GB2135713A - Micellar slug for oil recovery - Google Patents

Abstract

A micellar slug for use in the recovery of oil, the slug containing a hydrocarbon, an aqueous medium, a surfactant, and a cosurfactant. The surfactant contains as an essential component an internal olefin sulfonate having 10 to 30 carbon atoms. This micellar slug has an excellent capability for decreasing an interfacial tension between oil and water and an excellent salinity tolerance and hard-water resistance. Furthermore, the micro-emulsion can be formed from this micellar slug in a wide composition range.

Description

SPECIFICATION Micellar slug for oil recovery This invention relates to a micellarsiug suitablefor use in a micellar drive for recovering oil from subterranean reservoirs. More specifically, it relates to a micellarslug capable offorming micro-emulsions at a high salt concentration.

It is well-known in the artthatthe so-called "primary recovery" methods, including pumping methods, can recover only a portion ofthe petroleum or crude oil (referred to as "oil" herein after) from subterranean reservoirs and leave substantial amounts of oil in the subterranean reservoirs.

In orderto recover the remaining large amounts of oil from the subterranean reservoirs, the so-called "secondary recovery" methods have been proposed, wherein, for example, water or gas is injected into the subterranean reservoirs from an injection well at a pressure sufficientto increase theflowability of oil, steam is injected into subterranean reservoirs so as to effectthe displacement of oil toward a production well, or oil in subterranean reservoirs is partially burned to heatthe subterranean reservoirs so as to decrease the viscosity of the oil and increase the flowabilityofthe oil.

Furthermore, the so-called various "tertiary recovery" methods, including a combination of secondary recovery methods and improved secondary recovery methods, have been proposed, wherein su rfactants or water-soluble polymers are utilized. These methods are generally called "enhanced oil recovery" (EOR) methods.

Among the surfactants EOR methods, the recent "micellar drive" methods are to be noted. According to these methods, a micellarslug, that is, a clear micro-emulsion derived from water and oil such as petroleum, petroleum distillates, or fuel oil, is injected under pressure into the subterranean reservoirs for the recovery of oil in the subterranean reservoirs.

There EOR methods are disclosed in, for example, U.S. Patent Nos. 3506070,3613786, 3740343,3983940, 4017405, and 4059154. These prior arts disclose that various kinds of surfactants including anionic-, nonionic-, and cationic-type surfactants can be used alone or in any mixture thereof in the formation of micellar slugs. Examples of such surfactants are petroleum sulfonates, alkylaryl sulfonates, dialkyl sulfosuccinates, alkane sulfonates, polyoxyetylene alkylether sulfates, polyoxyehtyl ene alkyl ethers, polyoxyethylene alkylphenylethers, polyol fatty acid esters, alkyltrimethyl ammonium salts, and dialkyldiemthly ammonium salts.

Thesurfactants used in theformation of a micellar slug must be available at a low cost, while still displaying the required performances, since a large amount of a micellar slug is necessaryto recover oil from subterranean reservoirs. In addition, the numerous oil production wells or oilfields are present in the world include subterranean reservoirs with a variety of properties. The available water also varies from soft water containing no substantial amount of inorganic salts to brine containing large amounts of inorganic salts and polyvalent metallic ions. Thus, the surfac- tants used in micellar slugs should also have good thermal stability, salinity tolerance, and hard-water resistance.

It is known in the art that petroleum sulfonate is an optimum surfactant usable as an injection fluid in a micellar drive due to its availability and low cost, since a large amount of an injection fluid is used in a micellar drive. However, a probiem exists in that petroleum sulfonate has an unsatisfactory salinity tolerance and hard-water resistance, and, therefore, can be applied onlyforcertain oilfields. Forthis reason, various attempts have been made to improve the properties of petroleum sulfonate by using petroleum sulfonate together with othersurfactants orwater-soluble polymer-thickening agents. However, micellarslugs having the desired properties and a satisfactory cost have not been obtained.

We have proposed, in U.S. Patent Application No.

415,840 filed on September8, 1982, the use of an alpha-olefin sulfonate as a surfactantcapable of providing a micellarslug having an interfacialtension decreasing capability equal to or more than that of a micellarslug containing petroleum sulfonate and having an excellent salinity tolerance and hard-water resistance and a relatively high viscosity. However, the micro-emulsionformedwhen a micellarslug is prepared by using an alpha-olefin sulfonate, is likely to be destroyed when injected under pressure into subterranean reservoirs due to thefactthatthe composition range within which a micro-emulsion can be formed is notverywide.Accordingly, this micellarslugshould befurtherimprovedfroma practical viewpoint.

The objects of the present invention are to eliminate the above-mentioned problems ofthe prior arts and to provide,forthe recovery of oil, a micellar slug, having an excel lent oil-water interfacial tension decreasing capability and an excellent salinity tolerance and hard-water resistance, and being capable of forming a micro-emulsion in a wide composition range.

Afurther object of the present invention is to provide an oil recovery process using a micellar slug.

Other objects and advantages ofthe present invention will be apparent from the following description.

In accordance with the present invention, there is provided a micellarslug, for the recovery of oil, consisting essentially of a hydrocarbon, an aqueous medium, a surfactant, and a cosurfactant, the surfac- tantcontaining, as an essential component, an internal olefin sulfonate having 10 to 30 carbon atoms.

In accordance with the present invention, there is also provided a process for producing oil from an oil-bearing subterranean reservoir penetrated by a well which comprises the steps of injecting into the reservoirthrough the well a micellar slug consisting essentially of a hydrocarbon, an aqueous medium, a surfactant, and a cosurfactant, the surfactant containing, as essential constituents, an internal olefin sulfonate having 10 to 30 carbon atoms; injecting into the reservoir at least one driving fluid; and recovering oil from the reservoir through the production well.

The micellar slugs desireably used for the recovery of oil are transparent micro-emulsions containing about4% to about 90% by weight of a hydrocarbon, about4% to about 92% by weight of an aqueous medium, about 3% to about 30% by weight of a surfactant containing, as an essential constituent, an internal olefin sulfonate having 10 to 30 carbon atoms, and about 0.1 % to about 20% by weight of a cosurfactant.

The aqueous medium usable in the formation ofthe micellarslug ofthe present invention includes soft water, water containing inorganic salts, and brine. For example, rain water, river water, lake water, subterranean water, oil stratum water, and seawater can be freely used in the formation ofthe micellarslug ofthe present invention.

As in the case of an alpha-olefin sulfonate, the internal olefin sulfonates (i.e., lOS) having good hard-water resistance used as an essential constituent ofthe surfactant in the micellar slugs ofthe present invention result in micellar slugs with an excellent hard-water resistance of about 5,000 ppm of a Mg ion (:.e., about 2.6% by weight of MgSo4). Furthermore, the micellar slugs ofthe present invention have a surprisingly high resistance to alkali metal salts and can contain water including about 10% by weight of alkaline metal salts irregardless of the kinds of alkali metal salts.When another adequate surfactant is used together with the internal olefin sulfonate or when a certain cosurfactant is selected, brine including upto about 15% by weight of inorganic salts can be used in the formation of the micellarslugsofthe present invention. Furthermore, it has been found that an increase in the concentration of inorganic salts in the micellarslugs ofthe present invention results in a further decrease in the interfacial tension between oil and water. Thus, water (or brine) usable in the formation of the micellarslugs of the present invention can contain 0% to about 15% by weight, desirably about 0.5% to about 12% by weight and more desirably about 1% to about 10% by weight, of inorganic salts.Typical examples ofthe inorganic salts contained in the water (or brine) are NaCI, KCI, Na2S04, and K2SO4. For instance, seawater contains about3.5% by weight of inorganic salts including about 1,600 ppm, in terms of a Mg ion, of divalent metal ions. This salt concentration is within the desirable salt concentration range of the present invention.

The internal olefin sulfonates usable as an essential surfactant in the present invention are those obtained by sulfonating internal olefins containing as a main constituentvinylene-type monoolefin having a gener formula: R - CH = CH wherein Rand R' are independently straight- or branched-chain saturated hydrocarbon radicals having 1 or more carbon atoms provided that the total carbon atom numbers of Rand R' is 8to 28, desirably 10 to 24, and optionally containing about 33% by weight (about one third ofthe olefins) or less of tri-substituted type monoolefins, followed by neutralizing the suifonated products with appropriate bases and,then, optionally, hydrolyzing the neutralized products.The internal olefin sulfonatesthus prepared generally contain about 20% to about 60% by weight of alkenyl sulfonates having double bonds and about 80% to about 40% by weight of hydroxyalkylene sulfonates and also contain about 80% byweight or more of monosulfonates and about 20% byweight or less of disulfonates. It should be noted, however, that internal olefin sulfonates having the compositions differentfrom the above-mentioned composition ratios can be prepared by appropriateiy selecting the sulfonation conditions and hydrolysis conditions.

Generally speaking, the increase in the carbon atom number of the internal olefin tends to result in an increase in the composition ratio ofthe alkenylsulfon ate. On the other hand, the increase in the mol ratio of the sulfonating agentto the internal olefin during the sulfonation tends to result in an increase in the composition ratio ofthe disulfonate.

A relatively high lipophilic internal olefin sulfonate ora relatively high hydrophilic internal olefin sulfonate can be optionally used in the micellar slugs according to the present invention depending upon the properties ofthe oilfields and subterranean reserviors, the waterto be used (or brine), and the cosurfactants. The internal olefin sulfonates used in the present invention are desirably those having 12 to 26 carbon atoms and, more desirably, those containing 50% by weight or more of internal olefin sulfonates having 14to 22 carbon atoms.

The internal olefin sulfonates usable in the present invention can be alkali metal salts, alkaline earth metal salts, ammonium salts, and organic amine salts thereof. The desirable counter cations are Na, K, Mg, Ca, NH4, and alkanolammonium. The sodium salts are readily available at a low cost.

Examples of internal olefin sulfonates usable in the formation ofthe micellarslugs ofthe present invention are: internal olefin sulfonate having 10,12,14,16, 18,20,22,24,26, 12-16,14-16,14-18, 14-20, 15-18, 15-20,16-18, 16-20, 18-20, 18-24, and 20-24 carbon atoms. These sulfonates may be used alone or in any mixture thereof.

As mentioned above, the micellarslugs of the present invention contain about 3% to about 30% by weight of the surfactant. However, the micellarslugs desirably contain about 5% to about 25% by weight of the surfactant, taking into consideration both low interfacial tensions and reasonable cost. The amount of the higher internal olefin sulfonates having 10 to 30 carbon atoms should be at least 50% by weight, desirably 60% by weight or more, based on the total amount of the surfactants contained in the micellar slugs.

The hydrocarbons usable as an oil component in the present invention include, for example, petroleum, liquefied petroleum gas, crude gasoline (naphtha), kerosine, diesel oil, and fuel oil. The recovered petroleum is desirably used due to its low cost and availability as well as its composition, which is similar to that ofthe oil contained in subterranean reservoirs.

As mentioned above,themicellarslugsofthepresent invention can contain about 4% to about 90% by weight of hydrocarbons. The desirable concentration of hydrocarbons is within the range of about 5% to about 40% by weight whereby an oil-in-watertype emulsion is formed, since the use of a large amount of hydrocarbons is not economical.

Thecosurfactants used in the formation ofthe micellarslugsofthe present invention are an essential constituentforforming micro-emulsions associated with the surfactants. The cosurfactants usable in the present invention are those having an alcoholichydroxyl group.The desirablecosurfactants are alcohols having the general formula: R3O(CH2CH2O)nH wherein n is a numberoffrom Oto about 4 and R3 is an alkyl or alkenyl group having 2 to 8 carbon atoms when n is zero and an alkyl, alkenyl, or alkylphenyl group having 6to 18 carbon atoms when n is not zero.

The aliphatic groups of R3 may be straight-chain or branched-chain groups.

Examples of such alcohols are ethanol, propanols, butanols, pentanols, hexanols, 2 - ethylhexanol or other octanols, polyoxyethylene hexylethers (n = 1), polyoxyethlene decylethers (in = 2), polyoxyethylene tridecylethers (K= 4), poloxyethylene butylphenylethers r= 2), polyoxyethylene nonylphenylethers ( = 3), and polyoxyethylene dodecylphenylethers (n =4).

As mentioned above, the micellar slugs ofthe present invention can contain about 0.1 % to about 20% by weight ofthe cosurfactants. However, the desirable concentration ofthe cosurfactants is within the range of about 1 % to about 10% byweightfrom the viewpoints of the stability of the micro-emulsions and the decreasing capacity for interfacial tension between oil and water.

As mentioned above, the micellarslugsofthe present invention contain internal olefin sulfonates as an essential or major constituent of the surfactants. However, other auxiliary surfactants can also be included, together with the internal olefin sulfon ates,taking into consideration the desired interfacial tension between oil and water, the desired viscosity, the adsorbability of the surfactants to rocks constituting the subterranean reservoirs, and the cost and availability ofthe surfactants.

Examples of such auxiliary surfactants are anionic surfactants and nonionicsurfactantssuch as petroleum sulfonates, alkylbenzene sulfonates, polyoxyethylene alkylether sulfates, dialkyl sulfosuccinates, alpha-olefin sulfonates, paraffin sulfonates, lower internal olefin sulfonates, soaps, higher alcohol ethoxylates, alkylphenol ethoxylates, polyol fatty acid esters, fatty acid alkylol amides, and polyox yethylene fatty acid am ides.

The micellar slugs of the present invention have an excellent hard-water resistance and a remarkably improved salinity tolerance and are capable of forming micro-emulsions in the presence of a large amount of inorganic salts due to the use of an internal olefin sulfonate as an essential constituentofthe surfactant. Furthermore, the micellarslug of the present invention can form the desired good microemulsions even when brine containing a large amount of inorganic salts is used. Accordingly, the desired viscosity ofthe micellarslugs can be readily adjusted within a wide range by changing the concentration of the inorganic salt in the micellar slugs. Especially, the interfacial tension decreasing capability of the internal olefin sulfonate is largerthan that of petroleum sulfonate and an alpha-olefin sulfonate.Therefore, the micellar slugs ofthe present invention can recover petroleum from an oil-bearing subterranean reservoir at a high recovery level.

Furthermore, when the micellar slugs ofthe present invention are injected under pressure into an oilbearing subterranean reservoir, the micro-emulsions can be maintained within a wide composition range against the changes in the composition thereof bythe mixing with oil and subterranean water since the internal olefin sulfonates can form micro-emulsions within a wide composition range. This advantageous feature of the micellar slugs of the present invention is especially very important in the micellar drive method sincethe maintaining ofthe micro-emulsions in the subterranean reservoirs largely affects the recovery of petroleum.

The viscosity ofthe micellarslugsofthe present invention is likely to be lowerthan thatofan alpha-olefin sulfonate. According, when a micellar slug having a high viscosity is desired, an appropriate known thickening agent such as a water-soluble polymer can be added to the micellarslugs. Examples of thickening agents usable in the formation of the micellar slugs are heteropolysaccharides produced by micro-organisms, naphthalenesulfonic acid-formaldehyde condensates, polyacrylamides, polyacrylates, hydroxyethylcelluloses, and carboxymethylcelluloses.

The micellarslugs of the present invention can be readily obtained by any known method of production.

For example, the hydrocarbons, the surfactants, the aqueous medium, and the cosurfactants can be mixed in any mixing order by using conventional mixing devices, mixing temperatures, and mixing pressures.

The recovery of oil from subterrean reservoirs can be carried out by means of any conventional micellar drive method by using the micellarslugs of the present invention. For instance, the micellar slugs are injected under pressure into at least one injection well ofthe subterranean reservoirs. Then, at least one driving fluid such as flood water and/or aqueous solution ofthe above-mentioned thickening agent is injected into the injection well so as to transfer or drive the remaining oil toward an oil production well and to recoverthe oil from the production well. The suitable amount of the micellarslugs injected into the injection well is about 5% to about 15% by volume of the porosity of the subterranean reservoirs.

As mentioned hereinabove, according to the present invention, micellar slugs having a good hardwater resistance, a good salinitytolerance, and a very small interfacial tension between oil and water are provided, and the viscosity of the micellar slugs can be readily controlled. Furthermore, according to the present invention, the micro-emulsion can be formed from the micellar slugs in a wide composition range.

As a result, the following remarkable advantageous features can be obtained: (1) Either soft water or hard water can be freely used as the aqeous medium ofthe micellarslugs; (2) The micellar slugs injected into the subterranean reservoirs are subjected to no substantial adverse affects by inorganic salts present in the subterranean reservoirs; (3) The micellar drive method can be readily applied in subterranean reservoirs containing oil having a lowviscosityto a high viscosity; and (4) A high oil recovery efficiency can be attained since the micro-emulsions are not destroyed by oils and water contained in the subterranean reservoirs.

The present invention now will be further illustrated by, but is by no means limited to, the following examples, in which the component ratios or amounts of samples used are based on "% by weight" unless otherwise specified.

Example I Micellar slug compositions containing anionic surfactants, cosu rfactants, hydrocarbons, and aqueous media were prepared.

The anionic surfactants used were sodium C14-C18 internal olefin sulfonate (IOS-Na), sodium C20-C24 internal olefin sulfonate (IOS-Na), sodium C14-C18 alpha-olefin sulfonate (AOS-Na), sodium C20-C24 alpha-olefin sulfonate (AOS-Na), or petroleum sulfonate TRS-10 (manufactured by Witco Chemical Corp.). The cosurfactants used were amyl alcohol or Isopropyl alcohol. The hydrocarbons used were kerosineorfuel oil (ASTM No.2fuel oil). The aqueous media used were seawater having a saline content of about 3.5% and an alkaline earth metal ion concentration of about 1,600 ppm, or soft water The micellarslugs were prepared by first mixing the surfactant and the aqueous medium and, then, adding the cosurfactant and the hydrocarbon to the mixtue, while stirring it.

The compositions and properties ofthe micellar slugsthus obtained are shown in Table 1.

In Table 1 and the following Tables, "IOS" and "AOS" are abbreviations for an internal olefin sulfonate and an alpha-olefin sulfonate, respectively. Visual appearance was determined according to the following: ...................................A micro-emulsion was formed x A suspension, rather than a micro-emulsion was formed.

The interfacial tensions shown in thefollowing tables are those between the micellarslugs and the oil. The petroleum recovery (% ) was determined according to a method of Yamazaki, etal, disclosed in Journal of the Japanese Association of Petroleum Technologists, Vol.45, No.3, pp. 125 to 132, May, 1980.

Sample Nos. 1,5,7,9,11,13 and 15to 19 arethose according to the present invention and sample Nos.

2,3,4,6,8,10,12,14, and 20to22 are comparative examples.

TabZ 1 Sample No. 1 2' 3t 4' 5 6t 7 8t 9 10' 11 Anionic surfactant C14-C18 ros-Na 16 14 10.5 C20-C24 ICS-Na 10.5 10.5 C14-C18 AOS-Na C20-C24 AOS-Na Petrolairn sulfonate 16 16 16 14 10.5 10.5 Cosurfastant lemyl alcohol 4 4 6 6 4.5 4.5 4.5 4.5 4.5 Isopropyl alcohol 4 4 llydrocarbon Kerosine 8 9 8 8 24 24 25.5 25.5 Fuel oil 8.5 3.5 17 Mater Seawater 72 72 72 56 56 59.5 59.5 76.5 76.5 68 Soft water 72 Properties Visual appearance o x x o o x o x o x o Interfacial tension (x 10-2 dyne/cm) 0.64 - - 0.72 0.69 - 0.12 - 0.11 - 0.09 Viscosity (centipoiss) . 18 - - 5 22 - 19 - 5 - . 7 Petroleum recovery (t1 92 - - 93 96 - 98 - 95 - 97 * Comparative example Table 1 (continued) Sample No. 12* 13 14* 15 16 17 18 19 20* 21* 22* Anionic surfactant C14-C18 IOS-Na 14 14 14 14 C20-C24 IOS-Na 7 14 C14-C18 AOS-Na 14 C20-C24 AOS-Na 14 14 Petroleum sulfonate 10.5 7 Cosurfactant Amyl alcohol 4.5 3 3 6 6 6 6 6 6 Isopropyl alcohol 6 6 Hydrcarbon Kerosene 24 40 24 Fuel oil 17 18 18 24 40 50 40 45 Water Sea water 68 72 72 56 56 40 30 40 56 40 40 Soft water Properties Visual appearance x o x o o o o o o x x Interfacial tension (x 10-2 dyne/cm) - 0.11 - 0.31 0.23 0.07 0.002 0.05 0.82 - Viscosity (centipose - 6 - 12 16 18 23 27 55 - - Petrolena recovery (%) - 97.2 - 95 96 95 98 95 - - * Comparative example Example 2 Micellarslug samples were prepared in the same manner as described in Example 1 exceptthatvarious brines obtained by dissolving sodium chloride in demineralized water to predetermined saline concen trations were used.

The compositions and the properties of the sam ples are shown in Table 2.

Example 3 Micellar slug samples were prepared in the same manner as described in Example 1 exceptthatvarious brines were obtained by adding 1 % byweight of sodium chloride and magnesium chloride and/or Ta calcium chloride so as to provide the predetermined bivalent metal ion concentration to demineralized water.

The compositions and the properties ofthe sam ples are shown in Table 3.

Example 4 Micellar slug samples were prepared in the same manner as described in Example 1 exceptthat a lower alcohol and anothercosurfactantwere used to decrease the viscosity of the micellar slug.

The composition and the properties of the samples are shown in Table 4.

Sample No. 23* 24* 25 26 27 28 29 30 Anionic surfactant C14-C18 IOS-Na 10.5 10.5 C20-C24 IOS-Na 10.5 14 10.5 10.5 Petroleum sulfonate 16 16 Cosurfactant Amyl alcohol 4.5 6 4.5 4.5 Isopropyl alcohol 3 4 4.5 4.5 Hydrocarbon Kerosine 16 8 8.5 8 25.5 Fuel oil 17 17 17 Water Brine NaCl 0.5t 64 68 59.5 " " 2.0% 72 68 " " 4.0% 76.5 72 " " 8.0% 68 Properties Visual appearance o x o o o o o o Interfacial tension (x 10-2 dyne/cm) 1.4 - 0.10 0.27 0.95 0.52 0.07 0.07 Viacceity (centipoise) 8 - 18 12 42 19 20 19 Petroleen recovery (0) 95 - 97 95 95 98 97 95 * comparative example Table 3 Sample No. 31 32 33 34 35 36 37 Anionic surfactant C14-C18 IOS-Na 12 12 16 C20-C24 IOS-Na 10.5 1 10.5 Petroleum sulfonate 16 Cosurfactant Amyl alcohol 3 8 4.5 4 3 4.5 Isopropyl alcohol 4 Hydrocarbon Kerosine 16 8.5 16 17 8 18 25.5 Water (NaCl: 1 wt3) Brine:Mg ion 500 PPM 64 76.5 " " 1,000 " 64 " " 3,000 " 68 " " 4,000 " 72 " Ca ion 1,500 " 72 Mg ion 2,000 ppm +Ca ion 1,000 ppm 59.5 Properties Visual appearance x o o o o o o Interfacial tension (x 10-2 dyne/cm) - 1.5 0.9 0.07 0.6 0.27 0.9 viscosity (centipoise) - 12 21 16 3 6 27 Petroleum recovery (%) - 95 97 98 96 98 98 * comparative example Table 4 Sample No. 38 39 40 41 42 43 44 45 Anionic surfactant C14-C18 IOS-Na 14 14 13 16 C20-C24 IOS-Na 10.5 10.5 10.5 14 Cosurfactant Butanol 6 Amyl alcohol 6 5 4.5 3 Polyoxyethylene nonylphenyl 3 2 3 ether (n=2) Hydrocarbon Kerosine 24 22 25.5 23 8 8 24 Fuel oil 17 Water Sea water 56 56 59.5 59.5 68 Brine (NaCl: 2 wt%) 72 72 56 Ethylene glykol 3 4 Propylene glykol 4 2 1.5 operties Visual appearance o o o o o o o o Interfacial tension (x 10-2 dyne/cm) 0.78 0.6 0.4 0.53 1.78 1.8 0.56 0.42 viscosity (centipoise) 32 12 32 6 7 4 5 25 Petrolem recovery (%) 95 96 98 95 96 96 97 98 Example5 Micellarslug samples were prepared in the same manner as described in Example 1 exceptthatthe counter ions of the internal olefin sulfonates were changed.

The compositions and the properties of the sam ples are shown in Table 5A (monovalentcations) and Table 5B(@ (divalent cations).

Example 6 Micellar slug samples were prepared inthe same manners described in Example 1 exceptthattwo or more internal olefin sulfonates were used together.

The compositions and the properties ofthe samples are shown in Table 6.

Table 5A

Sample No. 46 47 48 49 50 51 52 53 54 Anionic surfactant C13-C14 IOS-K 16 16 " -NH4 14 14 "-NH2 (C2H4OH)2 12 16 C18-C20 IOS-NH4 16 C25-C28 IOS-K 18 -NH4 14 Cosurfactant Butanol 6 3 4 3 Amyl alcohol 4 4 3 3 4 2 3 Hydrocarbon Kerosine 20 20 40 50 25 15 Fuel oil 5 30 35 40 Water Brine (NaCl 0.5%) 30 55 80 50 65 40 " ( " 2.0%) 45 Sea Water 60 40 Properties Visual appearance o o o o o o o o o Interfacial tension (x 10-2 dyne/cm) 0.85 1.03 0.92 2.52 2.75 1.19 1.13 0.73 3.41 viscosity (centipoise) 17 26 25 17 ' 9 30 18 25 23 Petroleum recovery (8) 95 97 95 95 95 95 95 96 95 Table 5B

Sample No. 55 56 57 58 - 59 60 Anionic surfactant C13-C14 IOS-Mg 7 7 " -Ca 11.5 11.5 C18-C20 IOS-Mg 8 C25-C28 IOS-Mg 9 Cosurgfactant Butanol -3 3 4.5 2 Amyl alcohol 4.5 1 Hydrocarbon Kersoine 10 Fuel oil 10 60 30 70 40 Water Brine (NaCl 0.5%) 55 15 80 2.0%) 80 30 50 Seawater Properties Visual appearance o o o o o o Interfacial tension (x 10-2 dyne/cm) 3.46 1.41 0.55 0.72 1.82 2.91 Viscosity (centipoise) 7.2 18 22 26 27 12 Petroleum recovery (%) 95 96 96 95 95 95 Table 6 Sample No. 61 62 63 64 65 Anionic surfactant C13-C14 IOS-Na 6 5 5 7 " -Ng 6 5 Ca 5 C18-C20 IOS-Na 5 7 " -Ng 7 C25-C28 IOS-Na 5 " IOSsIS14 7 Cosurfactant Butanol 3 Acryl alcohol - 5 5 6 6 Hydrocarbon Kerosine 5 15 20 30 Fuel oil 5 Water Brine (NaCl 0.5%) ' ( " 2.0%) 50 60 50 Seawater ' 65 75 Properties Visual appearance o o o o o Interfacial tension (x 10-2 dyne/cm) 0.34 0.08 0.02 0.24 0.04 Viscosity (centipoise) 9 12 7 27 22 Petroleum recovery (t) 96 98 97 96 97

Claims (5)

1. A micellar slug for use in the recovery of oil, said slug consisting essentially of a hydrocarbon, an aqeous medium, a surfactant, and a cosurfactant, said surfactant containing, as an essential component, an internal olefin sulfonate having 10 to 30 carbon atoms.

2. A micellar slug as claimed in claim 1, wherein said surfactant is an internal olefin sulfonate having 12to 26 carbon atoms.

3. A micellarslug as claimed in claim 1, wherein said micellar slug consists essentially of about 4% to about 90% by weight of the hydrocarbon, about 4% to about 92% by weight of the aqeous medium, about 3% to about 30% by weight of the surfactant, and about 0.1% to about 20% by weight of the cosurfactant.

4. A micellar slug as claimed in claim 1, wherein said cosurfactant has the general formula: R30(CH2CH20)nH wherein n is a number of from 0 to about 4 and R3 is an alkyl or alkenyl group having 2 to 8 carbon atoms when n is zero and an alkyl, alkenyl, or alkylphenyl group having 6to 18 carbon atoms.

5. A process for producing oil from an oil-bearing subterranean reservoir penetrated by a well which comprises the steps of: (1) injecting into said reservoirthrough said well the micellarslug consisting essentially of a hydrocarbon, an aqeous medium, a surfactant, and a cosurfactant, said surfactant containing, as an essential component, an internal olefin sulfonate having lOto 30 carbon atoms; (2) injecting into said reservoir at least one driving fluid; and (3) recoveri,lg oil from said reservoirthrough the production well.