RU2818192C2 - Injected fluids containing anionic surfactants and alkoxylated alcohols, and use of such fluids in methods of chemical enhanced oil recovery - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: group of inventions relates to surfactant compositions containing anionic surfactants along with nonionic surfactants, and to the use of such compositions in methods of chemical enhanced oil recovery. Surfactant composition for use in chemical enhanced oil recovery. Surfactant composition contains at least: i) an anionic salt of an alkyl alkoxylated sulphate and ii) a non-ionic alcohol ethoxylate, where the weight ratio of i)/ii) ranges from 6:1 to 1:6. Also disclosed is the use of a surfactant composition in chemical enhanced oil recovery, where said surfactant composition is a surfactant composition and a method for chemical enhanced oil recovery of a subterranean formation drilled by at least one injection well and one production well. Method includes i) pumping a surfactant composition into an injection well, whereby said surfactant composition is in contact with crude oil present in said subterranean formation, to reduce interfacial tension of said crude oil to ultra-low values at level of 10⁻² mN/m or lower and ii) extraction of crude oil from underground formation from production well. Said surfactant composition is capable of reducing interfacial tension values at temperatures from 25 °C to 70 °C and in saturated salt solutions, having from 4% to 15% of the total content of dissolved solids, at least part of said dissolved solids is divalent cations.

EFFECT: compositions provide ultra-low values of IFT at 10⁻² mN/m and less for a number of heavy and light crude oils with different properties (SARA composition and densities).

15 cl, 9 dwg, 7 tbl, 3 ex

Description

The present invention relates to surfactant compositions containing anionic surfactants along with nonionic surfactants, and to the use of such compositions in chemical enhanced oil recovery methods. In particular, the surfactant composition refers to mixtures of anionic salts of alkyl alkoxylated sulfates and nonionic alcohol ethoxylates for reducing interfacial tension for a wide range of crude oils with varying compositions and densities during chemical enhanced oil recovery processes over a wide range of temperatures and salinities. The invention also relates to a method for chemically enhancing oil recovery by injecting mixtures of salts of alkyl alkoxylated sulfates and alcohol ethoxylates.

BACKGROUND OF THE INVENTION AND DISCUSSION OF THE BACKGROUND ART

Over the past decades, various methods for extracting oil from underground formations have been developed. Problems encountered with chemical enhanced oil recovery (EOR) techniques applied to high temperature/high salinity formations, typically using surfactant formulations, are often associated with instability of solutions in aqueous environments. Under high temperature and/or high salinity conditions, surfactant compositions tend to phase separate or precipitate, resulting in reduced oil recovery. Co-surfactants and/or co-solvents can be used to correct instability in the aquatic environment. However, the addition of co-surfactants and/or co-solvents can also compromise the ability of the primary surfactant to reduce the interfacial tension (IFT) at the water/oil interface to ultra-low values - a necessary requirement for efficient oil mobilization and hence oil recovery .

A number of past studies have evaluated various surfactant systems for use in high temperature and/or high salinity formations. Puerto et al. (2012) evaluated mixtures of glycidyl sulfonate alkoxylate and internal olefin sulfonate (IOS) at temperatures up to 120°C and salinity up to 21% NaCl, without the presence of divalent cations (such as Ca2+, Mg2+, etc.) in water. However, the total surfactant concentration was unfortunately high at 2 wt% and no crude oil was used to confirm the results. Instead, mid-phase microemulsions were observed with octane as a model oil, without any specified IFT value. The surfactants evaluated (alkoxylate glycidyl sulfonates) are not available as commercial products and would be more expensive to produce than the corresponding sulfates or IOS.

Another study by Chou and Bae (1988) discussed surfactant formulations for high salinity, up to 21%. However, the brine solution used consisted only of NaCl, with no divalent cations present. It was not crude oil that was evaluated, but alkane oils (C6 - C16). Other studies (Han et al., 2013; Ghosh and Obassi, 2013; Jabbar et al., 2017) have identified surfactant systems that are stable in aqueous environments with ultra-low or no IFTs observed at high temperature and /or mineralization. However, these studies were only conducted on one specific crude oil or alkane oils. None of these studies have evaluated or identified an aquatic stable surfactant system that provides ultra-low IFT for a range of crude oils having different saturated hydrocarbons, aromatics, resins and asphaltenes (SARA) compositions and densities. in the range of mineralization and temperatures.

Prior art studies have failed to identify a single phase-stable composition that can produce ultra-low IFT for a range of crude oils with varying compositions and properties over a wide range of temperatures and salinities (see US 4,479,894; US 2009/0111717 A1; US 4,293,428 ; US 2011/0059873 A1; US 4269271; US 5358045;

US Pat. No. 9,828,815 B2 Baker Hughes describes foam fluids for high salinity conditions using surfactant mixtures consisting of anionic surfactants, sulfates or sulfonates, with nonionic surfactants as one type of cosurfactant. substances. Although the patent claims that such fluids are capable of producing IFTs of 10 ^-1 -10 ^-3 mN/m for various applications, including enhanced oil recovery, the patent does not provide experimental evidence or examples for such claims. The IFT range was mentioned without any indication of the type or properties of the oil. The compositions used for the examples are not described, and the experimental results are applicable only to gas lift operation.

US2011/0083847A1 also describes surfactant mixtures for tertiary crude oil recovery, but the desired ultra-low interfacial tension values over a wide salinity range were not obtained.

All prior art patents, patent publications and non-patent literature listed in this application are incorporated herein by reference for all purposes.

OBJECTIVE OF THE PRESENT INVENTION

Advantages of the described compositions of the invention include their use at low total surfactant concentrations of 0.5 wt%. and less in brine, in salinity ranges up to 15% (150,000 ppm) total dissolved solids (TDS), including up to 1% divalent cations (10,000 ppm) and temperatures up to 70°C. The compositions provide ultra-low IFT values of 10 ^-2 mN/m or less for a range of heavy and light crude oils with different properties (SARA composition and densities).

SUMMARY OF THE INVENTION

The present invention relates to a composition of a certain group of anionic surfactants in combination with nonionic surfactants. In particular, the present invention relates to a composition of anionic salts of alkyl alkoxy sulfates and nonionic alcohol ethoxylates for reducing interfacial tension with crude oils during enhanced oil recovery processes. The compositions can be effectively applied to a wide range of crude oils of varying composition and density, and are stable at temperatures up to 70°C and salinity up to 15%, including up to 1% divalent cations.

The present invention proposes the use of surfactant compositions in chemical enhanced oil recovery, wherein the composition contains:

i) an anionic salt of an alkyl alkoxy sulfate, wherein the alkyl alkoxy sulfate has a molecular structure as shown in [I]:

[I]

Where

R represents a linear, branched or mixture of linear and branched alkyl group having 10-20 carbon atoms, preferably 12-16 carbon atoms,

n=4-15,

m=0-10, more preferably m=0.

M ⁺ represents an alkali metal ion, an alkanolamine ion, an alkylamine ion, or an ammonium ion; And

ii) a nonionic alcohol ethoxylate, wherein said alcohol ethoxylate has the molecular structure as shown in [II]:

[II]

Where

R ₁ represents a linear, branched or mixture of linear and branched alkyl group having 8-24 carbon atoms, preferably 12-24 carbon atoms, most preferably 20+ carbon atoms,

y=20-100, preferably 40 < y ≤ 100, more preferably 50 ≤ y ≤ 100.

In a preferred embodiment of the invention, R represents a branched alkyl group, more preferably a branched 2-alkyl group.

The invention is further illustrated by surfactant concentrations where the weight ratio i)/ii) is from 6:1 to 1:6, more preferably from 4:1 to 1:4, most preferably from 3:2 to 2:3.

The invention is further illustrated by surfactant compositions in which the total concentration of i) and ii) does not exceed 0.5% by weight. the entire composition.

In a further embodiment of the invention, the surfactant composition reduces the interfacial tension of the crude oil to ultra-low values of 10 ^-1 mN/m or less, more preferably 10 ^-2 mN/m or less.

In addition, the surfactant composition is capable of reducing interfacial tension values of crude oils in brines with salinities ranging from 4% to 15% of total dissolved solids.

Another embodiment of the present invention is a method for chemically enhancing oil recovery of a subterranean formation penetrated by at least one injection well and one production well, comprising:

i) injecting into an injection well a surfactant composition whereby said surfactant composition is contacted with crude oil present in said subterranean formation to reduce the interfacial tension of said crude oil to ultra-low values of 10 ^-2 mN/m or less, wherein said surfactant composition is capable of reducing interfacial tension values at temperatures up to 70° C. and at salinity of up to 15% total dissolved solids, including up to 1% divalent cations, wherein said surfactant composition contains at least

a) an anionic salt of an alkyl alkoxy sulfate, wherein said alkyl alkoxy sulfate has the molecular structure as shown in [I]:

[I]

Where

R represents a linear, branched or mixture of linear and branched alkyl group having 10-20 carbon atoms, preferably 12-16 carbon atoms,

n=4-15,

m=0-10,

M ⁺ represents an alkali metal ion, an alkanolamine ion, an alkylamine ion, or an ammonium ion; And

b) a non-ionic alcohol ethoxylate, wherein said alcohol ethoxylate has the molecular structure as shown in [II]:

[II]

Where

R ₁ represents a linear, branched or mixture of linear and branched alkyl group having 8-24 carbon atoms, preferably 12-24 carbon atoms,

y=20-100, preferably 40 < y ≤ 100, more preferably 50 ≤ y ≤ 100,

ii) extraction of crude oil from a subterranean reservoir from a production well.

These and other features and advantages of the present invention will become apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows dynamic IFT in 4% TDS brine of MIPA ISALCHEM C12/C13-8 PO sulfate salt (0.4 wt%) and cosurfactant (0.1 wt%) compositions with heavy crude oil (H1 crude oil) in the temperature range 25-60°C.

Figure 2 shows dynamic IFT in a 4% TDS brine solution of MIPA ISALCHEM C12/C13-8 PO sulfate (0.4 wt%) and cosurfactant (0.1 wt%) with light crude oil. (crude oil L1) in the temperature range 25-60 °C.

Figure 3 shows dynamic IFT in a 4% TDS brine solution of MIPA ISALCHEM C12/C13-8 PO sulfate (0.4% wt) and cosurfactant (0.1% wt) for various crude oils. at 25°C.

Figure 4 shows dynamic IFT in a 4% TDS brine solution of MIPA ISALCHEM C12/C13-8 PO sulfate (0.4 wt%) and cosurfactant (0.1 wt%) for various crude oils. at 40°C.

Figure 5 shows dynamic IFT in a 4% TDS brine solution of MIPA ISALCHEM C12/C13-8 PO sulfate (0.4% wt) and cosurfactant (0.1% wt) for various crude oils. at 60°C.

Figure 6A shows the dynamic IFT of MIPA ISALCHEM C12/C13-8 PO sulfate salt and surfactant 1 at various surfactant concentration ratios in 4% TDS brine for H1 crude oil at 25°C.

Figure 6B shows the dynamic IFT of MIPA salt ISOFOL C16-8PO sulfate and surfactant 1 at various surfactant concentration ratios in 4% TDS brine for H1 crude oil at 25°C.

Figure 7 shows dynamic IFT in a 11.8% TDS brine solution of MIPA ISALCHEM C12/C13-4 PO sulfate (0.25 wt%) and surfactant 1 (0.25 wt%) for various crude oils at 25-40°C.

Figure 8 shows dynamic IFT in a 11.8% TDS brine solution of MIPA ISALCHEM C12/C13-4 PO sulfate (0.25 wt%) and cosurfactant (0.25 wt%) for various crude oils at 40°C.

DETAILED DESCRIPTION OF PREFERRED IMPLEMENTATION OPTIONS

The surfactant compositions of the present invention provide aqueous stable solutions over a range of temperatures and salinities and produce ultra-low interfacial tensions with a very wide range of crude oils. The performance of these compositions can be improved by matching the hydrophobic structures, along with the number of PO and/or EO units of both anionic and nonionic structures, to the needs of a particular well.

Materials

The surfactants used to prepare the surfactant compositions of the examples are mixtures of anionic and nonionic surfactants. Anionic surfactants specifically evaluated are, in particular, methyl isopropylamine (MIPA) and sodium (Na) salts of alkyl alkoxylated sulfates, and include, but are not limited to, surfactant structures derived from propoxy (PO) and/or ethoxy alcohols (EO) links as described in Table 1.

Table 1: Structures of anionic alkylalkoxylated sulfate salts

Name of alcohol Alcohol chain length Alcohol structure Number of PO EO number ZIEGLER C10 100% linear 4-15 1 ISALCHEM C12/C13 95% 2-alkyl branched 4-8 0 SAFOL23 C12/C13 50% internally branched, 50% linear 7-13 3 ISOFOL C12 - C16 100% 2-alkyl branched 8-15 0

The non-ionic co-surfactants used are alkoxylated alcohols, in particular ethoxylated alcohols. Suitable alcohols that can be used to synthesize the alkoxylated alcohols described above include, but are not limited to, linear alcohols such as linear C6 alcohols (eg, ALFOL 6) and C20+ alcohols (eg, ALFOL 20+), and branched alcohols such as 2 -alkyl-1-alkanols (Gerbet alcohols, e.g. ISOFOL 12 and ISOFOL 20), and isotridecyl alcohols (e.g. MARLIPAL O13, C13 oxoalcohol). All examples provided by trade names are sold by Sasol Performance Chemicals.

Table 2: Structures of nonionic ethoxylated alcohols.

Non-ionic co-surfactant Name of alcohol Alcohol chain length Alcohol structure EO number Surfactant 1 ALFOL20+ C20+ linear, long alkyl chain 20, 50, 75, 100 Surfactant 2 ISOFOL 20 C20 2-alkyl branched, long chain 50 Surfactant 3 ISOFOL 24 C24 2-alkyl branched, long chain 50 Surfactant 4 ALFOL20+ C20+ linear, long chain 25 Surfactant 5 iTDA
(isotridecanol) C13 branched, medium chain 50 Surfactant 6 ISOFOL 12 C12 2-alkyl branched, medium chain 50 Surfactant 7 ALFOL 6 C6 linear, short circuit 50 Surfactant 8 iTDA
(isotridecanol) C13 branched, medium chain thirty Surfactant 9 ISOFOL 12 C12 2-alkyl branched, medium chain 29 Surfactant 10 ALFOL 6 C6 linear, short circuit 15 Surfactant 11 iTDA
(isotridecanol) C13 branched, medium chain 8 Surfactant 12 2-ethylhexanol C8 branched, short chain 50

EXPERIMENTAL PART

The brines used in this study have the composition and total dissolved solids (TDS) content shown in Table 3. Brine A, brine B, and brine C have a total divalent ion concentration of 4%, 11 .8% and 15%, respectively.

Table 3. Composition of the saturated salt solutions used.

(a) Saturated saline solution A with 4% TDS

Component Composition, g/l NaCl 30.39 KCl 1.51 CaCl ₂ ∙2H ₂ O 6.73 MgCl ₂ ∙6H ₂ O 1.39 TDS 4%

(b) Saline B with 11.8% TDS

Component Composition, g/l NaCl 106.03 _{Na2SO4 ​} 0.74 MgCl ₂ ∙6H ₂ O 1.23 _CaCl2 10,767 TDS 11.8%

(c) Sat. C solution with 15% TDS

Component Composition, g/l NaCl 113.96 KCl 5.65 MgCl2∙6H2O 5.23 CaCl ₂ ∙2H ₂ O 25.25 TDS 15%

The crude oils used in this study have the compositions and densities shown in Table 4. As used herein, the terms “heavy crude oil” and “light crude oil” have the following meanings:

- heavy crude oil is crude oil that has less than 30% by weight. hydrocarbons having carbon chains less than C15 and API gravity below 30°; And

- light crude oil is crude oil that has 30% wt. or more hydrocarbons having carbon chains less than C15 and an API gravity of 30° or greater.

Table 4 . Composition and density of the crude oils used.

(a) Heavy crude oils

Raw oil %
<C15 %
Limit %
Aromatic %
Resins %
Asphaltenes Density at 20 ° C, g/ml Density in API degrees, ° Crude oil H1 13.90 50.27 26.52 22.67 0.53 0.8939 26.8 Crude oil H2 22.13 19.78 51.02 17.11 12.09 0.9745 13.7 Crude Oil H3 24.10 40.69 36.48 15.43 7.40 0.8920 27.1 Crude oil H4 28.96 18.33 44.55 23.79 13.33 0.9700 14.4

(b) Light crude oils

Raw oil %
<C15 %
Limit %
Aromatic %
Resins %
Asphaltenes Density at 20 ° C, g/ml Density in API degrees, ° Crude oil L1 55.46 60.13 32.29 7.35 0.22 0.8334 38.1 Crude oil L2 42.28 45.57 41.62 12.81 0.00 0.8549 34.0

Experimental methods

Sample preparation

Stock solutions of 10% each of anionic sulfates and nonionic alcohol ethoxylates (AE) in Nanopure water were prepared prior to formulation.

The compositions are subsequently adjusted to the desired concentration of each surfactant from the stock solutions in each of the brines listed in Table 3. The concentration of anionic sulfate in the composition preferably varies in the range of 0.15-0.4 wt%. The concentration of nonionic ethoxylate in the composition preferably varies in the range of 0.1-0.35 wt%. The total surfactant concentration in the composition was kept constant at 0.5 wt%.

Aquatic stability test

The prepared compositions were placed in an oven at a temperature in the range of 25-70 °C for a period of at least 3 months. The compositions were visually inspected over a long period of time for any phase separation (PS), turbidity, or precipitation. Compositions that showed signs of phase separation, cloudiness, or precipitation were not tested for stability in an aqueous environment. Compositions that remained clear over time were tested for stability in an aqueous environment.

Unless otherwise stated, throughout this application, aqueous stability tests were conducted in accordance with the method described above.

Dynamic IFT measurement

For compositions tested for aqueous stability, dynamic IFT was measured for each of the crude oils in Table 4 at various temperatures using a DataPhysics interfacial tension tensiometer. The capillary tube was filled with ~2 ml of a denser phase, which was a surfactant composition. Oil in an amount of 2-3 μl, which was a less dense phase, was introduced into a capillary tube filled with a surfactant solution to form a drop. The capillary tube was then inserted into the rotating compartment of the device. As the tube rotated, the oil droplet began to stretch and an IFT value was created. IFT changed gradually at first and in most cases became constant after 15 min. Once the IFT value became constant, it was recorded.

Unless otherwise stated, throughout this application, dynamic IFT measurements were performed in accordance with the method described above.

results

Compositions containing only anionic surfactants, namely the alkylpropoxyethoxy sulfate salts described in this invention, prepared in the saturated salt solutions listed in Table 3, have not been tested for stability in an aqueous environment in the temperature range of 25-70 °C. Therefore, a co-surfactant (non-ionic surfactant) was required to improve the aqueous stability of anionic sulfate surfactants.

Experiment 1 : Aqueous stability tests (compositions of anionic and nonionic surfactants)

Aqueous stability of anionic surfactant compositions, namely MIPA C12/C13-8 PO sulfate salt (0.4% wt), and various nonionic alcohol ethoxylates (AE) cosurfactants (0.1 % wt) were assessed over a temperature range of 25–60 °C in 4% TDS saturated saline. The results are shown in Table 5.

Table 5 . Stability in aqueous environment 0.4% wt. salts MIPA ISALCHEM C12/C13-8PO sulfate and 0.1% wt. co-surfactant in 4% TDS saturated saline (RF/cloudy=solution separates into phases and becomes cloudy when stirred).

Co-surfactant Name of alcohol Alcohol chain length Alcohol structure #EO 25°C 40°C 60°C Surfactant 1 ALFOL20+ C20+ linear, heavy chain 50 transparent transparent transparent Surfactant 2 ISOFOL 20 C20 2-alkyl branched, long chain 50 transparent transparent transparent Surfactant 3 ISOFOL 24 C24 2-alkyl branched,
heavy chain 50 transparent transparent transparent Surfactant 4 ALFOL20+ C20+ linear, heavy chain 25 transparent transparent transparent Surfactant 5 iTDA
(isotridecanol) C13 branched, medium chain 50 transparent transparent transparent Surfactant 6 ISOFOL 12 C12 2-alkyl branched, medium chain 50 transparent transparent transparent Surfactant 7 ALFOL
6 C6 linear, short circuit 50 transparent transparent RF/muddy Surfactant 8 iTDA
(isotridecanol) C13 branched, medium chain thirty transparent transparent RF/muddy Surfactant 9 ISOFOL 12 C12 2-alkyl branched, medium chain 29 transparent transparent RF/muddy Surfactant 10 ALFOL 6 C6 linear, short circuit 15 transparent transparent RF/muddy Surfactant 11 iTDA
(isotridecanol) C13 branched, medium chain 8 transparent turbid RF/muddy

As can be seen in Table 5, short chain AE (C6) formulations containing 15 and 50 EO units (surfactant 7 and surfactant 10) as co-surfactant failed the aqueous stability test. environment at 60°C. Medium chain AE (C12/C13) formulations containing 30 or fewer EO units (surfactant 8, surfactant 9, and surfactant 10) also failed aqueous stability testing at 60°C C. Formulations using medium chain AE containing 50 EO units and long heavy chain AE containing 25 or more EO units were tested for stability in aqueous media over the entire temperature range.

EXPERIMENT 2 : Determination of dynamic interfacial tension (IFT) values (various crude oils)

For compositions using surfactants 1 to 6, (since they were tested for stability in aqueous environments up to 70°C), the dynamic IFT was measured for various crude oils at different temperatures.

Experiment 2.1:

Dynamic IFT values for formulations containing surfactants 1-6 (0.1 wt%) together with the anionic surfactant ISALCHEM C12/13-8PO sulfate salt MIPA (0.4 wt%) were determined in heavy crude oil (H1) in the temperature range 25-60 °C (4% TDS brine). The results are shown in Figure 1.

Formulations using long heavy chain co-surfactants with 25 and 50 EO units (surfactants 1 to 4) gave ultra-low IFT (<0.01 mN/m) for heavy crude oil (H1 crude oil) at all temperatures in the range 25-60 °C. Formulations using medium chain co-surfactants with 50 EO units (surfactant 5 and surfactant 6) failed to produce ultra-low IFT for H1 crude oil as seen in FIG. 1.

Experiment 2.2:

In addition, dynamic IFT values for compositions containing surfactants 1-6 (0.1 wt.%) together with the anionic surfactant ISALCHEM C12/13-8PO sulfate salt MIPA (0.4 wt. %). ), evaluated in light crude oil (L1) over a temperature range of 25-60 °C (4% TDS brine). The results are shown in Figure 2.

Only surfactant 5 and surfactant 6 (medium chain co-surfactants with 50 EO units) were able to produce ultra-low IFT for light crude oil (L1 crude oil) over the entire temperature range, as shown in Fig. 2 .

Experiment 2.3:

To further confirm the results obtained in Experiments 2.1 and 2.2, the dynamic IFT values for formulations containing surfactants 1, 4, 5 and 6 (0.1 wt.%) together with the anionic surfactant ISALCHEM C12/13 -8PO MIPA sulfate salt (0.4% wt) was evaluated in various crude oils over the temperature range 25-60 °C (4% TDS brine). The results are shown in Fig.3 - Fig.5.

The IFT results presented in Figure 3 - Figure 5 further support the findings that surfactants 1 to 4 are capable of producing ultra-low IFT for heavy crude oils, and both surfactant 5 and surfactant 6 are capable create ultra-low IFT for light crude oils in the temperature range 25-60 °C.

EXPERIMENT 3: Effect of mixing ratio of anionic and nonionic surfactants on aqueous stability and IFT values

In order to demonstrate the effect of different mixing ratios between anionic and non-ionic surfactants on aqueous stability and IFT values, two anionic surfactants, namely the salts MIPA ISALCHEM C12/13-8PO sulfate and ISOFOL C16-8PO sulfate, were evaluated. together with nonionic surfactant 1.

Experiment 3.1: Aquatic stability tests

The aqueous stability of the anionic surfactant composition ISALCHEM C12/13-8PO sulfate (MIPA salt) and surfactant 1 (in various proportions) was determined in saturated saline with 4% TDS at temperatures of 25-70 °C. The results are shown in Table 6.

Table 6. Aqueous stability of mixtures of anionic sulfate and nonionic ethoxylated alcohol at various surfactant ratios in 4% TDS brine at temperatures up to 70°C.

(a) Anionic sulfate is a salt of MIPA ISALCHEM C12/C13-8PO sulfate

Anionic sulfate, wt.% Surfactant 1,
% wt. 25°C 40°C 60°C 70°C 0.5 0 Turbid turbid RF/muddy RF/muddy 0.45 0.05 Transparent transparent RF/muddy RF/muddy 0.4 0.1 Transparent transparent Transparent Transparent 0.35 0.15 Transparent transparent Transparent Transparent 0.3 0.2 Transparent transparent Transparent Transparent 0.25 0.25 Transparent transparent Transparent Transparent 0.2 0.3 Transparent transparent Transparent Transparent 0.15 0.35 Transparent transparent Transparent Transparent 0.1 0.4 Transparent transparent Transparent Transparent

(b) The anionic sulfate is the salt of MIPA ISOFOL C16-8PO sulfate

Anionic sulfate, wt.% Surfactant 1,
% wt. 25°C 40°C 60°C 70°C 0.5 0 Turbid turbid RF/muddy RF/muddy 0.45 0.05 Transparent transparent RF/muddy RF/muddy 0.4 0.1 Transparent transparent Transparent Transparent 0.35 0.15 Transparent transparent Transparent Transparent 0.3 0.2 Transparent transparent Transparent Transparent 0.25 0.25 Transparent transparent Transparent Transparent 0.2 0.3 Transparent transparent Transparent Transparent 0.15 0.35 Transparent transparent Transparent Transparent 0.1 0.4 Transparent transparent Transparent Transparent

Without an auxiliary surfactant, an anionic sulfate solution with a concentration of 0.5% wt. in 4% TDS brine was cloudy at temperatures between 25°C and 70°C. Anionic/nonionic surfactant mixtures were clear only when the nonionic surfactant concentration was 0.1 wt%. or more with a total surfactant concentration of 0.5% wt.

Experiment 3.2: Determination of IFT values for different surfactant ratios in heavy crude oils

Dynamic IFT values in heavy crude oil (H1 crude oil) composition of anionic surfactant ISALCHEM C12/13-8PO sulfate (MIPA salt) and surfactant 1 (in various ratios) were determined in brine with 4% TDS at 25°C. The results are shown in Figure 6.

Figure 6 shows that the dynamic IFT for H1 crude oil is affected by the anionic/nonionic surfactant ratio. For MIPA salt ISALCHEM C12/C13-8PO sulfate IFT was lowest at an anionic/nonionic surfactant ratio of 0.4 wt%/0.1 wt%, while the ratio was 0.35 wt%. 0.15% wt. for MIPA salt ISOFOL C16-8PO sulfate.

Experiment 3.3: High % TDS brine IFT values in various crude oils

a) Dynamic IFT values for a mixture of 0.25 wt%. anionic surfactant (ISALCHEM C12/C13-4PO sulfate, MIPA salt)/0.25% wt. nonionic surfactant (surfactant 1) was evaluated with various crude oils at temperatures of 25°C and 40°C using saturated saline with 11.8% TDS. The results are shown in Fig. 7.

Figure 7 shows that the MIPA composition of ISALCHEM C12/13-4PO salt (0.25% wt) and surfactant 1 (0.25% wt) in brine with 11.8% TDS for various crude oils at 25°C and 40°C allowed us to obtain ultra-low IFT values.

b) Dynamic IFT values for a mixture of 0.25 wt.%. anionic surfactant (ISALCHEM C12/C13-4PO sulfate, MIPA salt) and various non-ionic surfactants (surfactant 1, 5 and 6 - all at 0.25 wt% concentration) were evaluated with heavy crude oils (crude oil H1 and H2) at temperatures of 40°C, using saturated brine with 11.8% TDS. The results are shown in Fig. 8.

Nonionic surfactant 1 gave ultra-low IFT under the conditions described above.

In addition to the detailed experiments described above, the invention was further illustrated under an expanded range of experimental conditions for various surfactant combinations/surfactant ratios in heavy and light crude oils. The results for various anionic surfactants in combination with surfactant 1 (specifically ALFOL C20+ 50EO) are summarized in Table 7.1 below (Exp. 4-9). Table 7.2 further illustrates the variations of surfactant combinations and different conditions (Exp. 10-15). Aqueous stability and dynamic interfacial tensions were assessed according to the general procedures described previously.

Table 7.1 : Summary of results for various anionic surfactants in combination with surfactant 1 (specifically ALFOL C20+ 50EO), illustrated over a wide range of experimental conditions in heavy and light crude oils

EXP. ANIONIC SURFACTANT NONIONIC SURFACTANT TDS
(%) STABILITY IN AQUATIC ENVIRONMENT DYNAMIC INTERFACAL TENSION Appearance Heavy crude oil (H1) Light crude oil (L1) Name % wt. Name % wt. 25°C 40°C 70°C 25°C 40°C 70°C 25°C 40°C 70°C 4 Ziegler C10-4PO-1EO sulfate, Na salt Surfactant 1: 50EO 11.8 0.40 0.10 transparent transparent 0.0015 0.0432 0.35 0.15 transparent transparent 0.0011 0.0364 5 ISOFOL C12-15PO sulfate, MIPA salt Surfactant 1: 50EO 4.0 0.25 0.25 transparent transparent 0.3000 0.0015 0.15 0.35 transparent transparent 0.0930 0.0100 6 SAFOL C1213-13PO-3EO sulfate, MIPA salt Surfactant 1: 50EO 4.0 0.40 0.10 transparent transparent 0.0016 0.0127 0.25 0.25 transparent transparent 0.0550 0.0028 7 SAFOL C1213-7PO-3EO sulfate, MIPA salt Surfactant 1: 50EO 11.8 transparent transparent 0.30 0.20 transparent transparent 0.0027 0.0136 0.25 0.25 transparent transparent 0.0037 - 0.20 0.30 0.0170 0.0048 8 ISALCHEM C1213-4PO sulfate, Na salt Surfactant 1: 50EO 11.8 0.35 0.15 transparent 0.0011 0.0364 0.25 0.25 transparent 0.0089 0.0162 0.20 0.30 transparent 0.0031 0.0196 0.15 0.35 transparent 0.0153 0.0060 9 ISALCHEM C1213-4PO sulfate, Na salt Surfactant 1: 50EO 15.0 0.20 0.30 transparent transparent 0.0052 0.0059 0.0441 0.0145 0.15 0.35 transparent transparent 0.0354 0.0135 0.0095 0.0095

Table 7.2: Summary of results for various anionic surfactants in combination with various nonionic surfactants, illustrated over a wide range of experimental conditions in heavy and light crude oils

EXP. ANIONIC SURFACTANT NONIONIC SURFACTANT TDS
(%) STABILITY IN AQUATIC ENVIRONMENT DYNAMIC INTERFACAL TENSION Appearance Heavy Crude Oil (H1) Light crude oil (L1) Name % wt. Name % wt. 25°C 40°C 70°C 25°C 40°C 70°C 25°C 40°C 70°C 10 ISALCHEM C1213-8PO sulfate, Na salt Surfactant 12:50EO 4.0 0.20 0.30 transparent transparent 0.031 0.0025 0.15 0.35 transparent transparent
turbid 0.0426 0.0030 eleven ISALCHEM C1213-4PO sulfate, Na salt Surfactant 12: 50EO 11.8 0.35 0.15 transparent 0.0352 0.0030 0.30 0.20 transparent 0.0853 0.0190 12 ISALCHEM C1213-8PO sulfate, MIPA salt Surfactant 1: 75EO 4.0 0.30 0.20 transparent transparent transparent 0.0123 0.0060 0.0110 0.0083 0.25 0.25 transparent transparent transparent 0.0144 0.0049 0.0090 0.0017 0.15 0.35 transparent transparent transparent 0.0700 0.0132 13 ISALCHEM C1213-4PO sulfate, MIPA salt Surfactant 1: 75EO 11.8 0.25 0.25 transparent 0.0022 0.0080 0.20 0.30 transparent 0.0400 0.0070 0.15 0.35 transparent transparent 0.2378 0.0974 0.0175 0.0170 14 ISALCHEM C1213-4PO sulfate, MIPA salt Surfactant 1: 100EO 11.8 0.20 0.30 transparent 0.0030 0.0074 0.15 0.35 transparent transparent transparent 0.0285 0.0168 0.0268 0.0069 0.0065 0.0080 15 ISALCHEM C1213-8PO sulfate, MIPA salt Surfactant 1: 20EO 4.0 0.35 0.15 transparent 0.0010 0.25 0.25 transparent transparent transparent 0.0118 0.0080 0.0270 0.0097 0.0142 0.0036 0.20 0.30 transparent 0.0590 0.0020

Tables 7.1 and 7.2 illustrate the superior performance of the surfactant compositions of the invention, particularly with respect to aqueous stability and ultra-low IFT values obtained over a wide range of temperatures, salinities and concentrations.

Literature Cited

Puerto, M., Hirasaki, G.J., Miller, C.A. et al. 2012. Surfactant Systems for EOR in High-Temperature, High-Salinity Environments. SPE Journal, 17(1), 11-19. https://doi.org/10.2118/129675-PA.

Chou, S.I., Bae, J.H. 1988. Phase-Behavior Correlation for High-Salinity Surfactant Formulations. SPE Reservoir Engineering, 3(3), 778-90. https://doi.org/10.2118/14913-PA.

Han, M., AlSofi, A., Fuseni, A. et al. 2013. Development of Chemical EOR Formulations for a High Temperature and High Salinity Carbonate Reservoir. International Petroleum Technology Conference, Beijing, China, 26-28 March. https://doi.org/10.2523/IPTC-17084-MS.

Ghosh B. and Obassi, D. 2013. Eco-Friendly Surfactant for EOR in High Temperature, High Salinity Carbonate Reservoir. SPE Enhanced Oil Recovery Conference, Kuala Lumpur, Malaysia, 2-4 July. https://doi.org/10.2118/165219- MS.

Jabbar, M.Y., Sowaidi, A.A., Obeidli, A.A. et al. 2017. Chemical Formulation Design in High Salinity, High Temperature Carbonate Reservoir for a Super Giant Offshore Field in Middle East. Abu Dhabi International Petroleum Exhibition & Conference, Abu Dhabi, UAE, 13-16 November. https://doi.org/10.2118/188604- MS.

Claims (43)

1. A surfactant composition for use in chemical enhanced oil recovery, wherein said surfactant composition contains at least: i) an anionic salt of an alkyl alkoxy sulfate, wherein said alkyl alkoxy sulfate has the molecular structure as shown in [I]: [I] Where R represents a linear, branched or mixture of linear and branched alkyl group having from 10 to 20 carbon atoms, n=4-15, m=0-10, M ⁺ represents an alkali metal ion, an alkanolamine ion, an alkylamine ion, or an ammonium ion; And ii) a nonionic alcohol ethoxylate, wherein said alcohol ethoxylate has the molecular structure as shown in [II]: [II] Where R ₁ represents a linear, branched or mixture of linear and branched alkyl group having from 8 to 24 carbon atoms, 40 < y ≤ 100, where the mass ratio i)/ii) is from 6:1 to 1:6. 2. The surfactant composition according to claim 1, wherein R is a branched alkyl group. 3. The surfactant composition according to claim 2, wherein R is a branched 2-alkyl group. 4. Surfactant composition according to claims 1-3, where m=0. 5. The surfactant composition according to any one of the preceding claims, wherein R has from 12 to 16 carbon atoms. 6. A surfactant composition according to claims 1 to 4, where R ₁ =C12 - C24, more preferably where R ₁ =C20+. 7. The surfactant composition according to any of the preceding claims, where 50 ≤ y ≤ 100. 8. The surfactant composition according to any one of the preceding claims, wherein the weight ratio i)/ii) is from 4:1 to 1:4, most preferably from 3:2 to 2:3. 9. The surfactant composition according to any of the preceding claims, where the total concentration of i) and ii) does not exceed 0.5 wt.% of the entire composition. 10. The surfactant composition according to any one of the preceding claims, wherein said surfactant composition reduces the interfacial tension of crude oil to ultra-low values of 10 ^-1 mN/m or less, more preferably 10 ^-2 mN/m or less. 11. The surfactant composition of any one of the preceding claims, wherein said surfactant composition is capable of reducing interfacial tension values of crude oils in brines with salinities ranging from 4% to 15% total dissolved solids. 12. Use of a surfactant composition in chemical enhanced oil recovery, wherein said surfactant composition is a surfactant composition according to any one of claims 1 to 11. 13. Use according to claim 12, wherein said surfactant composition reduces the interfacial tension of the crude oil to ultra-low values of 10 ^-1 mN/m or less, more preferably 10 ^-2 mN/m or less. 14. Use according to claim 12, wherein said surfactant composition is capable of reducing interfacial tension values of crude oil in brines with salinities ranging from 4% to 15% total dissolved solids. 15. A method for chemically enhancing oil recovery of an underground formation penetrated by at least one injection well and one production well, including: i) injecting into an injection well a surfactant composition whereby said surfactant composition is contacted with crude oil present in said subterranean formation to reduce the interfacial tension of said crude oil to ultra-low values of 10 ^-2 mN/m or below, wherein said surfactant composition is capable of reducing interfacial tension values at temperatures from 25° C. to 70° C. and in brine solutions having from 4% to 15% total dissolved solids, at least a portion of said dissolved solids substances are divalent cations, wherein said surfactant composition contains at least a) an anionic salt of an alkyl alkoxy sulfate, wherein said alkyl alkoxy sulfate has the molecular structure as shown in [I]: [I] Where R represents a linear, branched or mixture of linear and branched alkyl group having from 10 to 20 carbon atoms, n=4-15, m=0-10, M ⁺ represents an alkali metal ion, an alkanolamine ion, an alkylamine ion, or an ammonium ion; And b) a non-ionic alcohol ethoxylate, wherein said alcohol ethoxylate has the molecular structure as shown in [II]: [II] Where R ₁ represents a linear, branched or mixture of linear and branched alkyl group having from 8 to 24 carbon atoms, 40 < y ≤ 100, where the mass ratio i)/ii) is from 6:1 to 1:6, ii) extraction of crude oil from a subterranean reservoir from a production well.