WO2018095881A1

WO2018095881A1 - Process for oil recovery

Info

Publication number: WO2018095881A1
Application number: PCT/EP2017/079843
Authority: WO
Inventors: Mark Lawrence Brewer
Original assignee: Shell Internationale Research Maatschappij B.V.; Shell Oil Company
Priority date: 2016-11-24
Filing date: 2017-11-21
Publication date: 2018-05-31

Abstract

Process for recovering oil from a formation containing oil and water by injecting into the formation an enhanced oil recovery formulation comprising enhanced oil recovery surfactant, which process comprises (i) injecting into the formation the enhanced oil recovery formulation, (ii) producing from the formation a mixture comprising water, enhanced oil recovery surfactant and oil, and (iii) contacting the produced mixture with additional surfactant and separating oil, wherein the additional surfactant is more hydrophilic than the enhanced oil recovery surfactant.

Description

PROCESS FOR OIL RECOVERY

FIELD OF THE INVENTION

The present disclosure relates to a process for

recovering oil from a formation comprising oil and water by injecting an enhanced oil recovery formulation into the formation.

BACKGROUND OF THE INVENTION

In natural mineral oil deposits, mineral oil is present in the cavities of porous formation rocks which tend to be sealed toward the surface of the earth by impermeable top layers. The cavities may be very fine cavities, capillaries, pores or the like.

In mineral oil production, a distinction is drawn between primary and subsequent production such as secondary and/or tertiary production.

In primary production, after commencement of drilling of the deposit, the mineral oil flows of its own accord through the borehole to the surface owing to the

autogeneous pressure of the deposit. The autogeneous pressure can be caused, for example, by gases present in the deposit, such as methane, ethane or propane. The autogeneous pressure of the deposit, however, generally declines relatively rapidly on extraction of mineral oil, such that usually only a limited amount of the mineral oil present in the deposit can be produced in this way. Primary production is no longer feasible if natural reservoir drive diminishes. In these instances, secondary recovery methods can be applied. Secondary methods typically rely on the supply of external energy into the reservoir in the form of injecting fluids to increase or maintain reservoir

pressure, hence replacing or increasing the natural reservoir drive with an artificial drive. Reservoir

pressure may be increased through the injection of water or gas such as carbon dioxide or steam. The injected fluid is typically immiscible, or predominantly immiscible with the in-situ hydrocarbon fluids.

After primary and/or secondary production, enhanced oil recovery can be applied typically involving injection of an enhanced oil recovery formulation into an injection well. Due to the presence of water in many formations such as aquifers, enhanced oil recovery tends to produce water besides oil. If an enhanced oil recovery formulation contains enhanced oil recovery surfactant, it has been observed that it is less easy to separate oil from the produced mixture comprising oil, water and surfactant.

The SPE paper 24117-PA by A.H. Falls, D.R. Thigpen, R.C. Nelson et al . "Field test of co-surfactant enhanced alkaline flooding", SPE Reserv. Eng. 1994; 9(3):217 describes a test of cosurfactant enhanced alkaline flooding and the type of produced fluids that can be expected from this type of operation.

US2015252248 describes a method for demulsifying emulsion with the help of substantially fully quaternized ammonium adduct of polyepihalohydrin . EP2781582 describes a process for demulsifying an emulsion which comprises oil and water with the help of a composition comprising a nitrogen of phosphorus containing cation more specifically a salt containing di (dodecyl ) dimethyl ammonium cation or di (tetradecyl) dimethyl ammonium cation . It is thought that the use of such structurally different compounds can increase the risk of sludge formation .

WO2015138429 describes oil recovery by injecting an enhanced oil recovery formulation comprising an "under^™ optimum" salinity alkaline-surfactant or alkaline- surfactant-polymer .

SUMMARY OF THE INVENTION

We now have found a process which allowed to reduce the amount of oil in the aqueous phase of a mixture

produced by enhanced oil recovery from a formation. Such process could facilitate separating oil from the mixture produced in surfactant enhanced oil recovery.

The present invention relates to a process for

recovering oil from a formation containing oil and water by injecting into the formation an enhanced oil recovery formulation comprising enhanced oil recovery surfactant, which process comprises (i) injecting into the formation the enhanced oil recovery formulation, (ii) producing from the formation a mixture comprising water, enhanced oil recovery surfactant and oil, and (iii) contacting the produced mixture with additional surfactant and separating oil, wherein the additional surfactant is more hydrophilic than the enhanced oil recovery surfactant.

The present invention further relates to a process for recovering oil from a formation containing oil and water by injecting into the formation an enhanced oil recovery formulation comprising alkali and polymer, which process comprises (i) injecting into the formation the enhanced oil recovery formulation, (ii) producing from the formation a mixture comprising water, oil and saponified hydrocarbons, and (iii) contacting the produced mixture with additional surfactant and separating oil, wherein the additional surfactant is more hydrophilic than the saponified

hydrocarbons of the produced mixture. The saponified hydrocarbons present in the produced mixture is formed by saponification by the alkali of hydrocarbons in the formation. The hydrophilicity of the saponified hydrocarbons is the mass average hydrophilicity of the saponified hydrcarbons in the produced mixture.

DETAILED DESCRIPTION OF THE INVENTION

Surfactant is any compound which stabilises mixtures of oil and water by reducing the interfacial tension at the interface between oil and water molecules. A surfactant generally comprises a hydrophilic part and a hydrophobic part .

Formulas in this specification represent a single molecule or class of molecules. If different molecules are present, the weight average numbers are to be used.

Within the present specification, a compound may be characterised by its carbon number and/or molecular weight. In case reference is made to an average carbon number and/or average molecular weight, this means weight average. The average carbon number may be determined by NMR

analysis .

Surfactant for use in the enhanced oil recovery formulation can be any surfactant known to be suitable by somebody skilled in the art. The enhanced oil recovery surfactant can be cationic, nonionic or anionic. Generally, the surfactant will be a nonionic surfactant or an anionic surfactant or a mixture of these. Examples of nonionic surfactants are alcohol ethoxylates such as NEODOL 91-8 and NEODOL 2512. NEODOL is a trademark of the Shell group of companies. Preferably, the anionic surfactant is chosen from the group consisting of hydrocarbon sulphates and hydrocarbon sulphonates wherein the hydrocarbon consists of hydrogen, carbon and optionally oxygen. Examples of

hydrocarbon sulphates and hydrocarbon sulphonates are alkyl sulphates, alkyl benzene sulfonates, internal olefin sulfonates, alpha olefin sulfonates, alkyl propoxy

sulfates, alkyl ethoxy sulfates, alkyl propoxy/ethoxy sulfates, alkyl propoxy carboxylates , alkyl ethoxy

carboxylates , alkyl propoxy/ethoxy carboxylates and alkyl alkoxy glycidyl sulfonates.

The enhanced oil recovery surfactant preferably comprises anionic surfactant and more preferably is an anionic surfactant, more specifically a compound containing a negatively charged portion and one or more counter cations which negatively charged portion comprises (i) a hydrophilic part which comprises a negatively charged group and (ii) a hydrophobic part. The surfactant preferably is selected from the group consisting of an alpha olefin sulfonate compound, an internal olefin sulfonate compound, a secondary alkyl sulfonate compound, a branched alkyl benzene sulfonate compound, a propylene oxide sulfate compound, an ethylene oxide sulfate compound, a propylene oxide-ethylene oxide sulfate compound, or a blend thereof. The enhanced oil recovery surfactant preferably contains of from 10 to 30 carbon atoms.

A preferred class of anionic surfactants are the surfactants of the following formula (I) [RV- [R' -0] _X-A^m~] [Mⁿ⁺]₀ wherein R is hydrogen or an organic group, V is a heteroatom, preferably 0 or N (wherein N can be NH) , R' -0 is an alkylene oxide group originating from alkylene oxide, x is 0 or more, A is a negatively charged group which may consist of one or more negatively charged components with the negative charge of all components together being m, M is a counter cation and the product of n and o (n*o) equals m. Preferably, x is of from 0 to 100, more specifically of from 0 to 30, more specifically of from 0 to 20, more specifically of from 0 to 14, more specifically of from 0 to 8. R can have a total number of from 5 to 100 and can be based on a Guerbet alcohol more specifically a 2-alkyl-l- alkanol having a total number of carbon atoms of from 10 to 50 or on tristyrylphenol . In the above exemplary formula

(I), m and n are integers which may be 1, 2 or 3. For a variety of compounds for which a weight average is to be used, m and n can be of from 1 to 3. Further, o may be any number which ensures that the anionic surfactant is

electrically neutral. That is to say, the product of n and o (n*o) should equal m. o may be a number in the range of from 0.25 to 3, preferably 0.5 to 3.

The alkylene oxide groups in above exemplary formula

(I) may comprise any alkylene oxide groups. For example, said alkylene oxide groups may comprise ethylene oxide groups, propylene oxide groups and butylene oxide groups or a mixture thereof, such as a mixture of ethylene oxide and propylene oxide groups. In case of a mixture of ethylene oxide and propylene oxide groups, the mixture may be random or blockwise.

The negatively charged group, denoted as A^m~ in above exemplary formula (I), may be any negatively charged group. Said negatively charged group is preferably a -SC>3^~ moiety

(either sulfate or sulfonate) . Further, said negatively charged group may be a group comprising the -C(=0)0^~ moiety

(carboxylate) .

The anionic surfactant in the surfactant composition of the present invention may be any one of the anionic surfactants, or a mixture of such surfactants, that are known to effect recovery of hydrocarbons from hydrocarbon containing formations. Preferably, the anionic surfactant in the composition of the present invention is selected from the group

consisting of:

a) alkyl aryl sulfonates,

b) alkyl carboxylates ;

c) alkyl alkoxy carboxylates;

d) alkyl alkoxy sulphates;

e) alkyl sulphates;

f) internal and alpha olefin sulfonates;

g) alkyl alkoxy glyceryl ether sulfonates; and

h) any mixture of the foregoing anionic surfactants.

More preferably, the anionic surfactant in the

composition of the present invention is selected from the group consisting of a surfactant as mentioned under a) above, a surfactant as mentioned under b) above, a

surfactant as mentioned under c) above or any mixture of said surfactants.

Surfactants as mentioned under a) can have attached a linear or branched alkyl group, preferably a predominantly linear alkyl group, for example C10-C30 preferably C15-C18 alkyl group, either via its terminal carbon atom or an internal carbon atom, to a benzene molecule which benzene molecule is also substituted with a sulfonate group on another position, preferably at the para position, and which benzene molecule may be further substituted at the remaining positions, for example with alkyl groups, such as a methyl group or ethyl group to form toluene or xylene or a derivative thereof. Examples of suitable alkyl aryl sulfonates that can be used as anionic surfactant in the present invention are disclosed in US20090163669.

US20090163669 describes tri-alkyl substituted benzene sulfonates, such as the sulfonates of the alkylation product of ortho-xylene with a mixture of Ci2^~C3o⁺ linear alpha-olefins . Examples of suitable alkyl aryl sulfonates that can also be used as anionic surfactant in the present invention are disclosed in WO0042140. Examples of a suitable alkylaryl sulfonate or sulphonic acids are sodium dodecyl benzene sulfonate, dodecyl benzene sulfonic acid, XOF-20S, XOF-23S, XOF-25S, XOF-26S, XOF-30S, XOF-20A, XOF- 23A, XOF-25A, XOF-26A, XOF-30A, as commercially available from Huntsman Chemicals, Aristonate L, Aristonate M,

Aristonate H, Aristonate VH2, Calsoft LAS-99, Pilot EM-99, as commercially available from Pilot Chemical and ENORDET LTS-18 alkyltoluene sulfonate surfactant as commercially available from Shell Chemicals.

The alkyl-carboxylates mentioned under b) , have the general formula R[C00H]b. R is a hydrocarbon chain

predominantly containing C and H but can also contain heteroatoms. R can be acyclic, linear, branched, cyclic or aromatic. R contains from 8 to 100 carbon atoms and b can be 1, 2 or 3. Preferably, the number of carbon atoms is at most 75, more specifically at most 50, more specifically at most 35, more specifically at most 25, more specifically at most 14. The alkyl-carboxylates can be from natural or petrochemical feedstock.

These anionic surfactants of b) can be directly derived from fatty acids. The alkyl carboxylates may be any fatty acid or mixture of fatty acids. Its fatty acid component (s) are preferably derived from a biological source, more preferably a vegetable source. They may be saturated or unsaturated; if the latter, they may have one or more, preferably up to 6, double bonds. They may be linear or branched, cyclic or polycyclic. Suitably they will have from 6 to 30, preferably 10 to 30, more suitably from 10 to 22 or from 10 to 18 carbon atoms including the acid group (s) —CO2H. A fatty acid will typically comprise a mixture of different fatty acids of different chain

lengths, depending on its source.

Fatty acid which can be used as alkyl-carboxylates mentioned under b) is preferably derived from tall oil, vegetable fatty acids and/or animal fatty acids.

In a preferred embodiment, the fatty acid composition contains fatty acids derived from plant sources such as tall oil and/or vegetable oils. A preferred composition contains less than 5%, preferably less than 3% saturated fatty acids calculated on the total weight of said fatty acids and more than 90%, preferably more than 95%, more preferably more than 98% unsaturated fatty acids calculated on the total weight of said fatty acids.

In another preferred embodiment, the fatty acid composition contains rosin acids derived from plant sources such as tall oil. A preferred composition contains more than 2 %wt, preferably more than 5 %wt, preferably more than 10 %wt, more preferably more than 20 %wt, more

preferably more than 30 %wt rosin acids calculated on the total weight of fatty acid. Rosin acids are monocarboxylic diterpene acids, the most common of which has the molecular formula C20H30O2. The rosin-based acids can be selected from abietic acid, dihydroabietic acid, dehydroabietic acid, neoabietic acid, pimaric acid, levopimaric acid, palustric acid, isopimaric and other derivatives based on the

diterpene structure which can be present as mixtures. The rosin acids can be obtained from tall oil or gum rosin.

The surfactants mentioned under c) may be derived from a fatty acid by converting the carboxylate group of the original fatty acid to an alcohol and subsequent alkoxylation and carboxylat ion to obtain the alkyl

alkoxylated carboxylate.

The anionic surfactant mentioned under f) above can be an internal olefin sulfonate. The average carbon number for the such internal olefin sulfonate may vary within wide ranges, such as from 5 to 40, suitably 10 to 35, more suitably 15 to 32. Internal olefin sulfonates can be made from an internal olefin molecule whose double bond is located anywhere along the carbon chain except at a

terminal carbon atom. Internal olefin molecules may be made by double bond isomerisat ion of alpha-olefin molecules whose double bond is located at a terminal position.

Generally, such isomerisat ion results in a mixture of internal olefin molecules whose double bonds are located at different internal positions. The mixture that results from such preparation may also comprise a minor amount of alpha- olefins, for example up to 5%, suitably up to 3%. Internal olefins can be converted into the corresponding anionic surfactants in any way known to be suitable by the person skilled in the art.

Internal olefin sulfonates may have a weight ratio of branched internal olefin sulfonates molecules to linear internal olefin sulfonates molecules which is greater than 0 to smaller than 11:89. Branched internal olefin

sulfonates molecules are internal olefin sulfonates molecules derived from internal olefin molecules which comprise one or more branches. Linear internal olefin sulfonates molecules are internal olefin sulfonates molecules derived from internal olefin molecules which are linear, that is to say which comprise no branches

(unbranched internal olefin molecules) . Said weight ratio of branched internal olefin sulfonates molecules to linear internal olefin sulfonates molecules may be determined by gas chromatography (GC) . Further, said determination may be performed on the internal olefin sulfonates precursor, that is to say on the olefin mixture before it is sulfonated. Preferably, said weight ratio of branched internal olefin sulfonates molecules to linear internal olefin sulfonates molecules is greater than 0 to smaller than 10:90, more preferably of from 0.1:99.9 to 9:91, even more preferably of from 1:99 to 8:92, and most preferably of from 2:98 to 7:93.

Branches in the above-mentioned branched internal olefin sulfonates molecules may include methyl, ethyl and/or higher molecular weight branches including propyl branches. Methyl branches may represent from 5 to 50%, more suitably from 10 to 40%, most suitably from 15 to 30%, of the total number of branches. Ethyl branches may represent from 10 to 60%, more suitably from 20 to 50%, most suitably from 25 to 40%, of the total number of branches. Other (higher molecular weight) branches other than methyl or ethyl may represent from 15 to 70%, more suitably from 30 to 60%, most suitably from 35 to 50%, of the total number of branches. Said percentages may be determined by 13C-NMR analysis. Further, said determination is preferably

performed on the internal olefin sulfonates precursor, that is to say on the olefin mixture before it is sulfonated.

The average carbon number for the internal olefin sulfonates may vary within wide ranges, such as from 5 to 40, suitably 10 to 35, more suitably 15 to 30, most

suitably 18 to 24. Further, the average molecular weight for the internal olefin sulfonates is neither essential and may also vary within wide ranges, such as from 100 to 500, suitably 150 to 450, more suitably 200 to 400 g/mole, most suitably 250 to 350 g/mole.

The anionic surfactant can be any combination of surfactants containing at least one of the foregoing anionic surfactants or mixture of anionic surfactants. The anionic surfactant can be a mixture of two or more of the foregoing anionic surfactants.

The enhanced oil recovery formulation can further contain alkali. Alkali may not only aid the enhanced oil recovery surfactant but may also interact with oil in the formation to form soap effective in reducing the

interfacial tension between oil and water in the formation. The alkali preferably is selected from the group consisting of ammonia, lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, lithium bicarbonate, sodium bicarbonate,

potassium bicarbonate, lithium silicate, sodium silicate, potassium silicate, lithium phosphate, sodium phosphate, potassium phosphate, and mixtures thereof. In some

instances, the alkali preferably is ammonia. In some instances, the alkali preferably is sodium carbonate.

The enhanced oil recovery formulation generally will contain water. In addition, the formation will contain water besides oil. The water present in the formation can be formation water or connate water or any other water such as an aquifer or previously injected water.

The amount of soap which can be formed by contacting the alkali and the oil depends on the amount of acids or acid precursors which are present in the oil. This is often referred to as the Total Acid Number (TAN) of a crude oil. The TAN can be determined by ASTM test method D664.

It is possible that the enhanced oil recovery

formulation does not contain alkali. If the enhanced oil recovery formulation comprises alkali, the amount of alkali present in the enhanced oil recovery formulation preferably is at least 0.001 %wt, more specifically at least 0.005 %wt, more specifically at least 0.01 %wt . If the oil in the formation contains a relatively large amount of compounds which can be converted into soap, such as oil having a high TAN, the enhanced oil recovery formulation can contain at least 0.5 %wt of alkali. The amount of alkali generally will be at most 5 %wt of the alkali, more specifically at most 4 %wt, more specifically at most 2 %wt, most

specifically at most 1 %wt of alkali. All these amounts are amount of alkali based on total amount of enhanced oil recovery formulation.

Generally, the enhanced oil recovery formulation will comprise water. The water used in the preparation of the formulation generally will have total dissolved solids (TDS) content of from 2 0 0 0 to 2 0 0,000 ppm as measured by ASTM D5907-13. More specifically, the water tends to have a TDS of at most 50,000 ppm, more specifically at most 35,000 ppm, more specifically at most 30,000 ppm, more

specifically at most 2 0,000 ppm, more specifically at most 15,000 ppm, most specifically at most 10,000 ppm.

It is especially advantageous if the water used for preparing the formulation contains a limited amount of divalent ions such as less than 4000 ppm, more specifically less than 2 0 0 0 ppm, more specifically less than 1000 ppm, more specifically at most 500 ppm, more specifically at most 100 ppm, most specifically at most 2 0 ppm of divalent ions based on total amount of water. More specifically, these amounts relate to the calcium and/or magnesium containing salts. Furthermore, the enhanced oil recovery formulation may additionally comprise one or more compounds selected from the group consisting of polymer, paraffin inhibitors, scale inhibitors and co-solvents.

The polymer can be a single compound or can be a mixture of compounds. Preferably, the polymer is selected from the group consisting of polyacrylamide; partially hydrolyzed polyacrylamide; polyacrylate; ethylenic

copolymer; carboxymethylcelloluse; polyvinyl alcohol;

polystyrene sulfonate; polyvinylpyrrolidone; biopolymers; copolymer of acrylamide and 2-acrylamido-2- methylpropanesulfonic acid (ATBS) ; terpolymer of ATBS, acrylic acid and acrylamide; styrene-acrylate copolymer; copolymers of acrylamide, acrylic acid, ATBS and n- vinylpyrrolidone; and combinations thereof. The copolymers and terpolymers can contain the various monomers in any ratio .

Examples of ethylenic copolymers include copolymers of acrylic acid and acrylamide, acrylic acid and lauryl acrylate, and lauryl acrylate and acrylamide. Examples of biopolymers include xanthan gum, guar gum, schizophyllan and scleroglucan .

More preferably, the polymer is selected from the group consisting of partially hydrolyzed polyacrylamide, copolymer of acrylamide and acrylate, copolymer of

acrylamide and acrylamido tertiary butyl sulfonate and terpolymer of acrylamide, acrylate and acrylamido tertiary butyl sulfonate. In these cases, the copolymer or

terpolymer can be prepared from acrylate or acrylic acid. The acrylate can be any acrylate including but not limited to sodium acrylate. Polymers which can be used are

commercially available from SNF such as partially hydrolyzed polyacrylamide sold under the name Flopaam

3630S, copolymer of acrylamide and acrylate sold under the name Flopaam 6030S and polyacrylamide sold under the name Flopaam EM533.

Paraffin inhibitors may be incorporated to inhibit the formation of a viscous paraffin-containing emulsion in the mobilized oil by inhibiting the agglomeration of paraffins in the oil. The paraffin inhibitor may be a compound effective to inhibit or suppress formation of a paraffin- containing emulsion. The paraffin inhibitor may be a compound effective to inhibit or suppress agglomeration of paraffins to inhibit or suppress paraffinic wax crystal growth in the oil of the formation upon contact of the hydrocarbon recovery formulation with the oil in the formation. The paraffin inhibitor may be any commercially available conventional crude oil pour point depressant or flow improver that is dispersible, and can be soluble, in the fluid of the hydrocarbon recovery formulation in the presence of the other components of the hydrocarbon

recovery formulation, and that is effective to inhibit or suppress formation of a paraffin-nucleated emulsion in the oil of the formation. The paraffin inhibitor may be

selected from the group consisting of alkyl acrylate copolymers, alkyl methacrylate copolymers, alkyl acrylate vinylpyridine copolymers, ethylene vinylacetate copolymers, maleic anhydride ester copolymers, styrene anhydride ester copolymers, branched polyethylenes , and combinations thereof. The paraffin inhibitor can be added as part of the water or separately. It can be advantageous if the paraffin inhibitor is present in the surfactant composition.

Commercially available paraffin inhibitors that may be used in the hydrocarbon recovery formulation include HiTEC 5714, HiTEC 5788, and HiTEC 672 available from Afton Chemical Corp; FLOTRON D1330 available from Champion Technologies; and INFINEUM V300 series available from Infineum

International .

Scale inhibitors are systems to delay, reduce and/or prevent scale deposition. These include acrylic acid polymers, maleic acid polymers and phosphonates inorganic phosphate, organophosphorous and organic polymer backbones. Examples include phosphonobutane-1 , 2 , 4-tricarboxylic acid, amino-trimethylene phosphonic acid and 1-hydroxyethylidene- 1 , 1-diphosphonic acid, polyacrylic acid,

phosphinopolyacrylates , polymaleic acids, maleic acid terpolymers, sulfonic acid copolymers, such as sulfonated phosphonocarboxylic acid, and polyvinyl sulfonates.

Preferably the scale inhibitors are selected from the group consisting of poly-phosphonocarboxylic acid and

diethylenetriamine-penta (methylene phosphonic acid) and mixtures thereof. Another type of scale inhibitors are chelating agents. Chelating agents can be

aminopolycarboxylic or polycarboxylic or carbohydrate in structure, they can be used in the acidic or salt form. Non limiting examples are iminodisuccinic acid, polyaspartic acid, ethylenediamine-N, N ' -disuccinic acid, L-glutamic acid N, N-diacetic acid, tetrasodium salt, iminodiacetic acid, nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, citric acid,

methylglycine Ν,Ν-diacetic acid, glucoheptonic acid, ethanoldiglycinic acid,

hydroxyethylethylenediaminetriacetic acid and mixtures thereof .

Additionally, a co-solvent may be incorporated in the enhanced oil recovery formulation where the co-solvent may be a low molecular weight alcohol including, but not limited to, methanol, ethanol, and iso-propanol , isobutyl alcohol, secondary butyl alcohol, n-butyl alcohol, t-butyl alcohol, or a glycol including, but not limited to,

ethylene glycol, 1 , 3-propanediol , 1 , 2-propandiol ,

diethylene glycol butyl ether, triethylene glycol butyl ether, or a sulfosuccinate including, but not limited to, sodium dihexyl sulfosuccinate . The co-solvent also can be an alkoxylated low molecular weight alcohol including, but not limited to isobutyl alcohol with 1-15 ethylene oxide groups, preferably 1-4 ethylene oxide groups. The alkylene oxide groups may comprise any alkylene oxide groups. For example, said alkylene oxide groups may comprise ethylene oxide groups, propylene oxide groups and butylene oxide groups or a mixture thereof, such as a mixture of ethylene oxide and propylene oxide groups. In case of a mixture of ethylene oxide and propylene oxide groups, the mixture may be random or blockwise.

The enhanced oil recovery formulation is injected into the oil-bearing formation. Preferably, the enhanced oil recovery formulation is injected via a first well. Enhanced oil recovery formulation moves through the formation either by introducing further formulation or by introducing a different composition such as water and/or gas. When the enhanced oil recovery formulation has reached a second well, the enhanced oil recovery formulation can be

recovered and produced in combination with oil and

optionally gas. From then onwards, the mixture which is being produced via the second well tends to comprise water, enhanced oil recovery surfactant, oil and optionally gas.

The mixture produced from the second well tends to additionally contain solids such as sand and particles originating from the formation. Solids can be separated by filtration or by allowing the solids to settle at the bottom of a vessel and form sediment or slurry at the vessel base.

Oil and optionally gas are recovered from the mixture produced. Recovery can be carried out in any way known to be suitable to somebody skilled in the art. Generally, the mixture produced is separated into gaseous and liquid components in a separator. A separator generally is a large vessel designed to separate production fluids into their constituent components of oil, gas and water. A separator can be operated at increased pressure, at ambient pressure or at decreased pressure. Separators generally operate at a pressure of from 1 to 100 x 10⁵ N/m²-

The produced mixture can be contacted with the

additional surfactant in any way known to the person skilled in the art. A preferred process comprises adding additional surfactant before separating off any fraction from the produced mixture. Another preferred process comprises separating gas from the produced mixture and subsequently adding the additional surfactant.

Generally, it is preferred that the produced mixture and additional surfactant are mixed. Without wishing to be bound by any theory, it is thought that adding the

additional surfactant increases the interfacial tension between the various phases and allowing the phases to separate more easily.

Preferably, the additional surfactant is contacted with all or part of the produced mixture by mixing the additional surfactant into the mixture in question.

Injection can be accomplished by means of one or more injection quills which are preferably located at the center of a pipe in a location of turbulent mixing such as

upstream of valves, pumps, pressure drops, or, in liquid flow, bends, and generally as far upstream as possible from the location where the enhanced oil recovery formulation is required. A preferred method is using a chemical injection quill. The use of a chemical injection quill can ensure that chemicals are evenly dispersed into the center of a pipe while preventing channeling of the additional

surfactant down the pipe wall.

The amount of additional surfactant to be added tends to depend on the amount and type of enhanced oil recovery surfactant produced from the formation, the produced amount of surfactant formed in the formation by saponification of compounds in the oil with alkali, if any, and the ionic strength of the mixture produced. Even if a relatively small amount of surfactant may have been injected into the formation, a relatively stable emulsion of oil-in-water tends to be produced which emulsion can become even more stable if a relatively large amount of naphthenic acids in the formation saponified with alkali present in the

enhanced oil recovery formulation or if the aqueous phase has a relatively high ionic strength due to the presence of relatively large amounts of alkali and/or salts.

Generally, it is preferred that weight ratio of enhanced oil recovery surfactant to additional surfactant is of from 10 : 1 to 1 : 40, more specifically of from 5 : 1 to 1 : 20, more specifically of from 3 : 1 to 1 : 10. Especially good results have been obtained by adding to the mixture produced from the formation of from 10 to 100,000 parts per million by weight (ppm) of more hydrophilic surfactant based an amount of liquid mixture produced, more specifically of from 20 to 80,000 ppm, more specifically at least 40 ppm, more specifically at least 80 ppm, more specifically at least 100 ppm, more specifically at least 150 ppm, more specifically at least 200 ppm, more

specifically at least 250 ppm, more specifically at least 300 ppm. The amount of additional surfactant preferably is at most 50,000 ppm, more specifically at most 40,000 ppm, more specifically at most 30,000 ppm, more specifically at most 20,000 ppm, more specifically at most 10,000 ppm, more specifically at most 5,000 ppm, more specifically at most 2,000 ppm, most specifically at most 1,000 ppm.

The additional surfactant is more hydrophilic than the enhanced oil recovery surfactant. The hydrophilicity of a surfactant can be determined in various ways. A method for characterizing a surfactant is establishing its hydrophile- lipophile (HLB) balance. This number indicates relatively the tendency to solubilize in oil or water. It is

determined by calculating values for the different regions of the molecule. The HLB of surfactants having ionic portions can be calculated by the Davies' method. For the current process, the hydrophilicity is determined based on the optimum salinity for an aqueous solution of the

surfactant in combination with a certain amount of a known hydrocarbon. The hydrocarbon is preferably dodecane or decane or the oil present in the formation. The optimum salinity is the salinity at which the lowest interfacial tension (IFT) is measured. The lowest interfacial tension tends to be accompanied by a microemulsion phase at the interface of oil and brine phases. A suitable method for testing has been described on pages 247-253 of the book "Modern Chemical Enhanced Oil Recovery. Theory and

Practice" by James J. Sheng, Elsevier 2011, ISBN-13: 978- 1856177450. The higher the optimum salinity for a given concentration of surfactant and hydrocarbon, the more hydrophilic the surfactant is considered to be.

If the enhanced oil recovery formulation contained a mixture of surfactants, the additional surfactant

preferably is more hydrophilic than the least hydrophilic enhanced oil recovery surfactant present in the produced mixture, more preferably more hydrophilic than the mass average hydrophilicity of the enhanced oil recovery

surfactants present in the mixture produced, most

preferably more hydrophilic than the most hydrophilic enhanced oil recovery surfactant present in the mixture produced .

The additional surfactant can be any surfactant known to be suitable by somebody skilled in the art. The

additional surfactant can be cationic, nonionic or anionic.

Examples of nonionic surfactants are alcohol ethoxylates such as NEODOL 91-8 and NEODOL 2512. NEODOL is a trademark of the Shell group of companies. If the enhanced oil recovery surfactant is anionic, the additional surfactant preferably is anionic or nonionic, more preferably anionic.

If the enhanced oil recovery surfactant is cationic, the additional surfactant preferably is cationic or nonionic, more preferably cationic.

The additonal surfactant preferably comprises anionic surfactant and more preferably is anionic surfactant, more specifically a compound containing a negatively charged portion and one or more counter cations which negatively charged portion comprises (i) a hydrophilic part which comprises a negatively charged group and (ii) a hydrophobic part .

The additional surfactant preferably is a surfactant according to formula (I) as discussed and described above in relation with the enhanced oil recovery surfactant. As the additional surfactant differs from the enhanced oil recovery surfactant, one or more of R, V, R'-O, A and/or M generally will differ from those of the enhanced oil recovery surfactant.

Preferably, an additional anionic surfactant is chosen from the group consisting of hydrocarbon sulphates and hydrocarbon sulphonates wherein the hydrocarbon consists of hydrogen, carbon and optionally oxygen. Examples of

carboxylates, alkyl propoxy/ethoxy carboxylates, alkyl alcoxy glycidyl sulfonates and blends thereof.

An additional anionic surfactant preferably is

selected from the group consisting of an alpha olefin sulfonate compound, an internal olefin sulfonate compound, a secondary alkyl sulfonate compound, a branched alkyl benzene sulfonate compound, a propylene oxide sulfate compound, an ethylene oxide sulfate compound, a propylene oxide-ethylene oxide sulfate compound, or a blend thereof. The additional surfactant preferably contains of from 8 to 30 carbon atoms. If a mixture of surfactants is present, the number of carbon atoms is the mass average of all surfactants which are present. The additional surfactant preferably contains at least 10, more preferably at least 11, more preferably at least 12 carbon atoms. The

additional surfactant preferably contains at most 20, more preferably at most 18, more preferably at most 16, more preferably at most 14 carbon atoms. Preferably, the additional surfactant contains of from 12 to 18 carbon atoms and is chosen from the group

consisting of lauryl sulphates, lauryl ether sulphonates and internal olefin sulfonates. The additional surfactant can be chosen from the group consisting of sodium lauryl sulphate, sodium lauryl ether sulphate and sodium

dodecylbenzene sulphonate.

Specific additional surfactants which can be used are ENORDET surfactant J771, ENORDET surfactant Jlllll, ENORDET surfactant J13131, ENORDET surfactant 0352, ENORDET

surfactant 0242, ENORDET surfactant 0332, ENORDET

surfactant 0342, ENORDET surfactant A771, PETR0STEP

surfactant Al, PETR0STEP surfactant A6, PETR0STEP

surfactant SI, PETR0STEP surfactant S2, PETR0STEP

surfactant S-8, PETR0STEP surfactant S-9, PETR0STEP

surfactant S-10, PETR0STEP surfactant S-13, STE0L

surfactant CS330, PETROSTEP surfactant C3, PETROSTEP surfactant C4, NEOPELEX G-25, Emal 30E, Emal 270, Witcolate WAQ and Witcolate LES60C. ENORDET is a trademark of the Shell group of companies. PETROSTEP and STEOL are

trademarks of Stepan Company. Neopelex and Emal are

trademarks of Kao Chemicals. Witcolate is a trademark of AkzoNobel .

The present disclosure is not limited to the

embodiments as described above and the appended claims.

Many modifications are conceivable and features of

respective embodiments may be combined.

The following examples of certain aspects of some embodiments are given to facilitate a better understanding of the present invention. In no way should these examples be read to limit, or define, the scope of the invention. Example An experiment was conducted to determine the effect of the addition of various additional surfactants.

The enhanced oil recovery surfactants are described in Table 1.

Table 1

The additional surfactants are described in Table 2.

Table 2

containing of

from 20 to 24

carbon atoms

Internal olefin

sulfonate

IOS 15-18 containing of 350 9-13 from 15 to 18

carbon atoms

Sodium lauryl

288 >10 sulphate

Sodium lauryl 3-

376 >10 ethoxy sulphonate

Compositions were prepared by adding to a mixture of crude oil and water (volume ratio 10/90), 0.03 % mass per mass (%wt) of EOR Surfactant 1, 0.2 %wt of NaHC0₃ and 0.02 %wt of Na2CC>3. To the compositions was added 400 parts per million by weight of surfactant. The mixtures obtained were allowed to settle during 60 seconds after which the colour intensity of the aqueous phase was determined by digitally imaging the tube and generating a colour intensity from the output. The colour intensity achieved with the various surfactants is described in Table 3

Table 3

Compositions were prepared by adding to a mixture of crude oil and water (volume ratio 10/90), 0.12 %wt of Na2CC>3 and additionally NaCl, NaHCC>3, EOR surfactant 2 and

isobutanol in the quantities indicated in Table 4. To the compositions were added the amounts of sodium lauryl sulphate described in Table 4. All amounts are in %wt . The mixtures obtained were allowed to settle during 60 seconds after which the colour intensity was determined by

digitally imaging the tube and generating a colour

intensity from the output.

Table 4

It is clear from the above examples that a surfactant which is more hydrophilic than the enhanced oil recovery surfactant gives an aqueous phase which has a higher colour intensity meaning that the aqueous phase is clearer and less dark indicating that the aqueous phase contains less oil.

Claims

1. Process for recovering oil from a formation containing oil and water by injecting into the formation an enhanced oil recovery formulation comprising enhanced oil recovery surfactant, which process comprises

(i) injecting into the formation the enhanced oil recovery formulation,

(ii) producing from the formation a mixture comprising water, enhanced oil recovery surfactant and oil, and

(iii) contacting the produced mixture with additional surfactant and separating oil,

wherein the additional surfactant is more hydrophilic than the enhanced oil recovery surfactant.

2. Process according to claim 1 in which the enhanced oil recovery surfactant comprises anionic surfactant.

3. Process according to claim 1 in which the additional surfactant comprises anionic surfactant.

4. Process according to claim 3 in which the additional surfactant contains of from 12 to 18 carbon atoms and is chosen from the group consisting of lauryl sulphates, lauryl ether sulphonates and internal olefin sulfonates.

5. Process according to claim 1 in which the enhanced oil recovery formulation further comprises one or more

compounds selected from the group consisting of polymer, paraffin inhibitors, scale inhibitors and co-solvents.

6. Process according to claim 1 in which the additional surfactant is added by an injection quill.

7. Process for recovering oil from a formation containing oil and water by injecting into the formation an enhanced oil recovery formulation comprising alkali and polymer, which process comprises (i) injecting into the formation the enhanced oil recovery formulation,

(ii) producing from the formation a mixture comprising water, saponified hydrocarbons and oil, and

wherein the additional surfactant is more hydrophilic than the saponified hydrocarbons of the produced mixture.