GB2138866A - Micellar slug for oil recovery - Google Patents

Abstract

A micellar slug for use in the recovery of oil consists essentially of a hydrocarbon, an aqueous medium, a surfactant, and a cosurfactant, said surfactant containing, as essential constituents, (a) an internal olefin sulfonate having 10 to 26 carbon atoms and (b) at least one ethoxylate selected from the group consisting of polyoxyethylene alkyl ethers and polyoxyethylene alkylphenylethers, the weight ratio of the component (a) to the component (b) being within the range of from 19/1 to 3/7. This micellar slug has an improved salinity tolerance and hard-water resistance and is capable of forming a micro-emulsion having a low interfacial tension and good stability. Furthermore, the viscosity of this micellar slug can be easily adjusted.

Description

SPECIFICATION Micellar slug for oil recovery BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a micellar slug suitable for use in a micellar drive for recovering oil (i.e., petroleum) from subterranean reservoirs. More specifically, it relates to a micellar slug capable of forming micro-emulsions at a high salt concentration and also capable of recovering oil from subterranean reservoirs at a high oil recovery efficiency and at a low cost.

Description of the Prior Art A micellar drive method is known in the art as one of the so-called "enhanced oil recovery (EOR)" methods for recovering oil from oil-bearing subterranean reservoirs. According to the micellar drive method, a micellar slug, that is, a micro-emulsion obtained by emulsifying water and oil with a surfactant, is injected under pressure into the subterranean reservoirs for the recovery of oil remaining in those subterranean reservoirs. Various processes and chemicals have been heretofore studied in the art. The micellar drive methods are disclosed in, for example, U.S. Patent Nos. 3506070, 3613786, 3740343, 3983940, 3990515, 4017405, and 4059154. These prior arts disclose various kinds of surfactants suitable for use in the formation of micellar slugs.Examples of such surfactants are petroleum sulfonates, alkylaryl sulfonates, dialkyl sulfosuccinates, alkane sulfonates, polyoxyethylene alkylether sulfates, alpha-olefin sulfonates, polyoxyethylene alkylethers, polyoxyethylene alkylphenylethers, polyol fatty acid esters, alkyltrimethyl ammonium salts, and dialkyldimethyl ammonium salts.

There are numerous oil production wells or oilfields in all parts of the world and, therefore, subterranean reservoirs have a wide variety of properties. Accordingly, oilfields to which EOR methods are applied must have various and different properties, and also must contain a variety of available oil stratum water, for example, from soft water containing a very small amount of inorganic salts to brine containing large amounts of inorganic salts and polyvalent metallic ions.

Furthermore, it is not unusual that the desired soft water is not available as formation water (i.e., water used in the formation of the micro-emulsions). Thus, surfactants used in the formation of the micro-emulsions). Thus, surfactants used in the formation of micellar slugs must have good salinity tolerance and hard-water resistance. Furthermore, the micellar slugs must have, in addition to good salinity tolerance and thermal stability, sufficiently low interfacial tensions between both the oil and the micro-emulsions and between the formation water and the microemulsions, must be readily adjusted to a viscosity slightly higher then that of the oil the present in subterranean reservoirs (i.e., can be capable of mobility control), and must form stable microemulsions, which are stably maintained during sweeping until an oil bank is formed.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide, for the recovery of oil, a micellar slug having good salinity tolerance and hard-water resistance, and capable of forming a microemulsion which has the sufficient low interfacial tensions and which can be readily adjusted to any desired viscosity.

Another object of the present invention is to provide a micellar slug capable of recovering oil from subterranean reservoirs at a high recovery efficiency.

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

In accordance with the present invention, there is provided a micellar slug for use in the recovery of oil, said slug consisting essentially of a hydrocarbon, an aqueous medium, a surfactant, and a cosurfactant. The surfactant contains, as essential constituents, (a) an internal olefin sulfonate having 10 to 26 carbon atoms and (b) at least one ethoxylate selected from the group consisting of polyoxyethylene alkyl ethers and polyoxyethylene alkylphenyl ethers, in which the weight ratio of the component (a) to the component (b) is within the range of from 19/1 to 3/7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present micellar slugs desirably used for the recovery of oil are transparent microemulsions containing about 2% to about 90% by weight of a hydrocarbon, about 4% to about 95% by weight of an aqueous medium, about 1% to about 30% by weight of surfactants containing, as essential constituents, (a) an internal olefin sulfonate and (b) an ethoxylate, and about 0.1% to about 20% by weight of a cosurfactant.

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

As mentioned above, the miceilar slugs of the present invention can contain about 2% to about 90% by weight of hydrocarbons. The preferable concentration of hydrocarbons is within the range of about 3% to about 40% by weight, since the use of a large amount of hydrocarbons is not economical.

The aqueous media usable in the formation of the micellar slug of the present invention are those having an inorganic salt concentration of O to about 10% by weight, preferably about 0.1% to about 8% by weight, since the surfactants contained in the present micellar slugs have good salinity tolerance and hard-water resistance. The aqueous medium usuable in the formation of the micellar slug of the present invention includes soft water and brine containing a medium amount of inorganic salts. For example, rain water, river water, lake water, formation water, oil stratum water, and seawater can be freely used in the formation of the micellar slug of the present invention. Typical examples of alkali metal salts contained in the brine are NaCI, KCl, Na2SO4, and K2SO4.Examples of bivalent metal ions are a Mg ion and a Ca ion, and these metal ions can be present up to about 4000 ppm in terms of Mg ion in the aqueous medium.

The internal olefin sulfonates usable as component (a) in the present invention are those obtained by sulfonating internal olefins containing as a main constituent vinylene-type monoolefin having 10 to 26 carbon atoms, desirably 112 to 24 carbon atoms, and having a general formula: R-CH=CH-R1 wherein R and R' are independently straight- or branched-chain saturated hydrocarbon radicals having 1 or more carbon atoms, provided that the total number of carbon atoms of R and R1 is 8 to 24, desirably 10 to 22, and optionally containing about 33% by weight (about one third of the olefins) or less of tri substituted type monoolefins, followed by neutralizing the sulfonated products with appropriate bases and then, optionally hydrolyzing the neutralized products.The internal olefin sulfonates thus prepared generally contain about 10% to about 60% by weight of alkenyl sulfonates having a double bond and about 90% to about 40% by weight of hydroxyalkane sulfonates, and also contain about 80% by weight or more of monosulfonates and about 20% by weight or less of disulfonates. It should be noted, however, that internal olefin sulfonates having compositions different from the above-mentioned compositions ratios can be prepared by appropriately 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 of the alkenylsulfonate. On the other hand, the increase in the mol ratio of the sulfonating agent to the internal olefin during the sulfonation tends to result in an increase in the composition ratio of the disulfonate.

The internal olefin sulfonates suitable for use in the present invention are those containing about 40% by weight or more, more preferably about 45% to about 90% by weight, of the hydroxyalkane sulfonates and about 20% by weight or less, more perferably about 0.1 % to about 15% by weight of the disulfonate. When these internal olefin sulfonates are used, microemulsion having a sufficiently low interfacial tension can be formed and, therefore, the desired oil recovery efficiency is increase.

The internal olefin sulfonates usable in the present invention can be alkali metal salts, ammonium salts, and organic amine salts thereof. The preferable counter cations are Na, K, Ca, NH4, and alkanolammonium.

Examples of internal olefin sulfonates usuabie in the formation of the micellar slugs of the present invention are: internal olefin sulfonates having 12, 13, 1 5, 16, 18, 20, 22, 24, 12-16, 13-14, 14-16, 14-18, 15-17, 16-18, 17-20, and 20-24 carbon atoms. These suifonates may be used alone or in any mixture thereof.

The ethoxylates usable as component (b) in the present invention are those having the following general formula I and II

wherein R2 is an alkyl or alkenyl group having 10 to 18 carbon atoms, R3 is an alkyl group having 6 to 1 5 carbon atoms, and R2 and R3 may be a straight- and branched chains, m is about 3 to about 10 on average, and n is about 3 to about 1 5 on average.

Typical examples of the ethoxylates (HAE) having the general formula (I) are polyoxyethylene decylethers (m = 3), polyoxyethylene dodecylethers (m = 4), polyoxyethylene tetradecylethers (m = 4), polyoxyethylene hexadecylethers (m = 8), and polyoxyethylene octadecylethers (m = 6).

Typical examples of the ethoxylate (APE) having the general formula (II) are polyoxyethylene octylphenylethers (n = 5), polyoxyethylene nonylphenylethers (n = 4, 5, and 6), polyoxyethylene decylphenylethers (n = 6), polyoxyethylene dodecylphenylethers (n = 7), polyoxyethylene tetradecylphenylethers (n = 8), and polyoxyethylene pentadecylphenylethers (n = 10).

According to the present invention, the internal olefin sulfonates (a) and the ethoxylates (b) should be contained in the micellar slug at a weight ratio of (a):(b) = 19/1 to 3/7, preferably 9/1 to 4/6, whereby the desired mobility controlled micro-emulsions having the sufficiently low surface tensions and good stability against the changes in the salt concentration of the formation water during sweeping and, therefore, exhibiting high oil recovery efficiency can be obtained.

The use of a too large amount of the component (a) results in the loss of the effect obtained by the combined use of the component (b) and, therefore, the mobility control of the microemulsions cannot be effected. Contrary to this, the use of a too small amount of the component (a) cannot produce the desired micro-emulsions having sufficiently low interfacial tensions.

As mentioned above, the micellar slugs of the present invention contain about 1 % to about 30% by weight of the surfactant. However, the micellar slugs desirably contain about 3% to about 25% by weight of the surfactant, taking into consideration both low interfacial tensions and reasonable cost.

The cosurfactants used in the formation of the micellar slugs of the present invention are an essential constituent for forming micro-emulsions associated with the surfactants. The cosurfactants usable in the present invention are alcohols selected from alcohols having 4 to 8 carbon atoms, the ethyleneglycol monoethers of alcohols having 4 to 8 carbon atoms, and the diethyleneglycol monoethers of alcohols having 4 to 8 carbon atoms. Typical examples of such alcohols are butanols, pentanols, hexanols, 2-ethylhexanol and the other octanols, butoxyethanols, octyloxyethanols and diethyleneglycol monobutylethers.

As mentioned above, the micellar slugs of the present invention can contain about 0.1 % to about 20% by weight of the cosurfactants. However, the preferable concentration of the cosurfactants is within the range of about 1 % to about 10% by weight from the viewpoint of the stability of the micro-emulsions and the decrease in capacity for the interfacial tensions.

As mentioned above, the micellar slugs of the present invention contain, as essential surfactants, internal olefin sulfonates and the ethoxylates. However, other auxiliary surfactants can also be included, together with the internal olefin sulfonates and the ethoxylates.

According to the present invention, since the internal olefin sulfonates and the ethyoxylates are used in the specified weight ratio, the micro-emulsions have various viscosities, that is, from low viscosities to relatively high viscosities. However, an appropriate known thickening agent can be used as an auxiliary in the present invention. Examples of thickening agents usable in the formation of the micellar slugs are heteropolysaccharides produced by microbes, naphthalenesul tonic acid-formaldehyde condensates, polyacrylamides, polyacrylates, hydroxyethylcelluloses, and carboxymethylcelluloses.

The micellar slugs 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 cosufactants can be mixed in any mixing order by using conventional mixing devices, mixing temperatures, and mixing pressures.

The recovery of oil from subterranean reservoirs can be carried out by means of any convention micellar drive method by using the micellar slugs of the present invention. For example, the micellar slugs are injected under pressure into at least one injection well of the subterranean reservoirs. Then, at least one driving fluid such as flood water and/or an aqueous solution of the above-mentioned thickening agent is injected into the injection well so as to transfer or to drive the remaining oil toward an oil production well and to recover the oil from the production well. The suitable amount of the micellar slugs injected into the injection well is about 5% to about 25% by volume of the porosity of the subterranean reservoirs.

As mentioned hereinabove, the micellar slugs of the present invention contain the internal olefin solfonates and the ethoxylate in the specified amount ratio. Therefore, the desired mobility controlled microemulsions have excellent salinity tolerance and hard-water resistance, sufficiently low interfacial tensions, and excellent stability against the change in the inorganic salt concentration of the formation water during sweeping.

EXAMPLES 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 1 Micro-emulsions were prepared by weighing 7% of C15-C17 IOS-Na (i.e., sodium internal olefin sulfonates) and 7% of the non ironic surfactants listed in Table 1 as surfactants, 6% of n-amyl alcohol as a cosurfactant, 40% of fuel oil (ASTM No. 2 oil) as a hydrocarbon, and 40% of an aqueous solution of 2% of sodium chloride dissolved in demineralized water as a brine. The resultant mixture was stirred at 100 rpm for 30 minutes at a temperature of 71 C The micro-emulsion forming capabilities were determined from the visual appearance of the micro-emulsions according to the following: 0 .. .. A transparent and homogenous micro-emuision was formed.

X ..... An opaque suspension was formed or the mixture was separated into two phases.

The inferfacial tensions were measured by a spinning drop type tensiometer at 71 'C in an appropriately diluted system.

The viscosities were measured at 25 C by a Brookfield viscometer.

The results, together with the compositions of the ingredients are shown in Table 1.

Table 1 Inter facial Visual tension Vis Sample appear- x 10-3 cosity No. Nonionic surfactant ance dyne/cm (cp) 1 Polyoxyethylene laurylether (m = 3) 0 3.12 51 2 II (m = 6) 0 6.34 23 3 ii (m=18) X - 4 Polyoxyethylene stearylether (m = 3) 0 7.45 34 5 I1 (m=7) 0 8.27 25 6 Polyoxyethylene octylphenylether (n = 3) 0 8.64 57 7 1I (n = 8) 0 6.81 26 8 Polyoxyethylene nonylphenylether (n = 4) 0 5.96 37 9 II (n=12) 0 4.13 18 10 1I (N=18) X - 11 Polyoxyethylene decylphenylether (n = 6) 0 6.42 33 12 " (n = 10) 0 8.74 12 13 Pluronic L44 1 x - 14 " P-84*2 X - 15 Tetronic 702*3 X - *1 Ethylene oxide addition product of polypropylene glycol (EO 40%, PPG's M.W. = 1200) *2 Ethylene oxide addition product of polypropylene glycol (EO 40%, PPG's M.W. = 2250) *3 Ethylene oxide addition product of polypropylene polyol using ethylenediamine as initiator (EO = 20%, PPG's M.W. = 2500) Example 2 Micro-emulsions were prepared by weighing 14% or 12% of a various mixture of C15-C17 IOS Na and polyoxyethylene laurylether (m = 3 or 5) as a surfactant, 6% of n-amyl alcohol or 3% of isopropyl alcohol as a cosurfactant, 40% of fuel oil or 30% of kerosine as a hydrocarbon, and 40% or 55% of an aqueous solution of 6% of sodium chloride dissolved in demineralized water as brine in a beaker. The resultant mixture was stirred at 100 rpm for 30 minutes at a temperature of 71 C.

The evaluation of the micro-emulsion forming capabilities and the measurements of the interfacial tensions and the viscosities were carried out in the same manner as in Example 1.

The results, together with the mixing ratios of the surfactants, are shown in Table 2.

As is clear from the results shown in Table 2, the mobility control can be facilitated by the combined use of the IOS with the ethoxylates.

Table 2 Sample No. 16 17 18 19 20 21 22 23 24 25 26 27 28 Anionic surfactant C15-C17 IOS-Na 14 13.5 11.4 8.3 6.8 4.6 3.1 - 10.6 9.5 6 5.9 3.4 Nonionic surfactant Polyoxyethylene laurylether (m = 3) - 0.5 2.6 5.7 7.2 9.4 10.9 14 1.4 - 6 - 8.6 " (m = 5) - - - - - - - - - 2.5 - 6.8 Cosurfactant Isopropyl alcohol - - - - - - - - 3 3 3 3 3 n-amyl alcohol 6 6 6 6 6 6 6 6 - - - - Hydrocarbon Kerosine - - - - - - - - 30 30 30 30 30 Fuel oil 40 40 40 40 40 40 40 40 - - - - Aqueous medium Brine (NaCl 6%) 40 40 40 40 40 40 40 40 55 55 55 55 55 Properties Visual appearance O O O O O O X X O O O O X Interfacial tension (x 10-3 dyne/cm) 2.32 2.67 3.15 3.87 4.36 8.43 - - 4.13 4.45 5.69 10.16 Viscosity (cp) 6 8 83 57 48 16 - - 87 54 35 28 - Example 3 Various micro-emulsions were prepared by weighing 8.3% of lOS-Na and 5.7% of polyoxyethylene laurylether (m = 3) as surfactants, 6% of n-amylalcohol as a cosurfactant, 62% of fuel oil as a hydrocarbon, and 40% of an aqueous solution of a given amount of (i) sodium chloride or (ii) sodium chloride and magnesium chloride or calcium chloride dissolved in demineralized water as brine in a beaker. The resultant mixture was stirred at 100 rpm for 30 minutes at a temperature of 71"C.

The evaluation of the micro-emulsion forming capabilities and the measurements of the tnterfacial tensions were carried out in the same manner as in Example 1. The oil recovery tests were carried out by using a Berea sandstone core having a size of 3.8 cm diameter and 28 cm length a permeability of about 500 mD, and a porosity of about 20%.

A core sufficiently saturated with brine was set in a core holder and then fuel oil was injected under pressure into the core at a feed rate of 6 cc/min until no brine was discharged. Brine was then injected under pressure at the same feed rate in a water drive method until the content of the fuel oil in the effluent became less then 0.1%. Thus, the fuel oil was recovered. After the water drive method, the core holder and the micro-emulsions were placed in a constant temperature bath at a temperature of 71 C for a micellar drive method.

The micro-emulsions were first injected under pressure into the core in an amount of 10% by volume of the pore volumes, a polymer solution (i.e. 1000 ppm of Xanthan gum solution in a brine solution) was the injected under pressure in an amount of 100% by volume of the pore volume and, finally, brine was injected under pressure in an amount of 100% by volume of the pore volume. Thus, the fuel oil was recovered. The injection rate under pressure was 2 feet/day.

The oil recovery efficiency was determined by measuring the amount of water in the core after the test in a toluene azeotropic method to convert the recovery amount of the fuel oil.

The results, together with the composition of the ingredients are shown in Table 3.

Table 3 Sample No. 29 30 31 32 33 34 35 Surfactant (%) C15-C17 lOS-Na 8.3 8.3 8.3 8.3 8.0 8.3 8.3 Polyoxyethylene laurylether (m = 3) 5.7 5.7 5.7 5.7 5.7 5.7 5.7 Brine (%) NaCI 0 2 4 6 8 4 4 CaC12 - - - - - 0.4 MgCl2 - - - - - - 0.4 Visual appearance 0 0 0 0 0 0 0 Interfacial tension (X10-3 dyne/cm) 4.18 4.03 3.94 3.87 4.06 3.85 3.84 Oil recovery efficiency (%) 87 89 90 92 89 91 91 Example 4 Various micro-emulsions were prepared by weighing the given amounts listed in Table 4 of (i) C1q-C14 lOS-NH4, C18-C20 lOS-K, polyoxyethylene laurylether (m = 3), and polyoxyethylene nonylpenhylether (m = 10) as a surfactant, (ii) isopropyl alcohol or n-amyl alcohol as a cosurfactant, (iii) kerosine or fuel oil as a hydrocarbon, and (iv) an aqueous solution of sodium chloride dissolved in mineralized water or an aqueous sodium chloride solution further containing magnesium chloride or calcium chloride dissolved therein in predetermined bivalent metal ion concentrations as brine in a beaker. The resultant mixture was stirred at 100 rpm for 30 minutes at a temperature of 71"C.

The evaluation of the micro-emulsion forming capabilities and the measurements of the interfacial tensions and the viscosities were carried out in the same manner as in Example 1.

The results are shown in Table 4.

Table 4 Sample No. 36 37 38 39 40 41 42 43 44 45 46 47 Anionic surfactant C13-C14 IOS-NH4 6.3 4.4 2.5 1.2 - - - 5.3 4.0 3.5 7.5 4.0 C18-C20 IOS-K - 1.2 1.5 1.8 5.6 3.4 4.8 - - 3.5 - Nonionic surfactant Polyoxyethylene laurylether (m = 3) 1.7 2.4 4.0 5.0 2.4 3.6 1.3 1.2 4.0 - 4.5 Polyoxyethylene nonylphenylether (m = 10) - - - - - - 0.0 0.5 - 3.0 - 7.0 Cosurfactant Isopropyl alcohol - - - - - 3.0 3.0 3.0 2.0 1.0 3.0 4.0 n-amyl alcohol 2.0 2.0 2.0 2.0 2.0 - - - 2.0 1.0 - Hydrocarbon Kerosine - - - - - 40 20 30 - 40 35 Fuel off 20 30 45 50 40 - - 20 30 - - 55 Aqueous medium -Brine (NaCL 4%) - - - 40 - 50 - - - - - 30 " (NaCl 2%, Mg++ 4000 ppm) - - 45 - 50 - 70 - - 48 - " (", Ca++ 1500 ppm) - 60 - - - - - 40 - - 50 " (", Mg++ 2000 ppm) 70 - - - - - - - 58 - - (", Ca++ 1000 ppm) Properties Visual appearance O O O O O O O O O O O O Interfacial tension (x 10-3 dyne/cm) 7.34 5.25 4.67 6.83 3.11 4.42 3.76 5.53 9.29 7.31 5.72 9.77 Viscosity (cp) 22 68 34 31 18 10 21 44 13 38 32 9

Claims (5)

1. A micellar slug for use in the recovery of oil, said slug consisting essentially of a hydrocarbon, an aqueous medium, a surfactant, and a cosurfactant, said surfactant containing, as essential constituents, (a) an internal olefin sulfonate having 10 to 26 carbon atoms and (b) at least one ethyoxylate selected from the group consisting of polyolethylene alkyl ethers and polyoxyethylene alkylphenyl ethers, the weight ratio of the component (a) to the component (b) being within the range of from 19/1 to 3/7.

2. A micellar slug as claimed in claim 1, wherein said micellar slug consists essentially of 2% of 90% by weight of the hydrocarbon, 4% to 95% by weight of the aqueous medium. 1% of 30% by weight of the surfactant, and 0.1 % to 20% by weight of the cosurfactant.

3. A micellar slug as claimed in claim 1, wherein said polyoxyethylene alkyl ethers is an ethoxylate having the general formula:

wherein R2 is an alkyl or alkenyl group having 10 to 18 carbon atoms and m is 3 to 1 5 on average.

4. A micellar slug as claimed in claim 1, wherein said polyoxyethylene alkylpenyl ether is an ethoxylate having the general formula:

wherein R3 is an alkyl group having 6 to 1 5 carbon atoms and n is 3 to 1 5 on average.

5. A process for producing oil from an oil-bearing subterranean reservoir penetrated by wells which comprises the step of: (1) injecting into said reservoir through an injection well the micellar slug consisting essentially of a hydrocarbon, an aqueous medium, a surfactant, and a cosurfactant, and surfactant containing, as essential components, (a) an internal olefin sulfonate having 10 to 26 carbon atoms and (b) at least one ethoxylate selected from the group consisting of polyoxyethylene alkyl ethers and polyoxyethylene alkylphenylethers, the weight ratio of the component (a) to the component (b) being within the range of from 19/1 to 3/7; (2) injecting into said reservoir at least one driving fluid; and (3) recovering oil from said reservoir through a production well.