INJECTION FLUIDS COMPRISING ANIONIC SURFACTANTS AND ALKOXYLATED ALCOHOLS AND THE USE OF SUCH FLUIDS IN ENHANCED OIL RECOVERY CHEMICAL PROCESSES

Abstract

A method for using a surfactant formulation in chemically enhanced oil recovery, wherein the surfactant formulation comprises at least: (i) an anionic salt of an alkyl alkoxylated sulfate, wherein the alkyl alkoxylated sulfate has a molecular structure as shown in (I), wherein R is a linear, branched, or mixture of linear and branched alkyl group having 10 to 20 carbon atoms, n = 4 - 15, m = 0 - 10, M+ is an alkali metal ion, an alkanolamine ion, an alkylamine ion, or an ammonium ion; and (ii) a nonionic alcohol ethoxylate, wherein the alcohol ethoxylate has a molecular structure as shown in (II), wherein R1 is a linear, branched, or mixture of linear and branched alkyl group having 8 to 24 carbon atoms, y = 20 - 100.

Description

INJECTION FLUIDS COMPRISING ANIONIC SURFACTANTS AND ALKOXYLATED ALCOHOLS AND THE USE OF SUCH FLUIDS IN ENHANCED OIL RECOVERY CHEMICAL PROCESSES The present invention relates to surfactant formulations comprising anionic surfactants together with nonionic surfactants and the use of such formulations in enhanced oil recovery chemical processes. More specifically, the surfactant formulation relates to mixtures of anionic salts of alkyl alkoxylated sulfates and nonionic alcohol ethoxylates for reducing interfacial tension in a wide range of crude oils with various compositions and densities during enhanced oil recovery chemical processes over broad temperature and salinity ranges. The invention further relates to an enhanced oil recovery chemical process that injects mixtures of alkyl alkoxylated sulfate salts and alcohol ethoxylates. BACKGROUND OF THE INVENTION AND DISCUSSION OF THE PRIOR ART Several methods for oil recovery from underground surfaces have been developed over the past decades. The challenges encountered with chemical enhanced oil recovery (EOR) techniques in high-temperature / high-salinity reservoirs, typically using surfactant formulations, are frequently associated with the aqueous instability of the solutions. N C N Under high temperature and / or high salinity conditions, surfactant formulations tend to separate into phases or precipitate, leading to reduced oil recovery. Cosurfactants and / or cosolvents can be used to address aqueous instability. However, the addition of cosurfactants and / or cosolvents can also compromise the ability of the primary surfactant to reduce the oil / water interfacial tension (IFT) to ultra-low values—an essential requirement for effective oil mobilization and, therefore, oil recovery. A number of past studies have evaluated various surfactant systems for application in high-temperature and / or high-salinity reservoirs. Puerto et al. (2012) evaluated mixtures of an alkoxylate glycidyl sulfonate and an 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 the water. The total surfactant concentration, however, was unfortunately high at 2 wt%, and crude oil was not used to confirm the results. Instead, intermediate-phase microemulsions were observed with octane as the model oil, with no reported IFT value. The surfactants evaluated (alkoxylate glycidyl sulfonates) were not readily available as products, and were more expensive to manufacture than the corresponding sulfates or IOS. In another study by Chou and Bae (1988), surfactant formulations for high salinity, up to 21%, were discussed. The brine used, however, consisted solely of NaCl, with no divalent cations present. Instead of crude oil, alkane oils (C6 to C16) were evaluated. Other studies (Han et al., 2013; Ghosh and Obassi, 2013; Jabbar et al., 2017) identified surfactant systems exhibiting aqueous stability with or without ultra-low IFT values ​​reported at high temperature and / or salinity. However, these studies were conducted only on specific crude oils or alkane oils. None of these studies evaluated and identified an aqueous stable surfactant system that produces ultra-low IFT for a range of crude oils having various saturated, aromatic, resin, and asphaltene (SARA) compositions and densities over a range of salinities and temperatures. Prior art investigations failed to identify a stable single-phase formulation that can produce ultra-low IFT for a range of crude oils of various compositions and properties over a wide temperature and salinity range (see documents US 4,479,894; US 2009 / 0111717 Al; US 4,293,428; US 2011 / 0059873 Al; US 4,269,271; US ​​5,358,045; and US 4,077,471). Baker Hughes document US 9,828,815 B2 describes > Π Ñ c NN Cü NNU foam fluids for high salinity conditions using surfactant mixtures with anionic surfactants, sulfates, or sulfonates, with nonionic surfactants as a type of cosurfactant. Although the patent claims that such fluids are capable of generating an IFT of 10⁻¹-10⁻³ mN / m for a variety of applications, including enhanced oil recovery, the patent provides no experimental evidence or examples of such claims. The IFT range was mentioned without any indication of the type or properties of the oil. The formulations used for examples are not described, and the experimental results are only applicable to gas lift operations. Document US2011 / 0083847A1 also describes surfactant mixtures for the production of tertiary mineral oil, but the ultra-low interfacial tension values ​​sought after over a wide salinity range are not obtained. All patents, patent publications, and non-patent literature of the prior art listed in this application are incorporated herein by reference for all purposes. OBJECT OF THE PRESENT INVENTION The advantages of the inventive formulations described include their use in low total surfactant concentrations of 0.5 wt% and lower in brine solutions, over a salinity range 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 formulations produce ultra-low IFT values ​​at and below 10⁻² mN / m for a range of heavy and light crude oils with various properties (SARA compositions and densities). BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a formulation of a specific group of anionic surfactants combined with nonionic surfactants. In particular, the present invention relates to a formulation of anionic salts of alkyl alkoxylated sulfates and nonionic alcohol ethoxylates for reducing interfacial tension with crude oils during enhanced oil recovery processes. The formulations can be effectively applied to a wide range of crude oils with various compositions and densities and are stable at temperatures up to 70°C and salinity ranges up to 15%, including up to 1% divalent cations. The present invention discloses the use of surfactant formulations in chemically enhanced oil recovery, wherein the formulation comprises: i) an anionic salt in an alkyl alkoxylate sulfate, wherein the alkyl alkoxylate sulfate has a structure > Π Ñ c NN C ü NNU molecular as shown in [I]: > Π Ñ c NN C ü NNU where R is a linear, branched or mixture of linear and branched alkyl group having 10 to 20 carbon atoms, preferably 12 to 16 carbon atoms, n = 4 - 15, m = 0 - 10, more preferably m = 0. M+ is an alkali metal ion, an alkanolamine ion, an alkylamine ion, or an ammonium ion; and ii) a nonionic alcohol ethoxylate, wherein the alcohol ethoxylate has a molecular structure as shown in [II]: [II] where R1 is a linear, branched or mixed linear and branched alkyl group having 8 to 24 carbon atoms, preferably 12 to 24 carbon atoms, much more preferably 20+ carbon atoms, y = 20 - 100, preferably 40 < y < 100, more preferably < y < 100. In a preferred embodiment of the invention, R is a branched alkyl group, more preferably a branched 2-alkyl group. The invention is further illustrated by surfactant concentrations wherein the weight ratio of i) / ii) is from 6:1 to 1:6, more preferably from 4:1 to 1:4, much more preferably from 3:2 to 2:3. The invention is further exemplified by surfactant formulations wherein the combined concentration of i) and ii) does not exceed 0.5% by weight of the total formulation. In a further embodiment of the invention, the surfactant formulation reduces the interfacial tension of crude oil to ultra-low values ​​of at or below 10-1mN / m, more preferably at or below 10-2mN / m. Furthermore, the surfactant formulation is able to decrease the interfacial tension values ​​of crude oil in brines with salinities of 4% to 15% total dissolved solids. Another embodiment of the present invention is a method for the chemically enhanced recovery of oil from a subsurface formation penetrated by at least one injection well and one production well, comprising: i) injecting into an injection well a surfactant formulation such that the surfactant formulation makes contact with the crude oil present in the subsurface formation to reduce the interfacial tension of the crude oil to ultra-low values ​​at or below 10-2 mN / m, the surfactant formulation being capable of reducing interfacial tension values ​​at temperatures up to 70°C and at salinities up to 15% total dissolved solids including up to 1% divalent cations, the surfactant formulation comprising at least a) an anionic salt of an alkyl alkoxylated sulfate, wherein the alkyl alkoxylated sulfate has a molecular structure as shown in [I]: where R is a linear, branched, or mixed linear and branched alkyl group having 10 to 20 carbon atoms, preferably 12 to 16 carbon atoms, n = 4 - 15, m = 0 - 10, M+ is an alkali metal ion, an alkanolamine ion, an alkylamine ion, or an ammonium ion; and b) a non-ionic alcohol ethoxylate, wherein the alcohol ethoxylate has a molecular structure as shown in [II]: > CNN C ü NNO where R1 is a linear, branched or mixed linear and branched alkyl group having 8 to 24 carbon atoms, preferably 12 to 24 carbon atoms and y = 20 - 100, preferably 40 < y < 100, more preferably 50 < y < 100. ii) recover the oil from the underground formation from a production well. These and additional features and advantages of the present invention will become evident from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows the dynamic IFT in 4% TDS brine of ISALCHEM MIPA salt formulations C12 / C13 - 8 PO sulfate (0.4% wt.) and co-surfactant (0.1% wt.) with heavy crude oil (H1 Crude) over the temperature range of 25 - 60°C. Figure 2 shows the dynamic IFT in 4% TDS brine of ISALCHEM MIPA salt C12 / C13 - 8 PO sulfate (0.4% by weight) and co-surfactant (0.1% by weight) with light crude oil (LI Crude) over the temperature range of 25 - 60°C. Figure 3 shows the dynamic IFT in 4% TDS brine of ISALCHEM C12 / C13 - 8 PO sulfate MIPA salt (0.4% in N C N N weight) and co-surfactant (0.1% by weight) for various crude oils at 25°C. Figure 4 shows the dynamic IFT in 4% TDS brine of ISALCHEM MIPA salt C12 / C13 - 8 PO sulfate (0.4% wt.) and co-surfactant (0.1% wt.) for various crude oils at 40°C. Figure 5 shows the dynamic IFT in 4% TDS brine of ISALCHEM MIPA salt C12 / C13 - 8 PO sulfate (0.4% wt.) and co-surfactant (0.1% wt.) for various crude oils at 60°C. Figure 6A shows the dynamic IFT of MIPA salt of ISALCHEM C12 / C13 - 8 PO sulfate and surfactant 1 in various surfactant concentration ratios in 4% TDS brine for H1 crude oil at 25°C. Figure 6B shows the dynamic IFT of MIPA salt of ISOFOL C16 - 8 PO sulfate and Surfactant 1 in various surfactant concentration ratios in 4% TDS brine for H1 crude oil at 25°C. Figure 7 shows the dynamic IFT in brine of 11.8% TDS of ISALCHEM MIPA salt C12 / C13 - 4 PO sulfate (0.25% by weight) and Surfactant 1 (0.25% by weight) for various crude oils at 25°C-40°C. Figure 8 shows the dynamic IFT in brine of 11.8% TDS of ISALCHEM MIPA salt C12 / C13 - 4 PO sulfate (0.25% by weight) and co-surfactant (0.25% by weight) for various > Π Ñ c NN C ü NNU crude oils at 40°C. DETAILED DESCRIPTION OF PREFERRED MODALITIES The surfactant formulations of the present invention provide stable aqueous solutions over a range of temperatures and salinities, and produce ultra-low interfacial tensions with a very wide variety of crude oils. The performance of these formulations can be improved by tailoring the hydrophobic structures, along with the number of PO and / or EO units of both the anionic and non-ionic structures, to the requirements of a specific well. Materials The surfactants used to prepare the surfactant formulations for the examples are mixtures of anionic and nonionic surfactants. The anionic surfactants specifically evaluated are, in particular, methyl isopropylamine (MIPA) and alkyl alkoxylated sodium (Na) sulfate salts, and include, but are not limited to, surfactant structures derived from alcohols with propoxy (PO) and / or ethoxy (EO) units, as described in Table 1. Table 1: Structures of anionic alkyl alkoxylated sulfate salts Name of alcohol Chain length of alcohol Structure of alcohol PO number EO number Ziegler CIO 100% linear 4-15 1 u NNU ISALCHEM C12 / C13 95% 2-alkyl branched 4-8 0 SAFOL23 C12 / C13 50% internally branched, 50% linear 7-13 3 ISOFOL C12-C16 10 0% 2-a 1qu i 1 or branched 8-15 0 The nonionic co-surfactants used are alkoxylated alcohols, particularly 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 alcohols of Linear C6 alcohols (e.g., ALFOL 6) and C20+ alcohols (e.g., ALFOL 20+), and branched alcohols such as 2-alkyl-1-alkanols (Guerbet alcohols, e.g., ISOFOL 12 and ISOFOL 20) and isotridecyl alcohols (e.g., MARLIPAL 10 013, a C13 oxo-alcohol). All examples represented by trade names are marketed by Sasol Performance Chemicals. Table 2: Structures of non-ionic ethoxylated alcohols Nonionic cosurfactant Alcohol name Alcohol chain length Alcohol structure EO number Surfactant 1 ALFOL20+ 020 + Long, linear alkyl chain 20, 50, 75, 100 > Π Ñ c NN C ü NNU Surfactant 2 ISOFOL 20 C20 2-alkyl branched, long chain 50 Surfactant 3 ISOFOL 24 024 2-alkyl branched, long chain 50 Surfactant 4 ALFOL20+ 020 + Long chain, linear 25 Surfactant 5 ITDA (isotridecanol) 013 Medium chain, branched 50 Surfactant 6 ISOFOL 12 012 2-alkyl branched, medium chain 50 Surfactant 7 ALFOL 6 06 Short chain, linear 50 Surfactant 8 ITDA (isotridecanol) C13 Medium chain, branched 30 Surfactant 9 ISOFOL 12 C12 2-alkyl branched, medium chain 29 Surfactant 10 ALFOL 6 06 Short chain, linear 15 Surfactant 11 ITDA (isotridecanol) C13 Medium chain, branched-chain 8 Surfactant 12 2-ethylhexanol 08 Short chain, branched-chain 50 EXPERIMENTAL SECTION The brines used in this study have the composition and total dissolved solids (TDS) as shown in Table 3. Brine A, Brine B, and Brine C have 5 total divalent concentrations of -4%, 11.8%, and 15%, respectively. > Π Ñ c NN C ü NNU Table 3. Composition of brines used (a) Brine A with 4% TDS Component Composition, g / L NaCl 30.39 KCl 1.51 CaCl2.2H2O 6.73 MgCl2.6H2O 1.39 TDS 4% (b) Brine B with 11.8% TDS Component Composition, g / L NaCl 106.03 Na2SO4 0.74 MgCl2-6H2O 1.23 CaCl2 10.767 TDS 11.8% (c) Brine C with 15% TDS Component Composition, g / L NaCl 113.96 KCl 5.65 MgCl2.6H2O 5.23 CaCl2.2H2O 25.25 TDS 15% The crude oils used in this study have the compositions and densities listed in Table 4. As used herein, the terms heavy crude and light crude are as follows: -Heavy crude is crude oil that has less than 30% by weight of hydrocarbons that have carbon chains of 5 less than C15 and an API gravity below 30°; and -Light crude is crude oil that has 30% or more by weight of hydrocarbons that have carbon chains shorter than C15, and an API gravity of 30° or above. Table 4 Composition and density of crude oils used (a) Heavy crude oils Crude oil Q. O <C15 g_ o Saturado o_ o Aromático o_ o Resina Q. O Asfalteño Densidad a 20°C, g / mL Gravedad API, °API H1 Crudo 13.90 50.27 26.52 22.67 0.53 0.8939 26.8 H2 Crudo 22.13 19.78 51.02 17.11 12.09 0.9745 13.7 H3 Crudo 24.10 40.69 36.48 15.43 7.40 0.8920 27.1 H4 Crudo 28.96 18.33 44.55 23.79 13.33 0.9700 14.4 (b) Light crude oils Crude oil oo <C15 O o Saturado O o Aromático O o Resina Asfalteño Densidad a 20°C, g / mL Gravedad API, °API L1 Crudo 55.46 60.13 32.29 7.35 0.22 0.8334 38.1 L2 Crudo 42.28 45.57 41.62 12.81 0.00 0.8549 34.0 Experimental Methods Preparing a sample > Π Ñ c NN C ü NNU 10% material solutions of each of the anionic sulfates and nonionic alcohol ethoxylates (AE's) in nanopure water were prepared prior to formulation. The formulations were subsequently prepared at the desired concentration of each surfactant from the material solutions in each of the brines listed in Table 3. The concentration of anionic sulfate in the preferred formulation ranged from 0.15 to 0.4 wt%. The concentration of nonionic ethoxylate in the formulation ranged from 0.1 to 0.35 wt. The concentration of total surfactant in the formulation was kept constant at 0.5 wt. Aqueous Stability Test The prepared formulations were placed in an oven at temperatures ranging from 25 to 70°C for a period of at least 3 months. The formulations were continuously inspected visually for any phase separation (PS), turbidity, and precipitation. Formulations that showed signs of phase separation, turbidity, or precipitation failed the aqueous stability test. Formulations that remained clear over time passed the aqueous stability test. Unless otherwise stated, for this entire application the performance of the aqueous stability tests followed the process set out above. Dynamic IFT measurement The formulations that passed the aqueous stability test were measured for dynamic interfacial tension (IFT) against each of the crude oils in Table 4 at different temperatures using the DataPhysics Interfacial Tensiometer. The capillary tube was filled with approximately 2 mL of the denser phase, which was the surfactant formulation. A 2–3 pL quantity of oil, the less dense phase, was injected into the capillary tube filled with the surfactant solution and formed a droplet. The capillary tube was then inserted into the instrument's rotation compartment. As the tube was rotated, the oil droplet began to stretch, and the IFT value was generated. The IFT gradually changed initially and became constant after 15 minutes in most cases. Once the IFT value remained constant, it was recorded. Unless otherwise stated, for this entire request the dynamic IFT measurement followed the process set out above. Results Formulations using only anionic surfactants, specifically the alkyl propoxy ethoxy sulfate salts described in this invention, prepared in the brines listed in Table 3, did not pass the aqueous stability test over the temperature range of 25 to 70°C. Therefore, a co-surfactant (non-ionic surfactant) was required. Π Ñ c NN C ü NNU to improve the aqueous stability of anionic sulfate surfactants. EXPERIMENT 1: Aqueous Stability Test (anionic and non-ionic surfactant formulations) The aqueous stabilities of formulations of an anionic surfactant, specifically a MIPA salt of C12 / C13 8 PO sulfate (0.4 wt%) and various non-ionic alcohol ethoxylates (AE) as co-surfactant (0.1 wt%) were determined over the temperature range of 25–60 °C in brine of 4% TDS. The results are shown in Table 5. Table 5. Aqueous stability of 0.4% by weight of ISALCHEM MIPA salt C12 / C13 - 8PO sulfate and 0.1% by weight of co-surfactant in 4% TDS brine (PS / turbid = the solution phase separates and becomes turbid upon mixing). Co-surfactant Alcohol Name Alcohol Chain Length Alcohol Structure # EO 25°C 40°C 60°C Surfactant 1 ALFOL20+ C20+ Heavy chain, linear 50 clear clear clear Surfactant 2 ISOFOL 20 C20 2-alkyl branched, long chain 50 clear clear clear Surfactant 3 ISOFOL 24 C24 2-alkyl branched, heavy chain 50 clear clear clear Surfactant 4 ALFOL20+ C20t Heavy chain, 1ineal 25 clear clear clear Surfactant 5 ITDA (isotridecanol) 013 Medium chain, branched 50 clear clear clear Surfactant 6 ISOFOL 12 C12 2-alkyl branched, medium chain 50 clear clear clear Surfactant 7 ALFOL 6 06 Short chain, 1ineal 50 clear clear PS / turbid Surfactant 8 ITDA (isotridecanol) 013 Medium chain, branched 30 clear clear PS / turbid Surfactant 9 ISOFOL 12 C12 2-alkyl branched, medium chain 29 clear clear PS / turbid Surfactant 10 ALFOL 6 06 Short chain, 1ineal 15 clear clear PS / turbid Surfactant 11 ITDA (isotridecanol) 013 Medium chain, branched 8 clear cloudy PS / murky See Table 5, the short (C6) containing 15 and Surfactant 10) as code for aqueous stability at 60°C. medium chain (C12 / C13) that As can be seen, formulations with 50 EO chain units (Surfactant 7 surfactant) did not pass the test. Formulations with > Π Ñ c NN Formulations containing 30 EO units and less (Surfactant 8, Surfactant 9, and Surfactant 10) also failed the aqueous stability test at 60 °C. Formulations using medium-chain essential oils containing 50 EO units and heavy-chain, long-chain essential oils containing 25 EO units and more passed the aqueous stability test over the entire temperature range. EXPERIMENT 2: Determination of dynamic Interfacial Tension (IFT) values ​​(various crude samples) The dynamic IFTs of the formulations using Surfactant 1 to Surfactant 6 (since they passed the aqueous stability test up to 70°C) were measured against various crude oils at different temperatures. Experiment 2.1: Dynamic IFT values ​​for formulations containing Surfactants 1-6 (0.1 wt%) along with the anionic surfactant, MIPA ISALCHEM C12 / 13-8PO sulfate salt (0.4 wt) were determined in heavy crude oil (Hl) over the temperature range of 25-60°C (4% TDS brine). The results are shown in Figure 1. Formulations using long-chain heavy co-surfactants with 25 and 50 EO units (Surfactant 1 to Surfactant 4) produce ultra-low IFT (< 0.01 mN / m) for heavy crude (Hl Crude) at all temperatures from 25 to 60°C. Formulations using medium-chain co-surfactants with 50 EO units (Surfactant 5 and Surfactant 6) were not able to produce ultra-low IFT for Crude H1, as shown in Fig. 1. Experiment 2.2: In addition, dynamic IFT values ​​for formulations containing Surfactants 1-6 (0.1 wt%) along with the anionic surfactant, MIPA ISALCHEM C12 / 13 8PO sulfate salt (0.4 wt) were determined in light crude oil (Ll) over the temperature range of 25-60°C (4% TDS brine). The results are shown in Figure 2. Only Surfactant 5 and Surfactant 6 (medium chain cosurfactants with 50 EO units) were able to produce ultra-low IFT for light crude (Ll Crude) over the entire temperature range as shown in Fig. 2. Experiment 2.3: To further validate the results obtained in Experiments 2.1 and 2.2, dynamic IFT values ​​for formulations containing Surfactants 1, 4, 5, and 6 (0.1 wt%) along with the anionic surfactant, MIPA ISALCHEM C12 / 13-8PO4 sulfate (0.4 wt%) were determined in various crude oils over the temperature range of 25 to 60°C (4% TDS brine). The results are shown in > Π Ñ c NN C ü NNU Figure 3-5. > Π Ñ c NN C ü NNO The IFT results in Figs. 3-5 further validate the findings that Surfactant 1 to Surfactant 4 were able to produce ultra-low IFT for heavy crude oils and Surfactant 5 and Surfactant 6 were able to produce ultra-low IFT for light crude oils over the temperature range of 25 to 60 °C. EXPERIMENT 3: Effect of anionic versus non-ionic surfactant mixing ratios on aqueous stability and IFT values In order to demonstrate the effect of various mixing ratios between anionic and non-ionic surfactants on aqueous stability and IFT values, two anionic surfactants, specifically MIPA salts of ISALCHEM C12 / 13-8PO sulfate and ISOFOL C16-8PO sulfate, along with non-ionic surfactant 1, were determined. Experiment 3.1: Aqueous stability test The aqueous stability of the formulation of both the anionic surfactant ISALCHEM C12 / 13-8PO sulfate (MIPA salt) and Surfactant 1 (various ratios) were determined in a 4% TDS brine solution at temperatures from 25 to 70°C. The results are shown in Table 6. Table 6. Aqueous stability of mixtures of anionic sulfate and non-ionic ethoxylated alcohol in various surfactant ratios in 4% TDS brine up to 70°C. (a) Anionic sulfate is the MIPA salt of ISALCHEM C12 / C13 23 8SO sulfate Anionic sulfate, % by weight Surfactant 1, % by weight 25°C 40°C 60°C 70°C 0.5 0 Cloudy cloudy PS / cloudy PS / cloudy 0.45 0.05 Clear clear PS / cloudy PS / cloudy 0.4 0 . 1 Clear clear Clear Clear 0.35 0.15 Clear clear Clear Clear 0.3 0.2 Clear clear Clear Clear 0.25 0.25 Clear clear Clear Clear 0.2 0.3 Clear clear Clear Clear 0.15 0.35 Clear clear Clear Clear 0.1 0 . 4 Clear clear Clear Clear (b) Anionic sulfate is the MIPA salt of ISOFOL C16 - 8P0 sulfate Anionic sulfate, % by weight Surfactant 1, % by weight 25°C 40°C 60°C 70°C 0.5 0 Cloudy cloudy PS / cloudy PS / cloudy 0.45 0.05 Clear clear PS / cloudy PS / cloudy 0.4 0 . 1 Clear clear Clear clear 0.35 0.15 Clear clear Clear clear 0.3 0.2 Clear clear Clear clear 0.25 0.25 Clear clear Clear clear 0.2 0 . 3 Clear clear Clear clear 0.15 0.35 Clear clear Clear clear 0.1 0 . 4 Clear clear Clear clear Without the co-surfactant, the anionic sulfate solution at a concentration of 0.5% by weight in 4% brine TDS was cloudy from 25°C up to 70°C. Anionic / nonionic surfactant mixtures were clear only when the concentration of the nonionic surfactant was 0.1% by weight or higher with a total surfactant concentration that is 0.5% by weight. Experiment 3.2: Determination of IFT values ​​for various surfactant ratios in heavy crude oil The dynamic IFT values ​​in heavy crude (H1 Crude) of the formulation of both the anionic surfactant ISALCHEM C12 / 13-8PO sulfate (MIPA salt) and Surfactant 1 (various ratios) were determined in a 4% TDS brine solution at 25°C. The results are shown in Figure 6. Figure 6 shows that the dynamic IFT for H1 Crude oil was affected by the anionic / nonionic ratio. For the ISALCHEM C12 / C13-8PO4 sulfate MIPA salt, the IFT was lowest at the anionic / nonionic ratio of 0.4 wt / 0.1 wt, while it was 0.35 wt / 0.15 wt for the ISOFOL C16-8PO4 sulfate MIPA salt. Experiment 3.3: IFT values ​​in a high % TDS brine solution in various crudes a) Dynamic IFT values ​​for a mixture of 0.25 wt% anionic surfactant (ISALCHEM C12 / C13-4PO4 sulfate, MIPA salt) / 0.25 wt% non-ionic surfactant > Π Ñ c NN C ü NNO (Surfactant 1) were determined in several crude oils at temperatures of 25 and 40°C, using an 11.8% brine solution of > Π Ñ c NN C ü NNU TDS. The results are shown in Figure 7. Fig. 7 demonstrates that the formulation of ISALCHEM MIPA salt C12 / 13-4PO (0.25 wt.) and Surfactant 1 (0.25 wt.) in 11.8% TDS brine for various crude oils at 25 and 40°C was able to produce ultra-low IFT values. b) Dynamic IFT values ​​for a mixture of 0.25 wt% anionic surfactant (ISALCHEM C12 / C13-4PO4 sulfate, MIPA salt) and several non-ionic surfactants (Surfactant 1, 5, and 6 - all 0.25 wt%) were determined with heavy crude oils (H1 and H2 Crude) at temperatures of 40°C, using an 11.8% TDS brine solution. The results are shown in Figure 8. Non-ionic surfactant 1 produced an ultra-low IFT value under the conditions described above. In addition to the detailed experiments described above, the invention was further exemplified over an extended range of experimental conditions for a variety of surfactant combinations / surfactant ratios in heavy and light crude oils. The results for several anionic surfactants combined with Surfactant 1 (specifically ALFOL C20+ 50EO) are summarized in Table 7.1 below (Exp. 4-9). Table 7.2 further illustrates variations of surfactant combinations and different conditions (Exp. 10-15). Aqueous stabilities and dynamic interfacial tensions were determined according to the general procedures described above. Table 7.1: Summary results for various anionic surfactants combined with Surfactant 1 (specifically ALFOL) C20+50EO), illustrated over an extended range of experimental conditions in heavy and light crude oil EXP ANIONIC SURFACTANT NON-IONIC SURFACTANT TDS <%) AQUEOUS STABILITY DYNAMIC INTERFACIAL TENSION Appearance Heavy Crude (Hl) Light Crude (Ll) Name % by weight Name % by weight 25°C 40°C 70°C 25°C 40°C 70°C 25°C 40°C 70°C 4 Ziegler C10-4PO- 1E0 sulfate, Na salt Surfactant 1: 50EO 11.8 0.43 0 . 10 clear clear 0.0015 0.0432 0.35 0 . 15 clear clear 0.0011 0.0364 5 ISOFOL C12-15PO sulfate, MIPA salt Surfactant 1: 53EO 4.0 0.25 0.25 clear clear 0.3000 0.0015 0.15 0.35 clear clear 0 . 0930 0.0100 6 SAFOL C121313PO-3EO sulfate, MIPA salt Surfactant 1:50EO 4 . 0 0.43 0 . 10 clear clear 0.0016 0.0127 0.25 0.25 clear clear 0 . 0550 0.0028 7 SAFOL C1213- 7PO-3EO sulfate, salt MIPA Surfactant 1: 50FO 11.8 clear clear 0.33 0.20 clear clear 0.0027 0.0136 0.25 0.25 clear clear 0.0037 - 0.23 0.30 0.0170 0.0048 > CNN C ü NNU 8 ISALCHEM C1213-4PO sulfate, salt Na Surfactant 1: 50EO 11.8 0.35 0 . 15 clear 0.0011 0.0364 0.25 0.25 clear 0.0089 0.0162 0.29 0.30 clear 0.0031 0.0196 0.15 0.35 clear 0.0153 0.0060 9 ISALCHEM C1213-4PO sulfate, salt Na Surfactant 1:50EO 15.0 0.23 0.30 clear clear 0.0052 0.0059 0.0441 0.0145 0.15 0.35 clear clear 0.0354 0.0135 0.0095 0.0095 Table 7.2: Summary results for various anionic surfactants combined with various non-ionic surfactants, illustrated over an extended range of experimental conditions in heavy and light crude oil. EXP ANIONIC SURFACTANT NON-IONIC SURFACTANT TDS (%) AQUEOUS STABILITY DYNAMIC INTERFACIAL TENSION Appearance Heavy Crude (Hl) Light Crude (Ll) Name % by weight Name % by weight 25°C 40°C 70°C 25°C 40°C 70°C 25°C 40°C 70°C 10 ISALCHEM C1213- 8P0 sulfate, salt Na Surfactant nt 12: 50EO 4.0 0.20 0.30 clear clear 0.031 0 . 0025 0.15 0.35 clear clear cloudy 0.0426 0 . 0030 11 ISALCHEM C1213- 4P0 sulphate, Surfactant nt 12: 50EO 11.8 0.35 0.15 clear 0.0352 0.0030 0.30 0.20 clear 0.0853 0.0190 sal Na 12 ISALCHEM C1213- 8 PO sulfate, salt MIPA Surfactant nt 1 : 75EO 4.0 0.30 0.20 clear clear clear 0.0123 0.0060 0.0110 0.0083 0.25 0.25 clear clear clear 0.0144 0.0049 0.0090 0.0017 0.15 0.35 clear clear clear 0.0700 0. 0132 13 ISALCHEM C1213-4PO sulfate, MIPA salt Surfactant nt 1: 75EO 11.8 0.25 0.25 clear 0.0022 0.0080 0.20 0.30 clear 0.0400 0.0070 0.15 0.35 clear clear 0.2378 0.0974 0.0175 0.0170 14 ISALCHEM C1213-4PO sulfate, MIPA salt Surfactant nt 1: 100EO 11.8 0.20 0.30 clear 0.0030 0.0074 0.15 0.35 clear clear clear 0.0285 0.0168 0.0268 0.0069 0.0065 0.0080 15 ISALCHEM C1213-8PO sulfate, MIPA salt Surfactant nt 1:20EO 4.0 0.35 0.15 clear 0.0010 0.25 0.25 clear clear clear 0.0118 0.0080 0.0270 0.0097 0.0142 0.0036 0.20 0.30 clear 0.0590 0.0020 Tables 7.1 and 7.2 illustrate the superior performance of the surfactant formulations of the invention specifically with respect to aqueous stability and ultra-low IFT values, obtained over a wide range of temperatures, salinities, and concentrations. References Puerto, M., Hirasaki, GJ, Miller, CA and collaborators 2012. > à Ñ c NNC ü Nu Surfactant Systems for EOR in High-Temperature, High-Salinity Environments. SPE Journal, 17 (1), 11-19. https: / / doi.org / 10.2118 / 129675-PA. Chou, SI, Bae, JH 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. , AISofi, A., Fuseni, A. y colaboradores 2013. Development of Chemical EOR Formula- tions for a High Temperature and High Salinity Carbonate Reservoir. Presented at the 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. Presented at the SPE Enhanced Oil Recov- ery Conference, Kuala Lumpur, Malaysia, 2-4 July. https: / / doi.org / 10.2118 / 165219- MS. Jabbar, M.Y., Sowaidi, A.A., Obeidli, A.A. y colaboradores 2017. Chemical Formulation Design in High Salinity, High Temperature Carbonate Reservoir for a Super Giant Offshore Field in Middle East. Presented at the Abu Dhabi International Petroleum Exhibition & Conference, Abu Dhabi, UAE, 13-16 November. https: / / doi.Org / 10.2118 / 188604- MS. > Π Ñ c N N C ü N N U

Claims

1. A surfactant formulation for use in chemically enhanced oil recovery, characterized in that the surfactant formulation comprises at least: i) an anionic salt of alkyl alkoxylate sulfate, wherein the alkyl alkoxylate sulfate has a molecular structure as shown in [I]: wherein R is a linear, branched or mixture of linear and branched alkyl group having 10 to 20 carbon atoms, n = 4 - 15, m = 0 - 10, M+ is an alkali metal ion, an alkanolamine ion, an alkylamine ion or an ammonium ion; and ii) a nonionic alcohol ethoxylate, wherein the alcohol ethoxylate has a molecular structure as shown in [II]: [11] wherein Ri is a linear, branched or mixture of linear and > Ϡ Ñ c NNC ü NNU branched alkyl group having 8 to 24 carbon atoms, y = 20 - 100.

2. The surfactant formulation according to claim 1, characterized in that R is a branched alkyl group.

3. The surfactant formulation according to claim 2, characterized in that R is a branched 2-alkyl group.

4. The surfactant formulation according to claims 1 to 3, characterized in that m = 0.

5. The surfactant formulation according to any of the preceding claims, characterized in that R has from 12 to 16 carbon atoms.

6. The surfactant formulation according to claims 1 to 4, characterized in that Ri = C12-C24, more preferably in that Ri = C2o+.

7. The surfactant formulation according to any of the preceding claims, characterized in that 40 < and < 100, more preferably 50 < and < 100.

8. The surfactant formulation according to any of the preceding claims, characterized in that the weight ratio of i) / ii) is from 6:1 to 1:6, more preferably from 4:1 to 1:4, much more preferably from 3:2 to 2:

3.

9. The surfactant formulation according to any of the preceding claims, characterized in that the combined concentration of i) and ii) does not exceed 0.5% by weight of the total formulation.

10. The surfactant formulation according to any of the preceding claims, characterized in that the surfactant formulation decreases the interfacial tension of crude oil to ultra-low values ​​of at or below 10⁻¹ mN / m, more preferably at or below 10⁻² mN / m.

11. The surfactant formulation according to any of the preceding claims, characterized in that the surfactant formulation is capable of reducing the interfacial tension values ​​of crude oil in brines with salinities of 4% to 15% total dissolved solids.

12. Use of a surfactant formulation in chemically enhanced oil recovery, characterized in that the surfactant formulation comprises at least: i) an anionic salt of an alkyl alkoxylated sulfate, wherein the alkyl alkoxylated sulfate has a molecular structure as shown in [I]: