CA1082101A - Process for displacing oil with aqueous sulphonate and alcohol surfactant system - Google Patents
Process for displacing oil with aqueous sulphonate and alcohol surfactant systemInfo
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- CA1082101A CA1082101A CA286,879A CA286879A CA1082101A CA 1082101 A CA1082101 A CA 1082101A CA 286879 A CA286879 A CA 286879A CA 1082101 A CA1082101 A CA 1082101A
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- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
- C09K8/58—Compositions for enhanced recovery methods for obtaining hydrocarbons, i.e. for improving the mobility of the oil, e.g. displacing fluids
- C09K8/584—Compositions for enhanced recovery methods for obtaining hydrocarbons, i.e. for improving the mobility of the oil, e.g. displacing fluids characterised by the use of specific surfactants
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Abstract
A B S T R A C T
In displacing oil within a subterranean reservoir with an aqueous surfactant system containing a mixture of petroleum sulphonate and alcohol, an improvement is provided by using particular kinds and amounts of those components. The selected surfactant is one that forms an active aqueous surfactant system in the presence of an effective kind and amount of dis-solved electrolyte. The selected alcohol is a preferentially oil-soluble alkanol that provides at least substantially equal activity when mixed with the selected surfactant in an aqueous system containing little or no dis-solved electrolyte.
In displacing oil within a subterranean reservoir with an aqueous surfactant system containing a mixture of petroleum sulphonate and alcohol, an improvement is provided by using particular kinds and amounts of those components. The selected surfactant is one that forms an active aqueous surfactant system in the presence of an effective kind and amount of dis-solved electrolyte. The selected alcohol is a preferentially oil-soluble alkanol that provides at least substantially equal activity when mixed with the selected surfactant in an aqueous system containing little or no dis-solved electrolyte.
Description
los2lal The invention relates to a process for displacing oil within a subterranean reservoir. It is useful for displacing a reservoir oil toward a location from which oil is produced, for displacing a residual oil away from a well to improve injectivity, or the like.
Aqueous anionic surfactant systems are known to be particularly efficient for displacing oil. Such an anionic surfactant system is a substantially homogeneous aqueous liquid composition that may comprise a solution, a micro-emulsion, or a micellar dispersion of anionic `` surfactant molecules and/or micelles. The water-solubilities and oil-solubilities of the surfactants in such a system are such that those materials tend to remain along an oil/water interface, rather than being completely dissolved or dispersed within either the water-phase or oil-phases of the system. The anionic surfactants comprise surface-active salts or soaps of organic or inorganic acids.
According to the present invention an oil is displaced within a subterranean reservoir by injecting an aqueous surfactant system in which a petroleum sulphonate surfactant composition is mixed with a kind and amount of an alcohol that increases both the oil-displacing activity and the effective viscosity of the surfactant system.
A petroleum sulphonate surfactant component is selected from among those capable of forming an active aqueous surfactant system when dissolved or dispersed in a selected proportion, such as from about 2 to 10% by weight, in an aqueous liquid that contains a surfactant activity-enhancing kind and amount of dissolved electrolyte.
- 25 A preferentially oil-soluble alkanol is selected from among those capable of increasing the interfacial tension lowering activity of a solution or dispersion of the selected surfactant in the selected concentration in distilled water to an activity substantially equalling that of the electrolyte-containing system.
An aqueous surfactant system is compounded by dissolving or dis-persing the selected surfactant composition in the selected concentration in an aqueous liquid which contains significantly less than said activity-enhancing amount of dissolved electrolyte and contains the selected alkanol in a proportion that increases the stability of an emulsion that can be formed within a test tube by mixing the so-compounded ~ .
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surfactant system with the oil to be displaced at the temperature of the subterranean reservoir. The so-compounded surfactant system is injected into the subterranean reservoir to contact and displace the oil.
The present invention relates to a process for displacing oil within a subterranean reservoir by injecting an aqueous surfactant system containing a petroleum sulphonate surfactant and an alcohol, in which an improved procedure is applied for correlating the kind and amount of the surfactant and the alcohol to increase both the : 10 oil-displacing activity and the effective viscosity of the system, which comprises:
selecting a petroleum sulphonate surfactant which is capable of forming an active aqueous surfactant system when it is dissolved or dispersed in an aqueous liquid solution containing an effective kind and amount of surfactant activity-enhancing electrolyte;
; selecting a preferentially oil-soluble alkanol which is capable of increasing the interfacial tension lowering activity of a solution or dispersion of the selected kind and amount. of petroleum sulphonate surfactant in distilled water to an activity at least substantially equa~ingthat of said electrolyte-containing surfactant system;
compounding an aqueous surfactant system by dissolving or dispersing the selected kind and amount of petroleum sulphonate surfactant in an aqueous liquid which contains less than said surfactant activity-enhancing amount of electrolyte and contains the selected alkanol in a proportion which, in a test tube, increases the stability of an emulsion of the surfactant system and the oil to be displaced : .
at the temperature of the subterranean earth formation; and injecting the so-compounded surfactant system into the sub- ..
terranean reservoir to contact and displace said oil.
According to the present invention it has been found that .
typical sulphonate surfactant compositions which are capable of forming active aqueous surfactant systems in aqueous liquids containing effective ~ ~
kinds and amounts of dissolved electrolytes are also capable of forming : :
substantially equally active surfactant systems in distilled water :
containing an effective kind and amount of an alkanol.
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108Zl(~l Such alkanol-enhanced surfactant systems have relatively high effective viscosities, such as for example from about 2 to 85 centipoises at 75 C and 6 rpm and containing preferably 2-10% by weight of petroleum sulphonate surfactant. The present alkanol-enhanced surfactant systems tend to displace an oil within a permeable oil formation in the form of an oil bank that is substantially free of any entrained or emulsified aqueous liquid or surfactant system components.
They also tend to displace any water that is co-present with the oil within a permeable earth formation to such an extent that the sur-factant system is unaffected by the dissolved salt content of that water, even when that salt content is high and includes multivalent cations.
Although the present invention is not dependent upon any particular mechanism, the following seems to be involved. The hydrocarbon core 1 15 of a surfactant aggregate or molecule tends to be a liquid or i liquid-like, but when the micelle is small, only a small amount of ; oil can be dissolved. However, when the micelles become large and are contacted by oil droplets within the pores of a permeable earth formation, the oil droplets are absorbed into the micelles along the interface between the oil and water phases of the liquids within the pores. This causes the interfacial tension between the surfactant system and the oil to approach zero and the interface to become less distinct and the phases to become more miscible with each other.
In this situation the oil droplets can readily be deformed and, as the surfactant system flows among the droplets, the droplets become elongated into fine streams that are able to flow through the necks of pores of the earth formation. ~uch a flow causes the larger droplets or portions of substantially clean oil to move ahead and form into an oil bank. Meanwhile, as the surfactant micelles absorb more oil their oleophilic cores tend to become more oil-like. As the micelles become saturated with the oil they undergo transitions, from aggregates having polar groups oriented outward to lamellar types of aggregates, and finally to aggregates with polar groups oriented inward in a hydro-carbon-rich environment. -,., ' ~ '. -~ " - , . ,. ' . ' ' .
- ' :' . . .
--- 108Z~l Such a mechanism appears to be brought about when a petroleum sulphonate surfactant composition is mixed with an effective amount of an alcohol having a composition such that the polar and hydrocarbon groups of the surfactant and the alcohol are properly matched with respect to a balance of electrical forces, geometric compatibility, and mutual solubility. For example, for a mixture of relatively water-soluble and water-insoluble alkyl aryl petroleum sulphonates, such as for example TRS-12B, alkanols containing from 6 to 12 carbon atoms are (at a temperature of 75C) significantly more effective than their higher or lower homologs. It appears that, when the number of carbon atoms is too low, the alcohol tends to go into the aqueous phase, but when the carbon number is too high, the alcohol tends to go into the hydrocarbon core of the surfactant micelle. Only the alcohols in the medium carbon number range appear to stay in the palisade layers of the micelles, where they produce the large surfactant micellar entities. In the case of amyl alcohol, large surfactant entities are formed at room temperature, but, those formed at 75C
appear to be unstable because of the increased thermal motion of the molecule.
The tendency for the present alkanol-enhanced surfactant systems to displace an oil within a subterranean reservoir without forming any relatively viscous or stable emulsions (between any components of the surfactant systems and fluids in the reservoir) is an important advantage. Aqueous anionic surfactant systems containing active surfactants such as petroleum sulphonates or mixtures of petroleum sulphonates with alcohol or alkoxy-alcohol sulphates often form emulsions with the oil and water they are displacing within a permeable medium. The present surfactant systems, which contain alkanol-expanded micelles, are comparatively resistant to the formation of stable or viscous emulsions. This is advantageous in avoiding a tendency for mixtures of the surfactant system and formation oil to be by-passed by dryine fluids such as a thickened aqueous liquid for displacing the oil and surfactant system through the reservoir.
As known to those skilled in the art, in an oil displacement process, the interfacial tension-lowering activity is particularly important. An "active" aqueous surfactant system, as used herein, is one in which the interfacial tension between it and the oil is less than about 0.01 dyne per centimetre.
-- 108Zl(~l.
As used herein the term "petroleum sulphonate surfactant compo-sition", or "component" refers to a mixture of relatively water-soluble and water-insoluble petroleum sulphonate surfactants and/or their mixtures with sulphated alcohol surfactants or other cosurfactants. The ones of such compositions which are selected for use in the present invention are those capable of forming active electrolyte-containing surfactant systems. Such a capability can readily be determined by a testing procedure. For example, visual observations are made of the clarity and stability of an aqueous solution or dispersion containing about 1% of an at least about 60% surface-active surfactant composition in distilled water. Compositions that form satisfactory solutions or dispersions are subjected to emulsion testing.
A series of aqueous solutions containing from about 1 to 5% of the sur-factant and different amour.ts of sodium chloridç are prepared. An oil at least equivalent to the oil to be displaced is added to those solutions in a 1 to 5 volumetric ratio within a substantially solids free liquid container, such as a test tube. mlhe mixtures are agitated and heated to a temperature at least substantially equivalent to the temperature at which the oil is to be displaced within a subterranean earth formation.
Samples which tend to form some foam without forming a rather high standing foam column (e.g., equivalent to 0.75 inches or more, within 0.5 inch diameter test tubes) are generally suited for best performance of the surfactant system. In a preferred procedure, after the initial evaluation of emulsion grade and foaming characteristics, the samples are maintained -at about 35C for 24 hours, evaluated before agitation, agitated again and re-evaluated. The temperature of the samples is increased to about 76C and after agitation, both foaming and emulsion characteristics are again evaluated.
Typically, a petroleum su~honate surfactant composition which is an active system and a potentially good oil recovery agent will form relatively stable emulsions with a range of sodium chloride concentrations.
Preferably the oil displacing capability of the compositions which provide relatively stable emulsions are confirmed by tests of the capability of recovering oil from cores.
As known to those skilled in the art, other testing procedures can be utilized to determine whether a given petroleum Sulphonate composi-los~lal tion is capable of providing an active surfactant system, e.g., measure-ments can be made of the interfacial tension provided between that system and the oil to be displaced at the temperature at which the oil is to be displaced, sand pack and/or core-oil recovery tests can be made, and the like.
Particularly suitable petroleum sulphonate surfactant compositions comprise mixtures of relatively water-soluble and water-insoluble alkali metal salts of petroleum sulphonates (such as alkylaryl sulphonates, alky-lated benzene sulphonates, and the like). For uses at temperatures below about 65C, such mixtures can include sulphatedpolyoxyalkylated alcohol surfactants. Petroleum sulphonate surfactants are commercially available, for example, as Petronates and Pyronates from Witco Chemical Company;
Promor Sulfonates from Mobil Oil Company; and the like. Surfactant sulphates of ethoxylated primary alcohols are available as ~EODOLS from Shell Chemical Company. Other surfactant sulphates of ethoxylated alcohols are available as Tergitols from Union Carbide, and the like.
The alcohols used in the present invention are preferentially oil soluble alkanols selected for their capability of functioning in a manner substantially equivalent to a dissolved electrolyte with respect to increasing the activity of the selected petroleum sulphonate surfactant composition. Such alcohols generally have straight or branched saturated aliphatic hydrocarbon chains and contain from about 6 to 12 carbon atoms.
The selection of a particular alcohol for use with a particular surfactant composition can readily be made by an emulsion test of the type described above with differing amounts of alcohol concentrations being used in the place of differing amounts of sodium chloride concentration. Very suitable alcohols are hexyl alcohol, noxyl alcohol and 2-ethylhexanol.
The aqueous liquid used in compounding the surfactant systems of the present invention can be substantially any aqueous liquid which is substantially electrolyte free but, where desirable, may comprise an ~ -electrolyte-containing aqueous solution which contains a fraction, such as for example up to about 75%, of the amount of dissolved electrolyte that is effective in enhancing the activity of the selected petroleum sulphonate surfactant composition.
... . . . ....
1~8ZlC~l In compounding the present surfactant systems, the concentration of the selected alcohol which is used with the selected amount and kind of petroleum sulphonate surfactant composition is arranged by means of tests analogous to th~e described above. Various concentrations of the selected alcohol are used with the selected kinds and concentrations of the surfactant composition in an aqueous liquid containing l^ss than the surfactant activity enhancing amount of dissolved electrolyte. Such compositions are emulsified (in containers equivalent to test tubes) with the oil to be displaced at substantially the temperature of the subterranean earth formation in which it is to be displaced. The selected concentration of the alcohol is one which substantially optimizes the stability of such emulsions in the sense that the emulsions tend to be less stable when more or less of the alcohol is used.
As known to those skilled in the art, the viscosity of an oil-displacing surfactant system should be relatively high, in order to provide mobility control and avoid the bypassing of the oil or emulsified mixtures of the oil and the surfactant system. Such a viscosity can be provided by dissolving a water-soluble polymer in the surfactant system. However, the viscosities of commonly used polymer solutions decrease with in-creasing salt concentration. For example, a 500 parts per million solution of a partially hydrolyzed polyacrylamide polymer (Pusher 700) in distilled water has a viscosity of 46 centipoises. But, in a 1 molar sodium chloride solution, the viscosity of the same proportion of polymer is only 3.6 centipoises. In a solution containing 1,000 parts per million calcium ion, the viscosity decreases to 2.5 centipoises. Those values refer to measurements at room temperature and 7.3 reciprocal seconds.
The capability of the present systems to provide a viscous solution free of polymer can be advantageous in various oil-displacing operations.
Water thickeners can be used in, or in conjunction with, the ~ 30 present surfactant systems. Such thickeners can be substantially any - water soluble natural or synthetic polymeric material, such as a carboxy-methyl cellulose, a polyethylene oxide, a hydroxyethylcellulose, a partially hydrolyzed polyacrylamide; a copolymer of acrylamide and acrylic acid; biopolymers, such as the polysaccharides; or the like.
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Preferablythe compounded aqueous surfactant system is aged at about the temperature of the reservoir for at least about 24 hours prior to injecting it into the reservoir.
An oil in a permeable material is displaced in accordance with this invention by injecting a surfactant system of the invention to contact and push the oil. The surfactant system can be preceded or followed by substantially any aqueous or oil-phase fluid with which it is compatible. Where a slug of the surfactant system is displaced through a reservoir (e.g., in a chemical flood process) it is preferably displaced by a thickened aqueous solution having a viscosity greater than (and/or a mobility less than) the surfactant system.
Figures 1 and 2 show the oil recovery curves obtained by displacing oils at a water-flood residual with various aqueous surfactant systems.
In these figuresthe horizontal axis indicates fluid injection, Vp and the vertical axis oil saturation, % Vp. The cores used were ~erea sandstone cores, 25 cm long and 5 cm in diameter. With one exception, the cores - were water-flooded to a waterflood residual with 0.025 M NaCl before injecting 1.2 pore volumes of the surfactant system. The surfactant systems (or chemical slugs) were followed by 0.025M NaCl solutions to provide the indicated amounts of injected fluids.
With respect to test 383 (Figure 2) the core was mounted in a horizontal position and was waterflooded with synthetic D-sand/water (SDSW) before chemical injection. The SDSW water contained the follow-ing ions in parts per million: 74 barium, 1670 calcium, 12 copper, 1290 magnesium, 42900 sodium, 30 strontium, and 195 HC03 ion. In test 383 the chemical slug amounted to only 0.1 pore volume and was followed by 1.2 pore volumes of an aqueous solution of 1800 ppm Kelzan (a polysaccharide fermentation product produced by Xanthomonas Campestric)in 1% SDSW water.
The viscosity of that polymer solution was 52.8 cp (75C, 6 rpm).
The compositions of the aqueous sulphonate surfactant system (chemical slug) and the crude oils used in the core tests are listed in Table 1. Table 1 shows the viscosity of the chemical slugs and the amount of residual oil which was left in the core at the end of the oil recovery test.
Table 2 shows the optimum range of alcohol concentration for -each concentration of the petroleum sulphonate surfactant component.
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As mentioned above, these ranges were determined primarily by comparing the emulsification properties of surfactant systems containing the selected percent of sulphonate and varying percentages of alcohol. In Table 2 under 'Separation' are shown the percents by volume of alcohol which caused the aqueous surfactant system to undergo a phase separation.
Table 1 ; CHEMICAL SLUGS AND CRUDES USED IN CORE EXPERIMENTS AT 75C
Core . .Viscosity Scrc No. Slug Composltlon (cp) Crude (Vp) 371 6/w TRS-12B + 2%v Hexyl Alcohol51.7 NRB 0.000 375 6~w TRS-12B + 1%v Nonyl Alcohol51.0 NRB 0.027 368 6%w TRS-12B + 3.5%v SDSW 3.8 NRB 0.023 378 4.5%w TRS-12B + 3.4~v Hexyl Alcohol 83.0 NRB 0.000 382 6%w TRS-12B + 1.2%v Octanol-1 60.0 27%v 0.035 Isooctane in N4RB
388 6%wTRS-12B + 0.97%v Dodecyl Alcohol 24.2 27%v 0.059 - Isooctane in N4RB
383 6~ow TRS-12B + 2.2%v Hexyl Alcohol 42.0 27%v 0.081 (0.1 Vp Chemical Slug) Isooctane in N4RB
~RB, N4RB : crude oil from particular US oil fields orc : residual oil saturation after chemical flooding Table 2 (IN DISTILLED WATER) Alcohol TRS-12BOptimum Region Separation (%w) (%v) (%v) Hexyl Alcohol 6.o 1.8-2.8 3.8 (Eastman, Practical) " 4.5 2.6-3.8 ~- " 3.0Not active, not viscous 3.0 " 1.5Not active, not viscous 2.4 Octanol-1 6.o 1.2-1.6 2.4 (Fischer, Certified) - Nonyl Alcohol 6.o 1.0-1.4 2.0 (Eastman, Practical) Dodecyl Alcohol 6.o 0.97-1.2 1-7 ~- (Eastman, Technical) ~` 15 .: . . .
The capability of an alkanol to provide an enhancement of petroleum sulphonate surfactant interfacial tension lowering activity equivalent to those obtained by an electrolyte is shown in the data plotted in Figure 1. In test 368 the mixture of electrolytes contained in SDSW water was used to enhance the activity of an aqueous 6% petroleum sulphonate surfactant system. Test 375 shows that generally equivalent but somewhat better results (a removal of more oil with less surfactant injected) was obtained from a system in which the electrolyte was re-placed by 1% by volume nonyl alcohol. Test 371 shows that still better results were obtained by an otherwise equivalent system in which the elec-trolyte was replaced by 2% by volume hexyl alcohol.
In addition, the data in Table 1 indicates that the test 371 hexyl alcohol and 375 nonyl alcohol systems had relatively very high viscosities (of more than 50 centipoises) as compared to a viscosity of less than 4 for the electrolyte-containing system of test 368. A partic-ularly suitable high viscosity (greater than 83 centipoise) system is typified by test 378, which (as shown in Figure 1) is an extremely effective system that removed substantially all of the residual oil.
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Figure 2 shows a comparison of systems containing octanol and dodecyl alcohol, tests 388 and 382. Relative to the highly effective nonyl alcohol system of test 375, the dodecyl alcohol system leaves a higher residual oil, although it recovered all but about 6%. This may indicate that, for the particular petroleum sulphonate used, a longer chain alcohol than dodecyl would have been still less effective. Amyl alcohol failed to provide an active system at 75C when as much as 14% of the alcohol was added. However, at room temperature an active system can be formulated with amyl alcohol. Figure 2 also demonstrates the relative immunity of the present surfactant systems to a highly saline formation water. ~ote that test 383, using the short slug of hexyl alcohol in a core that contained a significantly saline brine, recovered all but 8% of the residual oil.
The viscosities of the present alcohol-enhanced surfactant systems - tend to increase with time. The values shown in Table 1 were eachmeasured after two days of aging at 75C. In preparing the present systems - a particularly suitable procedure is to first mix the concentrated ,J~ , surfactant solution (about 15%) and the alkanol and then add that mixture j to distilled water or a relatively salt-free water. Using that sequence tends to ensure a relatively quick development of substantially the i' 20 highest viscosity obtainable by the system.
~ Tests analogous to those described above were made with a typical ~ branch chain alkanol, 2-ethylhexanol. Two tests were conducted with surfactant systems each containing 6% by weight TRS-12B petroleum sulphonate and 1.8% by volume of 2-ethylhexanol, in distilled water. After two days aging at 75C the viscosity of these slugs was 40.5 centipoises at 75C and 6 rpm. In one test, a one-tenth pore volume slug was injected into a core containing SDSW water, followed by 1.2 pore volumes 1800 ppm Kelzan in a 1% solution of SDSW water (providing a polymer solution viscosity of 60 centipoises at 75C and 6 rpm). In both cases, the oil was 27% by volume isooctane in a Gulf Coast crude oil. The short slug test recovered all but about 6.5% of the oil, and the test using a slug size of 1.16 pore volume, recovered substantially all of the oil.
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Aqueous anionic surfactant systems are known to be particularly efficient for displacing oil. Such an anionic surfactant system is a substantially homogeneous aqueous liquid composition that may comprise a solution, a micro-emulsion, or a micellar dispersion of anionic `` surfactant molecules and/or micelles. The water-solubilities and oil-solubilities of the surfactants in such a system are such that those materials tend to remain along an oil/water interface, rather than being completely dissolved or dispersed within either the water-phase or oil-phases of the system. The anionic surfactants comprise surface-active salts or soaps of organic or inorganic acids.
According to the present invention an oil is displaced within a subterranean reservoir by injecting an aqueous surfactant system in which a petroleum sulphonate surfactant composition is mixed with a kind and amount of an alcohol that increases both the oil-displacing activity and the effective viscosity of the surfactant system.
A petroleum sulphonate surfactant component is selected from among those capable of forming an active aqueous surfactant system when dissolved or dispersed in a selected proportion, such as from about 2 to 10% by weight, in an aqueous liquid that contains a surfactant activity-enhancing kind and amount of dissolved electrolyte.
- 25 A preferentially oil-soluble alkanol is selected from among those capable of increasing the interfacial tension lowering activity of a solution or dispersion of the selected surfactant in the selected concentration in distilled water to an activity substantially equalling that of the electrolyte-containing system.
An aqueous surfactant system is compounded by dissolving or dis-persing the selected surfactant composition in the selected concentration in an aqueous liquid which contains significantly less than said activity-enhancing amount of dissolved electrolyte and contains the selected alkanol in a proportion that increases the stability of an emulsion that can be formed within a test tube by mixing the so-compounded ~ .
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surfactant system with the oil to be displaced at the temperature of the subterranean reservoir. The so-compounded surfactant system is injected into the subterranean reservoir to contact and displace the oil.
The present invention relates to a process for displacing oil within a subterranean reservoir by injecting an aqueous surfactant system containing a petroleum sulphonate surfactant and an alcohol, in which an improved procedure is applied for correlating the kind and amount of the surfactant and the alcohol to increase both the : 10 oil-displacing activity and the effective viscosity of the system, which comprises:
selecting a petroleum sulphonate surfactant which is capable of forming an active aqueous surfactant system when it is dissolved or dispersed in an aqueous liquid solution containing an effective kind and amount of surfactant activity-enhancing electrolyte;
; selecting a preferentially oil-soluble alkanol which is capable of increasing the interfacial tension lowering activity of a solution or dispersion of the selected kind and amount. of petroleum sulphonate surfactant in distilled water to an activity at least substantially equa~ingthat of said electrolyte-containing surfactant system;
compounding an aqueous surfactant system by dissolving or dispersing the selected kind and amount of petroleum sulphonate surfactant in an aqueous liquid which contains less than said surfactant activity-enhancing amount of electrolyte and contains the selected alkanol in a proportion which, in a test tube, increases the stability of an emulsion of the surfactant system and the oil to be displaced : .
at the temperature of the subterranean earth formation; and injecting the so-compounded surfactant system into the sub- ..
terranean reservoir to contact and displace said oil.
According to the present invention it has been found that .
typical sulphonate surfactant compositions which are capable of forming active aqueous surfactant systems in aqueous liquids containing effective ~ ~
kinds and amounts of dissolved electrolytes are also capable of forming : :
substantially equally active surfactant systems in distilled water :
containing an effective kind and amount of an alkanol.
- -, . . ~ :
:.' ' : ' ' ~ ~ '' . ' ' .
': . ' ' ' '' ' ' ~ ' :
108Zl(~l Such alkanol-enhanced surfactant systems have relatively high effective viscosities, such as for example from about 2 to 85 centipoises at 75 C and 6 rpm and containing preferably 2-10% by weight of petroleum sulphonate surfactant. The present alkanol-enhanced surfactant systems tend to displace an oil within a permeable oil formation in the form of an oil bank that is substantially free of any entrained or emulsified aqueous liquid or surfactant system components.
They also tend to displace any water that is co-present with the oil within a permeable earth formation to such an extent that the sur-factant system is unaffected by the dissolved salt content of that water, even when that salt content is high and includes multivalent cations.
Although the present invention is not dependent upon any particular mechanism, the following seems to be involved. The hydrocarbon core 1 15 of a surfactant aggregate or molecule tends to be a liquid or i liquid-like, but when the micelle is small, only a small amount of ; oil can be dissolved. However, when the micelles become large and are contacted by oil droplets within the pores of a permeable earth formation, the oil droplets are absorbed into the micelles along the interface between the oil and water phases of the liquids within the pores. This causes the interfacial tension between the surfactant system and the oil to approach zero and the interface to become less distinct and the phases to become more miscible with each other.
In this situation the oil droplets can readily be deformed and, as the surfactant system flows among the droplets, the droplets become elongated into fine streams that are able to flow through the necks of pores of the earth formation. ~uch a flow causes the larger droplets or portions of substantially clean oil to move ahead and form into an oil bank. Meanwhile, as the surfactant micelles absorb more oil their oleophilic cores tend to become more oil-like. As the micelles become saturated with the oil they undergo transitions, from aggregates having polar groups oriented outward to lamellar types of aggregates, and finally to aggregates with polar groups oriented inward in a hydro-carbon-rich environment. -,., ' ~ '. -~ " - , . ,. ' . ' ' .
- ' :' . . .
--- 108Z~l Such a mechanism appears to be brought about when a petroleum sulphonate surfactant composition is mixed with an effective amount of an alcohol having a composition such that the polar and hydrocarbon groups of the surfactant and the alcohol are properly matched with respect to a balance of electrical forces, geometric compatibility, and mutual solubility. For example, for a mixture of relatively water-soluble and water-insoluble alkyl aryl petroleum sulphonates, such as for example TRS-12B, alkanols containing from 6 to 12 carbon atoms are (at a temperature of 75C) significantly more effective than their higher or lower homologs. It appears that, when the number of carbon atoms is too low, the alcohol tends to go into the aqueous phase, but when the carbon number is too high, the alcohol tends to go into the hydrocarbon core of the surfactant micelle. Only the alcohols in the medium carbon number range appear to stay in the palisade layers of the micelles, where they produce the large surfactant micellar entities. In the case of amyl alcohol, large surfactant entities are formed at room temperature, but, those formed at 75C
appear to be unstable because of the increased thermal motion of the molecule.
The tendency for the present alkanol-enhanced surfactant systems to displace an oil within a subterranean reservoir without forming any relatively viscous or stable emulsions (between any components of the surfactant systems and fluids in the reservoir) is an important advantage. Aqueous anionic surfactant systems containing active surfactants such as petroleum sulphonates or mixtures of petroleum sulphonates with alcohol or alkoxy-alcohol sulphates often form emulsions with the oil and water they are displacing within a permeable medium. The present surfactant systems, which contain alkanol-expanded micelles, are comparatively resistant to the formation of stable or viscous emulsions. This is advantageous in avoiding a tendency for mixtures of the surfactant system and formation oil to be by-passed by dryine fluids such as a thickened aqueous liquid for displacing the oil and surfactant system through the reservoir.
As known to those skilled in the art, in an oil displacement process, the interfacial tension-lowering activity is particularly important. An "active" aqueous surfactant system, as used herein, is one in which the interfacial tension between it and the oil is less than about 0.01 dyne per centimetre.
-- 108Zl(~l.
As used herein the term "petroleum sulphonate surfactant compo-sition", or "component" refers to a mixture of relatively water-soluble and water-insoluble petroleum sulphonate surfactants and/or their mixtures with sulphated alcohol surfactants or other cosurfactants. The ones of such compositions which are selected for use in the present invention are those capable of forming active electrolyte-containing surfactant systems. Such a capability can readily be determined by a testing procedure. For example, visual observations are made of the clarity and stability of an aqueous solution or dispersion containing about 1% of an at least about 60% surface-active surfactant composition in distilled water. Compositions that form satisfactory solutions or dispersions are subjected to emulsion testing.
A series of aqueous solutions containing from about 1 to 5% of the sur-factant and different amour.ts of sodium chloridç are prepared. An oil at least equivalent to the oil to be displaced is added to those solutions in a 1 to 5 volumetric ratio within a substantially solids free liquid container, such as a test tube. mlhe mixtures are agitated and heated to a temperature at least substantially equivalent to the temperature at which the oil is to be displaced within a subterranean earth formation.
Samples which tend to form some foam without forming a rather high standing foam column (e.g., equivalent to 0.75 inches or more, within 0.5 inch diameter test tubes) are generally suited for best performance of the surfactant system. In a preferred procedure, after the initial evaluation of emulsion grade and foaming characteristics, the samples are maintained -at about 35C for 24 hours, evaluated before agitation, agitated again and re-evaluated. The temperature of the samples is increased to about 76C and after agitation, both foaming and emulsion characteristics are again evaluated.
Typically, a petroleum su~honate surfactant composition which is an active system and a potentially good oil recovery agent will form relatively stable emulsions with a range of sodium chloride concentrations.
Preferably the oil displacing capability of the compositions which provide relatively stable emulsions are confirmed by tests of the capability of recovering oil from cores.
As known to those skilled in the art, other testing procedures can be utilized to determine whether a given petroleum Sulphonate composi-los~lal tion is capable of providing an active surfactant system, e.g., measure-ments can be made of the interfacial tension provided between that system and the oil to be displaced at the temperature at which the oil is to be displaced, sand pack and/or core-oil recovery tests can be made, and the like.
Particularly suitable petroleum sulphonate surfactant compositions comprise mixtures of relatively water-soluble and water-insoluble alkali metal salts of petroleum sulphonates (such as alkylaryl sulphonates, alky-lated benzene sulphonates, and the like). For uses at temperatures below about 65C, such mixtures can include sulphatedpolyoxyalkylated alcohol surfactants. Petroleum sulphonate surfactants are commercially available, for example, as Petronates and Pyronates from Witco Chemical Company;
Promor Sulfonates from Mobil Oil Company; and the like. Surfactant sulphates of ethoxylated primary alcohols are available as ~EODOLS from Shell Chemical Company. Other surfactant sulphates of ethoxylated alcohols are available as Tergitols from Union Carbide, and the like.
The alcohols used in the present invention are preferentially oil soluble alkanols selected for their capability of functioning in a manner substantially equivalent to a dissolved electrolyte with respect to increasing the activity of the selected petroleum sulphonate surfactant composition. Such alcohols generally have straight or branched saturated aliphatic hydrocarbon chains and contain from about 6 to 12 carbon atoms.
The selection of a particular alcohol for use with a particular surfactant composition can readily be made by an emulsion test of the type described above with differing amounts of alcohol concentrations being used in the place of differing amounts of sodium chloride concentration. Very suitable alcohols are hexyl alcohol, noxyl alcohol and 2-ethylhexanol.
The aqueous liquid used in compounding the surfactant systems of the present invention can be substantially any aqueous liquid which is substantially electrolyte free but, where desirable, may comprise an ~ -electrolyte-containing aqueous solution which contains a fraction, such as for example up to about 75%, of the amount of dissolved electrolyte that is effective in enhancing the activity of the selected petroleum sulphonate surfactant composition.
... . . . ....
1~8ZlC~l In compounding the present surfactant systems, the concentration of the selected alcohol which is used with the selected amount and kind of petroleum sulphonate surfactant composition is arranged by means of tests analogous to th~e described above. Various concentrations of the selected alcohol are used with the selected kinds and concentrations of the surfactant composition in an aqueous liquid containing l^ss than the surfactant activity enhancing amount of dissolved electrolyte. Such compositions are emulsified (in containers equivalent to test tubes) with the oil to be displaced at substantially the temperature of the subterranean earth formation in which it is to be displaced. The selected concentration of the alcohol is one which substantially optimizes the stability of such emulsions in the sense that the emulsions tend to be less stable when more or less of the alcohol is used.
As known to those skilled in the art, the viscosity of an oil-displacing surfactant system should be relatively high, in order to provide mobility control and avoid the bypassing of the oil or emulsified mixtures of the oil and the surfactant system. Such a viscosity can be provided by dissolving a water-soluble polymer in the surfactant system. However, the viscosities of commonly used polymer solutions decrease with in-creasing salt concentration. For example, a 500 parts per million solution of a partially hydrolyzed polyacrylamide polymer (Pusher 700) in distilled water has a viscosity of 46 centipoises. But, in a 1 molar sodium chloride solution, the viscosity of the same proportion of polymer is only 3.6 centipoises. In a solution containing 1,000 parts per million calcium ion, the viscosity decreases to 2.5 centipoises. Those values refer to measurements at room temperature and 7.3 reciprocal seconds.
The capability of the present systems to provide a viscous solution free of polymer can be advantageous in various oil-displacing operations.
Water thickeners can be used in, or in conjunction with, the ~ 30 present surfactant systems. Such thickeners can be substantially any - water soluble natural or synthetic polymeric material, such as a carboxy-methyl cellulose, a polyethylene oxide, a hydroxyethylcellulose, a partially hydrolyzed polyacrylamide; a copolymer of acrylamide and acrylic acid; biopolymers, such as the polysaccharides; or the like.
1(:?821(~
Preferablythe compounded aqueous surfactant system is aged at about the temperature of the reservoir for at least about 24 hours prior to injecting it into the reservoir.
An oil in a permeable material is displaced in accordance with this invention by injecting a surfactant system of the invention to contact and push the oil. The surfactant system can be preceded or followed by substantially any aqueous or oil-phase fluid with which it is compatible. Where a slug of the surfactant system is displaced through a reservoir (e.g., in a chemical flood process) it is preferably displaced by a thickened aqueous solution having a viscosity greater than (and/or a mobility less than) the surfactant system.
Figures 1 and 2 show the oil recovery curves obtained by displacing oils at a water-flood residual with various aqueous surfactant systems.
In these figuresthe horizontal axis indicates fluid injection, Vp and the vertical axis oil saturation, % Vp. The cores used were ~erea sandstone cores, 25 cm long and 5 cm in diameter. With one exception, the cores - were water-flooded to a waterflood residual with 0.025 M NaCl before injecting 1.2 pore volumes of the surfactant system. The surfactant systems (or chemical slugs) were followed by 0.025M NaCl solutions to provide the indicated amounts of injected fluids.
With respect to test 383 (Figure 2) the core was mounted in a horizontal position and was waterflooded with synthetic D-sand/water (SDSW) before chemical injection. The SDSW water contained the follow-ing ions in parts per million: 74 barium, 1670 calcium, 12 copper, 1290 magnesium, 42900 sodium, 30 strontium, and 195 HC03 ion. In test 383 the chemical slug amounted to only 0.1 pore volume and was followed by 1.2 pore volumes of an aqueous solution of 1800 ppm Kelzan (a polysaccharide fermentation product produced by Xanthomonas Campestric)in 1% SDSW water.
The viscosity of that polymer solution was 52.8 cp (75C, 6 rpm).
The compositions of the aqueous sulphonate surfactant system (chemical slug) and the crude oils used in the core tests are listed in Table 1. Table 1 shows the viscosity of the chemical slugs and the amount of residual oil which was left in the core at the end of the oil recovery test.
Table 2 shows the optimum range of alcohol concentration for -each concentration of the petroleum sulphonate surfactant component.
11~8Z~
As mentioned above, these ranges were determined primarily by comparing the emulsification properties of surfactant systems containing the selected percent of sulphonate and varying percentages of alcohol. In Table 2 under 'Separation' are shown the percents by volume of alcohol which caused the aqueous surfactant system to undergo a phase separation.
Table 1 ; CHEMICAL SLUGS AND CRUDES USED IN CORE EXPERIMENTS AT 75C
Core . .Viscosity Scrc No. Slug Composltlon (cp) Crude (Vp) 371 6/w TRS-12B + 2%v Hexyl Alcohol51.7 NRB 0.000 375 6~w TRS-12B + 1%v Nonyl Alcohol51.0 NRB 0.027 368 6%w TRS-12B + 3.5%v SDSW 3.8 NRB 0.023 378 4.5%w TRS-12B + 3.4~v Hexyl Alcohol 83.0 NRB 0.000 382 6%w TRS-12B + 1.2%v Octanol-1 60.0 27%v 0.035 Isooctane in N4RB
388 6%wTRS-12B + 0.97%v Dodecyl Alcohol 24.2 27%v 0.059 - Isooctane in N4RB
383 6~ow TRS-12B + 2.2%v Hexyl Alcohol 42.0 27%v 0.081 (0.1 Vp Chemical Slug) Isooctane in N4RB
~RB, N4RB : crude oil from particular US oil fields orc : residual oil saturation after chemical flooding Table 2 (IN DISTILLED WATER) Alcohol TRS-12BOptimum Region Separation (%w) (%v) (%v) Hexyl Alcohol 6.o 1.8-2.8 3.8 (Eastman, Practical) " 4.5 2.6-3.8 ~- " 3.0Not active, not viscous 3.0 " 1.5Not active, not viscous 2.4 Octanol-1 6.o 1.2-1.6 2.4 (Fischer, Certified) - Nonyl Alcohol 6.o 1.0-1.4 2.0 (Eastman, Practical) Dodecyl Alcohol 6.o 0.97-1.2 1-7 ~- (Eastman, Technical) ~` 15 .: . . .
The capability of an alkanol to provide an enhancement of petroleum sulphonate surfactant interfacial tension lowering activity equivalent to those obtained by an electrolyte is shown in the data plotted in Figure 1. In test 368 the mixture of electrolytes contained in SDSW water was used to enhance the activity of an aqueous 6% petroleum sulphonate surfactant system. Test 375 shows that generally equivalent but somewhat better results (a removal of more oil with less surfactant injected) was obtained from a system in which the electrolyte was re-placed by 1% by volume nonyl alcohol. Test 371 shows that still better results were obtained by an otherwise equivalent system in which the elec-trolyte was replaced by 2% by volume hexyl alcohol.
In addition, the data in Table 1 indicates that the test 371 hexyl alcohol and 375 nonyl alcohol systems had relatively very high viscosities (of more than 50 centipoises) as compared to a viscosity of less than 4 for the electrolyte-containing system of test 368. A partic-ularly suitable high viscosity (greater than 83 centipoise) system is typified by test 378, which (as shown in Figure 1) is an extremely effective system that removed substantially all of the residual oil.
, .
1082~
Figure 2 shows a comparison of systems containing octanol and dodecyl alcohol, tests 388 and 382. Relative to the highly effective nonyl alcohol system of test 375, the dodecyl alcohol system leaves a higher residual oil, although it recovered all but about 6%. This may indicate that, for the particular petroleum sulphonate used, a longer chain alcohol than dodecyl would have been still less effective. Amyl alcohol failed to provide an active system at 75C when as much as 14% of the alcohol was added. However, at room temperature an active system can be formulated with amyl alcohol. Figure 2 also demonstrates the relative immunity of the present surfactant systems to a highly saline formation water. ~ote that test 383, using the short slug of hexyl alcohol in a core that contained a significantly saline brine, recovered all but 8% of the residual oil.
The viscosities of the present alcohol-enhanced surfactant systems - tend to increase with time. The values shown in Table 1 were eachmeasured after two days of aging at 75C. In preparing the present systems - a particularly suitable procedure is to first mix the concentrated ,J~ , surfactant solution (about 15%) and the alkanol and then add that mixture j to distilled water or a relatively salt-free water. Using that sequence tends to ensure a relatively quick development of substantially the i' 20 highest viscosity obtainable by the system.
~ Tests analogous to those described above were made with a typical ~ branch chain alkanol, 2-ethylhexanol. Two tests were conducted with surfactant systems each containing 6% by weight TRS-12B petroleum sulphonate and 1.8% by volume of 2-ethylhexanol, in distilled water. After two days aging at 75C the viscosity of these slugs was 40.5 centipoises at 75C and 6 rpm. In one test, a one-tenth pore volume slug was injected into a core containing SDSW water, followed by 1.2 pore volumes 1800 ppm Kelzan in a 1% solution of SDSW water (providing a polymer solution viscosity of 60 centipoises at 75C and 6 rpm). In both cases, the oil was 27% by volume isooctane in a Gulf Coast crude oil. The short slug test recovered all but about 6.5% of the oil, and the test using a slug size of 1.16 pore volume, recovered substantially all of the oil.
:
,:
., : .
: . .. . . . . ..
, ,! ., ' ' ' ' ~
Claims (8)
1. In a process for displacing oil within a subterranean reservoir by injecting an aqueous surfactant system containing a petroleum sulphonate surfactant and an alcohol, an improved procedure for correlating the kind and amount of the surfactant and the alcohol to increase both the oil-displacing activity and the effective viscosity of the system, which comprises:
selecting a petroleum sulphonate surfactant which is capable of forming an active aqueous surfactant system when it is dissolved or dispersed in an aqueous liquid solution containing an effective kind and amount of surfactant activity-enhancing electrolyte;
selecting a preferentially oil-soluble alkanol which is capable of increasing the interfacial tension lowering activity of a solution or dispersion of the selected kind and amount of petroleum sulphonate surfactant in distilled water to an activity at least sub-stantially equalling that of said electrolyte-containing surfactant system;
compounding an aqueous surfactant system by dissolving or dispersing the selected kind and amount of petroleum sulphonate surfactant in an aqueous liquid which contains less than said surfactant activity-enhancing amount of electrolyte and contains the selected alkanol in a proportion which, in a test tube, increases the stability of an emulsion of the surfactant system and the oil to be displaced at the temperature of the subterranean earth formation; and injecting the so-compounded surfactant system into the subterranean reservoir to contact and displace said oil.
selecting a petroleum sulphonate surfactant which is capable of forming an active aqueous surfactant system when it is dissolved or dispersed in an aqueous liquid solution containing an effective kind and amount of surfactant activity-enhancing electrolyte;
selecting a preferentially oil-soluble alkanol which is capable of increasing the interfacial tension lowering activity of a solution or dispersion of the selected kind and amount of petroleum sulphonate surfactant in distilled water to an activity at least sub-stantially equalling that of said electrolyte-containing surfactant system;
compounding an aqueous surfactant system by dissolving or dispersing the selected kind and amount of petroleum sulphonate surfactant in an aqueous liquid which contains less than said surfactant activity-enhancing amount of electrolyte and contains the selected alkanol in a proportion which, in a test tube, increases the stability of an emulsion of the surfactant system and the oil to be displaced at the temperature of the subterranean earth formation; and injecting the so-compounded surfactant system into the subterranean reservoir to contact and displace said oil.
2. The process according to Claim 1 in which the compounded aqueous surfactant system contains about 2 - 10% by weight of petroleum sulphonate surfactant and has an effective viscosity of from about 2 - 85 centipoises at 75°C and 6 rpm.
3. The process according to Claim 1 or 2 in which the petroleum sulphonate surfactant is a mixture of relatively water-soluble and relatively water-insoluble alkyl aryl petroleum sulphonates.
4. The process according to claim 1 or 2 in which the compounded aqueous surfactant system is aged at about the temperature of the reservoir for at least about 24 hours prior to injecting it into the reservoir.
5. The process as claimed in Claim 1 in which the alcohol has straight or branched saturated aliphated hydrocarbon chains containing 6 - 12 carbon atoms.
6. The process of Claim 5 in which the alkanol is hexyl alcohol.
7. The process of Claim 5 in which the alcohol is nonyl alcohol.
8. The process of Claim 5 in which the alcohol is 2-ethylhexanol.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US72952476A | 1976-10-04 | 1976-10-04 | |
| US729,524 | 1976-10-04 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1082101A true CA1082101A (en) | 1980-07-22 |
Family
ID=24931444
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA286,879A Expired CA1082101A (en) | 1976-10-04 | 1977-09-16 | Process for displacing oil with aqueous sulphonate and alcohol surfactant system |
Country Status (4)
| Country | Link |
|---|---|
| CA (1) | CA1082101A (en) |
| DE (1) | DE2744384C2 (en) |
| GB (1) | GB1542166A (en) |
| NO (1) | NO773360L (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4193452A (en) * | 1978-08-07 | 1980-03-18 | Mobil Oil Corporation | Waterflooding employing thickened aqueous liquids |
| DE3644385A1 (en) * | 1986-12-24 | 1988-07-07 | Huels Chemische Werke Ag | METHOD FOR THE INCREASED EXTRACTION OF PETROLEUM FROM AN UNDERGROUND STORAGE DEPOSIT BY SURFACTANT FLOODS |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3126952A (en) * | 1964-03-31 | Waterflooding method | ||
| US3348611A (en) * | 1965-07-09 | 1967-10-24 | Shell Oil Co | Surfactants for oil recovery by waterfloods |
| US3468377A (en) * | 1967-10-09 | 1969-09-23 | Mobil Oil Corp | Waterflooding employing surfactant solution |
| US3506070A (en) * | 1967-12-26 | 1970-04-14 | Marathon Oil Co | Use of water-external micellar dispersions in oil recovery |
| US3480080A (en) * | 1968-03-22 | 1969-11-25 | Mobil Oil Corp | Waterflooding with an aqueous,saline solution of a hydrocarbon sulfonate having an optimum degree of sulfonation |
| US3675716A (en) * | 1970-03-09 | 1972-07-11 | Shell Oil Co | Heat-stable calcium-compatible waterflood surfactant |
| US4018278A (en) * | 1974-11-25 | 1977-04-19 | Texaco Inc. | Surfactant oil recovery process usable in high temperature formations |
-
1977
- 1977-09-16 CA CA286,879A patent/CA1082101A/en not_active Expired
- 1977-10-03 GB GB7740971A patent/GB1542166A/en not_active Expired
- 1977-10-03 NO NO773360A patent/NO773360L/en unknown
- 1977-10-03 DE DE2744384A patent/DE2744384C2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE2744384C2 (en) | 1986-10-16 |
| DE2744384A1 (en) | 1978-04-06 |
| GB1542166A (en) | 1979-03-14 |
| NO773360L (en) | 1978-04-05 |
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