Injection fluids containing anionic surfactants and alkoxylated alcohols and the use of such fluids in chemically enhanced oil recovery processes.

Abstract

A method for using a surfactant formulation in enhanced chemical oil recovery, wherein said surfactant formulation comprises at least the following:\ni) an anionic salt of an alkyl alkoxylated sulfate, wherein said alkyl alkoxylated sulfate has a molecular structure as shown in [I]:\n\n\n\na)\t[I]\n\nwherein R is a linear, branched, or a mixture of linear and branched alkyl groups having from 10 to 20 carbon atoms,\nn=4 to 15,\nm=0 to 10,\n+M is an alkali metal ion, an alkanolamine ion, an alkylamine ion or an ammonium ion; and\nii) a nonionic alcohol ethoxylate, wherein said alcohol ethoxylate has a molecular structure as shown in [II]:\n\n\n\n\n[II]\nwherein\nR1 is a linear, branched alkyl group or a mixture of linear and branched alkyl groups having from 8 to 24 carbon atoms,\ny=20 to 100.

Description

Injection fluids containing anionic surfactants and alkoxylated alcohols and the use of such fluids in chemically enhanced oil recovery processes. The present invention relates to surfactant formulations comprising anionic surfactants in combination with nonionic surfactants and the use of such formulations in chemically improved oil recovery processes. In particular, the surfactant formulation relates to a combination of anionic salts of alkyl alkoxylated sulfates and nonionic alcohol ethoxylates, for reducing the surface tension for a wide range of crude oils of varying composition and density during chemically improved oil recovery processes, over a wide range of temperatures and salinities. The invention further relates to a chemically improved oil recovery process by injecting mixtures of alkyl alkoxylated sulfate salts and alcohol ethoxylates. Background of the invention and discussion of prior art Various methods for recovering oil from subsurface surfaces have been developed over the past decades. The challenges experienced with chemically enhanced oil recovery (EOR) techniques applied in high temperature / high salinity reservoirs, typically using surfactant formulations, are often related to the aqueous instability of the solutions. Under high temperature and / or high salinity conditions, surfactant formulations tend to phase separate or precipitate, resulting in lower oil recovery. Cosurfactants and / or cosolvents can be used to overcome aqueous instability. However, the addition of surfactants and / or cosolvents can also compromise the ability of the primary surfactant to reduce the oil / water interfacial tension (IFT) to very low values ​​- an essential requirement for effective oil movement and, consequently, oil recovery. A number of previous studies have evaluated different surfactant systems for application in high temperature and / or high salinity reservoirs. Porto et al. (2012) evaluated combinations of a glycidyl sulfonate alkoxylate and an internal olefin sulfonate (IOS) at temperatures up to 120 °C and salinities up to 21% NaCl, in the absence of divalent cations (e.g. Ca2+, Mg2+, etc.) in water. The total surfactant concentration was unfortunately high at 2% wt and crude oil was not used to validate the results. Instead, interphase microemulsions with octane as a model oil were observed, with no reported IFT values. The surfactants evaluated (glycidyl sulfonates alkoxylate) were not available as commercial products and are more expensive 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 consisted of only table salt, without the presence of divalent cations. No crude oil was used, but instead alkane oils (C6 to C16) were evaluated. Other works (Han et al., 2013; Ghosh and Obassi, 2013; Jabbar et al., 2017) identified surfactant systems that have water stability with or without very low IFT values ​​reported at high temperature and / or salinity. However, these studies were conducted only on a specific crude oil or alkane oil. None of these studies evaluated and identified an aqueous stable surfactant system that produces very low IFT for a wide range of crude oils with different saturated, aromatic, resin, and asphaltene (SARA) compositions and densities over a wide range of salinities and temperatures. Prior art searches failed to identify a stable single-phase formulation that could produce very low IFT for a wide range of crude oils with different compositions and properties over a wide temperature and salinity range (see US 4,479,894; US 2009 / 0111717 A1; US ​​4,293,428; US 2011 / 0059873 A1; US ​​4,269,271; US ​​5,358,045; and US 4,077,471). Baker Hughes US 9,828,815 B2 describes foam fluids for high salinity conditions using a surfactant blend of anionic surfactants, sulfates or sulfonates, with nonionic surfactants as one type of cosurfactant. Even though this patent claims that such fluids are capable of producing IFTs of 10-1 to 10-3 mN / m for various applications including improved oil recovery, the patent does not provide any experimental or exemplary evidence for such claims. The IFT range is stated without any indication of the type or properties of the oil. The formulations used are not described for example and the experimental results are only applicable to gas lift operations. US2011 / 0083847A1 also describes mixtures of surfactants for the production of tertiary mineral oil, but very low surface tension values ​​are not achieved over a wide range of salinities. All prior art patents, patent publications, and non-patent texts listed in this application are incorporated herein by reference for all purposes. Purpose of the present invention The advantages of the inventive formulations described include their use at low total surfactant concentrations of 0.5 wt% and below in brine solutions, in salinities 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. These formulations produce very low IFT values ​​at and below 10-2mN / m, for a wide range of heavy and light crude oils with varying properties (SARA compositions and densities). Summary 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. These formulations can be effectively used for a wide range of crude oils with different compositions and densities and are stable at temperatures up to 70°C and salinity ranges up to 15% including divalent cations up to 1%. The present invention teaches the use of surfactant formulations in chemically improved oil recovery, wherein the formulation comprises: i) An anionic salt of an alkyl alkoxylated sulfate wherein the alkyl alkoxylated sulfate has a molecular structure shown in [I]: [I] in which R is a linear, branched or mixed linear and branched alkyl group having from 10 to 20 carbon atoms, preferably 12 to 16 carbon atoms, n=4 to 15, m=zero to 10, with m=zero being more preferred. M+ is an alkali metal ion, an alkanolamine ion, an alkylamine ion, or a Ammonium ion; and ii) A nonionic alcohol ethoxylate, wherein said alcohol ethoxylate has a molecular structure as shown in [II]: [II] in which R1 is a linear, branched alkyl group or a mixture of linear and branched alkyl groups having from 8 to 24 carbon atoms, preferably 12 to 24 carbon atoms, more preferably +20 carbon atoms, y=20 to 100, preferably 100 < y ≤ 40, more preferably 100 < y ≤ 50. In a preferred embodiment of the invention, R is a branched alkyl group, more preferably a branched 2-alkyl group. Furthermore, the invention is illustrated with a surfactant concentration in which the weight ratio (ii i) / is from 6:1 to 1:6, preferably from 4:1 to 1:4, more preferably from 3:2 to 2:3. The invention is also exemplified by surfactant formulations in which the combined concentration of i) and ii) does not exceed 0.5% by weight of the total formulation. In an additional embodiment of the invention, the surfactant formulation reduces the surface tension of the crude oil to very low values ​​or less than 1-10 mN / m, preferably less than 10-2 mN / m. Furthermore, the surfactant formulation is able to reduce the surface tension values ​​of crude oil in brine with salinities ranging from 4% to 15% total dissolved solids. Another embodiment of the present invention is a method for recovering chemically improved oil from a subterranean formation penetrated by at least one injection well and one production well, comprising: i) Injecting a surfactant formulation into an injection well such that said surfactant formulation contacts the crude oil contained in the subterranean formation to reduce the surface tension of said crude oil to very low values ​​of 10-10 mN / m2 or less, said surfactant formulation being capable of reducing surface tension values ​​at temperatures up to 70°C and at salinities up to 15% total dissolved solids including up to 1% divalent cations, said surfactant formulation comprising at least the following: a) An anionic salt of an alkyl alkoxylated sulfate wherein said alkyl alkoxylated sulfate has the molecular structure shown in [I]: b) [I] in which R is a linear, branched or mixed linear and branched alkyl group having from 10 to 20 carbon atoms, preferably 12 to 16 carbon atoms, n=4 to 15, m=zero to 10, M+ is an alkali metal ion, an alkanolamine ion, an alkylamine ion, or an ammonium ion; and b) a nonionic alcohol ethoxylate, wherein said alcohol ethoxylate has a molecular structure as shown in [II]: [II] in which R1 is a linear, branched alkyl group or a mixture of linear and branched alkyl groups having from 8 to 24 carbon atoms, preferably 12 to 24 carbon atoms, y=20 to 100, preferably 100 < y ≤ 40, more preferably 100 < y ≤ 50. ii) Recovery of oil from an underground formation from a producing well. These features and further advantages of the present invention will become apparent from the following detailed description. Brief description of the shapes Figure 1 shows the dynamic IFT in 4% TDS brine of ISALCHEM C12 / C13 - 8 PO sulfate MIPA salt formulation (0.4 wt%) and cosurfactant (0.1 wt%) with heavy crude oil (H1 crude) in the temperature range of 25 to 60°C. Figure 2 shows the dynamic IFT in 4% TDS brine of ISALCHEM C12 / C13 - 8 PO sulfate MIPA salt (0.4 wt%) and cosurfactant (0.1 wt%) with light crude oil (L1 crude) in the temperature range of 25 to 60°C. Figure 3 shows the dynamic IFT in 4% TDS brine of ISALCHEM C12 / C13 - 8 PO sulfate MIPA salt (0.4 wt%) and cosurfactant (0.1 wt%) for different crude oils at 25°C. Figure 4 shows the dynamic IFT in 4% TDS MIPA sulfate salt ISALCHEM C12 / C13 - 8 PO (0.4 wt%) and cosurfactant (0.1 wt%) for different crude oils at 40°C. Figure 5 shows the dynamic IFT in 4% TDS brine of ISALCHEM C12 / C13 - 8 PO sulfate MIPA salt (0.4 wt%) and cosurfactant (0.1 wt%) for different crude oils at 60°C. Figure A6 shows the IFT dynamics of ISALCHEM C12 / C13 -8 PO sulfate MIPA salt and surfactant 1 at different surfactant concentration ratios in 4% TDS brine for H1 crude oil at 25°C. Figure B6 shows the IFT dynamics of the MIPA sulfate salt ISOFOL C16 – 8PO and surfactant 1 at different surfactant concentration ratios in 4% TDS brine for H1 crude oil at 25°C. Figure 7 shows the dynamic IFT in 11.8% TDS brine containing ISALCHEM C12 / C13-4 PO sulfate MIPA salt (0.25 wt%) and surfactant 1 (0.25 wt%) for different crude oils at temperatures from 25°C to 40°C. Figure 8 shows the dynamic IFT in 11.8% TDS brine containing ISALCHEM C12 / C13-4 PO sulfate MIPA salt (0.25 wt%) and cosurfactant (0.25 wt%) for different crude oils at 40°C. Detailed Description of Preferred Embodiments The surfactant formulations of the present invention provide stable aqueous solutions over a wide range of temperatures and salinities and produce very low surface tensions with a wide range 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 anionic and nonionic structures, to the needs of a particular well. Materials The surfactants used to prepare the surfactant formulations for the samples are a mixture of anionic and nonionic surfactants. The anionic surfactants specifically evaluated are methyl isopropylamine (MIPA) and sodium (Na) salts of alkyl alkoxylated sulfates and include, but are not limited to, surfactant structures derived from alcohols containing propoxy (PO) and / or ethoxy (EO) units as described in Table 1. Table 1: Structures of anionic alkyl alkoxylated sulfate salts Alcohol Name Alcohol Chain Length Alcohol Structure PO Number 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 nonionic cosurfactants used are alkoxylated alcohols, particularly ethoxylated alcohols. Suitable alcohols that can be used for the synthesis of the alkoxylated alcohols described above include, but are not limited to, linear alcohols such as 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 O13, a C13 oxo alcohol). All examples shown by trade name are marketed by Sasol Performance Chemicals. Table 2: Structure of nonionic ethoxylated alcohols. Nonionic Co-Surfactants Alcohol Name 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- Branched Alkyl, Long Chain 50 Surfactant 3 ISOFOL 24 C24 2- Branched Alkyl, 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- Branched Alkyl, Medium Chain 50 Surfactant 7 ALFOL 6 C6 Linear, Short Chain 50 Surfactant 8 iTDA (Isotridecanol) C13 Branched, Medium Chain 30 Surfactant 9 ISOFOL 12 C12 2-alkyl branched, medium chain 29 Surfactant 10 ALFOL 6 C6 linear, short chain 15 Surfactant 11 iTDA (isotridecanol) C13 branched, short chain 8 Surfactant 12 2-ethylhexanol C8 branched, short chain 50 Experimental section The brines used in this study have the composition and total dissolved solids (TDS) shown in Table 3. Brine A, brine B, and brine C have total divalent concentrations of 4%, 11.8%, and 15%, respectively. Table 3: Composition of the brines used. (a) Brine A with 4% TDS Composition, grams per liter NaCl 30.39 KCl 1.51 CaCl 2 .2H 2 O 6.73 MgCl 2 .6H 2 O 1.39 TDS 4% (b) Brine B with 11.8% TDS Composition, grams per liter NaCl 106.03 Na2SO4 0.74 MgCl2.6H2O 1.23 CaCl2 10.767 TDS 11.8% (c) C brine with 15% TDS Composition, grams per liter NaCl 113.96 KCl 5.65 MgCl2.6H2O 5.23 CaCl2.2H2O 25.25 TDS 15% The crude oil used in this study has the compositions and densities listed 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 contains less than 30% by weight of hydrocarbons with a carbon chain length less than C15 and an API gravity of less than 30 degrees; and -Light crude oil is crude oil that contains 30% by weight or more of hydrocarbons with carbon chains shorter than C15 and an API gravity of 30 degrees or higher. Table 4 Composition and density of crude oils used. (a) Heavy crude oils Crude oil % <C15 درصد اشباع درصد آروماتیک درصد رزین درصد آسفالتین چگالی در 20 درجه سانتی‌گراد گرم بر لیتر گرانش API، درجه API Crude H1 13.90 50.27 26.52 22.67 0.53 0.8939 26.8 Crude H2 22.13 19.78 51.02 17.11 12.09 0.9745 13.7 Crude H3 24.10 40.69 36.48 15.43 7.40 0.8920 27.1 Crude H4 28.96 18.33 44.55 23.79 13.33 0.9700 14.4 (b) Light crude oils Crude oil % <C15 درصد اشباع درصد آروماتیک درصد رزین درصد آسفالتین چگالی در 20 درجه سانتی‌گراد گرم بر لیتر گرانش API، درجه API Crude L1 55.46 60.13 32.29 7.35 0.22 0.8334 38.1 Crude 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 before formulation. Formulations were subsequently prepared at the desired concentration of each surfactant from solutions in each of the brines listed in Table 3. The concentration of anionic sulfate in the formulation preferably ranges from 0.15 to 0.4 wt%. The concentration of nonionic ethoxylate in the formulation preferably ranges from 0.1 to 0.35 wt%. The total surfactant concentration in the formulation was kept constant at 0.5 wt%. Water stability test The prepared formulations were placed in an oven at 25–70°C for at least 3 months. The formulations were continuously visually inspected for any phase separation (PS), cloudiness, and precipitation. Formulations that showed signs of phase separation, cloudiness, or precipitation failed the aqueous stability test. Formulations that remained clear over time passed the aqueous stability test. Throughout this application, the performance of water stability tests followed the process outlined above unless otherwise specified. Dynamic IFT measurement Formulations that passed the water stability test were measured for dynamic IFT against each of the crude oils from Table 4 at different temperatures using a DataPhysics interfacial tensiometer. The capillary tube was filled with ~2 mL of the denser phase, which was the surfactant formulation. 2–3 μL of oil, which is the less dense phase, was injected into the capillary tube filled with the surfactant solution, forming a droplet. The capillary tube was then placed in the instrument’s rotating chamber. As the tube was rotated, the oil droplet began to stretch and the IFT value was generated. The IFT initially changed gradually and stabilized after 15 min in most cases. The IFT value was recorded after it stabilized. Throughout this application, dynamic IFT measurement follows the process outlined above unless otherwise specified. Results Formulations with only anionic surfactants, namely the alkyl propoxyethoxy sulfate salts described in this invention, prepared in the brines listed in Table 3, did not exhibit aqueous stability over the temperature range of 25 to 70°C; therefore, a surfactant (nonionic surfactant) was required to improve the aqueous stability of the anionic sulfate surfactants. Experiment 1: Water stability tests (formulation of anionic and nonionic surfactants) The aqueous stability of formulations of an anionic surfactant, namely MIPA salt of C12 / C13-8 PO sulfate (0.4 wt%) and various nonionic alcohol ethoxylates (AE) as cosurfactants (0.1 wt%) was determined in 4% TDS saline water over a temperature range of 25–60°C. The results are shown in Table 5. Table 5. Salt water stability of 0.4 wt% MIPA sulfate ISALCHEM C12 / C13 – 8PO and 0.1 wt% cosurfactant in 4% TDS brine (PS / Clody = the solution phase separates and becomes cloudy upon mixing). Cosurfactant Alcohol Name Alcohol Chain Length Alcohol Structure EO Number 25 oC 40 oC 60 oC Surfactant 1 ALFOL20+ C20+ Linear, Heavy Chain 50 Clear Clear Clear Surfactant 2 ISOFOL 20 C20 2- Branched Alkyl, Long Chain 50 Clear Clear Clear Surfactant 3 ISOFOL 24 C24 2- Branched Alkyl, Heavy Chain 50 Clear Clear Clear Surfactant 4 ALFOL20+ C20+ Linear, Heavy Chain 25 Clear Clear Clear Surfactant 5 iTDA (Isotridecanol) C13 Branched, Medium Chain 50 Clear Clear Clear Surfactant 6 ISOFOL 12 C12 2- Branched Alkyl, Medium Chain 50 Clear Clear Clear Surfactant 7 ALFOL 6 C6 Linear, Short Chain 50 Clear Clear PS / cloudy Surfactant 8 iTDA (Isotridecanol) C13 branched, medium chain 30 clear clear PS / cloudy Surfactant 9 ISOFOL 12 C12 2-alkyl branched, medium chain 29 clear clear PS / cloudy Surfactant 10 ALFOL 6 C6 linear, short chain 15 clear clear PS / cloudy Surfactant 11 iTDA (Isotridecanol) C13 branched, medium chain 8 clear clear PS / cloudy As can be seen in Table 5, formulations with short-chain AEs (C6) containing 15 and 50 EO units (Surfactant 7 and Surfactant 10) as cosurfactants failed the water stability test at 60°C. Formulations with medium-chain AEs (C12 / C13) containing 30 EO units and less (Surfactant 8, Surfactant 9 and Surfactant 10) also failed the water stability test at 60°C. Formulations using medium-chain AEs containing 50 EO units and long-chain AEs containing 25 EO units and higher passed the water stability test over the entire temperature range. Experiment 2: Determination of dynamic interfacial tension (IFT) values ​​(various crude oils) The dynamic IFTs of formulations using surfactant 1 to surfactant 6 (since they passed the water stability test up to 70°C) were measured against various crude oils at different temperatures. Experiment 2-1: Dynamic IFT values ​​were determined for formulations containing surfactants 1 to 6 (0.1 wt%) together with anionic surfactant ISALCHEM C12 / 13 - 8PO sulfate salt MIPA (0.4 wt%) in heavy crude oil (H1) in the temperature range of 25 to 60 °C (4% TDS brine). The results are shown in Figure 1. Formulations using long and heavy chain surfactants with 25 and 50 EO units (Surfactant 1 to Surfactant 4), very low IFT ( <mN / m 0.01) برای نفت خام سنگین (نفت خام H1) در تمام دماهای 25 تا 60 درجه سانتی‌گراد ایجاد می‌کند. همان‌طور که در شکل 1 مشاهده می‌شود، فرمولاسیون‌هایی با استفاده از کوسورفکتانت‌های زنجیره متوسط با 50 واحد EO (سورفکتانت 5 و سورفکتانت 6) قادر به تولید IFT بسیار کم برای نفت خام H1 نبودند. Experiment 2-2: In addition, dynamic IFT values ​​were determined for formulations containing surfactants 1 to 6 (0.1 wt%) along with anionic surfactant ISALCHEM C12 / 13 - 8PO sulfate salt MIPA (0.4 wt%) in light crude oil (L1) over a temperature range of 25 to 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 very low IFT for light crude oil (L1 crude oil) over the entire temperature range as seen in Figure 2. Experiment 2-3: In order to further validate the results obtained in Experiments 2-1 and 2-2, dynamic IFT values ​​were determined for formulations containing surfactants 1, 4, 5 and 6 (0.1 wt%) together with anionic surfactant ISALCHEM C12 / 13 - 8PO sulfate MIPA salt (0.4 wt%) in different crude oils in the temperature range of 25 to 60 °C (4% TDS brine). The results are shown in Figures 3 to 5. Also, the IFT results in Figures 3 to 5 confirm these findings that surfactants 1 to 4 were able to produce very low IFT for heavy crude oil and surfactants 5 and surfactant 6 were able to produce very low IFT for light crude oil in the temperature range of 25 to 60 °C. Experiment 3: Effect of anionic and nonionic surfactant mixing ratios on water stability and IFT values In order to demonstrate the effect of different mixing ratios between anionic and nonionic surfactants on the water stability and IFT values, two anionic surfactants, namely MIPA salts of ISALCHEM C12 / 13-8PO sulfate and ISOFOL C16-8PO sulfate, were determined together with nonionic surfactant 1. Experiment 3-1: Water Stability Tests The aqueous stability of both the ISALCHEM C12 / 13-8PO sulfate anionic surfactant formulations (MIPA salt) and surfactant 1 (various ratios) were determined in 4% TDS brine solution at temperatures ranging from 25 to 70°C. The results are shown in Table 6. Table 6. Aqueous stability of mixtures of anionic sulfate and nonionic ethoxylated alcohol at different surfactant ratios in 4% TDS brine up to 70°C. (a) Anionic sulfate is the MIPA salt of ISALCHEM sulfate C12 / C13 – 8PO. Anionic sulfate, wt% Surfactant 1, wt% 25 o C 40 o C 60 o C 70 o 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 sulfate C16 - 8PO. Anionic sulfate, wt% Surfactant 1, wt% 25 o C 40 o C 60 o C 70 o 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 cosurfactant, a solution of 0.5 wt% anionic sulfate in 4% TDS brine was cloudy at 25°C to 70°C. The anionic / nonionic surfactant combination was clear only when the nonionic surfactant concentration was 0.1 wt% or greater with a total surfactant concentration of 0.5 wt%. Experiment 3-2: Determination of IFT values ​​for different surfactant ratios in heavy crude oil Dynamic IFT values ​​in heavy crude oil (H1 crude oil) formulations of both ISALCHEM C12 / 13-8PO sulfate anionic surfactant (MIPA salt) and surfactant 1 (various ratios) were determined in 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 anion / nonionic ratio. For the MIPA salt of the ISALCHEM C12 / C13-8PO sulfate, the IFT was lowest at an anion / nonionic ratio of 0.4 wt% / 0.1 wt%, while for the MIPA salt of the ISOFOL C16-8PO sulfate it was 0.35 wt% / 0.15 wt%. Experiment 3-3: IFT values ​​in a high TDS brine solution in different crude oils a) Dynamic IFT values ​​were determined for a mixture of 0.25 wt% anionic surfactant (ISALCHEM C12 / C13-4PO sulfate, MIPA salt) / 0.25 wt% nonionic surfactant (Surfactant 1) with different crude oils at temperatures of 25 and 40 °C using 11.8% TDS brine solution. The results are shown in Figure 7. Figure 7 shows that the MIPA salt formulation of ISALCHEM C12 / 13-4PO (0.25 wt%) and surfactant 1 (0.25 wt%) in 11.8% TDS brine is capable of producing very low IFT values ​​for different crude oils at 25 and 40°C. b) Dynamic IFT values ​​were determined for a mixture of 0.25 wt% anionic surfactant (ISALCHEM C12 / C13-4PO sulfate, MIPA salt) and different nonionic surfactants (surfactants 1, 5 and 6 - all 0.25 wt%) with heavy crude oils (H1 and H2 crude oils) at 40°C, using a brine solution of 11.8% TDS. The results are shown in Figure 8. Nonionic surfactant 1 produced a very low IFT value under the conditions described above. In addition to the detailed tests described above, the invention was tested under a wide range of experimental conditions for a variety of surfactant compositions / 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 (Examples 4 to 9). Table 7-2 further shows the various surfactant compositions and conditions (Examples 10 to 15). The aqueous stabilities and dynamic surface tensions were determined according to the general methods previously described. Table 7-1: Summary results for various anionic surfactants combined with surfactant 1 (specifically ALFOL C20+50EO) shown under a wide range of experimental conditions in heavy and light crude oils. Test Anionic Surfactant Nonionic Surfactant TDS (%) Water Stability Interfacial Tension Dynamics Appearance Heavy Crude Oil (H1) Light Crude Oil (L1) Name Weight Percent Name Weight Percent 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 Clear Clear 0.0015 0.0432 0.35 0.15 Clear Clear 0.0011 0.0364 5 ISOFOL C12-15PO t Sulfate MIPA Salt Surfactant 1:50EO 4.0 0.25 0.25 Clear Clear 0.3000 0.0015 0.15 0.35 Clear Clear 0.0930 0.0100 6 SAFOL C1213-13PO-3EO Sulfate Na Salt Surfactant 1:50EO 4.0 0.40 0.10 Clear Clear 0.0016 0.0127 0.25 0.25 Clear Clear 0.0550 0.0028 7 SAFOL C1213-7PO-3EO Sulfate MIPA Salt Surfactant 1:50EO 11.8 Clear Clear 0.30 0.20 Clear Clear 0.0027 0.0136 0.25 0.25 Clear Clear 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 Clear 0.0011 0.0364 0.25 0.25 Clear 0.0089 0.0162 0.20 0.30 Clear 0.0031 0.0196 0.15 0.35 Clear 0.0153 0.0060 9 ISALCHEM C1213-4PO Sulfate Na Salt Surfactant 1:50EO 15.0 0.20 0.30 Clear Clear 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 results for various anionic surfactants combined with nonionic surfactants demonstrated over a wide range of experimental conditions in heavy and light crude oils. Test Anionic Surfactant Nonionic Surfactant TDS (%) Water Stability Dynamic Interfacial Tension Appearance Heavy Crude Oil (H1) Appearance Name Weight Percent Name Weight Percent 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 Clear Clear 0.031 0.0025 0.15 0.35 Clear Clear Opaque 0.0426 0.0030 11 ISALCHEM C1213-4PO Sulfate Na Salt Surfactant 12: 50EO 11.8 0.35 0.15 Clear 0.0352 0.0030 0.30 0.20 Clear 0.0853 0.0190 12 ISALCHEM C1213-8PO Sulfate MIPA Salt Surfactant 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 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 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 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 demonstrate the superior performance of the inventive surfactant formulations, particularly with respect to aqueous stability and very low IFT values ​​obtained over a wide range of temperatures, salinities, and concentrations. References Puerto, M., Hirasaki, GJ, Miller, CA 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, 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., AlSofi, A., Fuseni, A. et al. 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 Tempera- ture, 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. et al. 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.

Claims

1. A surfactant formulation for use in chemically enhanced oil recovery, wherein said surfactant formulation comprises at least the following: i) an anionic salt of an alkoxylated alkyl sulfate, wherein said alkoxylated alkyl sulfate has the molecular structure as follows: (I): (I) wherein, R is a linear, branched, or a combination 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 said alcohol ethoxylate has a molecular structure as set forth in (II) (II) wherein R1 is a linear, branched, or a combination of linear and branched alkyl group having 8 to 24 carbon atoms, 40 < y ≤ 100 and the weight ratio of i) / ii) is between 6:1 and 1:

6.

2. The surfactant formulation of claim 1 wherein R is a branched alkyl group.

3. The surfactant formulation of claim 2 wherein R is a branched 2-alkyl group.

4. The surfactant formulation of claims 1 to 3 wherein m = 0.

5. The surfactant formulation of any of the above claims wherein R has 12 to 16 carbon atoms.

6. The surfactant formulation of claims 1 to 4 wherein R1 = C12 - C24 and more preferably wherein R1 = C20+.

7. The surfactant formulation of any of the above claims wherein 50 ≤ y ≤ 100 8. The surfactant formulation of any of the above claims wherein the weight ratio of i) / ii) is from 4:1 to 1:4, more preferably from 3:2 to 2:

3.

9. The surfactant formulation of any of the above claims wherein the combined concentration of i) and ii) does not exceed 0.5% by weight of the total formulation.

10. The surfactant formulation of any of the above claims, wherein said surfactant formulation reduces the interfacial tension of crude oil to ultra-low indices equal to or less than 10-1 mN / m, more preferably at or less than 10-2 mN / m.

11. The surfactant formulation of any of the above claims, wherein said surfactant formulation is capable of reducing the interfacial tension indices of crude oil in brine with a salinity between 4% and 15% total dissolved solids.

12. Use of a surfactant formulation in chemically enhanced oil recovery, wherein said surfactant formulation comprises at least the following: i) an anionic salt of an alkoxylated alkyl sulfate, wherein said alkoxylated alkyl sulfate has the molecular structure as follows: (I): (I) wherein, R is a linear, branched, or a combination 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 said alcohol ethoxylate has a molecular structure as set forth in (II) (II) wherein R1 is a linear, branched, or a combination of linear and branched alkyl group having 8 to 24 carbon atoms, 40 < y ≤ 100 and the weight ratio of i) / ii) is between 6:1 and 1:

6.

13. The use of claim 12 wherein R is a branched alkyl group.

14. The use of claim 13 wherein R is a 2-branched alkyl group.

15. The operation of claim 12 wherein at m = 0.

16. The method of claim 12 wherein R has 12 to 16 carbon atoms.

17. The use of claim 12 wherein R1 = C12 - C24 and more preferably wherein R1 = C20+.

18. The operation of claim 12 where 50 ≤ y ≤ 100 19. The use of claim 12 wherein the weight ratio of i) / ii) is from 4:1 to 1:4, more preferably from 3:2 to 2:

3.

20. The use of claim 12 wherein the combined concentration of i) and ii) is not more than 0.5% by weight of the total formulation.

21. The use of claim 12 wherein said surfactant formulation reduces the interfacial tension of the crude oil to ultra-low indices equal to or less than 10-1 mN / m, more preferably at or less than 10-2 mN / m.

22. The use of claim 12, wherein said surfactant formulation is capable of reducing the interfacial tension indices of crude oil in brine with a salinity between 4% and 15% total dissolved solids.

23. A method for recovering chemically enhanced oil from a subterranean formation penetrated by at least one injection well and one production well, comprising: i) injecting a surfactant formulation into the injection well in such a manner that the surfactant formulation is contacted with crude oil contained in the subterranean formation to reduce the interfacial tension of the crude oil to ultralow indices equal to or less than 10-2 mN / m, said surfactant formulation being capable of reducing interfacial tension indices at temperatures between 25 and 70 degrees Celsius and in brine with 4% to 15% total dissolved solids, at least a portion of which dissolved solids are divalent cations, said surfactant formulation comprising at least: a) an anionic salt of an alkoxylated alkyl sulfate, wherein said alkoxylated alkyl sulfate has the molecular structure as set forth in (I): (I) wherein a) R is a linear, branched, or a combination of linear and branched alkyl groups of 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 b) an alcoholA nonionic ethoxylate wherein said alcohol ethoxylate has a molecular structure as set forth in (II) (II) wherein R1 is a linear, branched, or a combination of linear and branched alkyl group having 8 to 24 carbon atoms, 40 < y ≤ 100 and the weight ratio of i) / ii) is between 6:1 and 1:6, recovering oil from a subterranean formation from a producing well.

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