desired. If two components of different ethoxylation are 2 mixed, it is preferred that their degrees of ethoxylation 3 should differ by less than 10, more preferably less than 5, 4 most preferably less than 2. As a rule, mixing of different ethoxylation surfactants is recommended only for an exact con-6 trol of average ethoxylation where desired. Whenever eco~omi-7 cai, surfactant components having a single eth~xylation value 8 are preferred. Beyond liquid crystal stability, this is also 9 advantageous for reducing selective adsorption since adsorption ~ is also reduced by increased ethoxylation.
11 Largely for economic reasons, the application of 12 surfactant mixtures is so~etimes desired. For example, as 13 far as anionic surfactants are concerned, the mixing of in-14 e~pensive petroleum sulfonate salts with ethoxylated sur-~ factants can be advantageous. It is surprisingly found that 16 such mixtures with petroleum sulfonates, e.g., ethoxylated 17 sulfonRtes, sulfates and phosphates, are stabilized when 18 present in the liquid crystals of this invention.
19 - A preferred class of liquid crystals has surfactants containing moieties having direct and indirect temperature-2~ solubility relationships.in a balanced proportion. For ex-22 ample, such surfactants have appropriate segments of alkyl 23 groups wh~se solubility ~ncreases ~ith te~perature and poly-24 ethylene oxide segments which bec~me less soluble with ~n-creasing temperatures. The solubility of surfactants optimized 26 Ln this manner does ~t change signific ntly in a broad tempera-27 ture range. This cha~acteristic stabilizes the temperature 28 stability of the present lyotropic liquid crystals and con-29 sequently extends their applica~ion to varying ~il fields of ~13~i~39 l increasing temperature.
2 With respect to the chemically enhanced displace-3 ment of oil, the techniques for secondary or tertiary recovery 4 conventionall~ employed with microemulsions are applicable to liquid crystals. A t~iczl proc~dure includes the inject~o~
6 of a liquid crystal slug followed by a pusher slug and a 7 slug of unthickened water. The pusher ~hg is usually a 8 thickened brine so as to el~minate fingering effects. Any 9 of the conventional thickening agents may be use to provide viscosity control. Examples include polysaccharides and 11 biopolymers such as xanthan polYmers, partially hydr~lyzed 12 -polyacryl~mides, fat~y acid ssaps, algina~es, amines, glycerine 13 and the li~e.
14 The amount of li~uid crystal injected is that ef-15 fective to displace oil from the oil-bearing formation. Gen- -16 erally, from 0.01 to 1 0 pore volume based on the pore volume 17 of the formation is sufficient.
18 The brine used in the liquid crystal and/or pusher 19 is preferably similar to thst found in the formation.
The liquid crystals may contain as opticnal 21 add~tives, co-surfactants and/or co-solven,s. Preferred 22 co-surfactants and co-solvents include alcohols, ethox~lated-, 23 sulfated ethoxyl2ted- and sulfo~ated etho~lated alcohols, 24 all of ~hi~h are C3 to C20 in thP aliphatic chin as t~ell as ethoxylated-, sulfated ethoxylated- and sulfonated ethoxylsted al~l phenols.
27 The add-tion21 com~o~e~t~ can also include alcohol 28 solubilizers and cosurfactants, such as i-butanol, i-hexanols;
2~ sulfonate hydrotropes such as xylene sulfonate salts, poly-.

.
.

1:~3~39 _ 20 -1 acid salt chelating agents such as the sodium salt of tris-2 carboxymethyl ~hosphine, ~olymers such as branched po~y-3 ethylene o~ide, polysaccharide biopolymer~, polymeric sul-4 fonates. Unexpectedly, unlike most kno~m microemulsions, the present liquid crystals do not re~uire co~surfactants.
6 The present liquid crystals can be employed as a 7 homogeneous fluid or in an admixture with either isotropic 8 b~ine or microemulsion. Such mixtures are genera~ly emul-9 sion stabilized by the liquid cryst21 component. They are often formed directly from the liquid crystal components in 11 one step. Both homogeneous liquid crystals and liquid 12 crystal-brine mixtures can be emDloyed for oil recovery.
13 The liquid crystalline displacement fluids of the 14 present inventio~ can be emplPyed via conventional oil re-15 covery techniques, particularly those developed fos employ-16 ing microemulsions.
17 For further details on oil recovery techni~ues using 18 microemulsions, reference is made to R. W. ~ealy ~nd R. L.
19 Reed, Soclety of Petroleum Engineers, ~2~ 129 (1977) snd the papers cited therein.
21 In spite of the relatively high viscosity exhibited 22 by liquid crystals, it has been discovered ~at ~heir use in 23 oil recovery results in a more complete recovery at a faster 24 rate as compared t~ similar micr~emulsio~s. This is in con-25 ~rast to the general view of the art th~¢high viscosity is 2~ a disadvantage in terms chemically enhanced oil recovery.
27 In fact, typical prior art microemulsions have very ~w vis-28 cosities and require thickeners so as to avoid fingering ~9 effects. In additi~n, liquid crystals are usually f~und to ~3f:~39 _ 21 1 be more stsble to dilution by brine than microemulsions.
2 The method of the invention is further illustra~ed 3 by the following e~amples.

__ General Test Procedures. Oil recoveries are de-6 termined by conventional sand pack tests. The sand used is a 7 crushed Berea sandstone of 40 to 100 mesh size. Oil dis-8 placement measurements are determined from a glass burette g having a 15mm diameter, a total volume of 100 ml and cali-brated at 0.1 ml intervals.
11 Filter paper is positioned in the bottom of the 12 b~rette and the burette rotated while 75g of sand is slowly 13 ~dded over a period of about 15 minutes. Thereafter, a filter 14 paper and a magnetic stirrer ~re placed on top of the sand.
The total weigh~ of ssnd ischech~and its volume (~46ml) 16 determined~ -17 Air is purged from the burette by carb~n dio~ide 18 for 30 minutes. The column is ~hen flooded from ~he bottom 19 with 40 ml brine at a rate of about 20 ml per hour. The 20 brine used in the examples is T~r Springs Brine (TS~), ;
21 characteristic of the L~udon oil field. TSB contains about 22 1~ wt./vol. % of mixed sal~s with a 9 t~ 1 mono-to divalent 23 met~ salt ratio. The composition of the salts in grams/
24 liter is as follows: NaCl - 92.07; CaC12 - 7.89; MgC12 -4.93; BaC12-2~20 - 0.113; NaHC03 - O.lg5.
26 The brine is injected into the column with a Sa~e 27 Syringe Pu~p, Model 355, having 50 ml syTinges. The 20 ml 28 per hour delivery is provided at the 1/100 x 50~ setting from 29 the syringe through a 1/8 inch Teflon tubing fit~ed to the ~31~3g 1 bottom of the column. After the brine flooding, the supernatant 2 aqueous phase is removed and the column weighed to determine 3 the pore volume by difference. The pore volume is usually 4 about 18 ml.
Thereafter, the column is ag~in f~ooded, this time 6 with 35 ml oil (Loudon crude) at the same rate. The volume 7 of the top oil layer is measured to determine the volume of 8 the resident oil by difference. The resident oil is usually g about 10 ml.
lQ The final step of preparing the sand pack for testing 11 is flooding with 40 ml brine again at the same rate. The 12 volume of oil removed is then determined and the residual 13 oil saturation calculated. Its value is usually about 4 ml.
14 The excess liquids are then syphoned off from above the sand and the sand pack column i. ready for oil recovery testing.
16 The prepared test column is flooded from the bottom 17 with 40 ml of the displacement medium at a rate of 2 ml per 18 hour. This rate is provided b~ a l!loO0 x 40% setting. The 19 total volume out, volume of oil produced and the posi~ion of the advancing oil front are observed. The time of break-21 through for the aqueous media and the appearance of liquid 22 crystals below the oil are also ~oted. The main results of 23 the experlments are shown in the examples by appropriate 2~ fi~ures w~erein t~e fraction of pore volume liquid produced versus the percentage oil recovery Rre plotte~.
26 Exam~le 1 27 This example illustrates the improved ~il recovery 28 by a liquid crystal composition versus a microemulsion, wherein 29 the active component of both, i.e., the surfactant, is a combined anionic-cationic surfactant. The combined surfactan~s , ~ ~

1136~39 1 are quaternary ammonium sulfonates having sli~htly varying 2 degrees of ethoxylaeion and are described in the following 3 formula:
4 ~ (CH2CH20)XH
i-C12H25 ~ r S03 C18H37 l\
67 ~ _ H3C ~cH2cH2~)yH
x I y = 7, 7.5 8 The combined surfactants are prepared by mi~ing 9 stoichiome ric amounts of the sodium salt of the sulfonic acid with the ethoxylated quaternary ammonium chloride.
11 Two liquid cryseals (lc) and one microemulsion 12 (me) based on the above-described surfactant systems are 13 prepared. The first lc composition contains 12 wt. parts 14 combined surfactant (x + y ~ 7.5 prepared by c~mbining x + y 5 and x + y - 10 product~) in a 50/50 mi~ture of Tar Springs 16 Brine (TSB) and Dis~illed Loudon Crude Oil (Oil). This 17 composition was prepared by adding 4% of the combined sur-18 factant t~ the mi~ture of TSB and Oil. The resulting emul-19 sion was then centrifuged at 25,000 G for four hours. As a result, the lc composition sepArated as a birefringent mid-21 dle phase. This lc compositicn had a lamellar struc~ure 22 according to ~-ray diffraction studies. The repeat layer 23 distance was 68A;. Its apparent Brookfield viscos~ty is 80 cP
24 at a shear rate of l.6 sec~l. It is shear ~hinning, i.e., non-Newtonian in character, as lamellar liquid crystsls 26 ~enerally are.
27 The second lc compositisn was produced ~y adding 28 3 wt. parts of a similar surfactant having a sligh~ly lower 29 degree of ethoxylation ~ ~ y e 7) ~ 100 parts of a TSB,n-~3~~39 1 decane mixeure having a 93 to 7 volume ratio. Thic lc had 2 a lower Brookfield viscosity (30 cP at 1.6 sec 1) but was 3 also non Newtonian in character at low shear rates.
4 The third composition was a microemulsion produced by 2 parts per 100 of the surfactant of the first lc when 6 using a 93 to 7 TSB to n-decane ratio. This me had a very 7 low apparent viscosity, 3.6 cP at 7.3 sec~l.
8 The oil recovery results obtained using the three 9 compositions are summarized in Figure 1 by plotting fraction ~ of pore ~lume.fluid injected as a function of residual oil 11 recovered. In Figure 1, the symbols ~ , ~ and O reprçsent 12 the first and second liquid crystals and the microemulsion, 13 respectively. In essence, these results demonstrate that the 14 two liquid crystals displaced oil at a similar and much raster-1~ rate than the m~croemulsion.
16 The use of the first lc resuited in a rapid oil bank 17 for~atiDn and front advancement. Oil production started early 18 at 0.43 pore volume (PV) and continued at a rapid, steady 19 rate until 79Z of the oil was recovered at 0.77 PV. There-2n after, 11 ml of a separate brownish liquid crystal layer was 21 produced. In volume, this is double of that of the residual 22 oil. This layer apparently contained si~nificant quantities 23 of Loudon Crude(LC) Oil in addition to the distilled Loudon 24 Crude (DLC) Oil. The brine phase remained clear and trans-25 parent during this secondary oil production. The brtne 26 turbulence, usually charact~ristic of microemulsion break~
27 through, occurred only thereafter at 1.34 PV. Indica~ions 28 were for complete LC oil plus DLC oil recDvery.

. , .

~13~i~339 1 In the csse of the second lc, oil production also 2 started early (0.41 PV) and occurred at a fast, steady rate.
3 LC oil pick-up by this Liquid crystal was less. About 87%
4 of the LC oil was produced as the first separate layer at 0.79 PV, Thereafter, again a liquid crystal layer was produced.
6 The comparative experiment with the me composition 7 also resulted in 2 complete oil recovery but at a much slower 8 rate. Oil production started at 0.76 PV. ~reakthrough g occursed when 86% of the oil was recovered at 1.46 PV. The total apparent oil production ~as 104~.
11 Exam~le 2 12 The effect on oil recovery by liquid crystals based 13 on the different structure of the combined 5urfa~tants is 14 described in this example. The surfactants are set forth as follows:
16 ~~ ,(CH2cH2o)xH

18 i-CnH2n+l WsO3C18H37 N~(cH CH O) ~
19 1: ~ ~ n = 12 R = tl x + y = 6 (~ ~ 7) ~ : ~ n = 18 R = CH3 x ~ y = 9.3 ~9 ~ 10) 22 The compositions of the liquid crystals are summarized in 23 the following table.

~ Composition Viscosity No. Symbol 19~ 5bP~ cP
26 _ (7.3 sec~l) 27 1 ~ 92 8 2.4 18 .

.

~3~9 1 The surfactant is expressed in wt. parts per 100 2 psrts of TSB/oil mixture in which the oil is n-decane. The 3 smounts of TSB Rnd oil are parts by volume. It is noted that 4 the average degrees ~f etho~ylation for the two surfactants were selected to control their hydrophilic-lipophilic balance 6 so as to provide liquid crystals of high brine to hydrocarbon 7 ratio. The surfactant concentrations were close to the minimum 8 needed to produce liquid crystals. Boeh liquid crystals had 9 a non-Newtonian shear thinning character and comparable apparent viscosities.
11 The oil recovery results obtained frDm the tw~ dif-12 ferent liquid crystals as a function of pore vol~me injected 13 ~s. oil recovered are shown in Figure 2 in which the oil re-14 covery from lc (~) is designated by ~ and lc (Il) by ~, 15 These results i~dicate that both liquid crystals produced 16 oil early and at a fast rate, and are very similar to ~he 17 results obtained from the liquid crystals of Figure 1.
18 I~ the case of the i-do~ecyl benzene sulfonate based l9 combined surfactant (I), breakthrough occurred after 8370 of the oil was recovered at 0.79 PV. At higher pDre volumes, 21 most of the oil was produced in a mixture with the tisplace-22 ment fluid as a Liquid crystal. By the time 1.17 PV fluid 23 was injected, 8.6 ml diluted liquid crystal layer accumulated 24 belo~ the recovered oil (3.6 ml, 86%). ~n centrifugation, 0.3 ml (7%) additional oil separated from this liquid crystal 26 composition. Inclu~ing this, the amount of the total oil 27 recovery was 93%.
28 When using the i-octadecyl-D-~ylene sulfonate based 2g combined surfactsnt (II), breakthrough occurred after recover-1~ 339 1 ing ~OZ of the oil at 0.84 PV. The overall oil recovery 2 behsvior of thi~ liquid crystal was s~milar t~ that of the 3 previ~us comp~sition. At high brine concentrations, this 4 combined surfactant, unlike thc~se described previously, has a tendency to form lc rather than me comp~sitions.
6 Exam~le 3 7 This ex~mple is directed to the effect of different 8 hydrocarbo~s on liquid crystal compositions containLng the 9 s~me combined surfact~nt and brine. The hydrocarbons are 10 n-decane (D) and distilled Loudon Crude Oil ~DLC). The 11 combLned sur act2nt is described by the following formula 12 and Table:

4 1~ 3~ 53 ~Cl8H37 N~(CH CH O) H~

16 11 }n-Decane(D) x + y = 8 17 lll ~ Distllled Loudon x ~ y = 9.1(.~ + 10) Composition\rlscosity,cP
21 No . Symbol Hydrocarbon TSB Surf (sec~1 ) -22 Type - (1.6) (8) 24 11 ~ D 9.5 90.5 3.8 100 48 111 ~ DLC 10 9D 3.8 114 56 ~3~39 1 The surfactant c~ncentration is in parts by weight per 100 2 parts of hydrocarbon/~SB mixture expressed in parts ~y volume.
3 It is noted ~hat to achieve the required hydrophilic-4 lipophilic balance, the use ~f a more highly ethoxylated com-bined surfactant was necess~ry i~ the oil tha~ in the decane 6 mixtures. It should be also observed with regard to the two -7 decane systems that the system containing a higher concentra-8 tion of the surfactant had a higher hydrocarbon content. The 9 decane system of lower surfactant concentration was of lower viscosity as expected. ~o~ever, both systems exhibited non-11 Newtonian rheology in the shear ra~e region studied (1.6-12 16 sec 1) 13 As is sho~n by Figure 3, the oil recovery be-14 havior of the three systems was very s~milar. The rate of oil production characterized by the overa~l slope of the in-16 jection-recovery correlation was practically identical for 17 the two mix~ures of higher surfactant concentration.
18 In the case of the t~o decane systems, the one with 19 more surfactant started producing oil earlier. However,. both systems produced oil almost at the same rate and continued 21 to produce oil in the form of liquid crystal after break-22 through-23 Interestingly, the distilled Loudon crude oil based 24 s~stem required more surfactanL to produce liquid crystal organization. However, this oil system of relatively high sur-26 factant content in most respects behaved like the decane sys-27 tem of low surfactant content. It took the longest time to 28 pr~duce oil ~nd breakthrough occurred after a relatively small 29 oil recovery. However, recovery in ~he form of li~uid crystals .' , 1~L3~ 39 1 continued. It was estimated on the basis of centrifugal 2 separation that at 1.36 PV, the total oil reco~ery was 93%.
3 E~ample 4 4 The comparison of liquid crystals versus micro-emulsions wherein the surfactant system is based on a mixture 6 of a~ionic surfactants is demonstrated by this example. One 7 liquid crystal and one ~icroemulsion~ere prepared with the s m~
8 mixture of two anionic sulfonate surfactants. The first sYr-g factant was a petroleum su~fonate sodium salt of 465 avera~e n m~ecu~ar w~igh, ~etr~5~ep 465, ~enu actured h~ Stepan 11 Chemical Co. The second was the sod um sulfonate derivative 12 of an e~hoxylated n-alcohol, EOR 200 manufactured by Ethyl 13 Corp. As such, the first surfactant was li~ophilic; ;he second, 14 hydrophilic in ch~racter. An approprizte mixture was used 15 to provide the hydrophilic-lipophilic balance required.
16 The composition of the Petrostep 465 was 57.8%
17 active sulfonate, 15.5% ~ater, 2~770 inorganic salts mainly 18 sodium sulfate and 24% non-sulfonated petroleum hydrocarbon.
19 The latter provided the oil component ofthe liquid crystal.
2n The technical ethoxylated sulfonate had an active content of 21 29.3% total solids of 4~% and 2% "oil."
22 Interestingly, the lc and me compositions were 23 prepared using the same concentration of the same surfactant 24 mixture plus pentanol: 3% Petrostep 465 (1~77v active), 7%
25 E~R-200 (2% active), 2~ pentanol. When 5% aqueous sodium 26 chloride was used to make up the rest (88%), the liquid crystal 27 formed. When 2% aq. NaCl was employed instPad, a microemulsion 28 havin~ ~ viscosity of 16 cP at 8 sec ~ was produced. The Brook-29 field viscosities were 20 cP and 16 cP, respectively, at a ~ ~r~ ar~

~3~3~

30 -1 shear rate of 8 sec~l.
2 The liquid crystal had a non-Newtonian, i.e., shear 3 thinning, viscosity character. However~ its viscosity in-4 creased as shearing continued as indicated by the following 5 results of repeated Brookfield viscosity determinations:

TABLE III

8 . Apparent Yisc~sity, cP at Yari~us (Stirring Rates, rp~ Shear Rates, Sec~
9Sequence of (6) (12) ~30) (60) 10Yiscosity T~st 1.6 3.2 8 16 28 20 20 ~1 13 The m~croemu~sior was le~s v~scous and of a simple shear 14 thinning behavior. At the 7.3 sec~l shear rate, this mi~-ture had an apparent viscosity of 16 cP.
16 The pil recovery behavior for the liquid crystal 17 (~ ) and microemulsion (~ ) is shown in Figure 4. This figure 18 demonstrates the much superior behavior of the liquid crystal lg (lc) versus that of the microemulsion (me).
The use of the 5% NaCl aq. lc mixture, resulted in an 21 early oil production at a fast rate. By the t~me of the break-22 through at `1.07 PV, 94~/~ of the ~il was recovered. At 1.11 23 PV, complete recovery W2S observed. Thereafter, the formation 24 of a second liquid crystalline phase was observed between ~he recovered oil and displaced brine layer. The eventual oil 26 production was more than 100%, apparently due to the oil intro-27 duced 2S a component of the liquid crystal composition.
28 In contrast, the application of the 2% NaCl mi~ture 29 resulted in a comparatively delayed incomplete oil production.

113~;~39 Oil production started at 0.73 PV. After recovering only about 26~ of the-oil, breakthrough has occurred at 1 PV. The total recovery was about 82% after 1.56PV.
Example_5 This example lllustrates some properties of microemul-sions versus liquid crystals based on combined ammonium sulfonate surfactants. Ammoniate surfactants such as combined anionic-cationic surfactants of balanced hydrophilic-lipophilic character by definition will provide a middle phase containing equal volumes of oil and water (b~ine) and/or will reject equal amounts of oil and water (brine) when mixed in proper amounts with equal volumes of oil. Such middle phases can have a multiple phase character and a liquid cyrstalline, liquid crystalllne plus isotropic microemulsion or isotropic microemulsion only character as exemplified by the following.
Approximately balanced middle phases were obtained using three combined quaternary ammonium sulfonate surfactants prepared from the corresponding methyl esters of sulfonic acids. The esters are described in U.S. Patent 4,310,471 of A. A. Oswald and E. J. Mozeleski. The c~mbined quaternary sulfonates were pre-pared by reacting the ester with the appropriate ethoxylated amines. The structures of the three surfactants used are shown in Table IV. The other components of the mixtures were 0.4g (~v4%) surfactant, 5ml (~ 48%) distilled Loudon crude oil and 5ml (,v48%) of brine of varylng salt concentration. Homogeneous mixtures were prepared by Vortex* stirring for about 15 minutes. The mixtures were then centrifuged at 25 C for a total of three hours at 27,000G. To obtain *Trademark 113~39 1 stable three phase systems: Oil phase on the top, "micro-2 emulsion" middle phases and brine on the bottom. After the 3 centrifugation, the phase volumes were determined and the 4 middle phases were studied for visual appearance and bire-fringence. ~iddle phase samples were also investigated 6 using polarizing and phase contrast microscopy. The ob-7 servations are summarized in Table n.
With regard to phase distribution and salt insen-9 sitivity, the results are described as follows. The volu~es of the rejected oil and brine phases were generally compar-11 able and surprisingly independent of the salt concentrations.
12 Surprisingly, the investigaeion of the middle phases demon-- -13 strated that in the majority of cases, they contained aniso-14 tropic liquid crystals in isotropic fluid. It was par-1~ ticularly surprising that at hi~h brine concentrations., liquid 16 crystal formation appeared to be enhanced. The presence 17 of oil appar~ntly stabilized the liquid crystals.
18 The first combined surfactant9 a ~ure one component 19 compound (A), produced typical middle phase microemulsions at most brine concentrations. Significant liquid crystal 21 middle phase formation occurred only when Tar Springs Brine 22 (TSB) containing 10% of mixed salts including about 23 9.2% NaCl, 0.8% CaC12 and Q.5% CaC12 was used. .
24 The second combined surfactant (B), a quaternary ~5 analog of a combined surfactant havin~ an avera~e degree of 26 ethoxylation, produced birefringent liquid crystal middle 27 phases at all salt concentrations. To the naked eye, most 28 of these middle phases appeared to be typical trarslucent 29 microemulsions. However, under the microscope,it became ~n clear that they had lar~er droplet sizes.

.

~13-~39 _ 33 -1 The anisotropic liquid crystals separated from brine 2 mix~ures of different concentrations were microscopically 3 different as illustrated by the pictures of Figure 5. Most 4 often liquid crystal droplets of various size (in the 16~ region) were observed as found in 10% TSB (Pictures 6 A-l and A-2) At 5~ NaCl concentrat on, one of the liquid 7 crystal phases appeared definitely lamellar in character 8 (Pictures B-l and B-2). Finally, at 2% salt concentrat;on, g typical flow birefringence was observed (Picture C).
The third combined surfactant (C) of T~ble IV
11 based on an ethoxylated ether amine, produced liquid crystal-12 line phases similar to the Ethomeen derivative (B). Again 13 the translucent liquid crys~als had the typical microemulsion 14 appearance~
The behavior of eight centrifuged ~hree vhase sys-16 tems based on the two hydroxy terminated ethoxylated amine 17 derivatives ~B and C) were studied at various temperatures 18 ~o determine the stability of the liquid cry~tal phases.
19 Observations at 35, 50 ~nd 70C showed that the anisotropic liquid crystal character of the middle phases was maintained, 21 although the phase distributions changed somewhat.
22 Beyond the above microscopic studles, the structure 23 Of liquid crystals could be also diagnostically characterized 24 by nuclear magnetic resonance (nmr). ~mr indicated special structural interactions increasing the relaxation times of 26 nuclei. Investications of the above middle Phases and 27 other liquid crystal mixtures showed that the viscosity of 28 such liquid crystals is not necessarily too high and their 29 interfacial tension is a~ a minimum. Therefore, liquid ~3~i~39 - 34 _ 1 crystals possess oil displacement propereies attractive for 2 oil recovery.

. ` - ;

3~
- ~5 -_:~ _X
O O
~ ~ C~
Z ~ N U~
j O :~: T
C~ C
~, 1-- + 2 ~r Z T 't Z ~ 1 ' X

~ 5 _X _ J~ Cl c ~ , =i ~J ~ O K
J Z m , =~

IL o N N ~J

J

O C~ C

~ D ~ o Z Zo~ ~ I V
~ C~
C J ~r) z ~ ~ r m c~ u~
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. o ct ~31 3~i~39 . ~ E ~, ~ G

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E ~ ~t N ~ j Z
~ oJ ~ .' j , ~ i U~ ~ o ~
~ ~ c ~ . ~ C ", _ I _ z '5 E _ -- s: E , z ~
~ c ~ ~ ~' ~, t . ~ ~ , , s~ I =
Z 1~5 ~ CC) ~ O C7` N 1 c ~s ~ ~ ~
C o C~ i ' i Y i ' ~~ ~ Oc V~ V~ I ~
~n I_ ~ E c E ' ~ E E
H r _ ~ LL~ W ILI I _ I LLJ L~J
_ ~ i ' ~ 5 ~
_I ~I N I ~ N ~ CQ j ~1 _I t~l O ~ N N N ~J ~ ~ N N N j ~ ~1 N t~l D _ C~ I ~ ~ J N OD ~
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¦ C ' ~ U'l N ! O Lt'\ Ir~ N ! t~ u~ u~ N
-c~ ' m ~ 2 ~ 1~ 2 , ~ 6 j ~ i ' u~
o I -_~ !=-" i=~>

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3~

1 Exam~le 6 2 Oil recovery by liquid crystals was also examined 3 using a number of different types of surfactants and their 4 mixtures exemplified as follows. A translucent, flow bire-fringent mixture based on a 2.1% sodium i-dodecyl-o-xylene , ~ ~
6 sulfonate (88% active) and 1.9% Igepal DM-730 from GAF
7 Corp (a tetradocosa-ethoxylated dinonyl phenol) produced 8 a similar high and early oil recovery to the liquid crystal 9 compositions described above. This sho~s that mixtures of sulfonates, particularly alkylbenzene sulfonates, and 11 ethoxylated higher alkyl phenols, particularly higher dialkyl 12 substituted phenols are attractive surfactant mixtures for 13 obtaining liquid crystalline compositions for oil recovery.
14 As is ~enerally the case~ suc~ mixtures could be used with or without polymers.
16 A liquid crystalline mixture of 4Z Petrostep 465 17 and 2% Siponic L-7 which is an ethoxylated lauryl alcohol 18 manufactured by Alcolac, Inc., also produced excellent oil 19 recovery results.
~ Tradc ~

Claims (36)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for recovering oil from an oil-bearing formation in the presence of highly concentrated brine which com-prises displacing oil with a primary displacement fluid contain-ing lamellar lyotropic liquid crystals which exhibit decreasing viscosities at increasing shear rates and comprise 0.05 to 10 vol.%
of surfactant, 0.1 to 20 vol.% of an oil and the balance brine containing from 5 to 30 wt.% of inorganic salts having sodium chloride as the major component and salts of divalent metals as minor components, driving the liquid through the formation, and recovering the displaced oil.

2. An improved process for recovering oil from an oil-bearing formation by injecting into the formation a liquid contain-ing an effective amount of a surfactant to displace oil, driving the liquid through the formation and recovering the displaced oil, the improvement comprising using as the liquid a lamellar lyotropic liquid crystal which exhibits decreasinq viscosities at increasing shear rates and contains (a) 0.05 to 10 vol.~ of surfactant of balanced hydrophilic-lipophilic character, (b) 0.1 to 20 vol.% of an oil, and (c) the balance,brine containing from 5 to 30 wt.% of inorganic salts having sodium chloride as the major component and salts of divalent metals as minor com-ponents.

3. The process of claim 2 wherein the amount of oil is from 0.5 to 10 vol.%.

4. The process of claims 1 or 2 wherein the inorganic salts include Ca2+ and Mg2+.

5. The process of claims 1 or 2 wherein the oil is a distillate hydrocarbon oil.

6. The process of claim 2 wherein the surfactant is an anionic, cationic, nonionic, amphoteric surfactant, or mixtures thereof.

7. The process of claim 6 wherein the anionic surfactant is a sulfonate, sulfate or ester of phosphorus acid.

8. The process of claim 6 wherein at least one surfactant component is ethoxylated.

9. The process of claim 7 wherein the sulfonate is C18 to C56 alkylaryl or C12 to C60 aliphatic sulfonate.

10. The process of claim 7 wherein the sulfate is C12 to C40 aliphatic sulfate or a sulfated ethoxylated higher alcohol or alkyl phenol where the alkyl moiety of the alcohol or phenol is from C12 to C36 and C12 to C60, respectively.

11. The process of claim 7 wherein the ester is a C12 to C40 ester of a phosphorus acid or a phosphated ethoxylated C12 to C40 alcohol-

12. The process of claim 6 wherein the cationic surfactant is an ethoxylated derivative of C12 to C40 aliphatic amine, C12 to C40 diamine or triamine, C12 to C30 amine, C13 to C40 quaternary aliphatic ammonium or quaternary phosphonium salt having from 1 to 4 C12 to C40 aliphatic groups.

13. The process of claim 12 wherein cationic surfactant is ethoxylated with from 2 to 30 moles of ethylene oxide.

14. The process of claim 5 wherein the nonionic surfactant is an ethoxylated C12 to C40 alcohol.

15. The process of claim 6 wherein the nonionic surfactant is an ethoxylated phenol of the formula (CnH2n+l)m - A - [O(CH2CH2O)p]qH
where n is from 1 to 30, A is benzene, naphthalene or diphenyl, p is 2 to 30, q is 1 or 2 and m is from 1 to 5 with proviso that there is at least one C12 to C30 alkyl chain.

16. The process of claim 1 wherein said pri-mary displacement fluid contains a balanced surfactant.

17. The process of claim 1 wherein said primary displacement fluid contains a balanced ethoxylated surfactant.

18. The process of claim 1 wherein the primary displacement fluid contains balanced ethoxylated anionic, ethoxylated cationic and ethoxylated nonionic surfactants terminated by hydroxy groups.

19. The process of claim 1 wherein the primary displacement fluid contains an ethoxylated sulfonate surfactant.

20. The process of claim 19 wherein the ethoxyl-ated sulfonate surfactant is selected from the group consisting of C15 to C30 alkylaryl sulfonates or C16 to C40 aliphatic sulfonates.

21. The process of claim 1 wherein the primary displacement fluid contains an ethoxylated nonionic surfactant terminated by hydroxy groups.

22. The process of claim 21 wherein the ethoxylated nonionic surfactant is an ethoxylated alkylphenol.

23. The process of claim 1 wherein the surfactant is a balanced combined anionic-cationic surfactant biamphiphilic salt containing surfactant ions selected from the group consisting of anionic, cationic and amphoteric ions.

24. The process of claim 8 wherein the ethoxylated surfactant component is terminated by hydroxy groups.

25. The process of claim 8 wherein the ethoxylated surfactant component contains an alkyl substituent.

26. The process of claim 25 wherein the alkyl and poly-ethylene oxide moieties are selected to provide temperature stable liquid crystals.

27. The process of claim 24 wherein the surfactant com-ponent comprises a mixture of a petroleum sulfonate and ethoxylated surfactant or sulfonate surfactant and ethoxylated higher dialkyl phenol.

28. The process of claim 2 wherein the balanced surfac-tant comprises an ortho-substituted alkyl benzene sulfonate and an ethoxylated surfactant.

29. The process of claim 28 wherein the sulfonate is an alkyl xylene sulfonate.

30. An improved process for recovering oil from an oil bearing formation by injecting into the formation a liquid contain-ing an effective amount of a surfactant to displace oil, driving the liquid through the formation and recovering the displaced oil, the improvement comprising using as the liquid a lamellar lyotropic liquid crystal which exhibits decreasing viscosities at increasing shear rates and contains (a) 0.05 to 10 vol.% of a balanced combined surfactant biamphiphilic salt composed of surfactant ions of anionic, cationic and amphoteric surfactants, (b) 0.1 to 20 vol.% of an oil, and (c) the balance brine containing from 5 to 30 wt.% of in-organic salts having sodium chloride as the major component and salts of divalent metals as minor components.

31. An improved process for recovering oil from an oil bearing formation by injecting into the formation a liquid contain-ing an effective amount of a surfactant to displace oil, driving the liquid through the formation and recovering the displaced oil, the improvement comprising using as the liquid a lamellar lyotropic liquid crystal which exhibits decreasing viscosities at increasing shear rates and contains (a) 0.05 to 10 vol.% of a combined anionic-cationic surfactant biamphiphilic salt composed of surfactant ions of anionic, cationic and amphoteric surfactants, (b) 0.1 to 20 vol.% of an oil, and (c) the balance brine containing from S to 30 wt.% of inorganic salts having sodium chloride as the major component and salts of divalent metal as minor components.

32. The process of claims 30 or 31 wherein the combined surfactant biamphiphilic salt is composed of surfactant ions of anionic and cationic surfactants.

33. The process of claim 30 wherein the balanced hydrophilic-lipophilic character of the combined surfactant biam-phiphilic salt is achieved by adjusting the degree of ethoxylation in a surfactant component.

34. An improved process for recovering oil from an oil bearing formation by injecting into the formation a liquid contain-ing an effective amount of a surfactant to displace oil, driving the liquid through the formation and recovering the displaced oil, the improvement comprising using as the liquid a lamellar lyotropic liquid crystal which exhibits decreasing viscosities at increasing shear rates and contains:

(a) 0.05 to 10 vol.% of a combined surfactant of the formula wherein R is phenyl, tolyl or xylyl; R' is H or CH3; n is 12 to 40, m is 12 to 36 and x + y is 2 to 30;
(b) 0.1 to 20 vol.% of an oil; and (c) the balance brine containing from 5 to 30 wt.% of inorganic salts having sodium chloride as the major component and salts of divalent metals as minor components.

35. An improved process for recovering oil from an oil bearing formation by injecting into the formation a liquid contain-ing an effective amount of a surfactant to displace oil, driving the liquid through the formation and recovering the displaced oil, the improvement comprising using as the liquid a lamellar lyotropic liquid crystal which exhibits decreasing viscosities at increasing shear rates and contains (a) 7 vol.% of Loudon oil;
(b) 3 wt.% of a combined surfactant of the formula where x + y = 7 and (c) the balance brine containing 10 wt.% inorganic salts including about 9% sodium chloride and about 1%
salts of divalent metals.

36. An improved process for recovering oil from an oil bearing formation by injecting into the formation a liquid contain-ing an effective amount of a surfactant to displace oil, driving the liquid through the formation and recovering the displaced oil, the improvement comprising using as the liquid a lamellar lyotropic liquid crystal which exhibits decreasing viscosities at increasing shear rates and contains (a) 0.05 to 10 vol.% of balanced surfactant;
(b) 0.1 to 20 vol.% of an oil;
(c) a polymeric conventional thickening agent and (d) the balance brine containing 5 to 30 wt.% of inor-ganic salts having sodium chloride as the major com-ponent and salts of divalent metals as minor components.